A medium-temperature drilling fluid nano temporary plugging agent and a preparation method thereof

Abstract

The application 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 comprises the following raw materials in parts by mass: 10-15 parts of small-particle-size coated silica, 15-20 parts of medium-particle-size coated silica, 30-50 parts of large-particle-size coated silica, 15-20 parts of fibers, 5-8 parts of polyether diglycidyl ether, 5-8 parts of hyperbranched polyethylene imine, 1-1.5 parts of water-soluble cellulose, and 0.5-1 part of cationic quaternary ammonium salt. The coated silica is prepared by using chitosan and glutaraldehyde as wall material and silica as core material. The particle core material has a particle size of 0.3-1 mu m, the medium-particle-size particle core material has a particle size of 150-250 mu m, and the large-particle-size particle core material has a particle size of 250-350 mu m. The micro interpenetrating network formed by the reaction of the hyperbranched polyethylene imine and the polyether diglycidyl ether bonds the coated silica particles together, and the particles and the fibers are combined to improve the pressure-bearing strength.

Description

TECHNICAL FIELD

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

[0002] In the processes of killing, well flushing, acidizing, drilling and workover in oil development, due to strong formation heterogeneity, poor fluid compatibility and engineering measures, the oil phase permeability near the wellbore zone is often reduced, and the production capacity is reduced. This phenomenon is particularly prominent in shale formations. Due to the complex nano-scale pore throat structure and low permeability characteristics, the invasion of working fluid during shale oil development can easily cause serious water locking and clay mineral hydration damage. Before operation, temporary plugging agent is injected to plug the reservoir, which can effectively plug the high permeability layer or fracture, significantly reduce the permeability of the region, and prevent further damage of working fluid and subsequent fluid to the reservoir (especially shale oil reservoir). Subsequently, the plugging is removed by perforation, chemical dissolution or flowback, so that the formation permeability is restored, thereby reducing the loss and achieving the purpose of protecting the reservoir and maintaining the production capacity.

[0003] Temporary plugging agents are various, including bridging type (particles, fibers, sheet), oil-soluble type, water-soluble type, acid-soluble type and water-absorbing expansion type. Common bridging type temporary plugging agents use calcium carbonate, quartz sand, nutshell particles, resin, rubber and the like as raw materials, and realize efficient plugging by matching the particle size with the pore throat. For example, the patent CN101311243B discloses an oil and gas reservoir fracture temporary plugging agent, which is composed of 600-1100 mesh and 60-600 mesh ultra-fine calcium carbonate, plant fiber and oxidized pitch; CN116262875B introduces a high-efficiency drilling fluid plugging agent containing calcium carbonate, active fiber, vermiculite and mica. Such materials can effectively plug micro-cracks and larger pore throats in shale formations, and are particularly suitable for shale oil reservoirs with certain permeability difference.

[0004] Although the bridging type temporary plugging agent performs well in plugging high permeability layers, its plugging mechanism mainly relies on the physical bridging effect of particles in the throat. It is generally believed that the plugging effect is optimal when the particle diameter is about 1 / 3 of the throat radius. However, the binding force between particles of such materials is weak, mainly relying on mechanical interlocking and physical adsorption, which leads to limited pressure-bearing capacity and difficulty in adapting to complex and variable operating environments and formation conditions. For example, in the contact zone between abnormal high pressure shale section and low pressure reservoir, the interaction area between high permeability layer and low permeability layer, or in the case of uncontrolled formation pressure balance caused by high pressure fluid flushing, conventional temporary plugging agents are prone to failure, affecting the effect of shale oil reservoir modification.

[0005] The patent CN101638576B discloses a shielding temporary plugging gelling agent for drilling fluid and its production method and use method, and the shielding temporary plugging gelling agent for drilling fluid is composed of strong plugging powder, filtration reducer or flow pattern modifier, plant gelling agent, calcifying agent and expanded plant short fiber. Although the use of plant gelling agent and calcifying agent can improve the strength of the temporary plugging material by forming a gel, the ionic bond of the general ionic crosslinking type gel starts to dissociate at 60-80 DEG C, the gel starts to swell or soften, and the temperature continues to rise to intensify the molecular thermal motion until the gel network gradually collapses, the plugging performance of the temporary plugging material is reduced, and it is difficult to meet the temporary plugging demand under the temperature environment of deep shale oil reservoir.

