WO2014154814A1

WO2014154814A1 - Method for blocking permeable zones in oil and natural gas bearing subterranean formations by in-situ xyloglucan degalactosylation

Info

Publication number: WO2014154814A1
Application number: PCT/EP2014/056175
Authority: WO
Inventors: Meik Ranft; Vaidotas NAVICKAS; Lorenz Siggel; Andrea Assmann; Kai-Uwe Baldenius; Agnieszka PETERS; Joachim STEIDEL; Ute BENKERT
Original assignee: Basf Se; Wintershall Holding GmbH
Priority date: 2013-03-28
Filing date: 2014-03-27
Publication date: 2014-10-02

Abstract

A method for treating an oil and/or natural gas bearing subterranean formation penetrated by at least one well bore, comprising the steps of (a) providing an aqueous well treatment formulation (A) which comprises (A1 ) a xyloglucan having an average molecular weight (M_w) of from 200 000 to 1 500 000 Da, (A2) an enzyme preparation comprising β-galactosidase being capable of removing galactose from xyloglucan, and (A3) optionally one or more additives; (b) injecting said aqueous well treatment formulation into at least one well bore penetrating the oil and/or gas bearing subterranean formation; and (c) gelling of said aqueous well treatment formulation effected by partial degalactosylation of the said xyloglucan; thereby blocking highly permeable zones in the oil and/or natural gas bearing subterranean formation.

Description

Method for blocking permeable zones in oil and natural gas bearing subterranean formations by in-situ xyloglucan degalactosylation

Description

The present invention relates to a method for treating a subterranean oil and/or natural gas bearing formation penetrated by at least one well bore using aqueous well treatment formulations comprising xyloglucan and β-galactosidase. The invention also relates to a process for purifying β-galactosidase, and a β-galactosidase itself. The inven- tion features the full-length coding sequence of the amino acid sequence of the β- galactosidase, and variants thereof.

Oil and/or natural gas accumulated within subterranean formations is recovered or produced therefrom through wells, called production wells, penetrating the oil and/or gas bearing subterranean formation. However, a large amount of the oil and natural gas is left in the subterranean formations if produced only by primary depletion, i.e., where only formation energy is used to recover the oil. Where the initial formation energy is inadequate or has become depleted, supplemental operations, often referred to as secondary, tertiary, or enhanced oil recovery, are employed.

In the widely used secondary oil recovery operations, a fluid is injected into the formation by pumping it through one or more injection wells penetrating the subterranean formation. The fluid, generally water, or a miscible gas, is primarily employed to maintain the pressure of the reservoir and secondarily to displace additional oil from the reservoir. Thereby, oil is displaced and moved through the subterranean formation, and is produced from one or more production wells penetrating the subterranean formation. In a particular recovery operation of this sort, field water or field brine is employed as the injection fluid and the operation is referred to as water flooding. Although water is the most common fluid, injection fluids can include gaseous or supercritical fluids such as nitrogen, carbon dioxide, and the like.

Conventional water flooding is effective in obtaining additional oil and/or gas from oil and/or natural gas-bearing subterranean formations, but the technique does exhibit a number of shortcomings. One shortcoming is the tendency of flooding water to finger through an oil-bearing formation and thus bypass substantial portions thereof. By fingering is meant the development of unstable water fronts which advance toward the production wells more rapidly than the remainder of the flooding water. For example, the injection fluid generally flows along a low resistance route from the injection well to the production well. Accordingly the injection fluid often sweeps through geological zones of higher permeability and bypasses lower permeability zones of the subterrane- an formation resulting in a non-uniform displacement of oil. Such higher permeability geological zones of the subterranean formation are commonly called thief zones or high permeability streaks. To increase the recovery or the production of oil and/or natural gas in secondary and tertiary oil recovery operations, a substantially uniform permeability throughout the whole subterranean formation is desired.

If the formation permeability is heterogeneous, the injection fluids will seek areas of high water permeability, producing channeling and the passage of injection fluid to the producing well. As the more water-permeable zones of the subterranean formation are depleted of oil, the injection fluid has a tendency to follow such channels and increase water production, reflected in a higher water/oil ratio at the producing well. Improved diversion of water through oil bearing rock can be obtained in subterranean formations of non-uniform permeability by permeability corrections of the more water-permeable zones of the subterranean formation.

There are several strategies that can be used to reduce the water permeability of these more permeable zones of the subterranean formation. These involve mechanical block- ing devices or chemicals that at least partially plug the more water-permeable zones and achieve reduced water permeability in said zones. One approach of reducing water permeability in said zones and thus increasing the recovery or the production of oil is to use a comparatively low-viscosity formulation whose viscosity rises only under formation conditions, thereby blocking highly water-permeable zones (regions) of the sub- terranean formation.

Such formulations are commonly known as "thermogel" or "delayed gelling system". Such a formulation is hereinafter referred to as "delayed gelling formulation". For plugging highly water-permeable zones of the subterranean formations, the delayed gelling formulation is injected readily into a well bore penetrating the oil and/or natural gas bearing subterranean formation, and its viscosity rises significantly after injection into the subterranean formation.

Two families of delayed gelling formulations are typically used, delayed inorganic gel- ling formulations and delayed (organic) polymer gelling formulations. Delayed inorganic gelling formulations typically contain a metallic or silicate salt and an activator. The transformation to a gel occurs when the pH of the formulation is modified by reaction of the activator. This process is also triggered by time and temperature and can also be delayed to allow sufficient time for placement into the target zone of the subterranean formation. Delayed polymer gelling formulations typically contain an acrylamide poly- mer and a cross linker. The transformation to a gel occurs when the polymer is cross- linked. This process is triggered by time and temperature and can be delayed to allow sufficient time for placement into the target zone of the subterranean formation. In one approach of reducing water permeability and thus increasing recovery or production of oil, a delayed gelling formulation is injected under pressure into at least one injection well of the oil-bearing subterranean formation. The delayed gelling formulation injected through an injection well tends to sweep through higher permeability zones of the subterranean formation and does not uniformly flow through the lower permeability zones as said formulation naturally follows lower resistance paths to the production well(s). Therefore, the delayed gelling formulation flows preferentially through permeable zones depleted of oil, the so called thief zones.

After the transformation to a gel, the once highly water-permeable zone of the subter- ranean formation is plugged. As a result, the injection water is forced again to flow through the oil-saturated, low permeability zones of the subterranean formation. Such an approach is known as 'conformance control". Background information on conformance control can be found in Borling et al. 'Pushing out the oil with Conformance Control", Oilfield Review 1994, 44.

In another approach, a delayed gelling formulation is injected under pressure into at least one production well penetrating the oil and/or natural gas bearing subterranean formation. As delayed gelling formulations, the same formulations can be used as for the above described injection into the injection well. This approach is also called con- formance control or permeability modification. However, it is also frequently called 'water shut off' since its ultimate objective is to shut off the water or at least decrease the water/oil ratio at the production well. General background information on water shut off can be found in Bailey et al. 'Water control', Oilfield Review, 2000, 30. US 4,844,168 discloses a process for blocking sections of high-temperature mineral oil formations, in which polyacrylamide and a polyvalent metal ion, for example Fe(lll), Al(lll), Cr(lll) or Zr(IV), are forced into a mineral oil formation having a reservoir temperature of at least 60 °C. Under the conditions in the formation, some of the amide groups -CONH2 hydrolyze to -COOH groups, the metal ions crosslinking the -COOH groups formed so that a gel is formed with a certain time lag.

US 2008/0035344 discloses a method for blocking zones in underground formations using delayed gelling formulations, which comprises at least one acid-soluble cross- linkable polymer, for example partly hydrolyzed polyacrylamide; a partially neutralized aluminum salt, for example an aluminum hydroxychloride; and an activator which can liberate bases under formation conditions, such as, for example, urea, substituted urea or hexamethylenetetramine. The formulation gels at temperatures above 50 °C within 2 h to 10 d, depending on conditions of use. RU 2339803 discloses a two-step process for blocking highly permeable zones in subterranean formations. In a first process step, an aqueous formulation of carboxymethyl- cellulose and chromium acetate as a crosslinking agent is injected. In a second step, an aqueous formulation of polyacrylamide and a crosslinking agent is injected. L. K. Altunina et al., Oil & Gas Science and Technology-Rev. 2008, 63, 37-48, describe various thermogels and their use for oil production, including thermogels based on cellulose ethers.

Besides delayed gelling formulations it is also possible to use preformed gels like, for example, preformed particle gels, microgels or bright water. The application of xyloglucan as additive for fluids in oil field applications was already proposed in US 3,480,51 1 . Various other patent documents have disclosed the use of xyloglucan (frequently called tamarind or tamarind gum) as thickening or gelling agent in different oil field applications (see for example US 2009/0149353, US 2009/0093382, WO 2007/031722 and WO 2005/014754).

The use of substituted xyloglucan in oil field applications is mentioned in

US 2007/261848 which discloses a loss circulation fluid, comprising an alkali metal formate and a carboxymethyl-tamarind gum as thermally activated self-crosslinkable gel forming material for oil field drilling and completion operations.

US 2006/0142165 discloses a method of treating subterranean formations penetrated by a well bore using treating fluids comprising sulfonated tamarind gum as gelling agent polymer. WO 2007/058814 discloses the use of cationized tamarind gum in well serving fluid compositions. The cationized tamarind gum is thereby prepared by chemical means, e.g. quaternization with various quaternary amine compounds containing reactive chloride or epoxide sites. US 7,271 ,133 shows methods of treating subterranean formations using esterified and etherified tamarind gums as gelling agent polymers.

A. K. Andriola et al., Carbohydrate Polymers 2010, 555-562 disclose the production of xyloglucans having different galactose removal ratios, by reacting a 2 wt.-% aqueous solution of xylo-glucan with an enzyme preparation comprising β-galactosidase from Aspergillus oryzae. The enzyme preparation is thereby used as received from supplier. The so observed partially degalactosylated xyloglucans has significantly shorter back bone chain lengths than xyloglucan itself. In general, the higher the galactose removal ratio of the xyloglucan, the shorter becomes the back bone chain length.

The use of enzymes in oil field applications is rare. For example, US 8,058,212 B2 dis- closes a hydraulic fracturing method using guar gum (galactomannans) or guar gum derivatives as proppant carrier and mannanohydrolase enzymes as breakers. In this application, the mannanohydrolase enzyme effects the degradation ('breaking") of the highly viscous cross linked guar gum or guar gum derivatives after proppant transportation.

Many compositions or formulations proposed for conformance control are deemed environmentally unacceptable due to their high toxicity, poor biodegradability and enrichment ability. It is also to be expected that public concerns about ground water contamination, mishandling of waste and health effects might become a factor of even greater importance. Thus, it is highly desirable to provide improved non-toxic, biodegradable compositions and formulations that can be used in methods for treating subterranean oil and/or natural gas bearing formations penetrated by at least one wellbore.

Therefore, it is an object of the present invention to provide improved methods for treat- ing oil and/or natural gas bearing subterranean formations penetrated by at least one well bore.

The object of the present invention is solved by a method for treating an oil and/or natural gas bearing subterranean formation penetrated by at least one well bore, comprising the steps of

(a) providing an aqueous well treatment formulation (A) which comprises

(A1 ) a xyloglucan having an average molecular weight of from

200 000 to 1 500 000 Da,

(A2) an enzyme preparation comprising β-galactosidase being capable of removing galactose from xyloglucan, and

(A3) optionally one or more additives;

(b) injecting said aqueous well treatment formulation into at least one well bore penetrating the oil and gas bearing subterranean formation; and

(c) gelling of said aqueous well treatment formulation effected by partial degalactosylation of the said xyloglucan. Surprisingly, it has been found that the use of an aqueous well treatment formulation (A), which comprises a xyloglucan (A1 ), an enzyme preparation comprising β-galacto- sidase (A2) and optionally one or more additives (A3), is capable of blocking permea- ble zones of oil and/or natural gas bearing subterranean formations when injected into well bores.

The term 'blocking' or 'blocked' shall mean that the permeable zones are completely or at least partially blocked. 'Partially blocked' is intended to mean that the flow resistance of the permeable zones for aqueous media increases due to the treatment with the aqueous well treatment formulation. The blocking is thereby caused by the in-situ xyloglucan degalactosylation effected by β-galactosidase, and the formation temperature. Consequently, the partially degalactosylated xyloglucan forms a gel in the permeable zones of the formation and blocks them. The term Ίη-situ xyloglucan degalactosylation' means that the xyloglucan is partially degalactosylated by β-galactosidase in the permeable zones of the oil and/or natural gas bearing subterranean formation.

The aqueous well treatment formulation (A) has improved thermogelation properties compared to the same formulation without β-galactosidase. For example, the aqueous well treatment formulation (A) comprising the β-galactosidase displays sol-gel transition temperatures of from 0 to 100 °C, while the same formulation without β-galactosidase does not undergo sol-gel transition at all. Thus, the thermogelation properties of the aqueous well treatment formulation (A) allow oil and natural gas-field applications, especially in conformance control.

Furthermore, the partially degalactosylated xyloglucan created by in-situ xyloglucan degalactosylation displays higher gel-strenghts and higher viscosities than xyloglucan itself. At the same time, the partially degalactosylated xyloglucan is equally as good biodegradable and non-toxic as xyloglucan.

Additionally, it has been found that the sol-gel transition temperature as well as the viscosity and the gel-strength of the aqueous well treatment formulation (A) can easily be fine tuned by variation of the amount of salt and the amount of xyloglucan (A1 ) present in the aqueous well treatment formulation. This allows the use for several applica- tions, such as for example, conformance control at different formation temperatures.

According to the present invention, the method comprises at least the three steps (a), (b) and (c). In step (a) of the method, the aqueous well treatment formulation (A) is provided. Said formulation (A) comprises at least the xyloglucan (A1 ) and the β- galactosidase (A2).

The aqueous well treatment formulation (A) comprises usually from 0.01 to 20.00 % by weight of the xyloglucan (A1 ), based on the total weight of the aqueous well treatment formulation (A). The aqueous well treatment formulation (A) comprises preferably from 0.1 to 10.0 % by weight, more preferred of from 0.5 to 5.0 % by weight, most preferred of from 1.0 to 3.0 % by weight of the xyloglucan (A1 ) as defined above, based on the total weight of the aqueous well treatment formulation (A).

The amount of xyloglucan (A1 ) present in the aqueous well treatment formulation (A) affects mainly the viscosity and the gel strength while the sol-gel transition temperature remains almost unaffected. The higher the proportional amount of the xyloglucan (A1 ) in the aqueous well treatment formulation, the higher becomes the viscosity and the gel strength.

The xyloglucan (A1 ) can comprise xyloglucan isolated from one species or one tissue of a species; or mixtures of two, three, four or more xyloglucans isolated from different species and/or different tissues of the same species.

Xyloglucans are widespread in nature. They belong to a group of polysaccharides typically referred to as hemicelluloses and can be found in primary cell walls of different plants, such as for example plants belonging to the class dicotyledons and plants belonging to the sub-class non-graminacious monocotyledons.

