Plugging agent, preparation method and application thereof, and water-based drilling fluid

Abstract

The invention relates to the technical field of petroleum drilling, in particular to a plugging agent, a preparation method and application thereof and a water-based drilling fluid. The plugging agent comprises an inorganic core and a coating layer coating the inorganic core, wherein the coating layer contains a polymer containing a polydopamine structural unit and a grafted chain segment enabling the blocking agent to have a cloud point effect. When the plugging agent is used, the rheological property of the drilling fluid is not influenced, a tackifying effect is not shown in a drilling fluid system, chemical bond coupling of an elastic organic layer and rigid nanoparticle plugging can be achieved, and the effective anti-collapse plugging effect is achieved.

Description

Technical Field

[0001] This invention relates to the field of oil drilling technology, specifically to a plugging agent, its preparation method and application, and a water-based drilling fluid. Background Technology

[0002] To address the problems of inorganic nanoparticle plugging agents being prone to aggregation and difficult to disperse, and having unsatisfactory plugging effects when coupled with polymers, various types of organic / inorganic chemically coupled nanoparticle plugging agents have been developed both domestically and internationally.

[0003] To address the issue of insufficient plugging performance caused by phase separation between inorganic nanoparticles and organic materials, CN114381248B employs an amino-based silane coupling agent to couple butadiene compounds, diaminopropylbenzene compounds, and sulfonic acid compounds containing alkene bonds to the surface of nano-titanium dioxide, forming an adaptive, externally flexible, internally rigid nano-plugging agent suitable for nano-plugging of shale formations.

[0004] CN116444743A uses a silane coupling agent to attach carbon-carbon double bonds to the surface of nanoparticles, and uses azobisisobutyramidine hydrochloride as an initiator to graft quaternary ammonium salt and sulfonic acid groups onto the surface of nano-silica, thus preparing a temperature- and salt-resistant zwitterionic nano-plugging agent. This plugging agent has good high-temperature and salt resistance properties and can be used for sealing formation pores and fissures in extreme environments.

[0005] CN115806674A discloses a polypropylene glycol-bonded modified nano-SiO2 with a soft outer and rigid inner sealing structure, which can effectively seal cracks smaller than 1 mm.

[0006] CN113292973A uses amino-containing silanes as coupling agents to couple hydroxyl-containing hydrazine compounds, diallyl compounds, and enamine compounds onto the surface of silica using a stepwise synthesis method to form an organic / inorganic coupled nano-plugging agent. Its particle size is between 58-280 nm. Besides effectively improving its plugging performance, the multiple tertiary amine branches on the surface also have strong adsorption and inhibition properties. The above-mentioned organic / inorganic chemically coupled nano-plugging agents all utilize silane coupling agents to form chemical bonds with organic functional structures on the surface of inorganic nanoparticles, forming a core-shell structure of inorganic / organic hybrid nano-plugging agents. These agents can plug the pore throats of shale and mudstone at low concentrations, establishing artificial well walls with a certain strength. Silane coupling agents, besides effectively coupling carboxyl and hydroxyl groups on the surface of nanoparticles to form chemical bonds, can also couple the functional groups such as hydroxyl, amide, and carboxyl groups on the side chains of polymers in drilling fluids. They can act as crosslinking centers for most polymer treatment agents in water-based drilling fluids, posing a significant risk of deteriorating the rheological properties of the drilling fluid. When unreacted silane coupling agents remain in the plugging agent, these coupling agents can crosslink synthetic polymers and most naturally modified polymer treatment agents, causing the drilling fluid system to thicken rapidly and affecting the system's rheological stability. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of existing technologies where plugging agents cause drilling fluid systems to thicken rapidly, affecting the rheological stability of the system. This invention provides a new plugging agent, its preparation method, its application, and a water-based drilling fluid. This plugging agent, when used, can maintain stable drilling fluid viscosity and significantly reduce filtration loss under high temperature and high pressure.

[0008] To achieve the above objectives, a first aspect of the present invention provides a plugging agent comprising an inorganic core and a coating layer covering the inorganic core, wherein the coating layer comprises a polymer containing polydopamine structural units and grafted segments that give the plugging agent a cloud point effect.

[0009] A second aspect of the present invention provides a method for preparing a plugging agent, the method comprising: S1 introducing polydopamine in situ onto the surface of an inorganic core under alkaline conditions to obtain a material containing a polydopamine-coated inorganic core; S2, in the presence of a solvent, subjecting the polydopamine-coated inorganic core to a grafting reaction with a graft having a cloud point effect; wherein the graft contains reactive groups capable of reacting with polydopamine.

[0010] The third aspect of the present invention provides a plugging agent prepared by the preparation method described in the second aspect of the present invention.

[0011] The fourth aspect of the present invention provides the application of the plugging agent described in the first aspect of the present invention or the plugging agent described in the third aspect of the present invention in drilling.

[0012] The fifth aspect of the present invention provides a water-based drilling fluid containing the plugging agent described in the first aspect of the present invention or the plugging agent described in the third aspect of the present invention.

[0013] Through the above technical solution, the present invention has at least the following beneficial effects:

[0014] (1) The sealing agent in this invention can be uniformly dispersed in the solvent system and has good construction stability;

[0015] (2) The coating layer on the plugging agent in this invention includes polydopamine structural units and grafted chain segments grafted onto the polydopamine structural units, and can achieve chemical bond coupling between the elastic organic layer and the rigid nanoparticle plugging, thereby achieving an effective anti-collapse plugging effect.

[0016] (3) The plugging agent of the present invention has no effect on the rheological properties of drilling fluid during use and does not show a thickening effect in the drilling fluid system;

[0017] (4) The plugging agent of the present invention has the advantage of being environmentally friendly, and has strong plugging and filtration reduction capabilities, which is conducive to stabilizing the wellbore. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of a polyoxyethylene ether-grafted polydopamine-coated nano-oxide plugging agent in one embodiment of the present invention;

[0019] Figure 2 This is a schematic diagram of the reaction equation for the polymerization of dopamine monomers in one embodiment of the present invention;

[0020] Figure 3 This is the reaction process for preparing the plugging agent in one embodiment of the present invention. Detailed Implementation

[0021] 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.

[0022] A first aspect of the present invention provides a plugging agent comprising an inorganic core and a coating layer covering the inorganic core, wherein the coating layer comprises a polymer containing polydopamine structural units and grafted segments that give the plugging agent a cloud point effect.

