High-temperature and high-salt-adapted viscosity-increasing oil displacement system, preparation method and application thereof

Abstract

The application relates to the technical field of oil and gas field development, and discloses a high-temperature and high-salt adaptive variable-viscosity oil displacement system, a preparation method and application thereof, the oil displacement system comprising 0.06-0.15% of click grafting type fluorocarbon hydrophobic association polymer, 0.002-0.06% of fluorocarbon anion surfactant and the balance of water; the click grafting type fluorocarbon hydrophobic association polymer is polyacrylamide grafted with fluorocarbon hydrophobic groups through a thiol-ene click reaction; the oil displacement system is precisely grafted through a click chemistry technology, and the matching hydrophobic effect of the fluorocarbon groups is combined, so that the problem that an existing variable-viscosity oil displacement system cannot adapt to an ultrahigh-temperature and high-salt oil reservoir is solved; under extreme conditions of a temperature of 90-120 DEG C and a salinity of 100000-200000 mg / L, the oil displacement system can still maintain stable variable-viscosity performance, has strong shear resistance, can effectively improve a heavy oil recovery rate, and is suitable for development and application of an ultradepth heavy oil reservoir.

Description

Technical Field

[0001] This invention relates to the field of oil and gas field development technology, and more specifically, to a high-temperature and high-salinity adaptive viscosity displacement system, its preparation method, and its application. Background Technology

[0002] As conventional oil reservoir development progresses, ultra-high temperature and high salinity deep heavy oil reservoirs are gradually becoming the focus of development. Variable viscosity displacement technology, as a highly efficient heavy oil development technology, solves the problems of poor injectability and insufficient mobility control in polymer flooding by injecting low-viscosity oil and increasing formation viscosity.

[0003] However, existing viscosity-modifying oil displacement systems, which use alkyl hydrophobic associating polymers and anionic surfactants, are not suitable for deep heavy oil reservoirs with ultra-high temperature and high salinity. This is a technical problem that needs to be solved urgently: the hydrophobic associating polymers in existing technologies are all copolymerized with hydrophobic monomers and acrylamide free radicals. The hydrophobic monomers have poor water solubility and are prone to homopolymerization, resulting in uneven distribution of hydrophobic groups. Under high salinity and high temperature conditions, the associative effect is very easy to fail. At the same time, the alkyl hydrophobic groups and surfactants used in existing technologies have poor temperature and salt resistance. Under conditions where the temperature exceeds 90℃ and the salinity exceeds 100,000 mg / L, the hydrophobic effect will be greatly reduced, and stable viscosity-modifying performance cannot be achieved.

[0004] Therefore, developing a variable viscosity displacement system that can be adapted to ultra-high temperature and high salinity reservoirs is of great significance. Summary of the Invention

[0005] In view of this, the present invention provides a high-temperature and high-salinity adaptive viscosity displacement system, its preparation method and application. This displacement system, through click chemistry precise grafting technology, combined with the matching hydrophobic effect of fluorocarbon groups, solves the problem that existing viscosity displacement systems cannot be adapted to ultra-high temperature and high-salinity reservoirs. Under extreme conditions of 90~120℃ and salinity of 100,000~200,000 mg / L, it can still maintain stable viscosity-adjusting properties, has strong shear resistance, and can effectively improve the recovery rate of heavy oil, making it suitable for the development and application of ultra-deep heavy oil reservoirs.

[0006] The technical solution of this invention is as follows:

[0007] In a first aspect, the present invention provides a high-temperature and high-salt-adapted variable viscosity oil displacement system, the oil displacement system comprising 0.06% to 0.15% by mass of click-grafted fluorocarbon hydrophobic associative polymer, 0.002% to 0.06% by mass of fluorocarbon anionic surfactant and the balance being water;

[0008] The click-grafted fluorocarbon hydrophobic associative polymer is a polyacrylamide grafted with fluorocarbon hydrophobic groups via a mercapto-olefin click reaction.

[0009] Furthermore, the fluorocarbon hydrophobic group includes at least one of perfluorobutyl, perfluorohexyl, and perfluorooctyl.

[0010] Furthermore, the fluorocarbon anionic surfactant includes at least one of sodium perfluorohexyl sulfonate, sodium perfluorooctyl sulfonate, sodium perfluorohexyl phosphate, and sodium perfluorooctyl phosphate.

[0011] Further, it includes an oil displacement aid with a mass fraction of 0.001% to 0.01%, wherein the oil displacement aid includes at least one of a cosolvent, an antioxidant, and a demulsifier.

[0012] Further, the cosolvent includes at least one of ethylene glycol butyl ether and propylene glycol methyl ether; the antioxidant includes at least one of dilauryl thiodipropionate and 2,6-di-tert-butyl-p-cresol; and the demulsifier includes at least one of polyoxyethylene polyoxypropylene block copolymer and alkylphenol polyoxyethylene ether.

[0013] Furthermore, the grafting rate of fluorocarbon hydrophobic groups in the click-grafted fluorocarbon hydrophobic associative polymer is 1.5% to 3%.

[0014] Furthermore, the molecular weight of the click-grafted fluorocarbon hydrophobic associative polymer is 8 × 10⁻⁶. 6 ~1.5×10 7 .

[0015] Secondly, based on the same inventive concept, this invention provides a method for preparing the high-temperature, high-salt adaptive viscosity displacement system as described in any of the first aspects, comprising the following steps:

[0016] Acrylamide and mercaptoacetic acid were dissolved in deionized water to prepare a monomer solution with a mass concentration of 15%-20%. The solution was deoxygenated by purging with nitrogen for 30 min, and an initiator was added. The reaction was carried out at 30-40℃ for 6-8 h to obtain a mercapto-modified polyacrylamide backbone solution. The amount of mercaptoacetic acid used was 0.01%-0.1% of the total mass of the mercapto-modified polyacrylamide backbone solution.

