WO1987001758A1

WO1987001758A1 - Hydraulic fracturing process and compositions

Info

Publication number: WO1987001758A1
Application number: PCT/US1985/001765
Authority: WO
Inventors: Vernon G. Constien; Milton T. King
Original assignee: The Dow Chemical Company
Priority date: 1985-09-16
Filing date: 1985-09-16
Publication date: 1987-03-26
Also published as: BR8507281A; NO872045L; NO872045D0; EP0239568A4; EP0239568A1

Abstract

Improved fracturing processes which use novel aqueous hydraulic fracturing fluids. The fluids comprise: (a) an aqueous medium, and (b) a thickening amount of a thickener composition comprising (i) a water-soluble or water-dispersible interpolymer having pendant hydrophobic groups chemically bonded thereto, (ii) a nonionic surfactant having a hydrophobic group(s) that is capable of associating with the hydrophobic groups on said organic polymer, and (iii) a water-soluble electrolyte. Additionally, the fluids preferably contain a stabilizing amount of a thiosulfate salt. As an example, an interpolymer of acrylamide and dodecyl acrylate was used in combination with a nonionic surfactant (HLB of from 10 to 14) to thicken a dilute aqueous solution of KCl and sodium thiosulfate; the aqueous solution had excellent properties for use as a high temperature hydraulic fracturing fluid.

Description

HYDRAULIC FRACTURING PROCESS AND COMPOSITIONS

This invention pertains to novel compositions of matter and methods of using same in fracturing sub¬ terranean formations penetrated by a wellbore.

Hydraulic fracturing is a term that has been applied to a variety of methods used to stimulate the production of fluids (e.g. oil, natural gas, brines, etc.) from subterranean formations. In hydraulic fracturing, a fracturing fluid is injected down a wellbore and against the face of the formation at a pressure and flow rate at least sufficient to overcome the overburden pressure and to initiate and/or extend a fracture(s) into the formation. The fracturing fluid usually carries a proppant (e.g. 20-40 mesh sand, bauxite, glass beads, etc.) into a fracture which keeps the formation from closing back down upon itself when the pressure is released. The proppant-filled fractures provide permeable channels through which the formation fluids can flow to the wellbore and thereafter be with- drawn. Hydraulic fracturing has been used for many years as stimulation technique and extensive work has been done to solve problems present at each stage of the process. For example, the fracturing fluid is exposed to high temperatures and/or high pump rates and shear which can cause the fluids to degrade and to prematurely "drop" the proppant before the fracturing operation is completed. Considerable effort has, therefore, been spent trying to design fluids that will satisfactorily meet these rigorous conditions.

A wide variety of fluids has been developed, but most of the fracturing fluids used today are aqueous- based liquids which have been either gelled or foamed.

Aqueous gels are usually prepared by blending a polymeric gelling -agent with an aqueous medium. Most frequently, the polymeric gelling agent of choice is a solvatable polysaccharide. These solvatable poly- saccharides form a known class of compounds which include a variety of natural gums as well as certain cellulosic derivatives which have been rendered hydra- table by virtue of hydrophilic substituents chemically attached to the cellulose backbone. The solvatable polysaccharides therefore include galactomannan gums, glucomannan gums, cellulose derivatives, and the like.

The solvatable polysaccharides have a remark¬ able capacity to thicken aqueous liquids. Even small amounts are sufficient to increase the viscosity of such aqueous liquids from 10 to 100 times or more. In some instances, the thickened aqueous liquid has suf- ficient viscosity to carry the proppant during the course of the fracturing process and represents a satisfactory fracturing fluid. In other instances, however, it is necessary to crosslink the polysac- charide in order to form a gel having sufficient strength and^' viscosity to carry the proppant. A variety of crosslinkers have been developed to achieve this result at different pH ranges.

The borate ion has been used extensively as a crosslinking agent for hydrated guar gums and other galactomannans to form aqueous gels used in fracturing and other areas. For example, Kern described a cross- linked system in U.S. Patent No. 3,058,909 which was used extensively in the oil and gas industry as a fracturing fluid. A fracturing process which comprised crosslinking, guar-containing compositions on-the-fly with a borate crosslinker was described by Free in U.S. Patent No. 3,974,077. The borate-crosslinked systems require a basic pH (e.g. 8.5 to 10) for crosslinking to occur.

Other crosslinking agents were developed using certain transition metals. Chrisp described certain of these crosslinked systems in U.S. Patent No. 3,202,556 and U.S. Patent No. 3,301,723. In U.S. Patent No. 3,202,556, aqueous solutions of galacto- mannan gums were crosslinked at a pH of from about 5 to 13 with antimony or bismuth crosslinkers. In U.S.