A few among these plants (all of which are dicotyledons) use xyloglucans also as a carbohydrate reserve instead of the most common carbohydrate reserve starch. Seeds of these plants have thick cell walls containing vast quantities of xyloglucans. Examples of said plants are flowering plants of the genus Nasturtium, such as Nasturtium africanum, Nasturtium floridanum, Nasturtium gambelii, Nasturtium microphyllum, Onerow yellowcress and Nasturtium officinale; flowering plants of the genus Impatiens, such as Impatiens balfourii, Impatiens balsamina, Impatiens capensis, Impatiens edgeworthii, Impatiens glandulifera, Impatiens hians, Impatiens marianae, Impatiens niamniamensis, Impatiens noli-tangere, Impatiens parviflora Impatiens platypetala, Impatiens repens; flowering plants of the genus Annonas, such as Annona amambayen- sis, Annona acuminata, Annona ambotay, Annona asplundiana, Annona atabapensis, Annona bullata,, Annona biflora, Annona bicolor, Annona brasililensis, Annona cacans, Annona calophylla, Annona campestris, Annona cherimola, Annona chrysophylla, An- nona pubescens, Annona tripetala, Annona conica, Annona coriacea, Annona cornifo- lia, Annona crassiflora, Annona cristalensis, Annona crotonifolia, Annona deceptrix, Annona deminuta, Annona dioica, Annona diversifolia, Annona dolabripetala, Annona dolichophylla, Annona echinata, Annona ecuadorensis, Annona ekmanii, Annona ex- cellens, Annona glabra, Annona palustris, Annona glaucophylla, Annona haematantha, Annona hayesii, Annona hypoglauca, Annona hystricoides, Annona jahnii, Annona ja- maicensis, Annona longiflora, Annona lutescens, Annona macrocalyx, Annona malmeana, Annona manabiensis, Annona microcarpa, Annona montana, Annona marcgravii, Annona monticola, Annona muricata, Annona macrocarpa, Annona nitida, Annona nutans, Annona oligocarpa, Annona paludosa, Annona paraguayensis, Annona phaeoclados, Annona praetermissa, Annona purpurea, Annona pygmaea, Annona reticulata, Annona salzmannii, Annona scleroderma, Annona senegalensis, Annona sericea, Annona spinescens, Annona spraguei, Annona squamosa, Annona tes- tudinea, Annona tomentosa, Annona trunciflora, and trees of the genus Tamarindus such as Tamarindus indica.

Xyloglucan from seeds of one of these plant genus mentioned above is hereinafter referred to as seed xyloglucan. Xyloglucans comprise a back bone consisting essentially of 1 ,4-linked β-D- glucopyranose residues like cellulose. Said back bone is hereinafter referred to as xyloglucan back bone. The 1 ,4-linked β-D-glucopyranose residues of the xyloglucan back bone are either substituted or unsubstituted (subunit 'G'). The 1 ,4-linked β-D- glucopyranose residue may be substituted by 1 ,6-linked a-D-xylopyranose residue (creating subunit X) which themselves may be further substituted by one or two 1 ,2- linked β-D-galactopyranose residues (creating subunit 'L' or 'J') or, more rarely, one or two oL-arabinofuranose residues (creating subunit 'S' or 'T). Furthermore, said 1 ,2- linked β-D-galactopyranose residue may themself be further substituted by a 1 ,2- linked L-fucopyranose residue (creating subunit 'F').

It is known to the person skilled in the art that xyloglucans may comprise traces of other pyranose residues, furanose residues and/or the like besides the ones mentioned above. Thus, the expression 'consisting essentially of" means that the xyloglucan back bone consists of more than 90 %, preferably more than 95 %, even more preferred more than 98 %, often more than 99 % by weight of the 1 ,4-linked β-D-glucopyranose residues.

A single letter code is used to simplify representation of the structure of xyloglucan subunits. Said single letter code is shown below: i. G = -4)-3-D-Glcp-(1 - ii. X = a-D-Xylp-(1 -6)-3-D-Glcp-(1 -

4

† iii. F = a-L-Fucp-(1 -2)-3-D-Galp-(1 -2)-a-D-Xylp-(1 -6)-3-D-Glcp-(1 -

4

† iv. L = 3-D-Galp-(1 -2)-a-D-Xylp-(1 -6)-3-D-Glcp-(1 -

4

† v. S = a-L-Araf-(1 -2)-a-D-Xylp-(1 -6)-3-D-Glcp-(1 -

4

† vi. T = a-L-Araf-(1 -3)-a-L-Araf-(1 -2)-a-D-Xylp-(1 -6)-3-D-Glcp-(1 - 4

† vii. J = a-D-Galp-(1 -2)-3-D-Galp-(1 -2)-a-D-Xylp-(1 -6)-3-D-Glcp-(1 -

4

†

The term 'xyloglucan subunit' used herein relates to one single substituted or unsubsti- tuted β-D-glucopyranose residue of the xyloglucan back bone. Examples of said 'xyloglucan subunits' are G, X, F, L, S, T and J, as shown above.

In contrast thereto, the term 'xyloglucan individual unit' relates herein to four or five consecutive 1 ,4-linked β-D-glucopyranose residues of the xyloglucan back bone, wherein either two or three of said residues are further substituted with a D- xylopyranose residue which themself may be further substituted as shown above. Typi- cal examples of such xyloglucan individual units are XXXG, XXJG, FXXG and LXLG.

Usually, the structure of xyloglucans vary among plant species and also in a tissue specific manner. Furthermore, the structure of seed xyloglucan may also depend on the seeds' maturity. Nevertheless, xyloglucans can be classified in at least three types, namely 'XXXG'-type, 'XXGG'-type and 'XXGGG'-type. 'XXXG'-type xyloglucans have repeating units consisting of three consecutive 1 ,4- linked β-D-glucopyranose residues, wherein each one of said glucopyranose residues is at least substituted with one 1 ,6-linked oD-xylopyranose residue; and a fourth un- substituted 1 ,4-linked β-D-glucopyranose residue. 'XXXG"-type xyloglucan consists essentially of individual units connected by 3-1 ,4-glycosidic bonds, wherein the individual units are selected from the group consisting of XXXG, FXXG, LXXG, SXXG, TXXG, JXXG, XFXG, XLXG, XSXG, XTXG, XJXG, XXFG, XXLG, XXSG, XXTG, XXJG, FFXG, FLXG, FSXG, FTXG, FJXG, LFXG, LLXG, LSXG, LTXG, LJXG, SFXG, SLXG, SSXG, STXG, SJXG, TFXG, TLXG, TSXG, TTXG, TJXG, JFXG, JLXG, JSXG, JTXG, JJXG, FXFG, FXLG, FXSG, FXTG, FXJG, LXFG, LXLG, LXSG, LXTG, LXJG, SXFG, SXLG, SXSG, SXTG, SXJG, TXFG, TXLG, TXSG, TXTG, TXJG, JXFG, JXLG, JXSG, JXTG, JXJG, XFFG, XFLG, XFSG, XFTG, XFJG, XLFG, XLLG, XLSG, XLTG, XLJG, XSFG, XSLG, XSSG, XSTG, XSJG, XTFG, XTLG, XTSG, XTTG, XTJG, XJFG, XJLG, XJSG, XJTG, XJJG.

The expression 'consists essentially of means that more than 90 %, preferably more than 95 %, more preferred more than 98 % by weight of the xyloglucan consists of the individual units mentioned above, based on the total weight of the xyloglucan.

The term 'xyloglucan repeating unit' refers to the smallest recurring unit within the xyloglucan backbone. For example, the repeating unit of the 'XXXG'-type xyloglucans is XXXG. In this case, the backbone consists essentially of: -XXXG-XXXG-XXXG-XXXG- XXXG-XXXG- and so on, wherein the 1 ,4-linked β-D-glucopyranose residue ('G') is unsubstituted and the 1 ,6-linked oD-xylopyranose residue ('X') may be further substituted randomly with the fucose and/or pyranose residues shown above.

The length of the xyloglucan is best expressed by way of the average molecular weight (Mw) and the average number of repeating units (n).

Depending on the xyloglucan source, 'XXXG'-type xyloglucans have typically a glucopyranose (Glcp) : xylopyranose (Xylp) : galactopyranose (Galp) : fucopyranose (Fucp) : arabinofuranose (Ara/)-ratio of 4 : 2.7 to 3.3 : 1 .7 to 2.3 : 0.0 to 0.5 : 0.0 to 0.5 and an average molecular weight (M_w) of from 64 000 to 2 400 000 Da. Moreover, said xy- loglucans have typically an average number of repeating units (n) of from 50 to 1500 which corresponds to an average number of subunits of from 200 to 6000.

More details about xyloglucan structures and methods of structure determination can be found in S.F. Fry. J. Expt. Botany 1989, 40, 1 -1 1 ; A. Mishra et al., J. Mater. Chem. 2009, 19, 8528-8536; W. York et al., Carbohydr. Res. 1990, 200, 9-31 ; Hoffman et al., Carbohydr. Res. 2005, 340, 1826-1840; W. York et al., Carbohydr. Res. 1996, 285, 98- 128; and the literature cited therein.

Similarly, 'XXGG'-type xyloglucans have repeating units consisting of two consecutive 1 ,4-linked β-D-glucopyranose residues, wherein each one of said glucopyranose residues is substituted with at least a 1 ,6-linked oD-xylopyranose residue; and two consecutive unsubstituted 1 ,4-linked β-D-glucopyranose residues. 'XXGG'-type xyloglucans consist essentially of individual units connected by β-1 ,4-glycosidic bonds, wherein the individual units are selected from the group consisting of XXGG, FXGG, LXGG, SXGG, TXGG, JXGG, XFGG, XLGG, XSGG, XTGG, XJGG, FFGG; FLGG, FSGG, FTGG, FJGG, LFGG, LLGG, LSGG, LTGG, LJGG, SFGG, SLGG, SSGG, STGG, SJGG, TFGG, TLGG, TSGG, TTGG, TJGG, JFGG, JLGG, JSGG, JTGG, JJGG.

Depending on the xyloglucan source, 'XXGG'-type xyloglucans have typically a gluco- pyranose (Glcp) : xylopyranose (Xylp) : galactopyranose (Galp) : fucopyranose (Fucp) : arabinofuranose (Ara/)-ratio of 4 : 1.7 to 2.3 : 1 .7 to 2.3 : 0.0 to 0.5 : 0.0 to 0.5, an average molecular weight (M_w) of from 57 000 to 2 300 000 Da, and an average number of repeating units (n) of from 50 to 1500. 'XXGGG'-type xyloglucans have repeating units consisting of two consecutive 1 ,4- linked β-D-glucopyranose residues, wherein each one of said glucopyranose residue is substituted with at least a 1 ,6-linked oD-xylopyranose residue; and three consecutive unsubstituted 1 ,4-linked β-D-glucopyranose residues. 'XXGGG'-type xyloglucan consists essentially of individual units connected by β-1 ,4-glycosidic bonds, wherein the individual units are selected from the group consisting of XXGGG, FXGGG, LXGGG, SXGGG, TXGGG, JXGGG, XFGGG, XLGGG, XSGGG, XTGGG, XJGGG, FFGGG; FLGGG, FSGGG, FTGGG, FJGGG, LFGGG, LLGGG, LSGGG, LTGGG, LJGGG, SFGGG, SLGGG, SSGGG, STGGG, SJGGG, TFGGG, TLGGG, TSGGG, TTGGG, TJGGG, JFGGG, JLGGG, JSGGG, JTGGG, JJGGG.

Typically, 'XXGGG'-type xyloglucans have a glucopyranose (Glcp) : xylopyranose (Xylp) : galactopyranose (Galp) : fucopyranose (Fucp) : arabinofuranose (Ara/)- ratio of 5 : 1 .7 to 2.3 : 1 .7 to 2.3 : 0.0 to 0.5 : 0.0 to 0.5, an average molecular weight (Mw) of from 65 000 to 1 900 000 Da, and an average number of repeating units (n) of from 50 to 1200.

More details about xyloglucan structures can be found in the above cited literature (S.F. Fry., A. Mishra et al., Hoffman et al, W. York et al., Hoffman et al., W. York et al.) and the literature cited therein. Various attempts have been made to isolate xyloglucan from plant sources. Most of these attempts include the steps of first crushing or pulverizing the parts of the plant containing xyloglucan, and then treating the crushed or pulverized parts of the plant with air, water, or an organic solvent. Depending on the isolation procedure and the xyloglucan source, the so obtained xyloglucan may still have as main contaminations of from 0 to 40 % by weight of proteins, of from 0 to 20 % by weight of polysaccharides different from xyloglucan, and 0 to 25 % by weight of fats.

Details about the isolation of xyloglucans and their purities can be found, for example, in Y. Kato et al.; Agricultural and Biological Chemistry 1981 , 45, 2745-2753; J.-P. Jose- leau et al., Plant Physiology, 1984, 74, 694-700; T. Hayashi et al., Plant and Cell Physiology, 1980, 21 , 1405-1418; P. S. Rao, H. C. Srivastava, in R L Whistler (ed), Industrial Gums, 2^nd ed., Academic Press, New York, 1973, 369-41 1 ; G. Sawr et al., J. Biol. Chem. 1947, 172, 501 ; US 4,895,938 ; and the literature cited therein.

The method according to the present invention can principally be conducted with every xyloglucan type in any purity. However, for achieving improved thermogelation properties, xyloglucan having a purity of at least 50 % by weight is typically used. The xyloglucan (A1 ) has preferably a purity of at least 80 %, more preferred a purity of at least 90 %, and most preferred a purity of at least 95 % by weight.

As important as the purity of the xyloglucan is its water solubility. Highly desirable is that xyloglucan and its contaminants dissolve completely thereby forming an aqueous solution. Because a too large proportion of water insoluble particles in the aqueous well treatment formulation may create problems in most of its possible applications (for example, settling of insoluble particles in containers and/or pipes might damage pumps or result in the blocking of pipes), the amount of insoluble particles is preferably very low. Therefore, the proportion of water insoluble particles in said aqueous treating formula- tion is best kept low by using a highly water soluble xyloglucan. Alternatively, the amount of insoluble particles may be reduced, for example, by centrifugation and/or filtration.

The xyloglucan (A1 ) has an average molecular weight of from 200 000 to

1 500 000 Da. Having average molecular weights lower than 200 000 Da, the in-situ degalactosylated xyloglucan - the partially degalactosylated xyloglucan - does not have thermogelation properties at all. As a consequence, the blocking of the oil and/or natural gas bearing subterranean formation fails. However, the higher the average molecular weight of xyloglucan, the higher the viscosity and the gelation strength of the partial- ly degalactosylated xyloglucan becomes in the permeable zones of the subterranean formation, resulting in a decreased requirement of xyloglucan to achieve the desired viscosity and gelation strength. Thus, the xyloglucan (A1 ) has preferably an average molecular weight of from 400 000 to 1 500 000 Da, more preferred of from 600 000 to 1 500 000 Da, even more preferred of from 800 000 to 1 500 000 Da, and most pre- ferred of from 1 000 000 to 1 500 000 Da.

The average molecular weight can be determined by conventional methods, e.g. field flow fractionation (FFF). The average molecular weights given herein have been determined by FFF. Details about FFF can be found, for example, in B. Roda et al. Ana- lytica chimica acta 2009, 635, 132-143, and the literature cited therein.

Preferably, the method of the present invention is conducted with a xyloglucan (A1 ), wherein at least part of the xyloglucan (A1 ) is xyloglucan isolated from seeds of one of the genuses selected from the group consisting of Nasturtium, Impatiens, Annona and Tamarindus. More preferred, the xyloglucan (A1 ) comprises xyloglucan isolated from seeds of one of the species selected from the group consisting of Tamarindus indica, Annona squamosa and Annona cherimola. Even more preferred, the xyloglucan (A1 ) comprises xyloglucan isolated from seeds of the species Tamarindus indica. Latter Xyloglucan is herein referred to as tamarind xyloglucan. Tamarind xyloglucan belongs to the 'XXGG'-type xyloglucan and consists essentially of individual units connected by β-1 ,4-glycosidic bonds, wherein the individual units are selected from the group consisting of XXXG, XFXG, XLXG, XJXG, XXLG, XXJG, XFLG, XFJG, XLLG, XLJG, XJLG, XJJG. Tamarind xyloglucan can also be illustrated by general formula (II),

(II)

wherein

the average number of the β-D-galactopyranose residues per repeating unit

(gi + g₂) is from 1.70 to 2.30,

the average number of the a-L-fucopyranose residue per repeating unit (a) is from 0.00 to 0.20, and

the average number of the repeating units (n) is from 200 to 1400.