[0017] An alkenyl-modified fluorocarbon hydrophobic monomer and a photoinitiator were added to the thiolized polyacrylamide backbone solution. The click grafting reaction was carried out for 2-4 hours under ultraviolet light irradiation and at 20-30°C. The product was then precipitated with anhydrous ethanol, and the precipitate was collected and vacuum dried at 50-60°C to obtain a dry powder of the click-grafted fluorocarbon hydrophobic associative polymer.

[0018] The dry powder of the click-grafted fluorocarbon hydrophobic associative polymer was dissolved in water and stirred at 100-300 rpm for 1.5-3 hours at 35-50°C to prepare a polymer mother liquor with a mass concentration of 0.3%-0.4%.

[0019] Dissolve the fluorocarbon anionic surfactant in water and stir at 80-150 rpm for 0.3-1 h at 35-45℃ to prepare a surfactant stock solution with a mass concentration of 0.15%-0.2%.

[0020] The polymer mother liquor and the surfactant mother liquor are mixed with water and stirred at 35-45°C for 1-2 hours to obtain the oil displacement system.

[0021] Furthermore, the initiator includes at least one of azobisisobutyronitrile (AIBN) and ammonium persulfate-sodium bisulfite redox initiator; the photoinitiator is 2-hydroxy-2-methylphenylacetone.

[0022] Thirdly, based on the same inventive concept, this invention provides the application of the high-temperature and high-salt adaptive viscosity displacement system described in any one of the first aspects, or the high-temperature and high-salt adaptive viscosity displacement system prepared by the preparation method described in any one of the second aspects, in oil displacement in reservoirs with temperatures of 90-120℃ and salinity of 100,000-200,000 mg / L.

[0023] Compared with the prior art, the embodiments of the present invention have at least the following advantages or beneficial effects:

[0024] 1. Under extreme conditions of 120℃ and 200,000 mg / L salinity, the viscosity retention rate of the system of the present invention can reach more than 90% after aging for 7 days, which solves the long-standing technical problem that existing viscosity-changing systems cannot be adapted to ultra-high temperature and high-salinity reservoirs.

[0025] 2. The viscosity of the system of the present invention can vary by more than 10 times with the concentration of surfactant. The low viscosity ensures injectability during injection, and the viscosity-increasing effect in the formation regulates the mobility. The viscosity variation range is much higher than that of the prior art, which can effectively reduce the mobility ratio with heavy oil.

[0026] 3. After high-speed shearing, the viscosity retention rate of the system of the present invention can reach more than 90%, which ensures the effective viscosity of the agent after high shearing in the near-wellbore zone and avoids performance failure caused by shear degradation.

[0027] 4. The system of the present invention can increase the recovery rate by more than 7-8 percentage points on the basis of water flooding, with significant oil displacement effect, and can effectively improve the final recovery rate of the reservoir. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0030] To address the technical problems existing in the prior art, according to one aspect of the embodiments of this disclosure, a high-temperature and high-salt adaptive viscosity displacement system is provided. The displacement system includes 0.06% to 0.15% by mass of click-grafted fluorocarbon hydrophobic associative polymer, 0.002% to 0.06% by mass of fluorocarbon anionic surfactant, and the balance being water.

[0031] Click-grafted fluorocarbon hydrophobic associative polymers are polyacrylamides grafted with fluorocarbon hydrophobic groups via a mercapto-olefin click reaction.

[0032] In some examples, the mass fraction of the grafted fluorocarbon hydrophobic associative polymer can be selected from any value between 0.06% and 0.15%; the mass fraction of the fluorocarbon anionic surfactant can be selected from any value between 0.002% and 0.06%.

[0033] For example, the mass fraction of click-grafted fluorocarbon hydrophobic associating polymers includes, but is not limited to, 0.06%, 0.07%, 0.09%, 0.1%, 0.12%, 0.14%, or 0.15%; the mass fraction of fluorocarbon anionic surfactants includes, but is not limited to, 0.002%, 0.003%, 0.005%, 0.008%, 0.01%, 0.02%, 0.025%, 0.04%, or 0.06%.

[0034] In some examples, the fluorocarbon hydrophobic group includes at least one of perfluorobutyl, perfluorohexyl, and perfluorooctyl.

[0035] In some examples, the fluorocarbon anionic surfactant includes at least one of sodium perfluorohexyl sulfonate, sodium perfluorooctyl sulfonate, sodium perfluorohexyl phosphate, and sodium perfluorooctyl phosphate.

[0036] In some examples, the oil displacement agent is included at a mass fraction of 0.001% to 0.01%, and the oil displacement agent includes at least one of a cosolvent, an antioxidant, and a demulsifier.

[0037] In some examples, the cosolvent includes at least one of ethylene glycol butyl ether and propylene glycol methyl ether; the antioxidant includes at least one of dilauryl thiodipropionate and 2,6-di-tert-butyl-p-cresol; and the demulsifier includes at least one of polyoxyethylene polyoxypropylene block copolymer and alkylphenol polyoxyethylene ether.

[0038] In some examples, the grafting rate of fluorocarbon hydrophobic groups in click-grafted fluorocarbon hydrophobic associative polymers is 1.5% to 3%.

[0039] In some examples, the molecular weight of the click-grafted fluorocarbon hydrophobic associative polymer is 8 × 10⁻⁶. 6 ~1.5×10 7 .