Patent No. 3,301,723 Chrisp described the use of certain titanium, zirconium, and other transition metals as crosslinking agents for galactomannan gums at a pH also in the range from 6 to 13. In both Chrisp patents, a basic pH was used to prepare crosslinked materials having utility in the explosive industry. Another patent which described the use of titanium crosslinkers for solvatable polysaccharides was Tiner et al. in U.S. Patent No. 3,888,312. The crosslinked gels formed by Tiner were said to be useful as frac- turing fluids. The use of such -crosslinked gels was alleged to overcome the high friction loss experienced during the pumping of many high viscosity fracturing fluids previously known. This observation corroborated the disclosure by Chrisp in U.S. Patent No. 3,301,723 at column 10 that crosslinked gels formed using titanium, chromium, iron, and zirconium crosslinkers had a high surface tension (i.e. stickiness and tackiness are absent), ready workability and other desirable physical characteristics.

A class of thickeners was recently described by Syamalarao Evani in U.S. Patent application Serial Number 232,327, filed February 6, 1981, entitled "Water- -Dispersible Hydrophobic Thickening Agent". Evani indicated that such thickeners would be useful in a • variety of fluids, including fracturing fluids.

Reference is also made to the "Handbook of Water-Soluble Gums and Resins" by Robert L. Davidson, Editor as published by McGraw-Hill, Inc. (1980) for an excellent treatise on water-soluble polymers which includes a discussion on hydratable (or solvatable) polysaccharides. Reference is also made to "Hydraulic Fracturing" by G. C. Howard and C. R. Fast, Monograph Volume 2, Henry L. Doherty Series, published by the Society of Petroleum Engineers (1970) which is an excellent introduction to the subject of hydraulic fracturing, even though it is now somewhat dated. The present invention particularly resides in a process for fracturing a subterranean formation penetrated by a wellbore by injecting a hydraulic fracturing fluid through the wellbore and against said subterranean formation at a flow rate and pressure at least sufficient to initiate and/or extend a fracture into said formation, comprising using as said hydraulic fracturing fluid an aqueous composition having chemical and physical properties sufficient to render it useful as a hydraulic fracturing fluid at 275° F. , said composi¬ tion comprising:

A. an aqueous medium; and

B. a thickener composition in an amount sufficient to increase the viscosity of said aqueous medium, said thickener composition comprising:

(1) a water-soluble or water-dis- persible interpolymer having pendant hydrophobic groups chemically bonded thereto and containing, in interpolymer- ized form, from 99.0 to 99.4 mole percent of a water-sol- uble monomer or mixture of such monomers and from 1.0 to 0.6 mole percent of a water insoluble monomer or mixture of such monomers,

(2) a water-soluble or water-dis- persible nonionic surfactant having a HLB of from 10 to 14 and having a hydrophobic group capable of associating with the hydrophobic groups on said interpolymer, and

(3) a water-soluble electrolyte. The present invention also resides in an aqueous composition having chemical and physical pro¬ perties sufficient to render it useful as^~ a hydraulic fracturing fluid at 275°F, said composition comprising:

A. an aqueous medium; and

(1) a water-soluble or water-disper- sible interpolymer having pendant hydrophobic groups chemically bonded thereto and containing, in interpoly- merized form, from 99.0 to 99.4 mole percent of water- -soluble monomer or mixture of such monomers and from 1.0 to 0.6 mole percent of a water insoluble monomer or mixture of such monomers,

(2) a water-soluble or water-dispersible nonionic surfactant having a HLB of from 10 to 14 and having a hydrophobic group capable of associating with the hydrophobic groups on said interpolymer, and

(3) a water-soluble electrolyte.

These novel compositions contain species of thickeners within Evani's generic description.

The novel fluids are superior to the com¬ mercial fracturing fluids which contain organo-metallic crosslinked guar or hydroxypropylguar. The fluids of this invention can be easily formulated to achieve an acceptable initial viscosity, and the initial viscosity will be retained by the fluid for an extended time even under conditions of high temperature and/or shear. The stable rheology of the present fluids will result in better fracturing treatment design and control of the fracture geometry and proppant placement.

The new fluid compositions are formulated by blending the aqueous medium with the thickener composi¬ tions.

The aqueous medium is usually water, dilute acid (e.g. up to about 10 percent hydrochloric acid), aqueous alkanols (e.g. aqueous C. to C, alkanols), and the like. Water is preferred.

