1. The nano plugging agent is characterized by comprising the following raw materials in parts by weight: 10-50 parts of vinyl monomer, 10-25 parts of allyl monomer, 5-15 parts of sodium methacrylate, 2-10 parts of emulsifier, 1-1.5 parts of initiator, 15-55 parts of water, 5-10 parts of organic emulsion, 15-25 parts of filler and 5-10 parts of sepiolite;

the organic emulsion comprises the following components in parts by weight: 1-1.5 parts of polylactic acid, 0.5-1 part of lignocellulose, 1-4 parts of stannic chloride, 0.3-0.5 part of sodium dodecyl benzene sulfonate, 0.1-0.2 part of benzimidazole, 0.5-1 part of gelatin, 2-3 parts of dimethyl sulfoxide and 1-1.5 parts of white oil.

2. The nano plugging agent according to claim 1, wherein: the organic emulsion is prepared by the following method: (1) dissolving gelatin and polylactic acid in dimethyl sulfoxide, adding lignocellulose, and mixing uniformly to form a coating solution;

(2) mixing stannic chloride and benzimidazole, adding the mixture into deionized water, adding sodium dodecyl benzene sulfonate, uniformly mixing, heating to 90-140 ℃, stirring for 4-12h, washing, and drying at 80-90 ℃ for 2-3h to obtain an intermediate;

(3) and mixing the coating solution and the intermediate, performing spray drying to obtain a coating intermediate, and uniformly mixing the coating intermediate and the white oil to obtain the organic emulsion, wherein the mass ratio of the coating solution to the intermediate is 0.7-1:1, and the mass ratio of the coating intermediate to the white oil is 0.6-1: 1.

3. The nano plugging agent according to claim 2, wherein: in the step (2), the paraffin is heated to 50-70 ℃, atomized by compressed air, sprayed on the surface of the intermediate, and cooled, wherein the mass ratio of the paraffin to the intermediate is 0.5-0.8: 1.

4. The nano plugging agent according to claim 1, wherein the lignocellulose is prepared by the following method: mixing and grinding lignocellulose and succinic anhydride, adding DMF, stirring uniformly, reacting at 120-130 ℃ for 3-4h, filtering, drying, wherein the mass ratio of the lignocellulose to the succinic anhydride to the DMF is 1:3-4: 10-15.

5. The nano plugging agent according to claim 1, wherein the polylactic acid is pretreated by the following steps:

(1) dissolving polylactic acid in chloroform, adding 1-octyl-3-methylimidazole tetrafluoroborate, irradiating 10kGy on a cobalt-60 source with the irradiation metering rate of 2.2-2.5kGy/h, precipitating with methanol, and drying, wherein the mass ratio of the polylactic acid to the 1-octyl-3-methylimidazole tetrafluoroborate is 2-5: 1; (2) mixing the product obtained in the step (1) with triallyl isocyanurate, tin powder and a solvent, vacuumizing and heating to 190-.

6. The nano plugging agent according to claim 1, wherein the filler is formed by mixing nano calcium carbonate, polytetrafluoroethylene and elastic graphite according to a mass ratio of 1-3:3-5: 2-6.

7. The nano plugging agent according to claim 1, wherein the vinyl monomer comprises styrene and vinyl propionate in a mass ratio of 1: 0.42-0.75; the allyl monomer comprises acrylic acid, vinyl acrylate and cyclohexyl methacrylate in a mass ratio of 1:2: 1-2.

8. The nano plugging agent of claim 1, wherein the emulsifier is one or a combination of several of sodium fatty alcohol polyoxyethylene ether sulfate, octyl phenol polyoxyethylene ether OP-10, octyl phenol polyoxyethylene ether OP-8 and octyl phenol polyoxyethylene ether OP-6.

9. The nano plugging agent according to claim 1, wherein the initiator is sodium bisulfite and potassium persulfate in a mass ratio of 1: 1-2.

10. The method for preparing the nano plugging agent according to any one of claims 1 to 9, comprising the following steps:

s1, mixing the vinyl monomer, the allyl monomer, the sodium methacrylate, the emulsifier, the initiator and 1/6 of water uniformly in sequence to obtain a pre-emulsion;

s2, adding the pre-emulsion into the residual water, stirring for 2-3h at 70-80 ℃, cooling to room temperature, adding the filler, the sepiolite and the organic emulsion, and mixing uniformly to obtain the nano plugging agent.

Background

Well collapse is one of the most serious complex conditions in the oil and gas drilling process, the well wall stability of a shale stratum in the oil and gas drilling is always the important responsibility of drilling fluid, and the prevention of the penetration and invasion of drilling fluid filtrate to the shale well wall is the key of the drilling fluid anti-collapse technology, so that the stability of the well wall can be improved only by the compact plugging effect of the anti-collapse plugging agent for the drilling fluid.

At present, the particle size of the commonly used plugging material is between 0.1 and 100Um, the commonly used plugging material is mainly suitable for plugging 0.1 to 1mm of formation pore throats and cracks, the commonly used plugging material is difficult to enter shale to form an inner filter cake plugging layer, and a good plugging effect cannot be achieved, so that a nano-sized plugging agent must be added into the drilling fluid.

The nano plugging agent can be divided into organic nano plugging agent, inorganic nano plugging agent and organic/inorganic nano plugging agent in composition, and the inorganic nano plugging agent mainly comprises nano SiO₂Modified nano SiO₂Nano calcium carbonate, iron oxide, calcium-based/iron-based nanoparticles; the organic nano plugging agent mainly comprises nano polymers, aluminum complexes, nano micelle plugging agents, nano emulsion and the like; the organic/inorganic nano plugging agent is compounded by a rigid material and one or more deformable nano materials.

The commonly used nano plugging agent at present is mainly an inorganic nano plugging agent, and the plugging agent bridges and plugs micro cracks of a shale stratum, but the plugging effect is good, but the acting force between the nano particles and the stratum is small, so that the nano particles are difficult to stay in the cracks and are easy to separate again, and the plugging effect is influenced.

Disclosure of Invention

In order to increase the acting force between the nano plugging agent and the shale and improve the plugging capability of the nano plugging agent, the application provides the nano plugging agent and the preparation method thereof.

In a first aspect, the present application provides a nano plugging agent, which adopts the following technical scheme:

a nano plugging agent comprises the following raw materials in parts by weight: 10-50 parts of vinyl monomer, 10-25 parts of allyl monomer, 5-15 parts of sodium methacrylate, 2-10 parts of emulsifier, 1-1.5 parts of initiator, 15-55 parts of water, 5-10 parts of organic emulsion, 15-25 parts of filler and 5-10 parts of sepiolite;

the organic emulsion comprises the following components in parts by weight: 1-1.5 parts of polylactic acid, 0.5-1 part of lignocellulose, 1-4 parts of stannic chloride, 0.3-0.5 part of sodium dodecyl benzene sulfonate, 0.1-0.2 part of benzimidazole, 0.5-1 part of gelatin, 2-3 parts of dimethyl sulfoxide and 1-1.5 parts of white oil.