[0023] The plugging agent with a specific structure in this invention can achieve chemical bonding coupling between the elastic organic layer and the rigid particle plugging under well temperature conditions, thus achieving an effective anti-collapse plugging effect. Moreover, it has no effect on the rheological properties of the drilling fluid during use and does not show a viscosity-increasing effect in the drilling fluid system.

[0024] In this invention, the polydopamine structural unit refers to the structural unit obtained by reacting groups in polydopamine with other groups through copolymerization and / or condensation polymerization.

[0025] According to a preferred embodiment of the present invention, the number average molecular weight of the polydopamine structural unit is 100-300, preferably 120-180, and more preferably 149-153.

[0026] According to the present invention, the grafted segments of the present invention enable the plugging agent to exhibit a cloud point effect. The temperature at which the cloud point effect occurs is determined by the cloud point of the raw material providing the grafted segments, generally near the cloud point temperature of the raw material providing the grafted segments. Preferably, the plugging agent exhibits a cloud point effect above 30°C, more preferably in the range of 30-80°C, for example, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, or any two of the above values, preferably 50-70°C. The plugging agent of the aforementioned embodiments has excellent plugging and filtration loss reduction capabilities, which is beneficial for stabilizing the wellbore.

[0027] According to a preferred embodiment of the present invention, the grafted segments are selected from hydrophilic grafted segments and / or hydrophilic-oleophilic copolymer grafted segments. The plugging agent of the aforementioned embodiment can improve the ability of the drilling fluid system to inhibit shale hydration and dispersion, and the plugging agent has strong plugging and filtration loss reduction capabilities, which is beneficial to stabilizing the wellbore.

[0028] According to the present invention, there is no particular limitation on the type of hydrophilic grafting segment as long as the purpose of the present invention can be achieved. In a preferred embodiment, the hydrophilic grafting segment is selected from polyvinyl alcohol segments and / or polyoxyethylene ether segments.

[0029] According to a preferred embodiment of the present invention, the hydrophilic-oleophilic copolymer grafting segment is selected from polyoxyethylene-oxypropylene copolyether as a random copolymer segment, and preferably, in the polyoxyethylene-oxypropylene copolyether as a random copolymer segment, the weight ratio of ethylene oxide to propylene oxide is 9:1 to 6:4.

[0030] According to a preferred embodiment of the present invention, the grafted chain segment is selected from polyoxyethylene ether segments. The plugging agent of the aforementioned embodiment can improve the ability of the drilling fluid system to inhibit the hydration and dispersion of shale, and the plugging agent has strong plugging and filtration loss reduction capabilities, which is more conducive to stabilizing the wellbore.

[0031] According to the present invention, the grafted segments can provide elasticity to the organic layer, enabling the plugging agent to effectively prevent collapse and seal the well. Generally, they have relatively long segments, i.e., multiple repeating units linked together. As long as the purpose of the present invention is achieved, the degree of polymerization of the polyether segments is not particularly limited. In a preferred embodiment, the degree of polymerization of the grafted segments is 4-70, for example, 4, 10, 15, 20, 30, 40, 50, 60, 65, 70, or any two of the above values, preferably 4-50. The plugging agent of the aforementioned embodiments can improve the ability of the drilling fluid system to inhibit shale hydration and dispersion, and the plugging agent has strong sealing and filtration loss reduction capabilities, which is beneficial for stabilizing the wellbore.

[0032] According to a preferred embodiment of the present invention, the grafting rate of the grafted chain segment is 5-20 wt%, preferably 10-15 wt%. The plugging agent of the aforementioned embodiment can improve the ability of the drilling fluid system to inhibit the hydration and dispersion of shale, and the plugging agent has strong plugging and filtration loss reduction capabilities, which is beneficial to stabilizing the wellbore.

[0033] In this invention, the grafting rate is determined by the formula GR / % = (m G The grafting rate is calculated as (-m0) / m0×100%, where GR is the grafting rate, m G The quality of the grafted product is given by m0, where m0 represents the quality of the product before grafting.

[0034] According to the present invention, grafted segments are bonded to polydopamine structural units. In a preferred embodiment, the grafted segments are bonded to the polydopamine structural units via nitrogen and / or sulfur atoms. The plugging agent of the aforementioned embodiments can achieve chemical bonding coupling between the elastic organic layer and the rigid nanoparticle plugging under well temperature conditions, thereby achieving an effective anti-collapse plugging effect.

[0035] In this invention, when the grafted chain segment has multiple different segments, the arrangement and number of the different segments in the polyether chain segment can be adjusted to make them different, and this invention has no special limitations in this regard.

[0036] According to a particularly preferred embodiment of the present invention, the grafted chain segment is connected to the polydopamine structural unit via nitrogen atoms. The plugging agent of the aforementioned embodiment can better achieve chemical bonding coupling between the elastic organic layer and the rigid nanoparticle plugging under well temperature conditions, thus achieving an effective anti-collapse plugging effect.

[0037] According to a preferred embodiment of the present invention, such as Figure 1 The image shown is a schematic diagram of a polyoxyethylene ether-grafted polydopamine-coated nano-oxide plugging agent. Figure 1 The nitrogen atoms were hidden using conventional design methods.

[0038] According to the present invention, as long as the purpose of the present invention can be achieved, the size of the sealing agent is not particularly limited, and it can be at the nanoscale, capable of effectively sealing nanoscale cracks and pores in mudstone and shale formations. In one embodiment, the particle size range of the sealing agent is 40-250 nm, preferably 50-210 nm.

[0039] In this invention, the particle size of the sealing agent is obtained by testing with a particle size analyzer.

[0040] According to the present invention, the coating layer is elastic and coupled with the chemical bonds of the rigid nanoparticles to achieve an effective anti-collapse sealing effect. As long as the purpose of the present invention can be achieved, the thickness of the coating layer is not particularly limited. In a preferred embodiment, the thickness of the coating layer is 10-60 nm, for example, 10 nm, 12 nm, 23 nm, 32 nm, 40 nm, 50 nm, 52 nm, 60 nm, preferably 30-50 nm.

[0041] The thickness of the coating layer in this invention is obtained by testing with a laser particle size analyzer.

[0042] In this invention, to enable the inorganic core to better coat the shell with the coating layer, in one embodiment, the inorganic core is selected from nano-inorganic oxides. The plugging agent in the aforementioned embodiments has a chemical bond coupling between the elastic organic layer and the nano-inorganic oxides, which can effectively prevent collapse and achieve a plugging effect.

[0043] The inorganic oxides in this invention can be rigid nano-inorganic oxides commonly used in the art, including but not limited to at least one of nano-silicon dioxide, nano-titanium dioxide, nano-zirconium dioxide, nano-manganese dioxide, and nano-graphene oxide.

