Title of Invention	A PROCESS FOR THE SYNTHESIS OF STABILIZED COPOLYMERS USEFUL FOR ENHANCING PETROLEUM RECOVERY FROM HIGH TEMPERATURE SUBTERRANEAN PETROLEUM DEPOSITS
Abstract	The present invention provides a process for the preparation of stabilized copolymers by reacting monomer selected from an acrylamide as herein described with 2-acrylamido 2-methyl propane sulphonic acid by solution polymerization . The reaction facilitate in presence of a redox pair of initiators , at a temperature range 5-50 ° C, under inert atmosphere selected from nitrogen , helium, argon atmosphere , for a period of 4-10 hrs . The resultant co-polymer is neutralized with caustic soda solution and mixed with a thermal stabilizer selected from cross-linking agent N,N-methyl bis acrylamide , trimethylopropane triacrylate to get desired stabilized copolymer

Title of Invention

A PROCESS FOR THE SYNTHESIS OF STABILIZED COPOLYMERS USEFUL FOR ENHANCING PETROLEUM RECOVERY FROM HIGH TEMPERATURE SUBTERRANEAN PETROLEUM DEPOSITS

Abstract

The present invention provides a process for the preparation of stabilized copolymers by reacting monomer selected from an acrylamide as herein described with 2-acrylamido 2-methyl propane sulphonic acid by solution polymerization . The reaction facilitate in presence of a redox pair of initiators , at a temperature range 5-50 ° C, under inert atmosphere selected from nitrogen , helium, argon atmosphere , for a period of 4-10 hrs . The resultant co-polymer is neutralized with caustic soda solution and mixed with a thermal stabilizer selected from cross-linking agent N,N-methyl bis acrylamide , trimethylopropane triacrylate to get desired stabilized copolymer