Most preferred, the xyloglucan (A1 ) is tamarind xyloglucan having general formula (II). Some suppliers for tamarind flakes and powders are shown in table 1. Table 1

No. Xyloglucan suppliers Country Xyloglucan form Purity

1 Vishnu gum and chemicals India Deoild flakes & Powder

2 TCI Germany GmbH Germany Pure polysaccharide 95

3 Altrafine Gums India Deoild flakes & Powder

4 Balasanka India Deoild flakes & Powder

Ramachandra Pulverisers & In¬

5 India Deoild flakes & Powder

dustries

6 The Andhra starch India Deoild flakes & Powder

7 MYSORE India Deoild flakes & Powder

8 Dainippon Sumitomo Pharma Japan Pure polysaccharide 98 9 Vishnu Engeneering Works India Deoild flakes & Powder

10 Shree Vinayak Corporation India Deoild flakes & Powder

1 1 Megazyme Ireland Pure polysaccharide 95

Frequently, tamarind flours, flakes and powders comprise around 60 to 80 % by weight of tamarind xyloglucan and 20 to 40 % by weight of fats, proteins, polysaccharides (which are different from xyloglucan) and the like, based on the total weight of said flours, flakes and/or powders. Said flours and flakes typically have wide particle size distributions containing also particles being larger than 50 μηη as well as particles being smaller than 1 μηη. Especially the particles being larger than 50 μηη are frequently poorly water-soluble and therefore dissolve very inadequately resulting in an aqueous suspension. Therefore, said flakes or flours are first extracted, and then, the still remaining insoluble particles are separated off in a solid-liquid separation step.

For the extraction step, an aqueous suspension comprising between 0.5 and 5.0 %, preferably between 1.0 and 4.0 %, more preferred between 1 .5 and 3.0 % by weight of tamarind seed flours and/or tamarind seed flakes based on the total weight of the aqueous suspension is used. The extraction step is preferably carried out at temperatures of from 50 to 100 °C, more preferable of from 80 to 100 °C, most preferable of from 90 to 100 °C at ambient pressure. After an extraction time of around 0.5 to 8 h, most of the suspended particles are dissolved resulting in an aqueous suspension, wherein most of the xyloglucan of said flakes and/or flours is dissolved. In the solid- liquid separation step, the aqueous suspension is separated into a solid fraction and a liquid fraction. Preferably, this step involves centrifugation and/or filtration of said aqueous suspension. After separation, the solid fraction is removed and the liquid fraction is either directly used in the process of the present invention or stored. Said liquid fraction comprises between 0.3 and 4.0 %, preferably between 0.7 and 3.2 %, more preferred between 1 .0 and 2.4 % by weight of tamarind xyloglucan based on the total weight of the liquid fraction. Optionally, said liquid fraction is further subjected to evaporation and drying. The drying may involve spray-drying or freeze-drying.

In the method according to the present invention, the aqueous well treatment formula- tion (A) comprises besides the xyloglucan (A1 ) at least an enzyme preparation comprising β-galactosidase (A2) which is capable of removing galactose from xyloglucan. β-galactosidases (E.C.3.2.1.23) themselves do not degrade the xyloglucan backbone which consists essentially of 1 ,4-linked β-D-glucopyranose residues. If β-galactosi- dases are sufficiently pure, they are capable of catalyzing the hydrolysis of

β-0^3ΐ3θίορνΓ3ηο8νΙ-(1→2)-β-0-χνΙορνΓ3ηο8νΙ linkages within the xyloglucan without affecting the xyloglucan backbone. As a consequence, partially degalactosylated xy- loglucans were formed having high average molecular weights and, thus, improved thermogelation properties. As regards the selection of suitable β-galactosidases (A2), the main emphasis is on the β-galactosidase activity. Thus, in general, all kinds of β-galactosidases can be used as long as they are capable of removing galactose from xyloglucan. The term 'being capable of removing galactose from xyloglucan' means that the β-galactosidase catalyzes the hydrolysis of β-0^3ΐ3θίορνΓ3ηο8νΙ-(1→2)-β-0-χνΙορνΓ3ηο8νΙ linkages within xy- loglucan, therby forming D-galactose (D-galactopyranose) and partially degalactosified xyloglucan. Whether a specific β-galactosidase is capable of removing galactose from xyloglucan, can be determined by standard methods. Such methods are, for example, described in X. Zhang, H. Bremer, H., J. Biol. Chem. 1995, 270, 1 1 181 -1 1 189 and the literature cited therein, or in the SIGMA quality control test procedure 'Enzymatic assay of beta-galactosidase' which is available from Sigma-Aldrich.

Suitable β-galactosidases being capable of removing galactose from xyloglucan (A2) are, in general, all kinds of β-galactosidases (β-D-galactoside galactohydrolases, E.C. 3.2.1.23). Such β-galactosidases are, for example, β-galactosidases isolated from fungi WkeTrichoderma reesei, Kluyveromyces lactis, Penicillium sp., Aspergillus oryzae, Aspergillus niger, Aspergillus aculeatus, Aspergillus awamori, Aspergillus carbonarius, Aspergillus japonicus, Aspergillus flavus, Kluyveromyces marxianus, Lactobacillus sp., Neurospora crassa, Rhizopus oryzae, Saccharomyces sp., or Saccharomyces sp.; β- galactosidases isolated from bacteria like Caulobacter crescentus, Bacillus circulans, Escherichia coli, Bacteroides fragilis, arthrobacter sp., Thermus thermophiles, Alicyclo- bacillus acidocaldarius, Bifidobacterium sp., Geobacillus stearothermophilus, Pseudo- monas sp., Saccharopolyspora rectivirgula, Streptococcus sp., or Thermus sp.; β- galactosidases isolated from archaea like Sulfolobus solfataricus; β-galactosidases isolated from animals like Mus musculus; or humans. However, homologues or variants of the β-galactosidases isolated from the above mentioned source are also within the scope of the present invention.

Preferably, the β-galactosidase being capable of removing galactose from xyloglucan (A2) is selected from the group consisting of β-galactosidases isolated from the fungi Trichoderma reesei, Kluyveromyces lactis, Penicillium sp., Aspergillus oryzae, Aspergillus niger, Aspergillus aculeatus, Aspergillus awamori, Aspergillus carbonarius, Aspergillus japonicus, Aspergillus flavus, Kluyveromyces marxianus, Lactobacillus sp., Neurospora crassa, Rhizopus oryzae, Saccharomyces sp., or Saccharomyces sp.; β- galactosidases isolated from the bacteria Caulobacter crescentus, Bacillus circulans, Escherichia coli, Bacteroides fragilis, arthrobacter sp., Thermus thermophiles, Alicyclo- bacillus acidocaldarius, Bifidobacterium sp., Geobacillus stearothermophilus, Pseudo- monas sp., Saccharopolyspora rectivirgula, Streptococcus sp., or Thermus sp; and homologues or variants thereof. More preferred, the β-galactosidase being capable of removing galactose from xyloglucan (A2) is a β-galactosidase isolated from Aspergillus oryzae, Aspergillus niger, Aspergillus aculeatus, Aspergillus awamori, Aspergillus carbonarius, Aspergillus japoni- cus, Aspergillus flavus, or a homologue or variant thereof. In a particularly preferred embodiment of the present invention, the β-galactosidase being capable of removing galactose from xyloglucan (A2) is the β-galactosidase isolated from Aspergillus oryzae, or homologues or variants thereof.

The amount of β-galactosidase used in the process according to the present invention is difficult to determine in absolute terms (e.g. grams), as its purity may vary. Instead, the activitiy is given in terms of the β-D-galactosidase activity. The physical unit of activity is unit (U). One unit (1.0 U) is herein defined to be the amount of β-galactosidase that catalyses the hydrolysis of 1 micromole of onitrophenyl β-D-galactoside to o nitrophenol and D-galactose per minute at pH 6.0 at 37 °C. The β-D-galactosidase ac- tivities mentioned herein have been determined according to SIGMA quality control test procedure 'Enzymatic assay of beta-galactosidase'.

The quantity of β-galactosidase (A2) in the aqueous well treatment formulation (A) is preferably set to an amount of at least 500 U per g Xyloglucan, more preferred set to an amount of at least 750 U per g Xyloglucan, even more preferred set to an amount of at least 1000 U per g Xyloglucan, most preferred set to an amount of at least 1500 U per g Xyloglucan.

Typically, the aqueous well treatment formulation (A) comprises from 0.01 to 10.00 % by weight of the β-galactosidase (A2), based on the total weight of the aqueous well treatment formulation (A). The aqueous well treatment formulation (A) comprises preferably from 0.01 to 8.00 % by weight, more preferred from 0.05 to 5.00 % by weight and most preferred from 0.05 to 3.00 % by weight of the β-galactosidase (A2), based on the total weight of the aqueous well treatment formulation (A).

In a particularly preferred embodiment of the present invention, the enzyme preparation comprising β-galactosidase (A2) is essentially free of contaminants showing cellulase activity, β-galactosidases themselves do not degrade the xyloglucan back bone. However, β-galactosidases are generally isolated from sources that also contain endoglu- canases (EC 3.2.1.4), cellobiohydrolases (EC 3.2.1.91 ) and/or other enzymes, capable of hydrolyzing cellulose polymers to smaller oligosaccharides, cellobiose and/or glucose. Such enzymes do also catalyze the hyrolysis of 3(1→4)-glycosidic bonds in the back bone of xyloglucan. As a consequence, partially degalactosylated xyloglucan is being formed having lower average molecular weights and, thus, inferior thermogela- tion properties. Therefore, it is preferred to use enzyme preparations comprising β- galactosidase (A2) being essentially free of contaminants showing cellulase activity.

According to the present invention, the enzyme preparation comprising β-galactosidase (A2) is deemed to be essentially free of contaminants showing cellulase activity, if it has a specific cellulase activity below 2 U/g.

Preferably, the enzyme preparation comprising β-galactosidase (A2) has a specific cellulase activity below 2 U/g. The specific cellulase activity is more preferred below 1 U/g and most preferred below 0.1 U/g.

The term 'cellulase activity' used herein refers to enzyme preparations or solutions containing endoglucanases (EC 3.2.1 .4), cellobiohydrolases (EC 3.2.1.91 ) and/or other enzymes capable of hydrolyzing cellulose polymers to smaller oligosaccharides, cellobiose and/or glucose. A person skilled in the art is familiar with measurement methods of cellulase activity. Measurement methods of cellulase activity have been reviewed several times (see, for example, 'Determination methods of cellulase activity" T.

Shuangqi et al., African Journal of Biotechnology 201 1 , 10, 7122-7125; 'Cellulase activities in biomass conversion: Measurement methods and comparison' M. Dashtban et al, Critical Reviews in Biotechnology 2010, 1 -8).

The values of the cellulase activity mentioned herein have been determined according to the azo-xyloglucan assay. One unit (1.0 U) is herein defined to be the amount of enzymes that will catalyse the hydrolysis of 1 micromole of azo xyloglucan to low molecular weight fragments per minute. Said assay is specific for enc/o-1 ,4^-D-glucanase activity present in cellulase preparations. On incubation of azo xyloglucan with cellulase, said azo xyloglucan is depolymerized by an enc/omechanism to produce low- molecular weight fragments. After incubation the reaction is stopped by adding methanol. Then, high-molecular weight fragments are removed by centrifugation whereas low-molecular weight fragments remain in the supernatant solution. Said supernatant solution is poured into a spectrophotometer cuvette and the absorbance of blank and low-molecular weight fragment containing supernatant solution is measured at 590 nm. £nc/o-1 ,4^-D-glucanase activity is determined by reference to a standard curve to convert absorbance to cellulase activity. The aqueous well treatment formulation (A) comprises also water. The water used can be obtained from any acceptable source, and may include brine, fresh water, sea water, formation water and the like. Depending from the water source, the aqueous well treatment formulation (A) can comprise salt. Typically, the oil and natural gas bearing formations comprise formation waters having a greater or lesser salt content. Typical salts in such formation waters comprise especially alkali metal salts and alkaline earth metal salts. Examples of typical cations of such salts comprise Na⁺, K⁺, Mg²⁺ and Ca²⁺, and examples of typical anions of such salts comprise chloride, bromide, hydrogencar- bonate, sulfate or borate. Preferably, the aqueous well treatment formulation (A) com- prises as water component the formation water of the oil and/or natural gas bearing formation in which it is intended to be used.

In one embodiment of the present invention, the aqueous well treatment formulation (A) comprises salt. Typically, the aqueous well treatment formulation (A) comprises of from 0.001 to 40.00 % by weight of salt based on the total weight of the aqueous well treatment formulation (A). The aqueous well treatment formulation (A) comprises more preferred of from 0.02 to 30.00 % by weight, even more preferred of from 0.05 to 20.00 % by weight, most preferred of from 0.5 to 15.00 % by weight of salt based on the total weight of the aqueous treating formulation.

The salt content strongly influences the sol-gel transition temperature while the viscosity and the gel strength remain almost unaffected. As a rule, the higher the content of salt, the higher becomes the sol-gel transition temperature. Thus, the lowest sol-gel transition temperature is usually achieved if the water is deionized water. Accordingly, the highest sol-gel transition temperature can usually be achieved at a very high content of salt.

The aqueous well treatment formulation (A) comprises optionally one or more additives (A3).

Preferably, the aqueous well treatment formulation (A) comprises as an additive (A3) one or more additionally added salts. The term 'additionally added salts' means that salt is added in addition to the salt already present in the aqueous formulation (A1 ) due to the water used. This may be useful to fine tune the thermogelation properties. In general, all kinds of salt may be used as additionally added salt. Preferred additionally added salts are selected from the group consisting of Al2(S0₄)3, ethylene diamine tetra acetic acid trisodium salt (NasEDTA), cinnamic acid sodium salt, NaB02, Na2B₄07, NaCI, CaCI₂, AICI₃, FeS0₄, FeCI₃ and NDIIa. In a preferred embodiment of the present invention, the one or more additionally added salts are selected from salts having divalent cations. It has been found that the type of salt present in the aqueous treating formulation influences the gel strength and viscosity as well. Accordingly, the higher the ratio of salts having bivalent cations to salts hav- ing monovalent cations, the higher becomes the gelling strength and viscosity.

If said salts having monovalent, divalent and/or trivalent cations are additionally added, their concentration in the well treatment formulation (A) is in general of from 0.001 % to 30.0 % by weight based on the total weight of the aqueous well treatment formulation (A). Preferably, the additionally added one or more salts are present in concentrations of from 0.05 % to 15.0 % by weight based on the total weight of the aqueous well treatment formulation (A).

The in-situ xyloglucan degalactosylation is best performed at pH values of from 2 to 9, more preferred of from 3 to 8, even more preferred of from 4.5 to 7.5. Thus, the aqueous well treatment formulation (A) comprises as an additive (A3) preferably one or more acids. More preferred, the aqueous well treatment formulation (A) comprises one or more acids selected from the group consisting of kaffeic acid, frans-ferulic acid, tannic acid, 2,4-dihydroxybenzoic acid, 2,5-dihydroxybenzoic acid, boric acid, 2,4,6- trihydroxybenzoic acid, 2,4,6-trihydroxybenzoic acid, cinnamic acid and ricinoleic acid.

Where used, such acids are present in the aqueous well treatment formulation (A) in concentrations of from 0.001 % to 10.0 % by weight based on the total weight of the aqueous well treatment formulation (A). The aqueous well treatment formulation (A) comprises preferably of from 0.01 to 8.0 % by weight, more preferred of from 0.05 to 5.0 % by weight, most preferred of from 0.05 to 3.0 by weight of such acids based on the total weight of the aqueous well treatment formulation (A).

