Gel-coated temporary plugging agent as well as preparation method and application thereof

Abstract

The invention relates to the technical field of hydraulic fracturing exploitation of deep / ultra-deep oil and gas reservoirs, and discloses a gel-coated temporary plugging agent and a preparation method and application thereof.The gel-coated temporary plugging agent comprises a proppant inner core and a degradable gel shell coating the outer surface of the proppant inner core; the degradable gel shell is formed by a gel shell gelling solution, the gel shell gelling solution comprises small-molecule comonomers and a degradable cross-linking agent, and the small-molecule comonomers comprise acrylamide, N, N-dimethylformamide, N, N-dimethylformamide, N, N-dimethylformamide, N, N-dimethylformamide, N, N-dimethylformamide, N, N-dimethylformamide the initiator is one or more of N, N-dimethylacrylamide, acrylic acid, hydroxyethyl acrylate, benzyl acrylate, 2-propyl acrylic acid, 2-acrylamide-2-methylpropanesulfonic acid and N-vinyl pyrrolidone; and the initiator is one or more of N, N-dimethylacrylamide, acrylic acid, hydroxyethyl acrylate, benzyl acrylate, 2-propyl acrylic acid, 2-acrylamide-2-methylpropanesulfonic acid and N-vinyl pyrrolidone. The gel-coated temporary plugging agent can be used for effectively plugging in a fracturing time period at high temperature / ultrahigh temperature, and the flow conductivity of fractured cracks can be enhanced by exposing an internal propping agent after the gel-coated temporary plugging agent is degraded.

Description

Technical Field

[0001] The present invention relates to the technical field of hydraulic fracturing and exploitation of deep / ultra-deep oil and gas reservoirs, and in particular to a gel-coated temporary plugging agent, a preparation method thereof, and applications thereof. Background Art

[0002] Deep / ultra-deep reservoirs are characterized by high temperatures, high geostress, extensive secondary porosity and natural fractures, and high reservoir heterogeneity. Generic hydraulic fracturing is difficult to create complex fractures. Temporary plugging and diversion fracturing technology injects temporary plugging agents to seal dominant fractures, achieving balanced extension across fracture clusters and increasing the reservoir stimulation volume (SRV).

[0003] Temporary plugging agents, key materials in temporary plugging and diversion fracturing technology, face the challenges of high temperatures in deep and ultra-deep formations. Furthermore, due to the high closure stresses in the reservoir, the width of the fractures is small, making it difficult for high-concentration proppants to enter. In typical field temporary plugging operations, temporary plugging agents and proppants are simply mixed in a specific ratio to support the cavity fractures. After the temporary plugging agent is completely degraded, the high closure stresses can cause the oil flow channel to reclose, reducing the fracture conductivity.

[0004] Therefore, it is of great significance to research and develop a new temporary plugging agent. Summary of the Invention

[0005] The present invention aims to overcome the problems of prior art temporary plugging agents, such as poor temperature and salt resistance in deep / ultra-deep formations and low fracture conductivity after complete degradation of the temporary plugging agents. The present invention provides a gel-coated temporary plugging agent, a preparation method, and applications thereof. The gel-coated temporary plugging agent can effectively seal fractures under high / ultra-high temperature conditions within the fracturing period (typically 4-6 hours), and the exposure of internal proppants after degradation can enhance the conductivity of the fractured fractures.

[0006] To achieve the above-mentioned object, the present invention provides a gel-coated temporary plugging agent in a first aspect, wherein the gel-coated temporary plugging agent comprises a proppant core and a degradable gel shell coated on the outer surface of the proppant core, wherein the degradable gel shell is formed by a gel shell gelling liquid, and the gel shell gelling liquid comprises a small molecule comonomer and a degradable cross-linking agent, and the small molecule comonomer comprises one or more of acrylamide, N,N-dimethylacrylamide, acrylic acid, hydroxyethyl acrylate, benzyl acrylate, 2-propyl acrylic acid, 2-acrylamide-2-methylpropanesulfonic acid, and N-vinyl pyrrolidone.

[0007] The second aspect of the present invention provides a method for preparing the aforementioned gel-coated temporary plugging agent, wherein the preparation method comprises: (S1) spraying the gel shell gel solution onto the outer surface of the proppant core to polymerize it in situ to obtain a reaction product; (S2) washing, dehydrating, vibrating screening, and drying the reaction product to obtain a gel-coated temporary plugging agent.