Full Text	This invention relates to a process for the synthesis of stabilized copolymers useful for enhancing petroleum recovery from high temperature subterranean petroleum deposits. The high temperature stable copolymer comprises a cojolymer of acrylamide / alkyl acrylamide - olefinic acid containing sulphonic acid group in the form of Na salt along with the stabilizing agent. The stabilizing agent is usually a cross-linking agent, say, N, N' methylene bis acrylamide which work as thermal stabilizer in inert atmosphere, commonly nitrogen. In enhanced oil recovery techniques high molecular weight (>106) water soluble polymers are frequently used as mobility control agent in surfactant- polymer and polymer augmented water flooding processes. The injection of polymer solution can significantly increase oil production by providing mobility control and by reducing channeling in the reservoir. It reduces the permeability of reservoir rock to water by increasing the viscosity of aqueous fluid. In some of the wells where high permeable water channels exist, oil and gas are produced with a large volume of salt water. The cost of the separation and disposal of the salt water from the crude oil could be high resulting in considerable loss in the operation of the wells. In such cases, water soluble polymer solution is injected into the reservoir to increase oil production by blocking water channels preferentially. The most commonly applied polymer is the partially hydrolyzed polyacrylamide (PHPA). PHPA has some limitations. In general, PHPA is injected to the fresh water reservoirs having moderate temperature, say, 80- 90°C. It cannot be applied to high density brine fluid reservoirs. In presence of monovalent, divalent or multivalent brine, solution viscosity of PHPA degrades by many folds. Moreover, PHPA starts degradation at and above 120°C. It is established that in deeper reservoir, PHPA suffers excessive thermal hydrolysis and may also precipitate in presence of divalent cation. This present invention relates to a process that can be applied to high density brine fluid reservoirs where the reservoir existing temperature is more than 100°C. In the literature several types of copolymers suitable for high temperature and high salinity reservoir conditions have been reported. US patent 4,404,111 disclosed the method for the preparation of N,N-dimethylacrylamide - 2-acrylamido-2-methylpropane sulphonic acid (AMPS) copolymer suitable for using as viscosity control agent in aqueous copolymerisation for petroleum recovery from subterranean petroleum bearing formation. But this patent is silent on the application to high temperature, high density brine fluid reservoir. Only the viscosity degradation at 1.5% NaCl concentration was disclosed. It is observed that this copolymer prepared is not thermally stable. Loss of viscosity of the dilute polymer solution is observed when this copolymer solution is allowed to stand for a long period of time. US patent 4619.773 disclosed the use of water soluble polymers of 2-acrylamido-2-methylpropane sulphonic acid salts as high temperature stable high density brine fluids for drilling operation. The copolymers were composed of either AMPS-N-vinyl-N-methyl acetamide or terpolymers of AMPS-N-vinyl-N-methyl acetamide and acrylamide. In the US patent 4,547,299 a method for the preparation of copolymers for aqueous drilling fluid composition was described. The copolymers of N,N-dimethylacrylamide and a (meth)acrylamide, alkyl sulphonic acid or alkali metal salts thereof was used as aqueous drilling fluid. The polymer may be crosslinked with N,N-methylene-bis-acrylamide or other appropriate crosslinking agent. But this drilling fluid was used at 150°F. In the US patent 4.566.978 the use of terpolymer comprising maleic anhydride, styrene and a third monomer selected from acrylamide, methacrylamide, acrylic acid and methacrylic acid as high temperature drilling fluid was disclosed. But, the polymers which is suitable for drilling mud may not be suitable for enhanced oil recovery (EOR). In EOR the polymer should be thermally stable for a long period of time under harsh conditions of reservoir environment . West German patent 3 627 456,1987 describes the terpolymer composition involving acrylamide, sodium acrylates and acrylamido-N-dodecyl N-butyl sulphonate terpolymer as an useful candidate. It was also established that acrylamide terpolymers having a heterocyclic ring in the polymer backbone have been shown to exhibit improved viscosity and shear degradation properties. The main objective of the present invention is to provide a process for the synthesis of thermally stable copolymers of acrylamide - 2-acrylamido 2-methyl propane sulphonic acid salt for enhancing petroleum recovery from high temperature subterranean petroleum deposits. The second objective is that the polymer solution should be compatible with dense brine fluid in the reservoir . The polymer solution should not precipitate in presence of monovalent or multivalent brines present in the reservoir. Third objective is to provide a process for the preparation of the thermally stable co-polymer under reservoir conditions of salinity and temperature at least for a period of one month. Accordingly the present invention provides a process for the preparation of stabilized copolymers useful for enhancing petroleum recovery from high temperature subterranean petroleum deposits which comprises reacting monomer selected from an acrylamide as herein described with 2-acrylamido 2-methyl propane sulphonic acid by solution polymerization wherein weight of acrylamide ranges from 5-95 % weight of 2-acrylamido 2-methyl propane sulphonic acid ranges from 5-95% , in presence of a redox pair of initiators as defined herein , at a temperature range 5-50 ° C, under inert atmosphere selected from nitrogen , helium, argon atmosphere , for a period of 4-10 hrs , neutralizing the resultant polymer with caustic soda solution , adding a thermal stabilizer selected from cross-linking agent N,N-rnethyl bis acrylamide , trimethylopropane triacrylate to get desired stabilized copolymer . High temperature exists on deeper reservoirs where free oxygen is not available . For ideal study this invention is conducted under nitrogen atmosphere. In an embodiment of the present invention the redox initiator used is selected from sodium metadisulphite-ammonium persulphate , sodium metabisulphite-potassium persulphate , ferrous sulphate-hydrogen peroxide, ferrous sulphate-ammonium persulphate or mixture thereof. In another embodiment of the invention acrylamide used is selected acrylamide , substituted acrylamide such as N,N -dimethyl acrylamide . The thermal stabilizer used in this invention may be selected from crosslinking agent such as N,N-methyl bis acrylamide , trimethylopropane triacrylate in presence of ammonia , formaldehyde . In the another invention of this invention inert atmosphere is used instead of air. The inert atmosphere is selected from nitrogen , helium, argon which prevents any degradation of the polymer by oxidation. In a feature of the present invention the ratio of acrylamide and 2- acrylamido -2- methypropane sulphonic acid may be in the range of 5-95% and 95-5 % respectively. In another feature of the invention is the concentration of the redox pair of initiator may be in the range of 0, 05 - 1.0. wt% of the total monomer. Conventional method used for isolation of copolymer may be selected from precipitation method by using non-solvent such as acetone, isopropyl alcohol, t-butyl alcohol etc. The present invention provides a process for the preparation of a thermally stable copolymer which comprises of acrylamide/N,N-dialkyl