WO2009027680A1

WO2009027680A1 - Well treatment

Info

Publication number: WO2009027680A1
Application number: PCT/GB2008/002912
Authority: WO
Inventors: Hans Kristian Kotlar; Arild Moen; Ping Chen; Harry Montgomerie; Thomas Hagen; Hugh BOURNE
Original assignee: Statoilhydro Asa; Champion Technologies Ltd
Priority date: 2007-08-29
Filing date: 2008-08-29
Publication date: 2009-03-05
Also published as: GB0716784D0; GB2453317A; GB2453317B

Abstract

The invention provides a method for increasing the retention of a proppant within a hydrocarbon producing system (e.g. a subterranean formation), said method comprising contacting a formation comprising said proppant with an organosilane. Kits for use in such methods and which comprise a proppant and separately an organosilane are afso provided.

Description

WELL TREATMENT

The present invention relates to a method of increasing the permeability of a subterranean formation, and in particular, to a method of increasing the retention of proppant within a fracture present in the formation. The invention also relates to uses of organosilanes for increasing retention of proppant in a subterranean formation and to kits comprising an organosilane and separately a proppant.

Hydrocarbons (e.g. oil and gas) are generally recovered from subterranean formations by drilling a well bore into the formation and extracting the hydrocarbon. One of the factors that influences the rate of hydrocarbon production and therefore the productivity of the well is the hydrocarbon permeability of the formation. Formation permeability is essential to enable hydrocarbon to flow to a location, specifically the well bore, from where it can be pumped from the well. Sometimes, however, the permeability of the formation containing the hydrocarbon is insufficient for economic recovery of oil and/or gas. In other cases, although the initial permeability of the well may be sufficient to enable economically viable hydrocarbon production therefrom, permeability may decrease during operation.

To overcome these problems, it is commonplace to fracture formations by applying hydraulic pressure in the well bore adjacent to the formation requiring treatment. In some cases, the enlargement of an existing fracture or creation of a new one by fracturing is sufficient itself to increase permeability to a level that makes hydrocarbon recovery economical. In the majority of cases, however, it is additionally necessary to introduce a proppant into the open fracture to prevent it from closing and thereby reducing permeability. This is achieved by suspending a proppant in a fluid and forcing the fluid into the opening or fracture. An after-flush may then be carried out before putting the well back onto production. The important feature, however, is that the proppant stays in place and holds open the fracture.

The first proppant material to be used was sand, and in particular, rounded sand grains. Since the 1970's, however, there has been considerable development in proppant technology and a range of man made proppants have been developed.

These are generally ceramic materials that have greater strength than sand particles and thus are less likely to break down under formation pressure. The majority of man made proppants are ceramics comprising alumina (e.g. bauxite) and in some cases silica.

Problems are, however, encountered with use of man made ceramic proppants. It is not unusual, for example, for proppant to leach or escape from the fracture in which it was placed into the production fluids once operations are restarted. This causes a number of problems. For instance, the proppant particles can cause damage to the production equipment (e.g. by blocking valves) and must also be separated from the produced fluids. The proppant particles can also cause formation damage (e.g. by blocking pores or channels) and thereby further exacerbate permeability problems.

Most significantly, however, the loss of proppant from the formation causes the fractures in which they were present to close and it may become necessary to refracture the formation. However this requires the use of yet further proppant and production has to be stopped again which is clearly economically undesirable. In recent years there have been a few attempts to try to improve the retention of proppants in subterranean formations. These have focussed on the provision of resin coated proppant particles wherein the coatings are specifically designed to improve retention. Two different types of coatings have been developed, namely curable coatings and pre-cured coatings. Both coatings comprise chemical compounds that are capable of undergoing polymerisation, e.g. furaldehydes, phenols and epoxy containing compounds, to form a coating. In the case of curable coatings, the polymerisation reaction is designed to occur within the formation after delivery of the proppant particles thereto whereas with pre-cured coatings the polymerisation reaction is carried our prior to delivery of the proppant to the well. There are, however, problems associated with both of these types of coated particles. First the pressures used during injection of the proppant into fractures often causes the coating to break off or erode which means that it cannot function to aid retention of the particle once placed in a fracture. In fact in the case of curable coatings, the loss of material from the proppant particle surface may mean that no coating can form. Second the majority of the chemical agents used to form curable and pre-cured coated particles are not environmentally friendly. Hence there is still a need for alternative methods for increasing the retention of proppants in oil wells, and in particular, for methods that extend the lifetime of a proppant treatment. In addition the method should not damage the formation and, due to increased environmental concerns, the treatment chemicals employed should exhibit good biodegradation properties with low toxicity and low bioaccumulation.

It has now been surprisingly found that organosilanes can be used in a method of increasing the retention of proppants in a subterranean formation. Unlike the prior art methods, the organosilane is not coated onto the proppant to provide coated proppant particles, rather the organosilane is provided separately. The method now discovered therefore has the advantage that any conventional proppant particle can be used.

Viewed from a first aspect the present invention provides a method for increasing the retention of a proppant within a hydrocarbon producing system (e.g. a subterranean formation) comprising contacting a formation comprising said proppant with an organosilane.

In a preferred embodiment of the method of the present invention, said method further comprises the step of contacting said system with said proppant.

Viewed from another aspect the invention provides the use of an organosilane to increase the retention of a proppant in a hydrocarbon producing system (e.g. a subterranean formation).