By adopting the technical scheme, the vinyl monomer and the propenyl monomer are adopted to form oil-in-water emulsion under the action of the sodium methacrylate and the emulsifier, and the oil-in-water emulsion is used as the initiatorUnder the action of the drilling fluid, small molecular monomers are subjected to polymerization reaction to form a colloidal nano emulsion, the nano emulsion is used for a well wall of shale, can better enter micro-nano pores of the shale, forms a layer of compact membrane structure on the surface of the well wall, has a strong waterproof effect, blocks the pores of the shale to prevent the further filtration of the drilling fluid, can be filled into larger pores in the shale to realize the effect of gap filling and blocking, and contains a large number of alkaline centers (MgO) on the surface of sepiolite₆) And acid Sites (SiO)₄) The sepiolite has double central surfaces and stronger polarity, preferentially adsorbs substances with stronger polarity, water molecules are used as polar molecules, and the sepiolite has strong adsorption performance on the sepiolite, so that the plugging agent has higher consistency.

Tin tetrachloride, sodium dodecyl benzene sulfonate and benzimidazole in the organic emulsion are synthesized into a nano material by a hydrothermal method and a solvothermal method, the particle size of the nano material is smaller and is within 100nm, gelatin and polylactic acid can be dissolved in dimethyl sulfoxide, gelatin particles are spherical and have the particle size of hundreds of nanometers, aggregation is not easy to occur, the contact angle of the polylactic acid can be reduced, the hydrophilicity of the polylactic acid is improved, the gelatin and the polylactic acid are mixed, hydroxyl and amino in gelatin molecules and carboxyl and hydroxyl in the polylactic acid form hydrogen bonds and chemical bonds, so that a network polymer is formed and attached to the surface of nano particles in the plugging agent, lignocellulose has a capillary effect, the viscosity of the organic emulsion can be increased, the specific surface area is large, the adsorption force is strong, the acting force between the gelatin and polylactic acid blend membrane and the stratum can be increased, namely the acting force between the nano particles and the stratum is enhanced, thereby improving the blocking effect of the blocking agent, and improving the heat resistance of the gelatin and polylactic acid blend membrane due to the dimensional stability and the thermal stability of the carboxymethyl cellulose.

Preferably, the organic emulsion is prepared by the following method: (1) dissolving gelatin and polylactic acid in dimethyl sulfoxide, adding lignocellulose, and mixing uniformly to form a coating solution;

(2) mixing stannic chloride and benzimidazole, adding the mixture into deionized water, adding sodium dodecyl benzene sulfonate, uniformly mixing, heating to 90-140 ℃, stirring for 4-12h, washing, and drying at 80-90 ℃ for 2-3h to obtain an intermediate;

(3) and mixing the coating solution and the intermediate, performing spray drying to obtain a coating intermediate, and uniformly mixing the coating intermediate and the white oil to obtain the organic emulsion, wherein the mass ratio of the coating solution to the intermediate is 0.7-1:1, and the mass ratio of the coating intermediate to the white oil is 0.6-1: 1.

By adopting the technical scheme, firstly, dissolving gelatin and polylactic acid in dimethyl sulfoxide, adding lignocellulose to form a coating solution, then combining a hydrothermal method with a solvothermal method, preparing a nano intermediate from tin tetrachloride and benzimidazole under the action of sodium dodecyl benzene sulfonate, carrying out spray drying, volatilizing dimethyl sulfoxide in the coating solution to form a blended membrane of polylactic acid and gelatin, coating the blended membrane on the nano intermediate to form a coated intermediate, and forming an organic emulsion from the coated intermediate and white oil; the melting point of the gelatin is lower, the temperature of the well wall is increased along with the increase of the drilling depth, the gelatin is melted, the intermediate body coated by the blended film of the gelatin and the polylactic acid is released, the intermediate body is nano-scale particles, so that the intermediate body is filled into nano-scale pores, the well wall is effectively stabilized, in addition, after the intermediate body flows out, the strength of the polylactic acid shell is higher, the pores where the polylactic acid shell is positioned can still be supported and plugged, and the plugging effect is not influenced.

Preferably, in the step (2), the paraffin is heated to 50-70 ℃, atomized by compressed air, sprayed on the surface of the intermediate, and cooled, wherein the mass ratio of the paraffin to the intermediate is 0.5-0.8: 1.

By adopting the technical scheme, paraffin is heated and melted, compressed air is used for atomizing and coating the paraffin on the surface of the intermediate, then coating liquid formed by polylactic acid, gelatin and lignocellulose is sprayed and dried and coated on the surface of the paraffin, when gelatin begins to melt, a polylactic acid and gelatin blending film is broken, the paraffin-coated intermediate flows out, the paraffin can prevent the nano-scale intermediate from agglomerating and is difficult to flow out from the broken part of the polylactic acid and gelatin blending film, and the uniformly dispersed intermediate can increase the plugging effect; the paraffin-coated intermediate melts and flows out along with seepage of underground water and increase of well wall temperature to block the nanometer pores, and the melted paraffin has good inhibition and lubricity, can improve rheological property of drilling fluid and enhance blocking effect.

Preferably, the lignocellulose is prepared by the following method: mixing and grinding lignocellulose and succinic anhydride, adding DMF, stirring uniformly, reacting at 120-130 ℃ for 3-4h, filtering, drying, wherein the mass ratio of the lignocellulose to the succinic anhydride to the DMF is 1:3-4: 10-15.

By adopting the technical scheme, the hydroxyl on the surface of the lignocellulose treated by the DMF is released, the combinable succinic anhydride is increased, the roughness of the surface of the lignocellulose modified by the succinic anhydride is increased, the internal structure of the cellulose is exposed, and irregular holes are formed, so that the specific surface area of the lignocellulose is increased, the adsorption effect is enhanced, and the problem that the modified lignocellulose solves the problems that the abundant hydroxyl on the surface of the lignocellulose is easy to generate strong hydrogen bonds, large agglomeration is formed, and the uniform dispersion in dimethyl sulfoxide solution of polylactic acid and gelatin is difficult to realize is solved.

