Carbon dioxide-salt dual-response polymer thickening agent and preparation method thereof

Abstract

The invention belongs to the field of oil and gas exploitation, and particularly relates to a carbon dioxide-salt double-response polymer thickening agent and a preparation method thereof. The carbon dioxide-salt double-response polymer thickening agent provided by the invention is prepared from acrylamide, acrylic acid, alkyl polyether acrylate and amine carbon dioxide response monomers through solution polymerization; after corresponding monomers of amine carbon dioxide are protonated, polymer molecular chains are better stretched through electrostatic interaction, the viscosity of the fracturing fluid can be increased, complexation and crosslinking of oxyethyl, oxypropyl and calcium and magnesium ions are facilitated, and therefore the tackifying effect of alkyl polyether acrylate is improved; meanwhile, oxyethyl and oxypropyl jointly regulate and control the tightness degree of a network structure, so that a calcium and magnesium ion'salt bridge 'tackifying effect is presented. According to the carbon dioxide-salt double-response polymer thickening agent provided by the invention, the viscosity of the thickening agent is improved through carbon dioxide and calcium and magnesium ions, and meanwhile, a fracturing fluid has certain imbibition oil displacement capacity after gel breaking.

Description

Technical Field

[0001] The present invention belongs to the field of oil and gas exploitation, and particularly relates to a carbon dioxide-salt dual-responsive polymer thickening agent and a preparation method thereof. Background Art

[0002] With the reduction of conventional oil and gas production, unconventional oil and gas resources such as tight oil and shale oil play an increasingly important role in oil supply and will become the mainstream of future oil and gas exploration and development in China. Reservoir fracturing is a necessary means for the industrial production of unconventional oil and gas. At present, conventional fracturing fluids mainly include guar gum fracturing fluid, polymer fracturing fluid, and surfactant clean fracturing fluid. Guar gum fracturing fluid has strong thickening ability and is easy to crosslink, but after gel breaking and degradation, it has a high residue content and causes great damage to the formation; the produced water contains a large amount of metal ions, resulting in a low viscosity of its base fluid and difficulty in reuse. The thickening agent in polymer fracturing fluid is generally acrylamide-based thickening agent, and its thickening ability is generally inferior to that of guar gum. The gel formed by chemical crosslinking of anionic polyacrylamide (HPAM) molecules has the characteristics of good viscoelasticity, good gel breaking performance, and less residue, but the viscosity loss of the thickening agent is large under high salinity water, resulting in a significant increase in the cost of fracturing fluid and restricting its application. Surfactant clean fracturing fluid, also known as viscoelastic surfactant fracturing fluid, is a solution based on viscoelastic surfactant, which solves the problem that conventional fracturing fluid causes great damage to the permeability of oil and gas reservoirs due to incomplete gel breaking during the flowback process. In addition, due to the characteristics of carbon dioxide such as green environmental protection, low cost, and rich resources, viscoelastic polymers with carbon dioxide response characteristics have attracted the attention of many scientific researchers. Such substances are also called carbon dioxide-responsive viscoelastic polymers. They have specific functional groups in their molecular structures. When the polymer is affected by carbon dioxide, its macroscopic properties (viscosity, solubility, etc.) or microscopic properties (self-assembly morphology) will change. No by-products are generated during the reaction, and carbon dioxide gas is pollution-free. Therefore, carbon dioxide has potential application value in thickening polymer fracturing fluid.

[0003] Chinese Patent CN107142099A discloses a recyclable carbon dioxide-responsive clean fracturing fluid system, which is composed of a tertiary amine surfactant and an auxiliary agent that can respond to carbon dioxide. The viscosity of the 3% stearic acid amide propyl dimethylamine / p-toluenesulfonate system increases from 18 mPa·s to 300 mPa·s after introducing carbon dioxide at room temperature. At the same time, the system can be broken by N2, and the viscosity of the fracturing fluid after gel breaking is 15 mPa·s. This fracturing fluid has good carbon dioxide responsiveness and excellent recyclability potential for low-temperature reservoirs, but its temperature resistance is not strong, not exceeding 100 °C, and it is difficult to apply in high-temperature reservoirs such as shale oil reservoirs. Chinese Patent CN111234432A discloses a polymer-based carbon dioxide-responsive viscoelastic fluid and its preparation method. This polymer system is composed of 2,4,6-tris(dimethylaminomethyl)phenol, sodium polyacrylate, and sodium chloride. The zero-shear viscosity of the prepared fluid is 41 Pa·s. When carbon dioxide gas is introduced into the fluid at a rate of 0.3 L / min at 25 °C for 20 min, the zero-shear viscosity increases to 133 Pa·s. After carbon dioxide treatment, the zero-shear viscosity increases by 224%. However, using formation water with high salinity for liquid preparation will result in a low viscosity of the base fluid and an increase in the dosage of the thickening agent. Summary of the Invention

[0004] The object of the present invention is to provide a carbon dioxide-salt dual-responsive polymer thickening agent (CSDT) containing a carbon dioxide-responsive monomer and a calcium and magnesium ion-responsive monomer, which can increase the viscosity of the thickening agent through carbon dioxide and calcium and magnesium ions, and at the same time, the fracturing fluid has a certain imbibition oil displacement ability after gel breaking.

[0005] To achieve the above object, the present invention provides a carbon dioxide-salt dual-responsive polymer thickening agent, which is formed by solution polymerization of acrylamide (AM), acrylic acid (AA), alkyl polyether acrylate, and an amine-based carbon dioxide-responsive monomer. Its structural general formula is: ; Among them, a / (a + b + c + d) is 75% - 85%, b / (a + b + c + d) is 10% - 20%, c / (a + b + c + d) is 1% - 5%, and d / (a + b + c + d) is 1% - 10%.

[0006] Among them, the structural formula of X is: , , One of them; The R group is one of acrylate group (C3H3O2) or methacrylate group (C4H5O2).