[0006] Therefore, aiming at the characteristics of high shale formation temperature, complex pore throat and possible pressure mutation, it is urgent to develop a temporary plugging agent with excellent temperature resistance and high pressure bearing capacity to ensure the reservoir protection and operation safety in the process of efficient development of shale oil. SUMMARY

[0007] To solve the above technical problems, the present application provides a kind of middle temperature drilling fluid nano temporary plugging agent and its preparation method, by with chitosan, glutaraldehyde to the surface of silica is coated with the coating type silica that rich amino, hydroxyl is modified, amino, hydroxyl can continue and polyether diglycidyl ether on epoxy group reaction, hyperbranched polyethylene imine and polyether diglycidyl ether reaction form the interpenetrating network with certain strength in microcosm, the network will different particle size coating type silica particles tightly bonded together, with the effect of improving the pressure strength and plugging rate.

[0008] A kind of middle temperature drilling fluid nano temporary plugging agent, including the following mass parts of raw materials: 10-15 parts small particle size coating type silica, 15-20 parts medium particle size coating type silica, 30-50 parts large particle size coating type silica, 15-20 parts fiber, 5-8 parts polyether diglycidyl ether, 5-8 parts hyperbranched polyethylene imine, 1-1.5 parts water-soluble cellulose, 0.5-1 parts cationic quaternary ammonium salt, the coating type silica is all with chitosan, glutaraldehyde crosslinking condensate as wall material, silica as core material, the silica particle size of the small particle size coating type silica is 0.3-1 μm;The silica particle size of the medium particle size coating type silica is 150-250 μm;The silica particle size of the large particle size coating type silica is 250-350 μm.

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

[0010] The degree of deacetylation of the chitosan is greater than or equal to 90%, and the weight average molecular weight is 50,000-100,000. The silica is coated with chitosan and glutaraldehyde, which is conducive to the cross-linking reaction of the polyether glycidyl ether and the hyperbranched polyethyleneimine gathered on the surface of the coated silica particles, and the adjacent coated silica particles are bonded together, instead of forming self-cross-linked bodies in the aqueous phase far from the coated silica particles.

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

[0012] The epoxy groups are located at the chain ends of the polyether glycidyl ether. At low temperatures, the polyether glycidyl ether has weak molecular motion ability, and the flexible polyether chain is prone to entanglement or folding, which embeds the epoxy groups in the interior of the molecule, hindering the contact between the epoxy groups and the amino groups or hydroxyl groups on the hyperbranched polyethyleneimine and the coated silica. Therefore, the reaction probability of the polyether glycidyl ether with the hyperbranched polyethyleneimine and the coated silica is extremely low at low temperatures. At the same time, due to this reason, in the application of the drilling fluid temporary plugging agent, if the temperature is insufficient, the cross-linking reaction of the polyether glycidyl ether with the hyperbranched polyethyleneimine and the coated silica will be difficult to effectively proceed, resulting in low pressure-bearing strength of the temporary plugging agent.

[0013] When the temperature rises, the polyether glycidyl ether has enhanced molecular motion ability and intensified molecular motion, and the embedded epoxy groups are more likely to be exposed and contact with the amine groups and hydroxyl groups, increasing the reaction probability, and also providing sufficient collision energy to overcome the energy barrier to make the epoxy groups open and react with the amine groups and hydroxyl groups. By selecting a polyether glycidyl ether with a moderate molecular weight, the temperature-dependent reaction characteristics can be precisely regulated: the drilling fluid system containing the temporary plugging agent can be smoothly injected into the reservoir at low temperature, or rapidly injected into the reservoir at high temperature, and cross-linked at high temperature, realizing controllable temporary plugging and optimizing the pressure-bearing strength.