acrylamide-2acrylamiodo -2-methyl propane sulphonic acid copolymer by solution polymerization using redox pair of initiators at temperature range of 5- 50 °C neutralizing the resultant polymer with caustic soda solution and stabilizing with cross-linker which acts as a thermal stabilizer, the resultant product of which can be applied in deep reservoir having dense brine fluid. It is compatible with reservoir brine and will not precipitate in presence of Ca+ ion. As there is no free oxygen in the deeper reservoir, it is preferable to study the thermal stability under inert atmosphere like, nitrogen. A preferred water soluble copolymer consists of a random distribution of, Fig. 1 : Unit of the structure (a) (5-95%) and Unit of the structure (b) (5-95%). After the completion of the copolymer reaction, a small amount of a thermal stabilizer may be added as a physical mixture. This will enhance the thermal stability (>120°C) for a very long time. The thermal stabilizer may be selected from the list of cross linking agent for acrylamide preferably. The thermal stability enhances its limit under inert atmospheres. The effectiveness of the copolymer used according to the present invention as structural viscosity builders consists of two steps, 1) copolymerization followed by 2) stabilization with the help of thermal stabilizer. The stabilized copolymer can be applied to deeper reservoir which contains dense brine as well as higher temperatures. Accordingly, the copolymerization reaction is carried out in aqueous medium using redox pair of initiators. Slow addition of peroxy compound to monomer mixtures Structure of the monomer units in the polymer (Structure Removed ) Structure (a) : 5-95% by weight of the unit - Structure (b): 5-95% by weight of the unit – (Structure Removed ) Where RI and R2 are the same or different and each may hydrogen, methyl or ethyl and X+ is a cation preferably H+ containing the other members of the redox pair of initiators produces very high molecular weight copolymer. The polymerization in this present invention is carried out at 5- 50°C, preferably at room temperature. The reaction is carried out under nitrogen atmosphere for about 4-10 h. After the reaction the viscous polymer solution is neutralized with sodium hydroxide solution. The polymer is then isolated from the mixture by precipitating with a non-solvent like, acetone. The ratio of monomers and the intrinsic viscosity of the polymer are determined. The thermal stabilizer can be added as a physical mixture during the course of aging studies. It stabilizes the polymer solution for a long period under inert atmosphere. The US patent 4,404,111 also disclosed the use of N,N-dimethylacrylamide-2-acrylamido-2-methyl propane sulphonic acid(AMPS) copolymer for enhanced oil recovery from subterranean formations. Without thermal stabilizers, this copolymer was not found to be thermally stable even at 125°C for a month. But the present invention provides a process for the preparation of thermally stable polymer atleast for a long period of time, say, 1-2 months. The following examples are given to illustrate the invention but should not be construed to limit the scope of this invention. Example 1 Synthesis of the copolymer 1 Recrystallized 2-acrylamido -2-methyl propane sulphonic acid (9g) and distilled N,N-dimethyl acrylamide (21g) are dissolved in doubly distilled water (240 ml) in a three necked flask fitted with a condenser, a mechanical stirrer and a gas inlet tube. The whole assembly is taken in a thermostatic bath at a temperature of 30°C. Recrystallized Na-metabisulphite (0.33 wt.%) is added to the reaction mixture while a solution of recrystallized ammonium persulphate (0.23 wt.% in 60 ml distilled water) is slowly added from the top of the reaction vessel. Reaction proceeds slowly and completes within 5h. A small quantity of the reaction mixture is removed and purified by precipitation in acetone. It is then dried in vacuum oven for lOh. The percentage of the monomers and the intrinsic viscosity of the copolymer are presented in the Table 1. The viscous polymer prepared above is neutralized with sodium hydroxide solution (5% aqueous solution). The copolymer is then isolated by precipitating in acetone and dried in vacuum oven at 60°C for 10 h. Stabilization of viscous polymer solution About 4.0g of the copolymer prepared is dissolved in 500ml distilled water. 33 ppm of N,N'-methylene bis acrylamide is added to the polymer solution and is thoroughly mixed by using mechanical stirrer. The solution is then allowed to stand in a high temperature reactor under nitrogen atmosphere at 125°C. In every alternate day about 50 ml of the aging sample is withdrawn and their solution viscosity is determined at 25°C. The results are presented in Table 2. After two days of aging at that temperature, the polymer solution acquires stability and the reduction of solution viscosity is negligible. This polymer solution can also be applied to dense brine water reservoir. The data are reported in table 1. There is no precipitation of the polymer even at 1-2% of CaCl2 concentration. The solution viscosity decreases with the addition of monovalent or bivalent brine. There is an optimum limit of monovalent or bivalent brine concentration beyond which the reduction of solution viscosity is negligible. Example 2 Synthesis of the copolymer 2 Recrystallized 2-acrylamido -2-methyl propane sulphonic acid (7g) and distilled N,N-dimethyl acrylamide (13g) are dissolved in doubly distilled water (150 ml) in a three necked flask fitted with a condenser, a mechanical stirrer and a gas inlet tube. The whole assembly is taken in a thermostatic bath at a temperature of 15°C. Recrystallized Na-metabisulphite (0.22 wt.%) is added to the reaction mixture while a solution of recrystallized ammonium persulphate (0.33 wt.% in 20 ml distilled water) is slowly added from the top of the reaction vessel. Reaction proceeds slowly and completes within 5h. A small quantity of the reaction mixture is removed and purified by precipitation in acetone. It is then dried in vacuum oven for lOh. The percentage of the monomers and the intrinsic viscosity of the copolymer are presented in the Table 1. The viscous polymer prepared above is neutralized with sodium hydroxide solution (2% aqueous solution). The copolymer is then isolated by precipitating in acetone and dried in vacuum oven at 60°C for 10 h. Stabilization of viscous polymer solution About 4.0g of the copolymer prepared is dissolved in 500ml distilled water. 60 ppm of N,N'-methylene bis acrylamide is added to the polymer solution and is thoroughly mixed by using mechanical stirrer. The solution is then allowed to stand in a high temperature reactor under nitrogen atmosphere at 125°C. In every alternate day about 50 ml of the aging sample is withdrawn and their solution viscosity is determined at 25°C. The results are presented in Table 2. After two days of aging at that temperature, the polymer solution acquires stability and the reduction of solution viscosity is negligible.This polymer solution can also be applied to dense brine water reservoir. The data are reported in table 1. There is no precipitation of the polymer even at 1-2% of CaCla concentration. The solution viscosity decreases with the addition of monovalent or bivalent brine. There is an optimum limit of monovalent or bivalent brine concentration beyond which the reduction of solution viscosity is negligible. Example 3 Synthesis of the copolymer 3 Recrystallized 2-acrylamido -2-methyl propane sulphonic acid (6g) and recrystellized acrylamide (14g) are dissolved in doubly distilled water (160 ml) in a three necked flask fitted with a condenser, a mechanical stirrer and a gas inlet tube. The whole assembly is taken in a thermostatic bath at a temperature of 30°C. Recrystallized Na-metabisulphite (0.25 wt.