Viewed from a further aspect the invention provides the use of an organosilane in the manufacture of a treatment composition for increasing the retention of a proppant in a hydrocarbon producing system (e.g. a subterranean formation). Viewed from a still further aspect the invention provides a kit for increasing the retention of a proppant within a hydrocarbon producing system (e.g. a subterranean formation), said kit comprising a proppant and separately an organosilane.

As used herein, the term "hydrocarbon producing system" encompasses the subterranean formation (e.g. rock) from which hydrocarbon is extracted as well as the equipment used in the extraction process. The formation may be an oil or gas well, although the method is particularly suitable for treatment of oil wells. The equipment includes both subsurface and surface equipment (e.g. tubes, pipes, pumps, valves, nozzles, storage containers, screens, etc).

The term "subterranean formation" is used herein to refer to the material existing below the Earth's surface. The formation may comprise a range of components, e.g. minerals such as quartz, siliceous materials such as sand and clays, as well as the oil and/or gas that is extracted. The method of the present invention is particularly useful in sandstone formations.

As used herein, the term "permeability" refers to the capacity of a porous medium to transmit a fluid. It therefore provides a measure of the resistance of a formation to flow of a liquid (e.g. water and/or hydrocarbon) through the pores and channels forming its structure. Thus, "hydrocarbon permeability" means the capacity of a porous medium such as a subterranean formation to transmit hydrocarbon (e.g. oil) and "water permeability" means the corresponding capacity to transmit water. Permeability may be measured using Darcy's Law:

Q = k.ΔP.A/μL

where Q = flow rate (cmfVs)

ΔP = pressure drop (arm) across a cylinder having a length L (cm) and a cross-sectional area A (cm ) m = fluid viscosity (cp) k = permeability (Darcy)

In the method of the present invention, the permeability to hydrocarbon of the formation is increased. At the same time, the water permeability of the formation may also be increased. In either case, in preferred methods of the invention, the hydrocarbon present in the formation can be extracted therefrom more economically than prior to treatment as a result of the increased permeability.

Organosilanes for use in the invention are preferably dispersible or soluble in a hydrocarbon (e.g. a Ci_-2O alkane). Still more preferably, the organosilanes for use in the invention are also at least partially water soluble (e.g. water soluble). In some cases the organosilane for use^'in the invention will be more soluble in hydrocarbon than in water. More preferably, however, the organosilanes for use in the invention will be more soluble in water than in hydrocarbon. The organosilanes for use in the invention may, for example, partition between hydrocarbon and water in a ratio in the range 5:95 to 90:10, more preferably 10:90 to 70:30, for example, about 40:60. The ability to partition in this way enables the organosilanes to be delivered to the formation in a hydrocarbon carrier (i.e. substantially without undergoing reaction) whilst at the same time enabling it to undergo reaction on contact with water at the desired point of action. Preferably, the carrier is substantially free from water.

Organosilanes for use in the invention include, for example, organosilane hydrides, organosilane alkoxides and organosilane amines. Organosilane compounds have the advantage that they are typically oil-soluble and have the necessary reactivity with water. These are also biodegradable and environmentally acceptable (e.g. for DYNASYLAN AMEO: LC₅₀ fish = 934 mg/1; EC₅₀ daphnia = 331 mg/1; IC₅₀ algae = 603 mg/1, biodegradability 67 %,^'for DYNASYLAN bis- AMEO: LC₅₀ fish >200 mg/1; EC₅₀ daphnia >200 mg/1; IC₅₀ algae = 125 mg/1, biodegradability 64.5 %, as tested according to OECD 306). Organosilanes for use in the invention preferably have a biodegradability of at least 60 %. Whilst not wishing to be bound by theory, it is believed that organosilane compounds undergo hydrolysis upon contact with water. The resulting chemicals then react with the surfaces of proppant particles, as well as with the siliceous surfaces in the formation. These reactions are believed to "glue" the proppant particles together, as well to bind the proppant particles within the fracture of the formation.

Particularly preferred organosilane compounds for use in the method of the invention include those having at least one hydrolysable bond. By a "hydrolysable bond" is meant a bond that is capable of being cleaved on reaction with water. Preferably the hydrolysable bond will be attached to a silicon atom. In other words, the hydrolysable bond is preferably between Si and a second atom/group in the molecule. Still more preferably the hydrolysable bond is one which may hydrolyse to produce a silanol (i.e. -Si-OH). Although not wishing to be bound by theory, it is believed that the hydrolysis of an organosilane maybe critical to the success of the method herein described. More specifically it is thought that the organosilane, upon contact with water in the formation, hydrolyses to form a silanol:

RRRSi-O-Group + water — > RRRSi-OH + HO-Group

This silanol is then believed to react with other silanol molecules by forming -Si-O-Si- bonds and/or with active sites on the surface of proppant particles and/or with the surface of the formation (e.g. sand particles). Whilst the first reaction enables organosilanes to bond to each other, the second and third reactions serve to covalently bond the organosilane to proppant particles and to particles comprising the formation respectively. Bonds may subsequently form between organosilane moleules bound to proppant particles and/or to the formation. The organosilane is therefore believed to act as a "glue" to bind the proppant particles together, as well as bind the proppant particles to the formation. The binding of proppant particles together to form a matrix of proppant is believed to be the key reaction that serves to hold open a fracture present in the formation.-

