Temperature-resistant and corrosion-resistant plugging material for drilling fluid as well as preparation method and application of temperature-resistant and corrosion-resistant plugging material

Abstract

The invention provides a temperature-resistant and corrosion-resistant plugging material for drilling fluid as well as a preparation method and application of the temperature-resistant and corrosion-resistant plugging material. The plugging material provided by the invention is a microsphere material with a core-shell structure, a core layer is a degradable polyester material, and a shell layer is nano SiO2 particles. The obtained microsphere particles have the characteristics of small size, uniform particle size and the like, can enter micro-nano-scale micro cracks and pores to form a compact plugging layer, effectively reduce the pressure transmission rate, prevent further invasion of drilling fluid and achieve the purpose of stabilizing a well wall, are resistant to temperature and corrosion and can be automatically degraded in the natural environment.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil drilling oilfield chemicals, and particularly relates to a plugging material for a temperature-resistant and corrosion-resistant drilling fluid, a preparation method thereof, and an application thereof. Background Technique

[0002] In recent years, with the improvement of oil and gas exploration technologies, there are more and more complex wells such as marginal wells, deep wells, and special wells. Due to the complexity of these formations themselves and the influence of extraction means during the oil and gas extraction process, the pressure-bearing capacity of some formations has decreased significantly, and problems such as wellbore instability and lost circulation have become more and more numerous and prominent. Wellbore instability and lost circulation seriously affect the drilling construction progress and threaten drilling safety. For formations with developed pores, fractures or fragmentation, wellbore instability problems are likely to occur. Strengthening the plugging ability of the drilling fluid is one of the ways to improve wellbore stability and prevent lost circulation.

[0003] Adding treatment agents to the drilling fluid can prevent the transmission of pore pressure and extend the collapse period. Plugging agents are a type of treatment agent with a large dosage in the drilling fluid. In addition to having a plugging effect, they also have the functions of adjusting the dynamic shear force, static shear force, filtration loss property of the drilling fluid and improving the quality of the mud cake, thus having an important impact on wellbore stability and reservoir protection, etc. The plugging agent itself is a hydrophobic material that can be dispersed in water, or a hydrophilic material that can be dispersed in oil. Commonly used plugging agents are spherical granular or fibrous, but they need to be removed later after plugging. If the removal is not thorough, it will cause secondary damage to the formation. Therefore, high-performance plugging agents are needed to effectively physically and chemically plug micro-fractures to improve wellbore stability. In addition, to improve the formation plugging effect, the plugging agent should be matched with plugging materials of different particle sizes according to the size of formation pores and fractures. Currently, commonly used plugging agents at home and abroad are mainly asphalt, polyalcohol, silicate, latex plugging agents, etc. Asphalt-based plugging agents have strong fluorescence, and it is difficult to match the softening point with the formation. Latex plugging agents will affect the rheology of the drilling fluid and affect the drilling speed to a certain extent. Polyalcohol-based plugging agents have poor temperature resistance, and silicate-based plugging agents are pH-sensitive.

[0004] Polymer particle plugging materials have gradually become a current research hotspot due to their good application effects. For example, a particle plugging polymer MAX-SHIELD developed by Baker Hughes based on carboxylated styrene-butadiene latex or sulfonated styrene-butadiene latex can achieve good plugging effects and wellbore stability. The particle size of the plugging material is too large and does not match well with the micropores and microfractures of special shale formations, while a small particle size is not ideal enough in synthesis or actual application. Chinese invention patent CN 114479784A provides a polymer particle plugging material based on acrylamide, and Chinese invention patent CN 109666465A provides a composite plugging material of polystyrene and acrylate. These materials have good plugging effects. However, after the polymer absorbs water and swells, its strength is low, it is easily degraded at high temperatures, resulting in molecular chain breakage, poor salt tolerance, easy hydrolysis and other problems, thus losing the plugging effect. In addition, the residue of the polymer plugging agent will cause damage to the formation and environmental pollution. Chinese patent application CN 113528102 A discloses a drilling fluid plugging agent material prepared with polylactic acid as the base material. Although the polylactic acid material can solve the problems of residue and environmental pollution as a plugging agent, the polylactic acid material itself does not have heat and corrosion resistance, and it is easily eroded by microorganisms in the soil and causes too fast degradation, severely restricting its application as a bottom drilling fluid plugging material. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides a plugging material for a temperature- and corrosion-resistant drilling fluid and a preparation method thereof. The plugging material is a microsphere material that is temperature- and corrosion-resistant and can be self-degraded in the natural environment. The microsphere material is a microsphere material with a core-shell structure, the core layer is a degradable polyester material, and the shell layer is nano-SiO2 particles. In the present invention, a polymer is used as the core, and composite microspheres of different sizes can be obtained by changing the size of the polymer inner core, with stronger applicability; at the same time, SiO2 is modified and reacted on the surface of the polyester microspheres, which can significantly improve the loading rate of SiO2, and the SiO2 in the shell layer can improve the temperature- and corrosion-resistant performance of the plugging microsphere material.

[0006] One object of the present invention is to provide a plugging material for a temperature- and corrosion-resistant drilling fluid, including a microsphere material with a core-shell structure, the core layer of the microsphere material is a degradable polyester material, and the shell layer of the microsphere material is modified SiO2 particles.

[0007] According to the present invention, in the plugging material for the temperature- and corrosion-resistant drilling fluid:

[0008] The mass ratio of the degradable polyester material to the modified SiO2 particles is 1:(0.01 - 1), preferably 1:(0.5 - 1);

[0009] The thickness of the shell layer is 5 - 1000 nm, preferably 10 - 300 nm;

[0010] The particle size of the microsphere material is 0.1 to 5000 μm, preferably 0.5 to 600 μm.