The aqueous well treatment formulation (A) can comprise as an additive (A3) one or more biocides, inter alia, to protect the aqueous gelled partially degalactosylated xyloglucan from attack by bacteria or fungi. Such attacks may be problematic because they may lower the molecular weight of the partially degalactosified xyloglucan resulting in lower viscosities and thus poorer performance. Suitable biocides are known in the art. A person skilled in the art with the benefit of this disclosure will be able to iden- tify suitable biocides for a given application.

Suitable biocides include, for example, formaldehyde, sodium hypochlorite, 2,2- dibromo-3-nitrilopropionamide, 2-bromo-2-nitro-1 ,3-propanediol and glutardialdehyde. Preferred biocides are formaldehyde and glutardialdehyde. Where used, such biocides are present in concentrations sufficiently high to destroy all bacteria and fungi that may be present. Said biocides are usually present in the aqueous well treatment formulation (A) in concentrations of from 0.001 % to 0.50 % by weight based on the total weight of the aqueous well treatment formulation (A). Such biocides are preferably present in concentrations of from 0.001 % to 0.10 % by weight, more preferred of from 0.001 % to 0.01 % by weight based on the total weight of the aqueous well treatment formulation (A).

The aqueous well treatment formulation (A) can further comprise other additives (A3), including those which are common additives in well bore treating. Such additives are, for example, lignin, chitosan, hydrochinon, hydroxyhydrochinon, sucrose, guar gum, xanthan, schizophyllan, epigalocatechin gallate (EGCG), pyrogallol, pectin, Bretax C^®, Mimosa ME, Tamol^® NNOL, common buffers or water soluble organic solvents. Where used, such additives are present in the aqueous well treatment formulation (A) in concentrations of from 0.001 % to 15.0 % by weight based on the total weight of the aqueous well treatment formulation (A). The aqueous well treatment formulation (A) comprises preferably of from 0.01 to 10.0 % by weight, more preferred of from 0.05 to 7.0 % by weight, most preferred of from 0.05 to 5.0 % by weight of such additives based on the total weight of the aqueous well treatment formulation (A).

According to the present invention, the method comprises at least the steps (a), (b) and (c). In step (a), the aqueous well treatment formulation (A) as defined above is provided. The aqueous well treatment formulation (A) is generally provided by mixing water with the xyloglucan (A1 ), an enzyme preparation comprising β-galactosidase (A2) and optionally one or more additives (A3) shortly before the injection. However, mixing can also being done at an earlier occasion as long as the gel formation is prevented before the injection.

The aqueous well treatment formulation (A) as defined above should be approached on a specific project basis to meet objective in terms of sol-gel transition temperature, gel strength and viscosity. The sol-gel transition temperature of the aqueous well treatment formulation (A) is thereby especially dictated by the total amount of salt present in said formulation (A) and the galactose removal ratio of the partially degalactosylated xyloglucan. Typically, the lower the total salt content of the aqueous treating formulation and the higher the galactose removal ratio of the partially degalactosylated xyluglucan, the lower becomes the sol-gel transition temperature of said formulation. Consequent- ly, the sol-gel transition temperature of the aqueous well treatment formulation can be very precisely adapted to the formation temperature. Most important, however, is the chain length of the xyloglucan back bone of the partially degalactosylated xyloglucan. The longer the chain length of the xyloglucan back bone of the partially degalactosylated xyloglucan, the higher becomes the gelling strength and viscosity of the aqueous well treatment formulation.

In step (b), the aqueous well treatment formulation (A) is injected into at least one well bore penetrating the oil and/or natural gas bearing subterranean formation. The injection of the aqueous well treatment formulation (A) can be undertaken by means of cus- tomary apparatus. Said formulation (A) can be injected into one or more injection wells, or into one or more production wells by means of customary pumps.

Said wells are often lined with steel tubes cemented in place in the region of an oil and/or natural gas bearing subterranean formation, and the steel tubes are perforated at the desired point. In a manner known by the one skilled in the art, the pressure applied by means of the pumps fixes the flow rate of the aqueous treating formulation and hence also the shear stress with which the aqueous treating formulation enters the subterranean formation. The shear stress on entry into the subterranean formation can be calculated by the person skilled in the art in a manner known in principle on the ba- sis of the Hagen-Poiseuille law using the flow area on entry into the formation, the mean pore radius and the volume flow rate. The average permeability or porosity of the formation can be determined in a manner known in principle by measurements on drill cores. Of course, the greater the volume flow rate of aqueous formulation injected into the formation, the greater the shear stress.

The rate of injection can be fixed by the person skilled in the art according to the properties and the requirements of the subterranean formation (number of injectors, configuration thereof, etc.). Preferably, the shear rate on entry of the aqueous treating formulation into the subterranean formation is at least 30 000 s^_1, preferably at least

60 000 s-¹ and more preferred at least 90 000 s^"1.

According to the present invention, the subterranean formation is one which has a minimum down hole temperature of 0 °C, preferably 10 °C, more preferred 20 °C, most preferred 30 °C, and a maximum temperature of 120 °C, preferably of 1 10 °C, more preferred of 100 °C, most preferred 90 °C.

Thus, the oil and natural gas bearing subterranean formation has preferably, a down hole temperature between 10 and 1 10 °C. More preferred the down hole temperature is between 20 and 100 °C. In step (c), the aqueous well treatment formulation (A) forms a gel in the permeable zones of the oil and/or natural gas bearing subterranean formation. The gel formation is caused by the partial degalactosylation of the xyloglucan (A1 ) by the β-galactosidase (A2), and the formation temperature.

Generally, around 40 % of the D-galactopyranose residues of the xyloglucan (A1 ) are being removed when the partially degalactosylated xyloglucan starts gelling under the influence of the formation temperature. Depending on the activity of the β- galactosidase (A2) and the formation temperature, the time needed to achieve a galac- tose removal ratio of at least 0.4 varies between several minutes to several days.

The substitution pattern and the length of the partially degalactosylated xyloglucan depends on the plant source of which the xyloglucan has been isolated. The length is best expressed by the average number of repeating units (m) and the average molecu- lar weight (M_w). The partially degalactosylated xyloglucans have typically a glucopyra- nose (Glcp) : xylopyranose (Xylp) : galactopyranose (Galp) : fucopyranose (Fucp) : arabinofuranose (Ara/)-ratio of 4 : 2.1 to 3.3 : 0.0 to 1.7 : 0.0 to 0.6 : 0.0 to 0.6.

The partially degalactosylated xyloglucan according to the present invention has pref- erably an average molecular weight of from 200 000 to 1 500 000 Da.

Having average molecular weights lower than 200 000 Da, the partially degalactosylated xyloglucan does not have thermogelation properties at all. But with increasing average molecular weight, the viscosity and the gelation strength of the partially degalacto- sylated xyloglucan increase as well, resulting in a decreased requirement of the partially degalactosylated xyloglucan to achieve the desired viscosity and gelation strength in the aqueous treating formulation. Thus, the partially degalactosylated xyloglucan has more preferred an average molecular weight of from 400 000 to 1 500 000 Da, even more preferred of from 600 000 to 1 500 000 Da, even more preferred of from 800 000 to 1 500 000 Da, most preferred of from 1 000 000 to 1 500 000 Da.

The partially degalactosylated xyloglucan has preferably a galactose removal ratio of from 0.40 to 0.90. At higher galactose removal ratios, the partially degalactosylated xyloglucan reveals gelation over a broader temperature range. Moreover, the higher the galactose removal ratio, the higher becomes the viscosity and the gelation strength of the partially degalactosylated xyloglucan. As a result, lower concentrations of partially degalactosylated xyloglucan are required to achieve the desired viscosity and gelation strength. Thus, the degalactosylated xyloglucan has more preferred a galactose removal ratio of from 0.43 to 0.80, even more preferred of from 0.48 to 0.70, most preferred of from 0.50 to 0.60. The galactose removal ratio (GRR) was determined as:

GRR = (amount of galactose residues in xyloglucan - amount of galactose residues in the partially degalactosylated xyloglucan) / amount of galactose residues in xy- loglucan

The amount of galactose residues in xyloglucan and the amount of galactose residues in the partially degalactosylated xyloglucan was measured after total hydrolysis by heating the polysaccharides in 2 N sulfuric acid at 100 °C for 3 h according to M. Shi- rakawa et al. (M. Shirakawa et al., Food Hydrocolloids 1998, 12, 25-28).

The thermogelation properties of the aqueous well treatment formulation (A) can be evaluated by rheological experiments with Anton Paar MCR Rheometers. Temperature sweep experiments were done in a temperature range between 0 °C and 140 °C. A sealed geometry (pressure cell) was used with a double-gap geometry. Measurements were carried out at a constant shear rate of 10 s^_1 with a heating rate of 0.5 °C / min. Gel kinetic experiments were done in a concentric cylinder geometry with small amplitude oscillation shear (SAOS) measurements at 1 Hz with a deformation of 5 %. The geometry was set to the particular measurement temperature before the sample was filled. The initial sample temperature was about 4 °C. Right after the sample was filled into the geometry, the sample was covered with silicone oil. Silicone oil was used to prevent evaporation and salt crust formation at elevated temperatures. In order to have identical conditions, this procedure was kept constant for all kinetic measurements at all temperatures. Due to the overall handling procedure there was a time delay of about 60 - 90 seconds till the first data point could be collected.

The average number of repeating units (m) of the partially degalactosylated xyloglucan depends on the average molecular weight and the type of repeating unit of the xyloglucan used as well as the galactose removal ratio. The average number of repeating units (m) can easily be calculated from the average molecular weight, the galactose removal ratio and the average weight per repeating unit. The average number of repeating units (m) is from 200 to 1400. Preferably, the average number of repeating units (m) is from 300 to 1400. The average number of repeating units (m) is more preferred from 500 to 1400, even more preferred from 700 to 1400, most preferred from 900 to 1400. The method of the present invention provides partially degalactosylated xyloglucan, wherein the average number of repeating units of the partially degalactosylated xyloglucan (m) is at least 0.9 times the average number of repeating units of the xyloglu- can (n) such that the ratio m / n is from 0.90 to 1 (m / n = 0.90 to 1 ). The ratio m / n is preferably from 0.95 to 1 , more preferred of from 0.98 to 1 , most preferred of from 0.99 to 1 .

If the xyloglucan (A1 ) of the aqueous well treatment formulation (A) is tamarind xylogu- can having general formula (II), the partially degalactosylated tamarind xyloglucan having general formula (I) is being formed,

(I) wherein

the average number of the β-D-galactopyranose residues per repeating unit (di + d₂) is from 0.20 to 1.20,

the average number of the a-L-fucopyranose residues per repeating unit (a) is from 0.00 to 0.20, and

the average number of the repeating units (m) is from 200 to 1400. Preferably, the aqueous well treatment formulation (A) is used for conformance control.

Conformance control is a measure in which, for increasing the oil and/or natural gas production, highly permeable zones of the subterranean formation are plugged by in- jecting, for example, an aqueous gelling formulation which, after being forced into a well bore, forms a highly viscous gel under the influence of the temperature of the subterranean formation. As a result, highly permeable zones having low flow resistance are plugged and the flooding water flows again through the oil and/or natural gas satu- rated zones.

The term 'gelling' means that the formulation can in principle form gels under certain conditions but that the gel formation does not begin immediately after mixing of the components of the formulation. Instead, the formation of a gel is delayed and only starts once the gel formation temperature is achieved. It is clear for the person skilled in the art that the speed of gel formation may depend as a rule on both the time and the temperature. The person skilled in the art can determine the gel formation temperature exactly by measuring the gel formation speed of a certain formulation as a function of the temperature, followed by an extrapolation of the measured curve to a reaction rate at zero. In a pragmatic approach, the person skilled in the art can define the gel formation temperature approximately as the onset of gel formation after a time span relevant in practice. All that is important is that for comparison of the gel formation temperatures of the formulations used in each case, the same method for determining the gel formation temperature is used in each case.

The method according to the present invention can be employed especially in the case of oil and natural gas-bearing subterranean formations with an average permeability of around 100 mD to around 5 D (around 1 .0* 10^"13 m² to around 50*10^"13 m²), preferably around 150 mD to around 2 D (around 1 .5* 10^"13 m² to around 20*10^"13 m²), and more preferably around 200 mD to around 1 D (around 2.0x 10^"13 m² to around 10x10^"13).

The permeability of an oil and natural gas bearing subterranean formation can be determined from the flow rate of a liquid phase in the oil and natural gas bearing subterranean formation as a function of the pressure differential applied. Details thereof can be found, for example, in K. Weggen, G. Pusch, H. Rischmuller in Oil and Gas', pages 37 ff., Ullmann's Encyclopedia of Industrial Chemistry, Online edition, Wiley-VCH, Weinheim 2010.

Methods for temperature determinations of subterranean formations are known in prin- ciple to those skilled in the art. The temperature is generally undertaken from temperature measurements at particular sites in the formation.

The aqueous well treatment formulation (A) is provided and then injected through tubing into the well bore. While a high viscosity, high gelling strength formulation is highly desirable after the formulation is positioned in the highly permeable zone of the subter- ranean formation, large amounts of energy are required to pump such formulations through tubing into the formation. Therefore, delayed gelling is desired since it reduces the amount of energy required to pump the aqueous treating formulation through the tubing by permitting pumping of a relatively less viscous formulation having relatively low friction pressures within the well tubing.

In a preferred embodiment of the present invention, the aqueous well treatment formulation (A) is injected in step (b) into at least one well bore, wherein the well bore is an injection well penetrating the oil and/or gas bearing subterranean formation. Such an approach is called conformance control.

Thus, the object of the present invention is further solved by a method for treating an oil and/or natural gas bearing subterranean formation penetrated by at least one well bore, comprising the steps of

(a) providing an aqueous well treatment formulation (A) which comprises

(A1 ) a xyloglucan having an average molecular weight of from

200 000 to 1 500 000 Da,

(A2) an enzyme prepration comprising β-galactosidase being capable of removing galactose from xyloglucan, and

(A3) optionally one or more additives;

(b) injecting said aqueous well treatment formulation into at least one injection well penetrating the oil and gas bearing subterranean formation; and

(c) gelling of said aqueous well treatment formulation effected by partial

degalactosylation of the said xyloglucan.

In another preferred embodiment of the present invention, the aqueous treating formulation is injected in step (b) into at least one well bore, wherein the well bore is a production well penetrating the oil and natural gas bearing subterranean formation. Such an approach is also called conformance control or permeability modification. However, it is also frequently called 'water shut off'.

Thus, the object of the present invention is further solved by a method for treating an oil and/or natural gas bearing subterranean formation penetrated by at least one well bore, comprising the steps of (a) providing an aqueous well treatment formulation (A) which comprises

(A1 ) a xyloglucan having an average molecular weight of from

200 000 to 1 500 000 Da,

(A3) optionally one or more additives; (b) injecting said aqueous well treatment formulation into at least one production well penetrating the oil and gas bearing subterranean formation; and

(c) gelling of said aqueous well treatment formulation effected by partial

degalactosylation of the said xyloglucan.

In one aspect of the present invention, the at least one well bore penetrating the oil and gas bearing subterranean formation is, after blocking the permeable zone of the subterranean formation, water flooded to extract or produce oil and/or natural gas on at least one production well. To execute the method, at least one production well and at least one injection well were sunk into the subterranean formation. In general, an oil and/or natural gas bearing formation is provided with several injection wells and several production wells. The term 'oil' in this context does not mean only single-phase oil; instead, the term also comprises the customary crude oil-water emulsions. By virtue of the pressure generated by injection of the fluid, the oil and natural gas flows in the di- rection of the production well and is produced via the production well.