[0008] A third aspect of the present invention provides a use of the aforementioned gel-coated temporary plugging agent in temporary plugging and diversion fracturing of deep / ultra-deep layers.

[0009] Through the above technical solution, the beneficial effects of the present invention include: (1) The gel-coated temporary plugging agent of the present invention is composed of a modified proppant core and a degradable gel shell. At 170°C, the crack plugging strength is ≥30 MPa, and the crack permeability after degradation is >150 mD. It has high temporary plugging strength at high temperatures. The exposed proppant after degradation can support the fracturing crack, form an effective oil flow channel, and enhance the flow conductivity.

[0010] (2) The gel-coated temporary plugging agent of the present invention achieves multiple effects such as temporary plugging and fracture support, and solves operational difficulties such as temporary plugging and fracture support difficulties in high closure stress reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is the synthesis mechanism and structural diagram of the gel-coated temporary plugging agent provided by the present invention; Figure 2 This is an optical microscope photograph of the gel-coated temporary plugging agent prepared in Example 1 of the present invention; Figure 3 It is a schematic diagram of a preparation method of a gel-coated temporary plugging agent provided by the present invention. DETAILED DESCRIPTION

[0012] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0013] As described above, the first aspect of the present invention provides a gel-coated temporary plugging agent, wherein the gel-coated temporary plugging agent includes a proppant core and a degradable gel shell coated on the outer surface of the proppant core, wherein the degradable gel shell is formed by in-situ polymerization of a gel shell gelling liquid on the proppant surface, the gel shell gelling liquid includes a small molecule comonomer and a degradable cross-linking agent, and the small molecule comonomer includes one or more of acrylamide, N,N-dimethylacrylamide, acrylic acid, hydroxyethyl acrylate, benzyl acrylate, 2-propyl acrylic acid, 2-acrylamide-2-methylpropanesulfonic acid, and N-vinyl pyrrolidone.

[0014] In order to overcome the above technical difficulties, the inventors of the present invention provide a gel-coated temporary plugging agent, such as Figure 1 As shown, Figure 1 This is the synthesis mechanism and structure diagram of the gel-coated temporary plugging agent provided by the present invention. Figure 1 It can be seen that: first, the surface of the proppant core is subjected to a hydroxylation treatment; then, the proppant core is modified with a modifier to introduce monomer reactive groups on the proppant surface. The gel-forming solution mainly composed of small molecule comonomers and degradable cross-linking agent St is polymerized in situ on the proppant surface to form a gel-coated proppant structure, that is, the gel-coated temporary plugging agent includes a proppant core and a degradable gel shell coated on the outer surface of the proppant core. The gel-coated temporary plugging agent provided by the present invention has a soft-coated particle-type temporary plugging agent structure, the gel-coated temporary plugging agent includes a proppant core (solid phase core) and a degradable gel shell coated on the outer surface of the proppant core, wherein the proppant core (solid phase core) is a modified proppant core (solid phase core), and the modification method includes: First, the proppant is hydroxylated to obtain the schematic diagram The proppant represented by Secondly, The modified silane coupling agent shown is contacted for modification to expose the active reactive group Mt; Then, the small molecule comonomer, the degradable cross-linking agent St and the surface active reactive groups of the modified proppant come into contact with each other to react and obtain a product; Finally, the product is eluted and freeze-dried to obtain Figure 1 Gel-coated temporary plugging agent with the structure shown.

[0015] The gel-coated temporary plugging agent of the present invention can seal fractures. The solid-phase proppant core acts as a high-strength bridging support within the sealing structure, while the degradable gel shell fills the gaps formed between the bridged solid-phase particles, further enhancing the fracture sealing strength. Under reservoir temperature and fluid conditions, the degradable shell spontaneously degrades into a low-viscosity fluid after the fracturing operation (typically 4-6 hours), minimizing damage to the reservoir. The exposed proppant core effectively supports the fractured fractures. Under high in-situ stress in deep / ultra-deep formations, conventional gel-based temporary plugging agents can prematurely degrade in high-temperature environments, rendering the sealing layer ineffective, and form cavities after degradation / dissolution, causing the fractures opened by the fractures to reclose. Compared to conventional gel temporary plugging agent / proppant hybrid systems, the gel-coated temporary plugging agent of the present invention achieves multiple effects, including temporary plugging and fracture propping, while simultaneously addressing the difficulties of temporary plugging and fracture propping in reservoirs with high fracture closure stress.