[0040] It should be noted that this invention addresses the pain points in the development of ultra-high temperature and high salinity heavy oil reservoirs by systematically solving the inherent defects of existing technologies at the molecular level:

[0041] On the one hand, the alkyl hydrophobic groups used in conventional systems have limited bond energies in their CH bonds, making them prone to thermal degradation at high temperatures. At the same time, the hydrophobic effect of alkyl groups will rapidly decay under high salt conditions due to charge shielding, leading to the collapse of the association network. On the other hand, the free radical copolymerization method that the industry has used for decades inherently suffers from poor water solubility and easy homopolymerization of hydrophobic monomers, resulting in extremely uneven distribution of hydrophobic groups on the polymer chain. Some regions are too dense, while others are too sparse. Under extreme conditions, the sparse regions cannot form stable associations, while the dense regions are prone to intramolecular associations, ultimately causing the entire network to fail completely.

[0042] To fundamentally address these two shortcomings, this approach, starting from the logic of molecular synthesis and bypassing the inherent defects of copolymerization, adopts a two-step method: first synthesizing the main chain, then grafting hydrophobic groups. It introduces thiol-alkene click chemistry from the field of organic synthesis. First, a polyacrylamide main chain with site-specific thiol groups is synthesized through controlled free radical polymerization, precisely controlling the number and distribution of thiol groups. Then, through an efficient click reaction, fluorocarbon hydrophobic groups are precisely grafted onto the thiol sites. This process completely avoids the homopolymerization problem of hydrophobic monomers during copolymerization, resulting in a uniformly spaced distribution of fluorocarbon hydrophobic groups on the polymer chain. The distance between each hydrophobic group is completely controllable, ensuring that all hydrophobic groups can participate in intermolecular association under extreme conditions, preventing network collapse caused by uneven distribution.

[0043] Building upon this foundation, the stability of the hydrophobic groups themselves has been further enhanced by replacing the conventional CH bonds with CF bonds, which have a bond energy as high as 485 kJ / mol. The fluorocarbon groups exhibit extremely high chemical stability and will not undergo thermal degradation at a high temperature of 120°C. At the same time, the extremely low polarizability of fluorine atoms makes the hydrophobic interactions between fluorocarbon groups far stronger than those of conventional alkyl groups. This fluorine-fluorine interaction will not be attenuated by the charge shielding of high salt; on the contrary, it will be further enhanced under high salt conditions due to the salting-out effect, thus solving the problem of hydrophobic interaction failure under extreme conditions.

[0044] Furthermore, neither fluorocarbon polymers nor fluorocarbon surfactants alone can achieve optimal results. Only a matched system of both can maximize the advantages of fluorine-fluorine hydrophobic interactions by utilizing the synergistic effect of hydrophobic groups with the same structure. During the injection stage, the high concentration of fluorocarbon surfactants allows their hydrophobic chains to precisely insert into the fluorocarbon hydrophobic microregions of the polymer, completely disrupting intermolecular associations and resulting in an injection viscosity as low as about 8 mPa·s, ensuring excellent injectability. During the formation stage, as the surfactant is adsorbed by the rock and its concentration decreases, a uniform association network is reformed between the fluorocarbon groups of the polymer, increasing the viscosity to over 180 mPa·s, achieving a viscosity change of more than 20 times. Meanwhile, the rigid structure of the fluorocarbon groups and the uniform association network also greatly enhance the shear resistance of the system. When subjected to high shear, the association network will only be temporarily damaged. After the shear disappears, the hydrophobic effect will be quickly restored and no irreversible degradation will occur. Therefore, the viscosity retention rate can reach more than 90%, and after aging at 120℃ for 90 days, the viscosity retention rate can still exceed 92%, which fully meets the requirements of long-term oil displacement and finally achieves stable viscosity-changing oil displacement under extreme conditions.

[0045] According to another aspect of the embodiments of this application, a method for preparing a high-temperature and high-salt adaptive viscosity displacement system is also provided, specifically including: dissolving acrylamide and mercaptoacetic acid in deionized water to prepare a monomer solution with a mass concentration of 15%-20%, purging with nitrogen for 30 min to remove oxygen, adding an initiator, and reacting at 30-40°C for 6-8 h to obtain a mercapto-modified polyacrylamide backbone solution, wherein the amount of mercaptoacetic acid used is 0.01%-0.1% of the total mass of the mercapto-modified polyacrylamide backbone solution;

[0046] An alkenyl-modified fluorocarbon hydrophobic monomer and a photoinitiator were added to a solution of thiolized polyacrylamide backbone. The click grafting reaction was carried out for 2-4 hours under ultraviolet light irradiation and at 20-30℃. The product was then precipitated with anhydrous ethanol, and the precipitate was collected and vacuum dried at 50-60℃ to obtain a dry powder of click-grafted fluorocarbon hydrophobic associative polymer.

[0047] Dissolve the dry powder of the click-grafted fluorocarbon hydrophobic associative polymer in water and stir at 100-300 rpm for 1.5-3 hours at 35-50℃ to prepare a polymer mother liquor with a mass concentration of 0.3%-0.4%.

[0048] Dissolve the fluorocarbon anionic surfactant in water and stir at 80-150 rpm for 0.3-1 h at 35-45℃ to prepare a surfactant stock solution with a mass concentration of 0.15%-0.2%.

[0049] The polymer mother liquor and surfactant mother liquor are mixed with water and stirred at 35-45℃ for 1-2 hours to obtain the oil displacement system.

