Multicomponent copolymers, processes for their preparation and use

Abstract

This invention relates to the field of polymer compound preparation technology, specifically to a multi-component copolymer, its preparation method, and its applications. The multi-component copolymer comprises a first structural unit derived from a first polymeric monomer and a second structural unit derived from a second polymeric monomer, with a molar ratio of the first to the second structural unit of 20-100:1. The first polymeric monomer is a water-soluble vinyl monomer, and the second polymeric monomer contains carbon-carbon double bonds and β-keto ester groups. This multi-component copolymer can be used as a drag-reducing agent, and during its use as a drag-reducing agent, it can achieve controlled degradation of the main chain under the temperature conditions of shallow and medium-depth shale oil reservoirs, degrading the macromolecular polymer into smaller molecular fragments and avoiding the blockage and damage to reservoir pore throats caused by polymer residues.

Description

Technical Field

[0001] This invention relates to the field of polymer compound preparation technology, specifically to a multi-component copolymer, its preparation method, and its application. Background Technology

[0002] Shallow and medium-depth shale oil (burial depth <3500m, temperature <90℃) has become a key area for increasing shale oil reserves and production due to its relatively low development cost and high engineering technology maturity. These reservoirs are characterized by low porosity and low permeability, making extraction difficult. Hydraulic fracturing technology is the main technology for their development, with slickwater fracturing fluid being the core working fluid. However, during hydraulic fracturing, after the slickwater fracturing fluid is pressurized by a high-pressure pump and then pumped into the formation at high speed through the tubing string, severe turbulence occurs during fluid flow within the tubing under high pressure and high speed conditions. This results in significant frictional resistance between the fracturing fluid and the tubing wall, restricting fluid flow and reducing pipeline throughput while increasing energy loss. Therefore, it is necessary to add polymer drag-reducing agents to the fluid to reduce the impact of frictional resistance and improve construction efficiency.

[0003] However, current polymer drag reducer technology has the following drawbacks: Conventional polyacrylamide drag reducers have molecular sizes in the micrometer range, which is 2-3 orders of magnitude smaller than the nanometer-sized pores in shale reservoirs. This characteristic makes them highly susceptible to clogging microfractures and pore throat structures, causing reservoir damage. Furthermore, the fracturing fluid needs to undergo a flowback process to reduce potential reservoir damage. Polymer drag reducers can typically be broken down through mechanical degradation and chemical degradation. However, in the process of breaking down polyacrylamide, for example, a breaker (such as ammonium persulfate) is usually required to stimulate free radical reactions, thereby degrading the large polymer molecules into smaller molecules. In practice, however, fracturing fluid often fails to completely degrade during the breaking down process, leaving residual polymer fragments that continue to clog pore throats, leading to bottom blockage. Moreover, the timing of the breaking down process is difficult to match with the well shut-in cycle; premature degradation leads to proppant failure, while delayed degradation results in residual polymers causing reservoir damage.

[0004] Therefore, there is an urgent need for a polymer drag reducer that combines high drag reduction performance with controllable degradation characteristics. This polymer can remain stable during the construction phase to complete the drag reduction and sand carrying function, and degrade in a timely manner during the post-pressure well sump stage, thereby eliminating the damage to the reservoir caused by polymer residues from the root. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of existing drag-reducing agents often failing to completely degrade during the gel-breaking process, resulting in residual polymer fragments continuing to clog pore throats and causing bottom blockage; and the timing of gel-breaking being difficult to match with the well blockage cycle, with premature degradation leading to sand-carrying failure and delayed degradation causing reservoir damage due to residual polymers. This invention provides a multi-component copolymer, its preparation method, and its application. This multi-component copolymer can be used as a drag-reducing agent, and during its use as a drag-reducing agent, it can achieve controlled degradation of polymer molecules under the temperature conditions of shallow and medium-depth shale oil reservoirs, degrading large polymer molecules into smaller molecular fragments and avoiding the blockage damage to reservoir pore throats caused by residual polymers.

[0006] To achieve the above objectives, the present invention provides a multi-component copolymer comprising a first structural unit derived from a first polymeric monomer and a second structural unit derived from a second polymeric monomer, wherein the molar ratio of the first structural unit to the second structural unit is 20-100:1. The first polymerizable monomer is a water-soluble vinyl monomer, and the second polymerizable monomer contains carbon-carbon double bonds and β-keto ester groups.

[0007] Preferably, the second polymerizing monomer is selected from one or more of ethylene glycol acetoacetate methacrylate, allyl acetoacetate, and ethyl 2-(acryloyloxy)acetoacetate.