[0011] According to the present invention, in the plugging material for the high-temperature and corrosion-resistant drilling fluid:

[0012] The degradable polyester material is selected from at least one of polylactic acid, polyglycolic acid, polylactic acid-glycolic acid copolymer, polycaprolactone, poly(p-dioxanone), poly(amino acid-derived carbonate), polyorthoester, polyhydroxyalkanoate, polytrimethylene carbonate, oxalate and its polymer, poly(dioxolene ester);

[0013] The modified SiO2 particles are SiO2 particles modified with a silane coupling agent, and the silane coupling agent is preferably selected from at least one of vinyltrichlorosilane, vinyltriethoxysilane, vinyltrimethoxysilane, vinyltris(β-methoxyethoxy)silane, γ-(methacryloyloxy)propyltrimethoxysilane, and more preferably selected from at least one of γ-(methacryloyloxy)propyltrimethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane;

[0014] The particle size of the modified SiO2 particles is 5 to 100 nm, preferably 10 to 30 nm.

[0015] The second object of the present invention is to provide a preparation method of the above plugging material for the high-temperature and corrosion-resistant drilling fluid, including: stirring a dispersion liquid containing the modified SiO2 particles and the degradable polyester material to obtain a microsphere emulsion, and then through photocuring reaction and post-treatment to obtain the plugging material for the high-temperature and corrosion-resistant drilling fluid.

[0016] According to the present invention, the preparation method of the plugging material for the high-temperature and corrosion-resistant drilling fluid specifically includes the following steps:

[0017] (1) Dissolve the stabilizer in water, adjust the pH of the stabilizer aqueous solution to 5 to 8, and add the modified nano-SiO2 particles to the stabilizer aqueous solution and disperse evenly;

[0018] (2) Add the degradable polyester material to the organic solvent S1 to obtain a degradable polyester solution, and then add an initiator;

[0019] (3) Add the solution of step (2) to the solution of step (1), stir and then irradiate with light for photocuring reaction;

[0020] (4) Filter, wash and dry the product after the photocuring reaction to obtain the plugging material for the high-temperature and corrosion-resistant drilling fluid.

[0021] According to the present invention, in the preparation method of the plugging material for the high-temperature and corrosion-resistant drilling fluid, in step (1):

[0022] The stabilizer is selected from at least one of polyvinyl alcohol, polyethylene glycol, gelatin, agar, and water-soluble cellulose, preferably from at least one of polyvinyl alcohol, gelatin, carboxymethyl cellulose, and agar; the mass fraction of the stabilizer aqueous solution is 1-10%, preferably 1-3%;

[0023] The pH of the stabilizer aqueous solution is adjusted with an alkali solution and / or an acid solution. Preferably, the alkali in the alkali solution is selected from at least one of sodium hydroxide and ammonia water; the acid in the acid solution is selected from at least one of hydrochloric acid, sulfuric acid, and phosphoric acid; the concentrations of the alkali solution and the acid solution are not particularly limited, and it is sufficient to adjust the pH of the stabilizer aqueous solution to 5-8.

[0024] According to the present invention, in step (2) of the preparation method of the plugging material for the high-temperature and corrosion-resistant drilling fluid:

[0025] The organic solvent S1 is selected from at least one of dichloromethane, chloroform, ethyl acetate, dioxane, dimethyl sulfoxide, acetone, tetrahydrofuran, and isopropanol, preferably from at least one of dichloromethane, chloroform, and ethyl acetate;

[0026] The mass ratio of the degradable polyester material to the organic solvent S1 is 1:(10-100), preferably 1:(10-30);

[0027] The mass ratio of the degradable polyester material to the modified SiO2 particles is 1:(0.01-1), preferably 1:(0.5-1);

[0028] The volume ratio of the degradable polyester solution to the stabilizer aqueous solution containing nano-SiO2 is 1:(1-10), preferably 1:(3-5);

[0029] The initiator can be a commonly used photoinitiator in the art. For example, it is at least one of photoinitiator 184, 651, 819, 907, 1173, Irgacure 2959, and LAP; the dosage of the initiator is not particularly limited and can be added according to the common dosage. For example, the dosage of the photoinitiator is 0.1%-10% of the degradable polyester material;

[0030] The addition of the initiator is carried out under a protective atmosphere, and the protective atmosphere can be a commonly used protective gas, such as nitrogen.

[0031] According to the present invention, the stirring in step (3) of the preparation method of the plugging material for the high-temperature and corrosion-resistant drilling fluid specifically includes: first, high-speed homogenization stirring is carried out to obtain a microsphere emulsion, then stirring is carried out at a low speed under a protective gas atmosphere and heating, and then the microsphere emulsion is cooled, and the microsphere emulsion is irradiated with light to initiate a photocuring reaction; preferably,

[0032] The protective atmosphere can adopt common protective gases, such as nitrogen;

[0033] The conditions for high-speed stirring are: rotation speed 500 - 10000 rpm, stirring time 5 - 15 min;

[0034] The conditions for heating and low-speed stirring are: temperature 40 - 60 °C, rotation speed 100 - 350 rpm, stirring time 2 - 8 h;

[0035] The temperature for cooling is 20 - 40 °C;

[0036] The conditions for the photocuring reaction are: light irradiation wavelength 200 - 500 nm, reaction time 5 - 30 min.

[0037] According to the present invention, for the preparation method of the plugging material for temperature- and corrosion-resistant drilling fluid, the modified SiO2 particles are prepared by the following steps:

[0038] (a) Adjust the pH of the solvent S2 to 4 - 6 using an acidic regulator;

[0039] (b) Add a silane coupling agent to the solvent S2 and continuously stir and mix;

[0040] (c) Add nano-SiO2 to the mixture for reaction;

[0041] (d) After centrifuging, washing, and drying the reaction product, the modified nano-SiO2 particles are obtained.