Preferably, the polylactic acid is pretreated by the following steps:

(1) dissolving polylactic acid in chloroform, adding 1-octyl-3-methylimidazole tetrafluoroborate, irradiating 10kGy on a cobalt-60 source with the irradiation metering rate of 2.2-2.5kGy/h, precipitating with methanol, and drying, wherein the mass ratio of the polylactic acid to the 1-octyl-3-methylimidazole tetrafluoroborate is 2-5: 1; (2) mixing the product obtained in the step (1) with triallyl isocyanurate, tin powder and a solvent, vacuumizing and heating to 190-.

By adopting the technical scheme, when the polylactic acid and the 1-octyl-3-methylimidazole tetrafluoroborate are irradiated by gamma rays, generated polylactic acid macromolecular free radicals initiate polymerization of the 1-octyl-3-methylimidazole tetrafluoroborate or excite the 1-octyl-3-methylimidazole tetrafluoroborate to generate free radical coupling termination, the occurrence of chain scission reaction is inhibited, imidazole cations are grafted on a polylactic acid molecular chain, and the alkyl chain of the 1-octyl-3-methylimidazole tetrafluoroborate is longer, so that the adsorption force of the imidazole cations on the polylactic acid to a well wall is larger; and then, the polylactic acid grafted with imidazole cations and triallyl isocyanurate are subjected to a crosslinking reaction under the catalysis of tin powder, so that double bonds are introduced into the polylactic acid, the heat resistance of the polylactic acid is enhanced, when the drilling depth is increased and the borehole wall temperature is increased, the polylactic acid can still fill pores, and the polylactic acid is prevented from being melted due to higher borehole wall temperature and is difficult to continue to block the pores.

Preferably, the filler is formed by mixing nano calcium carbonate, polytetrafluoroethylene and elastic graphite according to the mass ratio of 1-3:3-5: 2-6.

Through adopting above-mentioned technical scheme, elastic graphite has lower true density and higher load value than conventional graphite, can reduce the settlement of drilling fluid neutralization, the partial graphitization of elastic graphite surface, thereby sufficient lubricating power has, reduce the frictional force between the granule, can also reduce the wearing and tearing of instrument, elastic graphite's anti crushing ability is strong, mutual gravitation is little between the macromolecule of polytetrafluoroethylene, the surface molecule is also very little to the free energy of attraction of other molecules, consequently, has very little coefficient of friction, there is the lubricity, and the wearability is strong, use elastic graphite, the shutoff effect of plugging agent can effectively be strengthened to the filler that polytetrafluoroethylene and nanometer calcium carbonate mix and form.

Preferably, the vinyl monomers comprise styrene and vinyl propionate in a mass ratio of 1: 0.42-0.75; the allyl monomer comprises acrylic acid, vinyl acrylate and cyclohexyl methacrylate in a mass ratio of 1:2: 1-2.

By adopting the technical scheme, the styrene and the acrylic acid are polymerized under the action of the initiator, the styrene, the acrylic acid and the vinyl acrylate are copolymerized, the vinyl acrylate and the acrylic acid are copolymerized, the cyclohexyl methacrylate and the styrene are copolymerized to generate the polystyrene, the polystyrene has high transparency, high rigidity, chemical corrosion resistance and high glass transition temperature, but is brittle, so that part of vinyl propionate is added into the styrene, and the vinyl propionate and the styrene are polymerized under the action of the emulsifier and the initiator to obtain the polymer which has the characteristics of acid and alkali resistance and good water resistance, and has good adhesion and blocking effects on shale gaps.

Preferably, the emulsifier is one or a combination of more of fatty alcohol-polyoxyethylene ether sodium sulfate, octylphenol-polyoxyethylene ether OP-10, octylphenol-polyoxyethylene ether OP-8 and octylphenol-polyoxyethylene ether OP-6.

By adopting the technical scheme, the emulsifier can disperse the polymerized monomers into tiny monomers to form compatibilized micelles, and the emulsifier is adsorbed on the surfaces of the monomers and the emulsion particles to form stable polymer emulsion.

Preferably, the initiator is sodium bisulfite and potassium persulfate with the mass ratio of 1: 1-2.

By adopting the technical scheme, the sodium bisulfite and the potassium persulfate can promote the polymerization of the monomers in the emulsion state, thereby forming the stable nano emulsion.

In a second aspect, the present application provides a method for preparing a nano plugging agent, which adopts the following technical scheme:

a preparation method of a nano plugging agent comprises the following steps:

s1, mixing the vinyl monomer, the allyl monomer, the sodium methacrylate, the emulsifier, the initiator and 1/6 of water uniformly in sequence to obtain a pre-emulsion;

s2, adding the pre-emulsion into the residual water, stirring for 2-3h at 70-80 ℃, cooling to room temperature, adding the filler, the sepiolite and the organic emulsion, and mixing uniformly to obtain the nano plugging agent.

By adopting the technical scheme, after the vinyl monomer, the propenyl monomer and other substances are mixed to form the pre-emulsion, the pre-emulsion is emulsified with water, and the filler, the sepiolite and the organic emulsion are added after cooling, so that the prepared plugging agent has more nano particles and better fluid loss reduction effect on shale.

In summary, the present application has the following beneficial effects:

1. because vinyl monomers and allyl monomers are subjected to polymerization reaction under the action of sodium methacrylate sulfonate, an emulsifier and an initiator to generate nano materials, and sepiolite and organic emulsion are added, the sepiolite has strong adsorption performance and can rapidly swell and disperse when meeting water, the consistency of the plugging agent can be increased, bridging is formed in pores, mutual dragging is carried out, a network structure is formed, gaps are plugged, in addition, the organic emulsion contains stannic chloride, polylactic acid, gelatin and other parts, stannic chloride and benzimidazole can generate nano particles, gelatin and polylactic acid can be combined to form a blend membrane which is coated on the nano particles, so that the blend membrane is filled on the nano particles, lignocellulose has large specific surface area and high thermal stability, the acting force between the blend membrane of the gelatin and the polylactic acid and a stratum can be enhanced, and the plugging effect of the plugging agent is improved, and improves the heat-resistant effect of the plugging agent.

2. In the application, polylactic acid, gelatin, lignocellulose and the like are preferably adopted to prepare organic emulsion through spray drying, the gelatin containing lignocellulose and the polylactic acid blended membrane are coated on the nano intermediate, the gelatin and polylactic acid blended membrane coated nano intermediate is filled in cracks of a well wall through the adsorption acting force of the lignocellulose, and the plugging effect is improved; the gelatin is melted along with the rise of the temperature of the well wall, the intermediate flows out of the blended film of the gelatin and the polylactic acid, the micro cracks can be further filled, the polylactic acid shell with higher hardness has higher strength, and the pore of the well wall where the intermediate is located is manufactured and plugged.