The thickener composition comprises a water- -soluble or water-dispersible interpolymer having pendant hydrophobic groups chemically bonded thereto. The interpolymer contains, in interpolymerized form, from 99.0 to 99.4 mole percent of a water-soluble monomer or mixture of such monomers and from 1.0 to 0.6 mole percent of a water-insoluble monomer or mixture of such monomers. Evani, supra, generically described these interpolymers (or copolymers, as they are sometimes referred to) and a method(s) for preparing such interpoly¬ mers. Any of the interpolymers described by Evani can be used herein so long as the polymer chosen meets the above-stated criteria. Preferred intepolymers are vinyl addition polymers in which two or more vinyl monomers with ethylenic unsaturation are reacted together under polymerization conditions. Of these, polymers containing at least one of the water-soluble monomers represented by formula I are preferred; -8-

R

CH₂ - C

C = 0

where R is hydrogen or methyl and Z is - H₂, -OH, -OR' where R' is a C. - C₄ alkyl group, -NH-R"-S0₃M wherein R" is an alkylene group of from 1 to about 24 carbon atoms (preferably C-, to C₄ alkylene) and M is hydrogen or an ammonium or alkali metal ion. Also preferred are those vinyl addition polymers which contain at least one water-insoluble monomer represented by formula II;

R t

CH - C t

C = 0

I

II X - R"'

where R is hydrogen or methyl; X is -0- or -NH-; and R" ' is a hydrophobic group. R"' is preferably an aliphatic hydrophobic group (e.g. and alkyl or alkenyl group of from 6 to 24^'carbon atoms or an inertly-substi¬ tuted such group, etc.) and is most preferably an alkyl group of from 8 to 24 carbon atoms.

The interpolymers are usually solid polymers having a number average molecular weight of about one million or more. It has been found that such polymers are more readily dispersed/ dissolved into the aqueous medium when ground to a mesh size of at least about 60. E.g. a mesh size of about 60 to 80 works quite well.

The thickener composition also comprises a nonionic surfactant having a hydrophilic-lipophilic balance (HLB) of from 10 to 14, and preferably from 11 to 12. Such nonionic surfactants constitute a known class of compounds having many members, any of which can be used herein. This class of compounds is illus- trated, for example, in the handbook of McCutcheons, Combined Edition (published by McCutcheons' Division, MC Publishing Company, Glen Rock, NJ). Blends of non¬ ionic surfactants can be used, if desired. Blends of nonionic surfactants and anionic surfactants can also be used, and generally are when the interpolymer is a vinyl addition polymer prepared by the preferred process in Evani. In Evani's process, an anionic surfactant (e.g. sodium lauryl sulfate) is used as an emulsifying agent during the emulsion polymerization and it is present in the dried polymer product.

The nonionic surfactants are prepared in many instances by reacting ethylene oxide with a compound having active hydrogen (i.e. active in the Zerewitinoff reaction) and are referred to as "ethoxylated" compounds. For example, nonionic surfactants have been prepared by reacting ethylene oxide with alcohols, amides, alkylated- -phenols, etc. Preferred nonionic surfactants are ethoxylated aliphatic alcohols, and most preferred are ethoxylated alkanols having from 8 to 24 carbon atoms in the alkanol moiety. The thickener composition additionally com¬ prises a water-soluble electrolyte. The electrolyte can be any of the known class of water-soluble electro¬ lytes. This class includes simple salts of inorganic and organic acids where the cation and/or anion are monovalent or polyvalent (e.g. NaCl, CaCl₂, Na acetate, etc.). Preferably, however, the electrolyte is a monovalent inorganic salt (i.e. both the cation and anion are monovalent); and among these, the sodium, potassium and ammonium halides are a preferred sub group. Potassium chloride is the electrolyte of choice in most instances where the fluid composition is to be used as a fracturing fluid.

The relative amounts of the above-named components in the thickener composition can be varied, generally, however, the interpolymer is included in amounts of from 0.3 to 1.5 weight percent, based on weight of aqueous medium; a preferred amount is from 0.4 to 1.0 weight percent. The nonionic surfactant is normally included in amounts of from 0.06 to 0.3 weight percent, and preferably from 0.08 to 0.2 weight percent, based on weight of aqueous medium. The water-soluble electrolyte is normally used in amounts of from 0.5 weight percent to 4 weight percent, based on weight of aqueous medium and preferably in amounts of from 0.75 to 1.5 weight percent. From Evani's disclosure, it was a surprise to discover that elevated viscosity fluids could be obtained with the above thickener compositions which utilize substantially lower surfactant levels and that the initial viscosity level could be increased or decreased by adjusting the electrolyte content and/or the hydrophobe content rather than the surfactant concentration. The result of this discovery is increased polymer efficiency and thermal/shear stability at electrolyte (e.g. salt) concentrations normally associated with fracturing fluids.

The pH of the fracturing fluids can be varied, but is usually selected in the range of from 6 to 10.