[0042] According to the present invention, in the preparation steps of the modified SiO2 particles:

[0043] In step (a), the acidic regulator is selected from organic acidic compounds or inorganic acidic compounds, preferably at least one of acetic acid, phosphoric acid, and hydrochloric acid; the solvent S2 is selected from at least one of water, ethanol, methanol, and isopropanol, preferably at least one of water and ethanol;

[0044] In step (b), the mass ratio of the silane coupling agent to the solvent S2 is 1:(10 - 1000), preferably 1:(10 - 100); the continuous stirring time is 1 - 3 h;

[0045] The mass ratio of the silane coupling agent to nano-SiO2 is 1:(1 - 100), preferably 1:(2 - 10);

[0046] In step (c), the particle size of the nano-SiO2 is 5 - 100 nm, preferably 10 - 30 nm; the reaction conditions are: reaction temperature 40 - 70 °C, reaction time 2 - 24 h;

[0047] In step (d), the drying conditions are a temperature of 30 to 60 °C and a time of 3 to 12 h. Preferably, the drying conditions are a temperature of 40 to 50 °C and a time of 4 to 8 h.

[0048] A third object of the present invention is to provide a drilling fluid plugging agent, which includes plugging materials of three different particle sizes. The plugging materials are the plugging materials for high-temperature and corrosion-resistant drilling fluids described in one of the objects of the present invention or the plugging materials for high-temperature and corrosion-resistant drilling fluids obtained by the preparation method described in the second object of the present invention. Preferably, in the drilling fluid plugging agent, the content of the plugging material with a particle size less than 10 μm is 10 to 20 wt%, the content of the plugging material with a particle size ranging from 10 to 200 μm is 45 to 75 wt%, and the content of the plugging material with a particle size greater than 200 μm is 15 to 35 wt%. The microsphere particles obtained by the present invention have characteristics such as small size and uniform particle size. The plugging agent used has microsphere materials of different sizes, which can enter micro-nano scale microcracks and pores to form a sealing plugging layer, effectively reducing the pressure transmission rate, preventing the further intrusion of drilling fluid, and achieving the purpose of stabilizing the wellbore.

[0049] A fourth object of the present invention is to provide an application of the plugging material for high-temperature and corrosion-resistant drilling fluids described in one of the objects of the present invention or the drilling fluid plugging agent described in the third object of the present invention in the field of oil drilling.

[0050] In view of the situation in the prior art that the plugging agent cannot be naturally degraded and the incomplete removal causes secondary damage to the reservoir, the present invention uses a biodegradable polyester material and corrosion-resistant nano-silica as raw materials to provide a completely degradable plugging agent for drilling fluid and its preparation method. It can be used in combination with drilling fluids of different temperatures and compositions and applied to formations of different temperatures. After drilling is completed, the material does not need to be removed secondarily and does not damage the reservoir, and can maximize the protection of the oil layer. The inner layer material of the micron-sized microspheres will degrade by itself, and the outer layer nanoparticles can still penetrate into small-sized gaps and then plug them, thus achieving the purpose of continuous plugging of large or small cracks and large or small pores.

[0051] The present invention provides a plugging material for temperature and corrosion resistant drilling fluid and a preparation method thereof, aiming to solve the problem of how to endow the plugging agent material with biodegradability and environmental friendliness on the basis of existing patents, and improve its high temperature resistance and corrosion resistance through optimization and modification. With the continuous increase of drilling depth in China, the temperature that the drilling fluid needs to withstand is getting higher and higher. Through the improvement of the existing technology of the plugging agent for drilling fluid, the present invention utilizes the synergistic effect of nano-silica and degradable polyester materials in the preparation of the plugging agent for drilling fluid, improves the high temperature resistance, high pressure resistance, corrosion resistance and degradability of the degradable polyester material, enables it to maintain good dispersibility at a higher temperature in the drilling fluid, realizes the effective plugging of nano-micron pores, and meets the replacement and popularization requirements of existing plugging agent materials.

[0052] The microsphere particles obtained in the present invention have characteristics such as small size and uniform particle size. The obtained plugging agent also has microsphere materials of different sizes, which can enter micro-nano scale microfractures and pores to form a tight plugging layer, effectively reducing the pressure transmission rate, preventing the further invasion of the drilling fluid, and achieving the purpose of stabilizing the wellbore. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 It is the electron microscope photograph of the plugging material with core-shell structure prepared in Example 1.

[0054] Figure 2 It is the electron microscope photograph of the polylactic acid microspheres in Comparative Example 1.

[0055] Figure 3 It is the infrared spectrum diagram of nano-SiO2 before and after modification in Example 1. From top to bottom, they are the infrared spectrum diagrams of modified nano-SiO2, unmodified SiO2, and silane coupling agent KH570.

[0056] Figure 4a ~d are the elemental analysis diagrams of the microsphere core and outer layer in the plugging material with core-shell structure prepared in Example 1. Figure 4a ~d are the electron microscope pictures of the microsphere particles, the C element detected in the microsphere core, the O element detected in the microsphere core and outer layer, and the Si element detected in the microsphere outer layer in sequence.

[0057] Figure 5 It is the thermogravimetric curve of the plugging materials prepared in Examples 1-3 and Comparative Example 1. SPECIFIC EMBODIMENTS

[0058] The present invention will be specifically described below in conjunction with specific embodiments. It is necessary to point out here that the following embodiments are only used for further illustration of the present invention and cannot be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art to the present invention according to the content of the present invention still fall within the protection scope of the present invention.

[0059] The testing instruments and testing conditions adopted in the embodiments are as follows:

[0060] (1) Infrared spectroscopy test

[0061] The transmission spectrum of the dried material was measured using a Bruker Tensor II Fourier transform infrared spectrometer. The spectral resolution during the infrared test was selected as 4 cm -1 , the number of scans was set to 16 times, and the wavenumber selection range was 4000 cm -1 -600 cm -1 .

[0062] (2) Scanning electron microscopy and energy-dispersive spectroscopy test

[0063] The dried material was sputter-coated with gold with a sputtering current of 4 - 5 mA and a sputtering time of 3 - 5 min. The microstructure of the material was observed using a field emission scanning electron microscope (SEM) with an acceleration voltage of 5 kV, and the elements in the shell layer and interior of the core-shell microspheres were analyzed using EDS energy spectroscopy simultaneously.

[0064] (3) Thermal property test

[0065] Approximately 10 mg of the material was taken and a thermogravimetric analyzer was used to heat the material from room temperature to 650 °C. During the process, a nitrogen protective atmosphere was adopted, the heating rate was 10 °C / min, and the flow rate of nitrogen was controlled at 50 mL / min to obtain the thermogravimetric curve of the material.