[0016] According to the present invention, the degradable shell is obtained by in-situ copolymerization and cross-linking of one or more comonomers and a degradable cross-linking agent on the surface of the modified proppant.

[0017] According to the present invention, the gel shell forming solution further comprises an initiator, a surfactant and water; preferably, based on the total weight of the gel shell forming solution, the content of the small molecule monomer is 10-24 weight percent, the content of the degradable cross-linking agent is 5-16 weight percent, the content of the initiator is 0.05-0.25 weight percent, the content of the surfactant is 0.1-0.5 weight percent, and the balance is water; preferably, based on the total weight of the gel shell forming solution, the content of the small molecule monomer is 18-22 weight percent, the content of the degradable cross-linking agent is 12-15 weight percent, the content of the initiator is 0.18-0.2 weight percent, the content of the surfactant is 0.25-0.4 weight percent, and the balance is water.

[0018] According to the present invention, the gel shell forming solution further comprises a pH regulator, the purpose of which is to adjust the pH value of the raw material to 7-8.

[0019] According to the present invention, the degradable crosslinking agent includes one or more of polyethylene glycol diacrylate, triethylene glycol diacrylate, neopentyl glycol diacrylate, 1,5-pentanediol diacrylate, ethoxylated trimethylolpropane triacrylate, and ditrimethylolpropane tetraacrylate, more preferably polyethylene glycol diacrylate (molecular weight 400).

[0020] According to the present invention, the initiator includes one or more of ammonium persulfate, potassium persulfate, a mixture of potassium persulfate and sodium bisulfite (mass ratio 1:1), azobisisobutylamidine hydrochloride, azobiscyanovaleric acid, and sodium azobisisopropylbenzenesulfonate, preferably azobisisobutylamidine hydrochloride; According to the present invention, the surfactant includes one or more of Triton X-100, coconut oil diethanolamide, coconut oil amidopropyl betaine, octadecyl dimethyl betaine, sodium dodecylbenzenesulfonate, and sodium alkylphenol polyoxyethylene ether carboxylate-10, and more preferably Triton X-100.

[0021] According to the present invention, the raw material of the proppant core is one or more of quartz sand, ceramsite, and high-purity calcium carbonate with a mesh size of 40-100 mesh, preferably 60-100 mesh. The raw material of the proppant will be rounded and sieved before use, and the roundness and sphericity will be not less than 0.8 and not less than 0.8.

[0022] According to the present invention, the proppant is modified by using a proppant modifier; preferably, the proppant modifier has a structure shown in formula (1): , formula (1); Wherein, R is one or more of C1-C5 alkylene groups; preferably, R is one or more of C1-C4 alkylene groups; Mt is -NH2, -CH3, -Cl, 、 One or more of .

[0023] According to the present invention, the proppant modifier is a silane coupling agent. Preferably, the proppant modifier includes one or more of vinyltriethoxysilane, vinyltrimethoxysilane, vinyltri(2-methoxyethoxy)silane, trichlorohexylsilane, 3-aminopropyltrimethoxysilane, 3-(methacryloyloxy)propyltrimethoxysilane, methacryloxypropyltri(trimethylsiloxy)silane, and octyltrimethoxysilane, more preferably vinyltrimethoxysilane.

[0024] According to the present invention, the average particle diameter of the proppant core is 150-380 μm, preferably 155-275 μm.

[0025] According to the present invention, the average thickness of the degradable gel shell is 245-432 μm, preferably 248-359 μm.

[0026] According to the present invention, the volume ratio of the gel-coated temporary plugging agent to the proppant core is (0.7-1.6):1, preferably (0.78-1.6):1.

[0027] According to the present invention, before modifying the proppant with a proppant modifier, the proppant surface may preferably be cleaned first. Specifically, 1000-2000 mL of piranha solution (a mixed solution of concentrated sulfuric acid and hydrogen peroxide in a mass ratio of 7:3) is used to clean the proppant surface. Then, the cleaned proppant surface is subjected to hydroxylation treatment.