%) is added to the reaction mixture while a solution of recrystallized ammonium persulphate (0.2 wt.% in 60 ml distilled water) is slowly added from the top of the reaction vessel. Reaction proceeds slowly and completes within 5h. A small quantity of the reaction mixture is removed and purified by precipitation in acetone. It is then dried in vacuum oven for lOh. The percentage of the monomers and the intrinsic viscosity of the copolymer are determined. The viscous polymer prepared above is neutralized with sodium hydroxide solution (2% aqueous solution). The copolymer is then isolated by precipitating in acetone and dried in vacuum oven at 60°C for 10 h. Stabilization of viscous polymer solution About 4.0g of the copolymer prepared is dissolved in 500ml distilled water. 50 ppm of N,N'-methylene bis acrylamide is added to the polymer solution and is thoroughly mixed by using mechanical stirrer. The solution is then allowed to stand in a high temperature reactor under nitrogen atmosphere at 125°C. In every alternate day about 50 ml of the aging sample is withdrawn and their solution viscosity is determined at 25°C. The polymer solution acquires stability under nitrogen atmosphere and the reduction of solution viscosity is negligible. This polymer solution can also be applied to dense brine water reservoir. There is no precipitation of the polymer even at 1-2% of CaCl2 concentration. The solution viscosity decreases with the addition of monovalent or bivalent brine. There is an optimum limit of monovalent or bivalent brine concentration beyond which the reduction of solution viscosity is negligible. Example 4 Synthesis of the copolymer 4 Recrystallized 2-acrylamido -2-methyl propane sulphonic acid (3g) and distilled N,N-dimethyl acrylamide (17g) are dissolved in doubly distilled water (150 ml) in a three necked flask fitted with a condenser, a mechanical stirrer and a gas inlet tube. The whole assembly is taken in a thermostatic bath at a temperature of 45 °C. Recrystallized Na-metabisulphite (0.2 wt.%) is added to the reaction mixture while a solution of recrystallized potassium persulphate (0.15 wt.% in 10 ml distilled water) is slowly added from the top of the reaction vessel. Reaction proceeds slowly and completes within 5h. A small quantity of the reaction mixture is removed and purified by precipitation in acetone. It is then dried in vacuum oven for lOh. The percentage of the monomers and the intrinsic viscosity of the copolymer are determined. The viscous polymer prepared above is neutralized with sodium hydroxide solution (2% aqueous solution). The copolymer is then isolated by precipitating in acetone and dried in vacuum oven at 60°C for 10 h. Stabilization of viscous polymer solution About 4.0g of the copolymer prepared is dissolved in 500ml distilled water. 55 ppm of N,N'-methylene bis acrylamide is added to the polymer solution and is thoroughly mixed by using mechanical stirrer. The solution is then allowed to stand in a high temperature reactor at 125°C unde nitrogen atmosphere. In every alternate day about 50 ml of the aging sample is withdrawn and their solution viscosity is determined at 25°C. After 3/4 days of aging at that temperature, the polymer solution acquires stability and the reduction of solution viscosity is negligible. This polymer solution can also be applied to dense brine water reservoir. The data are reported in table 1. There is no precipitation of the polymer even at 1-2% of CaCl2 concentration. The solution viscosity decreases with the addition of monovalent or bivalent brine. There is an optimum limit of monovalent or bivalent brine concentration beyond which the reduction of solution viscosity is negligible. Example 5 Synthesis of the copolymer 5 Recrystallized 2-acrylamido -2-methyl propane sulphonic acid (8g) and distilled N,N-dimethyl acrylamide (12g) are dissolved in doubly distilled water (140 ml) in a three necked flask fitted with a condenser, a mechanical stirrer and a gas inlet tube. The whole assembly is taken in a thermostatic bath at a temperature of 45°C. Recrystallized Na-metabisulphite (0.32 wt.%) is added to the reaction mixture while a solution of recrystallized potassium persulphate (0.23 wt.% in 20 ml distilled water) is slowly added from the top of the reaction vessel. Reaction proceeds slowly and completes within 5h. A small quantity of the reaction mixture is removed and purified by precipitation in acetone. It is then dried in vacuum oven for lOh. The percentage of the monomers and the intrinsic viscosity of the copolymer are determined. The viscous polymer prepared above is neutralized with sodium hydroxide solution (2% aqueous solution). The copolymer is then isolated by precipitating in acetone and dried in vacuum oven at 60°C for 10 h. Stabilization of viscous polymer solution About 4.0g of the copolymer prepared is dissolved in 500ml distilled water. 40 ppm of N,N'-methylene bis acrylamide is added to the polymer solution and is thoroughly mixed by using mechanical stirrer. The solution is then allowed to stand in a high temperature reactor at 125°C under nitrogen atmosphere. In every alternate day about 50 ml of the aging sample is withdrawn and their solution viscosity is determined at 25°C. The results are presented in Table 2. After 3/4days of aging at that temperature, the polymer solution acquires stability and the reduction of solution viscosity is negligible. This polymer solution can also be applied to dense brine water reservoir. There is no precipitation of the polymer even at 1-2% of CaCl2 concentration. The solution viscosity decreases with the addition of monovalent or bivalent brine. There is an optimum limit of monovalent or bivalent brine concentration beyond which the reduction of solution viscosity is negligible Table 1 (Table Removed ) *A=acrylamide/N,N-dimethylacrylamide; B = 2-acrylamido-2-methylpropane sulphonate Table 2 (Table Removed ) Solution without stabilizer We Claim 1. A process for the preparation of stabilized copolymers useful for enhancing petroleum recovery from high temperature subterranean petroleum deposits which comprises reacting monomer selected from an acrylamide as herein described with 2-acrylamido 2-methyl propane sulphonic acid by solution polymerization wherein weight of acrylamide ranges from 5-95 % weight of 2-acrylamido 2-methyl propane sulphonic acid ranges from 5-95% , in presence of a redox pair of initiators as defined herein , at a temperature range 5-50 ° C, under inert atmosphere selected from nitrogen , helium, argon atmosphere , for a period of 4-10 hrs , neutralizing the resultant polymer with caustic soda solution , adding a thermal stabilizer selected from cross-linking agent N,N-methyl bis acrylamide, trimethylopropane triacrylate to get desired stabilized copolymer . 2. A process as claimed in claim 1 wherein the redox pair of initiator used is selected from sodium metabisulphite-ammonium persulphate , sodium metabisulphite-potassium persulphate , ferrous sulphate-hydrogen peroxide, ferrous sulphate-ammonium persulphate or mixture thereof. 3. A process as claimed in claims 1 and 2 wherein the monomer to solvent ratio is in the range of 1:4 to 1:10. 4. A process as claimed in claims 1-3 wherein the amount of N,N-methyl bis acrylamide used to stabilize copolymer is ranging 30-600 ppm. 5. A process for the preparation of stabilized copolymers useful for enhancing petroleum recovery from high temperature subterranean petroleum deposits substantially as herein described with reference to the examples.