[0008] Preferably, the water-soluble vinyl monomer is selected from one or more of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, sodium p-styrenesulfonate, acrylic acid, N-vinylpyrrolidone and vinylimidazole.

[0009] A second aspect of the present invention provides a method for preparing a multi-component copolymer, the method comprising the following steps: (1) Mix the first monomer, the second monomer and water, and adjust the pH of the mixture to 6-7; (2) The material obtained in step (1) is subjected to deoxygenation treatment so that the deoxygenated material can undergo polymerization reaction with the initiator; The first polymerizing monomer is a water-soluble vinyl monomer, and the second polymerizing monomer contains carbon-carbon double bonds and β-keto ester groups; the molar ratio of the first polymerizing monomer to the second polymerizing monomer is 20-100:1.

[0010] Preferably, the second polymerizing monomer is selected from one or more of ethylene glycol acetoacetate methacrylate, allyl acetoacetate, and ethyl 2-(acryloyloxy)acetoacetate.

[0011] Preferably, the water-soluble vinyl monomer is selected from one or more of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, sodium p-styrenesulfonate, acrylic acid, N-vinylpyrrolidone and vinylimidazole.

[0012] Preferably, the amount of the initiator is 0.01-0.2 parts by weight relative to 100 parts by weight of the first polymerizing monomer.

[0013] Preferably, the initiator is selected from at least one of persulfate, azo initiators, and redox systems composed of persulfate and amine reducing agents.

[0014] Preferably, the conditions for the polymerization reaction include: a temperature of 20-50°C and a time of 5-10 hours.

[0015] Preferably, the specific process of step (1) includes: mixing the second polymer monomer with a cosolvent to obtain a mixture, then mixing the mixture, the first polymer monomer and water, and adjusting the pH of the mixture to 6-7.

[0016] Preferably, the co-solvent is ethanol.

[0017] A third aspect of the present invention provides a multi-component copolymer prepared by the above method.

[0018] A fourth aspect of the present invention provides the application of the aforementioned multi-component copolymer as a drag-reducing agent for fracturing in oil and gas fields.

[0019] The fifth aspect of the present invention provides a method for oil and gas extraction, the method comprising: injecting fracturing fluid containing the aforementioned multi-component copolymer into a shallow shale reservoir, and then performing oil and gas extraction.

[0020] Preferably, the temperature of the shallow to medium-depth shale reservoir is 60-80℃.

[0021] The multi-component copolymer described in this invention can be used as a drag-reducing agent for fracturing in oil and gas fields. The multi-component copolymer contains a first structural unit derived from a water-soluble vinyl monomer and a second structural unit derived from a second polymeric monomer containing both carbon-carbon double bonds and β-keto ester groups. The carbon-carbon double bonds in the water-soluble vinyl monomer and the second polymeric monomer polymerize to form the main chain of the multi-component copolymer. Furthermore, the second structural unit introduces self-degradable side groups containing β-keto ester groups onto the main chain. Under the temperature conditions of shallow shale reservoirs, the β-keto ester groups in the side groups attached to the main chain of the multi-component copolymer undergo gradual hydrolysis or pyrolysis, thereby reducing the degree of entanglement of the multi-component copolymer. Furthermore, the acidic substances generated by the hydrolysis or pyrolysis of the β-keto ester groups in the side groups of the multi-component copolymer can further accelerate the breakage of the main chain, causing the molecular weight of the multi-component copolymer to degrade from millions to small molecular fragments of thousands of Daltons, thus degrading the high molecular weight polymer into small molecular fragments and achieving controlled degradation of the multi-component copolymer.

[0022] Compared with the prior art, the multi-component copolymer described in this invention has the following beneficial effects: (1) Molecular design innovation: β-keto ester groups are directly connected to the main chain of the multi-component copolymer as side groups, and the degradation of the main chain of the multi-component copolymer is accelerated by the hydrolysis of the connected side groups, so as to realize the autonomous degradation of the polymer and solve the reservoir blockage problem caused by the residue of polymer drag reducer. (2) Controllable degradation timing: By adjusting the content of β-keto ester groups in the multi-component copolymer, the degradation rate can be matched with the well shut-in period in the range of 60-80℃, realizing the function of "fracture and sand carrying in the fracturing stage and autonomous degradation in the well shut-in stage"; (3) Reservoir protection: The degradation products obtained after degradation of the multi-component copolymer described in this invention match the nanopore size (<100 nm) of shale, and the core matrix permeability recovery rate can reach more than 95%, further avoiding damage to the shale reservoir. Detailed Implementation