[0028] The second aspect of the present invention provides a method for preparing the aforementioned gel-coated temporary plugging agent, wherein the preparation method comprises: (S1) spraying the gel shell gel solution onto the outer surface of the proppant core to polymerize it in situ to obtain a reaction product; (S2) washing, dehydrating, vibrating screening, and drying the reaction product to obtain a gel-coated temporary plugging agent.

[0029] According to the present invention, the weight ratio of the gel shell forming solution to the proppant core is (1-5):1, preferably (1-2.5):1.

[0030] According to the present invention, the spraying method includes a high-pressure spraying method. Preferably, the conditions of the high-pressure spraying method include: a pressure of 5-10 MPa, preferably 5-7 MPa.

[0031] According to the present invention, the proppant core and gel shell gel solution is placed in a mixer at a temperature of 95-130°C and a pot rotation speed of 200-600 rpm; preferably, the temperature is 100-130°C and the pot rotation speed is 300-600 rpm. The reaction time is preferably 2-2.5 hours. Alternatively, the gel shell gel solution can be prepared in the mixer.

[0032] According to the present invention, the preparation method further comprises: before step (S1), modifying the proppant core: (S1-1) hydroxylating the surface of the proppant core; (S1-2) In an organic alcohol solvent, the product obtained in step (S1-1) is contacted with a proppant modifier for modification to obtain a modified proppant.

[0033] According to the present invention, in step (S1-1), the conditions of the hydroxylation treatment include: pH=7-8, temperature of 20-25°C, and time of 2-4 hours.

[0034] According to the present invention, in step (S1-2), the conditions of the modification treatment include: pH value of 8-10, reaction temperature of 40-60°C, and reaction time of 2-4h.

[0035] According to a preferred embodiment of the present invention, Figure 3 As shown, a schematic diagram of a preparation method of a gel-coated temporary plugging agent provided by the present invention is shown. Figure 3 It can be seen that the preparation method of the granular gel-coated temporary plugging agent includes: (1) Clean the proppant surface first: Soak 60-100 mesh proppant (e.g., ceramsite) in a pre-prepared 1000-2000 mL piranha solution (a mixture of concentrated sulfuric acid and hydrogen peroxide at a mass ratio of 7:3). After cleaning the proppant surface, perform a hydroxylation treatment. Soak at room temperature (20-25°C) for 2-4 hours, filter, and rinse with pure water. Take the cleaning solution and measure the pH using a pH test paper. When the pH of the cleaning solution is 7-8, filter and dry to obtain surface hydroxylated solid particles. (2) Proppant modification: the concentration of the modifier (e.g., vinyltrimethoxysilane) is 1-7%, water is 2-10%, and the remaining components are alcohol solvents. The amount of the pH adjuster is such that the pH value of the raw material is adjusted to 8-10. The reaction temperature is 40-60°C and the reaction time is 2-4 hours to obtain a reactant. The reactant is washed with ethanol several times and then vacuum dried to obtain a modified proppant. (3) Take the gel shell gel solution (including small molecule comonomer, degradable crosslinking agent, initiator, surfactant and water, wherein the small molecule comonomer can be preferably acrylic acid, 2-acrylamide-2-methylpropanesulfonic acid, the degradable crosslinking agent is polyethylene glycol diacrylate, the initiator is 2,2'-azobisisobutylamidine dihydrochloride, and the surfactant is Triton X-100) and add 3-5 kg ​​of powder after drying to a mixer, heat the temperature to 95-130°C at a rate of 5°C / min, set the pot rotation speed at 200-400 rpm, and preheat for 20-80 minutes. Use high-pressure spraying to evenly spray the gel shell gel mixture into the modified proppant. The mass ratio of the gel shell gel solution to the proppant is preferably 2:1, and the reaction time is preferably 2-2.5 hours to obtain the reaction product; (4) The reaction product is washed, dehydrated, vibrated and screened, and dried to obtain a gel-coated temporary plugging agent.

[0036] A third aspect of the present invention provides a use of the aforementioned gel-coated temporary plugging agent in temporary plugging and diversion fracturing of deep / ultra-deep layers.

