Temperature-responsive crosslinking copolymer, method for preparing the same, and use thereof as flow pattern modifier

Abstract

The present application relates to oil and gas exploration technology field, disclose a kind of temperature response type crosslinking copolymer and its preparation method and as the application of flow pattern regulator.The crosslinking copolymer contains structural unit A provided by main chain monomer, structural unit B provided by first functional monomer, structural unit C provided by second functional monomer, structural unit D provided by third functional monomer, structural unit E provided by temperature-sensitive monomer.The regulator of the present application has the "temperature response" characteristics, that is, at low temperature, keep low viscosity to facilitate circulation, and at high temperature, viscosity and shear force are greatly improved through molecular conformation transformation.This innovative technical approach can fundamentally solve the rheological control problem in deep well and deep sea drilling, and has great theoretical value and broad application prospect.

Description

Technical Field

[0001] This invention relates to the field of oil and gas exploration technology, specifically to a temperature-responsive crosslinked copolymer, its preparation method, and its application as a flow pattern regulator. Background Technology

[0002] Deep and deep-sea oil and gas reserves are the strategic cornerstone for ensuring national energy security and the core area for increasing reserves and production. Statistics show that the world possesses abundant deep and ultra-deep oil and gas resources. However, to transform these strategic reserves into actual production capacity, the core prerequisite is to overcome the engineering and technological bottlenecks encountered in extreme downhole environments (such as high temperature, high pressure, and large temperature differences). Among these, drilling fluid technology is a crucial element.

[0003] Drilling fluid, as the "blood" of drilling operations, has core functions such as carrying cuttings, balancing formation pressure, stabilizing the wellbore, and cooling and lubricating the drill bit, making it crucial for ensuring the safe and efficient development of oil and gas. Flow modifiers (or viscosity improvers, shear enhancers) are key agents for controlling the rheological properties of drilling fluids, and their performance directly affects the safety and efficiency of drilling operations.

[0004] However, in extreme environments such as deep formations (bottom hole temperatures often ≥200℃) and deep seas (where high bottom hole temperatures coexist with low mudline temperatures (2-4℃), the contradiction of water-based drilling fluids being "difficult to pump at low temperatures and difficult to carry rock at high temperatures" becomes prominent. Under high-temperature conditions, due to the degradation of the molecular chains or conformational shrinkage of flow modifiers, the viscosity and shear force of the drilling fluid decrease sharply, severely losing its ability to suspend and carry solid phases, which can easily lead to downhole accidents such as difficulty in tripping in and out of the well, stuck pipe, and lost circulation. Under low-temperature conditions, the drilling fluid thickens significantly, leading to a surge in circulating pressure loss and large fluctuations in ECD, which can easily induce lost circulation or even blowouts in weak formations. In addition, high-salinity formations also place stringent requirements on the salt resistance of flow modifiers.

[0005] To address these challenges, scholars from various countries have developed a variety of flow pattern modifiers: Natural polymer modification: Chemical modification of natural polymers such as starch and cellulose typically limits their temperature resistance to over 150°C, failing to meet the requirements of deep well operations; Synthetic high-temperature resistant polymers: Synthesizing high-temperature resistant polymers by introducing high-temperature resistant monomers such as AMPS and NVP is currently the mainstream technology, which enhances the rigidity of the molecular chains to resist degradation at high temperatures. Although their temperature resistance can reach 200°C, they essentially only delay the "high-temperature thinning" trend and do not change the law that viscosity decreases with increasing temperature; Synergistic use of inorganic nanomaterials: Constructing a high-temperature resistant rigid network using nano-silica or attapulgite provides good temperature stability, but these materials are prone to aggregation and failure in brine environments, and high dosages can easily damage the reservoir.

[0006] In summary, existing technologies, whether naturally modified or artificially synthesized, are all based on a "passive resistance" approach, focusing on how to delay or reduce negative performance fluctuations caused by temperature changes. There is an urgent need in this field for a "smart" flow pattern regulator that can actively utilize ambient temperature as a performance driver. Summary of the Invention

[0007] This invention aims to solve the problem of "thickening at low temperatures and thinning at high temperatures" in existing drilling and completion fluids in extreme environments such as deep formations and deep seas.

[0008] To achieve the above objectives, a first aspect of the present invention provides a temperature-responsive crosslinked copolymer containing structural unit A provided by a main chain monomer, structural unit B provided by a first functional monomer, structural unit C provided by a second functional monomer, structural unit D provided by a third functional monomer, and structural unit E provided by a temperature-sensitive monomer. The main chain monomer is selected from at least one of acrylamide, N,N-dimethylacrylamide and N-vinylpyrrolidone; The first functional monomer is selected from at least one of 2-acrylamido-2-methylpropanesulfonate, styrene sulfonate, and vinyl sulfonate; The second functional monomer is selected from at least one of UPy-acrylic acid monomer and UPy-methacrylic acid monomer; The third functional monomer is selected from at least one of vinyltrimethoxysilane and vinyltri(2-methoxyethoxy)silane; The temperature-sensitive monomer is N-isopropylacrylamide.

