METHOD AND COMPOSITION FOR VISCOSIFYING HYDROCARBONS

Abstract: The viscosity of a liquid hydrocarbon can be increased, to make it suitable for use as a fracturing fluid, by mixing therewith a viscosifying agent comprising (i) a copolymer of N,N-dimethylacrylamide and dimethylaminopropyl methacrylamide, (ii) a monocarboxylic acid and (iii) an amine having an ethanolamine structure.

Description: The present invention relates to a method and composition for viscosifying or gelling hydrocarbon liquids such as diesel, kerosene and the like, to produce fluids useful for the treatment of subterranean formations. Hydraulic fracturing is an extensively used method for stimulating petroleum producing subterranean formations. Fracturing is commonly performed by contacting a subterranean formation with a viscous fracturing fluid having particulate solids, hereinafter referred to as propping agents, suspended therein, applying sufficient pressure to the fracturing fluid to open a fracture in the subterranean formation and maintaining this pressure while injecting the fracturing fluid into the fracture at a sufficient rate to extend the fracture into the subterranean formation. When the pressure on the fracturing fluid is reduced, the propping agent prevents the complete closure of the fracture. Viscous liquids are desirably used as fracturing fluids because they have been found to remain in the fracture long enough to permit build-up and maintenance of sufficient pressure to open a fracture. Additionally, a viscous fracturing fluid can support propping agents suspended therein. We have found that the viscosity of hydrocarbon liquids such as, for example, diesel or kerosene, can be increased to make them suitable for use as fracturing fluids, by mixing therewith a copolymer, a monocarboxylic acid and an amine. In particular, the present invention provides a method of viscosifying a hydrocarbon liquid which comprises forming a mixture of the hydrocarbon liquid and a viscosifying agent comprising (a) a copolymer of N,N-dimethylacrylamide and dimethylaminopropylmethacrylamide having a molecular weight of at least 400,000, and a molar ratio of N,N-dimethylacrylamide to dimethylaminopropylmethacrylamide in said copolymer in the range of from 20: 80 to 70: 30, (b) a monocarboxylic acid having the general formula R-COOH wherein R is an alkyl or alkenyl radical having 11 to 21 carbon atoms, said monocarboxylic acid being present in an amount sufficient to neutralize said copolymer through ion pair formation, and (c) a water-soluble amine having an ethanolamine or alkylethanolamine structure, said amine being present in an amount sufficient in combination with said copolymer and monocarboxylic acid to viscosify said hydrocarbon. The invention also includes a composition for viscosifying a hydrocarbon liquid comprising (a) a copolymer having the general structure: wherein x and y represent monomer mole percent and x is in the range 20 to 70 and y is in the range 30 to 80, and x + y = 100 and the copolymer has a molecular weight of at least 400,000; (b) a monocarboxylic acid or mixture of acids of the general formula: R-COOH wherein R represents an alkyl or alkenyl radical having from 11 to 21 carbon atoms present in an amount at least sufficient to neutralize said copolymer through ion pair formation; and (c) a water-soluble amine having an ethanolamine or alkylethanolamine structure present in an amount of at least 0.5 percent by weight of the liquid hydrocarbon to be viscosified by said composition. The viscosifying agents of the present invention comprise the reaction product, in the hydrocarbon fluid, of the monocarboxylic acid and water-soluble amines with a copolymer having the general formula I above. The copolymers used in the present invention may be prepared by conventional solution polymerization or inverse emulsion polymerization methods, such as those described in U.S. patents nos. 3,284,393, 3,624,019 and 3,724,547. In one preferred embodiment, the copolymer is prepared by inverse emulsion polymerization. In this method, for laboratory scale tests, a quantity of an aqueous solution of N,N-dimethylacrylamide is mixed with an aqueous solution of dimethylaminopropylmethacrylamide monomer in a container from which oxygen is purged by a constant flow of nitrogen gas. Preferably, the monomers comprise from about 25 percent to about 45 percent, and most preferably about 33 percent, by weight of the aqueous solutions. The particular portions of each solution are adjusted to provide the desired molar concentration in the copolymer. The monomers may be added to the container in any order. A surfactant, or blend of surfactants, is then mixed with an oil such as Isopar M, a refined kerosene marketed by Exxon Chemical Company, in a mixing vessel. The surfactant can comprise any surfactant which is capable of forming a water-in-oil emulsion of the monomers. Such surfactants are commonly referred to as emulsifiers. Oxygen is purged from the mixing vessel and the nitrogen-purged aqueous solution of monomers is slowly added to the mixing vessel at a rate such that a water-in-oil emulsion is formed. The emulsion then is mixed with a reaction initiator such as 2,2′-azobis(2,4-dimethylvaleronitrile) or any other suitable initiator, and maintained at a constant temperature in the range generally of from about 30°C to 50°C until the polymerization reaction begins. The precise reaction temperature is limited by the emulsifier utilized and the stability of the emulsion. This can be achieved on a laboratory scale by placing the reactants in a nitrogen purged stirred vessel in a constant temperature bath. In commercial applications, the reactor vessel can