[0037] The present invention will be described in detail below through examples.

[0038] In the following examples and comparative examples: In the present invention, unless otherwise specified, the raw materials used are commercially available products in the art.

[0039] The structure of the gel-coated temporary plugging agent in the present invention is measured by a Leica industrial inverted microscope, which is purchased from Leica Microsystems of Germany and has a model number of DMi8M / C / A. The temporary plugging strength and post-degradation permeability test of the gel-coated temporary plugging agent in the present invention is conducted by using a steel fake core to simulate a crack, wherein the crack length is 9.95-10.05 cm, the crack height is 4.5-10.1 mm, and the inner surface of the crack has a certain degree of roughness.

[0040] A carrier fluid (viscosity of 4-8 mPa·s) containing 3-5% of a temporary plugging agent was prepared using simulated formation water and placed in an intermediate container. The fluid was then aged in an oven at 170°C for 4-6 hours. The tracking confining pressure was adjusted to always be 2 MPa higher than the injection pressure. The fluid was injected into the simulated fracture at a constant flow rate of 3 mL / min. When the pressure rose to 10 MPa and steadily increased to 20 MPa, simulated formation water was injected at the same flow rate. As the fluid was injected, the injection pressure gradually increased until it reached a test point and then broke through. The injection pressure at this test point was considered the maximum temporary plugging pressure at which the temporary plugging agent formed a sealing layer, and the temporary plugging agent's fracture sealing strength was measured.

[0041] A temporary plugging agent was evenly applied at a thickness of 3-6 mm within a simulated core fracture. The temperature was set at 170°C, and the tracking confining pressure was adjusted to always be 2-3 MPa higher than the injection pressure. Simulated formation water was injected at a constant flow rate through the inlet. When the injection pressure rose to 15 MPa, the injection was switched to a constant pressure injection. During this period, no flow was observed at the outlet. After 8-15 hours, the temporary plugging section was breached. The permeability of the gel-coated temporary plugging agent after degradation was then measured using a constant flow rate of 5 mL / min.

[0042] Example 1 This example is intended to illustrate the preparation of a gel-coated temporary plugging agent: a gel (AA-AMPS-PEGDA)-coated (ceramsite) type granular temporary plugging agent.

[0043] The specific process flow of the gel-coated temporary plugging agent is as follows: Figure 3 As shown, the synthetic route for preparing the gel (AA-AMPS-PEGDA) coated (ceramsite) type particle temporary plugging agent in this embodiment includes: The specific preparation method includes two aspects: ceramsite modification and synthesis of gel (AA-AMPS-PEGDA) coated (ceramsite) type granular temporary plugging agent: (1) First, clean the surface of the proppant: soak 5 kg of 60-mesh ceramsite (roundness 0.9, sphericity 0.85) in a pre-prepared 1500 mL piranha solution (a mixed solution of concentrated sulfuric acid and hydrogen peroxide with a mass ratio of 7:3). After cleaning the surface of the ceramsite, perform a hydroxylation treatment. After soaking at room temperature (20°C) for 2 hours, filter and rinse with pure water. Take the cleaning solution and measure the pH with a test paper. When the pH of the cleaning solution is 7, filter and dry it to obtain surface hydroxylated solid phase particles. (2) Modification of solid phase proppant: 0.6 kg of vinyl trimethoxysilane (effective content > 98%) and 1 kg of pure water were dissolved in 8.3 kg of ethanol to obtain a modifier, and 0.2 kg of ammonia water (effective content 26%) was added to adjust the pH of the modifier to 9. 5 kg of cleaned ceramsite was mixed with 10 kg of the modifier (vinyl trimethoxysilane) and stirred. The temperature of the device was adjusted to 55 ° C and the stirring rate of the device was 300 rpm. The reaction was stopped after 4 hours. The mixture was filtered and the obtained ceramsite was repeatedly washed with ethanol 3-4 times. After filtering, it was dried in an oven at 100 ° C to obtain a modified proppant (modified ceramsite); (3) Acrylic acid (0.4 kg), 2-acrylamide-2-methylpropanesulfonic acid (0.8 kg), polyethylene glycol diacrylate (0.8 kg), a surfactant (0.015 kg), an initiator (0.01 kg) and the remaining water were mixed to form a solution. Sodium hydroxide was used as a pH adjuster and the pH of the solution was adjusted to 8. Triton X-100 and azobisisobutyramidine hydrochloride were used as surfactant and initiator respectively to complete the preparation of the gel shell gel solution. (4) Add 5 kg of modified ceramsite to the mixer and heat the temperature to 110 °C at a rate of 5 °C / min. Set the pot rotation rate at 200 rpm and preheat for 15 minutes. Use high-pressure spraying (high pressure of 6 MPa) to evenly spray the gelling liquid mixture into the modified proppant. The mass ratio of gelling liquid to proppant is preferably 2:1. The reaction time is 2 hours. After natural cooling, the reaction product is obtained. The reaction product is washed with ethanol, dehydrated, vibrated and screened, and then dried in a vacuum drying oven at 40 °C. The preparation of the gel (AA-AMPS-PEGDA) coated (ceramsite) type granular temporary plugging agent is completed.