3. In the application, 1-octyl-3-methylimidazole tetrafluoroborate, triallyl isocyanurate and the like are preferably used for pretreating polylactic acid, and through irradiation of gamma rays, imidazole cations are grafted on a polylactic acid molecular chain, while imidazole cations with longer alkyl chains can enhance the adsorption force of the polylactic acid, improve the adsorption force of a gelatin and polylactic acid blend membrane on a well wall, and further enhance the plugging effect; in addition, triallyl isocyanurate reacts with polylactic acid in a crosslinking way under the catalysis of tin powder, double bonds are introduced, the heat resistance of the polylactic acid is improved, the polylactic acid blocked in the cracks still has stronger hardness at high temperature, and the cracks are supported and blocked.

4. In the application, the lignocellulose is preferably modified by using DMF (dimethyl formamide) and succinic anhydride, the DMF exposes hydroxyl on the lignocellulose, and the succinic anhydride is combined with the hydroxyl on the lignocellulose, so that the roughness of the lignocellulose is increased, the specific surface area and the adsorption force are increased, and the problems that the hydroxyl on the surface of the lignocellulose is easy to generate hydrogen bonds, form agglomeration and is difficult to disperse uniformly in dimethyl sulfoxide solution of polylactic acid and gelatin are solved.

Detailed Description

Preparation examples 1 to 5 of polylactic acid

Preparation examples 1 to 5 of polylactic acid was selected from Shandong institute for medical devices, molecular weight 30000, type DL; the 1-octyl-3-methylimidazolium tetrafluoroborate is selected from Linzhou, City Kogyo materials science and technology Co., Ltd, CAS number 86560-94-6; the triallyl isocyanurate is selected from Guangxi Teng Jun Biotech Co., Ltd, with the product number of TJ-011-1; the tin powder is selected from Nangong vessel Macro metal materials Co, Ltd, the product number is 354, the 1-ethyl-3-methylimidazole tetrafluoroborate is selected from the Mooney chemical technology (Shanghai) Co, the CAS number is 143314-16-3.

Preparation example 1: (1) dissolving 2kg of polylactic acid in 50kg of chloroform, adding 1kg of 1-octyl-3-methylimidazole tetrafluoroborate, irradiating the mixture on a cobalt-60 source with the radiation metering rate of 2.2kGy/h for 10kGy, precipitating the mixture by using methanol, and drying the precipitate at the temperature of 60 ℃ for 2h, wherein the mass ratio of the polylactic acid to the 1-octyl-3-methylimidazole tetrafluoroborate is 2: 1; (2) mixing the product obtained in the step (1) with 1kg of triallyl isocyanurate, 0.2kg of tin powder and 2kg of solvent, vacuumizing and heating to 190 ℃, reacting for 2 hours, cooling to 140 ℃, keeping the temperature for 0.5 hour, cooling to room temperature, and crushing, wherein the mass ratio of the triallyl isocyanurate to the tin powder to the solvent to the polylactic acid is 0.5:0.1:1:1, and the solvent is dichloromethane.

Preparation example 2: (1) dissolving 3.5kg of polylactic acid in 55kg of chloroform, adding 1kg of 1-octyl-3-methylimidazole tetrafluoroborate, irradiating the mixture on a cobalt-60 source with the radiation metering rate of 2.3kGy/h for 10kGy, precipitating the mixture by using methanol, and drying the precipitate at 70 ℃ for 1.5h, wherein the mass ratio of the polylactic acid to the 1-octyl-3-methylimidazole tetrafluoroborate is 3.5: 1; (2) mixing the product obtained in the step (1) with 2.1kg of triallyl isocyanurate, 0.7kg of tin powder and 7kg of solvent, vacuumizing and heating to 190 ℃, reacting for 2h, cooling to 140 ℃, keeping the temperature for 0.5h, cooling to room temperature, and crushing, wherein the mass ratio of the triallyl isocyanurate to the tin powder to the solvent to the polylactic acid is 0.6:0.2:2:1, and the solvent is dichloromethane.

Preparation example 3: (1) dissolving 5kg of polylactic acid in 55kg of chloroform, adding 1kg of 1-octyl-3-methylimidazole tetrafluoroborate, irradiating the mixture on a cobalt-60 source with the radiation metering rate of 2.5kGy/h for 10kGy, precipitating the mixture by using methanol, and drying the mixture at 80 ℃ for 1h, wherein the mass ratio of the polylactic acid to the 1-octyl-3-methylimidazole tetrafluoroborate is 5: 1; (2) mixing the product obtained in the step (1) with 4kg of triallyl isocyanurate, 0.5kg of tin powder and 7.5kg of solvent, vacuumizing and heating to 190 ℃, reacting for 2 hours, cooling to 140 ℃, keeping the temperature for 0.5 hour, cooling to room temperature, and crushing, wherein the mass ratio of the triallyl isocyanurate to the tin powder to the solvent to the polylactic acid is 0.8:0.1:1.5:1, and the solvent is dichloromethane.

Preparation example 4: the difference from preparation example 1 is that 1-ethyl-3-methylimidazolium tetrafluoroborate was used in the same amount instead of 1-octyl-3-methylimidazolium tetrafluoroborate.

Preparation example 5: the difference from preparation example 1 is that step (2) was not performed.

Preparation examples 1 to 3 of lignocellulose

Preparation of lignocellulose in examples 1-3 was selected from Beijing Wan Diagram science and technology Co., Ltd., model No. CN 210; succinic anhydride is selected from Zheng Bolina trade company, Inc., under the trademark BLA.

Preparation example 1: grinding 1kg of lignocellulose and 3kg of succinic anhydride at the rotating speed of 2000r/min for 2h, adding 10kg of DMF, stirring uniformly, reacting at 120 ℃ for 4h, filtering, and drying at 80 ℃ for 1 h.

Preparation example 2: grinding 1kg of lignocellulose and 3.5kg of succinic anhydride at the rotating speed of 2000r/min for 2h, adding 13kg of DMF, stirring uniformly, reacting at 125 ℃ for 3.5h, filtering, and drying at 75 ℃ for 1.5 h.

Preparation example 3: grinding 1kg of lignocellulose and 4kg of succinic anhydride at the rotating speed of 2000r/min for 2h, adding 15kg of DMF, stirring uniformly, reacting at 130 ℃ for 3h, filtering, and drying at 70 ℃ for 2 h.

