CA1109356A - Gelled aqueous inorganic acid solutions and methods of using the same - Google Patents
Gelled aqueous inorganic acid solutions and methods of using the sameInfo
- Publication number
- CA1109356A CA1109356A CA311,659A CA311659A CA1109356A CA 1109356 A CA1109356 A CA 1109356A CA 311659 A CA311659 A CA 311659A CA 1109356 A CA1109356 A CA 1109356A
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- Canada
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- range
- carbon atoms
- acid solution
- gelling agent
- per molecule
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Classifications
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- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K8/00—Compositions for drilling of boreholes or wells; Compositions for treating boreholes or wells, e.g. for completion or for remedial operations
- C09K8/02—Well-drilling compositions
- C09K8/04—Aqueous well-drilling compositions
- C09K8/14—Clay-containing compositions
- C09K8/18—Clay-containing compositions characterised by the organic compounds
- C09K8/22—Synthetic organic compounds
Abstract
Abstract of the Disclosure Gelled aqueous inorganic acid solutions and methods of treating subterranean well formations using such solutions comprising water, at least one water soluble inorganic acid and a gelling agent comprised of a solution of a water soluble organic solvent and an ethoxylated fatty amine or a mixture of such amines.
Description
3~6 Acidizing and fracturing procedures usiny aqueous acid solutions are commonly carried out in subterranean well forma~ions to accomplish a number of purposes, one of which is to facilita~e the increase in the recovery o hydrocarbons therefrom. In acidizing procedures, aqueous acid solutions are introduced into wel1 ormations under pressure so that the acid solutions flow into the pore spaces of khe formations and react with materials con-tained therein whereby the pore spaces are enlarged and the permeability of the formations increased. In fracture acidizing procedures, one or more fractures are produced in the formations and the acid solutions are introduced into the fractures to etch flow channels therein and/or to enlarge the pore spaces in the fracture faces and in the formations.
Increasing the viscosity o~ an aqueous acid solution, hereinafter referred to as "gelling," by the inclusion of certain swellable materials or gelling agents therein has been accomplished heretofore. In acidizing and/or frac-ture acidizing subterranean formations, gelled aqueous acid solutions are useful in preventing the acid from be-coming prematurely spent and inactive. In addition, gelling of the acid solutions enables the development of wider fractures so that live acid can be forced further into the formation f:rom the well bore. Furthermore, increasing the ' . . , 3~
viscosities o ~he acid solutions a-lso permits better fluid loss control.
Gelled aqueous acid solutions have utilit~ in indus~
trial applications other than in the treatment of subterran-ean well ~ormations such as in the cleaning of industrial equipment.
Gelling agents such as hydratable gums and cellulose derivatives have been utilized to increase the viscosity o aqueous acid solutions. However, the gels produced using such gelling agents gene~ally have limited stabilit~
at high temperatures in the presence of acid. Other gell-ing agents which increase the viscosity o aqueous acid solutions have been developed and used, but they are often difficult to disperse and usually require considerable mixing or agitation to develop full viscosity. Still other prior art gelling agents can form an undesirable precipitate during the dissolution of formation materials such as lime-; stone or dolomite, which precipitate can remain in the formation to thereby damage it by decreasing the perme-ability thereof.
By the present i~vention, a gelling agent for increas-ing the viscosity of aqueous acid solutions, the resulting gelled aqueous acid solutions and methods of using such gelled aqueous acid solutions are provided. The gelling agent of the present invention can be easily dispersed into _3_ 3~
an aqueous acid solution and only a small quantity of it is required to rapidly increase the viscosity of the acid solution with a minimum of mixing and agitation. The resulting gelled aqueous acid solutions of the present invention have. excellent stability over a broad temperature range; they are relatively non-damaging to subterranean formations treated therewith; and, upon becoming spent in subterranean formations, and, without the inc].usion of chemical breakers or special additives kherein, they break to low viscosity liquids haviny excellent fines suspension properties.
The present invention relates to a gelled aqueous inorganic acid solution comprising water, at least one water soluble inorganic acid and a gelling agent, said gelling agent being comprised of a water soluble organic solvent selected from the group consisting of alkanols having in the range of from about 1 to 5 carbon atoms per molecule, ketones having in the range of about 3 to 6 carbon atoms per molecule, polyhydroxy compounds having in the range of about 2 to 6 carbon atoms per molecule, ethers having in the range of about 2 to 6 carbon atoms per molecule, compounds containing both ether and alcohol functions having in the range of about 4 to 8 carbon atoms per molecule, esters having in the range of about 2 to 6 carbon atoms per molecule, lactones having in the range of about 3 to 5 carbon atoms per molecule and mixtures of two or more of the foregoing compounds, and a mixture of ethoxylated fatty amines dissolved in said water soluble organic solvent having the general formula:
A
))XH
R - N
\ (CH2CH20)yH (1) wherein:
R is selected from saturated and unsaturated aliphatic groups having in the range of from about 8 to about 22 carbon atoms, and mixtures thereof, and x and y each have a value in the range of from about O to about 10. The preferred ethoxylated fatty amines and mixtures thereoE
useful herein are those wherein the average sum of the values of x and y in the amines used is in the range of from about 1.8 to about 2.2.
-4a-~A
3~
Mixtures of ethoxylated tertiary fatty amines derived from fats and oils such as coconut oil, soy bean oil, and tallow are particularly suitable or use in accordance with the present invention.
A preferred mixture of ethoxylated fatty amines for use in this invention is a mixture of amines of the general formula:
~(CH2CM20) xH
~ N\
\(CH2CH2O)yH (2, wherein:
R is selected from the group consisting of saturaked and unsaturated aliphatic groups having in the range of rom abo~lt 14 to about 18 carbon atoms and mixtures of such groups; and wherein the average sum of the values of x and y in the mixture of ethoxylated amines is equal to 2.
In the most preferred embodiment, x and y each have a value of 1 (oné).
Examples of such amines are those derived from fatty acids of the type hexadecyl, tallow, soya and oleyl, either saturated or unsaturated and either as pure components or mixtures.
A var:iety of organic solvents can be utilized in mak-ing the ge:Lling agents so long as such solvents are capable of dissolving the ethoxylated fatty amines and are also water soluble. Examples of such water soluble organic solvents include alkanols having in the range of about 1 to 5 carbon atoms per molecule, such as methanol, ethanol, 5i isopropanol and t-butanol; ketones having in the xange of about 3 to 6 carbon atoms per molecule~ such as acetone and methylethyl ketone polyhydroxy compounds having in the range of about 2 to 6 carbon a~oms per molecule, such as ethylene glycol and glycerine; ethers having in the range of about 2 to 6 carbon atoms per molecule, such as dioxane and tetrahydrofuran; compounds containing both ether and alcohol functions having in the range o-f about 4 to 8 car-bon atoms per molecule, such as diethylene glycol and tri-ethylene glycol; organic acids having in the range of about 1 to 10 carbon atoms per molecule, such as formic acid, malonic acid, acetic acid, gluconic acid, levuiinic acid . ~ and propionic acid; esters having in the range of about 2 : to 6 carbon atoms per molecule, such as methyl formate, dimethyl oxylate and dimethyl malonate; and lactones having in the range of about 3 to 5 carbon atoms per molecule, such as beta-propyl lactone and gamma-butyl lactone. Due to the desirably low freezing point and/or high flash point (tag closed cup) of the resulting yelling agent the organic acids are preerxed with acetic acid being the most prefeLred.
The water soluble organic solvent useful herein is 3~- ~
preferably in liquid phase at the temperature at which it is mixed with thé ethoxylated fatty amine. Furthermore, mixtures of the organic solvents can be used. An example is a mixture of me~hanol and gluconic acid.
The gelling agents useful herein can be pxepared by mixing the water soluble organic solvents with the ethoxy-lated fatty amines for a period of time suf~icient to com-pletely dissolve the amines in the solvents. The quantity of ethoxylated amines dissolved in the organic solvent range in an amount of from about 10 ko about 80, preferably from about 50 to about 60 percent amine by weight o~ the gelling agent.
As mentioned above, the organic solvents can be used singly, or in mixtures of solvents of the same chemical class (acids with acids, ketones with ketones and the like) or in mixtures of solvents of di~ferent chemical classes (acids with alcohols, ethers with ketones and the like). A
preferred organic solvent is a mixture of chemicals of dif-ferent chemical classes wherein at least one of the classes is an organic acid.
The ethoxylated fatty amines useful herein are very difficult to dissolve directly in aqueous inorganic acid solutions. However, the gelling agent of this invention, comprising a solution of the amines dissolved in a wa-ter soluble organic solvent, such as acetic acid, readily dis-solves in an aqueous inorganic acid solution and substan-tially Lmmediately increases the viscosity of the acid solution.
The gelling agents of the present invention cause an 3~$
increase in the viscosity of aqueous inorganic acid solu-tions having acid concentrations in the range from about 1 to abou~ 25 percent active acid by weight of the solu-tions. However, acid solutio.ns having acid concentrations of greater than abouk 25 percent can be mixed with the gelling agents of this invention and such acid solutions, upon being reacted, will begin to exhibit a noticeable increase in viscosity w~en the acid concentration, due to the reaction, is diminished to a value of about 25 percent.
Such increase in viscosity continues with continued decrease in acid concentration until the acid concentration reaches a value in the range of from about 10 percent to about 15 percent. To this extent then, this invention features a delayed gelling characteristic.