In this aspect of the present invention, the method for treating an oil and/or natural gas bearing subterranean formation penetrated by at least one well bore comprises the steps of

(a) providing an aqueous well treatment formulation (A) which comprises

(A1 ) a xyloglucan having an average molecular weight of from

200 000 to 1 500 000 Da,

(A2) an enzyme preparation comprising β-galactosidase being capable of removing galactose from xyloglucanand

(A3) optionally one or more additives; (b) injecting said aqueous well treatment formulation into at least one injection well penetrating the oil and gas bearing subterranean formation;

(c) gelling of said aqueous well treatment formulation effected by partial

degalactosylation of the said xyloglucan; and

(d) water flooding at least one injection well penetrating the oil and gas bearing subterranean formation to produce oil and natural gas on at least one production well.

After method steps (a), (b) and (c), the oil and/or natural gas production is continued through at least one production well. Preferably, the oil and natural gas production can be effected by customary methods by injecting a flooding medium through at least one injection well into the oil and natural gas bearing subterranean formation and producing oil and natural gas through at least one production well. The flooding medium may be in particular water or carbon dioxide. The at least one injection well may be the injection well(s) used for injecting the formulations or suitably arranged other injection wells. However, the oil and natural gas production can of course also be continued by means of other methods known in the art. For example, microorganisms which develop me- thane or carbon dioxide in the subterranean formation can be used and the pressure can be maintained in this manner. Furthermore, highly viscous formulations of thickening polymers, such as, for example, polyacrylamide or copolymers comprising acryla- mide, or certain polysaccharides can be used. In another aspect of the present invention, the at least one well bore penetrating the oil and/or gas bearing subterranean formation is, after blocking the permeable zone of the subterranean formation, used for the production of oil and/or natural gas, whereas at least one injection well is water flooded at the same time. To execute the method, at least one production well and at least one injection well were sunk into the subterrane- an formation. By virtue of the pressure generated by the fluid injection, the oil and natural gas flows in the direction of the production well and is produced via the production well.

In this aspect of the present invention, the method for treating a subterranean oil and/or natural gas bearing formation penetrated by at least one well bore comprises the steps of providing an aqueous well treatment formulation (A) which comprises (A1 ) a xyloglucan having an average molecular weight of from 200 000 to 1 500 000 Da,

(A3) optionally one or more additives;

(b) injecting said aqueous well treatment formulation into at least one injection well penetrating the oil and gas bearing subterranean formation; (c) gelling of said aqueous well treatment formulation effected by partial dega- lactosylation of the said xyloglucan; and

(d) producing oil and natural gas on at least one production well penetrating the oil and gas bearing subterranean formation by water flooding at least one in- jection well.

The object of the present invention is further solved by a method for treating an oil and/or natural gas bearing subterranean formation penetrated by at least one well bore, comprising the steps of

(a) injecting an aqueous xyloglucan formulation (X) into a well bore penetrating the oil and natural gas bearing subterranean formation, wherein the formulation (X) comprises (A1 ) a xyloglucan having an average molecular weight of from 200 000 to

1 500 000 Da, and

(A3) optionally one or more additives;

(b) injecting an aqueous β-galactosidase formulation (G) into the well bore pene- trating the oil and natural gas bearing subterranean formation, wherein the formulation (G) comprises

(A3) optionally one or more additives; (c) gelling of the mixed formulations effected by partial degalactosylation of the xyloglucan; wherein the steps (a) and (b) are performed simultaneously or consecutively in any order, each only once or several times.

It has been found that the xyloglucan (A1 ) and an enzyme preparation comprising β- galactosidase (A2) can also be injected as separate aqueous formulations either at the same time, or consecutively.

In one embodiment of the present invention, the steps (a) and (b) are performed simultaneously. In another embodiment of the present invention, the steps (a) and (b) are performed consecutively in any order. The aqueous xyloglucan formulation (X) comprises usually from 0.02 to 40.00 % by weight of the xyloglucan (A1 ), based on the total weight of the aqueous xyloglucan formulation (X). The aqueous xyloglucan formulation (X) comprises preferably from 0.2 to 20.0 % by weight, more preferred of from 1.0 to 10.0 % by weight, most preferred of from 2.0 to 6.0 % by weight of the xyloglucan (A1 ) as defined above, based on the total weight of the aqueous xyloglucan formulation (X).

The aqueous xyloglucan formulation (X) comprises preferably salt. Typically, the aqueous xyloglucan formulation (X) comprises of from 0.001 to 40.00 % by weight of salt based on the total weight of the aqueous xyloglucan formulation (X). The aqueous xy- loglucan formulation (X) comprises more preferred of from 0.02 to 30.00 % by weight, even more preferred of from 0.05 to 20.00 % by weight, most preferred of from 0.5 to 15.00 by weight of salt based on the total weight of the aqueous xyloglucan formulation. Preferred xyloglucans (A1 ) and additives (A3) that can preferably be added to the aqueous xyloglucan formulation (X) are already disclosed above in connection with the aqueous well treatment formulation (A).

The aqueous β-galactosidase formulation (G) comprises usually from 0.02 to 20.00 % by weight of the β-galactosidase (A2), based on the total weight of the aqueous β- galactosidase formulation (G). The aqueous β-galactosidase formulation (G) comprises preferably from 0.02 to 16.00 %, more preferred from 0.10 to 10.00 % by weight and most preferred from 0.10 to 6.00 % by weight of the β-galactosidase (A2), based on the total weight of the aqueous β-galactosidase formulation (G).

The aqueous β-galactosidase formulation (G) comprises preferably salt. Typically, the aqueous β-galactosidase formulation (G) comprises of from 0.001 to 40.00 % by weight of salt based on the total weight of the aqueous β-galactosidase formulation (G). The aqueous β-galactosidase formulation (G) comprises more preferred of from 0.02 to 30.00 % by weight, even more preferred of from 0.05 to 20.00 % by weight, most preferred of from 0.5 to 15.00 by weight of salt based on the total weight of the aqueous β- galactosidase formulation (G).

Preferred enzyme preparations comprising β-galactosidases (A2) and additives (A3) that can preferably be added to the aqueous β-galactosidase formulation (G) are already disclosed above in connection with the aqueous well treatment formulation (A).

Another aspect of the present invention is the use of the aqueous well treatment formulation (A) for conformance control measures or water shut-off measures.

Another aspect of the present invention is a method for producing enzyme preparations comprising β-galactosidase (A2), being essentially free of contaminants showing cellu- lase activity. β-galactosidases themselves do not catalyze the hydrolysis of β(1→4)-glycosidic bonds in the back bone of xyloglucan. However, β-galactosidases are generally isolat- ed from sources that also contain endoglucanases (EC 3.2.1 .4), cellobiohydrolases (EC 3.2.1 .91 ) and/or other enzymes, capable of hydrolyzing cellulose polymers to smaller oligosaccharides, cellobiose and/or glucose. Such enzymes do also catalyze the hydrolysis of β(1→4)-glycosidic bonds in the back bone of xyloglucan. As a consequence, partially degalactosylated xyloglucan is being formed having lower average molecular weights and, thus, inferior thermogelation properties.

According to the present invention, the enzyme preparations comprising β-galacto- sidase (A2) is deemed to be essentially free of contaminants showing cellulase activity, if its specific cellulase activity is below 2 U/g.

Preferably, the enzyme preparation comprising β-galactosidase (A2) has a specific cellulase activity below 2 U/g. The specific cellulase activity is more preferred below 1 U/g and most preferred below 0.1 U/g. This is achieved by the method for producing enzyme preparations comprising β- galactosidase (A2), showing specific cellulase activity below 2 U/g, comprising at least one anion exchange chromatographic step and at least one hydrophobic interaction chromatographic step, wherein said chromatographic steps can be conducted in arbi- trary order.

It has been found that it is possible to purify industrial enzyme preparations containing of from 0.02 to 95 % by weight of β-galactosidase, based on the dry weight of said industrial enzyme preparations, by means of an anion exchange chromatography and a hydrophobic interaction chromatography to achieve a purified enzyme preparation comprising β-galactosidase, as defined above, showing specific cellulase activity below 2 U/g.

The method for producing enzyme preparations comprising β-galactosidase (A2) com- prises two different chromatographic separation steps, namely the method of anion exchange on the basis of competitive interaction of charged ions and the method of hydrophobic interaction, which is characterized in that the nonpolar surface zones of a protein adsorb to the weakly hydrophobic ligands of a stationary phase at high salt concentrations. To be distinguished therefrom is the chromatographic separation prin- ciple of affinity chromatography which is based on the specific and reversible adsorption of a molecule to an individual matrix-bound bonding partner. The hydroxyapatite chromatography, which is based on the use of inorganic hydroxyapatite crystals, is a further separation method which differs from the anion exchange chromatography and the hydrophobic interaction chromatography.

All these chromatographic principles mentioned can easily be distinguished by the person skilled in the art (see, for example, Bioanalytik, F. Lottspeich, H. Zorbas (ed.), Heidelberg, Berlin, Germany, Spektrum Akad. Verlag 1998). So called "β-galactosidases" currently available from suppliers are industrial enzyme preparations containing of from 0.02 to 95 % by weight of β-galactosidase, based on the dry weight of said industrial enzyme preparations. Said industrial enzyme preparations containing β-galactosidase are commercially available, for example, Amano (Lactase F), Amano (LOacase 14-DS), Novozymes Lactozym® Pure, and Novozymes Lac- tozym® Pure 6500L.

For most of the desired applications, the purity of said industrial enzyme preparations containing β-galactosidase is high enough. However, higher purities are required in some particular applications, among them, the method of treating subterranean for- mations according to the present invention. As discussed above, the commercially available industrial enzyme preparations containing β-galactosidase comprise normally also other enzymes which may cause undesired side reactions, like fission of the β(1→4) glycosidic bond of the xyloglucan back bone. To avoid such side reactions, said industrial enzyme preparations containing β-galactosidase have to be purified. Most important in the context of the present invention is the separation of enzymes showing cellulase activity. The contaminations of the industrial enzyme preparations are mainly cell components, like other enzymes, polysaccharides, DNAs, RNAs etc.

According to the present invention it was found that β-galactosidases can be separated off from the contaminants showing cellulase activity by using at least one exchange chromatographic step and at least one hydrophobic interaction chromatographic step. The method for purification and/or isolation of β-galactosidases allows the separation of β-galactosidase from most of its contaminants present in the industrial enzyme preparations, especially from enzymes showing cellulase activity. As a result, the enzyme preparations comprising β-galactosidase (A2) obtained show specific cellulase activities below 2 U/g.

The term 'contaminants' used herein refers to all kinds of substances in the enzyme preparation being different from β-galactosidases. The contaminants may include sub- stances like, for example, endoglucanases or cellobiohydrolases. The contaminants may also include further substances such as DNAs, RNAs or polysaccharides, etc., and additives which had been used in the purification and isolation from the producing organism. Anion exchange chromatography primarily retains proteins and other molecules by the interaction of amine groups on the anion exchange matrix resin with aspartic or glutamic acid sidechains, having pKs values of around 4.4. The mobile phase is buffered at pH values greater than 4.4, below which acid side chains begin to protonate and retention decreases. Above a pH value of 4.4, retention of proteins and other molecules is largely dependent on the number of anionic side chains present in the proteins and other molecules. Proteins having different numbers of anionic side chains can often being separated by adjusting the pH value of the mobile phase to between 7 and 10 where histidine is not protonated and lysine begins to deprotonate. A mobile phase having a pH value of greater than 10 is not generally recommended because of possi- ble degradation of the proteins.

Suitable matrices and protocols for conducting the anion exchange chromatography can be taken from the product information of suppliers (for example GE Healthcare: http://www.gelife-science.com, Bio-Rad: http://www.bio-rad.com). Suitable anion exchange matrices include, for example, DEAE (diethylaminoethyl) se- pharose CI-4B, DEAE Sepharose Fast Flow, Q Sepharose (quaternary ammonium) Fast Flow, Q Sepharose High Performance from GE Healthcare; preferrably, quaternary ammonium matrices are used as matrix for the anion exchange chromatography. More preferred, Q sepharose Fast Flow and Q sepharose High Performance available by GE Healthcare are used. Most preferred Q sepharose Fast Flow is used as matrix for the anion exchange chromatography.

Typically, the chromatography is performed using an aqueous buffer system at pH val- ues of from about 5 to 10 and running a gradient from an aqueous solution containing said buffer system and one or more salts. Suitable buffer systems for the anion exchange chromatography include, for example, N-methyl piperazine/HCI, pipera- zine/HCI, L-histidine/HCI, Na₂HP04/NaH₂P04, triethanolamine/HCI, N-methyl- diethanolamine/HCI, diethanolamine/HCI, 1 ,3-diaminopropane/HCI, ethanolamine/HCI, piperazine/HCI. The preferred buffer systems are L-histidine/HCI, IS^HPC /Na^PC , triethanolamine/HCI. Most preferred is the buffer system IS^HPC Na^PC .

For purifying industrial enzyme preparations containing β-galactosidase (or prepurified β-galactosidase), the pH value of the buffer system should possibly be between 6.0 and 8.0. Preferably, the pH value is from 6.5 to 7.5. The concentration of the buffer system lies between 5 and 100 mM, preferably between 10 mM and 50 mM.

In the first step of the anion exchange chromatography, an aqueous buffer system having a pH value of between 6,0 and 8,0 is employed for equilibrating and washing the column.

Subsequently to washing, the industrial enzyme preparation containing β-galactosidase (or prepurified β-galactosidase) is injected onto the column under conditions where it will be strongly retained. Afterwards, an aqueous solution containing the buffer system and an increasing amount of one or more salts is applied to elute the industrial enzyme preparation containing β-galactosidase (or prepurified β-galactosidase) from the column. This is effected by means of increasing the ionic strength, which is effected by means of increasing salt concentration in the aqueous solution. Suitable salts are for example NaCI or KCI.

The hydrophobic interaction chromatography can be conducted with conventional resins. Suitable resins are, for example, butyl sepharose, octyl sepharose or phenyl sepharose from GE Healthcare; Macro-Prep^® methyl or Macro-Prep^® t-butyl from Bio- Rad; Fractogel^® EMD Phenyl (S), Fractogel^® EMD Propyl (S) from Merck; and TSK- GEL^® Ether-5PW (20), TSK-GEL^® Phenyl-5PW (20), TSK-GEL^® Ether-5PW (30), TSK- GEL^® Phenyl-5PW (30) from Tosoh Bioscience LLC. Preferably, the hydrophobic lig- ands are butyl, phenyl or octyl groups. More preferred are phenyl groups. Most preferred are phenyl sepharose, Fractogel^® EMD Phenyl (S), TSK-GEL^® Phenyl-5PW (20) and TSK-GEL^® Phenyl-5PW (30).

Conventional buffer systems, which are also employed in other types of chromatography, are suitable as buffer systems for the hydrophobic interaction chromatography. A preferred buffer system is Na₂HP0₄/NaH₂P0₄. In the first step of the hydrophobic interaction chromatography, the column is equilibrated with at least two column volumes of an aqueous solution comprising at least one salt and a buffer system.

Suitable salts are, for example, NH₄S0₄, K₂S0 , Na₂S0 , NH₄OC(0)CH₃, KOC(0)CH₃, NaOC(0)CH₃, NH₄CI, KCI or NaCI. Preferably, the salt is NH₄S0₄, K₂S0₄, Na₂S0₄. More preferred the salt is NH₄S0₄. The salt concentration in said aqueous solution is preferably from 0.5 to 3.0 mol/l, more preferred from 1 .0 to 2.5 mol/l. The pH value of said aqueous solution is usually between 6.0 and 8.0, preferably from 6.5 to 7.5. A preferred aqueous solution for hydrophobic interaction chromatography contains between 0.01 and 0.10 g/ml of a buffer system and 1 .5 and 2.0 g/mol of at least one salt.