[0044] A second aspect of the present invention provides a method for preparing a plugging agent, the method comprising: S1 introducing polydopamine in situ onto the surface of an inorganic core to obtain a material containing a polydopamine-coated inorganic core; S2, in the presence of a solvent, subjecting the polydopamine-coated inorganic core to a grafting reaction with a graft having a cloud point effect; wherein the graft contains a reactive group capable of reacting with polydopamine.

[0045] In the preparation method of this invention, polydopamine is introduced in situ onto the surface of an inorganic core in an alkaline environment, resulting in an inorganic core as the inner core and polydopamine as the structure in the coating layer. In addition, a graft with a cloud point effect is grafted onto the polydopamine layer. The resulting plugging agent can achieve chemical bonding coupling between the elastic organic layer and the rigid nanoparticles under well temperature conditions, thus achieving an effective anti-collapse plugging effect.

[0046] According to the present invention, the in-situ introduction of polydopamine on the surface of an inorganic core refers to the self-polymerization of dopamine, which grows and coats the surface of the inorganic core in situ. In a preferred embodiment, step S1, the method for in-situ introduction of polydopamine on the surface of the inorganic core, includes: in-situ polymerization of dopamine monomers in the presence of an alkaline buffer solution and an inorganic core. The plugging agent prepared by the aforementioned embodiments has uniform particle size, is stably dispersed in water without agglomeration, has good construction stability, and can effectively prevent collapse and plug, has strong plugging and filtration loss reduction capabilities, and is beneficial for stabilizing the wellbore.

[0047] According to the present invention, the alkaline buffer solution provides an alkaline environment for the self-polymerization of dopamine monomers, and in one embodiment, the pH of the alkaline buffer solution is 8-10.

[0048] According to the present invention, those skilled in the art know that the solvent in the alkaline buffer solution is water. As long as the purpose of the present invention can be achieved, the specific type of alkaline buffer solution is not particularly limited. In one embodiment, the alkaline buffer solution is selected from at least one of Tris-HCl buffer solution, sodium barbital-hydrochloric acid buffer solution and TBE buffer solution.

[0049] According to the present invention, there is no particular limitation on the specific type of dopamine monomer as long as the purpose of the present invention can be achieved. In one embodiment, the dopamine monomer is selected from at least one of dopamine hydrochloride, 5,6-dihydroxyindole and dopaquinone.

[0050] According to a preferred embodiment of the present invention, such as Figure 2 The figure shown is a schematic diagram of the reaction equation during the polymerization of dopamine monomers.

[0051] According to the present invention, when preparing polydopamine introduced in situ on the surface of an inorganic core, the amount of each raw material can be selected according to the needs of the final product. In one embodiment, the weight ratio of the inorganic core to the dopamine monomer is 10-120:1, for example, 10:1, 12:1, 13:1, 14:1, 16:1, 17:1, 25:1, 35:1, 40:1, 60:1, 80:1, 100:1, 120:1, or any two of the above ratios, preferably 10-60:1, more preferably 12-35:1.

[0052] According to the present invention, the size of the inorganic core is sufficient to achieve the blocking performance, generally at the nanometer level, and the present invention has no special limitations on this.

[0053] According to a preferred embodiment of the present invention, the inorganic core is selected from nano-inorganic oxides. The plugging agent prepared in the foregoing embodiments has an elastic organic layer and a chemical bond coupling of inorganic oxides, which can effectively prevent collapse and achieve a plugging effect.

[0054] According to the present invention, there is no particular limitation on the specific type of inorganic oxide, including but not limited to at least one of nano-silica, nano-titanium dioxide, nano-zirconium dioxide, nano-manganese dioxide and nano-graphene oxide.

[0055] According to the present invention, the alkaline buffer solution contains a solvent, and in-situ polymerization can be better performed in the presence of the solvent. That is, there is no particular limitation on the amount of alkaline buffer solution used, as long as it can provide an alkaline environment and promote the in-situ polymerization reaction. In one embodiment, the weight ratio of the inorganic core to the alkaline buffer solution is 0.05-0.24:1, for example, 0.05:1, 0.06:1, 0.08:1, 0.09:1, 0.12:1, 0.15:1, 0.20:1, 0.24:1, and any two of the above ratios, preferably 0.08-0.12:1.

[0056] According to the present invention, the conditions for in-situ polymerization can be selected based on the conditions under which dopamine monomers can self-polymerize. In one embodiment, the conditions for in-situ polymerization include: a temperature of room temperature and a time of 2-10 hours.

[0057] Unless otherwise specified, room temperature in this invention refers to 20-30°C.

[0058] According to a preferred embodiment of the present invention, the weight ratio of the graft to the inorganic core is 1:(2-6), for example, 1:2, 1:3, 1:3.7, 1:4, 1:5, 1:6, or any two of the above ratios, preferably 1:(3-5). The plugging agent prepared by the aforementioned embodiment has excellent plugging and filtration loss reduction capabilities, which is beneficial for stabilizing the wellbore.

[0059] According to the present invention, as described above, the graft has a cloud point effect. When preparing the plugging agent, the cloud point of the graft is not lower than 30°C, preferably 30-80°C, for example, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, or any two of the above values, more preferably 50-70°C. The plugging agent prepared by the aforementioned embodiments has excellent plugging and filtration reduction capabilities, which is beneficial for stabilizing the wellbore.

[0060] According to a preferred embodiment of the present invention, the graft material contains hydrophilic graft segments and / or hydrophilic-lipophilic copolymer graft segments during the preparation of the plugging agent. The plugging agent prepared by the aforementioned embodiment can effectively prevent collapse and plug, has strong filtration capacity, and is beneficial for stabilizing the wellbore.

[0061] According to a preferred embodiment of the present invention, the hydrophilic grafted segment is selected from polyvinyl alcohol segments and / or polyoxyethylene ether segments, preferably polyoxyethylene ether segments. The plugging agent prepared by the foregoing embodiments can effectively prevent collapse and plug, has strong filtration capacity, and is beneficial for stabilizing the wellbore.

[0062] According to a preferred embodiment of the present invention, the hydrophilic-oleophilic copolymer grafted segment is selected from polyoxyethylene-oxypropylene copolymer ether segments. The plugging agent prepared by the aforementioned embodiments can improve the ability of the drilling fluid system to inhibit shale hydration and dispersion, and the plugging agent has strong plugging and filtration loss reduction capabilities, which is beneficial for stabilizing the wellbore.

[0063] According to the present invention, the size of the graft is not particularly limited as long as the purpose of the present invention can be achieved. In a preferred embodiment, the average molecular weight of the graft is 200-4000, for example, 200, 400, 600, 1000, 2000, 4000, or any two of the above values.