[0023] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0024] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0025] In this invention, the multi-component copolymer is copolymerized by free radical polymerization of a first polymeric monomer and a second polymeric monomer via aqueous solution using carbon-carbon double bond polymerization. The first polymeric monomer is a water-soluble vinyl monomer, and the second polymeric monomer contains both carbon-carbon double bonds and β-keto ester groups. The carbon-carbon double bonds in the water-soluble vinyl monomer and the second polymeric monomer polymerize to form the hydrophilic backbone of the multi-component copolymer, providing excellent drag reduction and high-salt resistance. Furthermore, the second polymeric monomer introduces side groups containing β-keto ester groups onto the backbone, creating multiple sites for accelerating backbone breakage. The hydrolysis or pyrolysis of the β-keto ester groups in the side groups of the multi-component copolymer reduces entanglement between molecular chains. Additionally, the acidic substances generated by the hydrolysis or pyrolysis of the β-keto ester groups further accelerate the gradual hydrolysis of the multi-component copolymer backbone, degrading the high-molecular-weight polymer into smaller molecular fragments. This eliminates the need for additional chemical treatment of the fracturing fluid, further preventing the blockage and damage to reservoir pore throats caused by polymer residues.

[0026] In some preferred embodiments, the water-soluble vinyl monomer is selected from one or more of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, sodium p-styrenesulfonate, acrylic acid, N-vinylpyrrolidone, and vinylimidazole, preferably from two or more of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, sodium p-styrenesulfonate, acrylic acid, N-vinylpyrrolidone, and vinylimidazole.

[0027] In some preferred embodiments, in order to further improve the high temperature and high salt resistance of the drag-reducing agent without affecting the self-degradation performance of the multi-component copolymer, the water-soluble vinyl monomer is selected from two or more of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, sodium p-styrenesulfonate, acrylic acid, and N-vinylpyrrolidone, and is particularly preferred to be a combination of acrylamide, acrylic acid, and sodium p-styrenesulfonate.

[0028] In this invention, the second polymerizable monomer can be a commercially available product or can be prepared by methods commonly used in the art. Preferably, the second polymerizable monomer is selected from one or more of ethylene glycol acetoacetate, allyl acetoacetate, and ethyl 2-(acryloyloxy)acetoacetate, and is preferably ethylene glycol acetoacetate.

[0029] In this invention, the molar ratio of the first structural unit to the second structural unit is 20-100:1, preferably 20-95:1, more preferably 30-92:1, and even more preferably 40-90:1. By adjusting the molar ratio of the first structural unit to the second structural unit, the distribution density of the side groups containing β-keto ester groups attached to the main chain of the multi-component copolymer in the polymer molecule can be precisely controlled, thereby regulating the degradation rate to match the post-pressure well shut-in cycle, achieving the technical effect of timely degradation, and further reducing the risk of reservoir blockage. Specifically, the molar ratio of the first structural unit to the second structural unit can be 20:1, 25:1, 30:1, 35:1, 40:1, 45:1, 50:1, 55:1, 60:1, 65:1, 70:1, 75:1, 80:1, 85:1, or 90:1. In this invention, the molar ratio of the first structural unit and the second structural unit is calculated using the amount of the first polymeric monomer and the second polymeric monomer fed into the preparation process. It can be understood that the molar ratio of the first structural unit and the second structural unit is the molar ratio of the amount of the first polymeric monomer and the second polymeric monomer used.

[0030] In some embodiments, the weight-average molecular weight of the multi-component copolymer is 5 million to 10 million.

[0031] In some embodiments, an initiator is also added during the preparation of the multi-component copolymer. The initiator may be at least one selected from persulfate, azo initiators, and redox systems composed of persulfate and amine reducing agents.

[0032] In some embodiments, the persulfate is ammonium persulfate and / or potassium persulfate.

[0033] In some embodiments, the amine reducing agent is tetramethylethylenediamine and / or sodium bisulfite.

[0034] In some embodiments, the azo initiator is azobisisobutyramidine hydrochloride and / or azobisisobutyramidine imidazoline hydrochloride.

[0035] The multi-component copolymer described in this invention possesses both high-temperature and high-salt resistance, maintaining its efficient drag reduction performance even under high-temperature and high-salt conditions. Furthermore, the main chain of the multi-component copolymer is connected to side groups containing β-keto ester groups. The acidic substances generated by the gradual hydrolysis or pyrolysis of the β-keto ester groups on the side groups of the multi-component copolymer further accelerate the breakage of the main chain, degrading the molecular weight from millions to small molecular fragments of thousands of Daltons. This achieves controlled degradation, effectively avoiding the blockage damage to reservoir pores and throats caused by polymer residues. It also avoids the blockage of shale reservoirs caused by incomplete artificial gel breaking processes, thus improving reservoir protection.