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

[0015] The coated silica, the hyperbranched polyethyleneimine, and the polyether glycidyl ether jointly form a cross-linked network with a certain strength at the micro level and tightly bond the coated silica together, having the effect of improving the pressure-bearing strength and 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 the effect of increasing viscosity and improving the dispersion of the coated silica and the fibers.

[0017] The coated silica is prepared by a method comprising the following steps:

[0018] Chitosan, acetic acid solution is prepared chitosan solution, preparation of silica suspension, silica suspension is added to the chitosan solution mixed uniformly, add glutaraldehyde reaction, centrifugal separation, freeze drying coated silica.

[0019] The concentration of the acetic acid solution is 1-2wt%. The concentration of chitosan in the chitosan solution is 2-4wt%. The content of silica in the silica suspension is 1-3wt%; the reaction is stirred at 60-70℃ for 3-5h. The centrifuge speed is 3600r / min, and the centrifugal separation time is 10min±0.5min; the freeze drying is pre-cooled at-25℃ to-20℃ for 2-4h, then cooled to-60℃ to-40℃, the pressure is 10-20Pa freeze drying for 24-72h.

[0020] The fiber is a soluble acid or degradable fiber with a length of 0.5-1.9cm and a diameter of 10-20μm, selected from one or more than two combinations of polyvinyl alcohol fiber, polylactic acid fiber and modified polyester fiber.

[0021] Three different particle sizes of coated silica and fibers, through the hierarchical bridging-filling-reinforcing mechanism, synergistically produce good temporary plugging effect: large particle size coated silica as large particles enters large size pore throat or fracture to form initial bridging, medium particle size coated silica fills the gap between large particles to reduce pore size, small particle size coated silica further seals the remaining micropores, and the fiber penetrates and overlaps between the particles due to its high aspect ratio, forming a macroscopic physical three-dimensional network skeleton, which constitutes a composite plugging structure of "large particle bridging, medium particle filling, small particle sealing, and fiber reinforcing". The micro interpenetrating network formed by the reaction of hyperbranched polyethyleneimine and polyether glycidyl ether effectively bonds and fixes the coated silica through chemical bonding, which can effectively reduce the relative sliding and rolling of coated silica particles under high pressure. The combination of macroscopic three-dimensional network skeleton and microscopic interpenetrating network enables the plugging layer to withstand much higher pressure than single component or loose accumulation, achieving efficient plugging and structural reinforcement of the pores.

[0022] The cationic quaternary ammonium salt is selected from one or more than two combinations of dodecyltrimethylammonium chloride, hexadecyltrimethylammonium chloride, and octadecyltrimethylammonium chloride.

[0023] The application further provides a preparation method of the medium-temperature drilling fluid nano temporary plugging agent, which comprises the following steps: uniformly mixing small-particle-size coated silica, medium-particle-size coated silica, large-particle-size coated silica, fibers, polyether diglycidyl ether, hyperbranched polyethyleneimine and water-soluble cellulose and cationic quaternary ammonium salt to obtain the drilling fluid temporary plugging agent.

[0024] The application further provides application of the above-mentioned medium-temperature drilling fluid nano temporary plugging agent in the oil drilling process.

[0025] The drilling fluid is used for plugging a fractured leakage formation with cracks smaller than 1mm or a homogeneous leakage formation.

[0026] The mass / volume ratio g / mL of the drilling fluid temporary plugging agent to the drilling fluid base slurry in the drilling fluid used for the fractured leakage formation with cracks smaller than 1mm is 5-8:100.

[0027] The mass / volume ratio g / mL of the drilling fluid temporary plugging agent to the drilling fluid base slurry in the drilling fluid used for the homogeneous leakage formation is 3-5:100.

[0028] The drilling fluid has a use temperature of 80-120 DEG C.

[0029] The drilling fluid base slurry is not particularly limited, and the commonly used water-based drilling fluid base slurry in the art can be used, including but not limited to bentonite water-based drilling fluid base slurry.