Full Text

This invention relates to a process for the synthesis of stabilized copolymers useful for enhancing petroleum recovery from high temperature subterranean petroleum deposits. The high temperature stable copolymer comprises a cojolymer of acrylamide / alkyl acrylamide - olefinic acid containing sulphonic acid group in the form of Na salt along with the stabilizing agent. The stabilizing agent is usually a cross-linking agent, say, N, N' methylene bis acrylamide which work as thermal stabilizer in inert atmosphere, commonly nitrogen.
In enhanced oil recovery techniques high molecular weight (>106) water soluble polymers are frequently used as mobility control agent in surfactant- polymer and polymer augmented water flooding processes. The injection of polymer solution can significantly increase oil production by providing mobility control and by reducing channeling in the reservoir. It reduces the permeability of reservoir rock to water by increasing the viscosity of aqueous fluid. In some of the wells where high permeable water channels exist, oil and gas are produced with a large volume of salt water. The cost of the separation and disposal of the salt water from the crude oil could be high resulting in considerable loss in the operation of the wells. In such cases, water soluble polymer solution is injected into the reservoir to increase oil production by blocking water channels preferentially. The most commonly applied polymer is the partially hydrolyzed polyacrylamide (PHPA). PHPA has some limitations. In general, PHPA is injected to the fresh water reservoirs having moderate temperature, say, 80- 90°C. It cannot be applied to high density brine fluid reservoirs. In presence of monovalent, divalent or multivalent brine, solution viscosity of PHPA degrades by many folds. Moreover, PHPA starts degradation at and above 120°C. It is established that in deeper reservoir, PHPA suffers excessive thermal hydrolysis and may also precipitate in presence of divalent cation. This present invention relates to a process that can be applied to high density brine fluid reservoirs where the reservoir existing temperature is more than 100°C.
In the literature several types of copolymers suitable for high temperature and high salinity reservoir conditions have been reported. US patent 4,404,111 disclosed the
method for the preparation of N,N-dimethylacrylamide - 2-acrylamido-2-methylpropane sulphonic acid (AMPS) copolymer suitable for using as viscosity control agent in aqueous copolymerisation for petroleum recovery from subterranean petroleum bearing formation. But this patent is silent on the application to high temperature, high density brine fluid reservoir. Only the viscosity degradation at 1.5% NaCl concentration was disclosed. It is observed that this copolymer prepared is not thermally stable. Loss of viscosity of the dilute polymer solution is observed when this copolymer solution is allowed to stand for a long period of time. US patent 4619.773 disclosed the use of water soluble polymers of 2-acrylamido-2-methylpropane sulphonic acid salts as high temperature stable high density brine fluids for drilling operation. The copolymers were composed of either AMPS-N-vinyl-N-methyl acetamide or terpolymers of AMPS-N-vinyl-N-methyl acetamide and acrylamide. In the US patent 4,547,299 a method for the preparation of copolymers for aqueous drilling fluid composition was described. The copolymers of N,N-dimethylacrylamide and a (meth)acrylamide, alkyl sulphonic acid or alkali metal salts thereof was used as aqueous drilling fluid. The polymer may be crosslinked with N,N-methylene-bis-acrylamide or other appropriate crosslinking agent. But this drilling fluid was used at 150°F. In the US patent 4.566.978 the use of terpolymer comprising maleic anhydride, styrene and a third monomer selected from acrylamide, methacrylamide, acrylic acid and methacrylic acid as high temperature drilling fluid was disclosed. But, the polymers which is suitable for drilling mud may not be suitable for enhanced oil recovery (EOR). In EOR the polymer should be thermally stable for a long period of time under harsh conditions of reservoir environment . West German patent 3 627 456,1987 describes the terpolymer composition involving acrylamide, sodium acrylates and acrylamido-N-dodecyl N-butyl sulphonate terpolymer as an useful candidate. It was also established that acrylamide terpolymers having a heterocyclic ring in the polymer backbone have been shown to exhibit improved viscosity and shear degradation properties.
The main objective of the present invention is to provide a process for the synthesis of thermally stable copolymers of acrylamide - 2-acrylamido 2-methyl propane
sulphonic acid salt for enhancing petroleum recovery from high temperature subterranean petroleum deposits. The second objective is that the polymer solution should be compatible with dense brine fluid in the reservoir . The polymer solution should not precipitate in presence of monovalent or multivalent brines present in the reservoir. Third objective is to provide a process for the preparation of the thermally stable co-polymer under reservoir conditions of salinity and temperature at least for a period of one month.
Accordingly the present invention provides a process for the preparation of stabilized copolymers useful for enhancing petroleum recovery from high temperature subterranean petroleum deposits which comprises reacting monomer selected from an acrylamide as herein described with 2-acrylamido 2-methyl propane sulphonic acid by solution polymerization wherein weight of acrylamide ranges from 5-95 % weight of 2-acrylamido 2-methyl propane sulphonic acid ranges from 5-95% , in presence of a redox pair of initiators as defined herein , at a temperature range 5-50 ° C, under inert atmosphere selected from nitrogen , helium, argon atmosphere , for a period of 4-10 hrs , neutralizing the resultant polymer with caustic soda solution , adding a thermal stabilizer selected from cross-linking agent N,N-rnethyl bis acrylamide , trimethylopropane triacrylate to get desired stabilized copolymer . High temperature exists on deeper reservoirs where free oxygen is not available . For ideal study this invention is conducted under nitrogen atmosphere.
In an embodiment of the present invention the redox initiator used is selected from sodium metadisulphite-ammonium persulphate , sodium metabisulphite-potassium persulphate , ferrous sulphate-hydrogen peroxide, ferrous sulphate-ammonium persulphate or mixture thereof. In another embodiment of the invention acrylamide used is selected acrylamide , substituted acrylamide such as N,N -dimethyl acrylamide . The thermal stabilizer used in this invention may be selected from crosslinking agent such as N,N-methyl bis acrylamide , trimethylopropane triacrylate in presence of ammonia , formaldehyde . In the another invention of this invention inert atmosphere is used instead of air. The inert atmosphere is selected from nitrogen , helium, argon which prevents any degradation of the polymer by oxidation.