Preparation examples 1 to 15 of organic emulsions

Preparation examples 1 to 15 of organic emulsions, DL-type polylactic acid was selected from Shandong institute of medical devices, molecular weight 30000; the CN210 type lignocellulose is selected from Beijing Wan Diagram science and technology company; the GELATIN is selected from TIQIJIELIKOUQI, whose model is GELATIN; the stannic chloride is selected from the chemical industry, Limited liability company of Yancun, Beijing, and has the CAS number of 10026-06-9; the dimethyl sulfoxide is selected from chemical industry Limited of Intelligent selection of Jinnan, and the product number is 125165; the benzimidazole is selected from Jintenglong industry Co., Ltd, Shenzhen, and the CAS number is 51-17-2; the paraffin is selected from Shanghai Gaomi chemical group, Inc., with a product number of 25896;

preparation example 1: (1) according to the raw material ratio in table 1, 0.5kg of gelatin and 1kg of polylactic acid are dissolved in 2kg of dimethyl sulfoxide, 0.5kg of lignocellulose is added and mixed uniformly to form a coating solution, the polylactic acid is DL type polylactic acid, and the lignocellulose is CN210 type;

(2) mixing 1kg of stannic chloride and 0.1kg of benzimidazole, adding the mixture into 2kg of deionized water, adding 0.3kg of sodium dodecyl benzene sulfonate, uniformly mixing, heating to 90 ℃, stirring for 12 hours, washing, and drying at 80 ℃ for 3 hours to obtain an intermediate;

(3) mixing 0.7kg of coating solution with 1kg of intermediate, performing spray drying to obtain a coated intermediate, and uniformly mixing 0.6kg of coated intermediate with 1kg of white oil to obtain an organic emulsion, wherein the mass ratio of the coating solution to the intermediate is 0.7:1, the mass ratio of the coated intermediate to the white oil is 0.6:1, and the sample loading amount of spray drying is 1.6L/h.

Preparation example 2: (1) according to the raw material ratio in table 1, 0.8kg of gelatin and 1.3kg of polylactic acid are dissolved in 2.5kg of dimethyl sulfoxide, 0.8kg of lignocellulose is added and mixed uniformly to form a coating solution, the polylactic acid is DL type polylactic acid, and the lignocellulose is CN210 type;

(2) mixing 2.5kg of stannic chloride and 0.15kg of benzimidazole, adding the mixture into 2.5kg of deionized water, adding 0.4kg of sodium dodecyl benzene sulfonate, uniformly mixing, heating to 120 ℃, stirring for 8 hours, washing, and drying for 2.5 hours at 85 ℃ to obtain an intermediate;

(3) mixing 0.8kg of coating solution with 1kg of intermediate, spray-drying to obtain a coated intermediate, and uniformly mixing 1.04kg of coated intermediate with 1.3kg of white oil to obtain an organic emulsion, wherein the mass ratio of the coating solution to the intermediate is 0.8:1, the mass ratio of the coated intermediate to the white oil is 0.8:1, and the sample loading amount of spray-drying is 1.6L/h.

Preparation example 3: (1) according to the raw material ratio in table 1, 1kg of gelatin and 1.5kg of polylactic acid are dissolved in 3kg of dimethyl sulfoxide, 1kg of lignocellulose is added and mixed uniformly to form a coating solution, the polylactic acid is DL type polylactic acid, and the lignocellulose is CN210 type;

(2) mixing 4kg of stannic chloride and 0.2kg of benzimidazole, adding the mixture into 3kg of deionized water, adding 0.5kg of sodium dodecyl benzene sulfonate, uniformly mixing, heating to 140 ℃, stirring for 4 hours, washing, and drying for 2 hours at 90 ℃ to obtain an intermediate;

(3) mixing 1kg of coating solution and 1kg of intermediate, spray drying to obtain a coated intermediate, and uniformly mixing 1.5kg of coated intermediate and 1.5kg of white oil to obtain an organic emulsion, wherein the mass ratio of the coating solution to the intermediate is 1:1, the mass ratio of the coated intermediate to the white oil is 1:1, and the sample loading amount of spray drying is 1.6L/h.

Preparation example 4: the difference from preparation example 1 is that polylactic acid is selected from preparation example 1 of polylactic acid and lignocellulose is selected from preparation example 1 of lignocellulose, as shown in table 1.

Preparation example 5: the difference from preparation example 1 is that polylactic acid is selected from preparation example 2 of polylactic acid and lignocellulose is selected from preparation example 2 of lignocellulose, as shown in table 1.

Preparation example 6: the difference from preparation example 1 is that polylactic acid is selected from preparation example 3 of polylactic acid and lignocellulose is selected from preparation example 3 of lignocellulose, as shown in table 1.

Preparation example 7: the difference from preparation example 1 is that polylactic acid is selected from preparation example 4 of polylactic acid and lignocellulose is selected from preparation example 1 of lignocellulose, as shown in table 1.

Preparation example 8: the difference from preparation example 1 is that polylactic acid is selected from preparation example 5 of polylactic acid and lignocellulose is selected from preparation example 1 of lignocellulose

Preparation example 9: the difference from preparation example 1 is that polylactic acid is selected from preparation example 5 of polylactic acid and lignocellulose is of type CN 210.

Preparation example 10: the difference from preparation example 1 is that polylactic acid is selected from preparation example 4 of polylactic acid and lignocellulose is CN210 type, as shown in table 1.

Preparation example 11: the difference from preparation example 1 is that polylactic acid is selected from preparation example 1 of polylactic acid and lignocellulose is CN210 type, as shown in table 1.

Preparation example 12: the difference from preparation example 1 is that polylactic acid is selected as DL type polylactic acid and lignocellulose is selected from preparation example 1 of lignocellulose as shown in table 1.

TABLE 1 raw material ratios of organic emulsions in preparation examples 1 to 12

Preparation example 13: the difference from preparation example 4 is that in step (2), paraffin was heated to 50 ℃, atomized with compressed air, sprayed onto the surface of the intermediate, and cooled to room temperature, the mass ratio of paraffin to intermediate was 0.5:1, and the amount of compressed air was 1Nm³/h。

Preparation example 14: the difference from preparation example 4 is that in step (2), paraffin was heated to 60 ℃, atomized with compressed air, sprayed onto the surface of the intermediate, and cooled to room temperature, the mass ratio of paraffin to intermediate was 0.7:1, and the amount of compressed air was 1.3Nm³/h。

Preparation example 15: the difference from preparation example 4 is that in step (2), paraffin was heated to 70 ℃ under pressureAtomizing with compressed air, spraying onto the surface of intermediate, cooling to room temperature with paraffin and intermediate mass ratio of 0.8:1 and compressed air amount of 1.5Nm³/h。

Examples

The source of the raw materials in each example is shown in table 2.