[0007] The value of r is an integer from 14 to 18. If r is too small, the hydrophobic association of the carbon dioxide-salt dual-responsive polymer thickener is too weak, affecting its salt thickening performance. If r is too large, the solubility of the carbon dioxide-salt dual-responsive polymer thickener in water is too poor.

[0008] The value of m is an integer from 15 to 30, and the value of n is an integer from 2 to 15. If m or n is too small, the complexation with calcium and magnesium ions is too weak, affecting the salt responsiveness of CSDT. If m or n is too large, the long ethylene oxide (EO) chain or propylene oxide (PO) chain may hinder the reaction between monomers during polymerization, affecting the degree of polymerization or reaction rate, and thus affecting the molecular weight, resulting in a low base fluid viscosity of CSDT.

[0009] Optionally, Y is one of ethylene imino group (-C2H5N-), dimethylaminoethyl methacrylate group (-C8H 15 NO2-), allylamino group (-C3H7N-), diethylaminoethyl methacrylate group (-C 10 H 19 NO2-), dimethylamino styryl group (-C 10 H 13 N-).

[0010] The weight-average molecular weight of the carbon dioxide-salt dual-responsive polymer thickener is from 2 million to 3 million.

[0011] The carbon dioxide-salt dual-responsive polymer thickener is used for the exploitation of oilfields with high salinity formation water; The salinity of the formation water is 5000 - 100000 mg / L; the calcium and magnesium ion concentration in the formation water is 200 - 2500 mg / L. If the salinity is low and the calcium and magnesium ion concentration is small, the hydrophobic association and complexation are small, and the viscosity increasing effect is poor. If the salinity is too high and the calcium and magnesium ion concentration is large, the amount of complexed calcium and magnesium ions reaches the threshold, and the shielding effect of metal ions plays a dominant role, resulting in a decrease in solution viscosity.

[0012] The addition of calcium and magnesium ions increases the polarity of the CSDT solution, promotes the association of the non-polar hydrophobic tails on the alkyl polyoxyethylene ether monomers of the CSDT polymer chain, and thus increases the viscosity by enhancing the hydrophobic association. Secondly, calcium and magnesium ions complex with the ethylene oxide (EO) groups and propylene oxide (PO) groups on the alkyl polyoxyethylene ether monomers to form salt bridges, making the network structure of the CSDT polymer molecular chain more dense, thereby increasing the viscosity of the CSDT polymer.

[0013] The present invention also provides a preparation method of the carbon dioxide-salt dual-responsive polymer thickener, including the following steps: Step 1: Add acrylamide, acrylic acid, alkyl polyether acrylate, and amine-based carbon dioxide-responsive monomer into deionized water. After dissolution, a mixture solution is obtained. Step 2: Adjust the pH of the mixed solution to 6.5 - 7.5. Introduce nitrogen for 30 - 50 min, add an initiator, and polymerize at 45 - 55 °C for 4 - 6 h to obtain a copolymer rubber block. Step 3: Immerse the copolymer rubber block in ethanol to remove moisture, wash it repeatedly 3 - 5 times, and then dry and granulate it to obtain a carbon dioxide-salt dual-responsive polymer thickener.

[0014] Among them, in Step 1, The alkyl polyether acrylate is one of alkyl polyoxyethylene ether acrylate, alkyl polyoxypropylene ether acrylate, alkyl polyoxyethylene ether methacrylate, alkyl polyoxypropylene ether methacrylate, alkyl polyoxyethylene polyoxypropylene ether acrylate, and alkyl polyoxyethylene polyoxypropylene ether methacrylate; The amine-based carbon dioxide-responsive monomer is one of ethylene imine, dimethylaminoethyl methacrylate, allylamine, diethylaminoethyl methacrylate, and dimethylamino styrene.

[0015] The molar ratio of acrylamide, acrylic acid, alkyl polyether acrylate, and amine-based carbon dioxide-responsive monomer is (75 - 85):(10 - 20):(1 - 5):(1 - 10).

[0016] The total mass of acrylamide, acrylic acid, alkyl polyether acrylate, and amine-based carbon dioxide-responsive monomer is 25 - 35 wt% of the mixture solution.

[0017] In Step 2, adjust the pH by adding NaOH.

[0018] The initiator is azobisisobutyronitrile, The addition amount of the initiator is 0.02 - 0.1 wt% of the total mass of acrylamide, acrylic acid, alkyl polyether acrylate, and amine-based carbon dioxide-responsive monomer.

[0019] In Step 2, the purpose of introducing nitrogen is to remove oxygen.

[0020] The technical features and beneficial effects of the present invention: (1)The carbon dioxide-salt dual-responsive polymer thickener of the present invention. After the amine-based carbon dioxide-responsive monomer is protonated, the polymer molecular chains are better extended through electrostatic interaction, which can not only increase the viscosity of the fracturing fluid, but also facilitate the complexation cross-linking of oxyethyl and oxypropyl groups with calcium and magnesium ions, thereby increasing the viscosity-increasing effect of alkyl polyether acrylates. At the same time, the hydrophilicity of EO can prevent the polymer from completely precipitating under high salt conditions and maintain the solution stability, while the hydrophobicity of PO enhances the association effect. The two jointly regulate the tightness of the network structure, resulting in the viscosity-increasing effect of the calcium and magnesium ion "salt bridge".

[0021] (2)The carbon dioxide-salt dual-responsive polymer thickener of the present invention contains nonionic surfactant units such as alkyl polyoxyethylene ether, alkyl polyoxypropylene ether, or alkyl polyoxyethylene polyoxypropylene ether with imbibition oil-displacement function in the molecular structure after gel breaking, which can improve the imbibition oil-displacement effect of the fracturing fluid. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The drawings are used to provide a further understanding of the present invention, and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present invention, but do not constitute a limitation to the present invention.