The gelling agents of this invention will cause the viscosity of aqueous inorganic acid solutions having acid concentrations in the range of from about 1 to about 10 percent, and more particularly in the range of from about 1 to about 5 percent, to rapidly increase providing that the presence of dissolved salts in the acid solution is very low and preferably absent. In this connection, the presence of dissolved salts in the gelled acids of this invention cause the gels to break when the acid concentration is less than about 10 percent and particularly when the acid concentration is less than about 5 percent. This~breaking feature, as will be further explained below, can be of particular value when the acid gels of this invention are used to acid treat sub-terranean formations.
.
The gelling agents are particulaxly useful in increas-ing the viscosity o~ aqueous inorganic acid solutions such as hydrochloric acid solutions, sul~uric acid solutions, phosphoric acid solutions, hydrofluoric acid solutions and solutions containing mixtures of such acids.
In preparing a gelled aqueous acid solution of this invention, the acid or mixture of acids utilized can be, and is preferably, diluted with water to obtain an aqueous inorganic acid solution of desired acid concentration. A
gelling agent of the present invention, i.e., an ethoxylated fatty amine or mixture of such amines of the type described above dissolved in a water soluble organic solvent, is pre-ferably comb~ned with the aqueous acid solution in an amount in the range of from about 0.1 to about 10, and more prefer-ably in the range of from about 2 to 6, percent gelling agent by weight of the aqueous acid solution. The acid solu-tion and gelling agent are agitated or mixed for a short period of time whereupon the viscosity o the aqueous acid solution is increased. More specifically, some increase in viscosity is obtained when as little as 0.1 percent gelling agent is combined with the aqueous acid solution, and greater amounts of the gelling agent bring about increased _9_ ' 3~i6 viscosity. When the gelling agent is combined with the aqueous acid solution in an amount of about lO percent by weight of the solution, viscosities of about 150 centi-poises can be obtained.
Greater viscosity increase can be obtained through use of gelling agent amounts in excess of lO percent. Thus, l~ percent is not a limit on the capability of the gelling agent to increase the viscosity of acid, but is viewed as a working guide in view of current process economics and the practical capabilities of currently known liquid hand-ling and pumping equipment.
A gelled aqueous acid solution of this invention is comprised of water, a water soluble inorganic acid or mix-ture of such acids, and a gelling agent comprised of a solution of a water soluble organic solvent and an ethoxy-lated fatty amine having the general formula:
. ~cH2cH2o)xH
; R N\
~ C~2CH2O)yH (3) wherein:
R is selected from saturated and unsaturated aliphatic groups having in the range of from about 8 to about 22 car-bon atoms, and mixtures thereof, and x and y each have a value in the range of from about 0 to about 10.
A preferred selled aqueous acid solution of this inven-tion is comprised of an inorganic aqueous acid solution '.
, 3~g~
comprising water and a water soluble inorganic acid or mixture of such acids, and a gelling agent comprised o a solutlon of a water soluble organic solvent and a mix-ture of ethoxylated fatty amines having the general fo~mula:
(C}I;~CH20) xH
R----W ~
. ~ CH2CH20)~H (4) wherein:
R is selected from saturated and unsaturated aliphatic groups having in the range of from about 14 to about 18 car-bon atoms and mixtures of such groups; and x and y each have a value in the range of from 0 to about 10 with the average sum of the values of x and y in the mixture being in the range of fl-om about 1.8 to about 2.2.
The most preferred gelled aqueous acid solution of this invention is comprised o an aqueous acid solution comprising water and an inorganic water soluble acid or a mixture of such acids, and a gelliny agent present in the aqueous acid solution in an amount in the range of from about 1 to about 10 percent gelling agent by weight of the acid so:Lution. The gelling agent is comprised of a solution of a water soluble organic solvent, and a mixture of ethoxylated fatty amines present in the gelling agent in an amount of from about 10 to about 80 percent amines 3~
by weight of the gelling agent. The ethoxylated fatty amines have the general formula:
~c~l~cH2o) xH
R - N \
~ CH2CH20)yH (5) wherein:
R is selected from the group consisting of saturated and unsaturated aliphatic groups having in the range of from about 16 to about 18 carbon atoms and mixtures of such groups; and the average sum of the values of x and y in said mix-ture of ethoxylated amines is equal to 2.
In the most preferred embodiment, x and y in formula (S) each have a value of one (1).
The gelled aqueous acid solutions of this invention are stable over a wide temperature range and therefore will not chemically degrade with time, even at a temperature as high as 250F. It must be understood, however, that the gelled acids of this invention, like other liquids, do experiénce viscosity change with temperature change. Thus, for example, with increasing temperaturel the viscosity of these gels declines, but is regained upon decrease of tem-perature. Thus, gels made according to this invention have long storage life.
While the gelled aqueous acid solutions of this inven~
tion have a variety of uses, they are particularly suitable -12- .
3~;~
for carrying out acid treatments in subterranean well formations for increasing the production of hydrocaxbon fluids therefrom. When the gelled aqueous acid solutions are intraduced into subterranean well formation, the acid spends by reacting with materials in the formakion, e.g., lLmestone and/or dolomite, whereby salts (e.g., chlorides when HCl i5 used~ are formed. ~he formation of salts in the spent acid solution causes the viscosity of the solu-tion ko decrease. That is, as the acid spends and salks form, the viscosity of the spent acid solution begins to decrease when acid concentration is in the range of about 10 to 15 percent. Thus, chemicals known in the art as "breakers" are not required when the gelled acid solutions of this invention are used to acid treat subterranean well formations. The spent acid solutions, after breaking, have viscosities in the range of from about 5 to about 15 centi-poises and have excellent particle suspension properties which facilitates the efficient clean-up of a treated forma-tion.
In using the gelled aqueous acid solutions for carrying out acidizing treatments in a subterranean well formation, an aqueous acid solution of desired acid strength is first prepared. For example, in carrying out acidizing or acid fracturing treatments in limestone or dolomite formations, aqueous hydrochloric acid solutions in concentrations in 3~
the range of from about 3~ to about 28% by weight are often utilized. After the particular aqueous acid solu-tion to be used has been prepared and diluted to the desired strength, the gelliny agent o the present inven-tion is combined therewith, pre~erably in an amount in the range of from about 0.1 to about 10 percent by weight of the acid solution whereby the viscosity of the solution is increased. Other conventional well ormation treating additives, such as corrosion inhibitors, non-emulsifying agents, fluid loss additives, etc., can also be combined with the solution. The resultant gelled aqueous acid solution is introduced into the formation to carry out an acidizing or acid fracturing treatment therein. After the a~ueous acid solution has become spent by reaction with materials in the formation and thereby broken to a low viscosity fluid, it is produced from the formation and the formation is cleaned up using conventional clean-up procedures followed by placing the formation on production.
When a gelled aqueous hydrochloric acid solution of this invention having an initial acid concentration of be'ow about 22 percent by weight of solution spends on limestone or dolomite to thus form calcium chloride and magnesium chloride and cools, some water and the gelling agent can separate out of the solution as a thick viscous phase.
Separation does not occur when the initial hydrochloric 3~
acid concentration is above about 22 percent by weight. In order to prevent separation in spent solutions when acid concentrations below about 22 percent by weight are utilized, calcium chloride can be added to the aqueous hydrochloric acid solution prior to gelling in an amount such that after reaction, the spent solution contains a calcium chloride concentration equivalent to a spent 22 percent by weight hyd.rochloric acid solution. The amount of calcium chloride required generally falls within the range of from about 1 percent to about 10 percent by wei~ht o~ the spent solution.
That is, when a gelled aqueous hydrochloric acid solution having an acid concentration of above about 22 percent by weight of the solution is utilized in the treatment of sub-terranean well formations containing calcium, n4 calcium - 15 chloride is added to the live solution. When a gelled aqueous hydrochloric acid solution at a concentration of 20 percent by weight of solution is utilized, about 308 pounds of calcium chloride per 1000 gallons o~ aqueous acid solution are added thereto which prevents separation at low temperatures (150F and below). When a gelled aqueous hydrochloric acid solution having a concentration of 15 percent by weight is utilized, about 1040 pounds o~
calcium chloride per 1000 gallons of acid solu-tion are com-bined therewith to prevent such separation.
The following examples are gi~en in order to further 3~
.
illustrate the gelling agent and gelled aqueous acid solu-tions of the present invention.
Example 1 Gelling agents o the present invention are prepared S using various mixtures of ethoxylated fatty amines dissolved in glacial acetic acid. The gelling agents are added to aqueous acid solutions containing 15 percent by weight hydro-chloric acid, and the viscosities of the resultant gels determined. The viscosities of the gels are apparent visco-sities measured on a Model 35 FANN viscometer, no. 1 spring, standard bob and sleeve, at room temperature (72 - 76F) and at 300 rpm. The results of these tests are given in Table I
below.
~, :
l~D~3~$
TABLE I - VISCOSITIES OF GELLED AQUEOUS
HYDROCHLORIC ACID SOLUTIONS USING VARIOUS GELL~N~ AGENT~ .
