PH-responsive polymer, pH-responsive sol, pH-responsive gel, and preparation method and application of pH-responsive polymer, pH-responsive sol and pH-responsive gel

Abstract

The invention discloses a pH-responsive polymer, a pH-responsive sol, a pH-responsive gel, a preparation method and an application of the pH-responsive polymer, the pH-responsive sol and the pH-responsive gel. The preparation method comprises the following steps: dissolving acrylamide, a response monomer and 3-[[2-(acryloyloxy) ethyl] dimethylammonium] undecane-1-carboxylate in deionized water, reacting with a thermal initiator in a CO2 environment, polymerizing an aqueous solution, drying, and granulating to obtain the pH responsive polymer. Dissolving the pH responsive polymer and a micromolecular anionic cross-linking agent in deionized water to obtain a pH responsive sol; according to the invention, the electrostatic interaction of the tertiary amine group of the response monomer and the carboxylic acid group on the micromolecular anionic surfactant in a specific pH range is utilized to realize the self-assembly between molecules, the hydrophobic association effect of the hydrophobic tail chain of the micromolecular cross-linking agent is facilitated to realize gelation, and the deep profile control of the oil reservoir is realized.

Description

Technical Field

[0001] The invention relates to the field of petroleum extraction, and in particular to a pH responsive polymer, a pH responsive sol, a pH responsive gel, and a preparation method and application thereof. Background Art

[0002] Profile control is an important method to improve oil recovery. By plugging the existing dominant channels in the reservoir, the subsequent displacement fluid is promoted to enter the low-porosity and low-permeability area, and the crude oil in the area can be exploited. At present, deep profile control is one of the challenges in the profile control process, especially how to plug the plugging agent deep in the reservoir. For deep profile control, existing solutions include delayed gelation and smart gelation. Delayed gelation is achieved by dissolving the polymer and the delayed crosslinking agent in an aqueous solution and then injecting them into the reservoir, slowly gelling at the reservoir temperature to achieve delayed crosslinking. However, due to the high viscosity of the polymer solution, there is a general problem of difficulty in injection, resulting in additional equipment requirements and economic costs. Smart gel is a gel material with special properties, which is usually achieved by adding or embedding some smart materials or functional units into the base gel. Smart gels are controlled by pH, light, electricity, magnetism and CO 2 The morphology, structure or performance of the gel can be adjusted by environmental changes such as temperature and humidity. Conventional optical, electrical and magnetic responsive materials are not feasible for the application of smart gels in reservoirs. Therefore, it is of great significance to provide a smart plugging solution based on pH adjustment to achieve sol-to-gel transition for deep reservoir profile control. Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides a pH-responsive polymer, a pH-responsive sol, a pH-responsive gel, and a preparation method and application thereof. The present invention is suitable for deep profile control of oil fields. By adjusting the pH value of the injected solution, the sol system is gelled in situ in the deep reservoir, promoting the bypass flow of subsequent displacement fluids into unaffected areas, thereby achieving the purpose of profile control and improving recovery.

[0004] In a first aspect, the present invention provides a pH responsive polymer, which is achieved by adopting the following technical solution.

[0005] A pH responsive polymer is copolymerized by the following monomers in molar percentage: 19.5-4.5% of responsive monomer, 80-95% of acrylamide, and 0.5% of 3-[[2-(acryloyloxy)ethyl]dimethylammonium]undecane-1-carboxylate (DMAC11).

[0006] Furthermore, the responsive monomer is selected from any one of dimethylaminoethyl methacrylate, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N,N-diethylmethacrylamide, N-methoxy-2,N-dimethylacrylamide and dimethylaminopropylacrylamide.

[0007] In a second aspect, the present invention provides a method for preparing a pH responsive polymer, which is achieved by adopting the following technical scheme.