In a feature of the present invention the ratio of acrylamide and 2- acrylamido -2- methypropane sulphonic acid may be in the range of 5-95% and 95-5 % respectively. In another feature of the invention is the concentration of the redox pair of initiator may be in the range of 0, 05 - 1.0. wt% of the total monomer. Conventional method used for isolation of copolymer may be selected from precipitation method by using non-solvent such as acetone, isopropyl alcohol, t-butyl alcohol etc.
The present invention provides a process for the preparation of a thermally stable copolymer which comprises of acrylamide/N,N-dialkyl acrylamide-2acrylamiodo -2-methyl propane sulphonic acid copolymer by solution polymerization using redox pair of initiators at temperature range of 5- 50 °C neutralizing the resultant polymer with caustic soda solution and stabilizing with cross-linker which acts as a thermal stabilizer, the resultant product of which can be applied in deep reservoir having dense brine fluid. It is compatible with reservoir brine and will not precipitate in presence of Ca+ ion. As there is no free oxygen in the deeper reservoir, it is preferable to study the thermal stability under inert atmosphere like, nitrogen. A preferred water soluble copolymer consists of a random distribution of, Fig. 1 : Unit of the structure (a) (5-95%) and Unit of the structure (b) (5-95%).
After the completion of the copolymer reaction, a small amount of a thermal stabilizer may be added as a physical mixture. This will enhance the thermal stability (>120°C) for a very long time. The thermal stabilizer may be selected from the list of cross linking agent for acrylamide preferably. The thermal stability enhances its limit under inert atmospheres.
The effectiveness of the copolymer used according to the present invention as structural viscosity builders consists of two steps, 1) copolymerization followed by 2) stabilization with the help of thermal stabilizer. The stabilized copolymer can be applied to deeper reservoir which contains dense brine as well as higher temperatures. Accordingly, the copolymerization reaction is carried out in aqueous medium using redox pair of initiators. Slow addition of peroxy compound to monomer mixtures
Structure of the monomer units in the polymer
(Structure Removed )
Structure (a) : 5-95% by weight of the unit -
Structure (b): 5-95% by weight of the unit –
(Structure Removed )
Where RI and R2 are the same or different and each may hydrogen, methyl or ethyl and X+ is a cation preferably H+
containing the other members of the redox pair of initiators produces very high molecular weight copolymer.
The polymerization in this present invention is carried out at 5- 50°C, preferably at room temperature. The reaction is carried out under nitrogen atmosphere for about 4-10 h. After the reaction the viscous polymer solution is neutralized with sodium hydroxide solution. The polymer is then isolated from the mixture by precipitating with a non-solvent like, acetone. The ratio of monomers and the intrinsic viscosity of the polymer are determined. The thermal stabilizer can be added as a physical mixture during the course of aging studies. It stabilizes the polymer solution for a long period under inert atmosphere.
The US patent 4,404,111 also disclosed the use of N,N-dimethylacrylamide-2-acrylamido-2-methyl propane sulphonic acid(AMPS) copolymer for enhanced oil recovery from subterranean formations. Without thermal stabilizers, this copolymer was not found to be thermally stable even at 125°C for a month. But the present invention provides a process for the preparation of thermally stable polymer atleast for a long period of time, say, 1-2 months. The following examples are given to illustrate the invention but should not be construed to limit the scope of this invention.
Example 1
Synthesis of the copolymer 1
Recrystallized 2-acrylamido -2-methyl propane sulphonic acid (9g) and distilled
N,N-dimethyl acrylamide (21g) are dissolved in doubly distilled water (240 ml) in a three necked flask fitted with a condenser, a mechanical stirrer and a gas inlet tube. The whole assembly is taken in a thermostatic bath at a temperature of 30°C. Recrystallized Na-metabisulphite (0.33 wt.%) is added to the reaction mixture while a solution of recrystallized ammonium persulphate (0.23 wt.% in 60 ml distilled water) is slowly added from the top of the reaction vessel. Reaction proceeds slowly and
completes within 5h. A small quantity of the reaction mixture is removed and purified by precipitation in acetone. It is then dried in vacuum oven for lOh. The percentage of the monomers and the intrinsic viscosity of the copolymer are presented in the Table 1. The viscous polymer prepared above is neutralized with sodium hydroxide solution (5% aqueous solution). The copolymer is then isolated by precipitating in acetone and dried in vacuum oven at 60°C for 10 h.
Stabilization of viscous polymer solution
About 4.0g of the copolymer prepared is dissolved in 500ml distilled water. 33
ppm of N,N'-methylene bis acrylamide is added to the polymer solution and is thoroughly mixed by using mechanical stirrer. The solution is then allowed to stand in a high temperature reactor under nitrogen atmosphere at 125°C. In every alternate day about 50 ml of the aging sample is withdrawn and their solution viscosity is determined at 25°C. The results are presented in Table 2. After two days of aging at that temperature, the polymer solution acquires stability and the reduction of solution viscosity is negligible.
This polymer solution can also be applied to dense brine water reservoir. The data are reported in table 1. There is no precipitation of the polymer even at 1-2% of CaCl2 concentration. The solution viscosity decreases with the addition of monovalent or bivalent brine. There is an optimum limit of monovalent or bivalent brine concentration beyond which the reduction of solution viscosity is negligible.
Example 2
Synthesis of the copolymer 2
Recrystallized 2-acrylamido -2-methyl propane sulphonic acid (7g) and distilled
N,N-dimethyl acrylamide (13g) are dissolved in doubly distilled water (150 ml) in a three necked flask fitted with a condenser, a mechanical stirrer and a gas inlet tube. The whole assembly is taken in a thermostatic bath at a temperature of 15°C. Recrystallized Na-metabisulphite (0.22 wt.%) is added to the reaction mixture while a solution of recrystallized ammonium persulphate (0.33 wt.% in 20 ml distilled water)
is slowly added from the top of the reaction vessel. Reaction proceeds slowly and completes within 5h. A small quantity of the reaction mixture is removed and purified by precipitation in acetone. It is then dried in vacuum oven for lOh. The percentage of the monomers and the intrinsic viscosity of the copolymer are presented in the Table 1. The viscous polymer prepared above is neutralized with sodium hydroxide solution (2% aqueous solution). The copolymer is then isolated by precipitating in acetone and dried in vacuum oven at 60°C for 10 h.
Stabilization of viscous polymer solution
About 4.0g of the copolymer prepared is dissolved in 500ml distilled water. 60