[0066] (4) Particle size measurement

[0067] The particle size of the material was measured using an Anton Paar PSA 1190 laser particle size analyzer.

[0068] (5) Filtration loss determination

[0069] The filtration loss (API) of the plugging agent was determined according to GB / T 16783.1 - 2014 "Petroleum and natural gas industries - Field testing of drilling fluids - Part 1: Water-based drilling fluids". The main instruments were a filtration loss instrument, a drilling fluid cup, a timer, a graduated cylinder, and a roller oven. The plugging agent was added to the base mud or drilling fluid and stirred at high speed, then heat-rolled at a certain temperature for 16 h, taken out and cooled to room temperature, and the filtration loss was determined according to the standard GB / T 16783.1 - 2014 after high-speed stirring.

[0070] (6) Plugging effect test

[0071] Using clay and barite as raw materials, a mud cake with a certain thickness was prepared by using a GG42-2 type high-temperature and high-pressure filtration loss instrument to simulate the nano- and micron-scale formation. By measuring the average flow rate of the drilling fluid containing the plugging agent in the simulated formation, the permeability of the simulated formation before and after plugging was calculated, and thus the plugging rate of different plugging agents for the simulated formation was obtained.

[0072] For the raw materials used in the examples and comparative examples, if not specifically defined, they are all disclosed in the prior art. For example, they can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0073] Preparation of the drilling fluid plugging material in Example 1

[0074] Prepare 100 mL of a mixed solution of ethanol and water, where the mass fraction of ethanol is 90%. Adjust the pH value of the solvent to 5 with acetic acid; add γ-(methacryloyloxy)propyltrimethoxysilane (KH570) with a mass fraction of 3% to the solution, and stir at a speed of 200 rpm for 1 h at room temperature to completely hydrolyze γ-(methacryloyloxy)propyltrimethoxysilane; add 15 g of nano-SiO2 particles (particle size of 10 nm) to the silane mixture, ultrasonically disperse, and react at 50 °C for 18 h; perform centrifugation on the mixture, collect the modified SiO2 particles, wash them 3 times with water and ethanol respectively, and vacuum dry at 40 °C for 6 h to obtain modified nano-SiO2 particles.

[0075] Dissolve 6 g of polyvinyl alcohol in 300 mL of deionized water to prepare an aqueous polyvinyl alcohol solution, and adjust the pH to 6 with 0.1 mol / L dilute hydrochloric acid and 0.1 mol / L sodium hydroxide solution; add 3 g of modified nano-SiO2 particles to the aqueous polyvinyl alcohol solution and ultrasonically disperse it for 10 min at an ultrasonic frequency of 30 KHz.

[0076] Under the condition of 20 °C, add 5 g of poly-L-lactic acid to 100 mL of dichloromethane and fully dissolve it to obtain a dichloromethane solution of poly-L-lactic acid; under a nitrogen atmosphere, add 0.3 g of photoinitiator 819 to the poly-L-lactic acid solution and stir to disperse it evenly.

[0077] Add the above poly-L-lactic acid solution to the polyvinyl alcohol solution containing modified nano-SiO2, and homogenize and stir at a speed of 1500 rpm for 10 min to obtain a microsphere emulsion; under a nitrogen atmosphere and at a water bath temperature of 50 °C, stir the microsphere emulsion at 200 rpm for 6 h; then cool the emulsion to 20 °C and irradiate the microsphere emulsion with ultraviolet light with a wavelength of 405 nm for 10 min for photoinitiated polymerization and curing.

[0078] Remove the light, filter the microsphere emulsion, collect the microspheres, and wash them thoroughly with water and ethanol respectively; vacuum-dry the washed microspheres at 40 °C for 8 h to obtain the microsphere material S1 for the plugging agent used in drilling fluid.

[0079] Preparation of Drilling Fluid Plugging Material in Example 2

[0080] Prepare 80 mL of a mixed solution of ethanol and water, where the mass fraction of ethanol is 80%. Adjust the pH value of the solvent to 5 with acetic acid; add vinyltrimethoxysilane to the solution with a mass fraction of 4%, and stir at a speed of 200 rpm at room temperature for 1.5 h to completely hydrolyze vinyltrimethoxysilane in the solution; add 10 g of nano-SiO2 particles (particle size of 10 nm) to the silane mixture, disperse them by ultrasonic treatment, and react at 50 °C for 13 h; centrifuge the mixture, collect the modified SiO2 particles, wash them 3 times with water and ethanol respectively, and vacuum-dry them at 40 °C for 6 h to obtain modified nano-SiO2 particles.

[0081] Dissolve 5 g of carboxymethyl cellulose in 400 mL of deionized water to prepare an aqueous carboxymethyl cellulose solution, and adjust the pH to 5 with 0.1 mol / L dilute hydrochloric acid and 0.1 mol / L sodium hydroxide solution; add 4.5 g of modified nano-SiO2 particles to the aqueous carboxymethyl cellulose solution, and disperse them evenly by ultrasonic treatment for 10 min with an ultrasonic frequency of 30 KHz.

[0082] Under the condition of 20 °C, add 6 g of poly(lactic-co-glycolic acid) copolymer to 100 mL of chloroform, and fully dissolve it to obtain a chloroform solution of poly(lactic-co-glycolic acid) copolymer; under a nitrogen atmosphere, add 0.42 g of photoinitiator 1173 to the solution, and stir to disperse it evenly.

[0083] Add the above chloroform solution of poly(lactic-co-glycolic acid) copolymer to the carboxymethyl cellulose solution containing modified nano-SiO2, and homogenize and stir at a speed of 1000 rpm for 10 min to obtain a microsphere emulsion; under a nitrogen atmosphere and a water bath heating condition of 60 °C, stir the microsphere emulsion at 200 rpm for 3 h; then cool the emulsion to 20 °C, and irradiate the microsphere emulsion with ultraviolet light with a wavelength of 360 nm for 15 min for photoinitiated polymerization and curing.