[0008] A method for preparing the pH responsive polymer comprises the following steps: dissolving a responsive monomer, acrylamide and 3-[[2-(acryloyloxy)ethyl]dimethylammonium]undecane-1-carboxylate in deionized water, introducing CO 2 Removal of O 2 , adjust the pH to 4-5, then add initiator azobisisobutylamidine hydrochloride to polymerize at 50°C for 4-5h, and obtain pH responsive polymer after granulation and drying.

[0009] By adopting the above technical scheme, the initiator azobisisobutylamidine hydrochloride decomposes at the reaction temperature to form free radicals as active intermediates, and the free radicals attack double bonds to form new free radicals to form a chain reaction to form a long-chain polymer.

[0010] Furthermore, the monomer accounts for 20-30% of the aqueous solution by mass percentage.

[0011] Furthermore, in terms of mass percentage, the initiator azobisisobutylamidine hydrochloride accounts for 0.3-0.8% of the mass of the monomer.

[0012] In a third aspect, the present invention provides a pH-responsive sol, which is achieved by adopting the following technical solution.

[0013] A pH responsive sol comprises the following raw materials in mass percentage: 0.4-1wt% of the pH responsive polymer, 0.05-0.2wt% of a small molecule anionic cross-linking agent, and the balance being water.

[0014] By adopting the above technical solution, the pH responsive polymer and the small molecule anionic crosslinker are blended to form a sol, and the liquid form and low viscosity of the sol are conducive to the reservoir injectability of the pH responsive sol. The pH responsive sol has a low initial viscosity, and the viscosity at 25°C is 15-53mPa.s.

[0015] Furthermore, the small molecule anionic crosslinking agent includes sodium dodecylbenzene sulfonate, sodium sulfonate with a carbon chain length of 10 to 14, and sodium carboxylate with a carbon chain length of 12 to 14.

[0016] Preferably, the sodium sulfonate with a carbon chain length of 10 to 14 is selected from sodium dodecyl sulfonate and sodium tetradecyl sulfonate.

[0017] Preferably, the sodium carboxylate with a carbon chain length of 12 to 14 is selected from sodium dodecyl carboxylate and sodium tetradecyl carboxylate.

[0018] In a fourth aspect, the present invention provides a use of a pH-responsive sol, which is achieved by adopting the following technical solution.

[0019] An application of the pH responsive sol in deep reservoir profile control.

[0020] Furthermore, the pH value of the pH-responsive sol is adjusted to a pH value range for the transition from sol to gel by a pH adjusting agent to form a pH-responsive gel; the pH value range for the transition from sol to gel is 5-7.

[0021] By adopting the above technical scheme, the tertiary amine groups in the pH-responsive polymer in the solution are protonated within the pH range of the sol-to-gel transition, and are connected to the anionic groups on the small molecule anionic crosslinker by mutual attraction through electrostatic interaction, while the hydrophobic tail chains of the small molecule anionic crosslinker are crosslinked through hydrophobic association to form a three-dimensional spatial network structure to achieve the transition from sol to gel. The pH-responsive gel formed by the pH-responsive sol has a viscosity of 5000 to 120000 mPa.s at 25 to 70°C.

[0022] Specifically, the pH adjuster is a 0.1 mol / L hydrochloric acid solution.

[0023] Furthermore, under the action of an alkaline regulator, the pH value of the pH responsive gel is adjusted to a pH value range where the gel transforms into a sol, thereby achieving a reversible transformation of the pH responsive gel; the pH value where the gel transforms into a sol is 8 to 14.

[0024] By adopting the above technical solution, the alkaline regulator acts on the tertiary amine group of the pH-responsive polymer in the pH-responsive gel, the protonated tertiary amine group is reduced to a deprotonated tertiary amine group, and the electrostatic interaction between the small molecule anionic crosslinker and the pH-responsive polymer is removed, thereby achieving a reversible transformation from the pH-responsive gel to the pH-responsive sol. The pH-responsive sol transformed from the pH-responsive gel has a viscosity of 5 to 35 mPa.s at 25 to 70°C.