Subsequently to equilibration, the prepurified β-galactosidase (or the industrial enzyme preparation containing β-galactosidase) is injected onto the column in an aqueous solution having the same composition as the aqueous solution used for equilibration. Then, the prepurified β-galactosidase (or the industrial enzyme preparation containing β- galactosidase) is eluted from the column by reducing the hydrophobic interaction. This can be achieved by reducing the salt concentration in the mobile phase and/or by elut- ing with a non-polar organic solvent, like for example, ethylene glycol or isopropanol. While the β-galactosidase passes through the column, most of the contaminants of the prepurified β-galactosidase (or the industrial enzyme preparation of β-galactosidase) remain bound to the column or passes through only at decreased salt concentration or high non-polar organic solvent concentration.

More details about hydrophobic interaction chromatography can be taken from the rel- evant literature, for example from the product information of the suppliers mentioned above (GE Healthcare and Bio-Rad). In general, the person skilled in the art is familiar with the chromatographic principles utilized in the hydrophobic interaction chromatography according to the present invention. After at least one cation exchange chromatographic step and at least one hydrophobic interaction chromatographic step, an enzyme preparation comprising β-galactosidase may be isolated and dried, wherein said enzyme preparation is obtained as an amorphous solid, showing a specific cellulase activity below 2 U/g.

In one embodiment of the present invention, the method for producing an enzyme preparation comprising β-galactosidase (A2), as defined above, comprises only two chromatographic separation steps, namely one anion exchange chromatographic step and one hydrophobic interaction chromatographic step.

In a preferred embodiment of the present invention, the anion exchange chromatography is conducted as first step, and the hydrophobic interaction chromatography as second step. This preferred method for producing an enzyme preparation comprising β-galactosidase provides an enzyme preparation (A2) showing specific cellulase activi- ty below 2 U/g.

In a preferred embodiment of the invention the enzyme preparation comprises at least 95 % by weight of β-galactosidase, preferably at least 98 % by weight. Another aspect of the present invention is the specific β-galactosidase, namely β- galactosidase BGA1 , comprising the amino acid sequence set out in SEQ ID NO: 2 or variants thereof, wherein the variant β-galactosidases have at least 80 %, preferably at least 90 %, more preferred at least 95 %, most preferred at least 99 % sequence identity with the sequence set out in SEQ ID NO: 2.

The β-galactosidase BGA1 is obtainable by the method for producing an enzyme preparation comprising β-galactosidase as defined above from Lactase F "Amano" (produced from Aspergillus oryzae by Amano Pharmaceutical Co., Ltd. Nakaku, Nagoya, Japan).

It has been found that the β-galactosidase BGA1 according to the present invention has favorable properties, in particular a relatively high enzymatic activity in hydrolysing β-0^3ΐ3θίορνΓ3ηο8νΙ-(1→2)^-D-xylopyranosyl linkages. It will be apparent for the person skilled in the art that DNA sequence polymorphism may exist within a given population, which may lead to changes in the amino acid sequence of the β-galactosidase BGA1. Such genetic polymorphism may exist in cells from different populations or within a population due to natural allelic variation. Therefore, variants of the β-galactosidases, wherein the β-galactosidases have at least 80 %, preferable at least 90 %, more preferable at least 95 %, most preferable at least 99 % sequence identity with the sequence set out in SEQ ID NO: 2 are also part of the invention. Said variants of the β-galactosidase mentioned above comprise β-galactosidases having one or more alterations, such as substitutions, insertions, deletions and/or truncations of one or more specific amino acid residues at one or more specific positions in the β-galactosidase according to sequence SEQ ID NO: 2.

Another aspect of the present invention features isolated nucleic acid molecules that encode the β-galactosidase BGA1 for use in the methods of the invention. The term "nucleic acid molecule" includes DNA molecules (e.g., linear, circular, cDNA or chromosomal DNA) and RNA molecules (e.g., tRNA, rRNA, mRNA) and analogs of the DNA or RNA generated using nucleotide analogs. The nucleic acid molecule can be single-stranded or double-stranded, but preferably is double-stranded DNA. The term "isolated" nucleic acid molecule includes a nucleic acid molecule which is free of sequences which naturally flank the nucleic acid molecule (i.e., sequences located at the 5' and 3' ends of the nucleic acid molecule) in the chromosomal DNA of the organism from which the nucleic acid is derived.

In various embodiments, an isolated nucleic acid molecule can contain less than about 10 kb, 5 kb, 4kb, 3kb, 2kb, 1 kb, 0.5 kb, 0.1 kb, 50 bp, 25 bp or 10 bp of nucleotide sequences which naturally flank the nucleic acid molecule in chromosomal DNA of the microorganism from which the nucleic acid molecule is derived. Moreover, an "isolated" nucleic acid molecule, such as a cDNA molecule, can be substantially free of other cellular materials when produced by recombinant techniques, or substantially free of chemical precursors or other chemicals when chemically synthesized.

The term "gene," as used herein, includes a nucleic acid molecule (e.g., a DNA molecule or segment thereof), for example, a protein or RNA-encoding nucleic acid molecule, that in an organism, is separated from another gene or other genes, by intergenic DNA (i.e., intervening or spacer DNA which naturally flanks the gene and/or separates genes in the chromosomal DNA of the organism). A gene may direct synthesis of an enzyme or other protein molecule (e.g., may comprise coding sequences, for example, a contiguous open reading frame (ORF) which encodes a protein) or may itself be functional in the organism. A gene in an organism, may be clustered in an operon, as de- fined herein, said operon being separated from other genes and/or operons by the intergenic DNA. Individual genes contained within an operon may overlap without intergenic DNA between said individual genes. An "isolated gene", as used herein, includes a gene which is essentially free of sequences which naturally flank the gene in the chromosomal DNA of the organism from which the gene is derived (i.e., is free of adjacent coding sequences which encode a second or distinct protein or RNA mole- cule, adjacent structural sequences or the like) and optionally includes 5' and 3' regulatory sequences, for example promoter sequences and/or terminator sequences. Preferably, an isolated gene contains less than about 10 kb, 5 kb, 2 kb, 1 kb, 0.5 kb, 0.2 kb, 0.1 kb, 50 bp, 25 bp or 10 bp of nucleotide sequences which naturally flank the gene in the chromosomal DNA of the organism from which the gene is derived.

In one aspect, the methods of the present invention features use of isolated β- galactosidase nucleic acid sequences or genes. In a preferred embodiment, the nucleic acid or gene is derived from Aspergillus. The term "derived from Aspergillus" or "Aspergillus -derived" includes a nucleic acid or gene which is naturally found in microorganisms of the genus Aspergillus. Preferably, the nucleic acid or gene is derived from Aspergillus oryzae. In yet another preferred embodiment, the nucleic acid or gene is a Aspergillus gene homologue (e.g., is derived from a species distinct from Aspergillus but having significant homology to a Aspergillus gene of the present invention, for example, a Aspergillus β-galactosidase gene).

Included within the scope of the present invention are bacterial-derived nucleic acid molecules or genes and/or Aspergillus-derived nucleic acid molecules or genes (e.g., Aspergillus-derived nucleic acid molecules or genes), for example, the genes identified by the present inventors, for example, Aspergillus or A. oryzae beta-galactosidase genes.

Further included within the scope of the present invention are bacterial-derived nucleic acid molecules or genes and/or Aspergillus-derived nucleic acid molecules or genes (e.g., A. oryzae-derived nucleic acid molecules or genes) (e.g., A. oryzae nucleic acid molecules or genes) which differ from naturally-occurring Aspergillus nucleic acid molecules or genes (e.g., A. oryzae nucleic acid molecules or genes), for example, nucleic acid molecules or genes which have nucleic acids that are substituted, inserted or de- leted, but which encode proteins substantially similar to the naturally-occurring gene products of the present invention. In one embodiment, an isolated nucleic acid molecule comprises the nucleotide sequences set forth as SEQ ID NO:1 , or encodes the amino acid sequence set forth in SEQ ID NO:2. In another embodiment, an isolated nucleic acid molecule of the present invention comprises a nucleotide sequence which is at least about 60-65 %, preferably at least about 70-75 %, more preferable at least about 80-85 %, and even more preferably at least about 90-95 % or more identical to a nucleotide sequence set forth as SEQ ID NO:1. In another embodiment, an isolated nucleic acid molecule hybridizes under stringent conditions to a nucleic acid molecule having a nucleotide sequence set forth as SEQ ID NO:1. Such stringent conditions are known to those skilled in the art and can be found in Current Protocols in Molecular Biology, John Wiley & Sons, N.Y.

(1989), 6.3.1 -6.3.6. A preferred, non-limiting example of stringent (e.g. high stringency) hybridization conditions are hybridization in 6X sodium chloride/sodium citrate (SSC) at about 45°C, followed by one or more washes in 0.2 X SSC, 0.1 % SDS at 50-65°C. Preferably, an isolated nucleic acid molecule of the invention that hybridizes under stringent conditions to the sequence of SEQ ID NO:1 corresponds to a naturally- occurring nucleic acid molecule. As used herein, a "naturally-occurring" nucleic acid molecule refers to an RNA or DNA molecule having a nucleotide sequence that occurs in nature.

A nucleic acid molecule of the present invention (e.g., a nucleic acid molecule having the nucleotide sequence of SEQ ID NO:1 ) can be isolated using standard molecular biology techniques and the sequence information provided herein. For example, nucle- ic acid molecules can be isolated using standard hybridization and cloning techniques (e.g., as described in Sambrook, J., Fritsh, E. F., and Maniatis, T. Molecular Cloning: A Laboratory Manual. 2nd, ed., Cold Spring Harbor Laboratory, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY, 1989) or can be isolated by the polymerase chain reaction using synthetic oligonucleotide primers designed based upon the se- quence of SEQ ID NO:1. A nucleic acid of the invention can be amplified using cDNA, mRNA or alternatively, genomic DNA, as a template and appropriate oligonucleotide primers according to standard PCR amplification techniques. In another preferred embodiment, an isolated nucleic acid molecule of the invention comprises a nucleic acid molecule which is a complement of the nucleotide sequence shown in SEQ ID NO:1 .

In another embodiment, an isolated nucleic acid molecule is or includes a β-galacto- sidase gene, or portion or fragment thereof. In one embodiment, an isolated β-galacto- sidase nucleic acid molecule or gene comprises the nucleotide sequence as set forth in SEQ ID NO:1 .

In another embodiment, an isolated β-galactosidase nucleic acid molecule or gene comprises a nucleotide sequence that encodes the β-galactosidase BGA1 having the amino acid sequence as set forth in SEQ ID NO:2. In yet another embodiment, an isolated β-galactosidase nucleic acid molecule or gene encodes a homologue of β- galactosidase BGA1 having the amino acid sequence of SEQ ID NO:2. As used herein, the term "homologue" includes a protein or polypeptide sharing at least about 30- 35 %, preferably at least about 35-40 %, more preferably at least about 40-50 %, and even more preferably at least about 60 %, 70 %, 80 %, 90 % or more identity with the amino acid sequence of a wild-type protein or polypeptide described herein and having a substantially equivalent functional or biological activity as said wild-type protein or polypeptide. For example, a β-galactosidase homologue shares at least about 30- 35 %, preferably at least about 35-40 %, more preferably at least about 40-50 %, and even more preferably at least about 60 %, 70 %, 80 %, 90 % or more identity with the β-galactosidase BGA1 having the amino acid sequence set forth as SEQ ID NO:2 and has a substantially equivalent functional or biological activity (i.e., is a functional equivalent) of the β-galactosidase BGA1 having the amino acid sequence set forth as SEQ ID NO:2 (e.g., has a substantially equivalent cellulase activity). In a preferred embodiment, an isolated β-galactosidase nucleic acid molecule or gene comprises a nucleotide sequence that encodes a polypeptide as set forth in SEQ ID NO:2.

In another embodiment, an isolated β-galactosidase nucleic acid molecule hybridizes to all or a portion of a nucleic acid molecule having the nucleotide sequence set forth in SEQ ID NO:1 or hybridizes to all or a portion of a nucleic acid molecule having a nucleotide sequence that encodes a polypeptide having the amino acid sequence of SEQ ID NOs:2. Such hybridization conditions are known to those skilled in the art and can be found in Current Protocols in Molecular Biology, Ausubel et al., eds., John Wiley & Sons, Inc. (1995), sections 2, 4 and 6. Additional stringent conditions can be found in Molecular Cloning: A Laboratory Manual, Sambrook et al., Cold Spring Harbor Press, Cold Spring Harbor, NY (1989), chapters 7, 9 and 1 1. A preferred, non-limiting exam- pie of stringent hybridization conditions includes hybridization in 4X sodium chloride/sodium citrate (SSC), at about 65-70°C (or hybridization in 4X SSC plus 50% formamide at about 42-50°C) followed by one or more washes in 1 X SSC, at about 65- 70°C. A preferred, non-limiting example of highly stringent hybridization conditions includes hybridization in 1 X SSC, at about 65-70°C (or hybridization in 1X SSC plus 50% formamide at about 42-50°C) followed by one or more washes in 0.3X SSC, at about 65-70°C. A preferred, non-limiting example of reduced stringency hybridization conditions includes hybridization in 4X SSC, at about 50-60°C (or alternatively hybridization in 6X SSC plus 50% formamide at about 40-45°C) followed by one or more washes in 2X SSC, at about 50-60°C. Ranges intermediate to the above-recited val- ues, e.g., at 65-70°C or at 42-50°C are also intended to be encompassed by the present invention. SSPE (1X SSPE is 0.15 M NaCI, 10mM NaH₂P0₄, and 1.25 mM EDTA, pH 7.4) can be substituted for SSC (1X SSC is 0.15 M NaCI and 15 mM sodium citrate) in the hybridization and wash buffers; washes are performed for 15 minutes each after hybridization is complete. The hybridization temperature for hybrids antici- pated to be less than 50 base pairs in length should be 5-10°C less than the melting temperature (T_m) of the hybrid, where T_m is determined according to the following equations.

For hybrids less than 18 base pairs in length, T_m(°C) = 2(# of A + T bases) + 4(# of G + C bases). For hybrids between 18 and 49 base pairs in length, T_m(°C) = 81.5 + 16.6(logio[Na⁺]) + 0.41 (%G+C) - (600/N), where N is the number of bases in the hybrid, and [Na⁺] is the concentration of sodium ions in the hybridization buffer ([Na⁺] for 1X SSC = 0.165 M). It will also be recognized by the skilled practitioner that additional reagents may be added to hybridization and/or wash buffers to decrease non-specific hybridization of nucleic acid molecules to membranes, for example, nitrocellulose or nylon membranes, including but not limited to blocking agents (e.g., BSA or salmon or herring sperm carrier DNA), detergents (e.g., SDS), chelating agents (e.g., EDTA), Ficoll, PVP and the like. When using nylon membranes, in particular, an additional preferred, non-limiting example of stringent hybridization conditions is hybridization in 0.25-0.5M NaH₂P0₄, 7% SDS at about 65°C, followed by one or more washes at 0.02M NaH₂P0₄, 1 % SDS at 65°C, see e.g., Church and Gilbert (1984) Proc. Natl. Acad. Sci. USA 81 :1991 -1995, (or, alternatively, 0.2X SSC, 1 % SDS).

In another preferred embodiment, an isolated nucleic acid molecule comprises a nu- cleotide sequence that is complementary to a β-galactosidase nucleotide sequence as set forth herein (e.g., is the full complement of the nucleotide sequence set forth as SEQ ID NO:1 ).

The present invention further features recombinant nucleic acid molecules (e.g., re- combinant DNA molecules) that include nucleic acid molecules and/or genes described herein.

The present invention further features vectors (e.g., recombinant vectors) that include nucleic acid molecules (e.g., isolated or recombinant nucleic acid molecules and/or genes) described herein. In particular, recombinant vectors are featured that include nucleic acid sequences that encode gene products as described herein (e.g., β- galactosidase).