[0064] In a preferred embodiment of the present invention, the reactive group is selected from -SH groups and / or -NH2 groups. In the foregoing embodiments, the -SH group and -NH2 group can each be grafted onto the polydopamine PDA layer via a -NH2 group Schiff base reaction and / or Michael addition reaction. In this invention, the Schiff base reaction is used as a non-limiting illustration. Figure 1 As shown, in one embodiment, the reaction process for preparing the plugging agent is as follows: Figure 3 As shown, Figure 3 In this example, the inorganic core is illustrated using nano-oxide. The oxygen atoms in the oxide undergo hydroxylation in an alkaline environment, and the dihydropyrrole ring structure in the polydopamine molecule undergoes ring-opening to generate terminal amino groups. The two then condense, allowing polydopamine to adhere to the oxide surface. Figure 3 The nitrogen atom is hidden in the PDA according to the conventional design method. The mechanism of the Schiff base reaction between PDA and amino-containing molecules is as follows: under alkaline and aerobic conditions, the phenolic group in PDA is first oxidized to the corresponding quinone. Then the quinone reacts with the amino group in a Schiff base reaction. Due to steric hindrance and activity, the other quinone group will not undergo a Schiff base reaction.

[0065] In a preferred embodiment of the present invention, the reactive group is selected from the -NH2 group. The plugging agent prepared in the foregoing embodiments has no effect on the rheological properties of the drilling fluid during use, does not exhibit a thickening effect in the drilling fluid system, and can effectively prevent collapse and plug, has strong filtration loss reduction ability, and is beneficial to stabilizing the wellbore.

[0066] According to the present invention, the position of the reactive group on the grafted chain segment is not particularly limited as long as the purpose of the present invention can be achieved. In a preferred embodiment, the reactive group is the end group of the graft. The plugging agent prepared in the foregoing embodiments has no effect on the rheological properties of the drilling fluid during use, does not exhibit a thickening effect in the drilling fluid system, and can effectively prevent collapse and plug, has strong filtration loss reduction ability, and is beneficial to stabilizing the wellbore.

[0067] According to the present invention, as long as the purpose of the present invention can be achieved, the type of solvent in step S2 is not particularly limited, and an inert solvent is acceptable. After step S1 is completed, the system may contain water, that is, the solvent in step S2 is preferably water. The amount of water is not particularly limited. For example, the weight ratio of the polydopamine-coated inorganic core to the solvent is 0.15-0.8:1, such as 0.15:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, or any two of the above ratios, preferably 0.2-0.5:1.

[0068] In this invention, after step S1 is completed, a portion of the supernatant (water) can be removed as needed. After polydopamine is introduced in situ onto the inorganic core surface, the supernatant can be removed by centrifugation, and the lower concentrated suspension continues the grafting reaction described in step S2.

[0069] According to the present invention, as long as the purpose of the present invention can be achieved, the conditions of the grafting reaction in step S2 are not particularly limited. In a preferred embodiment, the conditions of the grafting reaction in step S2 include: pH 8-10, temperature room temperature, and time 12-48 hours.

[0070] After the grafting reaction in step S2 of this invention is completed, the system may still contain solvent and some unreacted graft material. Therefore, after the grafting reaction, water dialysis can be used to remove the unreacted graft material. The dialysis method is a conventional operation method in the art. For example, the semi-permeable membrane bag used for dialysis is a regenerated cellulose dialysis bag with a molecular weight cutoff of 4000-15000 DA. The final solid phase is used as a blocking agent. As needed, the concentration of the solid phase can be adjusted after dialysis to form a solid suspension with a solid phase (blocking agent) content of 20-30 wt%.

[0071] The third aspect of the present invention provides a plugging agent prepared by the preparation method described in the second aspect of the present invention.

[0072] The plugging agent prepared in this invention can achieve chemical bonding coupling between the elastic organic layer and the rigid particle plugging under well temperature conditions, thus achieving an effective anti-collapse plugging effect. Moreover, it has no effect on the rheological properties of the drilling fluid during use and does not show a thickening effect in the drilling fluid system.

[0073] The fourth aspect of the present invention provides the application of the plugging agent described in the first aspect of the present invention or the plugging agent prepared by the preparation method described in the third aspect of the present invention in drilling.

[0074] In this invention, the plugging agent described herein is used in drilling to achieve an effective anti-collapse and plugging effect. Moreover, the plugging agent has no effect on the rheological properties of the drilling fluid, does not exhibit a thickening effect in the drilling fluid system, has a strong ability to reduce filtration loss, and is conducive to stabilizing the wellbore.

[0075] The fifth aspect of the present invention provides a water-based drilling fluid, wherein the water-based drilling fluid contains the plugging agent described in the first aspect of the present invention or the plugging agent prepared by the preparation method described in the third aspect of the present invention.

[0076] When used, the water-based drilling fluid containing the plugging agent described in this invention has no effect on its rheological properties, does not exhibit a thickening effect in the drilling fluid system, has a strong ability to reduce filtration loss, and is beneficial for stabilizing the wellbore.

[0077] According to the present invention, those skilled in the art can select the amount of plugging agent in the water-based drilling fluid as needed, for example, the content of the plugging agent in the water-based drilling fluid is 1-3 wt%.

[0078] According to the present invention, the water-based drilling fluid contains water. The water-based drilling fluid of the present invention may also contain other components commonly used in the art, such as thickeners, coating agents, filtration reducers, lubricants, caustic soda, barite, bentonite, etc. The present invention has no special limitations in this regard, and will not elaborate further here.

[0079] The present invention will be described in detail below through embodiments. Unless otherwise specified, the raw materials used in the following embodiments are all commercially available.

[0080] Example 1

[0081] Prepare 5 parts by weight of dopamine hydrochloride, 60 parts of nano silica, 500 parts of 0.01M Tris-HCl buffer (pH 8.5), and 20 parts of monofunctional polyetheramine PEG200-NH2 (cloud point 80℃).

[0082] Five parts of dopamine hydrochloride and 60 parts of nano-silica were uniformly dispersed in 500 parts of 0.01M Tris-HCl buffer solution and magnetically stirred at room temperature for 5 hours to obtain mixed system A.

[0083] Mixed system A was centrifuged at 5 k rpm for 5 minutes to remove 200 parts of supernatant. It was then ultrasonically dispersed at room temperature for 5 minutes to form a concentrated suspension of nano-silica containing a PDA coating. 20 parts of PEG200-NH2 were then mixed with the above concentrated suspension and stirred for 24 hours to obtain a stable suspension product B.