[0030] Compared with the prior art, the application has the following beneficial effects:

[0031] Firstly, the application coats the silica with chitosan and glutaraldehyde to obtain particles with active amino groups and hydroxyl groups that can react with the epoxy groups on the polyether diglycidyl ether, and hyperbranched polyethyleneimine reacts with the polyether diglycidyl ether to form a micro interpenetrating network with a certain strength, which tightly bonds the coated silica particles with different particle sizes together and has the effect of improving the pressure-bearing strength and plugging rate.

[0032] Secondly, the micro crosslinking network formed among the coated silica particles, hyperbranched polyethyleneimine and polyether diglycidyl ether is different from the gel formed by ionic bonds and has good thermal stability.

[0033] Third, the three types of coated silica with different particle sizes and fibers of this invention form a macroscopic physical three-dimensional network skeleton, constituting a composite plugging structure of "large particles bridging, medium particles filling, small particles sealing, and fibers reinforcing". The microscopic interpenetrating network formed by the reaction of hyperbranched polyethyleneimine and polyether diglycidyl ether effectively bonds and fixes the coated silica through chemical bonding, which can effectively reduce the relative slippage 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 single components or loose packing, achieving efficient pore plugging and structural reinforcement.

[0034] Fourth, the glycosidic bonds on the chitosan of the coated silica wall material of this invention are easily hydrolyzed and broken, resulting in a high acidification and backflow rate of the temporary plugging agent.

[0035] V. The medium-temperature drilling fluid nano-plugging agent prepared by this invention has excellent temperature resistance and high pressure bearing capacity. It exhibits excellent temperature stability and high pressure bearing capacity in the medium temperature range of 80-120℃, and can effectively seal the nanoscale pore throats and micro-fractures in shale formations. It is one of the key materials for achieving shale reservoir protection and operational safety. Detailed Implementation

[0036] The present invention will be further described below with reference to specific embodiments, but is not limited to the contents of the specification. Unless otherwise specified, all "parts" mentioned in the embodiments of the present invention are parts by weight. All reagents used are commercially available in the art.

[0037] The silica has an average particle size of 0.3 μm and comes from Aladdin.

[0038] The silica has an average particle size of 1 μm and comes from Aladdin.

[0039] The silica has an average particle size of 150 μm and comes from Aladdin.

[0040] The silica has an average particle size of 250 μm and comes from Aladdin.

[0041] The silica has an average particle size of 350 μm and comes from Aladdin.

[0042] Chitosan, degree of deacetylation ≥95%, M W 50,000 units, item number C766421, from Shanghai Maclean Biochemical Technology Co., Ltd.

[0043] Polyvinyl alcohol fiber #1 is 1.9cm long and 10μm in diameter, and comes from Shandong Huayao Rubber & Plastic Co., Ltd.

[0044] Polyvinyl alcohol fiber #2 is 0.5cm long and 20μm in diameter, and comes from Shandong Huayao Rubber & Plastic Co., Ltd.

[0045] Polyethylene glycol diglycidyl ether, number average molecular weight 500, item number P134003, from Aldrich.

[0046] Polyethylene glycol diglycidyl ether, number average molecular weight 1000, item number P475492, from Aldrich.

[0047] Hyperbranched polyethyleneimine SP-200, number average molecular weight 10,000, amine value 18 mmol / g, with primary amine molar fraction 35%, secondary amine molar fraction 35%, tertiary amine molar fraction 30%, from Japan Catalyst Co., Ltd.

[0048] Hyperbranched polyethyleneimine HM-2000, number average molecular weight 30,000, amine value 18 mmol / g, with primary amine molar fraction 34%, secondary amine molar fraction 35%, tertiary amine molar fraction 31%, from Japan Catalyst Co., Ltd.