[0036] The present invention further provides a method for preparing a multi-component copolymer, the method comprising the following steps: (1) Mix the first monomer, the second monomer and water, and adjust the pH of the mixture to 6-7; (2) The material obtained in step (1) after adjusting the pH value is subjected to deoxygenation treatment so that the deoxygenated material can undergo polymerization reaction with the initiator.

[0037] In the method described in this invention, the first polymerizing monomer is a water-soluble vinyl monomer, and the second polymerizing monomer contains carbon-carbon double bonds and β-keto ester groups. The multi-component copolymer is obtained by free radical polymerization of the first and second polymerizing monomers in an aqueous solution. The water-soluble vinyl monomer and the carbon-carbon double bonds contained in the second polymerizing monomer polymerize to form the hydrophilic backbone of the multi-component copolymer. Furthermore, the second polymerizing monomer introduces side groups containing β-keto ester groups onto the polymer backbone, resulting in multiple sites on the multi-component copolymer backbone for accelerating backbone breakage. Through the hydrolysis or pyrolysis of the β-keto ester groups contained in the side groups of the multi-component copolymer, on the one hand, the entanglement between the multi-component copolymer molecular chains can be reduced; on the other hand, the acidic substances generated by the hydrolysis or pyrolysis of the β-keto ester groups can further accelerate the gradual hydrolysis of the multi-component copolymer backbone, degrading the high molecular weight polymer into smaller molecular fragments. This eliminates the need for additional chemical substances to break up the fracturing fluid used, thereby further avoiding the blockage and damage to reservoir pore throats caused by polymer residues.

[0038] In the method described in this invention, the water-soluble vinyl monomer is selected from one or more of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, sodium p-styrenesulfonate, acrylic acid, vinylpyrrolidone, and vinylimidazole; in a preferred embodiment, the water-soluble vinyl monomer is two or more compounds, that is, the water-soluble vinyl monomer is selected from at least two or more of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, sodium p-styrenesulfonate, acrylic acid, vinylpyrrolidone, and vinylimidazole, and is particularly preferred to be a combination of acrylamide, acrylic acid, and sodium p-styrenesulfonate.

[0039] In the method described in this invention, the second polymeric monomer can be a commercially available product or can be prepared by methods commonly used in the art. Preferably, the second polymeric monomer is selected from one or more of ethylene glycol acetoacetate methacrylate, allyl acetoacetate, and ethyl 2-(acryloyloxy)acetoacetate, and is preferably ethylene glycol acetoacetate methacrylate.

[0040] In the method described in this invention, the molar ratio of the first polymeric monomer to the second polymeric monomer is 20-100:1, preferably 20-95:1, more preferably 30-92:1, and even more preferably 40-90:1. By adjusting the relationship between the two polymeric monomers, the molar ratio of the first structural unit to the second structural unit in the synthesized multi-component copolymer can be further controlled. This allows for precise control of the distribution density of the side groups containing β-keto ester groups attached to the main chain of the multi-component copolymer in the polymer molecule, thereby regulating the degradation rate to match the post-pressure well shut-in cycle and achieving the technical effect of timely degradation, further reducing the risk of reservoir blockage. Specifically, the molar ratio of the soluble vinyl monomer to the monomer containing β-keto ester groups can be 20:1, 25:1, 30:1, 35:1, 40:1, 45:1, 50:1, 55:1, 60:1, 65:1, 70:1, 75:1, 80:1, 85:1, or 90:1.

[0041] In the method described in this invention, adjusting the pH of the obtained mixture to 6-7 in step (1) can effectively promote monomer polymerization and make the polymerization reaction more favorable.

[0042] In the method described in this invention, in step (1), in order to further improve the dispersibility of the second polymeric monomer in the reaction system, the second polymeric monomer can be mixed with a cosolvent first, and then the resulting mixture can be mixed with the water-soluble vinyl monomer and water. The specific process of step (1) includes: mixing the second polymeric monomer with a cosolvent to obtain a mixture, then mixing the mixture, the first polymeric monomer and water, and adjusting the pH of the mixture to 6-7.

[0043] In some embodiments, the co-solvent may be ethanol.