An advantage of the method of the present invention is that the matrix of proppant formed by the organosilane is believed to be resilient, e.g. to have high compressive and tensile strength. As a result the proppant matrix is able to withstand subsequent treatments with, for instance, high fluid pressures and/or temperatures. Treatment with proppant according to the method of the invention therefore does not preclude any other treatments for being carried out. The degree to which a proppant particle is retained within a formation may depend on the extent to which the above-mentioned reactions occur and therefore on the number of bonds the organosilane forms with the proppant particles and with the particles of the formation. This, in turn, at least partially depends on how many silanol groups can be formed per molecule. Preferred organosilane compounds for use in the invention comprise 1 to 12 hydrolysable bonds, more preferably 3 to 9 hydrolysable bonds, still more preferably about 6 hydrolysable bonds. Such compounds possessing hydrolysable bonds may well be able to self-condense and/or polymerise after hydrolysis of one or more of the hydrolysable bonds. The afore-mentione^'d preferred numbers of hydrolysable bonds therefore relates to the number present in the monomelic form of the compound (i.e. one which has not undergone oligomerisation or polymerisation). For example, aminotriethoxysilane contains 3 hydrolysable bonds (i.e. 3 x Si-OEt) and bis-(triethoxysilylpropyl)amine contains 6 hydrolysable bonds (i.e. 6 x Si-OEt). In the organosilane compounds for use in the invention, the hydrolysable bonds present may be different, but more preferably are the same.

In preferred organosilane compounds for use in the invention at least one hydrolysable bond comprises part of a terminal group. More preferably, all of the hydrolysable bonds comprise part of a terminal group. By a "terminal group" is meant a group that is located at one end of the molecule. This is in contrast to a side group or pendant group that is attached to another part of the molecule. For example, in the compound aminotriethoxysilane, the amino group and the -Si(OEt)₃ groups are terminal groups. In contrast in the compound bis-(triethoxysilylpropyl)- amine the -Si(OEt)₃ groups are terminal groups, whereas the amine group is not.

In particularly preferred compounds for use in the invention all bonds other than the afore-mentioned hydrolysable bonds, are stable to the conditions to which it is exposed in use (e.g. stable to hydrolysis in sea water). Preferably the remaining bonds in the molecule are carbon-carbon, carbon-hydrogen, silicon-carbon, nitrogen-carbon, oxygen-carbon and/or nitrogen-hydrogen bonds.

Preferred organosilane compounds may also include an amine group. Whilst not wishing to be bound by theory, the presence of the amine function is thought to result in better adsorption of the organosilane to the formation and to proppant particles. The presence of an amine group may also result in increased stability of the organosilane to high temperatures and/or pressures. This may be due to the fact that the amine group may form further bonds (e.g. covalent, hydrogen and/or ionic bonds) between the organosilane and the proppant particles and/or the formation. Preferably the amine is a primary amine (i.e. -NH₂), still more preferably a secondary amine (i.e. -NH-).

Particularly preferred are those organosilane compounds which include more than one functional group, e.g. bifunctional organosilanes, or those compounds which are capable of self-polymerisation to produce bifunctional molecules. By "bifunctional organosilane" is meant an organosilane comprising two separate Si atoms, each of which forms part of at least one hydrolysable bond. Bifunctional organosilanes therefore advantageously afford, upon contact with water, at least two separate -Si-OH groups, which may each undergo any of the above-described reactions (e.g. with a proppant particle). Bifunctional organosilanes therefore increase the extent of polymerisation. Bifunctional organosilanes containing an amine group are particularly preferred.

Monofunctional organosilanes are also useful in the method of the invention. By monofunctional organosilane is meant an organosilane comprising one Si atom that forms part of at least one hydrolysable bond. In contrast to bifunctional organosilanes, monofunctional organosilanes tend to allow for less bonding to occur between different organosilanes, particularly those bound to different particles in the formation and/or proppant particles. Monofunctional organosilanes containing an amine group are particularly preferred.

It is particularly preferred in the method of the invention to use a mixture of a bifunctional and a monofunctional organosilane. For instance, the mixture may comprise a bifunctional to monofunctional organosilane ratio of 75:25 to 25:75, more preferably 60:40 to 40:60, still more preferably about 50:50. These ratios of bifunctional to monofunctional organosilanes have, in many cases, been found to yield the desired balance of proppant particle condensation which may "glue" the proppant particles together whilst at the same time the resulting proppant particle matrix does not reduce the permeability of the formation.

Representative examples of organosilanes that are suitable for use in the invention are organosilane alkoxides, organosilane esters, organosilane oximes, organosilane halides and organosilane hydrides. These compounds contain at least one -Si-OR, -SiO(O)CR, -SiO-N=CRR¹, -SiX and -SiH group respectively (wherein R and R' may be C_1-20 alkyl and X is a halogen). Hydrolysis of compounds containing these groups yields, in addition to a silanol (i.e. -Si-OH), -ROH, -RC(O)OH, -R¹RC=NOH, -HX and -H₂ respectively wherein R, R' and X are as hereinbefore defined. Particularly preferred organosilane compounds are organosilane alkoxides and organosilane esters. These undergo hydrolysis to afford, in addition to a silanol, alkanols and weak acids respectively. Neither of these compounds generally causes problems (e.g. due to side reactions) in hydrocarbon wells. Preferred organosilane compounds for use in the invention comprise a group of the formula -Si-OR wherein R is C_1-2O alkyl, more preferably C_2-6 alkyl, e.g. ethyl. Other preferred organosilane compounds comprise a group of the formula Si-O(O)CR wherein R is C_1-20 alkyl, more preferably C_2-6 alkyl, e.g. methyl.