The fluids tend to be more stable at higher temperatures (e.g. 300° to 375° F) where the pH is alkaline. The pH is preferably from 8 to 10 for high temperature applica¬ tions.

A wide range of additives can be included, if desired, into the present fracturing fluids. For example, one can include a proppant material (e.g. 20 to 40 mesh sand, bauxite, glass beads, etc.), fluid loss additives (e.g. silica flour, kerosene, diesel, etc.), "energizing" gases (e.g. nitrogen, carbon dioxide, air, etc.) which are comingled with the fluids^*, breakers (e.g. persulfate salts, etc.) which reduces the viscosity of the fluid after a period of time, foaming agents (all foaming agents are surfactants, but not vice versa), crosslinking agents (e.g. aldehydes, polyvalent metal ions, etc.), stabilizers (e.g. methanol, an alkali metal or ammonium thiosulfate, etc.), and the like. The amount of additive(s) included can be varied to fit the particular need so long as a minimum amount is included to perform the desired function. It is easily within the expertise of one skilled in the fracturing art to determine such quantities.

The skilled artisan will also know that some additives (e.g. an alkali metal or ammonium thiosulfate) are also water-soluble electrolytes and, as such, will influence the fluid rheology as noted above. As a related aside, the water-soluble thiosulfate salts were particularly efficient in stabilizing the present fracturing fluids against thermal degradation-and subsequent loss of viscosity. Hence, it is advantageous to include the thiosulfate salts in small but stabilizing amounts. The alkali metal thiosulfates and ammonium thiosulfate are preferred, based on commercial availability and cost effectiveness.

The method of formulating the fracturing fluid can also be varied to convenience. The com¬ ponents can be "batch mixed" or blended in a "con- tinous" manner. For example, the thickener composition or components thereof can be added to the aqueous medium in a fracturing tank or similar vessel and the contents of the tank circulated with a pump until thorough blending is achieved. Preferably, however, the fracturing fluids are prepared by a continuous process in which at least one of the components of the thickener (preferably, the interpolymer and/or the soluble electrolyte) is added "on-the-fly" while the fluid is being pumped into the wellbore. The reason for this preference is the lower viscosity of the fluid without one of the key ingredients in the thickener. This makes it easier to pump the fluid out of its reservoir with lower hydraulic horsepower requirements. After the material is flowing in the pipeline, it is convenient to add the ingredient(s) and additives to the flowing stream by conventional means; e.g. through a "T" joint of a "Y" joint in the conduit, usually on the discharge side of the high pressure pump(s).

Proppant and fluid loss additives, such as kerosene or diesel, are usually added downstream after the aqueous medium and thickener composition have been blended together. After the fracturing fluid is formulated, it is injected through the wellbore against the face of the formation at a flow rate and pressure sufficient to initiate and/or extend a fracture(s) into the subterranean formation. This is conventional practice and the methods/hardware of implementing the fracturing process are known. In most fracturing processes, it is routine practice to inject a pad fluid of the same composition (or compatible composition) to establish injectivity and/or to initiate the fracture ahead of the fluid bearing the proppant. Examples of such compatible pad fluids include, aqueous ammonium chloride, dilute hydrochloric acid (e.g. 1 to 5 percent), stiff stable foam having a Mitchel foam quality of 0.60 to 0.85, etc. The use of a fracture pad fluid is good technique and is recommended in conjunction with the use of the present fracturing fluids. Overflush fluids are also normally used and are recommended. Overflush fluids are also of the same composition (or compatible composi- tion) but do not contain proppant. Such overflush fluids are used to clear the conduit and piping in the borehole of proppant-laden fluid and to force the proppant as far into the fracture as possible. The overflush fluid can be the same as the pad fluid or different.

Experimental

The following experiments will further illus¬ trate the invention.