[0044] In some embodiments, the deoxygenation process in step (2) includes introducing an inert gas into the pH-adjusted material obtained in step (1) for deoxygenation. Specifically, the inert gas refers to a gas that does not participate in the reaction, such as nitrogen and / or an inert gas (e.g., argon). The introduction time of the inert gas can be 20-50 minutes, preferably 30-40 minutes.

[0045] In some preferred embodiments, in step (2), the conditions for the polymerization reaction include: a temperature of 20-50°C, preferably 30-40°C; and a time of 5-10 hours, preferably 6-10 hours.

[0046] In the method described in this invention, the initiator is used to initiate the polymerization reaction between the water-soluble vinyl monomer and the second polymerizable monomer. The specific composition of the initiator used in the method described in this invention is not limited.

[0047] In a preferred embodiment, the initiator is selected from at least one of persulfate, azo initiators, and redox systems composed of persulfate and amine reducing agents. In some embodiments, the persulfate may be ammonium persulfate and / or potassium persulfate, the azo initiator may be azobisisobutyramidine hydrochloride and / or azobisisobutyramidine imidazoline hydrochloride, and the amine reducing agent may be tetramethylethylenediamine and / or sodium bisulfite.

[0048] In some embodiments, in step (2), the initiator can be mixed with water to obtain an initiator solution, and then the initiator solution can be added dropwise to the material after deoxygenation treatment to carry out the polymerization reaction.

[0049] In some embodiments, the amount of the initiator relative to 100 parts by weight of the first polymerizing monomer is 0.01-0.2 parts by weight, preferably 0.02-0.09 parts by weight, and more preferably 0.05-0.08 parts by weight. Specifically, the amount of the initiator relative to 100 parts by weight of the first polymerizing monomer can be 0.01 parts by weight, 0.02 parts by weight, 0.03 parts by weight, 0.04 parts by weight, 0.05 parts by weight, 0.06 parts by weight, 0.07 parts by weight, 0.08 parts by weight, 0.09 parts by weight, or 0.1 parts by weight.

[0050] In the method described in this invention, the method further includes post-processing the material after the polymerization reaction to obtain the multi-component copolymer. Specifically, the post-processing may involve mixing the material after the polymerization reaction with an organic solvent, followed by filtration, washing the resulting solid material, and then drying it. In some embodiments, the organic solvent used may be ethanol.

[0051] In some embodiments, the polymerized material can be added dropwise to an organic solvent to facilitate the better precipitation of the multi-component copolymers contained in the polymerized material.

[0052] The multi-component copolymer prepared by the method described in this invention comprises a first structural unit derived from a first polymeric monomer and a second structural unit derived from a second polymeric monomer. The carbon-carbon double bonds contained in the first and second polymeric monomers polymerize to form the hydrophilic backbone of the multi-component copolymer, providing excellent drag reduction and high-salt resistance. The second polymeric monomer introduces side groups containing β-keto ester groups onto the backbone, creating multiple sites on the multi-component copolymer molecule that accelerate backbone breakage. The hydrolysis or pyrolysis of the β-keto ester groups in the side groups of the multi-component copolymer reduces entanglement between molecular chains. Furthermore, the acidic substances generated by the hydrolysis or pyrolysis of the β-keto ester groups further accelerate the gradual hydrolysis of the multi-component copolymer backbone, degrading the high-molecular-weight polymer into smaller molecular fragments. Therefore, the multi-component copolymer of this invention possesses excellent drag reduction properties and excellent self-degradation properties, eliminating the need for additional gel breaking treatment of the fracturing fluid used, thereby further preventing the blockage and damage to reservoir pore throats by polymer residues. The multi-component copolymer described in this invention can be used as a drag reducer for fracturing in oil and gas fields, and can significantly reduce damage to shallow and medium-depth shale reservoirs.

[0053] The present invention further provides a fracturing fluid containing the aforementioned multi-component copolymer. This fracturing fluid is well-suited for use as a working fluid in hydraulic fracturing technology, and it causes less damage to the reservoir and is more environmentally friendly.

[0054] In some preferred embodiments, the content of the multi-component copolymer in the fracturing fluid is 0.05-0.5 wt%, preferably 0.08-0.3 wt%.

[0055] In some specific embodiments, the fracturing fluid also contains a flow aid and a clay stabilizer. The flow aid and the clay stabilizer can be common components in the art and are not specifically limited herein.