[0084] Remove the light, filter the microsphere emulsion, collect the microspheres, and wash them thoroughly with water and ethanol respectively; vacuum-dry the washed microspheres at 40 °C for 10 h to obtain the microsphere material S2 for the plugging agent used in drilling fluid.

[0085] Preparation of Drilling Fluid Plugging Material in Example 3

[0086] Prepare 100 mL of a mixed solution of methanol and water, where the mass fraction of methanol is 70%. Adjust the pH value of the solvent to 5 with acetic acid; add γ-(methacryloyloxy)propyltrimethoxysilane with a mass fraction of 2.5% to the solution, and stir at 200 rpm for 1.5 h at room temperature to completely hydrolyze γ-(methacryloyloxy)propyltrimethoxysilane; add 11 g of nano-SiO2 particles (particle size of 10 nm) to the silane mixture, disperse by ultrasonic treatment, and react at 55 °C for 18 h; centrifuge the mixture, collect the modified SiO2 particles, wash them 3 times with water and ethanol respectively, and dry them in vacuum at 40 °C for 8 h to obtain modified nano-SiO2 particles.

[0087] Dissolve 5 g of gelatin in 500 mL of deionized water to prepare a gelatin aqueous solution, and adjust the pH to 6 with 0.1 mol / L phosphoric acid and 0.1 mol / L sodium hydroxide solution; add 5 g of modified nano-SiO2 particles to the polyvinyl alcohol aqueous solution, and disperse them evenly by ultrasonic treatment for 10 min with an ultrasonic frequency of 30 KHz.

[0088] Under the condition of 20 °C, add 5 g of polycaprolactone to 100 mL of chloroform, and fully dissolve to obtain a chloroform solution of polycaprolactone; under a nitrogen atmosphere, add 0.48 g of photoinitiator 819 to the polycaprolactone solution, and stir to disperse it evenly.

[0089] Add the above polycaprolactone solution to the gelatin solution containing modified nano-SiO2, and homogenize and stir at 2000 rpm for 10 min to obtain a microsphere emulsion; under a nitrogen atmosphere and a water bath heating condition of 60 °C, stir the microsphere emulsion at 300 rpm for 3 h; then cool the emulsion to 20 °C, and irradiate the microsphere emulsion with ultraviolet light with a wavelength of 405 nm for 12 min for photoinitiated polymerization and curing.

[0090] Remove the light irradiation, filter the microsphere emulsion, collect the microspheres, and wash them thoroughly with water and ethanol respectively; dry the washed microspheres in vacuum at 40 °C for 8 h to obtain the microsphere material S3 for the plugging agent used in drilling fluid.

[0091] Preparation of the plugging material for the drilling fluid in Example 4

[0092] Prepare 100 mL of a mixed solution of ethanol and water, with the mass fraction of ethanol being 90%. Adjust the pH value of the solvent to 5 with acetic acid; add γ-(methacryloyloxy)propyltrimethoxysilane to the solution, with a mass fraction of 3%, and stir at 200 rpm for 1 h at room temperature to completely hydrolyze γ-(methacryloyloxy)propyltrimethoxysilane; add 15 g of nano-SiO2 particles (particle size of 10 nm) to the silane mixture, disperse by ultrasonic treatment, and react at 50 °C for 18 h; perform centrifugation on the mixture, collect the modified SiO2 particles, wash them 3 times with water and ethanol respectively, and dry them in vacuum at 40 °C for 6 h to obtain modified nano-SiO2 particles.

[0093] Dissolve 6 g of polyvinyl alcohol in 300 mL of deionized water to prepare an aqueous polyvinyl alcohol solution, and adjust the pH to 6 with 0.1 mol / L dilute hydrochloric acid and 0.1 mol / L sodium hydroxide solution; add 3 g of modified nano-SiO2 particles to the aqueous polyvinyl alcohol solution and disperse them evenly by ultrasonic treatment for 10 min, with an ultrasonic frequency of 30 KHz.

[0094] Under the condition of 20 °C, add 5 g of poly-L-lactic acid to 100 mL of dichloromethane and fully dissolve it to obtain a dichloromethane solution of poly-L-lactic acid; under a nitrogen atmosphere, add 0.3 g of photoinitiator 819 to the poly-L-lactic acid solution and stir to disperse it evenly.

[0095] Add the above poly-L-lactic acid solution to the polyvinyl alcohol solution containing modified nano-SiO2, and homogenize and stir at 500 rpm for 10 min to obtain a microsphere emulsion; under a nitrogen atmosphere and at 50 °C water bath heating condition, stir the microsphere emulsion at 300 rpm for 6 h; then cool the emulsion to 20 °C and irradiate the microsphere emulsion with ultraviolet light with a wavelength of 405 nm for 10 min for photoinitiated polymerization and curing.

[0096] Remove the light irradiation, filter the microsphere emulsion, collect the microspheres, and wash them thoroughly with water and ethanol respectively; dry the washed microspheres in vacuum at 40 °C for 8 h to obtain the microsphere material S4 for the plugging agent used in drilling fluid.

[0097] Preparation of the plugging material for the drilling fluid in Example 5

[0098] Prepare 100 mL of a mixed solution of ethanol and water, where the mass fraction of ethanol is 90%. Adjust the pH value of the solvent to 5 with acetic acid; add γ-(methacryloyloxy)propyltrimethoxysilane with a mass fraction of 3% to the solution, and stir at 200 rpm for 1 h at room temperature to completely hydrolyze γ-(methacryloyloxy)propyltrimethoxysilane; add 15 g of nano-SiO2 particles (particle size of 10 nm) to the silane mixture, disperse by ultrasound, and react at 50 °C for 18 h; centrifuge the mixture, collect the modified SiO2 particles, wash them 3 times with water and ethanol respectively, and dry them in vacuum at 40 °C for 6 h to obtain modified nano-SiO2 particles.