Organosilanes suitable for use in the invention include those compounds of formula I:

R¹R²R³Si-R⁴ (I)

(wherein R¹, R² and R³ are each independently selected from hydrogen and organic radicals having from 1 to 50 carbon atoms; and

R⁴ is hydrogen, an organic radical having from 1 to 50 carbon atoms, or a group -OR⁵ in which R⁵ is an organic radical having from 1 to 50 carbon atoms; with the proviso that at least one of R¹, R², R³ and R⁴ is other than hydrogen).

In the compounds of formula I, R¹ -R⁵ are preferably selected from optionally substituted alkyl, alkenyl, aryl and alkoxy groups having from 1 to 18, preferably from 1 to 10, e.g. 1 to 6, carbon atoms. Optional substituents which maybe present include alkoxy (e.g. C_1-6 alkoxy), amino, silyl and silyloxy groups. The groups R¹- R⁵ may further be interrupted by one or more heteroatoms, preferably by N, O or S, e.g. by a group -NR⁶ where R⁶ is H or Ci_-6 alkyl.

Preferred compounds for use in the invention are those represented by formula (II):

R⁷ _a(R⁸O)_3-aSi-R⁹ (II)

(wherein a is zero or a positive integer from 1 to 3, preferably 0 or 1, e.g. 0; ' each R⁷ is independently a substituted or unsubstituted, preferably unsubstituted, alkyl group having from 1 to 6 carbon atoms, e.g. Ci alkyl; each R is independently a substituted or unsubstituted, preferably unsubstituted, alkyl group having from 1 to 18 carbon atoms, e.g. 1 to 6 carbons, or a -COR¹⁰ group wherein R¹⁰ is an optionally substituted, preferably unsubstituted, C_1-18 alkyl, e.g. C_1-6 alkyl group; and

R⁹ is a substituted or unsubstituted alkyl group having from 1 to 40 carbon atoms (preferably 1 to 18 carbon atoms, e.g. 1 to 8 carbons) and which is optionally interrupted by one or more heteroatoms; or

R⁹ is a group of the formula -(CH₂)_x-A-(CH₂)_y-Si(OR⁸)₃ in which A is an organic linking group or a group comprising an atom having a lone pair of electrons (e.g. a N, P or S atom); x is 0 or a positive integer, preferably from 1 to 10, more preferably 1 to 4, e.g. 2 or 3; y is 0 or a positive integer, preferably from 1 to 10, more preferably 1 to 4, e.g. 2 or 3; and R⁸ is as hereinbefore defined).

In preferred compounds of formula II, R⁸ is a Ci_-6 alkyl group, more preferably a C_2-4 alkyl group, for example, methyl or ethyl. In particularly preferred compounds of formula II, each R⁸ is the same.

Preferred compounds of formula II are also those wherein R⁹ is an unsubstituted alkyl group (e.g. R⁹ may be propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl or dodecyl, especially preferably octyl).

In particularly preferred compounds of formula II, R⁹ is a substituted or unsubstituted, preferably substituted, alkyl group (e.g. a substituted Ci_-I2 alkyl group). Preferred alkyl groups include propyl and butyl. Substituents which may be present include -NH₂, -NHR¹ and -NR'R" wherein R¹ and R" independently represent C_1-6 alkyl groups.

Particularly preferred organosilanes for use in the invention are those represented by formula III:

(R¹¹O)₃Si - (CH₂)* - A - (CH₂)_y - Si(OR¹ ')₃ (III)

(wherein each R¹ ' is independently a substituted or unsubstituted, preferably unsubstituted, alkyl group having from 1 to 18 carbon atoms, e.g. 1 to 6 carbons, or a -COR¹² group wherein R¹² is an optionally substituted, preferably unsubstituted, C_1-18 alkyl, e.g. C_1-6 alkyl group; A is an organic linking group or a group comprising an atom having a lone pair of electrons (e.g. a N, P or S atom); x is 0 or a positive integer, preferably from 1 to 10₅ more preferably 1 to 4, e.g. 2 or 3; and y is 0 or a positive integer, preferably from 1 to 10, more preferably 1 to 4, e.g. 2 of 3).

In formulae II and III, the function of group A is as a linking moiety and its precise chemical nature is of lesser importance provided this function is fulfilled. Generally, however, it will comprise a chain 1 to 20 atoms long, preferably 1 to 10, especially 1 to 5. Examples of suitable linkers include both linear and branched alkylene chains which may be interrupted by heteroatoms such as nitrogen and oxygen.

In formulae II and III, x and y will generally be identical.

In preferred compounds of formula III, R¹¹ is a C_1-6 alkyl group, more preferably a C_2-4 alkyl group, for example, methyl or ethyl. In particularly preferred compounds each R¹¹ is the same.

Preferred compounds of formulae II and III are also those wherein A is a group comprising an atom having a lone pair of electrons, especially nitrogen. Preferably A will be a group -NH or -NR¹³ where R¹³ is Ci_-6 alkyl.