Ethoxylated Average Concentratlon Concentratlon Vlscoslty Fatty Amine Moles of o~ Amines Con- of Gelling of Gelled S Fatty Acid Ethylen~ tained in Gel- Agent inAqueous Origin Oxide ling Agent, % Hydrochloric HCl Per Mole ~y Welght of Acid Solution, - of Amine Acetic Acid- Solution, cp .. , Amine % by Weight Solution , Coconut (Mixture of Chains Hav-i~g 8, 10, 12, 14, 16 and 18 Car-bon Atoms) 2 33.3 9 3 Coconut (Mixture of Chains Hav-ing 8, 10, 12, 14, l~
and 18 Car-bon Atoms) 5 33.3 9 3 Soya (Mix-ture of Chains Hav-ing 14, 16 and 18 Car-bon Atoms) 2 33.3 9 77 Soya (Mix-ture of Chains Hav-ing 14, 16 and 18 Carbon Atoms) 5 33.3 9 3 Tallow (Mixture of Chains Having 14, 16 and 18 Carbon Atoms) 2 33.3 9 55 Oleyl (18 : Carbon Atoms) 2 33.3 9 82 Palmityl '(16 Car-bon Atoms) 2 50 6 52 .
t~ 3.~6 From Table I it can be seen that gelling agents con-taining ethoxylated fatty am:ines derived from coconut, soya, tallow, oleic, and palmitic fatty acids increase the viscosit,y,of aqueous hydroch:Loric acid solutions.
The results provided in Table I also make it clear that ethoxylated ~atty amines having an average of 2 moles of ethylene oxide per mole of amine and containing hydrocar-bon chain lengths of 14 to 18 carbon atoms significantly increase the viscosity of aqueous hydrochloric acid solutions~
Example 2 A gelling agent is prepared by dissolving 3 grams o~
ethoxylated soya amines having an average of 2 moles of ethylene oxide per mole of amine in 6 mls. (about 7 grams) of glacial acetic acid. The approximate composition of a commercial mixture of fatty acids from which the soya amine, is derived is as follows:
Acid % By Weight myristic (C14) 0 to 1%
palmitic (C16) 6 to 10%
steariC (C18) 2 to 4%
oleiC (C18) 21 to 29% .
linoleiC (C18) ' S0 to 59%
linoleniC (C18) 4 to 8%
The gelling agent is combined with 125 mls. (about 134 grams) of an aqueous hydrochloric acid solution containing ,.
D~3~fEi 15 percent by weight hydrochloric acid. After mixing, the aqueous hydrochloric acid solution has an apparent visco-sity of 95 centipoises measured on a Model 35 FANN visco-meter, no. 1 spring, standard bob and sleeve at room temperature (72 - 76F) and 300 rpm.
Example 3 Gelling agents are prepared by dissolving 5 grams of ethoxylated tallow amines having an average ethylene oxide content of 2 moles per mole o amine with vaxious organic solvents. The gelling agents are then each added in amounts of 10 mls. to 200 mls. of an aqueous acid solution prepared by combining 126.8 mls. of tap water with 73.2 mls. o~ a hydrochloric acid solution containing 37.5 percent by weight hydrochloric acid to thus produce 200 mls. of 15 percent HCl so,lution which weighed 215 grams. The solu-tion also contains 25 grams of calcium chloride and 0.4 ml. of a hydrochloric acid corrosion inhibitor. After mix-ing the gelling agents with the acid solutions, the apparent viscosities of the resulting gelled aqueous hydrochloric acid solutions are determined using a Model 35 FANN viscometer, no. 1 spring, standard bob and sleeve at 80F and 300 rpm.
The results o these tests are shown in Table II below.
r!~
TABLE II - VISCOSITIES OF GELLED AQUEOUS HYDROCHLORIC ACID
SOLUTIONS USING GELLING AGENTS CONTAINING VARIOUS ORGANIC ACIDS
Quantity of Organic Quantity Degree of Viscosity Ethoxylated Solvent of Difficulty of Gelled Tallow Organic in Dissolv- Aqueous Amines, ml Solvent, ing Amines Hydrochloric (grams) ml in Solvent Acid (grams) Used solutions ( 5 ) Propionic 5 (5.0) Easily 51 acid dissolved ( 5 ) Acetic 5 (5.2) Very easily 70 acid dissolved 5 ( 5 ) Formic S (5.9) Dif~icult 88 Acid - 88~
; 15 5 ( 5 ) Acetone 5 (3.9) Easily 67 dissolved ( 5 ) Ethylene 5 (5.5) Easily 75 Glycol dissolved ~.
Gelling agents are prepared by dissolving ethoxylated tallow amines~having an average of 2 moles of ethylene oxide per mole of amine in various organic acids in amounts of 50 percent by weight of amine-acid solution. Each of the gelling agents are combined with aqueous hydrochloric acid solutions in amounts of 5 percent gelling agent by weight of the acid solutions, and the viscosities of the resulting gelled aqueous acid solutions are determined at various tem-peratures. Each of the aqueous acid solutions contain 15 percent hydrochloric acid by weight, 12.5 grams of calcium chloride per 100 cc of acid solution, and 0.2 percent by weight of a hydrochloric acid corrosion inhibitor.
, -20-~'~'J1~3~l~
TABLE III - VISCOSITIES OF GELLED HYDROCHLORIC ACID SOLUTIONS
AT VARIOUS ~EMPERATUES USING GELLING AGENTS
CONTAINING VARIOtJS ORGANIC ACIDS
.
Organic Viscosities of Gelled Aqueous ~ICl Solutions, cp Acid .
90~F 100F 110F 120F 130F 140F 150F 160F 170F 180F
Formic 70 66 61 55 48.5 40 30 23.5 19 16 Acetic 67 61 54 46 :35 29 23 19 14.S 10.5 Prop-41.5 30 21.5 16 13 10.5 8 6 4.5 3.5 ionic As illustrated in Tables II and III above, gelling agents wherein formic acid is used as the amine solvent achieve the highest apparent viscosity in hydrochloric acid solutions. How-ever, because the dissolution of ethoxylated ~atty amines in formic acid is difficult, acetic acid is preferred for use in accordance with this invention.
. .:,", .
~ Fxample 5 A gelling agent is prepared by dissolving ethoxylated tallow amines having an average ethylene oxide content of 2 moles per mole of amine in acetic acid in an amount of 50 percent by weight of the amine-acid solution. Various amounts of the gelling agent are combined with aqueous hydrochloric acid solutions containing 15 percent by weight hydrochloric acid and 0.4 percent by weight hydrochloric acid corrosion inhibitor. The apparent viscosities of the resulting gelled aqueous hydroc:hloric acid solutions are determined at var~
ious temperatures using a Model 35 FANN viscometer, no. l 3r~
spring, standard bob and sleeve at 300 rpmO The results of these tests are given in Table IV below.
TABLE IV - VISCOSITIES OF GELhED AQUEOUS HYDROCHLORIC ACID
SOLUTIONS AT VARIOUS TEMPERATUES USING VARIOUS
QUANTITIES OF GELLING AGENT
Percent Viscosities of Gelled Aqueous ~Cl Solutions, cp Gelling Agent By ~
Weight of Acid Solu- 90F100F 110F 120F130F 140F 150F160F
kion ~~
Increasing the viscosity o~ an aqueous acid solution, hereinafter referred to as "gelling," by the inclusion of certain swellable materials or gelling agents therein has been accomplished heretofore. In acidizing and/or frac-ture acidizing subterranean formations, gelled aqueous acid solutions are useful in preventing the acid from be-coming prematurely spent and inactive. In addition, gelling of the acid solutions enables the development of wider fractures so that live acid can be forced further into the formation f:rom the well bore. Furthermore, increasing the ' . . , 3~
viscosities o ~he acid solutions a-lso permits better fluid loss control.
Gelled aqueous acid solutions have utilit~ in indus~
trial applications other than in the treatment of subterran-ean well ~ormations such as in the cleaning of industrial equipment.
Gelling agents such as hydratable gums and cellulose derivatives have been utilized to increase the viscosity o aqueous acid solutions. However, the gels produced using such gelling agents gene~ally have limited stabilit~
at high temperatures in the presence of acid. Other gell-ing agents which increase the viscosity o aqueous acid solutions have been developed and used, but they are often difficult to disperse and usually require considerable mixing or agitation to develop full viscosity. Still other prior art gelling agents can form an undesirable precipitate during the dissolution of formation materials such as lime-; stone or dolomite, which precipitate can remain in the formation to thereby damage it by decreasing the perme-ability thereof.
By the present i~vention, a gelling agent for increas-ing the viscosity of aqueous acid solutions, the resulting gelled aqueous acid solutions and methods of using such gelled aqueous acid solutions are provided. The gelling agent of the present invention can be easily dispersed into _3_ 3~
an aqueous acid solution and only a small quantity of it is required to rapidly increase the viscosity of the acid solution with a minimum of mixing and agitation. The resulting gelled aqueous acid solutions of the present invention have. excellent stability over a broad temperature range; they are relatively non-damaging to subterranean formations treated therewith; and, upon becoming spent in subterranean formations, and, without the inc].usion of chemical breakers or special additives kherein, they break to low viscosity liquids haviny excellent fines suspension properties.