[0050] It should be noted that the alkenyl-modified fluorocarbon hydrophobic monomer is the alkenylated product corresponding to the target fluorocarbon hydrophobic group: when the target grafted fluorocarbon hydrophobic group is perfluorohexyl, the monomer is perfluorohexylethylene; when the target grafted fluorocarbon hydrophobic group is perfluorooctyl, the monomer is perfluorooctylethylene; when the target grafted fluorocarbon hydrophobic group is perfluorobutyl, the monomer is perfluorobutylethylene.

[0051] The modification process involves introducing an alkenyl reaction site at the end of the fluorocarbon alkyl group to react with the thiol group of the main chain. After the reaction is completed, the alkenyl group is converted into a thioether bond connecting the main chain and the fluorocarbon hydrophobic group. The fluorocarbon hydrophobic group is finally grafted onto the polyacrylamide main chain.

[0052] Furthermore, the aforementioned mercaptoacetic acid, also known as thioglycolic acid, is used as a chain transfer agent in the polymerization reaction of the present invention.

[0053] It should also be noted that the mixing ratio of the polymer mother liquor and the surfactant mother liquor can be calculated based on the target component content of the final system and the concentration of the mother liquor. Since the system components of the present invention can be adjusted according to reservoir conditions, this ratio is an adjustable parameter. Those skilled in the art can calculate and adjust it according to actual needs, without the need for a fixed value, and it is not limited here.

[0054] In some examples, the initiator includes at least one of azobisisobutyronitrile (AIBN) and ammonium persulfate-sodium bisulfite redox initiator; the photoinitiator is 2-hydroxy-2-methylphenylacetone.

[0055] It should be noted that all the raw materials and reagents mentioned in the preparation process can be purchased commercially, and the raw materials purchased from different channels will not affect the technical effect of the present invention. Those skilled in the art can choose for themselves, and no limitation is made here.

[0056] According to another aspect of the embodiments of this application, the application of the high-temperature and high-salt adaptive viscosity displacement system described in any one of the first aspects or the high-temperature and high-salt adaptive viscosity displacement system prepared by the preparation method described in any one of the second aspects in oil displacement in reservoirs with temperatures of 90-120°C and salinity of 100,000-200,000 mg / L is also provided.

[0057] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless otherwise specified, are generally performed according to national standards. If no corresponding national standard exists, then generally accepted international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0058] Example 1

[0059] Example 1 provides a high-temperature, high-salt-adapted viscosity-modulating oil displacement system and its preparation method. The mass fraction of each component is as follows: 0.1% of a click-grafted fluorocarbon hydrophobic associative polymer, wherein the fluorocarbon hydrophobic group is perfluorohexyl, the grafting rate is 2%, and the polymer molecular weight is 1×10⁻⁶. 7 0.03% fluorocarbon anionic surfactant, sodium perfluorohexyl sulfonate; the balance is simulated formation water with a salinity of 200,000 mg / L and Ca... 2+ +Mg 2+ The content is 1500 mg / L, and the specific preparation method is as follows:

[0060] Acrylamide monomer and mercaptoacetic acid chain transfer agent were dissolved in deionized water to prepare a monomer solution with an acrylamide mass concentration of 18%, wherein the amount of mercaptoacetic acid was 0.05% of the total mass of the solution. After purging with nitrogen for 30 min to remove oxygen, ammonium persulfate-sodium bisulfite redox initiator was added, and a controlled free radical polymerization reaction was carried out at 35 °C for 7 h to obtain a mercapto-modified polyacrylamide main chain solution.

[0061] Perfluorohexylethylene and 2-hydroxy-2-methylphenylacetone photoinitiator were added to the above main chain solution, and the click grafting reaction was carried out at 25°C for 3 hours under 365nm ultraviolet light irradiation. The solution after reaction was precipitated with anhydrous ethanol, and the precipitate was dried under vacuum at 55°C to obtain the click-grafted fluorocarbon hydrophobic associative polymer dry powder.

[0062] The polymer powder obtained above was dissolved in simulated formation water and stirred at 200 rpm for 2 hours at 40°C to prepare a polymer mother liquor with a mass concentration of 0.35%.

[0063] Sodium perfluorohexyl sulfonate was dissolved in simulated formation water and stirred at 100 rpm for 0.5 h at 40 °C to prepare a surfactant stock solution with a mass concentration of 0.18%.

[0064] Two mother liquors were taken, simulated formation water was added, and the mixture was stirred at 40°C for 1.5 hours to obtain an oil displacement system.

[0065] Example 2

[0066] Example 2 provides a high-temperature, high-salt adaptive viscosity displacement system and its preparation method. The mass fraction of each component is as follows: 0.06% of click-grafted fluorocarbon hydrophobic associative polymer, wherein the fluorocarbon hydrophobic group is perfluorobutyl, the grafting rate is 1.5%, and the polymer molecular weight is 8 × 10⁻⁶. 6 0.002% fluorocarbon anionic surfactant, sodium perfluorobutyl sulfonate; the balance is simulated formation water with a salinity of 100,000 mg / L, Ca 2+ +Mg 2+The content is 1000 mg / L, and the specific preparation method is as follows:

[0067] Acrylamide monomer and mercaptoacetic acid chain transfer agent were dissolved in deionized water to prepare a monomer solution with an acrylamide mass concentration of 15%, wherein the amount of mercaptoacetic acid was 0.1% of the total mass of the solution. After purging with nitrogen for 30 min to remove oxygen, azobisisobutyronitrile initiator was added, and a controlled free radical polymerization reaction was carried out at 30 °C for 8 h to obtain a mercapto-modified polyacrylamide backbone solution.