[0049] Example 1

[0050] S1-1 A 2 wt% acetic acid solution of chitosan C766421 was mixed uniformly and stirred at 300 r / min until no solid was present, to obtain a 4 wt% chitosan solution;

[0051] 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 ultrasonic dispersion was performed at a power of 300 W for 2 h to obtain a 1 wt% silica suspension. 1375 parts by mass of the 4 wt% chitosan solution (chitosan 55 parts by mass) was added and mixed uniformly, 0.6 parts by mass of glutaraldehyde was added, and the temperature was raised to 70°C, and stirring was performed at a rotational speed of 300 r / min for 3 h. Centrifugal separation was performed, pre-freezing was performed at -20°C for 2 h, then the temperature was lowered to -60°C, and freeze-drying was performed at a gas pressure of 20 Pa for 24 h, to obtain small-particle-size coated silica;

[0052] 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 ultrasonic dispersion was performed at a power of 300 W for 1.5 h to obtain a 1 wt% silica suspension. 875 parts by mass of the 4 wt% chitosan solution (chitosan 35 parts by mass) was added and mixed uniformly, 0.4 parts by mass of glutaraldehyde was added, and the temperature was raised to 70°C, and stirring was performed at a rotational speed of 300 r / min for 3 h. Centrifugal separation was performed, pre-freezing was performed at -20°C for 2 h, then the temperature was lowered to -60°C, and freeze-drying was performed at a gas pressure of 20 Pa for 24 h, to obtain medium-particle-size coated silica;

[0053] 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 ultrasonic dispersion was performed at a power of 300 W for 1.5 h to obtain a 1 wt% silica suspension, 625 parts by mass of a 4 wt% chitosan solution (chitosan 25 parts by mass) was added and mixed uniformly, 0.2 parts by mass of glutaraldehyde was added, and the temperature was raised to 70°C, and stirring was performed at a rotation speed of 300 r / min for 3 h, centrifugal separation was performed, pre-freezing was performed at -20°C for 2 h, and then freezing drying was performed at -60°C under a gas pressure of 20 Pa for 24 h to obtain large particle size coated silica;

[0054] S2 15 parts by mass of small particle size coated silica, 20 parts by mass of medium particle size coated silica, 50 parts by mass of large particle size 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 cetyltrimethylammonium chloride were mixed uniformly to obtain a medium-temperature drilling fluid nano temporary plugging agent.

[0055] Example 2

[0056] The rest was the same as in Example 1, except that in step S2, the amount of polyethylene glycol diglycidyl ether P134003 was 5 parts by mass.

[0057] Example 3

[0058] The rest was the same as in Example 1, except that in step S2, the amount of hyperbranched polyethyleneimine SP-200 was 5 parts by mass.

[0059] Example 4

[0060] The rest was the same as in Example 1, except that in step S2, equal amounts of polyethylene glycol diglycidyl ether P475492 with a number average molecular weight of 1000 were used instead of polyethylene glycol diglycidyl ether P134003 with a number average molecular weight of 500.

[0061] Example 5

[0062] The rest was the same as in Example 1, except that in step S1-2, the amount of chitosan solution was 1000 parts by mass (chitosan 40 parts by mass); in step S1-3, the amount of chitosan solution was 625 parts by mass (chitosan 25 parts by mass); and in step S1-4, the amount of chitosan solution was 375 parts by mass (chitosan 15 parts by mass).

[0063] Example 6

[0064] The rest was the same as in Example 1, except that in step S2, equal amounts of hyperbranched polyethyleneimine HM-2000 were used instead of hyperbranched polyethyleneimine SP-200.

[0065] Example 7

[0066] S1-1 mixed chitosan C766421, 2wt% acetic acid solution uniformly, stirred at 300r / min until no solid, obtained 4wt% chitosan solution;

[0067] S1-2 added 100 parts by mass of average particle size 1μm silica to 9900 parts by mass of water, dispersed by ultrasonic power 300W for 2h to obtain 1wt% silica suspension, added 1375 parts by mass of 4wt% chitosan solution (chitosan 55 parts by mass) mixed uniformly, added 0.4 parts by mass of glutaraldehyde, warmed to 70℃, stirred at 300r / min for 3h, centrifuged, pre-cooled at-20℃ for 2h, then cooled to-60℃, freeze-dried at 20Pa for 24h, obtained small particle size coated silica;