be provided with suitable heating coils capable of maintaining an initial constant temperature in the reactant mixture suitable to initiate the polymerization reaction. The reaction is evidenced by a temperature exotherm. The polymerization reaction is considered complete about one hour after the temperature returns to the original temperature level of the mixture. The copolymer preferably has a molecular weight in the range of from 400,000 to about five million. The copolymer is mixed with the liquid hydrocarbon which is to be viscosified in an amount of at least about 0.25 percent by weight of the liquid hydrocarbon, and generally from 0.25 to about 6.0 percent. Preferably, the copolymer is mixed with the hydrocarbon liquid in an amount of from about 0.3 percent to about 4 percent, most preferably 0.5 to 2 percent, by weight of the liquid hydrocarbon. Such rates of mixing correspond generally to an amount of from about 0.24 to about 3.2 grams per 100 milliliters of liquid hydrocarbon, perferably about 0.4 to about 1.6 grams per 100 milliliters of liquid hydrocarbon. To the quantity of the foregoing copolymer in the liquid hydrocarbon is added the monocarboxylic acid and the water-soluble amine to viscosify the liquid hydrocarbon. The monocarboxylic acid can comprise oleic acid, lauric acid, tall oil fractions and the like. The monocarboxylic acid is defined generally by the formula R-COOH wherein R is an alkyl or alkenyl radical containing from 11 to 21 carbon atoms. The monocarboxylic acid is present in an amount at least sufficient to neutralize the copolymer through ion pair formation. The monocarboxylic acid imparts oil solubility to the copolymer which initially is in the form of an oil dispersible emulsion when initially mixed with the hydrocarbon to be viscosified. Most preferably, an excess of at least about 50 mole percent of that required to effect stoichiometric neutralization of the copolymer is preferred, to achieve enhanced viscosification. The monocarboxylic acid may be used in amounts of 6 to 10 times or more the stoichiometric requirements without adversely affecting the ability of the mixture to viscosify liquid hydrocarbons. Preferably, the monocarboxylic acid is present in an amount of from about 1.0 to about 10 percent by weight of the hydrocarbon to be viscosified. The selected water-soluble amines comprise compounds having the structure of an ethanolamine, such as for example, diethanolamine, diethylethanolamine, triethanolamine, N-methyldiethanolamine and the like. The selected amine is mixed in the hydrocarbon to be viscosified with the copolymer and monocarboxylic acid in an amount sufficient to effect viscosification of the liquid hydrocarbon. It has been found that an amount of the amine not less than 0.5 percent by weight of the liquid hydrocarbon is usually sufficient to increase the viscosity of the liquid hydrocarbon. To achieve maximum viscosification of a liquid hydrocarbon, the amine preferably is mixed with the copolymer in an amount of from 1.0 to 2.5 percent by weight of the liquid hydrocarbon. While not required to effect viscosification of a liquid hydrocarbon, enhanced performance has been noted in some instances when the quantity of the amine is increased as the quantity of the monocarboxylic acid increases in the viscosifying agent. The upper limit for addition of the amine is that quantity which results in precipitation of the copolymer from the liquid hydrocarbon. This quantity can vary depending upon the copolymer constituent ratio, copolymer concentration, monocarboxylic acid and acid concentration in the viscosifying agent. The order of addition of the copolymer, monocarboxylic acid and amine is not critical to the performance of the invention. Surprisingly, it has been found that a liquid hydrocarbon can be caused to rapidly and sometimes almost instantaneously gel by the addition of the monocarboxylic acid and amine followed by addition of the copolymer. The addition of the copolymer to a liquid hydrocarbon followed by the monocarboxylic acid and amine also results in the formation of a viscosified fluid, however, the rate of viscosity development is slower than in the other order of mixing. Surprisingly, it has been found that the viscosifying composition of the present invention functions, when present in small quantities, to reduce the frictional drag of an organic liquid in flow through pipes or conduits having a continuous bore therethrough. The method of utilizing such composition to reduce frictional drag of a liquid hydrocarbon comprises adding a quantity of the copolymer, monocarboxylic acid and selected amine to the hydrocarbon such that an acid-base reaction product is formed which imparts drag reduction to the hydrocarbon liquid through formation of a polymeric network. The viscosifying composition is utilized in the same proportionate amounts as for viscosification of the hydrocarbon, however, the copolymer is generally present in an amount of less than 0.25 percent by weight of the hydrocarbon liquid. More specifically the copolymer is believed to be preferably present in an amount of from about 0.001 to about 0.2 grams per 100 milliliters of the hydrocarbon liquid for purposes of drag reduction. To further illustrate the present invention, but not by way of limitation, the following Examples are provided. EXAMPLE I To illustrate the preparation of the copolymer utilized in the viscosifying agent of the present invention the following procedure was followed. Various quantities of the monomers set forth in Table I were mixed in the molar ratios identified below to form an aqueous mixture. This mixture then was added to a Waring Blendor jar containing a