The present invention relates to a gelled aqueous inorganic acid solution comprising water, at least one water soluble inorganic acid and a gelling agent, said gelling agent being comprised of a water soluble organic solvent selected from the group consisting of alkanols having in the range of from about 1 to 5 carbon atoms per molecule, ketones having in the range of about 3 to 6 carbon atoms per molecule, polyhydroxy compounds having in the range of about 2 to 6 carbon atoms per molecule, ethers having in the range of about 2 to 6 carbon atoms per molecule, compounds containing both ether and alcohol functions having in the range of about 4 to 8 carbon atoms per molecule, esters having in the range of about 2 to 6 carbon atoms per molecule, lactones having in the range of about 3 to 5 carbon atoms per molecule and mixtures of two or more of the foregoing compounds, and a mixture of ethoxylated fatty amines dissolved in said water soluble organic solvent having the general formula:
A
))XH
R - N
\ (CH2CH20)yH (1) wherein:
R is selected from saturated and unsaturated aliphatic groups having in the range of from about 8 to about 22 carbon atoms, and mixtures thereof, and x and y each have a value in the range of from about O to about 10. The preferred ethoxylated fatty amines and mixtures thereoE
useful herein are those wherein the average sum of the values of x and y in the amines used is in the range of from about 1.8 to about 2.2.
-4a-~A
3~
Mixtures of ethoxylated tertiary fatty amines derived from fats and oils such as coconut oil, soy bean oil, and tallow are particularly suitable or use in accordance with the present invention.
A preferred mixture of ethoxylated fatty amines for use in this invention is a mixture of amines of the general formula:
~(CH2CM20) xH
~ N\
\(CH2CH2O)yH (2, wherein:
R is selected from the group consisting of saturaked and unsaturated aliphatic groups having in the range of rom abo~lt 14 to about 18 carbon atoms and mixtures of such groups; and wherein the average sum of the values of x and y in the mixture of ethoxylated amines is equal to 2.
In the most preferred embodiment, x and y each have a value of 1 (oné).
Examples of such amines are those derived from fatty acids of the type hexadecyl, tallow, soya and oleyl, either saturated or unsaturated and either as pure components or mixtures.
A var:iety of organic solvents can be utilized in mak-ing the ge:Lling agents so long as such solvents are capable of dissolving the ethoxylated fatty amines and are also water soluble. Examples of such water soluble organic solvents include alkanols having in the range of about 1 to 5 carbon atoms per molecule, such as methanol, ethanol, 5i isopropanol and t-butanol; ketones having in the xange of about 3 to 6 carbon atoms per molecule~ such as acetone and methylethyl ketone polyhydroxy compounds having in the range of about 2 to 6 carbon a~oms per molecule, such as ethylene glycol and glycerine; ethers having in the range of about 2 to 6 carbon atoms per molecule, such as dioxane and tetrahydrofuran; compounds containing both ether and alcohol functions having in the range o-f about 4 to 8 car-bon atoms per molecule, such as diethylene glycol and tri-ethylene glycol; organic acids having in the range of about 1 to 10 carbon atoms per molecule, such as formic acid, malonic acid, acetic acid, gluconic acid, levuiinic acid . ~ and propionic acid; esters having in the range of about 2 : to 6 carbon atoms per molecule, such as methyl formate, dimethyl oxylate and dimethyl malonate; and lactones having in the range of about 3 to 5 carbon atoms per molecule, such as beta-propyl lactone and gamma-butyl lactone. Due to the desirably low freezing point and/or high flash point (tag closed cup) of the resulting yelling agent the organic acids are preerxed with acetic acid being the most prefeLred.
The water soluble organic solvent useful herein is 3~- ~
preferably in liquid phase at the temperature at which it is mixed with thé ethoxylated fatty amine. Furthermore, mixtures of the organic solvents can be used. An example is a mixture of me~hanol and gluconic acid.
The gelling agents useful herein can be pxepared by mixing the water soluble organic solvents with the ethoxy-lated fatty amines for a period of time suf~icient to com-pletely dissolve the amines in the solvents. The quantity of ethoxylated amines dissolved in the organic solvent range in an amount of from about 10 ko about 80, preferably from about 50 to about 60 percent amine by weight o~ the gelling agent.
As mentioned above, the organic solvents can be used singly, or in mixtures of solvents of the same chemical class (acids with acids, ketones with ketones and the like) or in mixtures of solvents of di~ferent chemical classes (acids with alcohols, ethers with ketones and the like). A
preferred organic solvent is a mixture of chemicals of dif-ferent chemical classes wherein at least one of the classes is an organic acid.
The ethoxylated fatty amines useful herein are very difficult to dissolve directly in aqueous inorganic acid solutions. However, the gelling agent of this invention, comprising a solution of the amines dissolved in a wa-ter soluble organic solvent, such as acetic acid, readily dis-solves in an aqueous inorganic acid solution and substan-tially Lmmediately increases the viscosity of the acid solution.
The gelling agents of the present invention cause an 3~$
increase in the viscosity of aqueous inorganic acid solu-tions having acid concentrations in the range from about 1 to abou~ 25 percent active acid by weight of the solu-tions. However, acid solutio.ns having acid concentrations of greater than abouk 25 percent can be mixed with the gelling agents of this invention and such acid solutions, upon being reacted, will begin to exhibit a noticeable increase in viscosity w~en the acid concentration, due to the reaction, is diminished to a value of about 25 percent.
Such increase in viscosity continues with continued decrease in acid concentration until the acid concentration reaches a value in the range of from about 10 percent to about 15 percent. To this extent then, this invention features a delayed gelling characteristic.
The gelling agents of this invention will cause the viscosity of aqueous inorganic acid solutions having acid concentrations in the range of from about 1 to about 10 percent, and more particularly in the range of from about 1 to about 5 percent, to rapidly increase providing that the presence of dissolved salts in the acid solution is very low and preferably absent. In this connection, the presence of dissolved salts in the gelled acids of this invention cause the gels to break when the acid concentration is less than about 10 percent and particularly when the acid concentration is less than about 5 percent. This~breaking feature, as will be further explained below, can be of particular value when the acid gels of this invention are used to acid treat sub-terranean formations.
.
The gelling agents are particulaxly useful in increas-ing the viscosity o~ aqueous inorganic acid solutions such as hydrochloric acid solutions, sul~uric acid solutions, phosphoric acid solutions, hydrofluoric acid solutions and solutions containing mixtures of such acids.
In preparing a gelled aqueous acid solution of this invention, the acid or mixture of acids utilized can be, and is preferably, diluted with water to obtain an aqueous inorganic acid solution of desired acid concentration. A
gelling agent of the present invention, i.e., an ethoxylated fatty amine or mixture of such amines of the type described above dissolved in a water soluble organic solvent, is pre-ferably comb~ned with the aqueous acid solution in an amount in the range of from about 0.1 to about 10, and more prefer-ably in the range of from about 2 to 6, percent gelling agent by weight of the aqueous acid solution. The acid solu-tion and gelling agent are agitated or mixed for a short period of time whereupon the viscosity o the aqueous acid solution is increased. More specifically, some increase in viscosity is obtained when as little as 0.1 percent gelling agent is combined with the aqueous acid solution, and greater amounts of the gelling agent bring about increased _9_ ' 3~i6 viscosity. When the gelling agent is combined with the aqueous acid solution in an amount of about lO percent by weight of the solution, viscosities of about 150 centi-poises can be obtained.
Greater viscosity increase can be obtained through use of gelling agent amounts in excess of lO percent. Thus, l~ percent is not a limit on the capability of the gelling agent to increase the viscosity of acid, but is viewed as a working guide in view of current process economics and the practical capabilities of currently known liquid hand-ling and pumping equipment.
A gelled aqueous acid solution of this invention is comprised of water, a water soluble inorganic acid or mix-ture of such acids, and a gelling agent comprised of a solution of a water soluble organic solvent and an ethoxy-lated fatty amine having the general formula:
. ~cH2cH2o)xH
; R N\
~ C~2CH2O)yH (3) wherein:
R is selected from saturated and unsaturated aliphatic groups having in the range of from about 8 to about 22 car-bon atoms, and mixtures thereof, and x and y each have a value in the range of from about 0 to about 10.
A preferred selled aqueous acid solution of this inven-tion is comprised of an inorganic aqueous acid solution '.
, 3~g~
comprising water and a water soluble inorganic acid or mixture of such acids, and a gelling agent comprised o a solutlon of a water soluble organic solvent and a mix-ture of ethoxylated fatty amines having the general fo~mula:
(C}I;~CH20) xH
R----W ~
. ~ CH2CH20)~H (4) wherein:
R is selected from saturated and unsaturated aliphatic groups having in the range of from about 14 to about 18 car-bon atoms and mixtures of such groups; and x and y each have a value in the range of from 0 to about 10 with the average sum of the values of x and y in the mixture being in the range of fl-om about 1.8 to about 2.2.
The most preferred gelled aqueous acid solution of this invention is comprised o an aqueous acid solution comprising water and an inorganic water soluble acid or a mixture of such acids, and a gelliny agent present in the aqueous acid solution in an amount in the range of from about 1 to about 10 percent gelling agent by weight of the acid so:Lution. The gelling agent is comprised of a solution of a water soluble organic solvent, and a mixture of ethoxylated fatty amines present in the gelling agent in an amount of from about 10 to about 80 percent amines 3~
by weight of the gelling agent. The ethoxylated fatty amines have the general formula:
~c~l~cH2o) xH
R - N \
~ CH2CH20)yH (5) wherein:
R is selected from the group consisting of saturated and unsaturated aliphatic groups having in the range of from about 16 to about 18 carbon atoms and mixtures of such groups; and the average sum of the values of x and y in said mix-ture of ethoxylated amines is equal to 2.
In the most preferred embodiment, x and y in formula (S) each have a value of one (1).