[0068] S1-3 added 100 parts by mass of average particle size 150μm silica to 9900 parts by mass of water, dispersed by ultrasonic power 300W for 1.5h to obtain 1wt% silica suspension, added 875 parts by mass of 4wt% chitosan solution (chitosan 35 parts by mass) mixed uniformly, added 0.2 parts by mass of glutaraldehyde, warmed to 70℃, stirred at 300r / min for 3h, centrifuged, pre-cooled at-20℃ for 2h, then cooled to-60℃, freeze-dried at 20Pa for 24h, obtained medium particle size coated silica;

[0069] S1-4 added 100 parts by mass of average particle size 250μm silica to 9900 parts by mass of water, dispersed by ultrasonic power 300W for 1.5h to obtain 1wt% silica suspension, added 625 parts by mass of 4wt% chitosan solution (chitosan 25 parts by mass) mixed uniformly, added 0.1 parts by mass of glutaraldehyde, warmed to 70℃, stirred at 300r / min for 3h, centrifuged, pre-cooled at-20℃ for 2h, then cooled to-60℃, freeze-dried at 20Pa for 24h, obtained large particle size coated silica;

[0070] S2 mixed 10 parts by mass of small particle size coated silica, 15 parts by mass of medium particle size coated silica, 30 parts by mass of large particle size 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, 0.5 parts by mass of cetyltrimethylammonium chloride uniformly, obtained medium temperature drilling fluid nano temporary plugging agent.

[0071] Example 8

[0072] S1-1 mixed chitosan C766421, 2wt% acetic acid solution uniformly, stirred at 300r / min until no solid, obtained 4wt% chitosan solution;

[0073] S1-2 added 100 parts by mass of average particle size 0.3μm silica to 9900 parts by mass of water, dispersed by ultrasonic at power 300W for 2h to obtain 1wt% silica suspension, added 1375 parts by mass of 4wt% chitosan solution (chitosan 55 parts by mass), mixed uniformly, added 0.6 parts by mass of glutaraldehyde, heated to 70℃, stirred at 300r / min for 3h, centrifuged, pre-frozen at -20℃ for 2h, then cooled to -60℃, freeze-dried at 20Pa for 24h, obtained small particle size coated silica;

[0074] S1-3 added 100 parts by mass of average particle size 250μm silica to 9900 parts by mass of water, dispersed by ultrasonic at power 300W for 1.5h to obtain 1wt% silica suspension, added 875 parts by mass of 4wt% chitosan solution (chitosan 35 parts by mass), mixed uniformly, added 0.4 parts by mass of glutaraldehyde, heated to 70℃, stirred at 300r / min for 3h, centrifuged, pre-frozen at -20℃ for 2h, then cooled to -60℃, freeze-dried at 20Pa for 24h, obtained medium particle size coated silica;

[0075] S1-4 added 100 parts by mass of average particle size 350μm silica to 9900 parts by mass of water, dispersed by ultrasonic at power 300W for 1.5h to obtain 1wt% silica suspension, added 625 parts by mass of 4wt% chitosan solution (chitosan 25 parts by mass), mixed uniformly, added 0.2 parts by mass of glutaraldehyde, heated to 70℃, stirred at 300r / min for 3h, centrifuged, pre-frozen at -20℃ for 2h, then cooled to -60℃, freeze-dried at 20Pa for 24h, obtained large particle size coated silica;

[0076] S2 mixed 15 parts by mass of small particle size coated silica, 20 parts by mass of medium particle size coated silica, 50 parts by mass of large particle size 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, 1 part by mass of cetyltrimethylammonium chloride, obtained medium temperature drilling fluid nanometer temporary plugging agent.

[0077] Comparative Example 1

[0078] The rest is the same as Example 1, the difference is that in step S2, equal mass of ethylene glycol diglycidyl ether is used instead of polyethylene glycol diglycidyl ether P134003.

[0079] Comparative Example 2

[0080] The rest is the same as Example 1, except that in step S2, the same mass of triethylene tetramine is used instead of hyperbranched polyethylene imine.