Preparation of the Interpolymers The method of preparation described by Evani was used to prepare interpolymers of acrylamide and dodecyl methacrylate. In this procedure, dodecyl methacrylate is emulsified in deionized water containing sodium laurylsulfate as an emulsifier and a nonionic surfactant C,₃H₂₇ 0 {CH₂CH₂0 ₆H, i.e. the condensation product of 6 moles of ethylene oxide onto tridecanol (HLB 11.4). Acrylamide monomer is added to this emulsion, followed by a chelant (Versenex 80), a free radical catalyst (Vazo 64), and sufficient dilution water to increase the volume of the reaction mixture to 250 milliliters. The citrate bottle containing the reaction mixture was then purged several times with nitrogen, sealed, and placed in a hot water bath (60°C) for periods of from 4 to 16 hours. After this heating period, the reaction mixture was removed from the citrate bottle and volatiles were stripped from the polymerization product using a heated drum drier. The resulting dried interpolymer, i.e. the reaction product obtained after the volatiles were removed, was thus obtained as a tough thin film which was later shredded to a desired "particle" size -or small flakes. In some instances, the dried interpolymer film was ground to a smaller and more definite particle size which passed through a 60 mesh sieve. To further illustrate this method of preparation, one such reaction mixture con¬ tained acrylamide (46.8 parts of a 51.9 weight percent solution of acrylamide monomer in water), dodecyl methacrylate (0.7 parts), sodium laurylsulfate (25 parts of a 10 weight percent solution of sodium lauryl¬ sulfate in water), nonionic surfactant C,₃H₂₇ 0 {C₂H₅0 ₆H (5 parts; Trycol TDA 6 by Emery Chemical Co.), chelant (2.5 parts of a 2 weight percent solution of Versenex in an aqueous acetic acid solvent), Catalyst (1 part of Vazo 64; azobisisobutyronitrile in t-butanol solvent) and water of dilution. This reaction mixture was purged with nitrogen and processed as noted above to give the interpolymer used in Example 1. The relative amounts of acrylamide and dodecyl methacrylate were varied in other instances to give interpolymers having different mole percents of the two monomers. Otherwise, the methods of preparation were maintained essentially the same.

Rheology-Testing Procedures

The rheology of the fracturing fluid formula¬ tions was determined on a Fann 50C viscometer. Such viscometers are commercial instruments and are widely used in the industry. In this instrument, the sample (50 cc) is loaded into a chamber (cup), a bob equipped with torque-recording means is immersed in the sample, the chamber containing the sample is pressurized, (400 psi), and the chamber is then rotated at a constant rate of rotation for a pre-determined period of time. An electronic reading is then recorded showing the amount of torque on the bob which results from^'the fluid being sheared by the rotating sample cup. Usually the temperature of the sample is increased at a constant rate to the desired test temperature as well. The experimental data from the Fann 50C runs are mathematically treated using the classical Power Law Fluid Model equations. In this mathematical treatment the data are plotted on a graph of log (shear stress) as the Y-axis vs log (shear rate) as the X-axis. The experimental points approximate a straight line in this graphical representation; the slope of this straight line is identified as n (the "behavior index") and the inter¬ cept with the Y-axis is identified as K or ^κ _v-j_scometer ⁽the "consistency index"⁾. ^κ _vigcometer ~~^{s conver'ted to}

^K (/pr-i--p- ^Kr

vr ^J(311 + 1 ) ^e-11.

Once t e Power Law constan s n an

4n K" have been determined, the apparent viscosity at any given shear rate is calculated using the equation:

Viscosity (cps) = 47,800 K . The constant n

(shear rate)¹

(or n¹ some literature reports) is related to the

Newtonian behavior of the fluid. If n is 1, then the fluid is called a Newtonian fluid; if n is less than 1, then the fluid is not Newtonian in its behavior. The constant K (or K' in some literature reports) is a measure of initial viscosity at one (1) reciprocal second shear rate. From the above equation it is seen that K is directly proportional and is considered an important factor when assessing the proppant transport capacity of the fluid, for example.

An "ideal" fracturing fluid is presently envisioned as one having a constant, high viscosity (n = 0; K≠ 0) until the fluid has- created the fracture and/or positioned the proppant in the fracture, and then instantaneously "breaks" -to form a liquid having a viscosity the same as water, or less (n = 1; K = 0). Such "ideal" fluids are not presently available, but the fracturing fluids of this invention are surprisingly temperature and shear stable and can be tailored to meet various viscosity requirements.

Preparation of the Fracturing Fluids

The test fluids were formulated by adding, with stirring and low heat, the dried and shredded interpolymer to a water solution usually containing small amount of KCl (about 0.1 to 0.2 weight percent) and a nonionic surfactant C₁₂ ^H25° fCH₂CH₂0}-,₀H to assist in dispersion and hydration. Stirring was continued until a smooth homogeneous mixture was obtained. Aliquots of this masterbatch solution were then diluted with water containing various levels of KCl and other additives, such as sodium thiosulfate, to give the fracturing fluid formulations tested below, each of which contained 0.12 weight percent sodium thiosulfate.