[0025] Specifically, the alkaline regulator is a 0.1 mol / L sodium hydroxide solution.

[0026] In a fourth aspect, the present invention provides a pH responsive gel, which is achieved by adopting the following technical solution.

[0027] A pH responsive gel is prepared by adjusting the pH value of the pH responsive sol to 5 to 7. The viscosity of the pH responsive gel at 25 to 70° C. is 5000 to 120000 mPa.s.

[0028] This application has the following beneficial effects.

[0029] The present invention copolymerizes a pH-responsive monomer, acrylamide, and 3-[[2-(acryloyloxy)ethyl]dimethylammonium]undecane-1-carboxylate to prepare a pH-responsive polymer. The pH-responsive polymer and a small molecule anion crosslinker are prepared into an aqueous solution in a certain proportion to obtain a low-viscosity pH-responsive sol system. By adjusting the pH value of the sol system, the sol is transformed into a sol. The low-viscosity sol system ensures its injection performance and deep migration ability as an injection liquid, and the sol-to-gel transformation under pH regulation realizes the plugging of deep hypertonic areas. The present invention provides an intelligent plugging scheme for deep reservoir profile control based on pH regulation to achieve sol-to-gel transformation. Through the action of pH-responsive polymers and small molecule anion crosslinkers, the injectability problem faced in deep profile control is solved; gelation is achieved through the stimulation of acid, solving the deep gelation problem faced in deep profile control. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a three-dimensional network structure diagram of the gel after the pH-responsive sol in Example 1 of the present invention is transformed into a pH-responsive gel under the condition of pH 5.5;

[0031] Figure 2 This is a graph showing the viscosity of the pH-responsive sol in Example 1 of the present invention after it is transformed into a pH-responsive gel at a pH of 5.5 at a temperature of 25° C. to 70° C.;

[0032] Figure 3 is a microscopic morphology of the sol after the pH responsive gel in Example 1 of the present invention is transformed into a pH responsive sol under the condition of pH 9;

[0033] Figure 4 This is a graph showing the viscosity of the pH-responsive sol in Example 2 of the present invention after it is transformed into a pH-responsive gel at a pH of 6 at a temperature between 25° C. and 70° C.;

[0034] Figure 5 It is a graph showing the changes in injection pressure during the core displacement experiment in the performance test of the present invention;

[0035] Figure 6 It is a schematic diagram of the preparation process of the pH responsive gel of the present invention. DETAILED DESCRIPTION

[0036] The present patent application is further described below in conjunction with embodiments.

[0037] The DMAC11 used in the following examples of the present invention is prepared from DMAEMA (dimethylaminoethyl methacrylate) and 11-bromodecane acid, both of which are purchased from Shanghai Aladdin Biological Co., Ltd. (98%). The preparation method is as follows: 2.50g dimethylaminoethyl methacrylate (DMAEMA) and 5.05g 11-bromodecane acid are added to a three-necked flask at a molar ratio of 1:1.2, with 100mL of anhydrous ethanol as solvent and 0.2g of potassium iodide as catalyst. Nitrogen is passed through the three-necked flask for 30 minutes to remove oxygen. The reaction is carried out for 72 hours in a constant temperature water bath at 35°C under nitrogen protection and magnetic stirring. The product solution is filtered, ethanol is removed under reduced pressure, and the crude product is dried at 35°C for 24 hours. The dried crude product is dissolved in water, extracted with ether three times, and the obtained aqueous phase is freeze-dried to obtain a white powder, namely 2-methacryloyloxyethyl dimethyl-11-undecanoic acid ammonium bromide (DMAC11).