[0068] Perfluorobutylethylene and 2-hydroxy-2-methylphenylacetone photoinitiator were added to the above main chain solution, and the click grafting reaction was carried out at 20°C for 4 hours under 365nm ultraviolet light irradiation. The solution after reaction was precipitated with anhydrous ethanol, and the precipitate was dried under vacuum at 50°C to obtain the click-grafted fluorocarbon hydrophobic associative polymer dry powder.

[0069] The polymer powder obtained above was dissolved in simulated formation water and stirred at 100 rpm for 3 hours at 35°C to prepare a polymer mother liquor with a mass concentration of 0.3%.

[0070] Sodium perfluorobutyl sulfonate was dissolved in simulated formation water and stirred at 80 rpm for 1 hour at 35°C to prepare a surfactant stock solution with a mass concentration of 0.15%.

[0071] Two mother liquors were taken, simulated formation water was added, and the mixture was stirred at 35°C for 2 hours to obtain an oil displacement system.

[0072] Example 3

[0073] Example 3 provides a high-temperature, high-salt adaptive viscosity displacement system and its preparation method. The mass fraction of each component is as follows: 0.15% of click-grafted fluorocarbon hydrophobic associative polymer, wherein the fluorocarbon hydrophobic group is perfluorooctyl, the grafting rate is 3%, and the polymer molecular weight is 1.5 × 10⁻⁶. 7 0.06% fluorocarbon anionic surfactant, sodium perfluorooctyl phosphate; the balance is simulated formation water with a salinity of 180,000 mg / L, Ca... 2+ +Mg 2+ The content is 1200 mg / L, and the specific preparation method is as follows:

[0074] Acrylamide monomer and mercaptoacetic acid chain transfer agent were dissolved in deionized water to prepare a monomer solution with an acrylamide mass concentration of 20%, wherein the amount of mercaptoacetic acid was 0.01% of the total mass of the solution. After purging with nitrogen for 30 min to remove oxygen, ammonium persulfate-sodium bisulfite redox initiator was added, and a controlled free radical polymerization reaction was carried out at 40 °C for 6 h to obtain a mercapto-modified polyacrylamide backbone solution.

[0075] Perfluorooctylethylene and 2-hydroxy-2-methylphenylacetone photoinitiator were added to the above main chain solution, and a click grafting reaction was carried out at 30°C for 2 hours under 365nm ultraviolet light irradiation. The solution after reaction was precipitated with anhydrous ethanol, and the precipitate was dried under vacuum at 60°C to obtain a dry powder of click-grafted fluorocarbon hydrophobic associative polymer.

[0076] The polymer powder obtained above was dissolved in simulated formation water and stirred at 300 rpm for 1.5 h at 50°C to prepare a polymer mother liquor with a mass concentration of 0.4%.

[0077] Sodium perfluorooctyl phosphate was dissolved in simulated formation water and stirred at 150 rpm for 0.3 h at 45 °C to prepare a surfactant stock solution with a mass concentration of 0.2%.

[0078] Two mother liquors were taken, simulated formation water was added, and the mixture was stirred at 45°C for 1 hour to obtain an oil displacement system.

[0079] Example 4

[0080] Example 4 provides a high-temperature, high-salt adaptive viscosity displacement system and its preparation method. The mass fraction of each component is as follows: 0.12% of click-grafted fluorocarbon hydrophobic associative polymer, wherein the fluorocarbon hydrophobic group is perfluorohexyl, the grafting rate is 2.5%, and the polymer molecular weight is 1.2 × 10⁻⁶. 7 ; 0.04% fluorocarbon anionic surfactant, sodium perfluorohexyl phosphate; 0.007% oil displacement aid, including 0.005% ethylene glycol butyl ether and 0.002% 2,6-di-tert-butyl-p-cresol; the balance is simulated formation water with a salinity of 150,000 mg / L, Ca 2+ +Mg 2+ The content is 1100 mg / L, and the specific preparation method is as follows:

[0081] Acrylamide monomer and mercaptoacetic acid chain transfer agent were dissolved in deionized water to prepare a monomer solution with an acrylamide mass concentration of 17%, wherein the amount of mercaptoacetic acid was 0.03% of the total mass of the solution. After purging with nitrogen for 30 min to remove oxygen, azobisisobutyronitrile initiator was added, and a controlled free radical polymerization reaction was carried out at 38 °C for 7 h to obtain a mercapto-modified polyacrylamide backbone solution.

[0082] Perfluorohexylethylene and 2-hydroxy-2-methylphenylacetone photoinitiator were added to the above main chain solution, and the click grafting reaction was carried out at 25°C for 3 hours under 365nm ultraviolet light irradiation. The solution after reaction was precipitated with anhydrous ethanol, and the precipitate was dried under vacuum at 55°C to obtain the click-grafted fluorocarbon hydrophobic associative polymer dry powder.

[0083] The polymer powder obtained above was dissolved in simulated formation water and stirred at 250 rpm for 1.8 h at 45°C to prepare a polymer mother liquor with a mass concentration of 0.38%.

[0084] Sodium perfluorohexyl phosphate, ethylene glycol butyl ether, and 2,6-di-tert-butyl-p-cresol were dissolved in simulated formation water and stirred at 120 rpm for 0.6 h at 40 °C to prepare a surfactant stock solution with a mass concentration of 0.19%.

[0085] Two mother liquors were taken, simulated formation water was added, and the mixture was stirred at 40°C for 1.2 hours to obtain an oil displacement system.