[0023] Figure 1 Apparent viscosity curve of 0.5% CSDT after injecting carbon dioxide in Example 1; Figure 2 Apparent viscosity curves of CSDT prepared in Example 1, Comparative Example 1, and Comparative Example 2 after injecting carbon dioxide in calcium ion solution; Figure 3 Apparent viscosity curves of CSDT prepared in Example 1, Comparative Example 1, and Comparative Example 2 after injecting carbon dioxide in magnesium ion solution; Figure 4 Steady-state shear rheological curve of CSDT prepared in Example 1; Figure 5 Viscoelastic modulus change curve of CSDT prepared in Example 1; Figure 6 Thixotropic property curve of CSDT prepared in Example 1; Figure 7 Temperature and shear resistance curve of 0.5% CSDT prepared in Example 1; Figure 8 Imbibition recovery rate curve of the gel-breaking fluid of 0.5% CSDT prepared in Example 1; Figure 9 Infrared spectrum of CSDT prepared in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0024] The technical solution of the present invention will be further described in detail below in conjunction with specific embodiments. However, the protection scope of the present invention is not limited to the following. Unless otherwise specified, the following raw materials are all commercially available products. The alkyl polyoxyethylene polyoxypropylene ether methacrylate was purchased from Zhangjiagang Renda Chemical Co., Ltd.

[0025] In the following examples and comparative examples, the synthesis steps of the alkyl polyoxyethylene polyoxypropylene ether acrylate are as follows: First, weigh 0.25 mol of alkyl polyoxyethylene polyoxypropylene ether and 0.10 mol of triethylamine and place them in a three-necked flask equipped with a circulating cooling reflux water device. Dilute the alkyl polyoxyethylene polyoxypropylene ether with acetone to a mass fraction of 50%, and start the stirrer to stir. Dilute 0.375 mol of acryloyl chloride with acetone to a mass fraction of 50% of acryloyl chloride, and use a constant-pressure separatory funnel to drop it into the three-necked flask drop by drop. React for 12 h under the conditions of a temperature of 50 ± 0.1 °C and a stirring rate of 250 - 300 r / min to obtain a light yellow crude product of alkyl polyoxyethylene polyoxypropylene ether acrylate. Filter the light yellow crude product of alkyl polyoxyethylene polyoxypropylene ether acrylate to remove salts, remove the solvent with a rotary evaporator at 50 ± 0.1 °C, then extract with ether, and vacuum dry at room temperature for 24 h to obtain pure alkyl polyoxyethylene polyoxypropylene ether acrylate.

[0026] Example 1: A carbon dioxide-salt dual-responsive polymer thickener is prepared from the following raw materials: Acrylamide monomer AM, acrylic acid AA, dimethylaminoethyl methacrylate, octadecyl polyoxyethylene polyoxypropylene ether acrylate (EO number is 25, PO number is 5), initiator azobisisobutyronitrile AIBN.

[0027] Among them, AM is 18.7 g, AA is 2.64 g, dimethylaminoethyl methacrylate is 3.14 g, octadecyl polyoxyethylene polyoxypropylene ether acrylate is 22.88 g, and initiator AIBN is 0.029 g.

[0028] A preparation method of a carbon dioxide-salt dual-responsive polymer thickener includes the following steps: The first step: Weigh 121.79 g of deionized water and place it in a polymerization reaction vessel, and then sequentially add 18.7 g of AM, 2.64 g of AA, 3.14 g of dimethylaminoethyl methacrylate, and 22.88 g of octadecyl polyoxyethylene polyoxypropylene ether acrylate to the vessel, and stir well to dissolve to obtain a mixed solution.

[0029] Step 2: Adjust the pH value of the mixed solution to 7 with NaOH. Subsequently, introduce N2 into the solution to remove oxygen for 30 min. Add 0.029 g of AIBN, adjust the temperature of the reaction vessel to 48 °C, and polymerize for 5 h to obtain a copolymer block.

[0030] Step 3: Immerse the copolymer block in ethanol to remove moisture, wash it repeatedly 5 times, then dry and granulate it to obtain a carbon dioxide-salt dual-responsive polymer thickening agent.

[0031] Example 2: A carbon dioxide-salt dual-responsive polymer thickening agent is prepared from the following raw materials: Acrylamide monomer AM, acrylic acid AA, dimethylaminoethyl methacrylate, octadecyl polyoxyethylene ether acrylate (EO number is 25), initiator azobisisobutyronitrile AIBN.

[0032] Among them, AM is 17.75 g, AA is 3.66 g, dimethylaminoethyl methacrylate is 3.67 g, octadecyl polyoxyethylene ether acrylate is 14.24 g, and initiator AIBN is 0.02 g.

[0033] A preparation method of a carbon dioxide-salt dual-responsive polymer thickening agent includes the following steps: Step 1: Weigh 91.6 g of deionized water and place it in a polymerization reaction vessel. Then, sequentially add 17.75 g of AM, 3.66 g of AA, 3.67 g of dimethylaminoethyl methacrylate, and 14.24 g of octadecyl polyoxyethylene ether acrylate to the vessel, and stir well to dissolve to obtain a mixed solution.

[0034] Step 2: Adjust the pH value of the mixed solution to 7 with NaOH. Subsequently, introduce N2 into the solution to remove oxygen for 30 min. Add 0.02 g of AIBN, adjust the temperature of the reaction vessel to 45 °C, and polymerize for 6 h to obtain a copolymer block.

[0035] Step 3: Immerse the copolymer block in ethanol to remove moisture, wash it repeatedly 5 times, then dry and granulate it to obtain a carbon dioxide-salt dual-responsive polymer thickening agent.

[0036] Example 3: A carbon dioxide-salt dual-responsive polymer thickening agent is prepared from the following raw materials: Acrylamide monomer AM, acrylic acid AA, diethylaminoethyl methacrylate, hexadecyl polyoxypropylene ether acrylate (PO number is 10), initiator azobisisobutyronitrile AIBN.