[0038] Example 1

[0039] A method for preparing a pH responsive gel comprises the following steps:

[0040] A monomer containing 20 g of dimethylaminoethyl methacrylate, acrylamide (AM) and DMAC11 in a molar ratio of 9.5:90:0.5 was dissolved in 80 g of deionized water and CO was introduced. 2 Removal of O 2 The pH was adjusted to 4.5, 0.1 g of azobisisobutylamidine hydrochloride was added and polymerized at 50° C. for 4 h, and a pH-responsive polymer was obtained after granulation and drying.

[0041] A pH-responsive sol was prepared containing 0.6 wt % of a pH-responsive polymer and 0.11 wt % of sodium dodecylbenzene sulfonate. The viscosity of the sol at 25° C. was 24 mPa.s., which was suitable as a low-viscosity injection fluid.

[0042] The pH of the pH-responsive sol was adjusted to 5.5 by using a pH regulator to obtain a pH-responsive gel. The viscosity of the gel at 25°C was 113000 mPa.s. Figure 1 As shown in Figure 2, the pH-responsive gel has a dense three-dimensional spatial network structure. Figure 2 As shown, with the increase of temperature, the viscosity of the gel gradually decreases. At 70°C, the viscosity decreases to 36400 mPa.s.

[0043] The pH value of the pH-responsive gel was adjusted to 9 using an alkaline regulator. Figure 3 As shown in the figure, the dense three-dimensional network structure of the pH-responsive gel gradually changes into a sparse network structure. The viscosity of the sol at 25°C is 25mPa.s. As the temperature increases, the viscosity of the sol gradually decreases, and at 70°C, the viscosity decreases to 23mPa.s.

[0044] Example 2

[0045] A method for preparing a pH responsive gel comprises the following steps:

[0046] A monomer solution containing 20 g of dimethylaminoethyl methacrylate, acrylamide (AM) and DMAC11 in a molar ratio of 19.5:80:0.5 was dissolved in 80 g of deionized water and CO was introduced. 2 Removal of O 2 The pH was adjusted to 4.5, 0.12 g of azobisisobutylamidine hydrochloride was added and polymerized at 50° C. for 4 h, and a pH-responsive polymer was obtained after granulation and drying.

[0047] A pH-responsive sol was prepared containing 0.4 wt % of a pH-responsive polymer and 0.06 wt % of sodium dodecyl sulfate. The viscosity of the sol at 25° C. was 32 mPa.s., which was suitable as a low-viscosity injection fluid.

[0048] The pH value of the pH-responsive sol was adjusted to 6 by using a pH regulator to obtain a pH-responsive gel. The viscosity of the gel at 25°C was 31300 mPa.s. Figure 4 As shown, with the increase of temperature, the viscosity of the gel gradually decreases. At 70°C, the viscosity decreases to 7300 mPa.s.

[0049] The pH value of the pH-responsive gel was adjusted to 9 by an alkaline regulator. The viscosity of the sol was 29 mPa.s at 25°C. As the temperature increased, the viscosity of the sol gradually decreased, and at 70°C, the viscosity decreased to 27 mPa.s.

[0050] Example 3

[0051] A method for preparing a pH responsive gel comprises the following steps:

[0052] A monomer solution containing 20 g of N,N-dimethylmethacrylamide, acrylamide (AM) and DMAC11 in a molar ratio of 14.5:85:0.5 was dissolved in 80 g of deionized water and CO was introduced. 2 Removal of O 2 The pH was adjusted to 4.5, 0.14 g of azobisisobutylamidine hydrochloride was added and polymerized at 50° C. for 4 h, and a pH-responsive polymer was obtained after granulation and drying.

[0053] A pH-responsive sol was prepared containing 0.4 wt % of a pH-responsive polymer and 0.07 wt % of sodium tetradecylcarboxylate. The viscosity of the sol at 25° C. was 26 mPa.s., which was suitable as a low-viscosity injection fluid.