[0009] A second aspect of the present invention provides a method for preparing the crosslinked copolymer described in the first aspect, the method comprising: subjecting a monomer material containing a main-chain monomer, a first functional monomer, a second functional monomer, a third functional monomer and a temperature-sensitive monomer to a free radical copolymerization reaction in the presence of an initiator to obtain the crosslinked copolymer; The main chain monomer is selected from at least one of acrylamide, N,N-dimethylacrylamide and N-vinylpyrrolidone; The first functional monomer is selected from at least one of 2-acrylamido-2-methylpropanesulfonate, styrene sulfonate, and vinyl sulfonate; The second functional monomer is selected from at least one of UPy-acrylic acid monomer and UPy-methacrylic acid monomer; The third functional monomer is selected from at least one of vinyltrimethoxysilane and vinyltri(2-methoxyethoxy)silane; The temperature-sensitive monomer is N-isopropylacrylamide.

[0010] In a third aspect of the present invention, there is provided use of the crosslinked copolymer described in the first aspect as a temperature-responsive water-based drilling fluid flow pattern regulator.

[0011] The flow pattern regulator of the present invention adopts the lower critical solution temperature (LCST) phase transition behavior as the temperature response mechanism. The core principle is as follows: at low temperatures (<LCST), the molecular chains of the flow pattern regulator remain dissolved and stretched, resulting in low system viscosity; at high temperatures (>LCST), conformational transition occurs to the molecular chains, and the hydrophobic groups thereof spontaneously assemble into a dynamic reversible gel network through intermolecular association, so that the viscosity is greatly increased to meet the requirement of efficient cuttings carrying at the bottom of the well, fundamentally solving the contradiction of rheology control in deep well and deep sea drilling, and ensuring the safety and efficiency of drilling operations under complex working conditions.

[0012] The technical solution provided by the present invention has at least the following advantages: 1: The present invention adopts the lower critical solution temperature (LCST) phase transition behavior as the temperature response mechanism, realizing intelligent response of drilling fluid rheology to wellbore temperature, that is, maintaining low viscosity at low temperature to facilitate pumping, and increasing viscosity and shear force at high temperature to efficiently carry cuttings, effectively solving the core technical contradiction of "difficult pumping caused by low-temperature thickening" and "difficult cuttings carrying caused by high-temperature thinning" in deep well and deep sea drilling; 2: The molecular structure design of the present invention gives consideration to the thermal stability of the main chain and the salt resistance of side chain groups, ensuring that the regulator can still maintain its core temperature response characteristic and long-term stability under multiple extreme downhole conditions such as "high temperature, high salt, and large temperature difference".

[0013] The regulator of the present invention has the "temperature response" characteristic, that is, it maintains low viscosity at low temperature to facilitate circulation, and greatly increases viscosity and shear force through molecular conformational transition at high temperature. This innovative technical idea can fundamentally solve the problem of rheology control in deep well and deep sea drilling, and has great theoretical value and broad application prospects. Detailed Description

[0014] The endpoints and any values of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values shall be construed as including values close to these ranges or values. For numerical ranges, one or more new numerical ranges can be obtained by combining the endpoints of each range, combining the endpoints of each range with individual point values, and combining individual point values with each other, and these new numerical ranges shall be regarded as specifically disclosed herein.

[0015] As described above, a first aspect of the present invention provides a crosslinked copolymer, which contains a structural unit A provided by a main chain monomer, a structural unit B provided by a first functional monomer, a structural unit C provided by a second functional monomer, a structural unit D provided by a third functional monomer, and a structural unit E provided by a temperature-sensitive monomer; The main chain monomer is selected from at least one of acrylamide, N,N-dimethylacrylamide and N-vinylpyrrolidone; The first functional monomer is selected from at least one of 2-acrylamido-2-methylpropanesulfonate, styrene sulfonate, and vinyl sulfonate; The second functional monomer is selected from at least one of UPy-acrylic acid monomer and UPy-methacrylic acid monomer; The third functional monomer is selected from at least one of vinyltrimethoxysilane and vinyltri(2-methoxyethoxy)silane; The temperature-sensitive monomer is N-isopropylacrylamide.

[0016] The salt involved in the first functional monomer of the present invention can be an alkali metal salt, such as a sodium salt, potassium salt, etc.

[0017] Preferably, the weight ratio of the content of structural unit A, structural unit B, structural unit C, structural unit D and structural unit E is 1:0.1-0.5:0.005-0.08:0.002-0.03:0.01-0.08.

[0018] In a preferred embodiment, the molecular weight of the crosslinked copolymer is 700,000 g / mol to 3,000,000 g / mol, and more preferably 800,000 g / mol to 6,000,000 g / mol.

[0019] As previously stated, a second aspect of the present invention provides a method for preparing the crosslinked copolymer described in the first aspect, the method comprising: subjecting a monomer material containing a main-chain monomer, a first functional monomer, a second functional monomer, a third functional monomer and a thermosensitive monomer to a free radical copolymerization reaction in the presence of an initiator to obtain the crosslinked copolymer; The main chain monomer is selected from at least one of acrylamide, N,N-dimethylacrylamide and N-vinylpyrrolidone; The first functional monomer is selected from at least one of 2-acrylamido-2-methylpropanesulfonate, styrene sulfonate, and vinyl sulfonate; The second functional monomer is selected from at least one of UPy-acrylic acid monomer and UPy-methacrylic acid monomer; The third functional monomer is selected from at least one of vinyltrimethoxysilane and vinyltri(2-methoxyethoxy)silane; The temperature-sensitive monomer is N-isopropylacrylamide.