[0084] The suspended product B was centrifuged at 5 k rpm for 10 minutes to collect the PEG-grafted nano-silica and dialyzed with deionized water. The molecular weight cutoff of the dialysis bag was 2000 DA to remove unreacted PEG200-NH2. After dialysis, the solid phase concentration was adjusted to form a solid suspension with a solid phase content of 30 wt% (polyoxyethylene ether-grafted polydopamine-coated nano-silica blocker).

[0085] In the polyoxyethylene ether-grafted polydopamine-coated nano-silica plugging agent, the grafting rate of polyoxyethylene ether is 13.9%, the molecular weight of the polydopamine structural unit is 149, and the thickness of the coating layer is 32nm.

[0086] Example 2

[0087] Prepare 4 parts by weight of 5,6-dihydroxyindole, 55 parts of nano-titanium dioxide, 550 parts of 0.01M Tris-HCl buffer (pH 8.5), and 15 parts of monofunctional polyetheramine PEG600-NH2 (cloud point 65℃).

[0088] Four parts of 5,6-dihydroxyindole and 55 parts of nano-titanium dioxide were uniformly dispersed in 550 parts of 0.01M Tris-HCl buffer solution and magnetically stirred at room temperature for 5 hours to obtain mixed system A.

[0089] Mixed system A was centrifuged at 5 k rpm for 5 minutes to remove 250 parts of supernatant. It was then ultrasonically dispersed at room temperature for 5 minutes to form a concentrated suspension of nano-titanium dioxide containing a PDA coating. 15 parts of PEG600-NH2 were then mixed with the above concentrated suspension and stirred for 24 hours to obtain a stable suspension product B.

[0090] The suspended product B was centrifuged at 5 k rpm for 10 minutes to collect the PEG-grafted nano-titanium dioxide and dialyzed with deionized water. The dialysis bag had a molecular weight cutoff of 6000 DA to remove unreacted PEG600-NH2. After dialysis, the solid phase concentration was adjusted to form a solid suspension with a solid phase content of 25 wt% (polyoxyethylene ether-grafted polydopamine-coated nano-titanium dioxide blocking agent).

[0091] In the polyoxyethylene ether-grafted polydopamine-coated nano-titanium dioxide plugging agent, the grafting rate of polyoxyethylene ether is 13.5%, the molecular weight of the polydopamine structural unit is 151, and the thickness of the coating layer is 39 nm.

[0092] Example 3

[0093] Prepare 3 parts by weight of dopamine hydrochloride, 50 parts of nano-zirconia, 600 parts of 0.01M sodium barbital-hydrochloric acid (pH 8.4), and 10 parts of monofunctional polyetheramine PEG1000-NH2 (cloud point 63℃).

[0094] Three parts of dopamine hydrochloride and 50 parts of nano-zirconia were uniformly dispersed in 600 parts of 0.01M sodium barbital-hydrochloric acid buffer solution and magnetically stirred at room temperature for 5 hours to obtain mixed system A.

[0095] Mixed system A was centrifuged at 5 k rpm for 5 minutes to remove 300 parts of supernatant. It was then ultrasonically dispersed at room temperature for 5 minutes to form a concentrated suspension of nano-zirconia containing a PDA coating. 10 parts of PEG1000-NH2 were then mixed with the above concentrated suspension and stirred for 24 hours to obtain a stable suspension product B.

[0096] The suspended product B was centrifuged at 5 k rpm for 10 minutes to collect the PEG-grafted nano-zirconia and dialyzed with deionized water. The molecular weight cutoff of the dialysis bag was 8000 DA to remove unreacted PEG1000-NH2. After dialysis, the solid phase concentration was adjusted to form a solid suspension with a solid phase content of 20 wt% (polyoxyethylene ether-grafted polydopamine-coated nano-zirconia blocking agent).

[0097] In the polyoxyethylene ether-grafted polydopamine-coated nano-zirconia plugging agent, the grafting rate of polyoxyethylene ether is 12.6%, the molecular weight of the polydopamine structural unit is 153, and the thickness of the coating layer is 45nm.

[0098] Example 4

[0099] Prepare 2 parts by weight of dopaquinone, 50 parts of nano-graphene oxide, 600 parts of 0.01M TBE buffer (pH 8.3), and 10 parts of monofunctional polyetheramine PEG2000-NH2 (cloud point 55℃).

[0100] Two parts of dopaquinone and 50 parts of nano-graphene oxide were uniformly dispersed in 600 parts of 0.01M TBE buffer and magnetically stirred at room temperature for 5 hours to obtain mixed system A.

[0101] The mixture A was centrifuged at 5 k rpm for 5 minutes to remove 300 parts of supernatant. It was then ultrasonically dispersed at room temperature for 5 minutes to form a concentrated suspension of nano-graphene oxide containing a PDA coating. 10 parts of PEG2000-NH2 were then mixed with the above concentrated suspension and stirred for 24 hours to obtain a stable suspension product B.

[0102] The suspended product B was centrifuged at 5 k rpm for 10 minutes to collect the PEG-grafted nano-graphene oxide and dialyzed with deionized water. The molecular weight cutoff of the dialysis bag was 10,000 DA to remove unreacted PEG2000-NH2. After dialysis, the solid phase concentration was adjusted to form a solid suspension with a solid phase content of 20 wt% (polyoxyethylene ether-grafted polydopamine-coated nano-graphene oxide blocking agent).

[0103] In the polyoxyethylene ether-grafted polydopamine-coated nano-graphene oxide plugging agent, the grafting rate of polyoxyethylene ether is 10.3%, the molecular weight of the polydopamine structural unit is 150, and the thickness of the coating layer is 33 nm.

[0104] Example 5

[0105] Prepare 5 parts by weight of dopamine hydrochloride, 60 parts of nano silica, 500 parts of 0.01M Tris-HCl buffer (pH 8.5), and 20 parts of monofunctional polyoxyethylene-polyoxypropylene-NH2 (amino-terminated polyoxyethylene polyoxypropylene ether, cloud point 30℃, ethylene oxide to propylene oxide weight ratio 70:30, molecular weight 4000).

[0106] Five parts of dopamine hydrochloride and 60 parts of nano-silica were uniformly dispersed in 500 parts of 0.01M Tris-HCl buffer solution and magnetically stirred at room temperature for 5 hours to obtain mixed system A.