[0037] The monomers are calculated by weight. Among them, AM is 18.46 g, AA is 3.12 g, diethylaminoethyl methacrylate is 3.7 g, cetyl polyoxypropylene ether acrylate is 8.77 g, and the initiator AIBN is 0.0136 g.

[0038] A preparation method of a carbon dioxide-salt dual-responsive polymer thickening agent includes the following steps: The first step: Weigh 72.37 g of deionized water and place it in a polymerization reaction vessel. Then, sequentially add 18.46 g of AM, 3.12 g of AA, 3.7 g of diethylaminoethyl methacrylate, and 8.77 g of cetyl polyoxypropylene ether acrylate into the vessel, and stir well to dissolve to obtain a mixed solution.

[0039] The second step: Use NaOH to adjust the pH value of the mixed solution to 7. Subsequently, introduce N2 into the solution to remove oxygen for 30 min, add 0.0136 g of AIBN, adjust the temperature of the reaction vessel to 50 °C, and polymerize for 4 h to obtain a copolymer rubber block.

[0040] The third step: Immerse the copolymer rubber block in ethanol to remove moisture, wash it repeatedly 5 times, and then dry and granulate it to obtain a carbon dioxide-salt dual-responsive polymer thickening agent.

[0041] Example 4: A carbon dioxide-salt dual-responsive polymer thickening agent is prepared from the following raw materials: Acrylamide monomer AM, acrylic acid AA, dimethylamino styrene, cetyl polyoxyethylene polyoxypropylene ether methacrylate (EO number is 15, PO number is 8), initiator azobisisobutyronitrile AIBN.

[0042] Among them, AM is 19.17 g, AA is 2.64 g, dimethylamino styrene is 1.96 g, cetyl polyoxyethylene polyoxypropylene ether methacrylate is 19.14 g, and the initiator AIBN is 0.0129 g.

[0043] A preparation method of a carbon dioxide-salt dual-responsive polymer thickening agent includes the following steps: The first step: Weigh 110.35 g of deionized water and place it in a polymerization reaction vessel. Then, sequentially add 19.17 g of AM, 2.64 g of AA, 1.96 of dimethylamino styrene, and 19.14 g of cetyl polyoxyethylene polyoxypropylene ether methacrylate into the vessel, and stir well to dissolve to obtain a mixed solution.

[0044] The second step: Use NaOH to adjust the pH value of the mixed solution to 7. Subsequently, introduce N2 into the solution to remove oxygen for 30 min, add 0.0129 g of AIBN, adjust the temperature of the reaction vessel to 55 °C, and polymerize for 4 h to obtain a copolymer rubber block.

[0045] Step 3: Immerse the copolymer rubber block in ethanol to remove moisture, wash it repeatedly 5 times, then dry and granulate it to obtain a carbon dioxide-salt dual-responsive polymer thickening agent.

[0046] Example 5: A carbon dioxide-salt dual-responsive polymer thickening agent is prepared from the following raw materials: Acrylamide monomer AM, acrylic acid AA, diethylaminoethyl methacrylate, octadecyl polyoxyethylene ether acrylate (EO number is 20), initiator azobisisobutyronitrile AIBN.

[0047] Among them, AM is 18.93 g, AA is 2.64 g, diethylaminoethyl methacrylate is 3.09 g, octadecyl polyoxyethylene ether acrylate is 16.04 g, and initiator AIBN is 0.0163 g.

[0048] A preparation method of a carbon dioxide-salt dual-responsive polymer thickening agent includes the following steps: Step 1: Weigh 90.59 g of deionized water and place it in a polymerization reaction vessel. Then, add 18.93 g of AM, 2.64 g of AA, 3.09 g of diethylaminoethyl methacrylate, and 16.04 g of octadecyl polyoxyethylene ether acrylate into the vessel in sequence, and stir well to dissolve to obtain a mixed solution.

[0049] Step 2: Adjust the pH value of the mixed solution to 7 with NaOH. Subsequently, pass N2 into the solution to remove oxygen for 30 min, add 0.0163 g of AIBN, adjust the temperature of the reaction vessel to 52 °C, and polymerize for 5 h to obtain a copolymer rubber block.

[0050] Step 3: Immerse the copolymer rubber block in ethanol to remove moisture, wash it repeatedly 5 times, then dry and granulate it to obtain a carbon dioxide-salt dual-responsive polymer thickening agent.

[0051] Example 6: A carbon dioxide-salt dual-responsive polymer thickening agent is prepared from the following raw materials: Acrylamide monomer AM, acrylic acid AA, allylamine, cetyl polyoxyethylene ether methacrylate (EO number is 20), initiator azobisisobutyronitrile AIBN.

[0052] Calculated by weight of the monomers, among them, AM is 17.99 g, AA is 2.88 g, allylamine is 1.33 g, cetyl polyoxyethylene ether methacrylate is 19.88 g, and initiator AIBN is 0.0127 g.

[0053] A preparation method of a carbon dioxide-salt dual-responsive polymer thickening agent includes the following steps: Step 1: Weigh 85.41 g of deionized water and place it in a polymerization reaction vessel. Then, sequentially add 17.99 g of AM, 2.88 g of AA, 1.33 g of allylamine, and 19.88 g of cetyl polyoxyethylene ether methacrylate to the vessel, and stir well to dissolve to obtain a mixed solution.

[0054] Step 2: Adjust the pH value of the mixed solution to 7 with NaOH. Subsequently, introduce N2 into the solution to remove oxygen for 30 min, add 0.0127 g of AIBN, adjust the temperature of the reaction vessel to 47 °C, and polymerize for 6 h to obtain a copolymer rubber block.

[0055] Step 3: Immerse the copolymer rubber block in ethanol to remove moisture, wash it repeatedly 5 times, then dry and granulate it to obtain a carbon dioxide-salt dual-responsive polymer thickening agent.