[0020] Preferably, the initiator is a water-soluble free radical initiator.

[0021] In a preferred embodiment, the amount of initiator is 0.05wt%-1.0wt%, based on the total mass of the monomers. The total mass of the monomers represents the sum of the masses of the main-chain monomer, the first functional monomer, the second functional monomer, the third functional monomer, and the thermosensitive monomer.

[0022] Particularly preferably, the initiator is selected from at least one of potassium persulfate, ammonium persulfate, and tetramethylethylenediamine.

[0023] Preferably, the free radical copolymerization reaction is carried out in the presence of a pH adjuster.

[0024] In a preferred embodiment, the amount of pH adjuster used is such that the pH value of the free radical copolymerization system is maintained at 5-8.

[0025] Preferably, the pH adjuster is selected from at least one of ammonia solution and acetic acid solution. Particularly preferably, the pH adjuster is dilute ammonia solution and / or acetic acid buffer solution.

[0026] According to a preferred embodiment, the conditions for the free radical copolymerization reaction include: carrying out the reaction under inert gas protection, a reaction temperature of 50-80°C, and a reaction time of 2-4 hours. The reaction temperature of the free radical copolymerization reaction described in this invention refers to the system temperature at the time the last monomer is added, and the starting point for the reaction time is also the moment the last monomer is added.

[0027] In a preferred embodiment, the weight ratio of the main chain monomer, the first functional monomer, the second functional monomer, the third functional monomer, and the temperature-sensitive monomer is 1:0.1-0.5:0.005-0.08:0.002-0.03:0.01-0.08.

[0028] Preferably, the free radical copolymerization reaction is carried out using water as a solvent. Optionally, the reaction system may also contain an organic solvent, wherein the organic solvent is selected from at least one of ethanol, acetone, and isopropanol.

[0029] Preferably, the free radical copolymerization reaction is carried out under anaerobic conditions. For example, oxygen (including dissolved oxygen) in the system can be removed by introducing an inert gas into the reaction system. The present invention does not have particular requirements regarding the type of inert gas; for example, nitrogen can be used.

[0030] The method of the present invention may also include post-processing steps known and commonly used in the art. The present invention does not have special requirements for the operation of post-processing, such as filtration, washing, drying, etc. The present invention will not describe them in detail here, and those skilled in the art should not understand them as limitations on the present invention.

[0031] As previously stated, the third aspect of the present invention provides the application of the crosslinked copolymer described in the first aspect as a temperature-responsive water-based drilling fluid flow modifier.

[0032] According to a particularly preferred embodiment, a method for preparing the crosslinked copolymer described in the first aspect comprises: a) Add an appropriate amount of organic solvent to the reaction vessel and pass an inert gas through the system under stirring to remove dissolved oxygen. b) Add the main chain monomer, the first functional monomer and the temperature-sensitive monomer in sequence according to the predetermined feed ratio, ensuring that each component is uniformly dispersed in the organic solvent and adjusting the pH value of the solution to a suitable range. c) Add a certain amount of the second functional monomer to the mixed solution obtained in step b) to ensure that it is completely dissolved; d) Add an initiator to the mixed solution obtained in step c), then heat the reaction system to a predetermined temperature and polymerize at that temperature for 4-6 hours; e) Gradually heat the reaction system to the predetermined temperature, add an appropriate amount of the third functional monomer, adjust the pH of the solution to a suitable range, and continue the reaction for 2-4 hours to obtain a solid polymer; f) Use deionized water to filter and wash the solid polymer after the reaction. Repeat the washing process 2-3 times to thoroughly remove unreacted monomers, initiators and other impurities to ensure the purity of the product. g) The dried solid product is taken out and crushed using mechanical crushing equipment. The crushed product is then screened to ensure uniform particle size distribution, thus obtaining a temperature-responsive water-based drilling fluid flow modifier.

[0033] The present invention will be described in detail below through embodiments. Unless otherwise specified, the raw materials used in the following embodiments are all common commercially available products.

[0034] Each part or weight represents 1g. All sieves mentioned below are Chinese standard sieves. Room temperature below refers to 25±5℃.

[0035] Example 1 A temperature-responsive water-based drilling fluid flow modifier was prepared. The formulation of this embodiment is listed below: Solvent: Deionized water, 200 parts by weight; Main chain monomers: Acrylamide, 60 parts by weight; N-vinylpyrrolidone, 20 parts by weight; First functional monomer: Sodium styrene sulfonate, 15 parts by weight; Sodium 2-acrylamido-2-methylpropanesulfonate, 5 parts by weight; Thermosensitive monomer: N-isopropylacrylamide, 5 parts by weight; Second functional monomer: UPy-acrylic acid monomer, 5 parts by weight; Third functional monomer: Vinyltrimethoxysilane, 2 parts by weight; Initiator system: ammonium persulfate, 0.5 parts by weight; tetramethylethylenediamine, 0.2 parts by weight.