[0107] Mixed system A was centrifuged at 5 k rpm for 5 minutes to remove 200 parts of supernatant. It was then ultrasonically dispersed at room temperature for 5 minutes to form a concentrated suspension of nano-silica containing a PDA coating. 20 parts of Polyoxyethylene-polyoxypropylene-NH2 were then mixed with the above concentrated suspension and stirred for 24 hours to obtain a stable suspension product B.

[0108] The suspension product B was centrifuged at 5 k rpm for 10 minutes to collect the grafted polyether nano-silica and dialyzed with deionized water. The molecular weight cutoff of the dialysis bag was 6000 DA to remove unreacted polyoxyethylene-polyoxypropylene-NH2. After dialysis, the solid phase concentration was adjusted to form a solid suspension with a solid phase content of 30 wt% (polyether grafted polydopamine coated nano-silica blocker).

[0109] In the polyether-grafted polydopamine-coated nano-silica plugging agent, the polyether grafting rate is 12.2%, the molecular weight of the polydopamine structural unit is 149, and the thickness of the coating layer is 40 nm.

[0110] Example 6

[0111] Prepare 4 parts by weight of 5,6-dihydroxyindole, 55 parts of nano-titanium dioxide, 600 parts of 0.01M Tris-HCl buffer (pH 8.5), and 15 parts of monofunctional polyvinyl alcohol amine PVA2000-NH2 (cloud point 50℃).

[0112] Four parts of 5,6-dihydroxyindole and 55 parts of nano-titanium dioxide were uniformly dispersed in 550 parts of 0.01M Tris-HCl buffer solution and magnetically stirred at room temperature for 5 hours to obtain mixed system A.

[0113] The mixture A was centrifuged at 5 k rpm for 5 minutes to remove 250 parts of supernatant. It was then ultrasonically dispersed at room temperature for 5 minutes to form a concentrated suspension of nano-titanium dioxide containing a PDA coating. 15 parts of PVA2000-NH2 were then mixed with the above concentrated suspension and stirred for 24 hours to obtain a stable suspension product B.

[0114] The suspended product B was centrifuged at 5 k rpm for 10 minutes to collect the PEG-grafted nano-titanium dioxide and dialyzed with deionized water. The dialysis bag had a molecular weight cutoff of 4000 DA to remove unreacted PVA2000-NH2. After dialysis, the solid phase concentration was adjusted to form a solid suspension with a solid phase content of 25 wt% (polyoxyethylene ether-grafted polydopamine-coated nano-titanium dioxide blocker).

[0115] In the polyoxyethylene ether-grafted polydopamine-coated nano-titanium dioxide plugging agent, the grafting rate of polyoxyethylene ether is 12.9%, the molecular weight of the polydopamine structural unit is 151, and the thickness of the coating layer is 37 nm.

[0116] Example 7

[0117] Prepare 3 parts by weight of dopamine hydrochloride, 50 parts of nano-zirconia, 600 parts of 0.01M Tris-HCl buffer sodium barbital-hydrochloric acid (pH 8.4), and 10 parts of monofunctional polyetheramine PEG1000-SH (cloud point 63℃).

[0118] Three parts of dopamine hydrochloride and 50 parts of nano-zirconia were uniformly dispersed in 600 parts of 0.01M sodium barbital-hydrochloric acid buffer solution and magnetically stirred at room temperature for 5 hours to obtain mixed system A.

[0119] Mixed system A was centrifuged at 5 k rpm for 5 minutes to remove 300 parts of supernatant. It was then ultrasonically dispersed at room temperature for 5 minutes to form a concentrated suspension of nano-zirconia containing a PDA coating. 10 parts of PEG1000-SH were then mixed with the above concentrated suspension and stirred for 24 hours to obtain a stable suspension product B.

[0120] The suspension product B was centrifuged at 5 k rpm for 10 minutes to collect the PEG-grafted nano-zirconia and dialyzed with deionized water. The molecular weight cutoff of the dialysis bag was 8000 DA to remove unreacted PEG1000-SH. After dialysis, the solid phase concentration was adjusted to form a solid suspension with a solid phase content of 20 wt% (polyvinyl alcohol grafted polydopamine coated nano-zirconia blocker).

[0121] In the polyvinyl alcohol-grafted polydopamine-coated nano-zirconia plugging agent, the polyvinyl alcohol grafting rate is 9.4%, the molecular weight of the polydopamine structural unit is 153, and the thickness of the coating layer is 23 nm.

[0122] Example 8

[0123] Prepare 5 parts by weight of dopamine hydrochloride, 60 parts of nano silica, 500 parts of 0.01M Tris-HCl buffer (pH 8.5), and 50 parts of monofunctional polyetheramine PEG600-NH2 (cloud point 65℃).

[0124] Five parts of dopamine hydrochloride and 60 parts of nano-silica were uniformly dispersed in 500 parts of 0.01M Tris-HCl buffer solution and magnetically stirred at room temperature for 5 hours to obtain mixed system A.

[0125] Mixed system A was centrifuged at 5 k rpm for 5 minutes to remove 200 parts of supernatant. It was then ultrasonically dispersed at room temperature for 5 minutes to form a concentrated suspension of nano-silica containing a PDA coating. 50 parts of PEG600-NH2 were then mixed with the above concentrated suspension and stirred for 24 hours to obtain a stable suspension product B.

[0126] The suspended product B was centrifuged at 5 k rpm for 10 minutes to collect the PEG-grafted nano-silica and dialyzed with deionized water. The molecular weight cutoff of the dialysis bag was 2000 DA to remove unreacted PEG400-NH2. After dialysis, the solid phase concentration was adjusted to form a solid suspension with a solid phase content of 30 wt% (polyoxyethylene ether-grafted polydopamine-coated nano-silica blocker).

[0127] In the polyoxyethylene ether-grafted polydopamine-coated nano-silica plugging agent, the grafting rate of polyoxyethylene ether is 17.5%, the molecular weight of the polydopamine structural unit is 149, and the thickness of the coating layer is 52nm.

[0128] Example 9

[0129] Prepare 5 parts by weight of dopamine hydrochloride, 60 parts of nano silica, 500 parts of 0.01M Tris-HCl buffer (pH 8.5), and 10 parts of monofunctional polyetheramine PEG200-NH2 (cloud point 80℃).

[0130] Five parts of dopamine hydrochloride and 60 parts of nano-silica were uniformly dispersed in 500 parts of 0.01M Tris-HCl buffer solution and magnetically stirred at room temperature for 5 hours to obtain mixed system A.

[0131] Mixed system A was centrifuged at 5 k rpm for 5 minutes to remove 200 parts of supernatant. It was then ultrasonically dispersed at room temperature for 5 minutes to form a concentrated suspension of nano-silica containing a PDA coating. 10 parts of PEG200-NH2 were then mixed with the above concentrated suspension and stirred for 24 hours to obtain a stable suspension product B.