[0044] The gel-coated temporary plugging agent includes a proppant core and a degradable gel shell coated on the outer surface of the proppant core, wherein the average particle diameter of the proppant core is 270µm; the average thickness of the degradable gel shell is 340µm; and the volume ratio of the gel-coated temporary plugging agent to the proppant core is 1.26:1.

[0045] Fracture temporary plugging experiments were conducted using the gel-coated temporary plugging agent prepared in this example. A steel dummy core simulated a fracture with a length of 9.8 cm, a height of 10 mm, and a rough inner surface. A carrier fluid (viscosity of 5.6 mPa·s) containing 3% of the temporary plugging agent was prepared using simulated formation water and placed in an intermediate container. The fluid was then aged at 170°C for 6 hours. The tracking confining pressure was adjusted to always exceed the injection pressure by 2 MPa. The fluid was injected into the simulated fracture at a constant flow rate of 3 mL / min. When the pressure reached 10 MPa and steadily increased to 20 MPa, simulated formation water was injected at the same flow rate. As the fluid was injected, the injection pressure gradually increased, reaching a test point where it broke through. The injection pressure at this test point was considered the maximum temporary plugging pressure of the temporary plugging agent, and the measured fracture plugging strength of the temporary plugging agent was 45 MPa.

[0046] A temporary plugging agent was evenly applied at a thickness of 5 mm within a simulated fracture core. The temperature was set at 170°C, and the tracking confining pressure was adjusted to always exceed the injection pressure by 2 MPa. Simulated formation water was injected at a constant flow rate through the inlet section. When the injection pressure increased to 15 MPa, the injection was switched to a constant pressure injection, with no liquid at the outlet. After 12 hours, the temporary plugging section was breached. Further injection was performed at a constant flow rate of 5 mL / min, and the permeability of the gel-coated temporary plugging agent after degradation was measured to be 452 mD.

[0047] The structure of the gel-coated temporary plugging agent is observed under a Leica industrial inverted microscope. Figure 2 As shown, Figure 2 This is a microscope photo of the gel-coated temporary plugging agent prepared in Example 1 of the present invention. Figure 2 It can be seen that after coating, the overall particles are spherical. After the aqueous solution is stable, the particle size of the gel-coated temporary plugging agent is 610μm, the particle size of the core proppant (ceramsite) is 270μm, and the thickness of the gel coating layer is 340μm.

[0048] Example 2 This embodiment is intended to illustrate the gel-coated temporary plugging agent prepared by the method of the present invention.

[0049] (1) Clean the surface of 5 kg of 60-mesh ceramsite in the same manner as in step (1) of Example 1.

[0050] (2) The surface of 5 kg of 60-mesh clean ceramsite was modified in the same manner as in step (2) of Example 1.

[0051] (3) Acrylic acid (0.35 kg), N-vinyl pyrrolidone (0.65 kg), polyethylene glycol diacrylate (0.7 kg), surfactant (0.015 kg), initiator (0.02 kg) and the remaining amount of water were mixed to form a solution. Sodium hydroxide was used as the pH adjuster and the pH of the solution was adjusted to 8. Triton X-100 and azobisisobutylamidine hydrochloride were used as the surfactant and initiator, respectively. The gelling solution was prepared.