[0036] a) Add 200 parts of deionized water as solvent to a three-necked round-bottom flask equipped with a mechanical stirrer, and purge with high-purity nitrogen to remove dissolved oxygen; then add the main chain monomer and the first functional monomer in sequence, ensuring complete dissolution and uniform distribution under continuous stirring; next, add the temperature-sensitive monomer and continue stirring until uniformly dispersed; finally, adjust the pH of the solution to 5.0 using acetate buffer and stir under nitrogen protection until a nearly transparent mixed solution is formed.

[0037] b) Prepare a solution of the second functional monomer separately, dissolve it in dimethyl sulfoxide (DMSO) to form a 10 v% solution to prevent it from self-polymerizing in the aqueous phase; slowly add this solution dropwise to the monomer mixture above.

[0038] c) Dissolve ammonium persulfate in 20 mL of deionized water and add tetramethylethylenediamine as an initiator; slowly add the initiator solution dropwise to the above monomer mixture, ensuring uniform distribution; place the reaction flask in a 35°C constant temperature water bath and react for 5 h.

[0039] d) After the reaction is complete, gradually raise the temperature to 60°C, add the third functional monomer, and add dilute ammonia dropwise to adjust the pH to 6.0. Continue the reaction for 3 hours.

[0040] e) After the polymerization and crosslinking reaction is completed, the reaction solution is transferred into a dialysis bag and dialyzed with deionized water to remove unreacted monomers, initiators and byproducts until the conductivity is close to the reference value of deionized water; then, the sample is placed in a vacuum drying oven and dried at 60°C for 24 hours to obtain a solid temperature-responsive water-based drilling fluid flow modifier.

[0041] f) The dried solid product is taken out and crushed using mechanical crushing equipment. The crushed product is then screened (through a 100-mesh sieve, and the undersize material is collected) to ensure uniform particle size distribution, resulting in temperature-responsive water-based drilling fluid flow modifier T1 with a weight-average molecular weight of 800,000.

[0042] Example 2 The formulation in this embodiment is similar to that in Example 1, except that the thermosensitive monomer in this embodiment is 2 parts by weight and the third functional monomer is 1 part by weight.

[0043] a) Add 200 parts of deionized water as solvent to a three-necked round-bottom flask equipped with a mechanical stirrer, and purge with high-purity nitrogen to remove dissolved oxygen; then add the main chain monomer and the first functional monomer in sequence, ensuring complete dissolution and uniform distribution under continuous stirring; next, add the temperature-sensitive monomer and continue stirring until uniformly dispersed; finally, adjust the pH of the solution to 4.5 using acetate buffer and stir under nitrogen protection until a nearly transparent mixed solution is formed.

[0044] b) Prepare a solution of the second functional monomer separately, dissolve it in dimethyl sulfoxide (DMSO) to form a 10 v% solution to prevent it from self-polymerizing in the aqueous phase; slowly add this solution dropwise to the monomer mixture above.

[0045] c) Dissolve ammonium persulfate in 20 mL of deionized water and add tetramethylethylenediamine as an initiator; slowly add the initiator solution dropwise to the above monomer mixture, ensuring uniform distribution; place the reaction flask in a 35°C constant temperature water bath and react for 6 h.

[0046] d) After the reaction is complete, gradually raise the temperature to 55°C, add the third functional monomer, and add dilute ammonia dropwise to adjust the pH to 6.5. Continue the reaction for 2 hours.

[0047] e) After the polymerization and crosslinking reactions are completed, the reaction solution is transferred to a dialysis bag and dialyzed with deionized water to remove unreacted monomers, initiators, and byproducts until the conductivity is close to the reference value for deionized water. Then, the sample is placed in a vacuum drying oven and dried at 60°C for 24 hours to obtain a solid temperature-responsive water-based drilling fluid flow modifier.

[0048] f) The dried solid product is taken out and crushed using mechanical crushing equipment. The crushed product is then screened (through a 100-mesh sieve) to ensure uniform particle size distribution, resulting in temperature-responsive water-based drilling fluid flow modifier T2 with a weight-average molecular weight of 750,000.

[0049] Example 3 The formulation in this embodiment is similar to that in Example 1, except that the thermosensitive monomer in this embodiment is 2 parts by weight and the second functional monomer is 1 part by weight.

[0050] a) Add 200 parts of deionized water as solvent to a three-necked round-bottom flask equipped with a mechanical stirrer, and purge with high-purity nitrogen to remove dissolved oxygen; then add the main chain monomer and the first functional monomer in sequence, ensuring complete dissolution and uniform distribution under continuous stirring; next, add the temperature-sensitive monomer and continue stirring until uniformly dispersed; finally, adjust the pH of the solution to 4.5 using acetate buffer and stir under nitrogen protection until a nearly transparent mixed solution is formed.

[0051] b) Prepare a solution of the second functional monomer separately, dissolve it in dimethyl sulfoxide (DMSO) to form a 10 v% solution to prevent it from self-polymerizing in the aqueous phase; slowly add this solution dropwise to the monomer mixture above.

[0052] c) Dissolve ammonium persulfate in 20 mL of deionized water and add tetramethylethylenediamine as an initiator; slowly add the initiator solution dropwise to the above monomer mixture, ensuring uniform distribution; place the reaction flask in a 35°C constant temperature water bath and react for 4 h.