[0132] The suspended product B was centrifuged at 5 k rpm for 10 minutes to collect the PEG-grafted nano-silica and dialyzed with deionized water. The molecular weight cutoff of the dialysis bag was 2000 DA to remove unreacted PEG200-NH2. After dialysis, the solid phase concentration was adjusted to form a solid suspension with a solid phase content of 30 wt% (polyoxyethylene ether-grafted polydopamine-coated nano-silica blocker).

[0133] In the polyoxyethylene ether-grafted polydopamine-coated nano-silica plugging agent, the grafting rate of polyoxyethylene ether is 6.8%, the molecular weight of the polydopamine structural unit is 149, and the thickness of the coating layer is 12nm.

[0134] Example 10

[0135] Prepare 3 parts by weight of dopamine hydrochloride, 50 parts of nano-zirconia, 600 parts of 0.01M Tris-HCl buffer (pH 8.5), and 10 parts of monofunctional polyetheramine PEG1000-NH2 (cloud point 63℃).

[0136] Add 3 parts of dopamine hydrochloride to 600 parts of 0.01M Tris-HCl buffer and stir magnetically at room temperature for 5 hours to obtain mixed system A;

[0137] 300 parts of water were removed from the mixture A by atmospheric distillation, and then ultrasonically dispersed at room temperature for 5 minutes. 10 parts of PEG1000-NH2 were mixed with the mixture A and stirred for 24 hours to obtain product B.

[0138] Product B was centrifuged at 5 k rpm for 10 minutes and dialyzed with deionized water. The molecular weight cutoff of the dialysis bag was 8000 DA to remove unreacted PEG1000-NH2. After dialysis, 50 parts of nano-zirconia were added to the product to adjust the solid phase concentration and form a solid suspension with a solid phase content of 20 wt% (polyoxyethylene ether grafted polydopamine coated nano-zirconia blocker).

[0139] In the polyoxyethylene ether-grafted polydopamine-coated nano-zirconia plugging agent, the grafting rate of polyoxyethylene ether is 12.6%, the molecular weight of the polydopamine structural unit is 153, and the thickness of the coating layer is 43 nm.

[0140] Comparative Example 1

[0141] 50 parts of nano-silica and 20 parts of PEG200 were ultrasonically dispersed in 160 parts of deionized water at room temperature to form a stable suspension.

[0142] Comparative Example 2

[0143] 55 parts of nano-silica and 15 parts of PEG1000 were ultrasonically dispersed in 160 parts of deionized water at room temperature to form a stable suspension.

[0144] Comparative Example 3

[0145] 50 parts of nano-graphene oxide and 10 parts of PEG2000 were ultrasonically dispersed in 140 parts of deionized water at room temperature to form a stable suspension.

[0146] Comparative Example 4

[0147] Add 30 parts of 10 parts of hydroxyl-terminated PEG1000, 50 parts of nano-zirconia, 200 parts of deionized water, and 0.5 parts of hydrochloric acid to a reaction flask, start stirring, and raise the temperature to 60°C. Add 3 parts of butyltrimethoxysilane dropwise to the reaction flask within 50 minutes. After the addition is complete, react at this temperature for 4 hours. Then adjust the pH of the system to 8.0, raise the temperature to 120°C, and react for 3 hours. The resulting suspension is the silane-coupled polyether zirconia nano-blocking agent.

[0148] Among them, the polyoxyethylene ether-grafted nano-zirconia plugging agent coupled with silane has a grafting rate of 17.2% and a coating thickness of 63 nm.

[0149] Test case

[0150] 1. Particle size distribution test of the plugging agent: Sample solutions of the examples and comparative examples with a mass fraction of 2% were prepared using deionized water. 5 mL of each solid suspension of the examples and comparative examples were taken and the particle size distribution of each example and comparative example was measured using a Malvern Zetasizer Nano ZS particle size analyzer according to the instrument operation procedure. The results are shown in Table 1.

[0151] Table 1

[0152]

[0153] As shown in Table 1, the particle size distribution of the plugging agent prepared in the examples is in the range of 40-250 nm, which is at the nanoscale. It can effectively plug nanoscale cracks and pores in shale formations and stabilize the wellbore.

[0154] 2. Basic performance test of drilling fluid: The basic formula is 400ml of 3wt% soil slurry + 0.3wt% FA367 + 0.8wt% NH4HPAN + 1.5wt% DFT-1 + 1.5wt% OSAM-K + 2wt% KD-21C + 0.2wt% caustic soda, weighted with barite to a density of 1.2g / cm³. 3 2 wt% of the plugging agent from the examples and comparative examples were added, with the balance being water. The drilling fluid without any example plugging agent was used as a control. Subsequently, the system was hot-rolled at 160°C for 16 hours, and the basic properties of the system were measured at room temperature. The results are shown in Table 2.

[0155] Table 2

[0156]

[0157] As shown in Table 2, after aging at 160℃ for 16 hours, the viscosity of the drilling fluid treated with the plugging agent from the embodiments of the present invention remained stable, and the high-temperature and high-pressure filtration loss was significantly reduced to below 14 ml. For example, the high-temperature and high-pressure filtration loss of Example 3 was 11.5 ml, demonstrating good plugging effect. Example 5 used polyoxyethylene-polyoxypropylene segment-grafted nanoparticles. The organic segments contained hydrophobic segments, and the turbidity point was significantly reduced. The viscosity of the prepared drilling fluid was significantly lower than that of the reference sample, and the high-temperature and high-pressure filtration loss was 15 ml, demonstrating good plugging effect, but slightly worse than that of the polyoxyethylene segment-grafted plugging agent. The viscosity of the drilling fluid system in Examples 6-10 did not change much. Although the plugging effect was better than that of the reference sample, the filtration loss was always higher than 15 ml. Comparative Examples 1-3 were blends of polyoxyethylene ether and nanoparticles, which had little effect on viscosity but resulted in higher filtration loss. Comparative Example 4, using a silane coupling agent to form a plugging agent, showed a significant thickening effect on the drilling fluid and was therefore unsuitable for use as a plugging agent. Performance data from the examples and comparative examples in drilling fluid show that the plugging agent used comprises an inorganic core and a coating layer encapsulating the inorganic core. The coating layer contains at least polydopamine structural units, has no effect on drilling fluid viscosity, and exhibits good plugging performance.