Other preferred organosilanes for use in the invention are those represented by formula IV:

R¹⁴ _b(R¹⁵O)₃-_bSi-(CH₂)_z-NR¹⁶R¹⁷ (IV)

(wherein R¹⁶ and R¹⁷ are independently hydrogen or a substituted or unsubstituted, preferably unsubstituted, alkyl group having from 1 to 6 carbon atoms; z is a positive integer, preferably from 1 to 20, more preferably 1 to 8, e.g. 3 or 8; b is zero or a positive integer from 1 to 3, preferably 0 or 1 (e.g. 0); each R¹⁴ is independently a substituted or unsubstituted, preferably unsubstituted, alkyl group having from 1 to 6 carbon atoms (e.g. C₁); and each R¹⁵ is independently a substituted or unsubstituted, preferably unsubstituted, alkyl group having from 1 to 18 carbon atoms, e.g. 1 to 6 carbons, or a -COR¹⁸ group wherein R¹⁸ is an optionally substituted, preferably unsubstituted, C_1-18 alkyl, e.g. C_1-6 alkyl group). In preferred compounds of formula IV, R¹⁵ is a C_1-6 alkyl group, more preferably a C_2-4 alkyl group, for example, methyl or ethyl. In particularly preferred compounds of formula II, each R¹⁵ is the same.

In preferred compounds of formula IV, at least one of R¹⁶ and R¹⁷ is hydrogen. More preferably both R and R are hydrogen. Further preferred compounds of formula IV are those wherein z is at least 2, still more preferably z is at least 3 (e.g. z is 3).

Unless otherwise specified, any alkyl or alkenyl group referred to herein may be mono- or poly-substituted and may be branched or unbranched.

It is particularly preferred in the method of the invention to use a mixture of a compound of formula III and a compound of formula IV. For instance, the mixture may comprise a compound of formula III to a compound of formula IV in a ratio of 75:25 to 25:75, more preferably 60:40 to 40:60, still more preferably about 50:50.

Suitable organosilanes include 3-amino-propyltriethoxysilane, bis(triethoxysilylpropyl)amine, 3 -(diethoxymethylsilyl)ρropylamine, trimethpxyoctylsilane, triethoxyoctylsilane, 4,4, 15,15-tetraethoxy-3 , 16-dioxa- 8,9, 10,11 -tetrathia-4, 15-disilaoctadecane, and any combination thereof. Such compounds are available commercially, e.g. from Degussa (Hanau, Germany) under the tradenames DYNASYLAN 1126, DYNASYLAN 1122, DYNASYLAN 1506, DYNASYLAN OCTMO, DYNASYLAN OCTEO, DYNASYLAN AMEO and Si 69. A preferred combination of organosilanes for use in the invention is that comprising 3-aminopropyltriethoxysilane and bis(triethoxy silylpropyl)amine, preferably in a ratio of 75:25 to 25:75, more preferably 60:40 to 40:60, still more preferably about 50:50. A particularly preferred mixture is that sold under the tradename DYNASYLAN 1126.

The amount of organosilane to be used will vary widely depending on factors such as the nature of the particular organosilane used, the nature (e.g. permeability, temperature, etc.) of the formation, the nature of the proppant present and so on. In general, the amount of organosilane used will be sufficient to retain proppant in the formation at economically viable hydrocarbon flow rates and may be readily determined by those skilled in the art. The organosilanes for use in the method of the invention are preferably applied as a dispersion or solution in a liquid carrier. The liquid carrier may be aqueous or non-aqueous. Preferably, this will comprise a non-aqueous organic liquid, e.g. a hydrocarbon or hydrocarbon mixture, typically a C₃ to Ci₅ hydrocarbon, or oil, e.g. base oil, crude oil or lamp oil. Other suitable carrier liquids include aromatic hydrocarbons such as naphtha and diesel. Diesel is particularly preferred.

In the method of the invention it is generally preferred to use a hydrocarbon carrier since these this will minimise the exposure of the organosilane to water. This means that reaction (e.g. hydrolysis) during passage down into the well to the formation to be treated is minimised or prevented. Preferably the hydrocarbon carrier is substantially anhydrous. For example the hydrocarbon carrier preferably contains less than 5 % water, more preferably less than 2 % water, still more preferably less than 0.5 % water, e.g. less than 0.1 % water.

Preferably the liquid carrier comprising organosilane for use in the invention will be substantially free from other polymer materials. For example, this will be substantially free from a homo or copolymer of acrylamide, polyvinylalcohol, polysiloxane, a natural gum or chemically modified derivative thereof. The organosilane may, for example, be substantially free from polymer material other than that formed by polymerisation of the organosilane therein. For example, the amount of any other polymer material will typically be less than 10 wt.%, preferably less than 0.5 wt.%, more preferably less than 0.1 wt.%, e.g. less than 0.01 wt.%. Preferably any polymer material present in the organosilane will have a weight average molecular weight of less than 50,000 g/rnole.

Suitable hydrocarbon carrier liquids include crude oil, base oil, lamp oil, an aliphatic hydrocarbon (e.g. hexane), an aromatic hydrocarbon (e.g. benzene or toluene) or a petroleum distillation product or fraction (e.g. kerosene, naphthas or diesel fuel). Preferably the hydrocarbon comprises a petroleum distillation product, especially diesel fuel.