The term "recombinant nucleic acid molecule" includes a nucleic acid molecule (e.g., a DNA molecule) that has been altered, modified or engineered such that it differs in nucleotide sequence from the native or natural nucleic acid molecule from which the recombinant nucleic acid molecule was derived (e.g., by addition, deletion or substitution of one or more nucleotides). Preferably, a recombinant nucleic acid molecule (e.g., a recombinant DNA molecule) includes an isolated nucleic acid molecule or gene of the present invention (e.g., an isolated β-galactosidase gene) operably linked to regulatory sequences.

The term "recombinant vector" includes a vector (e.g., plasmid, phage, phasmid, virus, cosmid or other purified nucleic acid vector) that has been altered, modified or engi- neered such that it contains greater, fewer or different nucleic acid sequences than those included in the native or natural nucleic acid molecule from which the recombinant vector was derived. Preferably, the recombinant vector includes a β-galactosi- dase gene or recombinant nucleic acid molecule including such β-galactosidase gene, operably linked to regulatory sequences, for example, promoter sequences, terminator sequences and/or artificial ribosome binding sites (RBSs).

The phrase "operably linked to regulatory sequence(s)" means that the nucleotide sequence of the nucleic acid molecule or gene of interest is linked to the regulatory sequence^) in a manner which allows for expression (e.g., enhanced, increased, consti- tutive, basal, attenuated, decreased or repressed expression) of the nucleotide sequence, preferably expression of a gene product encoded by the nucleotide sequence (e.g., when the recombinant nucleic acid molecule is included in a recombinant vector, as defined herein, and is introduced into a microorganism). The term "regulatory sequence" includes nucleic acid sequences which affect (e.g., modulate or regulate) expression of other nucleic acid sequences. In one embodiment, a regulatory sequence is included in a recombinant nucleic acid molecule or recombinant vector in a similar or identical position and/or orientation relative to a particular gene of interest as is observed for the regulatory sequence and gene of interest as it appears in nature, e.g., in a native position and/or orientation. For example, a gene of interest can be included in a recombinant nucleic acid molecule or recombinant vector operably linked to a regulatory sequence which accompanies or is adjacent to the gene of interest in the natural organism (e.g., operably linked to "native" regulatory sequences, for example, to the "native" promoter). Alternatively, a gene of interest can be in- eluded in a recombinant nucleic acid molecule or recombinant vector operably linked to a regulatory sequence which accompanies or is adjacent to another (e.g., a different) gene in the natural organism. Alternatively, a gene of interest can be included in a recombinant nucleic acid molecule or recombinant vector operably linked to a regulatory sequence from another organism. For example, regulatory sequences from other mi- crobes (e.g., other bacterial regulatory sequences, bacteriophage regulatory sequences and the like) can be operably linked to a particular gene of interest.

In one embodiment, a regulatory sequence is a non-native or non-naturally-occurring sequence (e.g., a sequence which has been modified, mutated, substituted, derivat- ized, deleted including sequences which are chemically synthesized). Preferred regulatory sequences include promoters, enhancers, termination signals, anti-termination signals and other expression control elements (e.g., sequences to which repressors or inducers bind and/or binding sites for transcriptional and/or translational regulatory proteins, for example, in the transcribed mRNA). Such regulatory sequences are de- scribed, for example, in Sambrook, J., Fritsh, E. F., and Maniatis, T. Molecular Cloning: A Laboratory Manual. 2nd, ed., Cold Spring Harbor Laboratory, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY, 1989. Regulatory sequences include those which direct constitutive expression of a nucleotide sequence in a microorganism (e.g., constitutive promoters and strong constitutive promoters), those which direct inducible expression of a nucleotide sequence in a microorganism (e.g., inducible promoters, for example, xylose inducible promoters) and those which attenuate or repress expression of a nucleotide sequence in a microorganism (e.g., attenuation signals or repressor sequences). It is also within the scope of the present invention to regulate expression of a gene of interest by removing or deleting regulatory sequences. For example, se- quences involved in the negative regulation of transcription can be removed such that expression of a gene of interest is enhanced.

In one embodiment, a recombinant nucleic acid molecule or recombinant vector of the present invention includes a nucleic acid sequence or gene that encodes a β- galactosidase operably linked to a promoter or promoter sequence. Such promoters or promoter sequences are known in the art.

In another embodiment, a recombinant nucleic acid molecule or recombinant vector of the present invention includes a terminator sequence or terminator sequences (e.g., transcription terminator sequences). The term "terminator sequences" includes regulatory sequences which serve to terminate transcription of a gene. Terminator sequences (or tandem transcription terminators) can further serve to stabilize mRNA (e.g., by adding structure to mRNA), for example, against nucleases. It will further be appreciated by one of skill in the art that the design of a vector can be tailored depending on such factors as the choice of microorganism to be genetically engineered, the level of expression of gene product desired and the like.

Another aspect of the present invention features isolated β-galactosidase BGA1 . In one embodiment, β-galactosidase BGA1 is produced by recombinant DNA techniques and can be isolated from microorganisms of the present invention by an appropriate purification scheme using standard protein purification techniques. In another embodiment, proteins are synthesized chemically using standard peptide synthesis techniques. An "isolated" or "purified" protein (e.g., an isolated or purified biosynthetic enzyme) is substantially free of cellular material or other contaminating proteins from the microorganism from which the protein is derived, or substantially free from chemical precursors or other chemicals when chemically synthesized. In one embodiment, an isolated or purified protein has less than about 30% (by dry weight) of contaminating protein or chemicals, more preferably less than about 20% of contaminating protein or chemicals, still more preferably less than about 10% of contaminating protein or chemicals, and most preferably less than about 5% contaminating protein or chemicals.

In other embodiments, an isolated β-galactosidase of the present invention is a homo- logue of the β-galactosidase set forth as SEQ ID NO:2, (e.g., comprises an amino acid sequence at least about 30-40 % identical, preferably about 40-50 % identical, more preferably about 50-60 % identical, and even more preferably about 60-70 %, 70-80 %, 80-90 %, 90-95 % or more identical to the amino acid sequence of SEQ ID NO:2, and has an activity that is substantially similar to that of the protein encoded by the amino acid sequence of SEQ ID NO:2.

To determine the percent homology of two amino acid sequences or of two nucleic acids, the sequences are aligned for optimal comparison purposes (e.g., gaps can be introduced in the sequence of a first amino acid or nucleic acid sequence for optimal alignment with a second amino or nucleic acid sequence). When a position in the first sequence is occupied by the same amino acid residue or nucleotide as the corresponding position in the second sequence, then the molecules are identical at that position. The percent identity between the two sequences is a function of the number of identical positions shared by the sequences (i.e., % identity = # of identical positions/total # of positions x 100), preferably taking into account the number of gaps and size of said gaps necessary to produce an optimal alignment.

The comparison of sequences and determination of percent homology between two sequences can be accomplished using a mathematical algorithm. A preferred, non- limiting example of a mathematical algorithm utilized for the comparison of sequences is the algorithm of Karlin and Altschul (1990) Proc. Natl. Acad. Sci. USA 87:2264-68, modified as in Karlin and Altschul (1993) Proc. Natl. Acad. Sci. USA 90:5873-77. Such an algorithm is incorporated into the NBLAST and XBLAST programs (version 2.0) of Altschul et al. (1990) J. Mol. Biol. 215:403-10. BLAST nucleotide searches can be per- formed with the NBLAST program, score = 100, wordlength = 12 to obtain nucleotide sequences homologous to nucleic acid molecules of the invention. BLAST protein searches can be performed with the XBLAST program, score = 50, wordlength = 3 to obtain amino acid sequences homologous to protein molecules of the invention. To obtain gapped alignments for comparison purposes, Gapped BLAST can be utilized as described in Altschul ef al. (1997) Nucleic Acids Research 25(17):3389-3402.

When utilizing BLAST and Gapped BLAST programs, the default parameters of the respective programs (e.g., XBLAST and NBLAST) can be used. See

http://www.ncbi.nlm.nih.gov. Another preferred, non-limiting example of a mathematical algorithm utilized for the comparison of sequences is the algorithm of Myers and Miller (1988) Comput Appl Biosci. 4:1 1 -17. Such an algorithm is incorporated into the ALIGN program available, for example, at the GENESTREAM network server, IGH Montpel- lier, FRANCE (http://vega.igh.cnrs.fr) or at the ISREC server

(http://www.ch.embnet.org). When utilizing the ALIGN program for comparing amino acid sequences, a PAM120 weight residue table, a gap length penalty of 12, and a gap penalty of 4 can be used.

In another preferred embodiment, the percent homology between two amino acid sequences can be determined using the GAP program in the GCG software package (available at http://www.gcg.com), using either a Blossom 62 matrix or a PAM250 matrix, and a gap weight of 12, 10, 8, 6, or 4 and a length weight of 2, 3, or 4. In yet another preferred embodiment, the percent homology between two nucleic acid sequences can be accomplished using the GAP program in the GCG software package (available at http://www.gcg.com), using a gap weight of 50 and a length weight of 3.

The methodologies of the present invention feature microorganisms, e.g., recombinant microorganisms, preferably including vectors or genes as described herein and/or cultured in a manner which results in the production of β-galactosidase BGA1 . The term "recombinant" microorganism includes a microorganism (e.g., bacteria, yeast cell, fun- gal cell, etc.) which has been genetically altered, modified or engineered (e.g., genetically engineered) such that it exhibits an altered, modified or different genotype and/or phenotype (e.g., when the genetic modification affects coding nucleic acid sequences of the microorganism) as compared to the naturally-occurring microorganism from which it was derived. Preferably, a "recombinant" microorganism of the present inven- tion has been genetically engineered such that it overexpresses at least one gene or gene product as described herein, preferably a beta-galactosidase, included within the genome of said microorganism as described herein and/or a beta-galactosidase expressed from a recombinant vector. The ordinary skilled will appreciate that a microorganism expressing or overexpressing a gene product produces or overproduces the gene product as a result of expression or overexpression of nucleic acid sequences and/or genes encoding the gene product.

The present invention is illustrated in more detail by the following examples and patent claims.

Examples

Fig. 1 shows rheological properties of a (partially) degalactosified xyloglucan in water and NDIIa. Gelation of the degalactosified xyloglucan occurs at higher temperature in NDIIa. Fig. 2 shows rheological differences between a (partially) degalactosified and non- modified xyloglucan. Gelling behaviouor is pronounced solely by (partial) degalactosifi- cation of xyloglucan.

Fig. 3 shows a comparison of three different (partially) degalactosified xyloglucans. The higher the galactose removal ratio (GRR), the higher the gel-strength becomes.

Fig. 4 shows a comparison of four different aqueous formulations containing a (partial- ly) degalactosified xyloglucan. Two formulations do contain EGCG (epigallocatechin gallate) as an additive. EGCG shifts the gelling temperature.

Fig. 5 shows the viscosity values of two different aqueous (Landau water) well treatment formulations as a function of time (in hours after the formulation's preparation). The formulation, comprising xyloglucan and purified β-galactosidase being essentially free of contaminants showing cellulose activity, does form a stable gel, whereas the formulation comprising non-purified β-galactosidase does not.

Fig. 6 shows a macroscopic picture of a (partially) degalactosified xyloglucan

(GRR = 0.53; 1 .5 wt% in NDIIa) at different temperatures.

Fig. 7 shows viscosity values of an aqueous (50% by volume of basically salt-free water and 50% by volume of NDIIa water, based on the total volume of (salt) water) well treatment formulation comprising xyloglucan and beta-galactosidase as a function of time.

Example 1 : Enzyme Purification - Step 1

In the first chromatographic step, anion exchange chromatography is employed. A Q Sepharose Fast Flow column (height (h): 22 cm, diameter (d): 5.0 cm, volume (V): 432 ml) from GE Healthcare is used for chromatographic separation. The chromatography is conducted at pH 7 using the aqueous buffer solutions A and B:

Aqueous buffer solution A: 20 mmol/l IS^HPC /NahbPC , pH 7.0;

Aqueous buffer solution B: 20 mmol/l Na2HP0₄/NaH₂P04, 0.5 mol/l NaCI, pH 7.0.

55 g Lactase F "Amano" (obtained from Amano) is added to 900 ml water and the pH of the mixture obtained is adjusted to pH 7 by adding an appropriate amount of a 1 M aqueous NaOH solution. The Lactase F "Amano" mixture is loaded onto the Q Se- pharose Fast Flow column equilibrated with aqueous buffer solution A. The Lactase F mixture is eluted from the column using a linear gradient to 100 % by volume of aqueous buffer solution B (1200 ml) and afterwards 400 ml aqueous buffer solution B. β- Galactosidase activity of the collected fractions is verified by using p-Nitrophenyl^-D- galactopyranosid which is cleaved upon the enzymatic activity whereby the absorption at 405 nm increases (for details see Miller, J.H. 1972. Experiments in Molecular Genetics: Assay of β-Galactosidase. CSH Laboratory Press, Cold Spring Harbor, NY: 352- 355.). The β-galactosidase elutes at 60 - 80 % by volume aqueous buffer solution B. The combined β-galactosidase containing fractions (Volume: 300 ml) having a protein content of 7.624 mg/ml (determined by the Bradford assay, for details of said assay see "Rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding", M. M. Bradford, Anal. Biochem. 1976, 72, 248-254.).

Determination of cellulase activity

Cellulase activity has been determined using an azo xyloglucan based assay. Therefore, 50 μΙ of a collected β-galactosidase fraction is mixed with 50 μΙ of an aqueous azo xyloglucan solution (1.0 % by weight azo xyloglucan, 0.05 M sodium citrate (pH 5.5)). Then, 10 μΙ of a 1 M aqueous sodium citrate buffer (pH 5.5) is added to keep the pH value constant. After incubation the reaction is stopped by adding 170 μΙ methanol. The precipitate is removed by centrifugation and the supernatant solution is directly poured into a spectrophotometer cuvette and the absorbance of blank and supernatant solution is measured at 590 nm. Example 2: Enzyme Purification - Step 2

In the second chromatographic step, hydrophobic interaction chromatography is employed. A TSK-GEL^® Phenyl-5PW (20) column (h: 28 cm, d: 5.0 cm, V: 530 ml) from GE Healthcare is used for chromatographic separation. The chromatography is con- ducted at pH 7 using the aqueous buffer solutions C and D:

Aqueous buffer solution C: 20 mmol/l Na₂HP04/NaH₂P04, 60 wt.-% (NH₄)₂S0₄, pH 7.0;

Aqueous buffer solution D: 20 mmol/l Na₂HP0₄/NaH₂P0 , pH 7.0.

A β-galactosidase containing solution (V: 619 ml, protein content: 8.562 mg/ml (Bradford), total protein content: 5300 mg) obtained by anion exchange chromatography is supplemented with ammonium sulphate to 60 wt.-% saturation (room temperature) and loaded on the Phenyl-Sepahrose Fast Flow column previously incubated with aqueous buffer solution C. Whereas the β-galactosidase passes through the column using a linear gradient to 100 % by volume of aqueous buffer solution D (1200 ml) and afterwards 400 ml aqueous buffer solution D, the proteins showing cellulase activity remain, to a large extent, bound to the column. β-Galactosidase activity of the collected fractions is again verified by using p-Nitrophenyl^-D-galactopyranosid (for details see Miller, J.H. 1972. Experiments in Molecular Genetics: Assay of β-galactosidase. CSH Laboratory Press, Cold Spring Harbor, NY: 352-355.). The combined β-galactosidase containing fractions (V: 350 ml) having a protein content of 10.363 mg / ml.

Cellulase activity has been determined as described in example 1. β-galactosidase fractions showing a cellulase activity not exceeding 0.1 U / ml were used for all degalactosification experiments.