[0053] d) After the reaction is complete, gradually raise the temperature to 50°C, add the third functional monomer, and add dilute ammonia dropwise to adjust the pH to 5.5. Continue the reaction for 4 hours.

[0054] e) After the polymerization and crosslinking reactions are completed, the reaction solution is transferred to a dialysis bag and dialyzed with deionized water to remove unreacted monomers, initiators, and byproducts until the conductivity is close to the reference value for deionized water. Then, the sample is placed in a vacuum drying oven and dried at 60°C for 24 hours to obtain a solid temperature-responsive water-based drilling fluid flow modifier.

[0055] f) The dried solid product is taken out and crushed using mechanical crushing equipment. The crushed product is then screened (through a 100-mesh sieve) to ensure uniform particle size distribution, resulting in temperature-responsive water-based drilling fluid flow modifier T3 with a weight-average molecular weight of 780,000.

[0056] Example 4 The formula for this embodiment is listed below: Solvent: Deionized water, 200 parts by weight; Main chain monomers: N,N-dimethylacrylamide, 65 parts by weight; N-vinylpyrrolidone, 20 parts by weight; First functional monomer: Sodium 2-acrylamido-2-methylpropanesulfonate, 10 parts by weight; Sodium vinylsulfonate, 10 parts by weight; Thermosensitive monomer: N-isopropylacrylamide, 4 parts by weight; Second functional monomer: UPy-methacrylic acid monomer, 4 parts by weight; Third functional monomer: vinyltris(2-methoxyethoxy)silane, 1.5 parts by weight; Initiator system: potassium persulfate, 0.6 parts by weight.

[0057] a) Add 200 parts of deionized water as solvent to a three-necked round-bottom flask equipped with a mechanical stirrer, and purge with high-purity nitrogen for 30 minutes to remove dissolved oxygen; then add the main chain monomer and the first functional monomer in sequence, ensuring complete dissolution and uniform distribution under continuous stirring; next, add the temperature-sensitive monomer and continue stirring until uniformly dispersed; finally, adjust the pH of the solution to 5.5 using acetate buffer and stir under nitrogen protection until a nearly transparent mixed solution is formed.

[0058] b) Prepare a solution of the second functional monomer separately, dissolve it in dimethyl sulfoxide (DMSO) to form a 10 v% solution; slowly add this solution dropwise to the monomer mixture above.

[0059] c) Dissolve potassium persulfate in 20 mL of deionized water as an initiator; slowly add the initiator solution dropwise to the above monomer mixture, ensuring uniform distribution; place the reaction flask in a 40°C constant temperature water bath and react for 5 h.

[0060] d) After the reaction is complete, gradually raise the temperature to 65°C, add the third functional monomer, and add dilute ammonia dropwise to adjust the pH to 7.0. Continue the reaction for 2.5 h.

[0061] e) After the polymerization and crosslinking reactions are completed, the reaction solution is transferred to a dialysis bag and dialyzed with deionized water to remove unreacted monomers, initiators, and byproducts until the conductivity is close to the reference value for deionized water. Then, the sample is placed in a vacuum drying oven and dried at 60°C for 24 hours to obtain a solid temperature-responsive water-based drilling fluid flow modifier.

[0062] f) The dried solid product is taken out and crushed using mechanical crushing equipment. The crushed product is passed through a 100-mesh sieve to ensure uniform particle size distribution, resulting in temperature-responsive water-based drilling fluid flow modifier T4 with a weight-average molecular weight of 950,000.

[0063] Example 5 The formula for this embodiment is listed below: Solvent: Deionized water, 200 parts by weight; Main chain monomers: Acrylamide, 40 parts by weight; N,N-dimethylacrylamide, 20 parts by weight; N-vinylpyrrolidone, 20 parts by weight; First functional monomer: styrene sulfonate, 10 parts by weight; vinyl sulfonate, 5 parts by weight; Thermosensitive monomer: N-isopropylacrylamide, 6 parts by weight; Secondary functional monomers: UPy-acrylic acid monomer, 2 parts by weight; UPy-methacrylic acid monomer, 2 parts by weight; Third functional monomer: vinyltrimethoxysilane, 1 part by weight; vinyltri(2-methoxyethoxy)silane, 1 part by weight; Initiator system: ammonium persulfate, 0.5 parts by weight; tetramethylethylenediamine, 0.2 parts by weight.

[0064] a) Add 200 parts of deionized water as solvent to a three-necked round-bottom flask equipped with a mechanical stirrer, and purge with high-purity nitrogen for 30 minutes to remove dissolved oxygen; then add the main chain monomer and the first functional monomer in sequence, ensuring complete dissolution and uniform distribution under continuous stirring; next, add the temperature-sensitive monomer and continue stirring until uniformly dispersed; finally, adjust the pH of the solution to 4.0 using acetate buffer and stir under nitrogen protection until a nearly transparent mixed solution is formed.

[0065] b) Dissolve the second functional monomer in dimethyl sulfoxide (DMSO) to form a mixed solution; slowly add the solution dropwise to the monomer mixture above.