[0099] Dissolve 6 g of polyvinyl alcohol in 300 mL of deionized water to prepare an aqueous solution of polyvinyl alcohol, and adjust the pH to 6 with 0.1 mol / L dilute hydrochloric acid and 0.1 mol / L sodium hydroxide solution; add 3 g of modified nano-SiO2 particles to the aqueous solution of polyvinyl alcohol, and disperse them evenly by ultrasound for 10 min with an ultrasound frequency of 30 KHz.

[0100] Under the condition of 20 °C, add 5 g of poly-L-lactic acid to 100 mL of dichloromethane, and fully dissolve to obtain a dichloromethane solution of poly-L-lactic acid; under a nitrogen atmosphere, add 0.3 g of photoinitiator 819 to the poly-L-lactic acid solution, and stir to disperse it evenly.

[0101] Add the above poly-L-lactic acid solution to the polyvinyl alcohol solution containing modified nano-SiO2, and homogenize and stir at 1000 rpm for 10 min to obtain a microsphere emulsion; under a nitrogen atmosphere and at a water bath temperature of 50 °C, stir the microsphere emulsion at 200 rpm for 6 h; then cool the emulsion to 20 °C, and irradiate the microsphere emulsion with ultraviolet light with a wavelength of 405 nm for 10 min for photoinitiated polymerization and curing.

[0102] Remove the light irradiation, filter the microsphere emulsion, collect the microspheres, and wash them thoroughly with water and ethanol respectively; dry the washed microspheres in vacuum at 40 °C for 8 h to obtain the microsphere material S5 for the plugging agent used in drilling fluid.

[0103] Preparation of the plugging agent for drilling fluid in Example 6

[0104] Prepare the plugging agent according to the following mass percentages: 15% S1 (the microsphere material prepared in Example 1), 35% S4 (the microsphere material prepared in Example 4), and 50% S5 (the microsphere material prepared in Example 5). Mix the microsphere powders evenly to obtain the plugging agent D0.

[0105] Comparative Example 1 (pure polylactic acid microspheres, without nano-SiO2)

[0106] Dissolve 6 g of polyvinyl alcohol in 300 mL of deionized water to prepare an aqueous polyvinyl alcohol solution. At 20 °C, add 5 g of poly-L-lactic acid to 100 mL of dichloromethane and dissolve it thoroughly to obtain a dichloromethane solution of poly-L-lactic acid. Add the poly-L-lactic acid solution to the polyvinyl alcohol solution and homogenize and stir for 10 min to obtain a microsphere emulsion; under a nitrogen atmosphere and with water bath heating at 50 °C, stir the microsphere emulsion at 200 - 300 rpm for 6 h. Filter the microsphere emulsion, collect the microspheres, and wash them thoroughly with water and ethanol respectively; vacuum dry the washed microspheres at 40 °C for 8 h to obtain the polylactic acid microsphere material.

[0107] By changing the homogenization stirring rate (500 rpm, 1000 rpm, 1500 rpm), three kinds of poly-L-lactic acid microsphere materials with different particle sizes are obtained, named P1, P2, and P3.

[0108] Mix the three kinds of microsphere materials with different particle sizes obtained by mixing according to the mass percentages of 35% P1, 50% P2, and 15% P3 to obtain a microsphere mixture as plugging agent D1.

[0109] Comparative Example 2

[0110] Fully mix the microsphere mixture obtained in Comparative Example 1 with 3 g of nano-SiO2 in a dry state to prepare plugging agent D2.

[0111] Comparative Example 3

[0112] Use the method in Example 1 of Chinese Patent Publication No. CN 113528102A to prepare plugging agent D3. The specific steps are as follows:

[0113] (1) Weigh 1 g of polyvinyl alcohol and 0.2 g of Tween 80, put them into 200 mL of distilled water, and stir appropriately with a constant temperature magnetic stirrer, heat up to dissolve them thoroughly, filter the prepared solution and pour it into a 500 mL three-necked flask. Weigh 0.5 g of polylactic acid (PLA), add it to 100 mL of dichloromethane, stir it with a glass rod to completely dissolve it, and then disperse it thoroughly with an ultrasonic cleaner. Install the 500 mL three-necked flask containing the aqueous phase on a powerful electric stirrer, start the stirrer, and stir at a constant speed. Use a syringe to drip the oil phase into the three-necked flask at a fixed dropping rate, and control the dropping time within 10 min. Continuously stir for 3 hours, and then heat the water bath to volatilize dichloromethane. After the emulsion foam disappears, perform centrifugal separation, pour off the supernatant, and repeatedly wash the centrifuged product with distilled water. Vacuum dry the thoroughly washed product in a vacuum drying oven to obtain powdery milky white microspheres.

[0114] (2) Weigh 2.5 g of polylactic acid (PLA), add it to 100 mL of dichloromethane, stir it with a glass rod until it is completely dissolved, and then disperse it fully with an ultrasonic cleaner. The prepared spinning solution is received at a voltage of 18 kV and a distance of 4 cm between the receiving plate and the needle. The temperature of the spinning solution is controlled at 20 - 25 °C, and nanofibrous plugging agents are prepared through an electrospinning device. After the spinning is completely cooled and formed, the spun fibers are cut into 0.5 mm fibrous plugging agents.

[0115] (3) Preparation of polylactic acid sheet plugging agent: Weigh 10 g of polylactic acid (PLA), add it to 100 mL of polylactic acid solvent, and mix it at a low speed with a powerful stirrer to prepare a polylactic acid paste. Place the polylactic acid paste on a sheet machine with films laid on both sides, and compact it with the pressing roller of the sheet machine to form a sheet. The sheet is wound up and placed in a constant-temperature drying oven to thicken, obtaining a polylactic acid sheet molding compound that can be cut. Cut the sheet molding compound into polylactic acid sheet plugging agents with a length and width of 2 mm.

[0116] (4) The components in the polylactic acid plugging agent are in the following mass percentages: 5% of polylactic acid microsphere plugging agent, 45% of polylactic acid granular plugging agent, 45% of polylactic acid fibrous plugging agent, and 5% of polylactic acid sheet plugging agent.

[0117] Comparative Example 4

[0118] Take 8 g of nano-SiO2 powder as plugging agent D4.

[0119] Test Example 1

[0120] The nano-SiO2 was modified with the silane coupling agent γ-(methacryloyloxy)propyltrimethoxysilane (KH570) described in Example 1. The infrared spectra of the nanoparticles before and after modification are as Figure 1 shown. After modification with the silane coupling agent, the -OH characteristic peak at 3200 - 3400 cm -1 disappeared in the infrared spectrum of the modified SiO2, while a new C=O characteristic peak appeared at around 1700 cm -1 , proving that the modification was successful and modified SiO2 nanoparticles were obtained.

[0121] Test Example 2

[0122] Energy spectrum analysis was performed on the internal core and surface shell layer of the obtained core-shell structure microspheres. The test results showed that the inner cores of the microspheres were all composed of C and O elements, without Si element; the Si element was mainly concentrated in the outer shell layer of the microspheres, indicating that the microspheres had a core-shell structure, with the inside mainly being a degradable polymer and the outside being firmly bonded modified nano-SiO2 particles.

[0123] Test Example 3

[0124] The thermogravimetric analyzer was used to test the thermogravimetric curves of the microsphere materials in Examples 1 to 3 and Comparative Example 1, as Figure 5 shown. The initial thermal decomposition temperature of the pure polyester microspheres in Comparative Example 1 was 170 °C (the composition of the material obtained in Comparative Example 3 was the same as that in Comparative Example 1, and the thermal decomposition performance was consistent with that in Comparative Example 1). The initial thermal decomposition temperatures of Examples 1-3 were significantly increased, exceeding 260 °C, indicating that the core-shell structured composite microspheres obtained in the present invention have more excellent heat resistance than the degradable polyesters described in Comparative Example 1 and Comparative Example 3.

[0125] Test Example 4

[0126] The particle sizes of the microsphere materials in Examples 1 to 5 and Comparative Example 1 are shown in Table 1. The shell-structured microspheres obtained in the present invention can achieve adjustable particle sizes in a relatively large range.

[0127] Table 1 Particle Sizes of Different Microsphere Materials

[0128] Microsphere material Particle size / μm Shell thickness / nm S1 8.1±1.1 19.5±5.3 S2 82.5±10.3 14.1±6.0 S3 0.6±0.1 33.2±7.5 S4 376.8±32.9 12.1±1.7 S5 74.4±7.1 15.0±2.5 P1 299.2±27.0 - P2 57.5±6.2 - P3 4.7±0.8 -

[0129] Test Example 5 Evaluation of the Filtration Loss Performance of the Plugging Agent

[0130] The filtration loss performance of the plugging agents in Example 6 and Comparative Examples 1 to 4 was evaluated, and the test results are shown in Table 2. As can be seen from Table 2, compared with the base mud, the AV and PV of the drilling fluid with 1% plugging agent added changed very little, indicating that the plugging agent had basically no effect on the rheology of the drilling fluid under high-temperature conditions. Compared with other plugging agent materials, after high-temperature aging at 150 °C, the D0 plugging agent reduced the API filtration loss of the base mud by the largest margin, from 25 mL to 11.6 mL, and had the most excellent plugging effect.

[0131] Table 2 Evaluation of the Filtration Loss Performance of Different Plugging Agents

[0132] Material Condition AV / mPa·s PV / mPa·s <![CDATA[FL API / mL <!-- 9 -->]]> Base mud 150℃+16h 7 5.5 25 Base mud + 1% D0 150℃+16h 7.5 4.5 11.6 Base mud + 1% D1 150℃+16h 7 4 19.8 Base mud + 1% D2 150℃+16h 8.5 4.5 13.5 Base mud + 1% D3 150℃+16h 7.5 4 15.8 Base mud + 1% D4 150℃+16h 8 5 16.4

[0133] Test Example 6 Evaluation of the Plugging Ability of the Plugging Agent

[0134] The plugging ability of the plugging agents in Example 6 and Comparative Examples 1 to 4 was evaluated, and the test results are shown in Table 3.

[0135] Table 3 Evaluation of the Plugging Performance of Different Plugging Agents

[0136] Sample <![CDATA[Permeability / 10 -2 mD]]> Blocking rate / % Blank 792 0 D0 57 92.80 D1 542 31.56 D2 251.4 68.26 D3 258.5 67.36 D4 199 74.87

[0137] As can be seen from Table 3, the plugging agent D0 obtained in the present invention has good plugging ability for the micron-pore formation, and the plugging rate can reach 92.8%, which is much higher than that of the pure polyester materials D1 or D3, the mixture of nano-SiO2 particles and polyester materials D2, and the nano-SiO2 particles D4.

Claims

1. A plugging material for high-temperature and corrosion-resistant drilling fluids, comprising microsphere materials with a core-shell structure. The core layer of the microsphere materials is a degradable polyester material, and the shell layer of the microsphere materials is modified SiO2 particles.

2. The plugging material for high-temperature and corrosion-resistant drilling fluids according to claim 1, wherein the mass ratio of the degradable polyester material to the modified SiO2 particles is 1:(0.01 - 1), preferably 1:(0.5 - 1); and / or, the thickness of the shell layer is 5 - 1000 nm, preferably 10 - 300 nm; and / or, the particle size of the microsphere materials is 0.1 - 5000 μm, preferably 0.5 - 600 μm.

3. The plugging material for high-temperature and corrosion-resistant drilling fluids according to claim 1, wherein the degradable polyester material is selected from at least one of polylactic acid, polyglycolic acid, poly(lactic acid - glycolic acid) copolymer, polycaprolactone, poly(p-dioxanone), poly(amino acid-derived carbonate), polyorthoester, polyhydroxyalkanoate, polytrimethylene carbonate, oxalate and polymers, poly(dioxolene ester); and / or, the modified SiO2 particles are SiO2 particles modified with a silane coupling agent. The silane coupling agent is preferably selected from at least one of vinyltrichlorosilane, vinyltriethoxysilane, vinyltrimethoxysilane, vinyltris(β-methoxyethoxy)silane, γ-(methacryloyloxy)propyltrimethoxysilane, more preferably from at least one of γ-(methacryloyloxy)propyltrimethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane; and / or, the particle size of the modified SiO2 particles is 5 - 100 nm, preferably 10 - 30 nm.

4. A preparation method of the plugging material for the temperature- and corrosion-resistant drilling fluid according to any one of claims 1 to 3, comprising: The dispersion liquid containing the modified SiO2 particles and the degradable polyester material is stirred to obtain a microsphere emulsion, and then through photocuring reaction and post-treatment, the plugging material for high-temperature and corrosion-resistant drilling fluids is obtained.

5. The preparation method according to claim 4, characterized in that, The preparation method specifically includes the following steps: (1) Dissolve the stabilizer in water, adjust the pH of the stabilizer aqueous solution to 5 - 8, and add the modified nano-SiO2 particles to the stabilizer aqueous solution and disperse evenly; (2) Add the degradable polyester material to the organic solvent S1 to obtain a degradable polyester solution, and then add an initiator; (3) Add the solution in step (2) to the solution in step (1), stir and irradiate for photocuring reaction; (4) After filtering, washing and drying the product after the photocuring reaction, the plugging material for high-temperature and corrosion-resistant drilling fluids is obtained.

6. The preparation method according to claim 5, characterized in that, In step (1): the stabilizer is selected from at least one of polyvinyl alcohol, polyethylene glycol, gelatin, agar, water-soluble cellulose, preferably from at least one of polyvinyl alcohol, gelatin, carboxymethyl cellulose, agar; and / or, the mass fraction of the stabilizer in the stabilizer aqueous solution is 1 - 10%, preferably 1 - 3%; and / or, the pH of the stabilizer aqueous solution is adjusted by an alkali solution and / or an acid solution. Preferably, the alkali in the alkali solution is selected from at least one of sodium hydroxide and ammonia water; and / or, the acid in the acid solution is selected from at least one of hydrochloric acid, sulfuric acid and phosphoric acid.

7. The preparation method according to claim 5, characterized in that, In the step (2): The organic solvent S1 is selected from at least one of dichloromethane, chloroform, ethyl acetate, dioxane, dimethyl sulfoxide, acetone, tetrahydrofuran, and isopropanol, preferably at least one of dichloromethane, chloroform, and ethyl acetate; and / or, The mass ratio of the biodegradable polyester material to the organic solvent S1 is 1:(10 - 100), preferably 1:(10 - 30); and / or, The mass ratio of the biodegradable polyester material to the modified SiO2 particles is 1:(0.01 - 1), preferably 1:(0.5 - 1); and / or, The volume ratio of the biodegradable polyester solution to the stabilizer aqueous solution containing nano-SiO2 is 1:(1 - 10), preferably 1:(3 - 5); and / or, The addition of the initiator is carried out under a protective atmosphere.

8. The preparation method according to claim 5, wherein The stirring in the step (3) specifically includes: first, high-speed homogenization stirring to obtain a microsphere emulsion, then stirring at a low speed under a protective gas atmosphere and heating, and then cooling the microsphere emulsion, and irradiating the microsphere emulsion with light to initiate a photocuring reaction; preferably, The conditions for the high-speed stirring are: a rotation speed of 500 - 10000 rpm and a stirring time of 5 - 15 min; and / or, The conditions for the heating and low-speed stirring are: a temperature of 40 - 60 °C, a rotation speed of 100 - 350 rpm, and a stirring time of 2 - 8 h; and / or, The temperature for the cooling is 20 - 40 °C; and / or, The conditions for the photocuring reaction are: a light irradiation wavelength of 200 - 500 nm and a light irradiation time of 5 - 30 min.

9. The preparation method according to claim 5, characterized in that, The modified SiO2 particles are prepared by the following steps: (a) Adjust the pH of the solvent S2 to 4 - 6 using an acidic regulator; (b) Add a silane coupling agent to the solvent S2 and continuously stir and mix; (c) Add nano-SiO2 to the mixture for reaction; (d) After centrifuging, washing, and drying the reaction product, the modified nano-SiO2 particles are obtained.

10. The preparation method according to claim 9, wherein In the step (a), the acidic regulator is selected from organic acidic compounds or inorganic acidic compounds, preferably at least one of acetic acid, phosphoric acid, and hydrochloric acid; and / or, the solvent S2 is selected from at least one of water, ethanol, methanol, and isopropanol, preferably at least one of water and ethanol; and / or, In the step (b), the mass ratio of the silane coupling agent to the solvent S2 is 1:(10 - 1000), preferably 1:(10 - 100); and / or, the continuous stirring time is 1 - 3 h; and / or, The mass ratio of the silane coupling agent to nano-SiO2 is 1:(1 - 100), preferably 1:(2 - 10); and / or, In the step (c), the particle size of the nano-SiO2 is 5 - 100 nm, preferably 10 - 30 nm; and / or, the reaction conditions are: a reaction temperature of 40 - 70 °C and a reaction time of 2 - 24 h; and / or, The drying conditions in step (d) are a temperature of 30 to 60°C and a time of 3 to 12 h. Preferably, the drying conditions are a temperature of 40 to 50°C and a time of 4 to 8 h.

11. A drilling fluid plugging agent comprising plugging materials with three or more different particle sizes. The plugging materials are the plugging materials for high-temperature and corrosion-resistant drilling fluids described in any one of claims 1 to 3 or the plugging materials for high-temperature and corrosion-resistant drilling fluids obtained by the preparation method described in claims 4 to 10. Preferably, in the drilling fluid plugging agent, the content of the plugging material with a particle size less than 10 μm is 10 to 20 wt%, the content of the plugging material with a particle size ranging from 10 to 200 μm is 45 to 75 wt%, and the content of the plugging material with a particle size greater than 200 μm is 15 to 35 wt%.

12. Use of the plugging material for high-temperature and corrosion-resistant drilling fluids described in any one of claims 1 to 3 or the drilling fluid plugging agent described in claim 11 in the field of oil drilling.

Images