[0086] Example 5

[0087] Example 5 provides a high-temperature, high-salt adaptive viscosity displacement system and its preparation method. The mass fraction of each component is as follows: 0.08% of click-grafted fluorocarbon hydrophobic associative polymer, wherein the fluorocarbon hydrophobic groups are perfluorohexyl and perfluorobutyl (mass ratio 1:1), the grafting rate is 2%, and the polymer molecular weight is 1.1 × 10⁻⁶. 7 0.01% fluorocarbon anionic surfactant, consisting of sodium perfluorohexyl sulfonate and sodium perfluorooctyl sulfonate (mass ratio 1:1); the balance is simulated formation water with a salinity of 120,000 mg / L and Ca... 2+ +Mg 2+ The content is 900 mg / L, and the specific preparation method is as follows:

[0088] Acrylamide monomer and mercaptoacetic acid chain transfer agent were dissolved in deionized water to prepare a monomer solution with an acrylamide mass concentration of 16%, wherein the amount of mercaptoacetic acid was 0.06% of the total mass of the solution. After purging with nitrogen for 30 min to remove oxygen, ammonium persulfate-sodium bisulfite redox initiator was added, and a controlled free radical polymerization reaction was carried out at 36 °C for 7.5 h to obtain a mercapto-modified polyacrylamide backbone solution.

[0089] To the above main chain solution, perfluorohexylethylene and perfluorobutylethylene (mass ratio 1:1), as well as 2-hydroxy-2-methylphenylacetone photoinitiator, were added. The click grafting reaction was carried out at 25°C for 3 hours under 365nm ultraviolet light irradiation. The resulting solution was precipitated with anhydrous ethanol, and the precipitate was dried under vacuum at 55°C to obtain a dry powder of click-grafted fluorocarbon hydrophobic associative polymer.

[0090] The polymer powder obtained above was dissolved in simulated formation water and stirred at 150 rpm for 2.5 h at 38°C to prepare a polymer mother liquor with a mass concentration of 0.32%.

[0091] Sodium perfluorohexyl sulfonate and sodium perfluorooctyl sulfonate were dissolved in simulated formation water and stirred at 100 rpm for 0.8 h at 38 °C to prepare a surfactant stock solution with a mass concentration of 0.16%.

[0092] Two mother liquors were taken, simulated formation water was added, and the mixture was stirred at 38°C for 1.8 hours to obtain an oil displacement system.

[0093] Comparative Example 1

[0094] Comparative Example 1 provides an oil displacement system and its preparation method. The mass fraction of each component is as follows: 0.1% alkyl hydrophobic modified polyacrylamide polymer; 0.03% sodium dodecylbenzenesulfonate (SDBS); and the balance is simulated formation water, which is the same as in Example 1. The preparation method is to directly dissolve the two raw materials in water and stir evenly. Comparative Example 1 is used to verify the performance improvement of the present invention compared with the conventional system of the prior art.

[0095] Comparative Example 2

[0096] Comparative Example 2 provides an oil displacement system and its preparation method, which is a fluorocarbon hydrophobic associating polymer system prepared by copolymerization. The mass fractions of each component are as follows: 0.1% of the copolymerized fluorocarbon hydrophobic associating polymer, which is prepared by free radical copolymerization of a hydrophobic monomer and acrylamide. The hydrophobic monomer is perfluorohexylmethacrylamide, and the other parameters are the same as those of the polymer in Example 1; 0.03% of the fluorocarbon anionic surfactant, which is sodium perfluorohexyl sulfonate; and the balance is the same as that of simulated formation water in Example 1. In the preparation method, the polymer is prepared by free radical copolymerization, and the other steps are the same as those in Example 1, to verify the effect of click grafting modification and the resulting performance improvement.

[0097] Comparative Example 3

[0098] Comparative Example 3 provides an oil displacement system and its preparation method, which is a system of click-grafted fluorocarbon polymer and conventional surfactant. The mass fraction of each component is as follows: 0.1% click-grafted fluorocarbon hydrophobic associative polymer, the same as the polymer in Example 1; 0.03% sodium dodecylbenzenesulfonate (SDBS); the balance is simulated formation water, the same as in Example 1. The preparation method is the same as in Example 1, except that the surfactant is replaced, to verify the matching effect of fluorocarbon surfactant and the performance improvement brought about by fluorine-fluorine matching hydrophobic effect.

[0099] Comparative Example 4

[0100] Comparative Example 4 provides an oil displacement system and its preparation method, which is a system containing only fluorocarbon surfactants. The mass fraction of each component is as follows: 0.03% fluorocarbon anionic surfactant, which is sodium perfluorohexyl sulfonate; the balance is simulated formation water, which is the same as in Example 1. The preparation method is the same as in Example 1, except that the polymer component is removed to verify the role of the polymer component and the role of the polymer-surfactant composite system.

[0101] To better understand the present invention, performance tests were conducted on the systems of the above embodiments and comparative examples. The test conditions were: temperature 120℃, simulated formation water salinity 200,000 mg / L, and the results are as follows:

[0102] It should be noted that all tests were conducted on the performance of the system at its highest viscosity state, that is, when the surfactant concentration drops to the optimal association concentration. This state is the effective working state of the system in the formation. Therefore, the initial viscosity benchmark for all tests is the same, which is the initial viscosity under this state.

[0103] Test 1

[0104] Test 1 is a viscosity variation test, conducted according to SY / T 5862-2020 "Technical Requirements for Polymers for Oil Displacement". A Hacker rheometer equipped with a high-temperature, high-pressure testing module was used to simulate high-temperature, high-pressure conditions in the formation. For each sample, a series of solutions with different surfactant concentrations were prepared, ranging from 0.001% to 0.06%, to simulate the gradual decrease in surfactant concentration in the system after adsorption by the rock during formation migration. All prepared solutions were placed in a high-temperature, high-pressure autoclave at 120℃ and 30MPa for 2 hours to ensure the system reached a stable state. The viscosity was then measured using a rheometer at a shear rate of 7.34 s⁻¹. -1 Under the given conditions, the apparent viscosity of the solution at each concentration was tested sequentially; the lowest viscosity (corresponding to the injection stage, when the surfactant concentration was highest) and the highest viscosity (corresponding to the formation viscosity enhancement stage, when the surfactant concentration was optimal) were recorded, and the viscosity change range (highest viscosity / lowest viscosity) was calculated. The test results are shown in Table 1.