[0056] The multi-component copolymer described in this invention is particularly suitable for oil and gas extraction from shallow to medium-depth shale reservoirs. Therefore, this invention also provides a method for oil and gas extraction, the method comprising: injecting fracturing fluid containing the multi-component copolymer into a shallow to medium-depth shale reservoir, followed by oil and gas extraction. In some preferred embodiments, the temperature of the shallow to medium-depth shale reservoir is 60-80°C, for example, 60°C, 65°C, 70°C, 75°C, or 80°C.

[0057] Using fracturing fluid containing the multi-component copolymer described in this invention as a drag-reducing agent for oil and gas extraction in shallow and medium-depth shale reservoirs can effectively achieve the effects of "fracture creation and propagation during the fracturing stage, and autonomous degradation during the well-clogging stage." The specific mechanism is as follows: (1) Wellbore / fracture injection stage. The multi-component copolymer exists as a drag reducer with a complete high molecular weight (5 million-10 million) structure. The main chain of the multi-component copolymer provides drag reduction performance, and the β-keto ester groups contained in the main chain have a low hydrolysis rate below 60°C, and the molecular structure remains stable. It can maintain excellent drag reduction performance (drag reduction rate >70%) under high shear conditions in the wellbore. (2) Post-compression well blockage stage. Under the continuous action of temperature in the shallow and medium-depth shale reservoir, the β-keto ester groups contained in the side groups connected to the main chain of the multi-component copolymer undergo gradual hydrolysis. Under the action of acidic substances obtained from the hydrolysis of the side groups, the polymer main chain is further accelerated to break at multiple sites, and the molecular weight gradually decreases from millions to thousands of Daltons, eventually degrading into small molecular fragments. These small molecular fragments match the shale nanopores (<100 nm) scale, solving the problem of polymer residues blocking and damaging the reservoir pore throats.

[0058] The present invention will be described in detail below through embodiments, but the scope of protection of the present invention is not limited thereto.

[0059] Unless otherwise specified, the raw materials used in the following examples are common commercially available products, and the methods used are common methods unless otherwise specified.

[0060] Specifically, the CAS number of the ethylene glycol acetoacetate methacrylate used is 21282-97-3; The CAS number of allyl acetoacetate used is 1118-84-9; The CAS number of ethyl 2-(acryloyloxy)acetoacetate used is 21282-96-2.

[0061] Example 1 (1) Dissolve 12.5 mg of ammonium persulfate and 12.5 mg of tetramethylethylenediamine in 10 g of water respectively, shake well and set aside; (2) Dissolve 0.6g of ethylene glycol acetoacetate methacrylate in 5g of anhydrous ethanol; (3) Mix the solution in (2) with 100g water, 1g sodium p-styrene sulfonate, 1g acrylic acid and 17.5g acrylamide, and then adjust the pH of the resulting mixture to 6.5; (4) Next, nitrogen gas is introduced into the obtained material for 30 minutes to remove oxygen; (5) Add an initiator solution to the deoxygenated material in (4) to carry out a polymerization reaction. React at 35°C for 10 hours to obtain a solution containing polymer. (6) The polymer-containing solution was slowly added dropwise to excess ethanol to precipitate the polymer, filtered, washed three times with ethanol, and dried under vacuum at 50°C to constant weight to obtain polymer P1.

[0062] Example 2 (1) Dissolve 12.4 mg of ammonium persulfate and 12.4 mg of tetramethylethylenediamine in 10 g of water respectively, shake well and set aside; (2) Dissolve 0.6g of allyl acetoacetate in 5g of anhydrous ethanol; (3) Mix the solution in (2) with 100g water, 1g 2-acrylamido-2-methylpropanesulfonic acid, 1g acrylic acid and 17.5g acrylamide, and then adjust the pH of the resulting mixture to 6; (4) Next, nitrogen gas is introduced into the material for 30 minutes to remove oxygen; (5) Add an initiator solution to the deoxygenated material in (4) to carry out a polymerization reaction. React at 25°C for 8 hours to obtain a solution containing polymer. (6) The polymer-containing solution was slowly added dropwise to excess ethanol to precipitate the polymer, filtered, washed three times with ethanol, and dried under vacuum at 50°C to constant weight to obtain polymer P2.