[0052] (4) Add 5 kg of modified ceramsite to the mixer, heat the temperature to 105 °C at a rate of 5 °C / min, set the pot rotation speed at 300 rpm, and preheat for 50 min. Use high-pressure spraying to evenly spray the gelling liquid mixture into the modified proppant. The mass ratio of gelling liquid to proppant is preferably 2:1. The reaction time is 2.5 h, and the reaction product is obtained after natural cooling. The reaction product is washed with ethanol, dehydrated, vibrated and screened, and dried in a vacuum drying oven at 40 °C. The preparation of the gel (AA-NVP-PEGDA) coated (ceramsite) type granular temporary plugging agent is completed.

[0053] The gel-coated temporary plugging agent includes a proppant core and a degradable gel shell coated on the outer surface of the proppant core, wherein the average particle diameter of the proppant core is 256µm; the average thickness of the degradable gel shell is 359µm; and the volume ratio of the gel-coated temporary plugging agent to the proppant core is 1.4:1.

[0054] Fracture temporary plugging experiments were conducted using the gel-coated temporary plugging agent prepared in this example. A steel dummy core simulated a fracture with a length of 10 cm, a height of 6 mm, and a rough inner surface. A carrier fluid (viscosity of 4.8 mPa·s) containing 4% of the temporary plugging agent was prepared using simulated formation water and placed in an intermediate container. The fluid was then heated to 170°C and aged for 5 hours. The tracking confining pressure was adjusted to always exceed the injection pressure by 2.5 MPa. The fluid was injected into the simulated fracture at a constant flow rate of 5 mL / min. When the pressure rose to 10 MPa and steadily increased to 15 MPa, simulated formation water was injected at the same flow rate. As the fluid was injected, the injection pressure gradually increased, reaching a test point where it broke through. The injection pressure at this test point was considered the maximum temporary plugging pressure of the temporary plugging agent, and the measured fracture plugging strength of the temporary plugging agent was 37 MPa.

[0055] A temporary plugging agent was evenly applied at a thickness of 3 mm within a simulated core fracture. The temperature was set at 170°C, and the tracking confining pressure was adjusted to always exceed the injection pressure by 2 MPa. Simulated formation water was injected at a constant flow rate through the inlet section. When the injection pressure increased to 15 MPa, the injection was switched to a constant pressure injection. During this period, no liquid was injected at the outlet. After 10 hours, the temporary plugging section was breached. Further injection was performed at a constant flow rate of 5 mL / min, and the permeability of the gel-coated temporary plugging agent after degradation was measured to be 337 mD.

[0056] Example 3 This embodiment is intended to illustrate the gel-coated temporary plugging agent prepared by the method of the present invention.

[0057] (1) Clean the surface of 5 kg of 100-mesh quartz sand as in step (1) of Example 1.

[0058] (2) The surface of 5 kg of 100-mesh clean quartz sand was modified in the same manner as in step (2) of Example 1.

[0059] (3) Acrylic acid (0.4 kg), 2-acrylamide-2-methylpropanesulfonic acid (0.4 kg), polyethylene glycol diacrylate (0.5 kg), surfactant (0.02 kg), initiator (0.01 kg) and the remaining amount of water were mixed to form a solution. Sodium hydroxide was used as the pH adjuster and the pH of the solution was adjusted to 7. Triton X-100 and azobisisobutylamidine hydrochloride were used as the surfactant and initiator, respectively. The gelling solution was prepared.

[0060] (4) Add 5 kg of modified quartz sand to the mixer, heat the temperature to 95 ° C at a rate of 5 ° C / min, set the pot rotation rate at 300 rpm, and preheat for 15 minutes. Use high-pressure spraying (5.5 MPa) to evenly spray the gelling liquid mixture into the modified proppant. The mass ratio of gelling liquid to proppant is preferably 1:1. The reaction time is 2.5 hours. After natural cooling, the reaction product is obtained. The reaction product is washed with ethanol, dehydrated, vibrated and screened, and placed in a vacuum drying oven at 40 ° C to dry. The preparation of the gel (AA-AMPS-PEGDA) coated (quartz sand) type particle temporary plugging agent is completed. The gel-coated temporary plugging agent includes a proppant core and a degradable gel shell coated on the outer surface of the proppant core, wherein the average particle diameter of the proppant core is 155µm; the average thickness of the degradable gel shell is 248µm; and the volume ratio of the gel-coated temporary plugging agent to the proppant core is 1.6:1.