[0066] c) Dissolve ammonium persulfate in 20 mL of deionized water and add tetramethylethylenediamine as an initiator; slowly add the initiator solution dropwise to the above monomer mixture, ensuring uniform distribution; place the reaction flask in a 30°C constant temperature water bath and react for 6 h.

[0067] d) After the reaction is complete, gradually raise the temperature to 55°C, add the third functional monomer, and add dilute ammonia dropwise to adjust the pH to 6.5, and continue the reaction for 3.5 h.

[0068] e) After the polymerization and crosslinking reactions are completed, the reaction solution is transferred to a dialysis bag and dialyzed with deionized water to remove unreacted monomers, initiators, and byproducts until the conductivity is close to the reference value for deionized water. Then, the sample is placed in a vacuum drying oven and dried at 60°C for 24 hours to obtain a solid temperature-responsive water-based drilling fluid flow modifier.

[0069] f) The dried solid product is taken out and crushed using mechanical crushing equipment. The crushed product is passed through a 100-mesh sieve to ensure uniform particle size distribution, resulting in temperature-responsive water-based drilling fluid flow modifier T5 with a weight-average molecular weight of 850,000.

[0070] Comparative Example 1 a) Add 200 parts of deionized water to a three-necked round-bottom flask equipped with a mechanical stirrer, and purge with high-purity nitrogen to remove dissolved oxygen; then add acrylamide (60 parts), N-vinylpyrrolidone (20 parts), sodium styrene sulfonate (15 parts), and 2-acrylamido-2-methylpropanesulfonate (5 parts) in sequence, and ensure complete dissolution and uniform distribution under continuous stirring.

[0071] b) Dissolve ammonium persulfate (0.5 parts) in 20 mL of deionized water, and add tetramethylethylenediamine (0.2 parts) as an initiator; slowly add the initiator solution dropwise to the above mixture, ensuring uniform distribution; place the reaction flask in a constant temperature water bath at 35°C and react for 4 h.

[0072] e) After the reaction is complete, the reaction solution is transferred to a dialysis bag and dialyzed with deionized water to remove unreacted monomers, initiators, and byproducts until the conductivity is close to the reference value for deionized water. Then, the sample is placed in a vacuum drying oven and dried at 60°C for 24 hours to obtain the conditioning agent.

[0073] f) The dried solid product is taken out and crushed using mechanical crushing equipment. The crushed product is then sieved (through a 100-mesh sieve) to ensure uniform particle size distribution, resulting in regulator D-T1 with a weight-average molecular weight of 820,000.

[0074] Comparative Example 2 This comparative example was conducted using a method similar to that of Example 1, except that: The first functional monomer in this comparative example is acrylic acid, and the amount and weight of the first functional monomer are the same as in Example 1.

[0075] In this comparative example, the regulator D-T2 was obtained, with a weight-average molecular weight of 750,000.

[0076] Comparative Example 3 This comparative example was conducted using a method similar to that of Example 1, except that: The second functional monomer in this comparative example is N,N'-methylenebisacrylamide, and the amount and weight of the second functional monomer are the same as in Example 1.

[0077] In this comparative example, the regulator D-T3 was obtained, with a weight-average molecular weight of 1.2 million.

[0078] Comparative Example 4 This comparative example was conducted using a method similar to that of Example 1, except that: The third functional monomer in this comparative example is lauryl methacrylate, and the amount and weight of the third functional monomer are the same as in Example 1.

[0079] In this comparative example, the regulator D-T4 was obtained, with a weight-average molecular weight of 950,000.

[0080] Comparative Example 5 This comparative example was conducted using a method similar to that of Example 1, except that: In this comparative example, the same amount of N,N-dimethylacrylamide was used to replace the temperature-sensitive monomer in Example 1.

[0081] In this comparative example, the regulator D-T5 was obtained, with a weight-average molecular weight of 830,000.

[0082] Test case Performance evaluation methods 1. Temperature resistance test The temperature resistance performance of temperature-responsive flow modifiers in bentonite-based slurries was evaluated. The experimental slurry formulation was: water + 4 wt% bentonite + 1 wt% temperature-responsive flow modifier. The mass percentage of the formulation components was based on the total weight of the experimental slurry.

[0083] The apparent viscosity (AV), plastic viscosity (PV), and dynamic shear strength (YP) of the base slurry and the test slurry were determined using a six-speed viscometer. 6. 3. Initial cut, final cut, and use a roller heating furnace to evaluate the temperature resistance of the temperature-responsive flow modulator.

[0084] The specific method is as follows: Pour the slurry to be tested into a viscosity measuring cup, and read the viscosity readings sequentially using a six-speed viscometer at 50°C. 600 300 6. 3.

[0085] AV calculation formula:

[0086] PV calculation formula:

[0087] Formula for calculating dynamic shear force (YP):

[0088] The initial cut is calculated as follows: stir at 600 rpm for 10 seconds, let stand for 10 seconds, and then read the result. The maximum reading is 3, and then the maximum reading is divided by 2 to obtain the initial tangent.

[0089] The final cut is calculated as follows: stir at 600 rpm for 10 seconds, let stand for 10 minutes, and then read the result. The maximum reading is 3, and then the maximum reading is divided by 2 to get the final cut.