[0063] Example 3 (1) Dissolve 12.2 mg of ammonium persulfate and 12.2 mg of tetramethylethylenediamine in 10 g of water respectively, shake well and set aside; (2) Dissolve 0.94 g of ethyl 2-(acryloyloxy)acetoacetate in 5 g of anhydrous ethanol; (3) Mix the solution in (2) with 100g water, 1g sodium p-styrene sulfonate, 1g acrylic acid and 17.5g acrylamide, and then adjust the pH of the resulting mixture to 6.5; (4) Next, nitrogen gas is introduced into the obtained material for 30 minutes to remove oxygen; (5) Add an initiator solution to the deoxygenated material in (4) to carry out a polymerization reaction. React at 30°C for 9 hours to obtain a solution containing polymer. (6) The polymer-containing solution was slowly added dropwise to excess ethanol to precipitate the polymer, filtered, washed three times with ethanol, and dried under vacuum at 50°C to constant weight to obtain polymer P3.

[0064] Example 4 The method of Example 1 was carried out, except that the amount of ethylene glycol acetoacetate methacrylate was 1.32 g, and polymer P4 was prepared.

[0065] Example 5 The method of Example 1 was carried out, except that the amount of ethylene glycol acetoacetate methacrylate was 1.758 g, and polymer P5 was prepared.

[0066] Example 6 The method was carried out according to Example 1, except that the amount of ethylene glycol acetoacetate methacrylate was 2.63 g, and polymer P6 was prepared.

[0067] Example 7 (1) Dissolve 12.5 mg of ammonium persulfate and 12.5 mg of tetramethylethylenediamine in 10 g of water respectively, shake well and set aside; (2) Dissolve 0.6g of ethylene glycol acetoacetate methacrylate in 5g of anhydrous ethanol; (3) Mix the solution in (2) with 45g water, 10g acrylamide, 7.3g acrylic acid, 2g 2-acrylamido-2-methylpropanesulfonic acid and 0.2g N-vinylpyrrolidone, and then adjust the pH of the resulting mixture to 6.5; (4) Next, nitrogen gas is introduced into the obtained material for 30 minutes to remove oxygen; (5) Add an initiator solution to the deoxygenated material in (4) to carry out a polymerization reaction. React at 35°C for 10 hours to obtain a solution containing polymer. (6) The polymer-containing solution was slowly added dropwise to excess ethanol to precipitate the polymer, filtered, washed three times with ethanol, and dried under vacuum at 50°C to constant weight to obtain polymer P1.

[0068] Comparative Example 1 The method of Example 1 was carried out, except that ethylene glycol acetoacetate methacrylate was replaced with an equal weight of acrylamide to obtain polymer D1.

[0069] Comparative Example 2 The method of Example 1 was carried out, except that ethylene glycol acetoacetate methacrylate was replaced with an equal weight of diallyl polyoxyethylene ether to obtain polymer D2.

[0070] Comparative Example 3 The method was carried out according to Example 1, except that the amount of ethylene glycol acetoacetate methacrylate added was 3.78 g, and polymer D4 was obtained.

[0071] Comparative Example 4 The method was carried out according to Example 1, except that the amount of ethylene glycol acetoacetate methacrylate was 0.516 g, and polymer D5 was obtained.

[0072] Test case Test Example 1 Following the method in Chapter 7.8 of the oil and gas industry standard "SYT 7627-2021 Technical Requirements for Water-based Fracturing Fluids", the polymers prepared in Examples 1, 2 and Comparative Example 1 were mixed with water to prepare a solution with a polymer concentration of 0.1 wt%. The drag reduction rate of the solution at different temperatures was tested, and the results are shown in Table 1.

[0073] Table 1. Drag reduction rate under different temperature conditions

[0074] According to the results in Table 1, the polymer prepared by this invention has a stable drag reduction rate of over 70% in the range of 30-70℃, which is comparable to that of conventional polyacrylamide; the drag reduction rate decreases at 90℃, indicating that the β-keto ester undergoes hydrolysis.

[0075] Test Example 2 The polymers prepared in Examples 1, 2 and Comparative Example 1 were mixed with water to prepare a solution with a polymer concentration of 0.1 wt%. The solution was aged in an 80°C constant temperature oven for 14 days. Samples were taken at 3, 7 and 14 days to measure the viscosity of the solution. The viscosity retention rate was used to characterize the degree of polymer degradation in the solution. The results are shown in Table 2.

[0076] Table 2. Changes in the degree of degradation at 80℃ over time

[0077] The results show that the polymer prepared by this invention has a significant degradation response at 80℃, and the degradation rate matches the well-sealing cycle well; while conventional polymers degrade very slowly, and the viscosity retention rate is still >85% after 14 days.

[0078] Test Example 3 The polymer prepared in Example 1 was mixed with water to prepare a solution with a polymer concentration of 0.1 wt%. The solution was aged at 80 °C for 14 days, and then samples were taken to determine the molecular weight and distribution by gel permeation chromatography. The results are shown in Table 3.