[0081] Comparative Example 3

[0082] The rest is the same as Example 1, except that the silica is not coated with chitosan and glutaraldehyde, but is modified with 4-aminobutyl triethoxysilane:

[0083] S1-1, 100 parts by mass of silica with an average particle size of 1 μm is added to a solution with a 4-aminobutyl triethoxysilane concentration of 3 wt%, the solvent is toluene, and the temperature is raised to refluxing for 24 h, centrifugal separation, ethanol washing 3 times, 80℃ drying only constant weight, to get modified small particle size coated silica;

[0084] S1-2, 100 parts by mass of silica with an average particle size of 150 μm is added to a solution with a 4-aminobutyl triethoxysilane concentration of 3 wt%, the solvent is toluene, and the temperature is raised to refluxing for 24 h, centrifugal separation, ethanol washing 3 times, 80℃ drying only constant weight, to get modified medium particle size coated silica;

[0085] S1-3, 100 parts by mass of silica with an average particle size of 250 μm is added to a solution with a 4-aminobutyl triethoxysilane concentration of 3 wt%, the solvent is toluene, and the temperature is raised to refluxing for 24 h, centrifugal separation, ethanol washing 3 times, 80℃ drying only constant weight, to get modified large particle size coated silica;

[0086] S2, 15 parts by mass of modified small particle size coated silica, 20 parts by mass of modified medium particle size coated silica, 50 parts by mass of modified large particle size 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 polyethylene imine SP-200, 1 part by mass of hydroxyethyl cellulose, 1 part by mass of cetyl trimethyl ammonium chloride are mixed to get a medium temperature drilling fluid nanometer temporary plugging agent.

[0087] Application Example

[0088] Preparation of drilling fluid base paste: take 400 mL distilled water in a high-speed stirring cup, add 0.8 g of sodium hydroxide, 1.6 g of sodium carbonate, under stirring conditions, add 20 g of bentonite, high-speed stirring at 10,000 r / min for 20 min, stop every 4 min, continue stirring for 1 min, and stand at 25℃ for 24 h. Prepare multiple portions for standby.

[0089] Preparation of drilling fluid: 1L base slurry + 50g drilling fluid temporary plugging agent obtained from Example 1-8 or Comparative Example 1-3, stirring at 800r / min for 10min. Multiple portions are prepared for standby.

[0090] The drilling fluids prepared in the above application examples and comparative application examples are subjected to the following performance tests:

[0091] Basic performance of drilling fluid: refer to standard GB / T16783.1-2006, wherein AV represents apparent viscosity, FL represents filter loss, and AV and FL at 70℃, 80℃, 100℃, 120℃ and 150℃ are tested.

[0092] Plugging performance and pressure-bearing capacity: a 5.5cm long and 2.5cm diameter artificial fracture core with a porosity of 15.52% and a fracture width of 1mm is used to test the initial permeability K1 under a differential pressure of 2MPa confining pressure. The drilling fluid is injected into the contaminated core at 80℃ and 3.5MPa, and the injection amount of the temporary plugging agent is 2.0PV (the PV of the artificial fracture core is the sum of the fracture volume and the pore volume). The contaminated core is circulated for 3h, and the permeability K2 of the contaminated core is tested under a differential pressure of 2MPa confining pressure. The temporary plugging rate AK1= (K1-K2) / K1*100% is calculated.

[0093] a. The contaminated core is treated with 15% hydrochloric acid for 6h, and then the permeability K3 is tested under a differential pressure of 2MPa confining pressure. The core permeability recovery rate AK2=K3 / K1*100% is calculated.

[0094] b. Tighten the upper cover to make the tank body in a sealed state, and pressurize the contaminated core by introducing nitrogen through the upper gas valve. Increase the pressure by 1MPa every 30 minutes, and continue to pressurize if there is no pressure drop of ≥0.5MPa within 30 minutes. Record the breakthrough pressure, which is the pressure displayed after the last pressurization, as the pressure-bearing strength AK3. Repeat the above operation and record the pressure-bearing strength BK3 after injecting the temporary plugging agent into the contaminated core at 70℃ and 3.5MPa.