quantity of Isopar M refined oil and a mixture of surfactants comprising an ethoxylated sorbitan monooleate and a tall oil fatty acid diethanolamide. The reactants are mixed in the Waring Blendor to form an emulsion while being maintained under a nitrogen purge. The surfactant is present in an amount of about five percent by weight of the emulsion which is considered sufficient to effect emulsification of the aqueous mixture with the oil. This emulsion then is transferred to a stirred reactor vessel. The reactor vessel is purged with nitrogen gas and the emulsion aqueous monomer mixture is introduced into the reactor while also being maintained under a nitrogen purge. A quantity of about 1 gram per 1000 grams of reactants of 2,2′-azobis (2,4-dimethylvaleronitrile) is mixed with the emulsion in the reactor vessel as a polymerization initiator. The reactor vessel is positioned in a constant temperature water bath having a temperature of about 37°C. The reactor vessel is stirred at about 600 rpm throughout the duration of the reaction. Reaction initiation is noted a short time after addition of the initiator by a temperature rise in the reactor vessel. The temperature is monitored and the reaction is considered complete one hour after the temperature of the mixture returns to the original temperature of the mixture. All of the produced emulsions contained 25% by weight monomers before polymerization. Each of the produced polymerized emulsions was a water-in-oil emulsion. EXAMPLE II To illustrate the ability of the viscosifying agent of the present invention to gel liquid hydrocarbons, the following tests were performed. To a quantity of kerosene, 2.0% by volume of the kerosene of a 25 percent active, 50: 50 mole percent copolymer corresponding to Sample No. 3 of Example I, was added. To this mixture, varying quantities of tall oil and N-methyldiethanolamine then were added as indicated in Table II, below. The viscosity of the resultant mixture then was measured on a Model 35 Fann viscometer at ambient temperature. The data clearly indicate the necessity of having the copolymer, monocarboxylic acid and selected amine present in the viscosifying agent to effectively gel a hydrocarbon liquid. EXAMPLE III To illustrate the ability of the gelling agent of the present invention to viscosify various liquid hydrocarbons, the following tests were performed. A gelling agent comprising an admixture of: a 25 percent active, 50: 50 mole percent copolymer corresponding to Sample No. 3 of Example I, present in an amount of 2.0 percent by volume of the hydrocarbon liquid; oleic acid, present in an amount of 6 percent by volume of the hydrocarbon liquid; and N-methyldiethanolamine present in an amount of 1.0 percent by volume of the hydrocarbon is admixed in accordance with the method of the present invention with the hydrocarbons set forth in Table III. The initial viscosity of all of the fluids was 5 cp. or less as measured on a Model 35 Fann viscometer. The viscosity of the resultant mixture then was determined at ambient temperature. The results also are set forth in Table III. The foregoing results clearly demonstrate the ability of the gelling agent of the present invention to viscosify various hydrocarbon liquids. EXAMPLE IV To illustrate the utility of various compounds having the ethanolamine structure as the selected amine in the viscosifying agent of the present invention, the following tests were performed. A copolymer comprising a 25 percent active, 60: 40 mole percent copolymer corresponding to Sample No. 4 of Example I was admixed in various amounts as set forth below in Table IV with tall oil or oleic acid in the amounts indicated below and various amines to determine whether or not the composition would viscosify kerosene. The percentages set forth in Table IV are in volume percent of the total kerosene volume except as otherwise noted. The viscosity was measured on a Model 35 Fann viscometer at ambient temperature. The initial viscosity of the kerosene was about 4 cp. The results are set forth below: The foregoing data clearly illustrate the ability of compounds having an ethanolamine structure to function in the viscosifying agent of the present invention. EXAMPLE V To illustrate the effect the mixing order of the constituents of the present invention has upon the viscosification of a liquid hydrocarbon and to illustrate the criticality of the three constituents of the composition, the following tests were performed. To a quantity of kerosene, various volumes of copolymer, monocarboxylic acid and/or amine are admixed in a Waring Blendor as set forth in the following Table V. The admixture then is visually inspected to determine whether the kerosene has been viscosified by the constituents admixed therewith. The results of the inspection are set forth in Table V, below. The copolymer samples each comprised 25 percent active solutions. The results of the foregoing tests clearly demonstrate that all three constituents of the composition are required to viscosify a liquid hydrocarbon. The results of the series of tests 1-4, 5-7 and 10-12 clearly illustrate that the order of addition has no significant effect upon the ability of the composition of the present invention to viscosify a liquid hydrocarbon. In these series of samples, the additional component in each succeeding sample was sequentially added to the contents of the preceeding sample. While preferred embodiments of the invention have been described herein, it is to be understood that changes or modifications can be made in the composition and method by an individual skilled in the art without departing from the scope of the invention as set forth in the appended claims.