[0056] Example 7: A carbon dioxide-salt dual-responsive polymer thickening agent is prepared from the following raw materials: Acrylamide monomer AM, acrylic acid AA, allylamine, tetradecyl polyoxyethylene polyoxypropylene ether acrylate (EO number is 20, PO number is 5), initiator azobisisobutyronitrile AIBN.

[0057] Calculated by weight of the monomers, where AM is 18.22 g, AA is 3.36 g, allylamine is 1.14 g, tetradecyl polyoxyethylene polyoxypropylene ether acrylate is 14.4 g, and initiator AIBN is 0.0186 g.

[0058] A preparation method of a carbon dioxide-salt dual-responsive polymer thickening agent includes the following steps: Step 1: Weigh 72.06 g of deionized water and place it in a polymerization reaction vessel. Then, sequentially add 18.22 g of AM, 3.36 g of AA, 1.14 g of allylamine, and 14.4 g of tetradecyl polyoxyethylene polyoxypropylene ether acrylate to the vessel, and stir well to dissolve to obtain a mixed solution.

[0059] Step 2: Adjust the pH value of the mixed solution to 7 with NaOH. Subsequently, introduce N2 into the solution to remove oxygen for 30 min, add 0.0186 g of AIBN, adjust the temperature of the reaction vessel to 53 °C, and polymerize for 5 h to obtain a copolymer rubber block.

[0060] Step 3: Immerse the copolymer rubber block in ethanol to remove moisture, wash it repeatedly 5 times, then dry and granulate it to obtain a carbon dioxide-salt dual-responsive polymer thickening agent.

[0061] Comparative Example 1: This comparative example is the same as Example 1, except that 5.03 g of acrylic acid, 0.56 g of dimethylaminoethyl methacrylate, and 11.44 g of octadecyl polyoxyethylene ether acrylate are used.

[0062] Comparative Example 2: This comparative example is the same as Example 1, except that it does not contain dimethylaminoethyl methacrylate, that is, the polymer prepared in this comparative example does not contain the amine-based carbon dioxide-responsive monomer Y.

[0063] Experimental Example: Effect Measurement The carbon dioxide-salt dual-responsive polymer thickener CSDT prepared in Example 1 and Comparative Examples 1 and 2 was selected for testing, including carbon dioxide-responsive viscosity increase experiment, calcium and magnesium ion-responsive viscosity increase experiment, steady-state shear experiment, viscoelastic modulus experiment, thixotropic property experiment, temperature and shear resistance experiment, and gel-breaking fluid imbibition efficiency experiment. Unless otherwise specified, the following 0.5% CSDT solution means that the mass concentration of CSDT is 0.5%.

[0064] (1) Carbon Dioxide-Responsive Viscosity Increase Experiment ① Preparation of thickener: Take 350 mL of deionized water with a measuring cylinder and place it in a beaker. Adjust the stirring speed to 500 r / min. Take 1.75 g of CSDT prepared in Example 1 and Comparative Example 1 and dissolve it in deionized water. After stirring for 10 min to fully dissolve, a 0.5% CSDT solution is obtained. Pass carbon dioxide into the thickener solution at a speed of 300 mL / min. After passing carbon dioxide for 5 min each time, let the solution stand for 10 min and measure its apparent viscosity using a ZNN-D6II viscometer.

[0065] ② Measurement of apparent viscosity: Use a ZNN-D6II viscometer to measure the apparent viscosity of the CSDT solution. Place the prepared 350 ml CSDT solution in the measuring cylinder. The experimental conditions are normal temperature and a rotation speed of 100 r / min. According to Equation (1), the apparent viscosity value of the polymer solution can be calculated. Each sample is tested 3 times and the average value is taken.

[0066] (1) In the formula, μ —Apparent viscosity of the test sample, mPa·s; α —Reading of the viscometer pointer at a rotation speed of 100 r / min; 5.077—Shear stress value at 1, 10 -1 Pa; 1.704—Shear rate value when the rotation speed of the viscometer is 1 r / min, with the unit of s -1 .

[0067] (2) Calcium and Magnesium Ion-Responsive Viscosity Increase Experiment The 0.5% CSDT of Example 1 and Comparative Example 1 after injecting carbon dioxide for 50 minutes was evenly divided into several portions. Meanwhile, several portions of 0.5% CSDT of Comparative Example 2 were prepared. According to the experimental plan, calcium chloride and magnesium chloride solutions with concentrations of 0 - 2000 mg / L were added to them, and after stirring for 10 minutes, the viscosity change was measured.

[0068] (3)Steady - state shear experiment Using the CSDT prepared in Example 1, 0.5% CSDT, 0.5% CSDT + 500 mg / L CaCl2 + 500 mg / L MgCl2, and 0.5% CSDT + 500 mg / L CaCl2 + 500 mg / L MgCl2 + carbon dioxide thickening agent solutions were respectively prepared. The Anton Paar MCR302 rheometer was used for testing. The experimental temperature was room temperature, and the shear rate was set to 0.1 - 1000 s -1 , and the change in the apparent viscosity of the thickening agent was measured to obtain the apparent viscosity μ and its corresponding relationship with the shear rate.

[0069] (4)Viscoelastic modulus experiment Using the CSDT prepared in Example 1, 0.5% CSDT, 0.5% CSDT + 500 mg / L CaCl2 + 500 mg / L MgCl2, and 0.5% CSDT + 500 mg / L CaCl2 + 500 mg / L MgCl2 + carbon dioxide thickening agent solutions were respectively prepared. The cone - plate system of the Anton Paar MCR302 rheometer was used for testing. The experimental temperature was room temperature. First, the frequency was fixed at 1 rad / s, and a dynamic strain sweep was performed on the specimen to determine the linear viscoelastic plateau region. At a strain amplitude of 0.1% in the linear viscoelastic plateau region, a frequency sweep of the strain was carried out, with the ω range being 0.1 - 10 rad / s, to obtain the corresponding relationship between the viscoelastic moduli G' and G'' and ω.