In all of the following examples, the test formulations were prepared as noted above and the rheology was determined at 275°F at a shear rate of 170 and/or 511 reciprocal seconds. The test formulations and rheology data are summarized in Table I. All percentages are weight percentages. To further illustrate the preparation of the test formulation, in Example 1 the interpolymer (2 grams, g) containing a mole ratio of acrylamide/dodecyl methacrylate of 99.4/0.6 was dissolved in 98 milliliters (mL) of an aqueous medium containing 96 mL of deionized water and 2 mL of a 1 weight percent solution of a nonionic surfactant C₁₂H₂₅ 0 C₂H₅0-,_QH in water, and 0.2 g of KCl using slow stirring and mild heat; this gave the solution masterbatch. Fifty (50) mL of this masterbatch was diluted with 50 mL of a solution containing 2 weight percent of KCl and 0.24 weight percent of sodium thiosulfate in water; this gave the test formulation as a liquid solution containing 1.0 weight percent interpolymer, 2.1 weight percent KCl, 0.01 weight percent nonionic surfactant 12^H25 ° ^^C2^H5°^1₀ ^H' ^and °*¹² weight percent sodium thiosulfate. The rheology in this test formulation was then determined as indicated above and reported as Example 1 in Table I. All test formulations had a pH of about 8 to 10. TABLE I

Test Formulation - Components Rheology

Interpolymer

AAM/C₁₂* Amount KCl Surfactant 170 511

Ex. (Mole %) ( t. %) (wt. %) ( t. %) n K Sec^"1 Sec^"1 Hours

1. 99.4/0.6 1.0 2.1 0.01 .0949 .4829 221cps 82cps 1

.1727 .3296 225 91 2

.2127 .2722 228 96 3

.3137 .1547 218 103 4

.2769 .1646 192 87 5

.3048 .1368 184 86 6

.3131 .1238 174 82 7

2. 99.4/0.6 1.0 1.1 0.01 .3540 .1163 202 99 1 .4350 .0626 164 88 2 .4313 .0603 156 83 3

3.^' 99.4/.06 1.0 2.1 0.005 .1522 .3261 200 79 1 I .1537 .3369 209 82 2 t-^r OO .1814 .2919 208 85 3 .1887 .2800 208 85 4

4. 99.4/0.6 1.0 4.3 0.01 .3435 .0733 120 59 1 .3087 .0927 127 60 2 .3083 .0927 127 59 3 .3885 .0578 120 61 4 .3081 .0919 126 59 5 .3192 .0877 127 60 6 .3441 .0589 97 47 7

5. 99.4/0.6 1.0 1.0 0.0025 .2696 .2378 267 120 1 .2722 .2345 267 120 2 .2691 .2336 262 117 3

'AAM/C '' is mole ratio of acrylamide/dodecyl methacrylate

TABLE I

Test Formulation - Components Rheology

Interpolymer

AAM/C₁₂* Amount KCl Surfactant 170 511

Ex. (Mole %) (wt. %) (wt. %) (wt. %) n K Sec^"1 Sec^"1 Hours

6. 99.4/0.6 0.75 1.1 0.004 .1404 .2623 152 59 1

.1432 .2405 141 55 2

.1465 .2377 142 56 3

.1415 .2499 145 57 4

7. 99.4/0.6 0.5 0.58 0.0025 .2225 .0671 59 25 1 .2041 .0946 76 32 2 .1701 .1307 88 35 3

• .1576 .1409 89 35 4

8. 99.3/0.7 1.0 4.3 0.01 .3251 .0798 119 57 1 .3285 .0761 116 55 2 .3245 .0794 118 56 3

9. 99.3/0.7 1.0 1.1 0.0025 .1346 .6647 373 144 1 vD I .1274 .6118 331 127 2 .1458 .5202 309 121 3 .1494 .5031 305 120 4

10. 99.3/0.7 1.0 2.1 0.0025 .2975 .0967 125 58 1 .3074 .0828 113 53 2

11. 99.3/0.7 0.75 1.1 0.0025 .1374 .2134 122 47 1 .1366 .2268 129 50 2 .1504 .2072 126 50 3 .1540 .2010 125 49 4

12. 99.3/0.7 0.50 0.58 0.25 .2857 .0317 39 18 1

TABLE I

Test Formulation - Components Rheology

Interpolymer

AAM/C₁₂* Amount KCl Surfactant 170 511

Ex. (Mole %) ( t. %) ( t. %) ( t. %) n K Sec^"1 Sec^"1 Hours

13. 99.2/0.8 1.0 1.1 0.0025 .1514 .4884 299 118 1

.1512 .5159 315 124 2

.1603 .4996 320 127 3

.1235 .4401 318 130 4

14. 99.2/0.8 1.0 4.3 0.0025 .4910 .0234 82 47 1 .5028 .0223 83 48 2 .3393 .0726 117 56 3 .3950 .0489 105 54 4 .2666 .1212 134 60 5 .2804 .1090 129 59 6