[0079] Table 3. Changes in molecular weight before and after degradation

[0080] The results showed that the polymer described in this invention can undergo autonomous degradation at 80°C. After degradation, the molecular weight of the polymer decreased from 6.5 million to 38,000, with a reduction rate of >95%, confirming that the main chain had been broken and the degradation products were small molecular fragments.

[0081] Test Example 4 Polymers with different contents of ethylene glycol acetoacetate methacrylate prepared in Examples 4 to 6 were tested, and their degradation half-life (time required for viscosity to decrease by 50%) was measured at 80°C. The results are shown in Table 4.

[0082] Table 4 Relationship between Ethyl acetoacetate content and degradation half-life

[0083] The results show that by controlling the content of β-keto ester side groups attached to the main chain of the prepared polymer, the degradation half-life can be controlled within the range of 5-13 days, achieving precise matching with different well-closing cycles.

[0084] Test Example 5 The polymer prepared in Example 1 was mixed with water to form a solution with a polymer concentration of 0.1 wt%. The solution was aged at different temperatures for 7 days, and the viscosity retention rate was measured. The results are shown in Table 5.

[0085] Table 5 Viscosity retention rate after 7 days of degradation at different temperatures

[0086] The results show that the polymer prepared by this invention is structurally stable at ≤50℃, exhibits a significant degradation response in the shallow reservoir temperature range of 60-80℃, and degrades too rapidly at ≥90℃, indicating that it is particularly suitable for shallow and medium-depth shale reservoirs (formation temperature of 60-80℃).

[0087] Test Example 6 Following the method in Chapter 7.7 of "SYT 5107-2016 Performance Evaluation Method of Water-based Fracturing Fluid", the polymers prepared in the examples and comparative examples were mixed with water to form a solution with a concentration of 0.1 wt%. After aging for 14 days, a core flow experiment was conducted to test the degree of damage to the core permeability. The results are shown in Table 6.

[0088] Table 6 Core matrix permeability recovery rate

[0089] The results show that the polymer of the present invention has extremely low residue content after degradation, causes little damage to core permeability, and has a recovery rate of >95%; conventional polymers have high residue content and a permeability recovery rate of only 72.3%.

[0090] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A multi-component copolymer, characterized in that, The multi-component copolymer includes a first structural unit derived from a first polymeric monomer and a second structural unit derived from a second polymeric monomer, wherein the molar ratio of the first structural unit to the second structural unit is 20-100:

1. The first polymerizing monomer is a water-soluble vinyl monomer, which is selected from one or more of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, sodium p-styrenesulfonate, acrylic acid, N-vinylpyrrolidone and vinylimidazole; The second polymerizable monomer contains a carbon-carbon double bond and a β-keto ester group, and the second polymerizable monomer is selected from one or more of ethylene glycol acetoacetate methacrylate, allyl acetoacetate and ethyl 2-(acryloyloxy)acetoacetate.

2. A method for preparing the multi-component copolymer according to claim 1, characterized in that, The method includes the following steps: (1) Mix the first monomer, the second monomer and water, and adjust the pH of the mixture to 6-7; (2) The material obtained in step (1) is subjected to deoxygenation treatment so that the deoxygenated material can undergo polymerization reaction with the initiator; The molar ratio of the first polymeric monomer to the second polymeric monomer is 20-100:

1.

3. The method according to claim 2, characterized in that, The amount of the initiator is 0.01-0.2 parts by weight relative to 100 parts by weight of the first polymerizing monomer.

4. The method according to claim 2, characterized in that, The initiator is selected from at least one of persulfate, azo initiators, and redox systems composed of persulfate and amine reducing agents.

5. The method according to claim 2, characterized in that, The conditions for the polymerization reaction include: a temperature of 20-50℃ and a time of 5-10h.

6. The method according to claim 2, characterized in that, The specific process of step (1) includes: mixing the second polymer monomer with a cosolvent to obtain a mixture, then mixing the mixture, the first polymer monomer and water, and adjusting the pH of the mixture to 6-7.

7. The method according to claim 6, characterized in that, The co-solvent is ethanol.

8. The application of the multi-component copolymer of claim 1 as a drag reducer for fracturing in oil and gas fields.

9. A method for oil and gas extraction, characterized in that, The method includes: injecting fracturing fluid containing the multi-component copolymer of claim 1 into a shallow shale reservoir, followed by oil and gas extraction.

10. The method according to claim 9, characterized in that, The temperature of the shallow to medium-depth shale reservoir is 60-80℃.

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