The gelled aqueous acid solutions of this invention are stable over a wide temperature range and therefore will not chemically degrade with time, even at a temperature as high as 250F. It must be understood, however, that the gelled acids of this invention, like other liquids, do experiénce viscosity change with temperature change. Thus, for example, with increasing temperaturel the viscosity of these gels declines, but is regained upon decrease of tem-perature. Thus, gels made according to this invention have long storage life.
While the gelled aqueous acid solutions of this inven~
tion have a variety of uses, they are particularly suitable -12- .
3~;~
for carrying out acid treatments in subterranean well formations for increasing the production of hydrocaxbon fluids therefrom. When the gelled aqueous acid solutions are intraduced into subterranean well formation, the acid spends by reacting with materials in the formakion, e.g., lLmestone and/or dolomite, whereby salts (e.g., chlorides when HCl i5 used~ are formed. ~he formation of salts in the spent acid solution causes the viscosity of the solu-tion ko decrease. That is, as the acid spends and salks form, the viscosity of the spent acid solution begins to decrease when acid concentration is in the range of about 10 to 15 percent. Thus, chemicals known in the art as "breakers" are not required when the gelled acid solutions of this invention are used to acid treat subterranean well formations. The spent acid solutions, after breaking, have viscosities in the range of from about 5 to about 15 centi-poises and have excellent particle suspension properties which facilitates the efficient clean-up of a treated forma-tion.
In using the gelled aqueous acid solutions for carrying out acidizing treatments in a subterranean well formation, an aqueous acid solution of desired acid strength is first prepared. For example, in carrying out acidizing or acid fracturing treatments in limestone or dolomite formations, aqueous hydrochloric acid solutions in concentrations in 3~
the range of from about 3~ to about 28% by weight are often utilized. After the particular aqueous acid solu-tion to be used has been prepared and diluted to the desired strength, the gelliny agent o the present inven-tion is combined therewith, pre~erably in an amount in the range of from about 0.1 to about 10 percent by weight of the acid solution whereby the viscosity of the solution is increased. Other conventional well ormation treating additives, such as corrosion inhibitors, non-emulsifying agents, fluid loss additives, etc., can also be combined with the solution. The resultant gelled aqueous acid solution is introduced into the formation to carry out an acidizing or acid fracturing treatment therein. After the a~ueous acid solution has become spent by reaction with materials in the formation and thereby broken to a low viscosity fluid, it is produced from the formation and the formation is cleaned up using conventional clean-up procedures followed by placing the formation on production.
When a gelled aqueous hydrochloric acid solution of this invention having an initial acid concentration of be'ow about 22 percent by weight of solution spends on limestone or dolomite to thus form calcium chloride and magnesium chloride and cools, some water and the gelling agent can separate out of the solution as a thick viscous phase.
Separation does not occur when the initial hydrochloric 3~
acid concentration is above about 22 percent by weight. In order to prevent separation in spent solutions when acid concentrations below about 22 percent by weight are utilized, calcium chloride can be added to the aqueous hydrochloric acid solution prior to gelling in an amount such that after reaction, the spent solution contains a calcium chloride concentration equivalent to a spent 22 percent by weight hyd.rochloric acid solution. The amount of calcium chloride required generally falls within the range of from about 1 percent to about 10 percent by wei~ht o~ the spent solution.
That is, when a gelled aqueous hydrochloric acid solution having an acid concentration of above about 22 percent by weight of the solution is utilized in the treatment of sub-terranean well formations containing calcium, n4 calcium - 15 chloride is added to the live solution. When a gelled aqueous hydrochloric acid solution at a concentration of 20 percent by weight of solution is utilized, about 308 pounds of calcium chloride per 1000 gallons o~ aqueous acid solution are added thereto which prevents separation at low temperatures (150F and below). When a gelled aqueous hydrochloric acid solution having a concentration of 15 percent by weight is utilized, about 1040 pounds o~
calcium chloride per 1000 gallons of acid solu-tion are com-bined therewith to prevent such separation.
The following examples are gi~en in order to further 3~
.
illustrate the gelling agent and gelled aqueous acid solu-tions of the present invention.
Example 1 Gelling agents o the present invention are prepared S using various mixtures of ethoxylated fatty amines dissolved in glacial acetic acid. The gelling agents are added to aqueous acid solutions containing 15 percent by weight hydro-chloric acid, and the viscosities of the resultant gels determined. The viscosities of the gels are apparent visco-sities measured on a Model 35 FANN viscometer, no. 1 spring, standard bob and sleeve, at room temperature (72 - 76F) and at 300 rpm. The results of these tests are given in Table I
below.
~, :
l~D~3~$
TABLE I - VISCOSITIES OF GELLED AQUEOUS
HYDROCHLORIC ACID SOLUTIONS USING VARIOUS GELL~N~ AGENT~ .
Ethoxylated Average Concentratlon Concentratlon Vlscoslty Fatty Amine Moles of o~ Amines Con- of Gelling of Gelled S Fatty Acid Ethylen~ tained in Gel- Agent inAqueous Origin Oxide ling Agent, % Hydrochloric HCl Per Mole ~y Welght of Acid Solution, - of Amine Acetic Acid- Solution, cp .. , Amine % by Weight Solution , Coconut (Mixture of Chains Hav-i~g 8, 10, 12, 14, 16 and 18 Car-bon Atoms) 2 33.3 9 3 Coconut (Mixture of Chains Hav-ing 8, 10, 12, 14, l~
and 18 Car-bon Atoms) 5 33.3 9 3 Soya (Mix-ture of Chains Hav-ing 14, 16 and 18 Car-bon Atoms) 2 33.3 9 77 Soya (Mix-ture of Chains Hav-ing 14, 16 and 18 Carbon Atoms) 5 33.3 9 3 Tallow (Mixture of Chains Having 14, 16 and 18 Carbon Atoms) 2 33.3 9 55 Oleyl (18 : Carbon Atoms) 2 33.3 9 82 Palmityl '(16 Car-bon Atoms) 2 50 6 52 .
t~ 3.~6 From Table I it can be seen that gelling agents con-taining ethoxylated fatty am:ines derived from coconut, soya, tallow, oleic, and palmitic fatty acids increase the viscosit,y,of aqueous hydroch:Loric acid solutions.
The results provided in Table I also make it clear that ethoxylated ~atty amines having an average of 2 moles of ethylene oxide per mole of amine and containing hydrocar-bon chain lengths of 14 to 18 carbon atoms significantly increase the viscosity of aqueous hydrochloric acid solutions~
Example 2 A gelling agent is prepared by dissolving 3 grams o~
ethoxylated soya amines having an average of 2 moles of ethylene oxide per mole of amine in 6 mls. (about 7 grams) of glacial acetic acid. The approximate composition of a commercial mixture of fatty acids from which the soya amine, is derived is as follows:
Acid % By Weight myristic (C14) 0 to 1%
palmitic (C16) 6 to 10%
steariC (C18) 2 to 4%
oleiC (C18) 21 to 29% .
linoleiC (C18) ' S0 to 59%
linoleniC (C18) 4 to 8%
The gelling agent is combined with 125 mls. (about 134 grams) of an aqueous hydrochloric acid solution containing ,.
D~3~fEi 15 percent by weight hydrochloric acid. After mixing, the aqueous hydrochloric acid solution has an apparent visco-sity of 95 centipoises measured on a Model 35 FANN visco-meter, no. 1 spring, standard bob and sleeve at room temperature (72 - 76F) and 300 rpm.
Example 3 Gelling agents are prepared by dissolving 5 grams of ethoxylated tallow amines having an average ethylene oxide content of 2 moles per mole o amine with vaxious organic solvents. The gelling agents are then each added in amounts of 10 mls. to 200 mls. of an aqueous acid solution prepared by combining 126.8 mls. of tap water with 73.2 mls. o~ a hydrochloric acid solution containing 37.5 percent by weight hydrochloric acid to thus produce 200 mls. of 15 percent HCl so,lution which weighed 215 grams. The solu-tion also contains 25 grams of calcium chloride and 0.4 ml. of a hydrochloric acid corrosion inhibitor. After mix-ing the gelling agents with the acid solutions, the apparent viscosities of the resulting gelled aqueous hydrochloric acid solutions are determined using a Model 35 FANN viscometer, no. 1 spring, standard bob and sleeve at 80F and 300 rpm.
The results o these tests are shown in Table II below.
r!~
TABLE II - VISCOSITIES OF GELLED AQUEOUS HYDROCHLORIC ACID
SOLUTIONS USING GELLING AGENTS CONTAINING VARIOUS ORGANIC ACIDS
Quantity of Organic Quantity Degree of Viscosity Ethoxylated Solvent of Difficulty of Gelled Tallow Organic in Dissolv- Aqueous Amines, ml Solvent, ing Amines Hydrochloric (grams) ml in Solvent Acid (grams) Used solutions ( 5 ) Propionic 5 (5.0) Easily 51 acid dissolved ( 5 ) Acetic 5 (5.2) Very easily 70 acid dissolved 5 ( 5 ) Formic S (5.9) Dif~icult 88 Acid - 88~
; 15 5 ( 5 ) Acetone 5 (3.9) Easily 67 dissolved ( 5 ) Ethylene 5 (5.5) Easily 75 Glycol dissolved ~.