ppm of N,N'-methylene bis acrylamide is added to the polymer solution and is thoroughly mixed by using mechanical stirrer. The solution is then allowed to stand in a high temperature reactor under nitrogen atmosphere at 125°C. In every alternate day about 50 ml of the aging sample is withdrawn and their solution viscosity is determined at 25°C. The results are presented in Table 2. After two days of aging at that temperature, the polymer solution acquires stability and the reduction of solution viscosity is negligible.This polymer solution can also be applied to dense brine water reservoir. The data are reported in table 1. There is no precipitation of the polymer even at 1-2% of CaCla concentration. The solution viscosity decreases with the addition of monovalent or bivalent brine. There is an optimum limit of monovalent or bivalent brine concentration beyond which the reduction of solution viscosity is negligible.
Example 3
Synthesis of the copolymer 3
Recrystallized 2-acrylamido -2-methyl propane sulphonic acid (6g) and recrystellized acrylamide (14g) are dissolved in doubly distilled water (160 ml) in a three necked flask fitted with a condenser, a mechanical stirrer and a gas inlet tube. The whole assembly is taken in a thermostatic bath at a temperature of 30°C. Recrystallized Na-metabisulphite (0.25 wt.%) is added to the reaction mixture while a solution of recrystallized ammonium persulphate (0.2 wt.% in 60 ml distilled water)
is slowly added from the top of the reaction vessel. Reaction proceeds slowly and completes within 5h. A small quantity of the reaction mixture is removed and purified by precipitation in acetone. It is then dried in vacuum oven for lOh. The percentage of the monomers and the intrinsic viscosity of the copolymer are determined. The viscous polymer prepared above is neutralized with sodium hydroxide solution (2% aqueous solution). The copolymer is then isolated by precipitating in acetone and dried in vacuum oven at 60°C for 10 h.
Stabilization of viscous polymer solution
About 4.0g of the copolymer prepared is dissolved in 500ml distilled water. 50
ppm of N,N'-methylene bis acrylamide is added to the polymer solution and is thoroughly mixed by using mechanical stirrer. The solution is then allowed to stand in a high temperature reactor under nitrogen atmosphere at 125°C. In every alternate day about 50 ml of the aging sample is withdrawn and their solution viscosity is determined at 25°C. The polymer solution acquires stability under nitrogen atmosphere and the reduction of solution viscosity is negligible.
This polymer solution can also be applied to dense brine water reservoir. There is no precipitation of the polymer even at 1-2% of CaCl2 concentration. The solution viscosity decreases with the addition of monovalent or bivalent brine. There is an optimum limit of monovalent or bivalent brine concentration beyond which the reduction of solution viscosity is negligible.
Example 4
Synthesis of the copolymer 4
Recrystallized 2-acrylamido -2-methyl propane sulphonic acid (3g) and distilled N,N-dimethyl acrylamide (17g) are dissolved in doubly distilled water (150 ml) in a three necked flask fitted with a condenser, a mechanical stirrer and a gas inlet tube. The whole assembly is taken in a thermostatic bath at a temperature of 45 °C. Recrystallized Na-metabisulphite (0.2 wt.%) is added to the reaction mixture while a solution of recrystallized potassium persulphate (0.15 wt.% in 10 ml distilled water)
is slowly added from the top of the reaction vessel. Reaction proceeds slowly and completes within 5h. A small quantity of the reaction mixture is removed and purified by precipitation in acetone. It is then dried in vacuum oven for lOh. The percentage of the monomers and the intrinsic viscosity of the copolymer are determined. The viscous polymer prepared above is neutralized with sodium hydroxide solution (2% aqueous solution). The copolymer is then isolated by precipitating in acetone and dried in vacuum oven at 60°C for 10 h.
Stabilization of viscous polymer solution
About 4.0g of the copolymer prepared is dissolved in 500ml distilled water. 55 ppm of N,N'-methylene bis acrylamide is added to the polymer solution and is thoroughly mixed by using mechanical stirrer. The solution is then allowed to stand in a high temperature reactor at 125°C unde nitrogen atmosphere. In every alternate day about 50 ml of the aging sample is withdrawn and their solution viscosity is determined at 25°C. After 3/4 days of aging at that temperature, the polymer solution acquires stability and the reduction of solution viscosity is negligible.
This polymer solution can also be applied to dense brine water reservoir. The data are reported in table 1. There is no precipitation of the polymer even at 1-2% of CaCl2 concentration. The solution viscosity decreases with the addition of monovalent or bivalent brine. There is an optimum limit of monovalent or bivalent brine concentration beyond which the reduction of solution viscosity is negligible.
Example 5
Synthesis of the copolymer 5
Recrystallized 2-acrylamido -2-methyl propane sulphonic acid (8g) and distilled N,N-dimethyl acrylamide (12g) are dissolved in doubly distilled water (140 ml) in a three necked flask fitted with a condenser, a mechanical stirrer and a gas inlet tube. The whole assembly is taken in a thermostatic bath at a temperature of 45°C. Recrystallized Na-metabisulphite (0.32 wt.%) is added to the reaction mixture while a
solution of recrystallized potassium persulphate (0.23 wt.% in 20 ml distilled water) is slowly added from the top of the reaction vessel. Reaction proceeds slowly and completes within 5h. A small quantity of the reaction mixture is removed and purified by precipitation in acetone. It is then dried in vacuum oven for lOh. The percentage of the monomers and the intrinsic viscosity of the copolymer are determined. The viscous polymer prepared above is neutralized with sodium hydroxide solution (2% aqueous solution). The copolymer is then isolated by precipitating in acetone and dried in vacuum oven at 60°C for 10 h.
Stabilization of viscous polymer solution
About 4.0g of the copolymer prepared is dissolved in 500ml distilled water. 40 ppm of N,N'-methylene bis acrylamide is added to the polymer solution and is thoroughly mixed by using mechanical stirrer. The solution is then allowed to stand in a high temperature reactor at 125°C under nitrogen atmosphere. In every alternate day about 50 ml of the aging sample is withdrawn and their solution viscosity is determined at 25°C. The results are presented in Table 2. After 3/4days of aging at that temperature, the polymer solution acquires stability and the reduction of solution viscosity is negligible.
This polymer solution can also be applied to dense brine water reservoir. There is no precipitation of the polymer even at 1-2% of CaCl2 concentration. The solution viscosity decreases with the addition of monovalent or bivalent brine. There is an optimum limit of monovalent or bivalent brine concentration beyond which the reduction of solution viscosity is negligible
Table 1