Example 3: Preparation of xyloglucan from tamarind kernel flakes (TKF)

Extraction of xyloglucan polysaccharide from tamarind kernel flakes was done in three steps:

1 ) extraction in stirred tank reactor;

2) centrifugation in Sorvall bucket centrifuge;

3) clear filtration using pressure filter.

Extraction in stirred tank reactor and centrifugation:

In 20 L stirred tank reactor, equipped with propeller stirrer, was filled with tamarind kernel flakes and water (2.0 wt.-% of flakes). Final amount of this suspension was 16.0 L. The suspension was warmed to 95 °C (this took ca. 75 min with mixing at 700 upm) and the resulting temperature was then kept for 35 min. (while stirring). After this time, reaction mixture was divided into 4 equal portions. These were centrifuged in Sorvall bucket centrifuge (Type Sorvall RC-4) as follows: 15 min., C-value 5300. Solid content in a suspension was ca. 0.3 wt.-%.

Clear filtration using pressure filter:

For a clear filtration two pressure filters with a filtration area of 100 cm² were used. These were operated in parallel. As a filter medium a depth filter sheet of type K 300 (5-12 microns) from (PALL) was used. The pressure filters were also heated to 95 °C. The set constant pressure difference was 1 bar.

Xyloglucan concentration in the filtrate was determined to be 1 ,38 wt.-% and the aver- age molecular weight (M_w) found to be 1300 kDa (recovery rate 85 %). Average molecular weight determination

Average molecular weights (M_w) for un-modified (Example 3) and partially degalactosi- fied xyloglucans (Examples 4, 5 and Comparison example 1 ) were determined via field flow fractionation (FFF). Following equipment was used: field flow fractionation apparatus Eclipse 2, light-scattering detector Dawn Eos, concentration detector R.I. Optilab DSP (company Wyatt), spacer: 350 μηη, injection pump 0.20 mL/min, RC-membrane 10kDa. For a measurement concentration of 0.05 N NaN03, pH=6 was used. Polysac- charide samples were prepared as 1.0 g/L solutions and filtrated over 0.45 μηη PVDF filter before measurement.

Example 4: Preparation of partially degalactosified xyloglucan Preparation of partially degalactosified xyloglucan having a galactose removal ratio (GRR) of 0.43 using a solution of β-galactosidase which shows a cellulase activity not exceeding 0.1 U / ml_(reaction solution)

A 6.0 L glass reactor is filled with 6000 g of aqueous xyloglucan (XG) preparation, (1 .38 wt.-% XG, 83.0 g of XG, purity > 98 %, average molecular weight (M_w) = 1300 KDa stabilized with 500 ppm formaldehyde) followed by 120 ml. sodium citrate buffer (1 M, pH = 4.8). Then the temperature is set to 50 °C and 102 ml. of purified Amano Lactase F β-galactosidase (102 U / mL(3-galactosidase solution), 1 .7 mg / mL(3-galac- tosidase solution), 2000 U / g(XG) as a solution in 20 mM NaH₂P0₄/ Na₂HP0₄-buffer (pH = 7.0) and 30 - 40 % by weight of (NH₄)2S0₄) is added. The resulting reaction mixture is stirred at a constant temperature of 50 °C for 5.5 h. After this time, the reaction mixture is centrifuged (40 min, 5300 g and 40°C) and the supernatant separated. To a gel type precipitate obtained, 1 :1 (v/v) acetone is added and slowly stirred with a mechanical blade agitator. Precipitated material is filtrated using glass filter (porosity No. 2). The filter cake is then suspended in 1.5 L acetone and stirred until a clear-flowing suspension is obtained. The precipitate is filtrated and vacuum dried at 40 °C for ca. 12 h. The partially degalactosified xyloglucan is obtained as an amorphous powder which is grinded and stored in a closed flask at room temperature. Example 5: Preparation of partially degalactosified xyloglucan having a GRR of 0.50 using a solution of β-galactosidase which shows a cellulase activity not exceeding 0.1 U / mL(reaction solution) Partially degalactosified xyloglucan having a GRR of 0.50 is prepared according to the procedure described in example 4. Instead of a activity of 2000 U / g(XG), a activity of 1500 U / g(XG) is used. Moreover, the reaction mixture is stirred at 50°C for 24 h. Comparison example 1 : Preparation of partially degalactosified xyloglucan having a

GRR of 0.36 using a solution of β-galactosidase which shows a cellulase activity not exceeding 0.1 U / ml_(reaction solution)

Partially degalactosified xyloglucan having a GRR of 0.36 is prepared according to the procedure described in example 4. Instead of a activity of 2000 U / g(XG), a activity of 500 U / g(XG) is used. Moreover, the reaction mixture is stirred at 50°C for 20 h.

Average molecular weight found for xyloglucan from TKF after partial degalactosyfica- tion

The average molecular weight has been determined according to the procedure shown in example 3. Determination of galactose removal ratio (GRR)

Galactose removal ratio (GRR) was determined according to a slightly modified procedure from Shirakawa, M., Yamatoya, K., & Nishinari, K. (1998). Tailoring of xyloglucan properties using an enzyme. Food Hydrocolloids, 12, 25-28: In the first step native xyloglucan was hydrolyzed with 12M H2SO4 to obtain the total galactose (GAL) amount available from starting material. Degree of degalactosification was calculated as: GRR = GAL amount after enzyme, treatment/total GAL amount.

Example 6: Rheology measurements using partially degalactosified xyloglucan from Example 5

Sample preparations

A 100 mL beaker containing 22.92 g synthetic NDIIa water and 31 .19 g water was immersed into an ice-bath. The solution was stirred at 1600 rpm using 40 mm dissolver disc and 0.83 g of the partially degalactosified xyloglucan obtained in Example 5 (GRR 0.50) was added. Stirring was continued for 30 min followed by addition of 0.069 mL of formaldehyde (36.5% solution in water). After preparation the samples were kept at +4°C.

Composition of synthetic NDIIa water: CaCI₂x2H₂0: 67.71 g / L

MgCI₂x6H₂0: 26.90 g / L

NaCI: 158.4 g / L

Na₂S0₄: 0.32 g / L

NaB0₂x4H₂0 0.46 g / L Rheological experiments

The rheological experiments were done with Anton Paar MCR Rheometers. Temperature sweep experiments were done in a temperature range between 0°C and 140°C. A sealed geometry (pressure cell) was used with a double gap geometry. Measurements were carried out at a constant shear rate of 10 s^_1 with a heating rate of

0.5 °C / min.

Gel kinetic experiments were done in concentric cylinder geometry with small amplitude oscillation shear (SAOS) measurements at 1 Hz with a deformation of 5 %. The geometry was set to the particular measurement temperature before the sample was filled. The initial sample temperature was about 4 °C. Right after the sample was filled into the geometry, the sample was covered with silicone oil. Silicone oil was used to prevent evaporation and salt crust formation at elevated temperatures. In order to have identical conditions, this procedure was kept constant for all kinetic measurements at all temperatures. Due to the overall handling procedure there was a time delay of about 60-90 seconds till the first data point could be collected.

Sol-gel transition temperatures from temperature sweep experiments using the partially degalactosified xyloglucan obtained in Example 5 (GRR = 0.50)

* EGCG = epigalocatechin gallate

Sol-gel transition temperature were obtained from the minimum in the viscosity- temperature curves (Figures 1 - 4) Example 7: Rheology measurement: in-situ xyloglucan degalactosification in formation water (Landau water) To a 100 mL baker was added 68.99 g of Landau injection water. Then 1 .02 g of powdered polysaccharide tamarind xyloglucan (purity > 98%, average molecular weight (Mw) = 1300 kDa) was added. The solution was stirred at 1600 rpm using 40 mm dis- solver disc for ca. 30 min at room temperature. 0.88 mL of formaldehyde (36.50 wt.-% in water) was added. Additionally, pH was adjusted with cone. HCI to 5.5. To the result- ing sample following amount of purified Amano Lactase F β-galactosidase were added: 1 .806 mL β-galactosidase (803 U / mL(3-galactosidase solution), 1 .7 mg / mL(3- galactosidase solution), 2000 U / g(XG), as a solution in 20 mM Na₃P0₄ buffer (pH = 7.0) and 30 - 40% (NH₄)2S0₄).The sample was divided into two samples: a) sample A for determination of galactose removal ratio (GRR). This was found to be 0.46; b) sam- pie B to study the gelling behavior

Landau water was found to have the following ion concentrations:

Rheological experiments

The Rheological experiments were done with Anton Paar MCR Rheometers. Temperature sweep experiments were done in a temperature range between 0 °C and 140 °C. A sealed geometry (pressure cell) was used with a double gap geometry. Measurements were carried out at a constant shear rate of 10 s^_1 and at a constant 50 °C tem- perature of 50 °C. A pressure cell was preheated to 50 °C before xyloglucan and enzyme were added. After addition, cell was closed and measurement was started. Example 8: Rheology measurement: in-situ xyloglucan degalactosification in synthetic NDIIa water

To a 100 mL baker was added 68.99 g of synthetic NDIIa water (composition shown above). Then 1.02 g of powdered polysaccharide tamarind xyloglucan (purity > 98 %, average molecular weight (M_w) = 1300 kDa). The solution was stirred at 1600 rpm using 40 mm dissolver disc for ca. 30 min at room temperature. 0.88 mL of formaldehyde (36.50 wt.-% in water) was added. Additionally, pH was adjusted with cone. HCI to 5.5. To the resulting sample, the following amount of purified Amano Lactase F β- galactosidase was added: 2.401 mL β-galactosidase (604 U / mL(3-galactosidase solution), 1 .7 mg / mL(3-galactosidase solution), 2000 U / g(XG), as a solution in 20 mM Na₃P0₄ buffer (pH = 7.0) and 30 - 40% (NH₄)₂S0₄). The sample was divided into two samples: a) sample A for determination of galactose removal ratio (GRR); b) sample B to study the gelling behavior.

The Rheological experiments were done according to Example 7.

Example 9: Determination of purified β-galactosidase activity in different salty waters β-galactosidase activity in salty water was determined according to slightly modified procedure from SIGMA 'Enzymatic assay of β-galactosidase using o-nitrophenyl β-D- galactopyranoside as substrate'. Following residual activities were found: β-galactosidase Residual activity deionized water / salty water PH

activity [U / mL] [%]

100 / 0 + 50 mM NaCitrat 5,5 992 -

1 / 1 (NDIIa) 5,5 604 61

0 / 100 (NDIIa) 5,5 13 1

1 / 1 (Landau water) 5,5 709 71

0 / 100 (Landau water) 5,5 803 81

not

1 / 1 (NDIIa) 555 56

corrected^*

not

0 / 100 (NDIIa) 16 2

corrected^*

not

1 / 1 (Landau water) 749 76

corrected^*

not

0 / 100 (Landau water) 660 67

corrected^* ^* Term 'not corrected' means that no HCI was added to set the pH to 5.5 The Rheological experiments were done according to Example 7. Sample preparation for rheology measurements

To a tamarind xyloglucan solution (25.0 g, 1 .0 wt.-%), the β-galactosidase solution (1 ,281 mL, 976 U / mL(3-galactosidase solution), 5000 U / g(XG)) was added. The resulting solution was shortly stirred and then 6 mL was transferred to be measured. The rheological experiments were done according to Example 7.

Claims

Patent Claims

A method for treating an oil and/or natural gas bearing subterranean formation penetrated by at least one well bore, comprising the steps of

(a) providing an aqueous well treatment formulation (A) which comprises

(A1 ) a xyloglucan having an average molecular weight (M_w) of from

200 000 to 1 500 000 Da,

(A3) optionally one or more additives;

(b) injecting said aqueous well treatment formulation into at least one well bore penetrating the oil and/or natural gas bearing subterranean formation; and

(c) gelling of said aqueous well treatment formulation effected by partial degalactosylation of the said xyloglucan.

The method according to claim 1 , wherein the aqueous well treatment formulation (A) comprises from 0.01 to 20.00 % by weight of the xyloglucan (A1 ), based on the total weight of the aqueous well treatment formulation (A).

The method according to claims 1 or 2, wherein the aqueous well treatment formulation (A) comprises from 0.01 to 10.00 % by weight of the β-galactosidase (A2), based on the total weight of the aqueous well treatment formulation (A).

The method according to any one of claims 1 to 3, wherein the aqueous well treatment formulation (A) comprises one or more biocides as additives (A3).

The method according to any one of claims 1 to 4, wherein the aqueous well treatment formulation (A) comprises salt. 6. The method according to any one of claims 1 to 5, wherein the aqueous well treatment formulation (A) comprises from 0.02 to 40.00 % by weight of salt, based on the total weight of the aqueous well treatment formulation (A).

7. The method according to any one of claims 1 to 6, wherein the xyloglucan (A1 ) has an average molecular weight of from 400 000 to 1 500 000 Da.

8. The method according to any one of claims 1 to 7, wherein the xyloglucan (A1 ) has a purity of at least 80 % by weight.

9. The method according to any one of claims 1 to 8, wherein the xyloglucan (A1 ) is tamarind xyloglucan having general formula (II),

(II) wherein

the average number of the β-D-galactopyranose residues per repeating unit (gi + g₂) is from 1.70 to 2.30,

the average number of the oL-fucopyranose rediues per repeating unit (f) is from 0.00 to 0.20, and

the average number of the repeating units (n) is from 400 to 1400.

10. The method according to any one of claims 1 to 9, wherein the enzyme preparation comprising β-galactosidase (A2) has a β-galactosidase activity of at least 500 U per g of Xyloglucan.

1 1 . The method according to any one of claims 1 to 10, wherein the enzyme preparation has a cellulase activity below 2 U/g.

12. The method according to any one of claims 1 to 1 1 , wherein the oil and/or natural gas bearing subterranean formation has a down hole temperature between 20 and 100 °C.

13. The method according to any one of claims 1 to 12, wherein the well bore in step (b) is an injection well.

14. The method according to any one of claims 1 to 12, wherein the well bore in step (b) is a production well.

15. A method for treating an oil and/or natural gas bearing subterranean formation penetrated by at least one well bore, comprising the steps of (a) injecting an aqueous xyloglucan formulation (X) into a well bore penetrating the oil and/or natural gas bearing subterranean formation, wherein the formulation (X) comprises

(A1 ) a xyloglucan having an average molecular weight of from 200 000 to 1 500 000 Da, and

(A3) optionally one or more additives;

(b) injecting an aqueous β-galactosidase formulation (G) into the well bore penetrating the oil and/or natural gas bearing subterranean formation, wherein the formulation (G) comprises

(A3) optionally one or more additives;

(c) gelling of the mixed formulations effected by partial degalactosylation of the xyloglucan; wherein the steps (a) and (b) are performed simultaneously or consecutively in any order, each only once or several times.

16. The method according to claim 15, wherein the steps (a) and (b) are performed simultaneously.

17. The method according to claim 15, wherein the steps (a) and (b) are performed consecutively in any order.

18. Use of the aqueous well treatment formulation (A) as defined in any one of claims 1 to 1 1 for conformance control measures or water shut-off measures.

19. A method for producing an enzyme preparation comprising β-galactosidase being capable of removing galactose from xyloglucan (A2), comprising at least one anion exchange chromatographic step and at least one hydrophobic interaction chromatographic step, wherein said chromatographic steps can be conducted in arbitrary order.

20. The method according to claim19 comprising one anion exchange chromatographic step and one hydrophobic interaction chromatographic step, wherein the anion exchange chromatography is conducted as first step, and the hydrophobic interaction chromatography as second step.

21 . An isolated β-galactosidase homologue of the β-galactosidase set forth as SEQ ID NO:2 comprising an amino acid sequence which is at least about 50 to 60 % identical to the amino acid sequence of SEQ ID NO:2.

22. An isolated nucleic acid molecule comprising a nucleotide sequence which is at least about 60 to 65 % identical to a nucleotide sequence set forth as SEQ ID NO:1 .