Gelling agents are prepared by dissolving ethoxylated tallow amines~having an average of 2 moles of ethylene oxide per mole of amine in various organic acids in amounts of 50 percent by weight of amine-acid solution. Each of the gelling agents are combined with aqueous hydrochloric acid solutions in amounts of 5 percent gelling agent by weight of the acid solutions, and the viscosities of the resulting gelled aqueous acid solutions are determined at various tem-peratures. Each of the aqueous acid solutions contain 15 percent hydrochloric acid by weight, 12.5 grams of calcium chloride per 100 cc of acid solution, and 0.2 percent by weight of a hydrochloric acid corrosion inhibitor.
, -20-~'~'J1~3~l~
TABLE III - VISCOSITIES OF GELLED HYDROCHLORIC ACID SOLUTIONS
AT VARIOUS ~EMPERATUES USING GELLING AGENTS
CONTAINING VARIOtJS ORGANIC ACIDS
.
Organic Viscosities of Gelled Aqueous ~ICl Solutions, cp Acid .
90~F 100F 110F 120F 130F 140F 150F 160F 170F 180F
Formic 70 66 61 55 48.5 40 30 23.5 19 16 Acetic 67 61 54 46 :35 29 23 19 14.S 10.5 Prop-41.5 30 21.5 16 13 10.5 8 6 4.5 3.5 ionic As illustrated in Tables II and III above, gelling agents wherein formic acid is used as the amine solvent achieve the highest apparent viscosity in hydrochloric acid solutions. How-ever, because the dissolution of ethoxylated ~atty amines in formic acid is difficult, acetic acid is preferred for use in accordance with this invention.
. .:,", .
~ Fxample 5 A gelling agent is prepared by dissolving ethoxylated tallow amines having an average ethylene oxide content of 2 moles per mole of amine in acetic acid in an amount of 50 percent by weight of the amine-acid solution. Various amounts of the gelling agent are combined with aqueous hydrochloric acid solutions containing 15 percent by weight hydrochloric acid and 0.4 percent by weight hydrochloric acid corrosion inhibitor. The apparent viscosities of the resulting gelled aqueous hydroc:hloric acid solutions are determined at var~
ious temperatures using a Model 35 FANN viscometer, no. l 3r~
spring, standard bob and sleeve at 300 rpmO The results of these tests are given in Table IV below.
TABLE IV - VISCOSITIES OF GELhED AQUEOUS HYDROCHLORIC ACID
SOLUTIONS AT VARIOUS TEMPERATUES USING VARIOUS
QUANTITIES OF GELLING AGENT
Percent Viscosities of Gelled Aqueous ~Cl Solutions, cp Gelling Agent By ~
Weight of Acid Solu- 90F100F 110F 120F130F 140F 150F160F
kion ~~
2 l98.5 4 32.5
3 37.535 31.5 27 2l 15.5 6 2.5
4 48.545 40 31.524 18 14 10 S 68.565 50 38 31 24 19 14 From Table IV it can be seen that by increasing the amount of gelling agent combined with an aqueous solution, the viscosity of the resultant gelled solution is increased.
Example 6 A gelling agent is prepared by dissolving ethoxylated tallow amines having an ethylene oxide content of 2 moles per mole of amine in glacial acetic acid in an amount of 50 percent by weight o the resulting solution. A portion of the gelling agent is combined with an aqueous hydrochloric 25 acid solution in an amount of 5 percent by weight of the acid solution. The acid solution contains 15 percent by weight of hydrochloric acid, 12.5 grams of calcium chloride 3~;$
per 100 cc o~ the solution and 0.2 percent by weight of a hydrochloric acid corrosion inhibitor. The resulting gelled aqueous hydrochloric acid solution is spent to 10.3 percent by weight live hydrochloric acid b~ reacting the solution with lim,estone. Viscosities of the spent solution are determined at various temperatures using a Model 35 FANN
viscometer, no. 1 spring, standard bob and sleeve at 300 rpm. The results of these tests are given in Table V.
TABLE V - VISCOSITIES OF GELLED 15~ BY WEIGHT
AQUEOUS HYDROCHLORIC ACID SOLUTION AT VARIOUS TEMPERATURES
AFTER BEING SPENT TO 10.3% BY WEIGHT LIVE ACI~
__ _ _ Temperature, F Viscosity, cp , 8~ 70 loo ?
110 ' 5 130 , 2 From Table V it can be seen that when a gelled 15 percent by weight hydrochloric acid solution is spent to a live acid concentration of 10.3 percent by weight, the acid solution is broken to a ~iscosity of less than about 10 cp at a temperature o~ 100F.
.
, .. . ...... . ..
3~;
Example 7 A gelling agent is prepared as described in Example 6 and is combined with an aqueous hydrochloric acid solution in an amount of 5 percent hy weight of acid solution. The hydrochIoric acid solution contains 28 percent by weight hydrochloric acid and 0.5 percent by weight acid corrosion inhibitor. The resulting ge].led aqueous hydrochloric acid solution is spent by reaction with limestone to various live acid concentrations, and the viscosities of such partially spent solutions are determined at various temperatures using a Model 35 FANN viscometer, no. l spring, standard bob and sleeve at 300 rpm. The results o these tests are shown in Table VI below.
TABLE VI - VISCOSITIES OF GELLED 28% BY WEIGHT A~UEOUS
HYDROCHLORIC ACID SOLUTIONS AT VARIOUS TE~PERATURES
AFTER BEING SPENT TO VARIOUS LIVE ACID CONCENTRATIONS
Spent Solution Viscosities of Spent Acid Solutions, cp Live Acid Concentra-tion, %
By Weight 90F 100F 110F 120F 130F 140F 150F 160F
____ .
19.919,5 20 20 19 lB 16.5 15 13 15.97066.5 60 51 40 30 5 3 10.345 8.5 6 5 4 3 ~ 1.5 6.2 6 ~
From Table VI it can be seen that when a gelled a~ueous hydrochloric acid solution of this invention containing 28 -2~-3~i~
percent by weight hydrochloric acid is spent to a live acid concentration below abol~t 16 percent by weight, such spent solution is broken to a viscosity below about 5 cp at 150F~
:' . Example 8 A gelling agent of the present invention is prepared by dissolving ethoxylated tallow amines haviny an ethylene oxide content of 2 moles per mole of amine in glacial acetic acid in an amount of 50 percent by weight of the solu-tion. Portions of the gelling agent are added to aqueous hydrochloric acid solutions, and the resulting gelled hydro-chloric acid solutions are spent by reaction with limestone.
The apparent viscosities of the spent solutions are measured on a Model 35 FANN viscometer, no. 1 spring, standard bob and sleeve at 300 rpm. the particle or fines suspending properties of the spent acid solutions are determined by placing 2 grams of fines in 100 ml portions of the spent solutions, mixing the solutions and then allowing the fines to settle in the solutions for 6 hours. The fines remaining suspended in the solutions after the 6-hour periods are determined by collecting the fines by centrifugation, wash-ing, drying and wei~hing. The results of these tests are given in Table VII below.
D~3~
TABLE VII - FIME SUSPENSION ABILITY OF
SPENT GELLED AQUEOUS ACID SOLUTIONS
Gelled Aqueous Acid Solution Solution ~ _ Live , Acid Acid Suspended Caicium Corro Concen- Viscosity Fines in . Chloride, sion tration O Spent Spent Acid Grams/ Inhi- Gell:ing After Acid Solution HCl, l00 cc bitor, Agen1: Spending, After A~ter 6 by Acid ~ By % By % HCl By Solution, Hours, mg/
Weight Solution Weight Weight Wei~ht cp l00 cc 15 12.5 0.2 5 l.5 l0 (74F)206 20 3.7 0.2 5 1.2 5 (80F)279 28 0 0.2 5 1.4 7.S (64F) 330 Deionized water only 5 _ _ _ , _ .
From Table VI it can be seen tha~. the spent gelled aqueous aci~ solutions of this lnvention have excellent . fines suspension capability.
, ~:
Example 6 A gelling agent is prepared by dissolving ethoxylated tallow amines having an ethylene oxide content of 2 moles per mole of amine in glacial acetic acid in an amount of 50 percent by weight o the resulting solution. A portion of the gelling agent is combined with an aqueous hydrochloric 25 acid solution in an amount of 5 percent by weight of the acid solution. The acid solution contains 15 percent by weight of hydrochloric acid, 12.5 grams of calcium chloride 3~;$
per 100 cc o~ the solution and 0.2 percent by weight of a hydrochloric acid corrosion inhibitor. The resulting gelled aqueous hydrochloric acid solution is spent to 10.3 percent by weight live hydrochloric acid b~ reacting the solution with lim,estone. Viscosities of the spent solution are determined at various temperatures using a Model 35 FANN
viscometer, no. 1 spring, standard bob and sleeve at 300 rpm. The results of these tests are given in Table V.
TABLE V - VISCOSITIES OF GELLED 15~ BY WEIGHT
AQUEOUS HYDROCHLORIC ACID SOLUTION AT VARIOUS TEMPERATURES
AFTER BEING SPENT TO 10.3% BY WEIGHT LIVE ACI~
__ _ _ Temperature, F Viscosity, cp , 8~ 70 loo ?
110 ' 5 130 , 2 From Table V it can be seen that when a gelled 15 percent by weight hydrochloric acid solution is spent to a live acid concentration of 10.3 percent by weight, the acid solution is broken to a ~iscosity of less than about 10 cp at a temperature o~ 100F.
.
, .. . ...... . ..