Table 2 sources of raw materials in each example

Raw materials	Manufacturer of the product	Model number
			Styrene (meth) acrylic acid ester	Bailingwei science and technology	M-502-42
Vinyl propionate	Wuhan Fuxin Yuanjin Tech Co Ltd	FXY
			Acrylic acid	Nantong Runfeng petrochemical Co., Ltd	79-10-7
Vinyl acrylate	Bailingwei science and technology	434620
			Cyclohexyl methacrylate	Beijing Zhongji Youth science & technology Co., Ltd	M0594
Methacrylic acid sodium sulfonate	Bailingwei science and technology	464358
			Octyl phenol polyoxyethylene ether OP-10	Jiangsu Hai'an petrochemical plant	OP-10
Octyl phenol polyoxyethylene ether OP-8	Jiangsu Hai'an petrochemical plant	OP-8
			Octyl phenol polyoxyethylene ether OP-6	Jiangsu Hai'an petrochemical plant	OP-6
Sodium fatty alcohol Ether sulfate	Shenzhen jintenglong trading Limited	AES
			Nano calcium carbonate	Jingjiang City Notification chemical Co Ltd	50nm
Polytetrafluoroethylene	Tetrafluoro New Material (Suzhou) Co., Ltd	L-5F
			Elastic graphite	QINGDAO YANHAI CARBON MATERIAL Co.,Ltd.	TX-850
Sepiolite	Lingshou county sky Hao ore production factory	0124

Example 1: the raw material formulation of the nano plugging agent is shown in Table 3, and the preparation method of the nano plugging agent comprises the following steps:

s1, mixing vinyl monomers, propenyl monomers, sodium methacrylate sulfonate, an emulsifier, an initiator and 1/6 water uniformly in sequence to prepare a pre-emulsion, wherein the vinyl monomers comprise styrene and vinyl propionate in a mass ratio of 1:0.42, the propenyl monomers comprise acrylic acid, vinyl acrylate and cyclohexyl methacrylate in a mass ratio of 1:2:1, the emulsifier is octyl phenol polyoxyethylene ether OP-8 and octyl phenol polyoxyethylene ether OP-6 in a mass ratio of 1:1, and the initiator is sodium bisulfite and potassium persulfate in a mass ratio of 1: 1;

s2, adding the pre-emulsion into the residual water, stirring for 3 hours at 70 ℃, cooling to room temperature, adding a filler, sepiolite and organic emulsion, and mixing uniformly to obtain the nano plugging agent, wherein the filler is nano calcium carbonate, polytetrafluoroethylene and elastic graphite, the mass ratio of the nano calcium carbonate to the polytetrafluoroethylene to the elastic graphite is 1:3:2, and the organic emulsion is prepared by mixing 1kg of polylactic acid, 0.5kg of lignocellulose, 1kg of stannic chloride, 0.3kg of sodium dodecyl benzene sulfonate, 0.1kg of benzimidazole, 0.5kg of gelatin, 2kg of dimethyl sulfoxide and 1kg of white oil.

TABLE 3 raw material ratios of the nano blocking agent in examples 1-5

Example 2: the raw material formulation of the nano plugging agent is shown in Table 3, and the preparation method of the nano plugging agent comprises the following steps:

s1, mixing vinyl monomers, propenyl monomers, sodium methacrylate sulfonate, an emulsifier, an initiator and 1/6 water uniformly in sequence to prepare a pre-emulsion, wherein the vinyl monomers comprise styrene and vinyl propionate in a mass ratio of 1:0.6, the propenyl monomers comprise acrylic acid, vinyl acrylate and cyclohexyl methacrylate in a mass ratio of 1:2:1.5, the emulsifier is octyl phenol polyoxyethylene ether OP-10 and octyl phenol polyoxyethylene ether OP-6 in a mass ratio of 1:1, and the initiator is sodium bisulfite and potassium persulfate in a mass ratio of 1: 1.5;

s2, adding the pre-emulsion into the residual water, stirring for 2.5h at 75 ℃, cooling to room temperature, adding a filler, sepiolite and organic emulsion, and mixing uniformly to obtain the nano plugging agent, wherein the filler is nano calcium carbonate, polytetrafluoroethylene and elastic graphite, the mass ratio of the nano calcium carbonate to the polytetrafluoroethylene to the elastic graphite is 2:4:4, and the organic emulsion is prepared by mixing 1kg of polylactic acid, 0.5kg of lignocellulose, 1kg of tin tetrachloride, 0.3kg of sodium dodecyl benzene sulfonate, 0.1kg of benzimidazole, 0.5kg of gelatin, 2kg of dimethyl sulfoxide and 1kg of white oil.

Example 3: the raw material formulation of the nano plugging agent is shown in Table 3, and the preparation method of the nano plugging agent comprises the following steps:

s1, mixing vinyl monomers, propenyl monomers, sodium methacrylate sulfonate, an emulsifier, an initiator and 1/6 water uniformly in sequence to prepare a pre-emulsion, wherein the vinyl monomers comprise styrene and vinyl propionate in a mass ratio of 1:0.75, the propenyl monomers comprise acrylic acid, vinyl acrylate and cyclohexyl methacrylate in a mass ratio of 1:2:2, the emulsifier is sodium fatty alcohol polyoxyethylene ether sulfate, and the initiator comprises sodium bisulfite and potassium persulfate in a mass ratio of 1: 2;

s2, adding the pre-emulsion into the residual water, stirring for 2 hours at 80 ℃, cooling to room temperature, adding a filler, sepiolite and organic emulsion, and mixing uniformly to obtain the nano plugging agent, wherein the filler is nano calcium carbonate, polytetrafluoroethylene and elastic graphite, the mass ratio of the nano calcium carbonate to the polytetrafluoroethylene to the elastic graphite is 3:5:6, and the organic emulsion is prepared by mixing 1kg of polylactic acid, 0.5kg of lignocellulose, 1kg of stannic chloride, 0.3kg of sodium dodecyl benzene sulfonate, 0.1kg of benzimidazole, 0.5kg of gelatin, 2kg of dimethyl sulfoxide and 1kg of white oil.

Examples 4 to 5: a nano blocking agent is different from the nano blocking agent in example 1 in that the raw material formulation is shown in Table 3.

Example 6: a nano blocking agent, which is different from example 1 in that an organic emulsion is prepared from preparation example 1 of the organic emulsion.

Example 7: a nano blocking agent, which is different from example 1 in that an organic emulsion is prepared from preparation example 2 of the organic emulsion.

Example 8: a nano blocking agent, which is different from example 1 in that an organic emulsion is prepared from preparation example 3 of the organic emulsion.

Example 9: a nano blocking agent, which is different from example 1 in that an organic emulsion is prepared from preparation example 4 of the organic emulsion.