[0090] After testing, the base slurry and experimental slurry were placed in a roller furnace and aged at 200°C for 16 hours. After being removed and cooled to room temperature, AV, PV, YP, and other parameters were measured. 6. 3. Initial cut, final cut.

[0091] The experimental results are shown in Table 1.

[0092] Table 1: Performance Evaluation of Temperature-Response Flow Modifiers in Bentonite-Based Slurries

[0093] The results show that the bentonite-based slurry without a flow modifier had low apparent viscosity and dynamic shear strength before hot rolling, and its rheological properties deteriorated significantly after high-temperature hot rolling. In contrast, Examples 1 to 5 significantly improved the rheological properties of the slurry before hot rolling, with increases in apparent viscosity, plastic viscosity, and dynamic shear strength. Example 1 exhibited the best rheological properties, demonstrating good "low viscosity, high shear" rheological characteristics. After high-temperature hot rolling, the rheological properties of Examples 1 to 5 remained at a high level. In particular, the apparent viscosity and dynamic shear strength of Example 1 remained relatively stable, indicating good temperature stability under high-temperature conditions. In contrast, although Comparative Example 1 improved the rheological properties of the slurry before hot rolling, the improvement was significantly less than that of the Examples, and the rheological properties deteriorated sharply after hot rolling, with apparent viscosity and dynamic shear strength almost dropping to the level of the bentonite-based slurry without a flow modifier.

[0094] Therefore, it can be seen that the temperature-responsive flow modifier provided by the present invention can significantly improve the rheological properties of drilling fluid and maintain excellent stability after high-temperature aging, which is significantly better than the comparative example, fully demonstrating the outstanding technical effect of the present invention.

[0095] 2. Temperature Response Test The temperature response characteristics of a temperature-responsive flow pattern modifier were evaluated in bentonite-based slurry. The experimental slurry formulation was: water + 4 wt% bentonite + 1 wt% temperature-responsive flow pattern modifier. The mass percentage of the formulation components was based on the total weight of the experimental slurry.

[0096] The viscosity-temperature profiles of the samples were measured using a Hacker rheometer at temperatures ranging from 50°C to 180°C, with a shear rate of 10 s⁻¹. -1 The viscosity of the samples under different temperature conditions was evaluated by measuring the stable viscosity of the samples at different temperatures. The experimental results are shown in Table 2.

[0097] Table 2: Evaluation of Sample Temperature Response Performance

[0098] The results above show that the viscosity of the bentonite-based slurry after adding a temperature-responsive flow modifier exhibits significant temperature-responsive characteristics at different temperatures. Example 1 showed a prominent thickening effect at all temperatures, especially at 120°C, 150°C, and 180°C, with viscosities reaching 4847 mPa·s, 6025 mPa·s, and 5747 mPa·s, respectively, significantly higher than the viscosity at room temperature, indicating excellent thickening performance and stability under high-temperature conditions. The viscosity of Comparative Example 1 was significantly lower than that of the experimental group at all temperatures, especially at high temperatures, where its viscosity dropped sharply, reaching only 202 mPa·s at 180°C, showing a clear high-temperature thinning trend, far lower than the example with the added flow modifier.

[0099] The results above show that the temperature-responsive flow modifier provided by the present invention can significantly improve the rheological properties of drilling fluids under high-temperature conditions and maintain a high viscosity at high temperatures, which is significantly better than the comparative example, fully demonstrating the outstanding technical advantages of the present invention in the application of high-temperature drilling fluids.

[0100] 3. High-temperature and high-pressure rheological testing The rheological properties of the samples under high temperature and high pressure conditions were measured using a high-temperature and high-pressure rheometer. 155 mL of pre-stirred sample was added to the test vessel, ensuring the rotor rotated freely. A series of measures were taken to ensure equipment safety and sealing at high temperatures, including but not limited to installing a drop weight, applying high-temperature lubricating oil, and tightening the threads of the test vessel. Subsequently, the device was placed in the high-temperature and high-pressure rheometer, and the pressure pipeline was fixed and connected. The test temperature range was 25℃, 120℃, and 200℃, and the test pressure was 10 MPa. The rheological parameters of the drilling fluid samples were accurately measured at different rotation speeds (600, 300, 200, 100, 6, and 3 rpm). The experimental results are shown in Table 3.

[0101] Table 3: Evaluation of High-Temperature and High-Pressure Rheological Properties of Samples

[0102] As can be seen from the above-mentioned high-temperature and high-pressure rheological performance evaluation results, the temperature-responsive flow modifier provided by the present invention exhibits excellent temperature response characteristics in bentonite-based slurries, effectively alleviating the temperature thinning trend of drilling fluid. It still has high viscosity and shear force retention rate at high temperatures. Among them, Example 1 is particularly outstanding. It can still maintain a plastic viscosity of 27.3 mPa·s and a dynamic shear force of 7.2 Pa at a high temperature of 200℃. Its PV and YP retention rates are as high as 79% and 88%, respectively, which are far superior to the comparative example.

[0103] Therefore, it can be seen that the temperature-responsive flow modifier provided by the present invention has good temperature response characteristics, can effectively alleviate the high-temperature thinning trend of drilling and completion fluids, and maintains high viscosity at high temperatures, which is significantly better than the comparative example, fully demonstrating the outstanding technical advantages of the present invention in the application of high-temperature drilling fluids.