The liquid carrier (e.g. hydrocarbon carrier) may also contain other additives known in the art for use in well treatment. Such additives may include surfactants, thickeners, diversion agents, pH buffers and catalysts. Preferably the carrier does not contain a catalyst and/or a polymer, especially a polymer. It will be appreciated that the organosilanes for use in the invention are capable of forming polymers upon contact with water in the formation. Thus the preferred absence of a polymer refers to the organosilane prior to its contact with water. Still more preferably the organosilane comprises less than 500 ppm polymer, more preferably less than 100 ppm polymer. Particularly preferably the liquid carrier containing organosilane consists essentially of (e.g. consists of) an organosilane and a liquid (e.g. hydrocarbon) carrier.

Preferably, the concentration of the organosilane in the liquid carrier will be in the range of 0.05-50 % w/v, preferably 0.1 to 20 % w/v, more preferably 1 to 10 % w/v, e.g. about 3 to 5 % w/v. A higher concentration will generally be used for deeper perforations. Typically about 50 to 1000 litres (e.g. 100 to 400 litres) of hydrocarbon carrier per m³ of formation to be treated will be used.

The method of the invention may employ any conventional proppant. As used herein the term "proppant" means any substance that increases the permeability of a hydrocarbon producing system by enlarging or maintaining open fractures within the formation. Proppants are well known to those skilled in the art and include, for example, sand, glass, metal (e.g. steel) and ceramic particles. Sand particle proppants and ceramic particle proppants are preferred. Preferably the proppant for use in the method of the invention comprises ceramic particles. Particularly preferred ceramic particles comprise alumina and/or silica. Without wishing to be bound by theory, it is thought that ceramic particles have active sites on their surface that readily react with organosilane. Such particles are therefore particularly suitable for use in the method of the invention.

Preferably the ceramics are sintered. The proppant particles may be coated or uncoated, preferably uncoated. If the particles are coated, they are preferably coated with a well treatment agent, e.g. a scale inhibitor, a corrosion inhibitor, etc.

Preferred proppant particles for use in the invention are substantially spherical (e.g. spherical) since it is known that such particles are most effective at holding open formation fractures. The particle size of the proppant may vary over fairly wide ranges and will depend on certain characteristics of the formation such as, for example, its permeability prior to fracturing and the overburden pressure. The particles should be small enough to pass into cracks or fractures produced by the hydraulic fracturing but not so small as to cause the formation to exhibit low permability due to proppant deposition in the formation. The optimum particle size can be readily determined in each case by a skilled man in the art. In general the particle size ranges from 0.1-2 mm, e.g. 0.5-1 mm.

Representative examples of commercially available proppants that are suitable for use in the method of the invention include CR, CR4000_c, Black Plus, Blacky SB Excel, SB Prime₀, SiberProp, XRT Gold, PR6000, PR6000_w, PR6000_c, XRT Ceramax I, XRT Ceramax P, XRT Ceramax E, XRT Ceramax V, XRT Ceramax M, SiberMax I (all available from Hexion Speciality Chemicals),

Carbohsp 2000, Carboprop, Carbolite, Carboeconprop (all available from Carbo Ceramics) and Ottawa sand (available from Badger Mining Company).

The proppant is preferably applied to the hydrocarbon producing system as a dispersion in a liquid carrier. The liquid carrier may be aqueous or non-aqueous. Suitable non-aqueous carriers include alkanols, particularly polyols (e.g. a glycol). Particularly preferred glycols include those of the formula (CH₂)_n(OH)₂ wherein n is 2 to 6 (e.g. ethylene glycol). Still more preferably the liquid carrier is aqueous (e.g. sea water).

The concentration of the proppant in the carrier liquid will be an amount effective to enlarge or maintain open fractures in the formation and will be readily determined by those skilled in the art. Typically, however, the proppant will be present in the liquid carrier at a concentration of 0.1-20 kg/litre more preferably 0.5-

15 kg/litre, e.g. about 1-10 kg/litre.

The proppant and the organosilane are preferably formulated in separate liquid carriers. In this case, the organosilane may be injected before, during and/or after injection of the proppant. Preferably, however, the hydrocarbon producing system is contacted with proppant in a first step and with organosilane in a second step.

Alternatively the proppant and organosilane may be present together in a liquid carrier (e.g. in an emulsion). An emulsion comprising: a first phase comprising proppant and a second phase comprising organosilane therefore forms a further aspect of the invention. When present together the compounds are injected simultaneously. Thus in this alternative method of the invention, the hydrocarbon system is contacted with proppant and organosilane in a single step. This method has the advantage that it is simple and less time consuming. The above-mentioned two step process is, however, preferred.

In both cases the organosilane is preferably shut-in following its entry into the formation. The shut-in period is a function of the conditions in the well (e.g. temperature, pressure etc) which affect the rate at which polymerisation of the organosilane occurs. Typically, however, the shut-in period will be from 3 to 24 hours, preferably 4 to 12 hours, for example, 6 to 9 hours. Following shut in, the well is preferably put back onto production.

The liquid carriers may also contain other additives known in the art for use in well treatment. Such additives include surfactants, thickeners, diversion agents, corrosion inhibitors, pH buffers and catalysts. Preferably the liquid carriers consist essentially of (e.g. consist of) a proppant and/or an organosilane as hereinbefore described.