Example 10: a nano blocking agent, which is different from example 1 in that an organic emulsion is prepared from preparation example 5 of the organic emulsion.

Example 11: a nano blocking agent, which is different from example 1 in that an organic emulsion is prepared from preparation example 6 of the organic emulsion.

Example 12: a nano blocking agent, which is different from example 1 in that an organic emulsion was prepared from preparation example 7 of the organic emulsion.

Example 13: a nano blocking agent, which is different from example 1 in that an organic emulsion is prepared from preparation example 8 of the organic emulsion.

Example 14: a nano blocking agent, which is different from example 1 in that an organic emulsion is prepared from preparation example 9 of the organic emulsion.

Example 15: a nano blocking agent, which is different from example 1 in that an organic emulsion is prepared from preparation example 10 of the organic emulsion.

Example 16: a nano blocking agent, which is different from example 1 in that an organic emulsion is prepared from preparation example 11 of the organic emulsion.

Example 17: a nano blocking agent, which is different from example 1 in that an organic emulsion is prepared from preparation example 12 of the organic emulsion.

Example 18: a nano blocking agent, which is different from example 1 in that an organic emulsion is prepared from preparation example 12 of the organic emulsion.

Example 19: a nano blocking agent, which is different from example 1 in that an organic emulsion is prepared from preparation example 12 of the organic emulsion.

Example 20: a nano blocking agent, which is different from example 1 in that an organic emulsion is prepared from preparation example 12 of the organic emulsion.

Comparative example

Comparative example 1: a nano blocking agent, which differs from example 1 in that no organic emulsion is added.

Comparative example 2: a nano blocking agent, which is different from the nano blocking agent in the embodiment 1 in that tin tetrachloride, sodium dodecyl benzene sulfonate and benzimidazole are not added into the organic emulsion.

Comparative example 3: a nano blocking agent, which is different from the nano blocking agent in example 1 in that no lignocellulose is added to the organic emulsion.

Comparative example 4: a nano blocking agent, which is different from the nano blocking agent in the embodiment 1 in that polylactic acid is not added into the organic emulsion.

Comparative example 5: a nano blocking agent, which is different from the nano blocking agent in example 1 in that sepiolite is not added.

Comparative example 6: a nano blocking agent, differing from example 1 in that an equal amount of white oil was used instead of the organic emulsion.

Comparative example 7: a preparation method of a shale micro-nano particle plugging agent for drilling fluid comprises the steps of adding 200mL of distilled water into a reaction kettle provided with a stirrer, a thermometer and a heating device, adding 100mL of acetone, 12.3g of methyl methacrylate and 9.6g of styrene while stirring, stirring at a high speed of 1500r/min to form a stable dispersion system, heating in a water bath to 70 ℃, adding 0.08g of potassium persulfate, reacting for 2.5 hours, and naturally cooling to obtain the shale micro-nano particle plugging agent for drilling fluid.

Comparative example 8: a waterproof plugging agent for a drilling oil field is selected from the New grass material science and technology (Shanghai) company Limited, and the model is H-015.

Performance test

The blocking agents prepared in the examples and comparative examples were measured for their properties according to the following methods, and the results are shown in Table 4.

1. The particle size distribution characteristics of the plugging agents in the different examples and comparative examples were tested using a laser particle size distribution tester.

2. Plugging rate: the air permeability is (10-100) x 10^-3μm²The artificial core of (1) was saturated with white oil and then measured for its white oil permeability K1 in the forward direction, and after adding 2% of a blocking agent to white oil and then contamination in the forward direction (80 ℃, 3.5MPa,120min), the white oil permeability K2 was measured in the forward direction and the blocking rate was calculated according to the following formula, η ═ K1-K2)/K1 × 100%.

3. Measurement of filtration loss reduction rate at 200 ℃: (1) preparing base slurry: preparing base slurry according to the mass ratio of distilled water to experimental slurry preparation soil to anhydrous sodium carbonate of 400:20:1, stirring at 1500r/min for 20min, stopping at least for 2 times during the stirring, scraping clay adhered to the wall of the container, and sealing and maintaining at room temperature for 24h to obtain the base slurry;

(2) and (3) base slurry performance determination: taking 400mL of the base slurry prepared in the step (1), stirring at a rotating speed of 1500r/min for 5min, then measuring the filtration loss of the base slurry, wherein the measurement result is within the range of 40-60mL, otherwise, adjusting the addition amount of the test slurry preparation soil;

(3) test slurry 200 ℃ performance determination: adding 12g of the sample plugging agent into 400mL of the base slurry adjusted in the step (2) by stirring, stirring at 1500r/min for 20min, stopping at least 2 times during the stirring, scraping off the slurry adhered to the wall of the container, and calculating the rate of decrease in the fluid loss at 200 ℃ and 3450KPa, which is (A-B)/A × 100%, according to the following formula, wherein A is the fluid loss of the base slurry at 200 ℃ and 3450KPa in the step (2), and B is the fluid loss of the test slurry at 200 ℃ and 3450KPa in the step (3).

4. Filter cake thickness and filter cake permeability: removing 200mL of distilled water, adding 14g of bentonite and 0.6g of sodium carbonate, stirring at 600r/min for 4h, standing for 24h to obtain slurry(ii) a Adding 140g of barite and 35g of polyacrylamide into the soil slurry in sequence, stirring for 2h at the rotating speed of 600r/min, stirring for 30min at the rotating speed of 9000r/min, dehydrating for 30min at the temperature of 25 ℃ and the pressure of 3.5MPa to prepare a filter cake, taking the plugging agent prepared in each embodiment and each pair of proportions, ultrasonically dispersing for 10min by using 100mL of deionized water as a solvent, transferring into a high-temperature and high-pressure dehydration instrument filled with the filter cake, testing at the temperature of 25 ℃ and the pressure of 3.5MPa, recording a reading every 5min, measuring for 30min, taking out the filter cake, drying to obtain a measured thickness, and obtaining the thickness of the filter cake according to the K of quL (A delta P) multiplied by 10 according to the K^-1And calculating the permeability of the filter cake, wherein K is the permeability and the unit is mum²Q is the volume flow in cm³U is the fluid viscosity in mPas, A is the volume of the filter cake in cm²And L is the axial length of the filter cake, cm.

TABLE 4 test results of the properties of the blocking agents prepared in examples and comparative examples

In examples 1 to 5, the acrylic monomer, the vinyl monomer and the like are used to prepare the nano emulsion, the nano-level particles in the particles have a high proportion, D90 is less than 500nm, the plugging rate is 93.4 to 94.6 percent, and the plugging agent has low permeability in a filter cake and good plugging effect.