[0105] Table 1. Variable viscosity performance test data

[0106]

[0107] As shown in Table 1, the five embodiments of the present invention can achieve a viscosity increase of more than 20 times under extreme conditions, which is much higher than the 3.6 times of Comparative Example 1. The results of the comparative examples show that the viscosity increase of Comparative Example 2 is only 8.3 times, which is much lower than that of the embodiments of the present invention. This proves that the precise modification method of click grafting solves the problem of uneven distribution of conventional copolymer hydrophobic groups and is the core to achieve a high viscosity increase. The viscosity increases of Comparative Examples 3 and 4 are both less than 10 times, which proves that only the matching system of fluorocarbon polymer and fluorocarbon surfactant can utilize the strong fluorine-fluorine hydrophobic interaction to achieve stable association under extreme conditions. This test fully demonstrates that the viscosity increase performance of the present invention is far superior to the prior art and can achieve stable injection low viscosity and formation viscosity increase effect under ultra-high temperature and high salt conditions.

[0108] Test 2

[0109] Test 2 is a shear resistance test, conducted according to the shear resistance test method in SY / T 5862-2020 "Technical Requirements for Polymers for Oil Displacement". A high-speed stirrer equipped with a temperature control module was used to perform the shear test under high-temperature conditions. The sample solution was placed in a high-speed stirrer preheated to 120℃ and sheared at 10000 rpm for 60 seconds. This shear strength is equivalent to the high shear action near the wellbore borehole, simulating the shear failure experienced during reagent injection. After shearing, the solution was immediately transferred to a rheometer and tested at the same temperature of 120℃ for 7.34 seconds. -1 Under the given conditions, the viscosity of the solution after shearing was tested; the viscosity retention rate was calculated as (viscosity after shearing / initial viscosity) × 100%, which was used to evaluate the shear resistance of the system. The test results are shown in Table 2.

[0110] Table 2 Shear resistance test data

[0111]

[0112] As shown in Table 2, in the embodiments of the present invention, the viscosity retention rate remained stable at over 90% after high shear, which is much higher than the 59.9% of Comparative Example 1. This is because the fluorocarbon hydrophobic groups of the present invention have a rigid structure, and combined with the uniform distribution brought about by click grafting, the associative network has extremely strong resistance to damage. Even after high-intensity shear, the association can be quickly restored and irreversible degradation will not occur. In contrast, the conventional copolyfluorocarbon system of Comparative Example 2, due to the uneven distribution of hydrophobic groups, has excessively strong association in some areas and excessively weak association in others, making it prone to irreversible damage after shear. Therefore, the retention rate is only 73%, which is much lower than that of the present invention. This test proves that the system of the present invention has extremely strong shear resistance and can ensure that the agent can still maintain effective viscosity in the formation after high shear in the near-wellbore zone and will not fail due to shear degradation.

[0113] Test 3

[0114] Test 3 is a temperature stability test. Based on the thermal stability test method in SY / T 5862-2020 "Technical Requirements for Polymers for Oil Displacement", a high-temperature, high-pressure aging tank was used to simulate the long-term high-temperature, high-pressure aging environment of the formation. The solution was sealed in the high-temperature, high-pressure aging tank, deoxygenated with nitrogen, and then placed in a constant temperature chamber at 120℃ for aging at an aging pressure of 30MPa to simulate formation pressure. Samples were taken out after 30, 60, and 90 days of aging, cooled to room temperature, and then reheated to 120℃ to test their viscosity after aging. The viscosity retention rate at different aging times was calculated as (viscosity after aging / initial viscosity) × 100% to evaluate the long-term temperature stability of the system. The test results are shown in Table 3.

[0115] Table 3 Temperature stability test data

[0116]

[0117] As shown in Table 3, the viscosity retention rate of the embodiments of the present invention remained above 92% after aging at 120°C for 90 days, while that of Comparative Example 1 was only 41.2%, a significant difference. This is because the CF bond energy of the fluorocarbon group is extremely high, much higher than that of the CH bond of the alkyl group, and will not undergo thermal degradation at high temperatures. At the same time, the uniform hydrophobic association network also avoids molecular chain curling and hydrophobic effect failure at high temperatures. In contrast, in conventional alkyl systems, the hydrophobic effect of alkyl groups will be greatly reduced at high temperatures, and the molecular chains are prone to thermal oxidative degradation, leading to a rapid decrease in viscosity. This test proves that the system of the present invention can exist stably for a long time in ultra-high temperature reservoirs and will not fail over time, thus meeting the requirements for long-term oil displacement.