(Table Removed )
*A=acrylamide/N,N-dimethylacrylamide; B = 2-acrylamido-2-methylpropane sulphonate
Table 2

(Table Removed )
Solution without stabilizer

We Claim
1. A process for the preparation of stabilized copolymers useful for enhancing petroleum
recovery from high temperature subterranean petroleum deposits which comprises
reacting monomer selected from an acrylamide as herein described with 2-acrylamido
2-methyl propane sulphonic acid by solution polymerization wherein weight of
acrylamide ranges from 5-95 % weight of 2-acrylamido 2-methyl propane sulphonic acid
ranges from 5-95% , in presence of a redox pair of initiators as defined herein , at a
temperature range 5-50 ° C, under inert atmosphere selected from nitrogen , helium, argon
atmosphere , for a period of 4-10 hrs , neutralizing the resultant polymer with caustic
soda solution , adding a thermal stabilizer selected from cross-linking agent N,N-methyl
bis acrylamide, trimethylopropane triacrylate to get desired stabilized copolymer .
2. A process as claimed in claim 1 wherein the redox pair of initiator used is selected from
sodium metabisulphite-ammonium persulphate , sodium metabisulphite-potassium
persulphate , ferrous sulphate-hydrogen peroxide, ferrous sulphate-ammonium
persulphate or mixture thereof.
3. A process as claimed in claims 1 and 2 wherein the monomer to solvent ratio is in the
range of 1:4 to 1:10.
4. A process as claimed in claims 1-3 wherein the amount of N,N-methyl bis acrylamide
used to stabilize copolymer is ranging 30-600 ppm.
5. A process for the preparation of stabilized copolymers useful for enhancing petroleum recovery from high temperature subterranean petroleum deposits substantially as herein described with reference to the examples.

Documents:

223-del-2001-abstract.pdf

223-del-2001-claims.pdf

223-del-2001-correspondence-others.pdf

223-del-2001-correspondence-po.pdf

223-del-2001-description (complete).pdf

223-del-2001-form-1.pdf

223-del-2001-form-19.pdf

223-del-2001-form-2.pdf

223-del-2001-form-3.pdf

« Previous Patent

Next Patent »

Patent Number

231672

Indian Patent Application Number

223/DEL/2001

PG Journal Number

13/2009

Publication Date

27-Mar-2009

Grant Date

07-Mar-2009

Date of Filing

28-Feb-2001

Name of Patentee

COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH

Applicant Address

RAFI MARG, NEW DELHI-110001, INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	ANUPOM SABHAPONDIT	REGIONAL RESEARCH LABORATORY, JORHAT-785006, ASSAM, INDIA.
2	ANUJJAL SARMAH	REGIONAL RESEARCH LABORATORY, JORHAT-785006, ASSAM, INDIA.
3	ARUN BORTHAKUR	REGIONAL RESEARCH LABORATORY, JORHAT-785006, ASSAM, INDIA.

PCT International Classification Number

E21 B48/22

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA