Medium-temperature drilling fluid nanometer temporary plugging agent and preparation method thereof

Abstract

The invention belongs to the technical field of temporary plugging agents, and relates to a medium-temperature drilling fluid nano temporary plugging agent and a preparation method thereof. The temporary plugging agent is prepared from the following raw materials in parts by mass: 10 to 15 parts of small-particle-size coated silicon dioxide, 15 to 20 parts of medium-particle-size coated silicon dioxide, 30 to 50 parts of large-particle-size coated silicon dioxide, 15 to 20 parts of fiber, 5 to 8 parts of polyether diglycidyl ether, 5 to 8 parts of hyperbranched polyethyleneimine, 1 to 1.5 parts of water-soluble cellulose and 0.5 to 1 part of cationic quaternary ammonium salt. The coated silicon dioxide takes chitosan and glutaraldehyde as wall raw materials and silicon dioxide as a core material, and the particle size of the small-particle-size core material is 0.3-1 mu m; the particle size of the medium-particle-size particle core material is 150-250 microns; the particle size of the large-particle-size particle core material is 250-350 microns, the coated silicon dioxide particles are bonded together through a microscopic interpenetrating network formed by the reaction of hyperbranched polyethyleneimine and polyether diglycidyl ether, and the particles are matched with fibers to improve the bearing strength.

Description

Technical Field

[0001] The invention belongs to the technical field of temporary plugging agents, and particularly relates to a nano temporary plugging agent for medium-temperature drilling fluid and a preparation method thereof. Background Art

[0002] During oil development processes such as well killing, well cleaning, acidizing, drilling, and workover, factors such as strong formation heterogeneity, poor fluid compatibility, and engineering measures often lead to decreased oil permeability and productivity in the near-wellbore zone. This phenomenon is particularly prominent in shale formations. Due to their complex nanoscale pore-throat structure and low permeability, the intrusion of working fluids during shale oil development can easily lead to severe water locks and clay mineral hydration damage. Before operations begin, injecting temporary plugging agents into the reservoir effectively seals high-permeability zones or fractures, significantly reducing permeability in those areas and preventing further damage to the reservoir (particularly shale oil reservoirs) from working fluids and subsequent fluids. Subsequent unblocking through perforation, chemical dissolution, or flowback can restore formation permeability, thereby reducing losses and ultimately protecting the reservoir and maintaining productivity.

[0003] Temporary plugging agents come in a variety of types, including bridging agents (granular, fibrous, and flake), oil-soluble, water-soluble, acid-soluble, and water-swellable. Common bridging agents are made from materials such as calcium carbonate, quartz sand, nutshells, resin, and rubber, achieving efficient plugging by matching their particle size with pore throats. For example, patent CN101311243B discloses a temporary plugging agent for oil and gas reservoir fractures, comprising a combination of 600-1100 mesh and 60-600 mesh ultrafine calcium carbonate, plant fibers, and oxidized asphalt. CN116262875B describes a highly effective drilling fluid plugging agent containing calcium carbonate, activated fibers, vermiculite, and mica. These materials can effectively plug microfractures and larger pore throats in shale formations and are particularly suitable for shale oil reservoirs with varying permeability.

[0004] Although bridging temporary plugging agents perform well in plugging high-permeability layers, their plugging mechanism mainly relies on the physical bridging effect of particles at the throat. It is generally believed that the plugging effect is optimal when the particle diameter is approximately 1 / 3 of the throat radius. However, the bonding force between particles of this type of material is weak, mainly mechanical intercalation and physical adsorption, resulting in limited pressure bearing capacity and difficulty in adapting to complex and changing operating environments and formation conditions. For example, in the contact zone between abnormally high-pressure shale layers and low-pressure reservoirs, in the interaction area between high-permeability layers and low-permeability layers, or in situations where high-pressure fluid flushing causes the formation pressure balance to lose control, conventional temporary plugging agents are prone to failure, affecting the transformation effect of shale oil reservoirs.

[0005] Patent CN101638576B discloses a shielding temporary plugging gelling agent for drilling fluid, as well as its production and use methods. The shielding temporary plugging gelling agent for drilling fluid is composed of a strong plugging powder, a fluid loss control agent or flow modifier, a plant gelling agent, a calcifying agent, and expandable plant staple fibers. Although the gel-forming properties of the plant gelling agent and the calcifying agent improve the strength of the temporary plugging material, ionically crosslinked gels typically begin to dissociate at 60-80°C, causing the gel to swell or soften. Continued temperature increases exacerbate molecular thermal motion until the gel network gradually disintegrates, reducing the temporary plugging performance of the temporary plugging material and making it difficult to meet the temporary plugging requirements in the temperature environments of deep shale oil reservoirs.

[0006] Therefore, given the characteristics of shale formations such as high temperature, complex pore throats, and possible pressure mutations, there is an urgent need to develop a temporary plugging agent with excellent temperature resistance and high-pressure bearing capacity to ensure reservoir protection and operational safety during the efficient development of shale oil. Summary of the Invention

[0007] To solve the above technical problems, the present invention provides a nano-temporary plugging agent for medium-temperature drilling fluid and a preparation method thereof. Silicon dioxide is coated with chitosan and glutaraldehyde to obtain coated silica with a surface rich in amino and hydroxyl groups. The amino and hydroxyl groups can further react with epoxy groups on polyether diglycidyl ether. Hyperbranched polyethyleneimine reacts with the polyether diglycidyl ether to form an interpenetrating network with a certain microscopic strength. This network tightly bonds coated silica particles of different particle sizes together, thereby improving the compressive strength and plugging rate.

[0008] A nanometer temporary plugging agent for medium-temperature drilling fluid comprises the following raw materials in parts by weight: 10-15 parts of small-particle coated silica, 15-20 parts of medium-particle coated silica, 30-50 parts of large-particle coated silica, 15-20 parts of fiber, 5-8 parts of polyether diglycidyl ether, 5-8 parts of hyperbranched polyethyleneimine, 1-1.5 parts of water-soluble cellulose, and 0.5-1 part of a cationic quaternary ammonium salt. The coated silicas all use a cross-linked condensate of chitosan and glutaraldehyde as a wall material and silica as a core material. The small-particle coated silica has a silica particle size of 0.3-1 μm; the medium-particle coated silica has a silica particle size of 150-250 μm; and the large-particle coated silica has a silica particle size of 250-350 μm.

[0009] The mass ratio of chitosan, glutaraldehyde and silica as raw materials for the small-particle coated silica is 40-55:0.4-0.6:100; the mass ratio of chitosan, glutaraldehyde and silica as raw materials for the medium-particle coated silica is 25-35:0.2-0.4:100; and the mass ratio of chitosan, glutaraldehyde and silica as raw materials for the large-particle coated silica is 15-25:0.1-0.2:100.

[0010] The chitosan has a deacetylation degree of ≥90% and a weight-average molecular weight of 50,000-100,000. The use of chitosan and glutaraldehyde to coat silica facilitates the aggregation of polyether diglycidyl ether and hyperbranched polyethyleneimine on the surface of the coated silica particles for cross-linking reaction, bonding adjacent coated silica particles rather than forming self-crosslinked bodies in the aqueous phase away from the coated silica particles.

[0011] The polyether diglycidyl ether has a number average molecular weight of 500-1000 and is selected from one or a combination of polyethylene glycol glycidyl ether and poly(propylene glycol) diglycidyl ether.

[0012] The epoxy group is located at the chain end of the polyether diglycidyl ether. At low temperatures, the molecular mobility of the polyether diglycidyl ether is weak, and the flexible polyether chain is prone to chain entanglement or folding, which buries the epoxy group inside the molecule and hinders its contact with the amino or hydroxyl groups on the hyperbranched polyethyleneimine and coated silica. Therefore, at low temperatures, the reaction probability of polyether diglycidyl ether with hyperbranched polyethyleneimine and coated silica is extremely low. For this reason, in the application of drilling fluid temporary plugging agents, if the temperature is insufficient, the cross-linking reaction of polyether diglycidyl ether with hyperbranched polyethyleneimine and coated silica will be difficult to proceed effectively, resulting in low compressive strength of the temporary plugging agent.

[0013] As the temperature rises, the molecular mobility of polyether diglycidyl ether increases, and molecular motion intensifies. Embedded epoxy groups are more easily exposed and come into contact with amine and hydroxyl groups, increasing the probability of reaction while also providing sufficient collision energy to overcome the energy barrier and allow the epoxy groups to open and react with the amine and hydroxyl groups. By selecting polyether diglycidyl ether with an appropriate molecular weight, this temperature-dependent reaction characteristic can be precisely controlled: a drilling fluid system containing a temporary plugging agent can be smoothly injected into the reservoir at low temperatures or rapidly injected into the reservoir at high temperatures. At high temperatures, cross-linking occurs, achieving controllable temporary plugging and optimizing pressure-bearing strength.

[0014] The hyperbranched polyethyleneimine has a number average molecular weight of 10,000-30,000, an amine value of 18 mmol / g, a primary amine molar ratio of 34-35%, a secondary amine molar ratio of 35%, and a tertiary amine molar ratio of 30-31%.

[0015] The coated silica, hyperbranched polyethyleneimine and polyether diglycidyl ether work together to form a cross-linked network with a certain strength at the microscopic level and tightly bond the coated silica together, which has the effect of improving the pressure bearing strength and the plugging rate.

[0016] The water-soluble cellulose is selected from one or a combination of hydroxyethyl cellulose and hydroxymethyl cellulose. The water-soluble cellulose has a viscosity-increasing effect and improves the dispersibility of the coated silica and the fiber.

[0017] The coated silicon dioxide is prepared by a method comprising the following steps: Chitosan solution is prepared by chitosan and acetic acid solution, and silicon dioxide suspension is prepared. The silicon dioxide suspension is added to the chitosan solution and mixed evenly. Glutaraldehyde is added to react, and the coated silicon dioxide is obtained by centrifugation and freeze drying.

[0018] The acetic acid solution has a concentration of 1-2 wt %. The chitosan solution has a chitosan concentration of 2-4 wt %. The silica suspension has a silica content of 1-3 wt %. The reaction is stirred at 60-70° C. for 3-5 hours. The centrifuge speed is 3600 rpm, and the centrifugation time is 10 min ± 0.5 min. The freeze-drying step involves pre-freezing at -25° C. to -20° C. for 2-4 hours, followed by cooling to -60° C. to -40° C. and freeze-drying at an air pressure of 10-20 Pa for 24-72 hours.

[0019] The fiber is an acid-soluble or degradable fiber with a length of 0.5-1.9 cm and a diameter of 10-20 μm, and is selected from one or a combination of two or more of polyvinyl alcohol fiber, polylactic acid fiber, and modified polyester fiber.

[0020] Three different particle sizes of coated silica and fibers work together to achieve a superior temporary plugging effect through a hierarchical bridging-filling-reinforcement mechanism: the large-particle coated silica acts as a large particle, entering large pore throats or fractures to form initial bridges. The medium-particle coated silica fills the gaps between large particles, reducing pore size. The small-particle coated silica further seals the remaining micropores. The fibers, with their high aspect ratio, interweave and overlap between the particles, forming a macroscopic, three-dimensional network framework. This composite plugging structure features "large particles bridging, medium particles filling, small particles sealing, and fiber reinforcement." The microscopic interpenetrating network formed by the reaction of hyperbranched polyethyleneimine and polyether diglycidyl ether effectively bonds and secures the coated silica particles through chemical bonding, effectively reducing relative slip and rolling of the coated silica particles under high pressure. This combination of the macroscopic three-dimensional network framework and the microscopic interpenetrating network enables the plugging layer to withstand pressures far exceeding those of a single component or a loosely packed structure, achieving efficient pore plugging and structural reinforcement.

[0021] The cationic quaternary ammonium salt is selected from one or a combination of two or more of dodecyltrimethylammonium chloride, hexadecyltrimethylammonium chloride, and octadecyltrimethylammonium chloride.

[0022] The present invention also provides a method for preparing a medium-temperature drilling fluid nano-temporary plugging agent, comprising the following steps: mixing small-particle coated silica, medium-particle coated silica, large-particle coated silica, fiber, polyether diglycidyl ether, hyperbranched polyethyleneimine, water-soluble cellulose, and cationic quaternary ammonium salt to obtain the drilling fluid temporary plugging agent.

[0023] The present invention also provides the use of the above-mentioned medium-temperature drilling fluid nano temporary plugging agent in the oil drilling process. The drilling fluid temporary plugging agent and drilling fluid base slurry are mixed to prepare the drilling fluid, and the drilling fluid is used in the oil drilling process.

[0024] The drilling fluid is used for plugging fractured leakage formations with cracks less than 1 mm or homogeneous leakage formations.

[0025] The mass volume ratio of the drilling fluid temporary plugging agent to the drilling fluid base slurry in the drilling fluid for the fractured leakage formation with cracks less than 1 mm is 5-8:100 g / mL.

[0026] The mass volume ratio of the drilling fluid temporary plugging agent to the drilling fluid base slurry in the drilling fluid for the homogeneous leakage formation is 3-5:100 g / mL.

[0027] The operating temperature of the drilling fluid is 80-120°C.

[0028] The drilling fluid base slurry is not particularly limited and can be any water-based drilling fluid base slurry commonly used in the art, including but not limited to bentonite water-based drilling fluid base slurry.

[0029] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention coats silica with chitosan and glutaraldehyde to obtain particles with active amino and hydroxyl groups on the surface that can react with the epoxy groups on polyether diglycidyl ether. Hyperbranched polyethyleneimine reacts with polyether diglycidyl ether to form a microscopic interpenetrating network with a certain strength. This network tightly bonds the coated silica particles of different particle sizes together, thereby improving the compressive strength and plugging rate.

[0030] 2. The microscopic cross-linked network formed between the coated silica particles, hyperbranched polyethyleneimine and polyether diglycidyl ether of the present invention is different from the gel formed by ionic bonds and has good thermal stability.

[0031] Third, the three coated silica particles of different particle sizes and the fibers of the present invention form a macroscopically physical three-dimensional network skeleton, constituting a composite plugging structure characterized by "large particles bridging, medium particles filling, small particles sealing, and fiber reinforcement." The microscopic interpenetrating network formed by the reaction of hyperbranched polyethyleneimine and polyether diglycidyl ether effectively bonds and secures the coated silica particles through chemical bonding, effectively reducing relative slip and rolling of the coated silica particles under high pressure. The combination of the macroscopic three-dimensional network skeleton and the microscopic interpenetrating network enables the plugging layer to withstand pressures far exceeding those of a single component or loose accumulation, achieving efficient pore plugging and structural reinforcement.

[0032] Fourth, the glycosidic bonds on the chitosan, the wall material of the coated silica of the present invention, are easily hydrolyzed and broken, and the acidification flowback rate of the temporary plugging agent is high.

[0033] 5. The medium-temperature drilling fluid nano-temporary plugging agent prepared by the present invention has excellent temperature resistance and high-pressure bearing capacity. It shows excellent temperature stability and high-pressure bearing capacity in the medium temperature range of 80-120°C, and can effectively seal nano-scale pores and micro-cracks in shale formations. It is one of the key materials for achieving shale reservoir protection and operational safety. DETAILED DESCRIPTION

[0034] The present invention will be further described below in conjunction with specific embodiment, but is not limited to the content on the specification sheets. Unless otherwise specified, "parts" described in the embodiments of the present invention are all parts by weight. All reagents used are commercially available reagents in this area.

[0035] The average particle size of silica is 0.3 μm and is from Aladdin.

[0036] The average particle size of silica is 1 μm and is from Aladdin.

[0037] The silica had an average particle size of 150 μm and was sourced from Aladdin.

[0038] The silica had an average particle size of 250 μm and was sourced from Aladdin.

[0039] The average particle size of silica was 350 μm and was obtained from Aladdin.

[0040] Chitosan, deacetylation degree ≥95%, M W 50,000, item number C766421, from Shanghai McLean Biochemical Technology Co., Ltd.

[0041] Polyvinyl alcohol fiber 1# is 1.9 cm long and 10 μm in diameter and is from Shandong Huayao Rubber & Plastic Co., Ltd.

[0042] Polyvinyl alcohol fiber 2#, 0.5 cm long and 20 μm in diameter, was obtained from Shandong Huayao Rubber & Plastic Co., Ltd.

[0043] Polyethylene glycol diglycidyl ether has a number average molecular weight of 500, product number P134003, and is from Aladdin.

[0044] Polyethylene glycol diglycidyl ether has a number average molecular weight of 1000, product number P475492, and is from Aladdin.

[0045] Hyperbranched polyethyleneimine SP-200 has a number average molecular weight of 10,000, an amine value of 18 mmol / g, a primary amine molar ratio of 35%, a secondary amine molar ratio of 35%, and a tertiary amine molar ratio of 30%, and is sourced from Nippon Shokubai Co., Ltd.

[0046] Hyperbranched polyethyleneimine HM-2000 has a number-average molecular weight of 30,000, an amine value of 18 mmol / g, a primary amine molar ratio of 34%, a secondary amine molar ratio of 35%, and a tertiary amine molar ratio of 31%, and is sourced from Nippon Shokubai Co., Ltd.

[0047] Example 1

[0048] S1-1: Chitosan C766421 and 2 wt% acetic acid solution were mixed uniformly and stirred at 300 r / min until no solids were left to obtain a 4 wt% chitosan solution; S1-2: 100 parts by mass of silica with an average particle size of 1 μm was added to 9900 parts by mass of water, and ultrasonically dispersed at a power of 300 W for 2 hours to obtain a 1 wt% silica suspension. 1375 parts by mass of a 4 wt% chitosan solution (55 parts by mass of chitosan) was added, and the mixture was uniformly mixed. 0.6 parts by mass of glutaraldehyde was added, and the mixture was heated to 70°C and stirred at a speed of 300 r / min for 3 hours. The mixture was centrifuged and pre-frozen at -20°C for 2 hours. The mixture was then cooled to -60°C and freeze-dried at an air pressure of 20 Pa for 24 hours to obtain small-particle-size coated silica. S1-3: 100 parts by mass of silica with an average particle size of 150 μm was added to 9900 parts by mass of water, and ultrasonically dispersed at a power of 300 W for 1.5 hours to obtain a 1 wt% silica suspension. 875 parts by mass of a 4 wt% chitosan solution (35 parts by mass of chitosan) was added and mixed uniformly. 0.4 parts by mass of glutaraldehyde was added, and the temperature was raised to 70°C, and the mixture was stirred at a speed of 300 r / min for 3 hours. The mixture was centrifuged and pre-frozen at -20°C for 2 hours, and then cooled to -60°C and freeze-dried at an air pressure of 20 Pa for 24 hours to obtain medium-sized coated silica. S1-4: 100 parts by mass of silica with an average particle size of 250 μm was added to 9900 parts by mass of water, and ultrasonically dispersed at a power of 300 W for 1.5 hours to obtain a 1 wt% silica suspension. 625 parts by mass of a 4 wt% chitosan solution (25 parts by mass of chitosan) was added and mixed uniformly. 0.2 parts by mass of glutaraldehyde was added, and the temperature was raised to 70°C, and the mixture was stirred at a speed of 300 r / min for 3 hours. The mixture was centrifuged and pre-frozen at -20°C for 2 hours. The mixture was then cooled to -60°C and freeze-dried at an air pressure of 20 Pa for 24 hours to obtain large-particle-size coated silica. S2: 15 parts by mass of small-particle coated silica, 20 parts by mass of medium-particle coated silica, 50 parts by mass of large-particle coated silica, 15 parts by mass of polyvinyl alcohol fiber 1#, 8 parts by mass of polyethylene glycol diglycidyl ether P134003, 8 parts by mass of hyperbranched polyethyleneimine SP-200, 1 part by mass of hydroxyethyl cellulose, and 1 part by mass of hexadecyltrimethylammonium chloride are mixed to obtain a medium-temperature drilling fluid nano temporary plugging agent.

[0049] Example 2

[0050] The rest is the same as Example 1, except that in step S2, the amount of polyethylene glycol diglycidyl ether P134003 used is 5 parts by mass.

[0051] Example 3

[0052] The rest is the same as Example 1, except that in step S2, the amount of hyperbranched polyethyleneimine SP-200 used is 5 parts by mass.

[0053] Example 4

[0054] The rest is the same as Example 1, except that in step S2, polyethylene glycol diglycidyl ether P475492 with a number average molecular weight of 1000 is used instead of polyethylene glycol diglycidyl ether P134003 with a number average molecular weight of 500.

[0055] Example 5

[0056] The rest is the same as Example 1, except that in step S1-2, the amount of chitosan solution used is 1000 parts by mass (40 parts by mass of chitosan); in step S1-3, the amount of chitosan solution used is 625 parts by mass (25 parts by mass of chitosan); and in step S1-4, the amount of chitosan solution used is 375 parts by mass (15 parts by mass of chitosan).

[0057] Example 6

[0058] The rest is the same as Example 1, except that in step S2, hyperbranched polyethyleneimine HM-2000 of equal mass is used instead of hyperbranched polyethyleneimine SP-200.

[0059] Example 7

[0060] S1-1: Chitosan C766421 and 2 wt% acetic acid solution were mixed uniformly and stirred at 300 r / min until no solids were left to obtain a 4 wt% chitosan solution; S1-2: 100 parts by mass of silica with an average particle size of 1 μm was added to 9900 parts by mass of water, and ultrasonically dispersed at a power of 300 W for 2 hours to obtain a 1 wt% silica suspension. 1375 parts by mass of a 4 wt% chitosan solution (55 parts by mass of chitosan) was added and mixed uniformly. 0.4 parts by mass of glutaraldehyde was added, and the temperature was raised to 70°C, and the reaction was stirred at a speed of 300 r / min for 3 hours. The mixture was centrifuged and pre-frozen at -20°C for 2 hours, then cooled to -60°C and freeze-dried at an air pressure of 20 Pa for 24 hours to obtain small-particle-size coated silica. S1-3: 100 parts by mass of silica with an average particle size of 150 μm was added to 9900 parts by mass of water, and ultrasonically dispersed at a power of 300 W for 1.5 hours to obtain a 1 wt% silica suspension. 875 parts by mass of a 4 wt% chitosan solution (35 parts by mass of chitosan) was added and mixed uniformly. 0.2 parts by mass of glutaraldehyde was added, and the temperature was raised to 70°C, and the mixture was stirred at a speed of 300 r / min for 3 hours. The mixture was centrifuged and pre-frozen at -20°C for 2 hours, and then cooled to -60°C and freeze-dried at an air pressure of 20 Pa for 24 hours to obtain medium-sized coated silica. S1-4: 100 parts by mass of silica with an average particle size of 250 μm was added to 9900 parts by mass of water, and ultrasonically dispersed at a power of 300 W for 1.5 hours to obtain a 1 wt% silica suspension. 625 parts by mass of a 4 wt% chitosan solution (25 parts by mass of chitosan) was added and mixed uniformly. 0.1 parts by mass of glutaraldehyde was added, and the temperature was raised to 70°C, and the mixture was stirred at a speed of 300 r / min for 3 hours. The mixture was centrifuged and pre-frozen at -20°C for 2 hours, and then cooled to -60°C and freeze-dried at an air pressure of 20 Pa for 24 hours to obtain large-particle-size coated silica. S2: 10 parts by mass of small-particle coated silica, 15 parts by mass of medium-particle coated silica, 30 parts by mass of large-particle coated silica, 20 parts by mass of polyvinyl alcohol fiber 1#, 8 parts by mass of polyethylene glycol diglycidyl ether P134003, 5 parts by mass of hyperbranched polyethyleneimine SP-200, 1.5 parts by mass of hydroxyethyl cellulose, and 0.5 parts by mass of hexadecyltrimethylammonium chloride are mixed to obtain a medium-temperature drilling fluid nano temporary plugging agent.

[0061] Example 8

[0062] S1-1: Chitosan C766421 and 2 wt% acetic acid solution were mixed uniformly and stirred at 300 r / min until no solids were left to obtain a 4 wt% chitosan solution; S1-2: 100 parts by mass of silica with an average particle size of 0.3 μm was added to 9900 parts by mass of water, and ultrasonically dispersed at a power of 300 W for 2 hours to obtain a 1 wt% silica suspension. 1375 parts by mass of a 4 wt% chitosan solution (55 parts by mass of chitosan) was added, and the mixture was mixed uniformly. 0.6 parts by mass of glutaraldehyde was added, and the mixture was heated to 70°C and stirred at a speed of 300 r / min for 3 hours. The mixture was centrifuged and pre-frozen at -20°C for 2 hours. The mixture was then cooled to -60°C and freeze-dried at an air pressure of 20 Pa for 24 hours to obtain small-particle-size coated silica. S1-3: 100 parts by mass of silica with an average particle size of 250 μm was added to 9900 parts by mass of water, and ultrasonically dispersed at a power of 300 W for 1.5 hours to obtain a 1 wt% silica suspension. 875 parts by mass of a 4 wt% chitosan solution (35 parts by mass of chitosan) was added and mixed uniformly. 0.4 parts by mass of glutaraldehyde was added, and the mixture was heated to 70°C and stirred at a speed of 300 r / min for 3 hours. The mixture was centrifuged and pre-frozen at -20°C for 2 hours. The mixture was then cooled to -60°C and freeze-dried at an air pressure of 20 Pa for 24 hours to obtain medium-sized coated silica. S1-4: 100 parts by mass of silica with an average particle size of 350 μm was added to 9900 parts by mass of water, and ultrasonically dispersed at a power of 300 W for 1.5 hours to obtain a 1 wt% silica suspension. 625 parts by mass of a 4 wt% chitosan solution (25 parts by mass of chitosan) was added and mixed uniformly. 0.2 parts by mass of glutaraldehyde was added, and the temperature was raised to 70°C, and the mixture was stirred at a speed of 300 r / min for 3 hours. The mixture was centrifuged and pre-frozen at -20°C for 2 hours. The mixture was then cooled to -60°C and freeze-dried at an air pressure of 20 Pa for 24 hours to obtain large-particle-size coated silica. S2: 15 parts by mass of small-particle coated silica, 20 parts by mass of medium-particle coated silica, 50 parts by mass of large-particle coated silica, 15 parts by mass of polyvinyl alcohol fiber 2#, 8 parts by mass of polyethylene glycol diglycidyl ether P134003, 8 parts by mass of hyperbranched polyethyleneimine SP-200, 1 part by mass of hydroxyethyl cellulose, and 1 part by mass of hexadecyltrimethylammonium chloride are mixed to obtain a medium-temperature drilling fluid nano temporary plugging agent.

[0063] Comparative Example 1

[0064] The rest is the same as Example 1, except that in step S2, ethylene glycol diglycidyl ether of equal mass is used to replace polyethylene glycol diglycidyl ether P134003.

[0065] Comparative Example 2

[0066] The rest is the same as Example 1, except that in step S2, an equal mass of triethylenetetramine is used to replace the hyperbranched polyethyleneimine.

[0067] Comparative Example 3

[0068] The rest is the same as Example 1, except that the silicon dioxide is not coated with chitosan or glutaraldehyde, but is modified with 4-aminobutyltriethoxysilane: S1-1. 100 parts by mass of silica with an average particle size of 1 μm was added to a solution with a concentration of 3 wt% of 4-aminobutyltriethoxysilane at a mass-to-volume ratio of 1:50. The solvent was toluene. The temperature was raised to reflux and the reaction was carried out for 24 hours. The mixture was centrifuged, washed with ethanol three times, and dried at 80°C to a constant weight to obtain a modified small-particle coated silica. S1-2, adding 100 parts by mass of silica with an average particle size of 150 μm to a solution with a concentration of 3 wt% of 4-aminobutyltriethoxysilane at a mass-to-volume ratio of 1:50, using toluene as the solvent, heating to reflux and reacting for 24 h, centrifuging, washing with ethanol three times, and drying at 80° C. to constant weight to obtain modified medium-particle-size coated silica; S1-3, adding 100 parts by mass of silica with an average particle size of 250 μm to a solution with a concentration of 3 wt% of 4-aminobutyltriethoxysilane at a mass-to-volume ratio of 1:50, using toluene as the solvent, heating to reflux and reacting for 24 h, centrifuging, washing with ethanol three times, and drying at 80° C. to constant weight to obtain modified large-particle coated silica; S2. Mix 15 parts by mass of modified small-particle coated silica, 20 parts by mass of modified medium-particle coated silica, 50 parts by mass of modified large-particle coated silica, 20 parts by mass of polyvinyl alcohol fiber 1#, 8 parts by mass of polyethylene glycol diglycidyl ether P134003, 8 parts by mass of hyperbranched polyethyleneimine SP-200, 1 part by mass of hydroxyethyl cellulose, and 1 part by mass of hexadecyltrimethylammonium chloride to obtain a nano temporary plugging agent for medium-temperature drilling fluid.

[0069] Application Examples

[0070] Prepare drilling fluid base slurry: Place 400 mL of distilled water in a high-speed stirring cup, add 0.8 g of sodium hydroxide and 1.6 g of sodium carbonate, and while stirring, add 20 g of bentonite. Stir at 10,000 rpm for 20 minutes, stopping every 4 minutes and continuing stirring for 1 minute. Let it stand at 25°C for 24 hours before use. Prepare multiple portions for future use.

[0071] Prepare drilling fluid: 1L base slurry + 50g drilling fluid temporary plugging agent obtained in Example 1-8 or Comparative Example 1-3, stir at 800 rpm for 10 minutes. Prepare multiple portions for future use.

[0072] The drilling fluids prepared in the above application examples and comparative application examples were subjected to the following performance tests:

[0073] Basic properties of drilling fluid: refer to standard GB / T16783.1-2006, where AV represents apparent viscosity and FL represents fluid loss. AV and FL are tested at 70℃, 80℃, 100℃, 120℃ and 150℃.

[0074] Plugging performance and pressure bearing capacity: For artificially fractured cores with a length of 5.5 cm, a diameter of 2.5 cm, a porosity of 15.52%, and a fracture width of 1 mm, the initial permeability K1 was tested at a confining pressure of 2 MPa. A temporary plugging agent was injected into the core at 80°C and 3.5 MPa using a high-temperature and high-pressure dynamic filtration simulation instrument. The temporary plugging agent injection volume was 2.0 PV (the PV of the artificially fractured core is the sum of the fracture volume and the pore volume). The core was contaminated with circulating drilling fluid for 3 hours under these conditions, and the permeability K2 of the contaminated core was tested at a confining pressure of 2 MPa. The temporary plugging ratio AK1 was calculated as (K1-K2) / K1*100%.

[0075] a. Treat the contaminated core with 15% hydrochloric acid for 6 hours, then test the permeability K3 at a confining pressure differential of 2 MPa. Calculate the core permeability recovery rate AK2 = K3 / K1*100%.

[0076] b. Tighten the upper cover to seal the tank. Pressurize the contaminated core with nitrogen through the upper air valve, increasing the pressure by 1 MPa every 30 minutes. Continue pressurizing until there is no sudden drop in pressure greater than or equal to 0.5 MPa within 30 minutes. Record the pressure at breakthrough, which is the pressure displayed after the last pressurization, as the pressure strength AK3. Then, inject a temporary plugging agent at 70°C and 3.5 MPa to contaminate the core. Repeat the above steps and record the pressure strength BK3.

[0077] Table 1 Performance test results project 70℃ Filtration loss mL Filtration loss at 80℃ mL 100℃ Filtration loss mL 120℃ Filtration loss mL 150℃ Filtration loss mL <![CDATA[AK1 temporary plugging rate %]]> <![CDATA[AK2 Permeability Recovery Rate %]]> <![CDATA[AK3 bearing strength MPa]]> <![CDATA[BK3 bearing strength MPa]]> Application Example 1 2.4 2.4 5.2 7.7 56.2 100.0 90.6 13.2 6.8 Application Example 2 3.1 3.2 6.1 8.4 47.5 98.7 92.3 12.5 7.1 Application Example 3 4.4 4.3 7.4 9.5 52.4 96.5 92.0 12.8 7.1 Application Example 4 3.5 3.5 6.7 8.8 49.2 98.1 91.4 12.7 6.5 Application Example 5 4.6 4.6 8.5 10.0 47.0 96.2 91.9 12.1 6.2 Application Example 6 2.8 2.9 5.8 8.1 47.7 99.3 91.7 12.6 8.0 Application Example 7 3.9 3.9 7.1 9.6 47.0 97.0 92.5 12.2 7.7 Application Example 8 3.3 3.3 6.4 8.5 49.6 98.0 91.8 12.6 7.3 Comparative Example 1 17.2 17.2 25.2 27.8 66.6 88.8 84.1 8.8 5.4 Comparative Example 2 16.4 16.3 28.3 33.2 67.7 89.6 83.2 9.3 6.0 Comparative Example 3 23.1 23.0 31.1 36.5 72.1 91.3 75.5 7.7 5.1 The fluid loss test results in Table 1 show that the temporary plugging agent of the present invention has a fluid loss reduction function, but is suitable for temporary plugging operations at well temperatures of 120°C and below: the fluid loss at temperatures of 70°C and 80°C is almost the same. When the temperature rises to 120°C, the fluid loss increases slightly, indicating that a certain number of epoxy groups on the polyethylene glycol diglycidyl ether at 120°C have already opened and reacted, but the fluid loss can still be maintained in a low range of ≤10mL. When the temperature is further raised to 150°C, the fluid loss increases significantly, indicating that a large number of epoxy groups on the polyethylene glycol diglycidyl ether at the high temperature of 150°C have opened and reacted, reaching a level that causes the coated silica particles to agglomerate or cross-link with the hyperbranched polyethyleneimine, and cannot effectively plug the pores. The compressive strength test results at 70°C and 80°C show that the compressive strength of the temporary plugging agent at 80°C is >10 MPa, significantly higher than that at 70°C. This indicates that the number of epoxy ring-opening reactions on polyethylene glycol diglycidyl ether at 70°C is relatively low. In summary, the temporary plugging agent of the present invention is suitable for use at temperatures between 80°C and 120°C.

[0078] It can be seen from the temporary plugging rate test results that the temporary plugging agent of the present invention has a good plugging effect, with a temporary plugging rate of up to 100%, a permeability recovery rate after acid dissolution of more than 90%, and a compressive strength of up to 13.2 MPa.

[0079] The above detailed description is a specific description of one feasible embodiment of the present invention. This embodiment is not intended to limit the patent scope of the present invention. Any equivalent implementation or modification that does not depart from the present invention should be included in the scope of the technical solution of the present invention.

Claims

1. A nano temporary plugging agent for medium-temperature drilling fluid, characterized in that: The invention comprises the following raw materials in parts by mass: 10-15 parts of small-particle coated silica, 15-20 parts of medium-particle coated silica, 30-50 parts of large-particle coated silica, 15-20 parts of fiber, 5-8 parts of polyether diglycidyl ether, 5-8 parts of hyperbranched polyethyleneimine, 1-1.5 parts of water-soluble cellulose, and 0.5-1 part of cationic quaternary ammonium salt. The coated silica uses chitosan and glutaraldehyde cross-linked condensate as wall materials and silica as core materials. The silica particle size of the small-particle coated silica is 0.3-1 μm; the silica particle size of the medium-particle coated silica is 150-250 μm; and the silica particle size of the large-particle coated silica is 250-350 μm.

2. The nano temporary plugging agent for medium-temperature drilling fluid according to claim 1, characterized in that: The mass ratio of chitosan, glutaraldehyde and silica as raw materials for the small-particle coated silica is 40-55:0.4-0.6:100; the mass ratio of chitosan, glutaraldehyde and silica as raw materials for the medium-particle coated silica is 25-35:0.2-0.4:100; and the mass ratio of chitosan, glutaraldehyde and silica as raw materials for the large-particle coated silica is 15-25:0.1-0.2:

100.

3. The nano temporary plugging agent for medium-temperature drilling fluid according to claim 1, characterized in that: The chitosan has a deacetylation degree of ≥90% and a weight average molecular weight of 50,000-100,000.

4. The nano temporary plugging agent for medium-temperature drilling fluid according to claim 1, characterized in that: The polyether diglycidyl ether has a number average molecular weight of 500-1000 and is selected from one or a combination of polyethylene glycol glycidyl ether and poly(propylene glycol) diglycidyl ether; the hyperbranched polyethyleneimine has a number average molecular weight of 10,000-30,000, an amine value of 18 mmol / g, a primary amine molar ratio of 34-35%, a secondary amine molar ratio of 35%, and a tertiary amine molar ratio of 30-31%.

5. The nano temporary plugging agent for medium-temperature drilling fluid according to claim 1, characterized in that: The coated silicon dioxide is prepared by a method comprising the following steps: Chitosan solution is prepared by chitosan and acetic acid solution, and silicon dioxide suspension is prepared. The silicon dioxide suspension is added to the chitosan solution and mixed evenly. Glutaraldehyde is added to react, and the coated silicon dioxide is obtained by centrifugation and freeze drying.

6. The nano temporary plugging agent for medium-temperature drilling fluid according to claim 1, characterized in that: The water-soluble cellulose is selected from one or a combination of hydroxyethyl cellulose and hydroxymethyl cellulose; the fiber is an acid-soluble or degradable fiber with a length of 0.5-1.9 cm and a diameter of 10-20 μm, selected from one or a combination of two or more of polyvinyl alcohol fiber, polylactic acid fiber, and modified polyester fiber.

7. The method for preparing the nano temporary plugging agent for medium-temperature drilling fluid according to any one of claims 1 to 6, characterized in that: The method comprises the following steps: uniformly mixing small-particle coated silica, medium-particle coated silica, large-particle coated silica, fiber, polyether diglycidyl ether, hyperbranched polyethyleneimine, water-soluble cellulose and cationic quaternary ammonium salt to obtain a drilling fluid temporary plugging agent.

8. Use of the nanometer temporary plugging agent for medium-temperature drilling fluid according to any one of claims 1 to 6 in a petroleum drilling process, characterized in that: The drilling fluid temporary plugging agent and the drilling fluid base slurry are mixed evenly to prepare the drilling fluid, which is used in the oil drilling process.

9. The use of the nano temporary plugging agent for medium-temperature drilling fluid in a petroleum drilling process according to claim 8, characterized in that: The drilling fluid is used for plugging fractured leakage formations with cracks less than 1 mm or homogeneous leakage formations.

10. The use of the medium-temperature drilling fluid nano temporary plugging agent in a petroleum drilling process according to claim 9, characterized in that: The mass volume ratio of the drilling fluid temporary plugging agent and the drilling fluid base slurry in the drilling fluid for the fractured leakage formation with cracks less than 1 mm is 5-8:100 g / mL; the mass volume ratio of the drilling fluid temporary plugging agent and the drilling fluid base slurry in the drilling fluid for the homogeneous leakage formation is 3-5:100 g / mL.