The total amount of proppant and organosilane to be used will vary widely depending on factors such as the initial permeability of the formation, the depth of the hydrocarbon reservoir, the nature of the fracture created, the nature of the proppant particles and so on. The appropriate amount of proppant and organosilane will be readily determined by those skilled in the art. It is envisaged that treatment with an organosilane in accordance with the method herein described could be at any stage in hydrocarbon production, i.e. before and/or after hydrocarbon production (i.e. extraction of oil or gas from the well) has begun. In some cases, the treatment will be prior to hydrocarbon production in order to facilitate economically viable extraction of hydrocarbon. In other cases, treatment is carried out once a permeability problem is identified or potential for such a problem is identified. It may often be beneficial to carry out treatment in accordance with the invention before permeability problems become severe. Nevertheless the treatment method herein described may be repeated as necessary in order to maximise hydrocarbon recovery. Thus, a well may be treated prior to production and then again after a potential permeability problem is identified.

Treatment is conducted by contacting the formation with a proppant and organosilane generally through a well bore, and typically employing pressures sufficient to penetrate the formation. By "contacting" is meant pumping, injecting, pouring, releasing, circulating or otherwise placing the treatment agent (i.e. organosilane and/or proppant) within a well, well bore and/or formation. Any method known in the art may be used. Treatment times or period of shut-in will depend on a number of factors including the nature of the formation and the volume of water present, the nature and concentration of the organosilane employed, the depth of perforations, etc. Typical shut-in times may be determined by those skilled in the art and will generally range from 2 to 10 hours, preferably from 3 to 8 hours, e.g. about 4 to 6 hours.

Any conventional treatment methods may be used to supply the proppant and organosilane to the well. Such methods will include bull-heading and coil tubing. Zonal isolation (e.g. with packers) may be used. Of these methods, bull-heading will generally be preferred. An advantage of bull-heading is that the whole well is treated and at relatively low cost. Bull-heading can be used for treatment of both vertical and horizontal wells and treatment can be effected during short production intervals. Suitable injection flow rates may be readily determined by those skilled in the art, however preferred flow rates may lie in the range 2500 to 3000 litres/min. In general, the injection flow rate will not be lower than about 500 litres/min. Coiled tubing (CT) methods are less desirable for economic reasons but may nevertheless be successfully used to supply the materials to the well. Such methods are generally more appropriate for treating long horizontal sections of the well. Suitable CT methods include those conventionally used in the field, e.g. roto pulse method, concentric coiled tubing, etc.

The method of the invention preferably has a lifetime of 2-80 months, more preferably 12-60 months, e.g. 24-48 months. The method of the invention can also be repeated as necessary.

The method of the of invention preferably increases the permeability of the formation. Thus alternately viewed the invention provides a method of increasing the permeability of a hydrocarbon producing system (e.g. a subterranean formation), said method comprising the steps:

(i) fracturing said system (e.g. by application of hydraulic pressure);

(ii) contacting said system with a proppant as hereinbefore described; and (iii) contacting said system with an organosilane as hereinbefore described.

Other conventional well treatments such as stimulation treatment, scale reduction treatment and scale dissolving treatment may also be used in conjunction with the methods of the invention. These may precede or follow the methods of the invention. Preferably, however, the well is ready to be put back onto production immediately after treatment in accordance with the methods of the invention.

The invention will now be described further with reference to the following non-limiting examples wherein: •

Figure 1 is a graph of Produced Proppant % versus Flow Rate for a sample treated with an organosilane according to the invention and an untreated sample

Example 1

The ability of 5 %vol DYNASYLAN 1126 (Degussa AG, Germany) to improve the retention of the proppant, Carbolite HSR (Halliburton) was tested. Tordis formation water was used in the test. It has the composition shown the Table below. Tordis Formation Water

*Reduced from 630 mg/1

Experimental procedure: 1. Carbolite HSR (1.8 g) was packed into teflon tubing having the dimensions: 10 cm (length) x 0.64 cm (diameter).

2. 100 ml of Tordis synthetic formation water was injected into the packed tube

3. 100 ml of diesel was inj ected into the packed tube

4. 50 ml of 5 %vol DYNASYLAN in diesel was injected into the packed tube at a flow rate of 5 ml/min

5. The tube was heated to 70 ⁰C and then shut in for 3 hours

6. 90 ml aliquots of Tordis formation water was then pumped into the packed tube at increasing flow rates (10 ml/ml, 20 ml/min, 30 ml/min, 40 ml/min and 50 ml/min). The amount of produced proppant was measured by weighing the proppant collected at the end of the tubing (after separation from produced fluid by filtering). This was done for each flow rate used.

A comparative experiment was also carried out in an identical manner except that in step 4 only diesel was injected. The results are shown in the Table below and in Figure 1.

The results show that DYNASYLAN 1126 is capable of significantly decreasing the amount of Carbolite HSR produced during a pumping operation. Without treatment with DYNASYLAN 1126, Carbolite HSR was produced at a flow rate of 30 ml/min, whereas when treatment was carried out Carbolite HSR was not detected until a flow rate of 50 ml/min was employed.

Claims

CLAIMS:

^ι l. A method for increasing the retention of a proppant within a hydrocarbon producing system (e.g. a subterranean formation), said method comprising contacting a formation comprising said proppant with an organosilane.

2. A method as claimed in any preceding claim further comprising the step of contacting said system with said proppant.

3. . A method as claimed in claim 1 or claim 2, wherein said organosilane comprises an amine group.