In examples 6 to 8 using the organic emulsions prepared in examples 1 to 3 in which polylactic acid and lignocellulose were commercially available products, D10 was found to be comparable to those of examples 1 to 5 in terms of particle size distribution when polylactic acid, lignocellulose and gelatin were coated on an intermediate formed of tin tetrachloride and the like, but D50 was increased to 188-197nm and D90 was increased to 354-368nm, and although the particle sizes of D50 and D90 were increased, many fine particles having a particle size of 84 to 98nm were present, and thus fine cracks could be blocked and the blocking effect was enhanced.

In examples 9 to 11 using the organic emulsions prepared in examples 4 to 6 of the present application, in which polylactic acid prepared in examples 1 to 3 and lignocellulose prepared in examples 1 to 3 were used, the particle size distribution of the plugging agent was not much different from that of example 6, but the plugging rate was increased in examples 9 to 11, and the plugging agent was firmly attached to the borehole wall due to the increased adsorption force of polylactic acid and lignocellulose to the borehole wall, thereby increasing the force acting between the nanoparticles and the formation, decreasing the permeability, and increasing the heat resistance of the plugging agent.

In example 12, the organic emulsion prepared in preparation example 7 was used, wherein polylactic acid was selected from preparation example 4 of polylactic acid and lignocellulose was selected from preparation example 1 of lignocellulose, and compared with example 9, the particle size distribution of the blocking agent prepared in example 12 was not much different, and the rate of decrease in fluid loss at 200 ℃ was not significantly changed, but the blocking rate was decreased and the permeability was increased, which indicates that the pretreatment of polylactic acid with 1-ethyl-3-methylimidazolium tetrafluoroborate instead of 1-octyl-3-methylimidazolium tetrafluoroborate did not have a good pretreatment effect with 1-octyl-3-methylimidazolium tetrafluoroborate.

In example 13 using the organic emulsion prepared in organic emulsion preparation 8, wherein polylactic acid is selected from polylactic acid preparation 4, but lignocellulose is selected from a commercially available product, the plugging effect of the plugging agent in example 13 is decreased compared to example 12, indicating that the lignocellulose prepared in the present application can increase the plugging effect of the plugging agent.

In example 14, the organic emulsion prepared in preparation example 9 was used, wherein the polylactic acid was selected from preparation example 5 of polylactic acid, the lignocellulose was selected from preparation example 1 of lignocellulose, and the polylactic acid was not pretreated with triallyl isocyanurate or the like, so that the filtration loss reduction rate of the prepared plugging agent at 200 ℃ was remarkably reduced, and the plugging rate and the permeability were not much different from those of example 9, which indicates that the heat resistance of the plugging agent can be increased by pretreating the polylactic acid with triallyl isocyanurate and tin powder.

In example 15 using an organic emulsion prepared in preparation example 10 in which polylactic acid is selected from preparation example 5 of polylactic acid and lignocellulose is selected from a commercially available product, the filtration loss reduction rate of the blocking agent at 200 ℃ is reduced and the permeability is increased in example 15 as compared with example 9, and in combination with example 9 and example 14, pretreatment of polylactic acid with tin powder and triallyl isocyanurate can increase the heat resistance of the blocking agent, and the blocking effect of the blocking agent can be improved using lignocellulose prepared in the present application.

In example 16, the organic emulsion prepared in preparation example 11 in which polylactic acid was selected from preparation example 1 and lignocellulose was selected from a commercially available product was used, and in example 17, the organic emulsion prepared in preparation example 12 in which polylactic acid was selected from a commercially available product and lignocellulose was selected from preparation example 1 in lignocellulose, example 16 and example 17 showed less change in particle size distribution, but the plugging rate decreased, the permeability increased, and the plugging effect decreased, as compared with example 9.

In examples 18 to 20, the organic emulsions prepared in preparation examples 13 to 15 of the organic emulsion were used, in which polylactic acid was prepared from preparation example 1 of polylactic acid, lignocellulose was prepared from preparation example 1 of lignocellulose, and paraffin was coated on the intermediate, and in the thus prepared blocking agent, D10 was not much different from example 1, and since paraffin was coated on the intermediate, the particle diameters of D50 and D90 were increased but still within 500nm, and a good micro-crack filling effect was exhibited, and when the paraffin-coated intermediate flowed out of the polylactic acid-coated film, it was not easily agglomerated, and the dispersibility was good, thereby further improving the blocking rate and reducing the permeability.

Compared with the example 1, the organic emulsion is not added in the comparative example 1, the D10 in the plugging agent prepared in the comparative example 1 is 103nm, and the differences between the D50 and the D90 are not obvious compared with the example 1, which shows that the added organic emulsion can form finer particles, thereby effectively plugging the shale well wall.

Comparative example 2 compared to example 1, without the addition of tin tetrachloride, sodium dodecylbenzenesulfonate and benzimidazole, the D10 of the blocking agent prepared in comparative example 2 increased to 105nm, whereas D50 and D90 did not differ much from example 1, and D10 in comparative example 2 was similar to D10 in comparative example 1, and the blocking rate decreased in comparative example 2, indicating that fine particles in the blocking agent were formed from tin tetrachloride, sodium dodecylbenzenesulfonate and benzimidazole.

Comparative example 3 and comparative example 4 compared with example 1, no lignocellulose was added to the organic emulsion, no polylactic acid was added to comparative example 4, the particle size distribution of the plugging agent prepared in comparative example 3 and comparative example 4 was not much different from that of example 1, but the difference between the plugging rate and the permeability was large, which indicates that the lignocellulose and polylactic acid can increase the plugging effect of the plugging agent and reduce the permeability, and the filtration loss reduction rate at 200 ℃ in comparative example 3 is reduced, indicating that the lignocellulose can increase the heat resistance of the plugging agent.

In comparative example 5, the particle size of the plugging agent was reduced by 91.8% although the D90 of 213nm was reduced in comparison with example 1 without adding sepiolite, indicating that the plugging effect was also reduced even though the particle size of the plugging agent was reduced by adding sepiolite.

Comparative example 6 compared to example 1, using the same amount of white oil instead of the organic emulsion, the particle size of D10 in comparative example 6 increased, the plugging rate decreased, the permeability increased, and the plugging effect decreased.

Comparative example 7 is a blocking agent prepared by the prior art, which has a large D90 of 13242nm and a blocking rate which is significantly reduced compared to example 1, and comparative example 8 is a commercially available blocking agent which has a blocking effect inferior to that of the present application.

The present embodiment is only for explaining the present application, and it is not limited to the present application, and those skilled in the art can make modifications of the present embodiment without inventive contribution as needed after reading the present specification, but all of them are protected by patent law within the scope of the claims of the present application.