[0054] The pH value of the pH-responsive sol was adjusted to 6.5 by using a pH regulator to obtain a pH-responsive gel. The viscosity of the gel was 28300 mPa.s at 25°C. As the temperature increased, the viscosity of the gel gradually decreased, and at 70°C, the viscosity decreased to 5200 mPa.s.

[0055] The pH value of the pH-responsive gel was adjusted to 11 by an alkaline regulator. The viscosity of the sol was 18 mPa.s at 25°C. As the temperature increased, the viscosity of the sol gradually decreased, and at 70°C, the viscosity was 17 mPa.s.

[0056] Performance Testing

[0057] The profile control performance of the pH responsive gel in Example 1 was determined by core flooding experiments. Core size: 30*4.5*4.5 homogeneous, permeability: 2000md.

[0058] like Figure 5 As shown, the first water flooding was started with a water flooding volume of 2 PV, and the pressure was 1.82 MPa after the first water flooding pressure stabilized. Then 1 PV of pH-responsive sol was injected, and the injection pressure was increased to 2.90 MPa.

[0059] The secondary water flooding was carried out with acid solution of pH 5 as the injection fluid. During the secondary water flooding process, the pressure value increased rapidly, and the maximum pressure value was 3.63 MPa. The above results show that the pH responsive gel of the present invention can achieve deep profile control under acidic conditions.

[0060] The embodiments of this specific implementation method are all preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Therefore, any equivalent changes made based on the structure, shape, and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A pH responsive polymer, characterized in that: The invention is copolymerized by the following monomers in molar percentage: 19.5-4.5% of the response monomer, 80-95% of acrylamide, and 0.5% of 3-[[2-(acryloyloxy)ethyl]dimethylammonium]undecane-1-carboxylate.

2. A pH responsive polymer according to claim 1, characterized in that: The responsive monomer is selected from any one of dimethylaminoethyl methacrylate, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N,N-diethylmethacrylamide, N-methoxy-2,N-dimethylacrylamide and dimethylaminopropylacrylamide.

3. A method for preparing the pH responsive polymer according to claim 1 or 2, characterized in that: The following steps are involved: The responsive monomer, acrylamide and 3-[[2-(acryloyloxy)ethyl]dimethylammonium]undecane-1-carboxylate were dissolved in deionized water, CO2 was introduced to remove O2, the pH was adjusted to 4-5, and then the initiator azobisisobutyramidine hydrochloride was added to polymerize at 50°C for 4-5h. After granulation and drying, a pH responsive polymer was obtained.

4. A method for preparing a pH responsive polymer according to claim 3, characterized in that: In terms of mass percentage, the monomer accounts for 20-30% of the aqueous solution.

5. A pH-responsive sol, characterized in that: The method comprises the following raw materials in percentage by weight: 0.4-1 wt % of the pH responsive polymer according to claim 1 or 2, 0.05-0.2 wt % of a small molecule anionic cross-linking agent, and the balance being water.

6. A pH responsive sol according to claim 5, characterized in that: The small molecule anionic crosslinking agent includes sodium dodecylbenzene sulfonate, sodium sulfonate with a carbon chain length of 10 to 14, and sodium carboxylate with a carbon chain length of 12 to 14.

7. Use of the pH responsive sol according to claim 5 or 6 in deep reservoir profile control.

8. The use according to claim 7, characterized in that: The pH value of the pH-responsive sol is adjusted to a pH value range of the sol-to-gel transition by a pH adjusting agent to form a pH-responsive gel; the pH value range of the sol-to-gel transition is 5-7.

9. The use according to claim 8, characterized in that: Under the action of an alkaline regulator, the pH value of the pH responsive gel is adjusted to a pH value range where the gel transforms into a sol, thereby achieving a reversible transformation of the pH responsive gel; the pH value where the gel transforms into a sol is 8 to 14.

10. A pH responsive gel, characterized in that: The pH responsive gel is prepared by adjusting the pH value of the pH responsive sol according to claim 5 or 6 to 5-7.

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