I .9857 .0016 69 68 7 t

15. 99.2/0.8 1.0 1.1 0.05 .6318 .0278 201 34 1 O I .5370 .0485 215 129 2 .5019 .0601 223 129 3 .4841 .0673 227 129 4

16. 99.2/0.8 1.0 2.1 0.0025 .1079 .5063 250 94 1 .2186 .2648 229 97 2 .2178 .2638 227 96 3 .2194 .2662 231 98 4

17. 99.2/0.8 0.75 1.1 0.0025 .1107 .3124 155 58 1 .1146 .2930 148 56 2 .1085 .3017 148 56 3 .1077 .3040 149 56 4

TABLE I

Test Formulation - Components Rheology

Interpolymer AAM/C * Amount KCl Surfactant 170 511

-1 -1

Ex. (Mole %) (wt. %) ( t. %) (wt . %) n K Sec Sec Hours 18. 99.0/1.0 1.0 4.3 0.005 .3539 .0706 122 60 1

.3525 .0603 104 51 2

.3295 .0808 123 59 3

.3141 .0855 121 57 4

.3200 .0745 127 60 5

.3485 .0876 126 61 6

19. 99.0/1.0 1.0 1.1 0.005 .3502 .2229 379 185 1

.2217 .3908 343 146 2

.2856 .2652 323 147 3

.3552 .1651 288 142 4

20. 99.0/1.0 1.0 1.1 0.0025 .1133 .7047 355 134 1 I

.1885 .5080 376 154 2 t t-*

.1745 .5414 373 151 3 I

.2273 .4018 363 155 4

21. 99.0/1.0 1.0 1.1 0.01 .7574 .0059 81 62 1

.8373 .0030 63 53 2

.8485 .0025 55 47 3

22. 99.0/1.0 0.75 0.61 0.0038 .2378 .1605 153 66 1

.1891 .2601 193 79 2

.1749 .3221 222 90 3

23. 99.0/1.0 0.75 0.61 0.0038 .2586 .0849 90 40 1

.2372 .1579 150 65 2

.2111 .2109 175 74 3

Rheology on Example 23 determined .1867 .2717 199 82 4 at 300°F instead of 275°F. .3816 .0771 154 78 5

.1766 .2739 191 77 6

.2407 .1700 165 71 7

.2469 .1579 158 69 8

TABLE I

•

Test Formulation - Components Rheology

Interpolymer

AAM/C₁₂* Amount KCl Surfactant 170 511

Ex. (Mole %) ( t. %) (wt. %) (wt. %) n K Sec^"1 Sec^"1 Hours

24. 99.0/1.0 0.75 2.1 0.004 .4004 .0292 64 33 1

.3667 .0419 78 39 2

.3186 .0636 92 43 3

.3246 .0634 94 45 4

.3181 .0720 104 49 5

.3085 .0802 110 51 6

.2990 .0874 114 53 7

25. 99.0/1.0 0.75 1.1 0.004 .1564 .2777 174 69 1 .1821 .2331 167 68 2 .1877 .2614 193 79 3 .1761 .2916 203 82 4 I t .1759 .3139 218 88 5 t I .1887 .3059 227 93 6

26. 99.0/1.0 0.5 1.1 0.0025 .4085 .0121 28 14 1 .3308 .0267 41 20 2 .2953 .0410 53 24 3 .2818 .0498 60 27 4

27. 99.0/1.0 0.5 0.58 0.0025 .2375 .0547 52 23 1 .2287 .0777 71 30 ^' 2 .2160 .0986 84 36 3 .2060 .1122 91 38 4

TABLE I

Test Formulation - Components Rheology

Interpolymer

AAM/C 12 Amount KCl Surfactant 170 511

Ex . (Mole ) (wt . %) (wt . %) ( t . %) n K Sec Sec Hours 28. 99.0/1.0 0.5 0.32 0.0025 .1983 .0436 34 14 1