[0095] Table 1 Performance test results

[0096] Item 70°C Filtration loss mL 80°C Filtration loss mL 100°C Filtration loss mL 120°C Filtration loss mL 150°C Filtration loss mL AK1 temporary plugging rate AK2 permeability recovery rate AK3 compressive strength MPa BK3 compressive 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

[0097] From the filtration loss test results in Table 1, it can be seen that the temporary plugging agent of the application has the function of reducing filtration loss, but is suitable for temporary plugging operation at well temperature of 120℃ or below: the filtration loss at temperature of 70℃ and 80℃ is nearly the same, the filtration loss slightly increases when the temperature rises to 120℃, indicating that a certain number of epoxy groups on the polyethylene glycol diglycidyl ether at 120℃ have been ring-opened and reacted, but the filtration loss can still be kept in the lower range of ≤10mL; when the temperature rises to 150℃, the filtration loss significantly increases, indicating that a large number of epoxy groups on the polyethylene glycol diglycidyl ether at 150℃ have been ring-opened and reacted, which has reached the extent of initiating the agglomeration of coated silica particles or crosslinking with hyperbranched polyethyleneimine, and cannot play a good plugging effect on the pores. From the compression strength test results at 70℃ and 80℃, it can be seen that the compression strength of the temporary plugging agent at 80℃ is >10MPa, and is significantly higher than that at 70℃, indicating that the number of ring-opening reactions of epoxy groups on the polyethylene glycol diglycidyl ether at 70℃ is relatively low. In summary, it is shown that the temporary plugging agent of the application is suitable for use at 80-120℃.

[0098] From the temporary plugging rate test results, it can be seen that the temporary plugging agent of the application has good plugging effect, the temporary plugging rate is as high as 100%, the permeability recovery rate after acid dissolution is above 90%, and the compression strength is as high as 13.2MPa.

[0099] The above detailed description is a specific description of one of the feasible embodiments of the application, which is not used to limit the patent scope of the application, and any equivalent implementation or change without departing from the application shall be included in the scope of the technical solutions of the application.

Claims

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

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

100.

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

4. The intermediate-temperature drilling fluid nano-temporary plugging agent 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 two 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, wherein the molar percentage of primary amine is 34-35%, the molar percentage of secondary amine is 35%, and the molar percentage of tertiary amine is 30-31%.

5. The intermediate-temperature drilling fluid nano-plugging agent according to claim 1, characterized in that, The coated silica is prepared by a method comprising the following steps: Chitosan solution is prepared by mixing chitosan and acetic acid solution. Silica suspension is prepared by adding silica suspension to chitosan solution and mixing thoroughly. Glutaraldehyde is added to react with the silica suspension. After centrifugation and freeze-drying, coated silica is obtained.

6. The intermediate-temperature drilling fluid nano-temporary plugging agent according to claim 1, characterized in that, The water-soluble cellulose is selected from one or a combination of two of hydroxyethyl cellulose and hydroxymethyl cellulose; the fiber is a soluble or biodegradable 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 intermediate-temperature drilling fluid nano-temporary plugging agent according to any one of claims 1-6, characterized in that, The process includes the following steps: mixing small-particle-size coated silica, medium-particle-size coated silica, large-particle-size 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. The application of the intermediate-temperature drilling fluid nano-plugging agent according to any one of claims 1-6 in the oil drilling process, characterized in that, Drilling fluid is prepared by mixing drilling fluid plugging agent and drilling fluid base slurry, and then used in the oil drilling process.

9. The application of the intermediate-temperature drilling fluid nano-temporary plugging agent according to claim 8 in the oil drilling process, characterized in that, The drilling fluid is used to seal fractured or homogeneous lost circulation formations with fractures less than 1 mm.

10. The application of the intermediate-temperature drilling fluid nano-plugging agent according to claim 9 in the oil drilling process, characterized in that, For the drilling fluid used in fractured lost circulation formations with fractures less than 1 mm, the mass-to-volume ratio of drilling fluid temporary plugging agent to drilling fluid-based slurry in the drilling fluid is 5-8:100 (g / mL); for the drilling fluid used in homogeneous lost circulation formations, the mass-to-volume ratio of drilling fluid temporary plugging agent to drilling fluid-based slurry in the drilling fluid is 3-5:100 (g / mL).