[0104] 4. Salt resistance test The temperature response characteristics of a temperature-responsive flow modifier were evaluated in a bentonite-based slurry containing salt. The experimental slurry formulation was: water (balance) + 4 wt% bentonite + 1 wt% temperature-responsive flow modifier + 20 wt% NaCl. The mass percentages of the formulation components were based on the total weight of the experimental slurry. The basic properties of the experimental slurry contaminated with sodium chloride before and after hot rolling at 200℃ for 16 h were evaluated. The experimental results are shown in Table 4.

[0105] Table 4: Performance Evaluation of Temperature-Response Flow Modifiers in Salt-Containing Slurries

[0106] The results above demonstrate that the temperature-responsive flow modifier of this invention exhibits excellent performance in high-salt-content slurries. Before hot rolling, Examples 1-5 effectively improved the apparent viscosity (AV), plastic viscosity (PV), and dynamic shear force (YP) of the salt-content slurry, with significantly better rheological properties than Comparative Example 1. After aging at 200℃ for 16 hours, Examples 1-3 still maintained good rheological properties. Among them, the dynamic shear force of Example 1 remained at a high level of 5 Pa, indicating that its molecular structure has good stability under the dual effects of high temperature and high salt. In contrast, the rheological properties of Comparative Example 1 deteriorated under the same conditions, with the dynamic shear force dropping sharply to 0.5 Pa, and the initial and final shear forces only reaching 0.5 Pa. These comparative test results strongly prove that the temperature-responsive flow modifier of this invention has excellent salt resistance, that is, it can still effectively improve the basic rheological properties of drilling fluids in high-salt environments.

[0107] 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 temperature-responsive crosslinked copolymer, characterized by, The crosslinked copolymer contains structural unit A provided by the main chain monomer, structural unit B provided by the first functional monomer, structural unit C provided by the second functional monomer, structural unit D provided by the third functional monomer, and structural unit E provided by the temperature-sensitive monomer; The main chain monomer is selected from at least one of acrylamide, N,N-dimethylacrylamide and N-vinylpyrrolidone; The first functional monomer is selected from at least one of 2-acrylamido-2-methylpropanesulfonate, styrene sulfonate, and vinyl sulfonate; The second functional monomer is selected from at least one of UPy-acrylic acid monomer and UPy-methacrylic acid monomer; The third functional monomer is selected from at least one of vinyltrimethoxysilane and vinyltri(2-methoxyethoxy)silane; The temperature-sensitive monomer is N-isopropylacrylamide; The weight ratio of the content of structural unit A, structural unit B, structural unit C, structural unit D and structural unit E is 1:0.1-0.5:0.005-0.08:0.002-0.03:0.01-0.

08.

2. The crosslinked copolymer of claim 1, wherein The molecular weight of the crosslinked copolymer is 800,000 g / mol to 6,000,000 g / mol.

3. A process for the preparation of the crosslinked copolymer of claim 1 or 2, characterized in that, The method includes: in the presence of an initiator, subjecting a monomer material containing a main-chain monomer, a first functional monomer, a second functional monomer, a third functional monomer and a temperature-sensitive monomer to a free radical copolymerization reaction to obtain the crosslinked copolymer; The main chain monomer is selected from at least one of acrylamide, N,N-dimethylacrylamide and N-vinylpyrrolidone; The first functional monomer is selected from at least one of 2-acrylamido-2-methylpropanesulfonate, styrene sulfonate, and vinyl sulfonate; The second functional monomer is selected from at least one of UPy-acrylic acid monomer and UPy-methacrylic acid monomer; The third functional monomer is selected from at least one of vinyltrimethoxysilane and vinyltri(2-methoxyethoxy)silane; The temperature-sensitive monomer is N-isopropylacrylamide; the weight ratio of the main chain monomer, the first functional monomer, the second functional monomer, the third functional monomer and the temperature-sensitive monomer is 1:0.1-0.5:0.005-0.08:0.002-0.03:0.01-0.

08.

4. The method of claim 3, wherein, The initiator is a water-soluble free radical initiator.

5. The method of claim 4, wherein, Based on the total mass of the monomers, the amount of the initiator is 0.05wt%-1.0wt%.

6. The method according to claim 5, characterized in that, The initiator is selected from at least one of potassium persulfate, ammonium persulfate, and tetramethylethylenediamine.

7. The method according to any one of claims 3-6, characterized in that, The free radical copolymerization reaction was carried out in the presence of a pH adjuster; And / or, the amount of the pH adjuster is such that the pH of the system of the free radical copolymerization reaction is maintained at 5-8.

8. The method according to claim 7, characterized in that, The pH adjuster is selected from at least one of ammonia solution and acetic acid solution.

9. The method according to any one of claims 3-6, characterized in that, The conditions for the free radical copolymerization reaction include: being carried out under inert gas protection, a reaction temperature of 50-80℃, and a reaction time of 2-4 hours.

10. The application of the crosslinked copolymer of claim 1 or 2 as a temperature-responsive water-based drilling fluid flow modifier.

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