3~;
Example 7 A gelling agent is prepared as described in Example 6 and is combined with an aqueous hydrochloric acid solution in an amount of 5 percent hy weight of acid solution. The hydrochIoric acid solution contains 28 percent by weight hydrochloric acid and 0.5 percent by weight acid corrosion inhibitor. The resulting ge].led aqueous hydrochloric acid solution is spent by reaction with limestone to various live acid concentrations, and the viscosities of such partially spent solutions are determined at various temperatures using a Model 35 FANN viscometer, no. l spring, standard bob and sleeve at 300 rpm. The results o these tests are shown in Table VI below.
TABLE VI - VISCOSITIES OF GELLED 28% BY WEIGHT A~UEOUS
HYDROCHLORIC ACID SOLUTIONS AT VARIOUS TE~PERATURES
AFTER BEING SPENT TO VARIOUS LIVE ACID CONCENTRATIONS
Spent Solution Viscosities of Spent Acid Solutions, cp Live Acid Concentra-tion, %
By Weight 90F 100F 110F 120F 130F 140F 150F 160F
____ .
19.919,5 20 20 19 lB 16.5 15 13 15.97066.5 60 51 40 30 5 3 10.345 8.5 6 5 4 3 ~ 1.5 6.2 6 ~
From Table VI it can be seen that when a gelled a~ueous hydrochloric acid solution of this invention containing 28 -2~-3~i~
percent by weight hydrochloric acid is spent to a live acid concentration below abol~t 16 percent by weight, such spent solution is broken to a viscosity below about 5 cp at 150F~
:' . Example 8 A gelling agent of the present invention is prepared by dissolving ethoxylated tallow amines haviny an ethylene oxide content of 2 moles per mole of amine in glacial acetic acid in an amount of 50 percent by weight of the solu-tion. Portions of the gelling agent are added to aqueous hydrochloric acid solutions, and the resulting gelled hydro-chloric acid solutions are spent by reaction with limestone.
The apparent viscosities of the spent solutions are measured on a Model 35 FANN viscometer, no. 1 spring, standard bob and sleeve at 300 rpm. the particle or fines suspending properties of the spent acid solutions are determined by placing 2 grams of fines in 100 ml portions of the spent solutions, mixing the solutions and then allowing the fines to settle in the solutions for 6 hours. The fines remaining suspended in the solutions after the 6-hour periods are determined by collecting the fines by centrifugation, wash-ing, drying and wei~hing. The results of these tests are given in Table VII below.
D~3~
TABLE VII - FIME SUSPENSION ABILITY OF
SPENT GELLED AQUEOUS ACID SOLUTIONS
Gelled Aqueous Acid Solution Solution ~ _ Live , Acid Acid Suspended Caicium Corro Concen- Viscosity Fines in . Chloride, sion tration O Spent Spent Acid Grams/ Inhi- Gell:ing After Acid Solution HCl, l00 cc bitor, Agen1: Spending, After A~ter 6 by Acid ~ By % By % HCl By Solution, Hours, mg/
Weight Solution Weight Weight Wei~ht cp l00 cc 15 12.5 0.2 5 l.5 l0 (74F)206 20 3.7 0.2 5 1.2 5 (80F)279 28 0 0.2 5 1.4 7.S (64F) 330 Deionized water only 5 _ _ _ , _ .
From Table VI it can be seen tha~. the spent gelled aqueous aci~ solutions of this lnvention have excellent . fines suspension capability.
, ~:
Claims (21)
1. A gelled aqueous inorganic acid solution comprising water, at least one water soluble inorganic acid and a gelling agent, said gelling agent being comprised of a water soluble organic solvent selected from the group consisting of alkanols having in the range of from about 1 to 5 carbon atoms per molecule, ketones having in the range of about 3 to 6 carbon atoms per molecule, poly-hydroxy compounds having in the range of about 2 to 6 carbon atoms per molecule, ethers having in the range of about 2 to 6 carbon atoms per molecule, compounds containing both ether and alcohol functions having in the range of about 4 to 8 carbon atoms per molecule, esters having in the range of about 2 to 6 carbon atoms per molecule, lactones having in the range of about 3 to 5 carbon atoms per molecule and mixtures of two or more of the foregoing compounds, and a mixture of ethoxylated fatty amines dissolved in said water soluble organic solvent having the general formula:
wherein:
R is selected from saturated and unsaturated aliphatic groups having in the range of from about 8 to about 22 carbon atoms and mixtures thereof, and x and y each have a value in the range of from 0 to about 10.
wherein:
R is selected from saturated and unsaturated aliphatic groups having in the range of from about 8 to about 22 carbon atoms and mixtures thereof, and x and y each have a value in the range of from 0 to about 10.
2. The gelled aqueous inorganic acid solution of claim 1 wherein the average sum of the values of x and y in said mixture of ethoxylated fatty amines is in the range of from about 1.8 to about 2.2.
3. The gelled aqueous inorganic acid solution of claim 2 wherein said gelling agent is present in said acid solution in an amount in the range of from about 0.1% to about 10% gelling agent by weight of said acid solution.
4. The gelled aqueous inorganic acid solution of claim 3 wherein R is selected from the group consisting of satur-ated and unsaturated aliphatic groups having in the range of from about 16 to about 18 carbon atoms and mixtures thereof, and wherein the average sum of the values of x and y in said mixture of ethoxylated fatty amines is equal to 2.
5. The gelled aqueous inorganic acid solution of claim 2 wherein said ethoxylated fatty amines are present in said gelling agent in an amount in the range of from about 10%
to about 80% by weight of said gelling agent.
to about 80% by weight of said gelling agent.
6. The gelled aqueous inorganic acid solution of claim 4 wherein said water soluble organic solvent is an alkanol selected from the group consisting of methanol, ethanol, isopropanol, t-butanol and mixtures thereof, and said ethyoxylated fatty amines are present in said gelling agent in an amount of about 50% by weight of said gelling agent.
7. The gelled aqueous inorganic acid solution of claim 2 wherein said water soluble inorganic acid is hydrochloric acid.
8. A gelled aqueous inorganic acid solution comprising water, an inorganic acid and a gelling agent, said gelling agent being comprised of a water soluble organic solvent selected from the group consisting of alkanols having in the range of from about 1 to 5 carbon atoms per molecule, ketones having in the range of about 3 to 6 carbon atoms per molecule, polyhydroxy compounds having in the range of about 2 to 6 carbon atoms per molecule, ethers having in the range of about 2 to 6 carbon atoms per molecule, compounds containing both ether and alcohol functions having in the range of about 4 to 8 carbon atoms per molecule, esters having in the range of about 2 to 6 carbon atoms per molecule, lactones having in the range of about 3 to 5 carbon atoms per molecule and mixtures of two or more of the foregoing compounds, and an ethoxylated fatty amine dissolved in said water soluble organic solvent having the general formula:
wherein:
R is selected from the group consisting of saturated and unsaturated aliphatic groups and mixtures thereof having in the range of from about 14 to about 18 carbon atoms.
wherein:
R is selected from the group consisting of saturated and unsaturated aliphatic groups and mixtures thereof having in the range of from about 14 to about 18 carbon atoms.
9. The gelled aqueous inorganic acid solution of claim 8 wherein R is selected from the group consisting of saturated and unsaturated aliphatic groups and mixtures thereof having in the range of from about 16 to about 18 carbon atoms.
10. The gelled aqueous inorganic acid solution of claim 9 wherein said water soluble organic solvent is an alkanol selected from the group consisting of methanol, ethanol, isopropanol, t-butanol and mixtures thereof.
11. The gelled aqueous inorganic acid solution of claim 9 wherein said ethoxylated fatty amine is present in said gelling agent in an amount in the range of from about 10%
to about 80% by weight of said gelling agent.
to about 80% by weight of said gelling agent.
12. The gelled aqueous inorganic acid solution of claim 9 wherein said water soluble inorganic solvent is methanol and said ethoxylated fatty amine is present in said gelling agent in an amount of about 50% by weight of said gelling agent.
13. The gelled aqueous inorganic acid solution of claim 12 wherein said gelling agent is present in said acid solution in an amount in the range of from about 0.1% to about 10%
by weight of said acid solution.
by weight of said acid solution.
14. A method of treating a subterranean well formation comprising the steps of:
combining a gelling agent with an aqueous inorganic acid solution in an amount in the range of from about 0.1 to about 10% by weight of said solution whereby the viscosity of said solution is increased, said gelling agent being comprised of a water soluble organic solvent selected from the group consisting of alkanols having in the range of from about 1 to 5 carbon atoms per molecule, ketones having in the range of about 3 to 6 carbon atoms per molecule, polyhydroxy compounds having in the range of about 2 to 6 carbon atoms per molecule, ethers having in the range of about 2 to 6 carbon atoms per molecule, compounds containing both ether and alcohol functions having in the range of about 4 to 8 carbon atoms per molecule, esters having in the range of about 2 to 6 carbon atoms per molecule, lactones having in the range of about 3 to 5 carbon atoms per molecule and mixtures of two or more of the foregoing compounds, and a mixture of ethoxylated fatty amines dissolved in said water soluble organic solvent having the general formula:
wherein:
R is selected from saturated and unsaturated aliphatic groups having in the range of from about 8 to about 22 carbon atoms and mixtures thereof and x and y each have a value in the range of from 0 to about 10 with the average sum of the values of x and y in said mixture being in the range of from about 1.8 to about 2.2; and introducing said solution into said subterranean formation.
combining a gelling agent with an aqueous inorganic acid solution in an amount in the range of from about 0.1 to about 10% by weight of said solution whereby the viscosity of said solution is increased, said gelling agent being comprised of a water soluble organic solvent selected from the group consisting of alkanols having in the range of from about 1 to 5 carbon atoms per molecule, ketones having in the range of about 3 to 6 carbon atoms per molecule, polyhydroxy compounds having in the range of about 2 to 6 carbon atoms per molecule, ethers having in the range of about 2 to 6 carbon atoms per molecule, compounds containing both ether and alcohol functions having in the range of about 4 to 8 carbon atoms per molecule, esters having in the range of about 2 to 6 carbon atoms per molecule, lactones having in the range of about 3 to 5 carbon atoms per molecule and mixtures of two or more of the foregoing compounds, and a mixture of ethoxylated fatty amines dissolved in said water soluble organic solvent having the general formula:
wherein:
R is selected from saturated and unsaturated aliphatic groups having in the range of from about 8 to about 22 carbon atoms and mixtures thereof and x and y each have a value in the range of from 0 to about 10 with the average sum of the values of x and y in said mixture being in the range of from about 1.8 to about 2.2; and introducing said solution into said subterranean formation.