[0070] (5)Thixotropic property experiment Using the CSDT prepared in Example 1, 0.5% CSDT, 0.5% CSDT + 500 mg / L CaCl2 + 500 mg / L MgCl2, and 0.5% CSDT + 500 mg / L CaCl2 + 500 mg / L MgCl2 + carbon dioxide thickening agent solutions were respectively prepared. The Anton Paar MCR302 rheometer was used for testing. The experimental temperature was room temperature. The yield stress during the cyclic scan was evaluated, and the shear rate scan range was 1 - 180 s -1 , and then it was reduced back to 1 s -1 , to obtain the shear stress thixotropic loop curves of the three thickening agent solutions.

[0071] (6)Temperature and Shear Resistance Experiment Using the CSDT prepared in Example 1, prepare 0.5% CSDT, 0.5% CSDT + 500 mg / L CaCl2 + 500 mg / L MgCl2, and 0.5% CSDT + 500 mg / L CaCl2 + 500 mg / L MgCl2 + carbon dioxide thickening agent solutions respectively, and use an Anton Paar MCR302 rheometer for testing. Set the shear rate at 170 s -1 , control the temperature from 3°C to 140°C, the test pressure is 500 psi, and the test time is 2 h. Finally, obtain the relationship curve between the test time and the thickening agent viscosity.

[0072] (7)Gel Breaking Fluid Imbibition Experiment ① Preparation of Gel Breaking Fluid Using the CSDT prepared in Example 1, prepare 0.5% CSDT + 500 mg / L CaCl2 + 500 mg / L MgCl2 + carbon dioxide thickening agent solution. After measuring 100 mL, add 0.25 g of ammonium persulfate gel breaker, stir evenly, seal it, and place it in an oven at 140°C for 2 h to break the gel and obtain the gel breaking fluid.

[0073] ② Imbibition Efficiency Experiment Take a clean core, weigh it, record the mass as m1, then place it in a vacuum saturation device and saturate it for 24 h under the condition of -0.1 MPa, then carry out the aging treatment, and finally weigh the mass of the saturated crude oil core and record it as m2. Place the saturated oil core in an imbibition instrument, then add the gel breaking fluid to the imbibition instrument for spontaneous imbibition experiment, and observe and record the change of the volume of oil in the graduated tube of the imbibition instrument v over time. The calculation formula for the imbibition recovery rate is shown in Equation (2).

[0074] (2) Wherein η — Core imbibition recovery rate, %; ρ — Saturated crude oil density, g / cm 3 ; v — Volume of the exuded crude oil, cm 3 ; m 1 — Mass of the unsaturated core, g; m 2 — Mass of the core saturated with crude oil, g.

[0075] From Figure 1It can be seen that as carbon dioxide is continuously introduced into the thickener solution, the viscosity of the solution continuously increases. After 50 minutes of carbon dioxide introduction in Example 1, the viscosity of the solution increased by 86.67 mPa·s compared to the initial state, and in Comparative Example 1, the viscosity increased by 58.54 mPa·s compared to the initial state. This indicates that the CSDT solution has obvious carbon dioxide responsiveness. After carbon dioxide is introduced, the quaternary ammonium groups in DMAEMA on the polymer molecular chain are protonated, making the quaternary ammonium groups carry positive charges, thereby generating electrostatic interactions that cause the polymer molecular chain to stretch more, and the solution viscosity increases. The concentration of DMAEMA in Example 1 is higher than that in Comparative Example 1. Therefore, the electrostatic repulsion between polymer molecular chains is stronger, the polymer molecular chains are more extended, and the viscosity-increasing effect is better.

[0076] It can be seen from Figure 2 and Figure 3 that as the concentration of calcium and magnesium ions in the solution increases, the viscosity of the thickener solution first increases and then decreases, indicating that the synthesized thickener solution has good salt responsiveness. The trend of the solution viscosity first increasing and then decreasing is because in the octadecyl polyoxyethylene polyoxypropylene ether acrylate DEOPOA in the thickener molecule, first, the octadecyl group is a strong hydrophobic group, which tends to aggregate due to hydrophobic interaction in the salt solution to form a physical cross-linked network, thereby increasing the viscosity; second, the EO group and the PO group have the ability to complex calcium and magnesium ions and can form weak coordination bonds with calcium and magnesium ions to promote local cross-linking. Finally, the hydrophilicity of EO can prevent the polymer from completely precipitating under high salt conditions and maintain the solution stability; the hydrophobicity of PO enhances the association effect, and the two jointly regulate the tightness of the network structure, thereby enabling the "salt bridge" viscosity-increasing effect. When the content of calcium and magnesium ions reaches a certain value, the viscosity of the thickener begins to decrease, indicating that the amount of calcium and magnesium ions complexed by the EO group and the PO group in the solution has reached the threshold, and then the shielding effect of calcium and magnesium ions begins to play a dominant role, resulting in a decrease in the solution viscosity. In Example 1, when the contents of CaCl2 and MgCl2 are about 1200 mg / L and 1000 mg / L, the viscosity reaches the maximum value. The solution viscosity increases by 127.47 mPa·s and 96.5 mPa·s respectively compared to the initial state, and the increase rates are 77.11% and 58.38% respectively. In Comparative Example 1, when the contents of CaCl2 and MgCl2 are 800 mg / L, the viscosity reaches the maximum value. The viscosity increases by 59 mPa·s and 39.3 mPa·s respectively compared to the initial state, and the increase rates are 40.6% and 27.05% respectively.

[0077] Comparing Example 1 and Comparative Example 1, the higher the concentration of the salt-responsive functional monomer, the more the content of the hydrophobic chain, which leads to an enhanced association effect, an increase in the initial viscosity of the polymer, and at the same time, the larger the number of EO groups and PO groups, and the stronger the complexing effect on calcium and magnesium ions, thus having a better response viscosity-increasing effect.