4. A method as claimed in any preceding claim, wherein said organosilane is bifunctional.

5. A method as claimed in any one of claims 1 to 4, wherein the organosilane comprises a compound of formula II:

R⁷ _a(R⁸O)_3-aSi-R⁹ (II)

(wherein a is zero or a positive integer from 1 to 3, preferably 0 or 1, e.g. 0; each R⁷ is independently a substituted or unsubstituted, preferably unsubstituted, alkyl group having from 1 to 6 carbon atoms, e.g. Ci alkyl; each R is independently a substituted or unsubstituted, preferably unsubstituted, alkyl group having from 1 to 18 carbon atoms, e.g. 1 to 6 carbons, or a -COR¹⁰ group wherein R¹⁰ is an optionally substituted, preferably unsubstituted, Ci_-18 alkyl, e.g. Ci_-6 alkyl group; and

R⁹ is a substituted or unsubstituted alkyl group having from 1 to 40 carbon atoms (preferably 1 to 18 carbon atoms, e.g. 1 to 8 carbons) and which is optionally interrupted by one or more heteroatoms; or R⁹ is a group of the formula -(CH₂)χ-A-(CH₂)_y-Si(OR⁸)₃ in which A is an organic linking group or a group comprising an atom having a lone pair of electrons (e.g. a N, P or S atom); x is 0 or a positive integer, preferably from 1 to 10, more preferably 1 to 4, e.g. 2 or 3; y is 0 or a positive integer, preferably from 1 to 10, more preferably 1 to 4, e.g. 2 or 3; and R⁸ is as hereinbefore defined).

6. A method as claimed in any one of claims 1 to 5, wherein the organosilane comprises a compound of formula III:

(R¹¹O)₃Si - (CH₂)* - A - (CH₂)_y - Si(OR¹ ')₃ (III)

(wherein each R¹¹ is independently a substituted or unsubstituted, preferably - unsubstituted, alkyl group having from 1 to 18 carbon atoms, e.g. 1 to 6 carbons, or a -COR¹² group wherein R¹² is" an optionally substituted, preferably unsubstituted, C_1-18 alkyl, e.g. C_1-6 alkyl group;

A is an organic linking group or a group comprising an atom having a lone pair of electrons (e.g.- a N, P or S atom); x is 0 or a positive integer, preferably from 1 to 10, more preferably 1 to 4, e.g. 2 or 3; and y is 0 or a positive integer).

7. A method as claimed in any one of claims 1 to 5, wherein the organosilane comprises a compound of formula IV:

R¹⁴ _b(R¹⁵O)_3-bSi-(CH₂)_z-NR¹⁶R¹⁷ (IV)

(wherein R¹⁶ and R¹⁷ are independently hydrogen or a substituted or unsubstituted, preferably unsubstituted, alkyl group having from 1 to 6 carbon atoms; z is a positive integer, preferably from 1 to 20, more preferably 1 to 8, e.g. 3 or 8; b is zero or a positive integer from 1 to 3, preferably 0 or 1 (e.g. 0); each R is independently a substituted or unsubstituted, preferably unsubstituted, alkyl group having from 1 to 6 carbon atoms (e.g. Ci); and each R¹⁵ is independently a substituted or unsubstituted, preferably unsubstituted, alkyl group having from 1 to 18 carbon atoms, e.g. 1 to 6 carbons, or a -COR¹⁸ group wherein R¹⁸ is an optionally substituted, preferably unsubstituted, C_1-18 alkyl, e.g. C_1-6 alkyl group).

8. A method as claimed in any one of claims 1 to 5 wherein said material comprises a mixture of a compound of formula III and a compound of formula IV.

9. A method as claimed in any one of claims 1 to 5, wherein the organosilane comprises 3-aminopropyltriethoxysilane, bis(triethoxysilylpropyl)amine, 3- (diethoxymethylsilyl)propylamine, trimethoxyoctylsilane, triethoxyoctylsilane, 3- aminopropyltriethoxysilane, 4,4,15, 15-tetraethoxy-3, 16-dioxa-8,9,10,l 1-tetrathia- 4,15-disilaoctadecane, or any combination thereof.

10. A method as claimed in any preceding claim wherein said organosilane is present in a substantially anhydrous hydrocarbon carrier.

11. A method as claimed in any preceding claim wherein said proppant comprises ceramic particles.

12. A method as claimed in any preceding claim wherein said proppant is present in a liquid carrier.

13. A method as claimed in any preceding claim further comprising the step of fracturing said formation.

14. Use of an organosilane to increase the retention of a proppant in a hydrocarbon producing system (e.g. a subterranean formation).

15. Use of an organosilane in the manufacture of a treatment composition for increasing the retention of a proppant in a hydrocarbon producing system (e.g. a subterranean formation)

16. A kit for increasing the retention of a proppant within a hydrocarbon producing system (e.g. a subterranean formation), said kit comprising a proppant and separately an organosilane.

17. An emulsion comprising: a first phase comprising a proppant and a second phase comprising an organosilane.

18. A method of increasing the permeability of a hydrocarbon producing system (e.g. a subterranean formation), said method comprising the steps:

(i) fracturing said system (e.g. by application of hydraulic pressure); (ii) contacting said system with a proppant; and

(iii) contacting said system with an organosilane.