[0158] 3. Sealing test

[0159] The basic drilling fluid formula is as follows: Measure 400 mL of clean water into a high-speed stirring cup and stir at a high speed of 5 k rpm. Then, slowly add 16 g of drilling-grade bentonite and 0.56 g of NaCO3 to the cup to obtain a 4 wt% bentonite-based slurry. Stir at high speed for 20 min and cure for 24 hours to obtain the base slurry. Prepare multiple portions of the above base slurry for later use.

[0160] 0.3wt% FA367, 0.8wt% NH4HPAN, 1.5wt% DFT-1, 1.5wt% OSAM-K, 2wt% KD-21C and 2wt% plugging agent (the plugging agents prepared in the above examples and comparative examples, respectively) were added to the base slurry and stirred at high speed for 20 min to prepare the sample slurry test solution. The test solution was put into an aging tank and aged at 160°C for 16 hours.

[0161] The plugging ability of the prepared plugging drilling fluid was evaluated using a sand bed evaluation test device. The device used sand with a particle size of 200 mesh. The penetration depth of the base slurry into the sand bed was tested for 15 minutes under a pressure of 0.7 MPa and before and after aging of the slurry. The experimental results are shown in Table 3.

[0162] Table 3

[0163]

[0164]

[0165] As shown in Table 3, the plugging agents prepared in the above examples have good plugging ability in drilling fluid. The penetration depth of Examples 1-4 before and after aging is less than 5 cm, which is better than that of the plugging agents prepared in the comparative examples. Examples 5-10 have a better penetration depth into the sand bed before and after aging than Comparative Examples 1-3, but the plugging effect is worse than that of Examples 1-4. Comparative Example 4 has a high penetration depth before aging and a penetration depth of 4.5 cm after aging, which is presumably due to the cross-linking effect of the residual silane coupling agent on organic matter.

[0166] 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 sealing agent, characterized in that, The plugging agent comprises an inorganic core and a coating layer covering the inorganic core; The coating layer comprises a polymer containing polydopamine structural units and grafted segments that give the plugging agent a cloud point effect.

2. The sealing agent according to claim 1, wherein, The number-average molecular weight of the polydopamine structural unit is 100-300, preferably 120-180, more preferably 149-153; and / or The sealing agent exhibits a cloud point effect at temperatures above 30°C, preferably between 30-80°C; and / or The grafted segments are selected from hydrophilic grafted segments and / or hydrophilic-lipophilic copolymer grafted segments; and / or Preferably, The hydrophilic grafted segments are selected from polyvinyl alcohol segments and / or polyoxyethylene ether segments; and / or The hydrophilic and oleophilic copolymer grafted segments are selected from polyoxyethylene-oxypropylene copolyether segments; More preferably, The grafted chain segment is selected from polyoxyethylene ether segments.

3. The sealing agent according to claim 1 or 2, wherein, The degree of polymerization of the grafted chain segments is 4-70, preferably 4-50; and / or The grafting rate of the grafted chain segment is 5-20 wt%, preferably 10-15 wt%. and / or The grafted chain segment is bonded to the polydopamine structural unit via nitrogen atoms and / or sulfur atoms, preferably via nitrogen atoms.

4. The sealing agent according to any one of claims 1-3, wherein, The particle size range of the plugging agent is 40-250 nm, preferably 50-210 nm; and / or The thickness of the coating layer is 10-60 nm, preferably 30-50 nm; and / or The inorganic core is selected from nano-inorganic oxides; Preferably, the nano-inorganic oxide is selected from at least one of nano-silica, nano-titanium dioxide, nano-zirconium dioxide, nano-manganese dioxide, and nano-graphene oxide.

5. A method for preparing a plugging agent, characterized in that, The preparation method includes: S1 introduces polydopamine in situ onto the surface of an inorganic core to obtain a material containing an inorganic core coated with polydopamine; In the presence of a solvent, S2 undergoes a grafting reaction between polydopamine-coated inorganic cores and grafts with a cloud point effect. The graft contains reactive groups that can react with polydopamine.

6. The preparation method according to claim 5, wherein, In step S1, the method of introducing polydopamine in situ onto the surface of the inorganic core includes: in situ polymerization of dopamine monomers in the presence of an alkaline buffer and an inorganic core; Preferably, The pH of the alkaline buffer solution is 8-10; and / or The alkaline buffer is selected from at least one of Tris-HCl buffer, sodium barbital-hydrochloric acid buffer, and TBE buffer; and / or The dopamine monomer is selected from at least one of dopamine hydrochloride, 5,6-dihydroxyindole, and dopaquinone.

7. The preparation method according to claim 6, wherein, In step S1, The inorganic core is selected from nano-inorganic oxides, preferably from at least one of nano-silica, nano-titanium dioxide, nano-zirconium dioxide, nano-manganese dioxide, and nano-graphene oxide; and / or The weight ratio of the inorganic core to the dopamine monomer is 10-120:1, preferably 10-60:1, more preferably 12-35:1; and / or The weight ratio of the inorganic core to the alkaline buffer solution is 0.05-0.24:1, preferably 0.08-0.12:1; and / or The conditions for the in-situ polymerization include: a temperature of room temperature and / or a time of 2-10 hours.

8. The preparation method according to any one of claims 5-7, wherein, In step S2, The weight ratio of the graft to the inorganic core is 1:(2-6), preferably 1:(3-5); and / or The cloud point of the graft is not lower than 30°C, preferably 30-80°C; and / or The graft contains hydrophilic graft segments and / or hydrophilic-lipophilic copolymer graft segments; and / or Preferably, The hydrophilic grafted segments are selected from polyvinyl alcohol segments and / or polyoxyethylene ether segments, preferably polyoxyethylene ether segments; and / or The hydrophilic and oleophilic copolymer grafted segments are selected from polyoxyethylene-oxypropylene copolyether segments; and / or The average molecular weight of the grafted material is 200-4000.

9. The preparation method according to any one of claims 5-8, wherein, In step S2, The reactive group is selected from -SH group and / or -NH2 group, preferably -NH2 group; The reactive group is a terminal group of the graft; and / or The solvent is selected from water; and / or The weight ratio of the polydopamine-coated inorganic core to the solvent is 0.15-0.8:1, preferably 0.2-0.5:1; and / or The grafting reaction conditions include: a temperature of room temperature and / or a time of 12-48 hours.

10. The sealing agent obtained by the preparation method according to any one of claims 5-9.

11. The application of the plugging agent according to any one of claims 1-4, 10 in drilling.

12. A water-based drilling fluid, characterized in that, The water-based drilling fluid contains the plugging agent according to any one of claims 1-4 and 10; Preferably, the content of the plugging agent in the water-based drilling fluid is 1-3 wt%.

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