[0078] Comparing Example 1 and Comparative Example 2, Example 1 has a better thickening effect in the calcium and magnesium ion solution. The maximum increase in viscosity in the calcium and magnesium ion solution reaches 127.47 mPa·s and 96.5 mPa·s. In Comparative Example 2, the viscosity reaches the maximum value when the content of CaCl2 and MgCl2 is 1000 mg / L, and the maximum increase in viscosity reaches 78.2 mPa·s and 72.2 mPa·s. This shows that, compared with Comparative Example 2, the threshold of the amount of complexed calcium and magnesium ions by the EO group and PO group in the CSDT prepared in Example 1 is higher. This is because after the surface functional monomer dimethylaminoethyl methacrylate monomer is protonated by carbon dioxide, the polymer molecular chain is better stretched through electrostatic interaction, which is more convenient for the complexation and cross-linking of oxyethyl and oxypropyl groups with calcium and magnesium ions, promoting the complexation with calcium and magnesium ions and making the thickening effect of the polymer better.

[0079] It can be seen from Figure 4 that when calcium and magnesium ions are added to the CSDT solution in sequence and carbon dioxide is introduced, the anti-shear ability of the thickener solution is significantly enhanced. The zero-shear viscosity of the solution increases from 510.94 mPa·s to 1911.29 mPa·s and 9415.46 mPa·s, and the viscosity increases significantly. When the shear rate is 1000 s -1 , the apparent viscosities are 6.80 mPa·s, 6.81 mPa·s, and 23.43 mPa·s respectively, indicating that the anti-shear ability of the thickener solution is improved after adding calcium and magnesium ions and carbon dioxide.

[0080] It can be seen from Figure 5 that under the condition of the test frequency of 0.1~10 rad / s, the viscous modulus G'' of the three solutions is always higher than the elastic modulus G'. This shows that the viscous characteristics in the thickener solution always dominate. After adding calcium and magnesium ions and introducing carbon dioxide, both the elastic modulus G' and the viscous modulus G'' of the thickener solution increase to a certain extent, and the viscous modulus G'' dominates, indicating that calcium and magnesium ions and carbon dioxide have a positive effect on enhancing the association performance of the polymer.

[0081] It can be seen from Figure 6 that as the shear rate increases from 0 to 200 s -1 and then decreases to 0, the shear stress increases and then decreases to form a closed loop. After adding calcium and magnesium ions and introducing carbon dioxide into the thickener solution, the area of the closed loop of the shear stress gradually increases, indicating that more and more energy is required to destroy the solution structure and the structure is difficult to be destroyed. This verifies that calcium and magnesium ions and carbon dioxide make the network structure of the thickener molecules more compact and powerful.

[0082] It can be seen from Figure 7 that when no calcium and magnesium ions and carbon dioxide are added to the 0.5% CSDT solution, at 140℃ and 170 s -1The viscosity after continuous shearing for 2 h under the condition of

[0083] is 16.83 mPa·s. The shearing viscosity in the solution of 500 mg / L CaCl2 + 500 mg / L MgCl2 is 36.2 mPa·s. After introducing carbon dioxide and shearing for 2 h, the viscosity is 58.8 mPa·s, indicating that after adding calcium and magnesium ions and carbon dioxide, the polymer significantly improves the temperature and shear resistance of the thickening agent, and at the same time can also utilize calcium and magnesium ions in high salinity formation water. Figure 7 It can be seen that the temperature and shear resistance of Example 1 is better than that of Comparative Example 1. The viscosities after continuous shearing for 2 h under the conditions of 140 °C and 170 s -1 are 58.8 mPa·s and 36.2 mPa·s respectively, indicating that after adding calcium and magnesium ions and carbon dioxide, the polymer significantly improves the temperature and shear resistance of the thickening agent, and at the same time can also utilize calcium and magnesium ions in high salinity formation water.

[0084] It can be seen from Figure 8 that after 60 h of spontaneous imbibition, the imbibition efficiency of the CSDT gel-breaking fluid is 16.98%, and the imbibition effect is improved by 12.66% compared with that of clear water. This is because the polymer molecular fragments in the CSDT gel-breaking fluid contain octadecyl polyoxyethylene polyoxypropylene ether non-ionic surfactant, which can improve the imbibition oil displacement effect of the gel-breaking fluid.

[0085] It can be seen from Figure 9 that 3173.28 cm -1 is the stretching vibration peak of N-H of amide bond, and 1650.19 cm -1 is the in-plane bending vibration absorption peak of C=O, which proves the existence of acrylamide in the polymer. The C-H stretching vibration peaks at 2879.32 cm -1 and 2833.45 cm -1 correspond to the stretching vibration absorption peaks related to -CH2- and -CH3 respectively. The in-plane bending vibration peak of -CH2 is at 1445.29 cm -1 . The stretching vibration peaks at 1113.11 cm -1 and 1089.1 cm -1 are the peaks of -C-O-C- in oxyethyl and oxypropyl of octadecyl polyoxyethylene polyoxypropylene ether acrylate monomer respectively, indicating that octadecyl polyoxyethylene polyoxypropylene ether acrylate is embedded in the polymer chain. The stretching vibration peak of -OH in the carboxyl group of acrylic acid is at 3285.14 cm -1 . The peaks at 1397.6 cm -1 and 1044.59 cm -1They are the stretching vibration peaks of -N-CH3 and -C-N- of the tertiary amino group in the dimethylaminoethyl methacrylate monomer. Infrared analysis shows that the target product contains characteristic groups such as amide groups, polyoxyethylene polyoxypropylene ethers, and tertiary amine groups, proving that the synthesized polymer is the target product.