15. The method of claim 14 wherein R is selected from the group consisting of saturated and unsaturated aliphatic groups having in the range of from about 14 to about 18 carbon atoms and mixtures thereof, and wherein the average sum of the values of x and y in said mixture of ethoxy-lated fatty amines is equal to 2.
16. The method of claim 15 wherein said ethoxylated fatty amines are present in said gelling agent in an amount in the range of from about 10% to about 80% by weight of said gelling agent.
17. The method of claim 16 wherein said water soluble organic solvent is an alkanol selected from the group consisting of methanol, ethanol, isopropanol, t-butanol and mixtures thereof and said ethoxylated fatty amine is present in said gelling agent in an amount of about 50%
by weight of said gelling agent.
by weight of said gelling agent.
18. The method of claim 14 wherein said inorganic acid is hydrochloric acid.
19. The method of claim 14 wherein said aqueous inorganic acid solution is an aqueous hydrochloric acid solution having a hydrochloric acid concentration of above about 22% by weight of said solution.
20. The method of claim 15 wherein said aqueous inorganic acid solution is an aqueous hydrochloric acid solution having a hydrochloric acid concentration of below about 22% by weight of said solution.
21. The method of claim 20 which is further characterized to include the step of combining calcium chloride with said aqueous hydrochloric acid solution in an amount in the range of from about 1% to about 10% by weight of said solution.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US87172478A | 1978-01-23 | 1978-01-23 | |
| US871,724 | 1986-06-06 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1109356A true CA1109356A (en) | 1981-09-22 |
Family
ID=25357989
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA311,659A Expired CA1109356A (en) | 1978-01-23 | 1978-09-20 | Gelled aqueous inorganic acid solutions and methods of using the same |
Country Status (7)
| Country | Link |
|---|---|
| AU (1) | AU4022178A (en) |
| BR (1) | BR7807829A (en) |
| CA (1) | CA1109356A (en) |
| FR (1) | FR2415134A1 (en) |
| IT (1) | IT1110044B (en) |
| NO (1) | NO790210L (en) |
| PT (1) | PT68609A (en) |
Cited By (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6306800B1 (en) | 1996-10-09 | 2001-10-23 | Schlumberger Technology Corporation | Methods of fracturing subterranean formations |
| US6435277B1 (en) | 1996-10-09 | 2002-08-20 | Schlumberger Technology Corporation | Compositions containing aqueous viscosifying surfactants and methods for applying such compositions in subterranean formations |
| US6482866B1 (en) | 1997-06-10 | 2002-11-19 | Schlumberger Technology Corporation | Viscoelastic surfactant fluids and related methods of use |
| US6881709B2 (en) | 2000-04-05 | 2005-04-19 | Schlumberger Technology Corporation | Viscosity reduction of viscoelastic surfactant based fluids |
| US6908888B2 (en) | 2001-04-04 | 2005-06-21 | Schlumberger Technology Corporation | Viscosity reduction of viscoelastic surfactant based fluids |
| US7028775B2 (en) | 2001-12-21 | 2006-04-18 | Schlumberger Technology Corporation | Compositions and methods for treating a subterranean formation |
| US7084095B2 (en) | 2001-04-04 | 2006-08-01 | Schlumberger Technology Corporation | Methods for controlling the rheological properties of viscoelastic surfactants based fluids |
| US7119050B2 (en) | 2001-12-21 | 2006-10-10 | Schlumberger Technology Corporation | Fluid system having controllable reversible viscosity |
| US7148184B2 (en) | 2003-07-22 | 2006-12-12 | Schlumberger Technology Corporation | Self-diverting foamed system |
| US7237608B2 (en) | 2004-10-20 | 2007-07-03 | Schlumberger Technology Corporation | Self diverting matrix acid |
| US7303018B2 (en) | 2003-07-22 | 2007-12-04 | Bj Services Company | Method of acidizing a subterranean formation with diverting foam or fluid |
| US7345012B2 (en) | 2004-12-15 | 2008-03-18 | Schlumberger Technology Corporation | Foamed viscoelastic surfactants |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4324669A (en) * | 1979-11-19 | 1982-04-13 | Halliburton Company | Foamed high viscosity aqueous inorganic acid solutions and methods of using the same |
| GB2328228B (en) * | 1997-08-16 | 2000-08-16 | Sofitech Nv | Shale-stabilizing additives |
-
1978
- 1978-09-20 CA CA311,659A patent/CA1109356A/en not_active Expired
- 1978-09-27 AU AU40221/78A patent/AU4022178A/en active Pending
- 1978-10-02 PT PT68609A patent/PT68609A/en unknown
- 1978-10-23 FR FR7830052A patent/FR2415134A1/en not_active Withdrawn
- 1978-11-29 BR BR7807829A patent/BR7807829A/en unknown
-
1979
- 1979-01-22 NO NO790210A patent/NO790210L/en unknown
- 1979-01-23 IT IT19541/79A patent/IT1110044B/en active
Cited By (19)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6306800B1 (en) | 1996-10-09 | 2001-10-23 | Schlumberger Technology Corporation | Methods of fracturing subterranean formations |
| US6412561B1 (en) * | 1996-10-09 | 2002-07-02 | Schlumberger Technology Corporation | Methods of fracturing subterranean formations |
| US6435277B1 (en) | 1996-10-09 | 2002-08-20 | Schlumberger Technology Corporation | Compositions containing aqueous viscosifying surfactants and methods for applying such compositions in subterranean formations |
| US6482866B1 (en) | 1997-06-10 | 2002-11-19 | Schlumberger Technology Corporation | Viscoelastic surfactant fluids and related methods of use |
| US6703352B2 (en) | 1997-06-10 | 2004-03-09 | Schlumberger Technology Corporation | Viscoelastic surfactant fluids and related methods of use |
| US7238648B2 (en) | 1997-06-10 | 2007-07-03 | Schlumberger Technology Corporation | Viscoelastic surfactant fluids and related methods of use |
| US6881709B2 (en) | 2000-04-05 | 2005-04-19 | Schlumberger Technology Corporation | Viscosity reduction of viscoelastic surfactant based fluids |
| US7084095B2 (en) | 2001-04-04 | 2006-08-01 | Schlumberger Technology Corporation | Methods for controlling the rheological properties of viscoelastic surfactants based fluids |
| US6908888B2 (en) | 2001-04-04 | 2005-06-21 | Schlumberger Technology Corporation | Viscosity reduction of viscoelastic surfactant based fluids |
| US7028775B2 (en) | 2001-12-21 | 2006-04-18 | Schlumberger Technology Corporation | Compositions and methods for treating a subterranean formation |
| US7119050B2 (en) | 2001-12-21 | 2006-10-10 | Schlumberger Technology Corporation | Fluid system having controllable reversible viscosity |
| US7666821B2 (en) | 2002-07-09 | 2010-02-23 | Schlumberger Technology Corporation | Self-diverting pre-flush acid for sandstone |
| US7148184B2 (en) | 2003-07-22 | 2006-12-12 | Schlumberger Technology Corporation | Self-diverting foamed system |
| US7303018B2 (en) | 2003-07-22 | 2007-12-04 | Bj Services Company | Method of acidizing a subterranean formation with diverting foam or fluid |
| US7510009B2 (en) | 2003-07-22 | 2009-03-31 | Bj Services Company | Method of acidizing a subterranean formation with diverting foam or fluid |
| US7237608B2 (en) | 2004-10-20 | 2007-07-03 | Schlumberger Technology Corporation | Self diverting matrix acid |
| US7575054B2 (en) | 2004-10-20 | 2009-08-18 | Schlumberger Technology Corporation | Self diverting matrix acid |
| US7770644B2 (en) | 2004-10-20 | 2010-08-10 | Schlumberger Technology Corporation | Self diverting matrix acid |
| US7345012B2 (en) | 2004-12-15 | 2008-03-18 | Schlumberger Technology Corporation | Foamed viscoelastic surfactants |
Also Published As
| Publication number | Publication date |
|---|---|
| FR2415134A1 (en) | 1979-08-17 |
| IT1110044B (en) | 1985-12-23 |
| IT7919541A0 (en) | 1979-01-23 |
| BR7807829A (en) | 1979-07-31 |
| PT68609A (en) | 1978-11-01 |
| AU4022178A (en) | 1980-04-03 |
| NO790210L (en) | 1979-07-24 |
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