Claims: 1. A method of viscosifying a hydrocarbon liquid which comprises forming a mixture of the hydrocarbon liquid and a viscosifying agent comprising (a) a copolymer of N,N-dimethylacrylamide and dimethylaminopropylmethacrylamide having a molecular weight of at least 400,000, and a molar ratio of N,N-dimethylacrylamide to dimethylaminopropylmethacrylamide in said copolymer in the range of from 20: 80 to 70: 30, (b) a monocarboxylic acid having the general formula R-COOH wherein R is an alkyl or alkenyl radical having 11 to 21 carbon atoms, said monocarboxylic acid being present in an amount sufficient to neutralize said copolymer through ion pair formation, and (c) a water-soluble amine having an ethanolamine or alkylethanolamine structure, said amine being present in an amount sufficient in combination with said copolymer and monocarboxylic acid to viscosify said hydrocarbon. 2. A method according to claim 1, wherein said monocarboxylic acid comprises at least one of tall oil, oleic acid and lauric acid. 3. A method according to claim 1 or 2, wherein said amine comprises at least one or methyldiethanolamine, diethanolamine, triethanolamine and their monocarboxylic acid salts. 4. A method according to claim 1, 2 or 3, wherein said viscosifying agent is present in an amount of from 0.5 to 6 percent by weight of said hydrocarbon liquid; and/or said monocarboxylic acid is present in an amount of from 0.5 to 10 percent by weight of said hydrocarbon liquid. 5. A method according to claim 1, 2, 3 or 4, wherein said copolymer has a molar ratio of N,N-dimethylacrylamide to dimethylaminopropyl methacrylamide of from 1: 3 to 2.3: 1; and/or has a molecular weight in the range of from 400,000 to five million. 6. A composition for viscosifying a hydrocarbon liquid comprising (a) a copolymer having the general structure: wherein x and y represent monomer mole percent and x is in the range 20 to 70 and y is in the range 30 to 80, and x + y = 100 and the copolymer has a molecular weight of at least 400,000; (b) a monocarboxylic acid or mixture of acids of the general formula: R-COOH wherein R represents an alkyl or alkenyl radical having from 11 to 21 carbon atoms present in an amount at least sufficient to neutralize said copolymer through ion pair formation; and (c) a water-soluble amine having an ethanolamine or alkylethanolamine structure present in an amount of at least 0.5 percent by weight of the liquid hydrocarbon to be viscosified by said composition. 7. A composition according to claim 6, wherein x is from 40 to 60 and y is from 40 to 60. 8. A composition according to claim 6 to 7, wherein said monocarboxylic acid component (b) comprises at least one of oleic acid, lauric acid and tall oil; and/or said amine component (c) comprises at least one of diethanolamine, methyldiethanolamine and triethanolamine. 9. A composition according to claim 6, 7 or 8, wherein said copolymer is present in an amount to provide, when mixed with liquid hydrocarbon, from 0.25 to 6% by weight of the liquid hydrocarbon; said monocarboxylic acid is present in an amount sufficient to provide a concentration in the liquid hydrocarbon of from 0.5 to 10 percent by weight of said liquid hydrocarbon; and said amine is present in an amount sufficient to provide a concentration in the liquid hydrocarbon of from about 1 to 2.5 percent by weight of said liquid hydrocarbon.

Inventors: HOLTMYER, MARLIN D., HUNT, CHARLES V.
Applicants: HALLIBURTON COMPANY
Application year: 1988
Main classification: E21B43
IPC codes: C09K8