[0086] The carbon dioxide-responsive viscosity-increasing experiments and calcium-magnesium ion-responsive viscosity-increasing experiments provided in Experimental Examples (1) and (2) were used to test the CSDT prepared in each example and comparative example. As shown in Table 1, Ca 2+ , Mg 2+ The viscosity-increasing data for the response is the viscosity-increasing result with the largest viscosity increase in the calcium-magnesium ion-responsive viscosity-increasing experiment; the CO2-responsive viscosity-increasing data is the viscosity-increasing result after passing CO2 for 50 min in the carbon dioxide-responsive viscosity-increasing experiment. It can be seen from Table 1 that the carbon dioxide-salt dual-responsive polymer prepared in the present invention has an increase in viscosity after injecting CO2 and calcium-magnesium ions. Combining Examples 1, 3, 4, and 6, the viscosity-increasing effects are different after polymerization using different carbon dioxide-responsive monomers. The CO2 viscosity-increasing effects corresponding to dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, dimethylamino styrene, and allylamine are 86.67 mPa·s, 74.4 mPa·s, 54.5 mPa·s, and 72.1 mPa·s respectively, indicating that dimethylaminoethyl methacrylate has the strongest response ability, followed by diethylaminoethyl methacrylate, allylamine, and dimethylamino styrene. Combining Examples 1, 5, and 6, the viscosity-increasing effects are also different for different alkyl numbers and oxyethyl numbers in the salt-responsive monomers. The calcium-magnesium ion viscosity-increasing effects of Examples 1, 5, and 6 are 127.47 mPa·s, 114.3 mPa·s, 104.1 mPa·s and 96.5 mPa·s, 82.1 mPa·s, 76.5 mPa·s respectively. The alkyl numbers of the salt-responsive monomers in Examples 2 and 5 are the same, and the EO number of Example 2 is higher than that of Example 5, so the complexing ability with calcium-magnesium ions is stronger, and the viscosity-increasing effect is better; the EO numbers of Examples 5 and 6 are the same, and the alkyl number of Example 5 is higher than that of Example 6, and the hydrophobic association effect is stronger, and the viscosity-increasing effect is better.

[0087] Table 1 Carbon dioxide and salt viscosity-increasing effects of CSDT prepared in each example and comparative example

[0088] The embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A carbon dioxide-salt dual-responsive polymer thickening agent, characterized in that, It is formed by solution polymerization of acrylamide, acrylic acid, alkyl polyether acrylate, and amine-based carbon dioxide-responsive monomer, and its general structural formula is: ； Among them, a / (a + b + c + d) is 75% - 85%, b / (a + b + c + d) is 10% - 20%, c / (a + b + c + d) is 1% - 5%, and d / (a + b + c + d) is 1% - 10%.

2. The carbon dioxide-salt dual-responsive polymer thickener according to claim 1, wherein The structural formula of X is: , , one of r is an integer from 14 to 18; m is an integer from 15 to 30, and n is an integer from 2 to 15.

3. The carbon dioxide-salt dual-responsive polymer thickener according to claim 1, wherein Y is one of ethylene imino group, dimethylaminoethyl methacrylate group, allylamino group, diethylaminoethyl methacrylate group, and dimethylamino styryl group.

4. The carbon dioxide-salt dual-responsive polymer thickener according to claim 2, wherein The R group is one of acrylate group or methacrylate group.

5. The carbon dioxide-salt dual-responsive polymer thickener according to claim 1, wherein The carbon dioxide-salt dual-responsive polymer thickener is used for the exploitation of oilfields with high salinity formation water; The salinity of the formation water is 5000 - 100000 mg / L; the concentration of calcium and magnesium ions in the formation water is 200 - 2500 mg / L.

6. A preparation method of the carbon dioxide-salt dual-responsive polymer thickening agent according to any one of claims 1 to 5, characterized in that, It includes the following steps: Step 1: Add acrylamide, acrylic acid, alkyl polyether acrylate, and amine-based carbon dioxide-responsive monomer into deionized water, and obtain a mixture solution after dissolution; Step 2: Adjust the pH of the mixed solution to 6.5 - 7.5, introduce nitrogen for 30 - 50 min, add an initiator, and polymerize at 45 - 55 °C for 4 - 6 h to obtain a copolymer rubber block; Step 3: Immerse the copolymer rubber block in ethanol to remove moisture, wash it repeatedly 3 - 5 times, and then dry and granulate to obtain the carbon dioxide-salt dual-responsive polymer thickener.

7. The preparation method of the carbon dioxide-salt dual-responsive polymer thickener according to claim 6, wherein The alkyl polyether acrylate is one of alkyl polyoxyethylene ether acrylate, alkyl polyoxypropylene ether acrylate, alkyl polyoxyethylene ether methacrylate, alkyl polyoxypropylene ether methacrylate, alkyl polyoxyethylene polyoxypropylene ether acrylate, and alkyl polyoxyethylene polyoxypropylene ether methacrylate; The amine-based carbon dioxide-responsive monomer is one of ethylene imine, dimethylaminoethyl methacrylate, allylamine, diethylaminoethyl methacrylate, and dimethylamino styrene.

8. The preparation method of the carbon dioxide-salt dual-responsive polymer thickener according to claim 6, wherein The molar ratio of acrylamide, acrylic acid, alkyl polyether acrylate, and amine-based carbon dioxide-responsive monomer is (75 - 85):(10 - 20):(1 - 5):(1 - 10).

9. The preparation method of the carbon dioxide-salt dual-responsive polymer thickener according to claim 6, wherein The total mass of the acrylamide, acrylic acid, alkyl polyether acrylate, and amine-based carbon dioxide-responsive monomer is 25 to 35 wt% of the mixture solution.

10. The preparation method of the carbon dioxide-salt dual-responsive polymer thickener according to claim 6, characterized in that the initiator is azobisisobutyronitrile, and the addition amount of the initiator is 0.02 to 0.1 wt% of the total mass of the acrylamide, acrylic acid, alkyl polyether acrylate, and amine-based carbon dioxide-responsive monomer.

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