.2175 .0241 21 9 2

.3212 .0092 14 6 3

.2789 .0089 11 5 4

29. 99.0/1.0 0.5 0.32 0.01 .1842 .0460 33 14 1

.0870 .1848 81 30 2

.0699 .2591 104 38 3

.0474 .3620 130 46 4

30. 99.0/1.0 0.5 0.58 0.01 .3220 .0275 40 19 1

.2964 .0490 63 29 2

.3023 .0518 69 32 3

31 . 99.0/1.0 0.5 0.58 0.005 .2322 .0695 64 28 1 I t

.2918 .0474 60 27 2 o

.2391 .0907 87 38 3 I

.2281 .1120 102 44 4

The typical laboratory test for determining the usefulness of a fracturing fluid is by determining the apparent viscosity of the fluid at temperature and at constant shear rate of 170 sec^" over a period of several hours. The fluid must maintain a minimum viscosity for the successful creation of the fracture and placement of proppant into the created fracture. Excessive viscosity is not desirable because it could lead to high friction pressures which can limit treat- ment designs due to hydraulic horsepower or pressure limitations. Also, some control of the geometry of the fracture may be achieved by carefully selecting fluid viscosity and pump rates. The minimim and maximum viscosities allowable for the fluid will vary depending on the individual treatment design which takes into consideration such things as formation properties, size of the desired fracture, amount of proppant to be placed, well temperature, and mechanical limitations. It is apparent that the minimum and maximum viscosity requirements for fluids can vary considerably; however, for laboratory evaluations some broad useful ranges can be identified. For the purposes of definition, we consider a^" fluid to be useful, as a fracturing fluid in this invention if it maintains apparent viscosity of at least about 30 centipoise (CPS) for at least 2 hours at 275°F at a shear rate of 170 reciprocal seconds as measured on a Fann 50c viscometer. All of the above fluids in Examples 1 to 31 meet this standard.

Claims

What Is Claimed Is:

1. A process for fracturing a subterranean formation penetrated by a wellbore by injecting a hydraulic fracturing fluid through said wellbore and against said subterranean formation at a flow rate and pressure at least sufficient to initiate and/or extend a fracture into said formation, comprising using as said hydraulic fracturing fluid an aqueous composition having chemical and physical properties sufficient to render it useful as a hydraulic fracturing fluid at 275° F, said composition comprising:

A. an aqueous medium; and

(1) a water-soluble or water-dis- persible interpolymer having pendant hydrophobic groups chemically bonded thereto and containing, in interpoly- merized form, from 99.0 to 99.4 mole percent of a water-soluble monomer or mixture of such monomers and from 1.0 to 0.6 mole percent of a water-insoluble monomer or mixture of such monomers,

(2) a water-soluble or water- dispersible nonionic surfactant having a HLB of from 10 to 14 and having a hydrophobic group capable of associ¬ ating with the hydrophobic groups on said interpolymer, and

(3) a water-soluble electrolyte.

2. The process defined by Claim 1 wherein said interpolymer is a vinyl addition polymer.

3. The process defined by Claim 1 or 2 wherein at least one of said water-soluble monomers is represented by the formula

R

I

CH_^ - C

C = 0 t

wherein, R is hydrogen or methyl and Z is -NH_?' -OH; -OR¹ where R' is a C₁-C₄ alkyl group; -NH-R"-S0₃ wherein R" is an alkylene group of from 1 to 24 carbon atoms and M is hydrogen or an ammonium or alkali metal ion.

4. The process defined by Claim 1 wherein said water-insoluble monomer is represented by the formula

R

I

CH.. - C 7

I

C = 0

I

II X - R^»«

wherein X is -O- or -NH- and R" ^! is a hydrophobic group.

5. The process defined by Claim 4 wherein R" ' is an aliphatic- hydrophobic group.

6. The process defined by Claim 5 wherein R"' is an alkyl group of from 8 to 24 carbon atoms.

7. The process defined by Claim 1 wherein said nonionic surfactant is an ethoxylated aliphatic alcohol.

8. The process defined by Claim 7 wherein said nonionic surfactant is an ethoxylated alkanol; said alkanol having from 8 to 24 carbon atoms.

9. The process defined by Claim 1 wherein said water-soluble electrolyte is a monovalent inorganic salt.

10. The process defined by Claim 9 wherein said salt is an ammonium, sodium and/or potassium halide.

11. The process defined by Claim 10 wherein said salt is KCl.

12. The process defined by Claim 1 including a stabilizing amount of a water-soluble thiosulfate.

13. The process defined by Claim 12 wherein said thiosulfate is ammonium thiosulfate and/or an alkali metal thiosulfate.

14. The process defined by Claim 1 wherein said fracturing fluid additionally comprises normally liquid hydrocarbon as a fluid loss additive.

15. The process defined by Claim 15 wherein said normally liquid hydrocarbon is kerosene or diesel oil.

16. The process defined by Claim 1 wherein said fracturing fluid additionally comprises a par- ticulate solid proppant.

17. An aqueous composition having chemical and physical properties sufficient to render it useful as a hydraulic fracturing fluid at 275°F, said composi¬ tion comprising:

A. an aqueous medium; and B. a thickener composition in an amount sufficient to increase the viscosity of said aqueous medium, said thickener composition comprising:

(1) a water-soluble or water-dispersible interpolymer having pendant hydrophobic groups chemically bonded thereto and containing, in interpolymerized form, from 99.0 to 99.4 mole percent of water-soluble monomer or mixture of such monomers and from 1.0 to 0.6 mole percent of a water-insoluble monomer or mixture of such monomers,

(3) a water-soluble electrolyte.