[0118] Test 4

[0119] Test 4 is the oil displacement effect test, conducted according to SY / T 6424-2014 "Performance Test Method for Composite Oil Displacement Systems". A core displacement device equipped with a high-temperature, high-pressure core holder was used to simulate the displacement process under formation conditions. An artificial core with a permeability of 100±5 mD and dimensions of φ2.5cm×10cm was selected. The core was dried, weighed, and then evacuated for 4 hours to saturate with simulated formation water. The porosity and permeability of the core were calculated. The core was then loaded into the core holder, with a confining pressure of 35 MPa and a temperature of 120℃, and then saturated with simulated heavy oil (viscosity 500 mPa·s). s), calculate the original oil saturation; perform water flooding, inject simulated formation water at a flow rate of 0.5 mL / min until the water cut of the produced fluid reaches 98%, and record the recovery rate after water flooding; inject 0.3 PV of the oil displacement system of this invention at the same flow rate of 0.5 mL / min; perform subsequent water flooding, continue to inject simulated formation water until the water cut of the produced fluid reaches 98% again, and record the final recovery rate; calculate the recovery rate enhancement value: final recovery rate - water flooding recovery rate, and use this to evaluate the oil displacement effect of the system. The test results are shown in Table 4:

[0120] Table 4 Oil displacement effect test data

[0121]

[0122] As shown in Table 4, the embodiments of the present invention can further improve the oil recovery rate by 7.8 to 8.9 percentage points on the basis of water flooding, which is much higher than the 4.8 percentage points of Comparative Example 1. The oil displacement effect is significantly improved. This is because the system of the present invention can still achieve effective mobility control under extreme conditions, and can effectively activate the remaining oil not utilized by water flooding. At the same time, the low injection viscosity ensures the swept volume of the system, and the high formation viscosity ensures the mobility control capability. The combination of the two achieves excellent oil displacement effect. In contrast, the system of the comparative example has poor viscosity-changing performance and poor mobility control capability, so the improvement in oil recovery rate is much lower than that of the present invention. This test fully demonstrates that the system of the present invention has a significant effect on improving the oil recovery rate in ultra-high temperature and high salinity heavy oil reservoirs, and can bring significant development benefits to the oilfield.

[0123] Various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible subranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the range referred to.

[0124] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A high-temperature, high-salt-adapted variable viscosity displacement system, characterized in that, The oil displacement system comprises 0.06% to 0.15% by mass of click-grafted fluorocarbon hydrophobic associative polymer, 0.002% to 0.06% by mass of fluorocarbon anionic surfactant, and the balance being water; The click-grafted fluorocarbon hydrophobic associative polymer is a polyacrylamide grafted with fluorocarbon hydrophobic groups via a mercapto-olefin click reaction.

2. The oil displacement system according to claim 1, characterized in that, The fluorocarbon hydrophobic group includes at least one of perfluorobutyl, perfluorohexyl, and perfluorooctyl.

3. The oil displacement system according to claim 1, characterized in that, The fluorocarbon anionic surfactant includes at least one of sodium perfluorohexyl sulfonate, sodium perfluorooctyl sulfonate, sodium perfluorohexyl phosphate, and sodium perfluorooctyl phosphate.

4. The oil displacement system according to claim 1, characterized in that, It includes an oil displacement agent with a mass fraction of 0.001% to 0.01%, wherein the oil displacement agent includes at least one of a cosolvent, an antioxidant, and a demulsifier.

5. The oil displacement system according to claim 4, characterized in that, The cosolvent includes at least one of ethylene glycol butyl ether and propylene glycol methyl ether; the antioxidant includes at least one of dilauryl thiodipropionate and 2,6-di-tert-butyl-p-cresol; and the demulsifier includes at least one of polyoxyethylene polyoxypropylene block copolymer and alkylphenol polyoxyethylene ether.

6. The oil displacement system according to claim 1, characterized in that, The grafting rate of fluorocarbon hydrophobic groups in the click-grafted fluorocarbon hydrophobic associative polymer is 1.5%~3%.

7. The oil displacement system according to claim 1, characterized in that, The molecular weight of the click-grafted fluorocarbon hydrophobic associative polymer is 8 × 10⁻⁶. 6 ~1.5×10 7 .

8. A method for preparing a high-temperature, high-salt adaptive viscosity displacement system according to any one of claims 1-7, characterized in that, Includes the following steps: Acrylamide and mercaptoacetic acid were dissolved in deionized water to prepare a monomer solution with a mass concentration of 15%-20%. The solution was deoxygenated by purging with nitrogen for 30 min, and an initiator was added. The reaction was carried out at 30-40℃ for 6-8 h to obtain a mercapto-modified polyacrylamide backbone solution. The amount of mercaptoacetic acid used was 0.01%-0.1% of the total mass of the mercapto-modified polyacrylamide backbone solution. An alkenyl-modified fluorocarbon hydrophobic monomer and a photoinitiator were added to the thiolized polyacrylamide backbone solution. The click grafting reaction was carried out for 2-4 hours under ultraviolet light irradiation and at 20-30°C. The product was then precipitated with anhydrous ethanol, and the precipitate was collected and vacuum dried at 50-60°C to obtain a dry powder of the click-grafted fluorocarbon hydrophobic associative polymer. The dry powder of the click-grafted fluorocarbon hydrophobic associative polymer was dissolved in water and stirred at 100-300 rpm for 1.5-3 hours at 35-50°C to prepare a polymer mother liquor with a mass concentration of 0.3%-0.4%. Dissolve the fluorocarbon anionic surfactant in water and stir at 80-150 rpm for 0.3-1 h at 35-45℃ to prepare a surfactant stock solution with a mass concentration of 0.15%-0.2%. The polymer mother liquor and the surfactant mother liquor are mixed with water and stirred at 35-45°C for 1-2 hours to obtain the oil displacement system.

9. The method according to claim 8, characterized in that, The initiator includes at least one of azobisisobutyronitrile and ammonium persulfate-sodium bisulfite redox initiator; the photoinitiator is 2-hydroxy-2-methylphenylacetone.

10. The application of a high-temperature, high-salinity adaptive viscosity displacement system according to any one of claims 1-7 in oil displacement in reservoirs with temperatures of 90-120℃ and salinity of 100,000-200,000 mg / L.

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