[0061] A temporary fracture plugging experiment was conducted using the gel-coated temporary plugging agent prepared in this example. A steel core simulated a fracture with a length of 10 cm, a height of 5 mm, and a rough inner surface. A carrier fluid containing 5% of the temporary plugging agent was prepared using simulated formation water and placed in an intermediate container. The mixture was then heated to 170°C and aged for 5 hours. The tracking confining pressure was adjusted to always exceed the injection pressure by 2 MPa. The fluid was injected into the simulated fracture at a constant flow rate of 5 mL / min. When the pressure rose to 10 MPa and steadily increased to 15 MPa, simulated formation water was injected at the same flow rate. As the fluid was injected, the injection pressure gradually increased, reaching a test point and breaking through. The injection pressure at this test point was considered the maximum temporary plugging pressure of the temporary plugging agent, and the measured crack plugging strength of the temporary plugging agent was 33 MPa.

[0062] A temporary plugging agent was evenly applied at a thickness of 2 mm within a simulated core fracture. The temperature was set at 170°C, and the tracking confining pressure was adjusted to always exceed the injection pressure by 2 MPa. Simulated formation water was injected at a constant flow rate through the inlet section. When the injection pressure increased to 15 MPa, the injection was switched to a constant pressure injection. During this period, no liquid was injected at the outlet. After 8 hours, the temporary plugging section was breached. Further injection was performed at a constant flow rate of 5 mL / min, and the permeability of the gel-coated temporary plugging agent after degradation was measured to be 154 mD.

[0063] Example 4 This embodiment is intended to illustrate the gel-coated temporary plugging agent prepared by the method of the present invention.

[0064] (1) Clean the surface of 5 kg of 50-mesh quartz sand in the same manner as in step (1) of Example 1.

[0065] (2) The surface of 5 kg of 50-mesh clean quartz sand was modified in the same manner as in step (2) of Example 1.

[0066] (3) Acrylic acid (0.6 kg), N-vinyl pyrrolidone (0.6 kg), polyethylene glycol diacrylate (0.8 kg), surfactant (0.01 kg), initiator (0.02 kg) and the remaining amount of water were mixed to form a solution. Sodium hydroxide was used as the pH adjuster and the pH of the solution was adjusted to 7. Triton X-100 and azobisisobutylamidine hydrochloride were used as the surfactant and initiator, respectively. The gelling solution was prepared.

[0067] (4) Add 5 kg of modified quartz sand to the mixer and heat the temperature to 130 °C at a rate of 5 °C / min. Set the pot rotation speed at 300 rpm and preheat for 15 min. Use high-pressure spraying (7 MPa) to evenly spray the gelling liquid mixture into the modified proppant. The mass ratio of gelling liquid to proppant is preferably 2.5:1. The reaction time is 2.5 h. After natural cooling, the reaction product is obtained. The reaction product is washed with ethanol, dehydrated, vibrated and screened, and then dried in a vacuum drying oven at 40 °C. The preparation of the gel (AA-NVP-PEGDA)-coated (quartz sand) type particle temporary plugging agent is completed.

[0068] The gel-coated temporary plugging agent includes a proppant core and a degradable gel shell coated on the outer surface of the proppant core, wherein the average particle diameter of the proppant core is 275µm; the average thickness of the degradable gel shell is 325µm; and the volume ratio of the gel-coated temporary plugging agent to the proppant core is 0.78:1.

[0069] A temporary fracture plugging experiment was conducted using the gel-coated temporary plugging agent prepared in this example. A steel core simulated a fracture with a length of 10 cm, a height of 5 mm, and a rough inner surface. A carrier fluid containing 5% by weight of the temporary plugging agent was prepared using simulated formation water and placed in an intermediate container. The temperature was set to 170°C and the mixture was aged for 5 hours. The tracking confining pressure was adjusted to always exceed the injection pressure by 2 MPa. The mixture was injected into the simulated fracture at a constant flow rate of 5 mL / min. When the pressure rose to 10 MPa and steadily increased to 15 MPa, simulated formation water was injected at the same flow rate. As the fluid was injected, the injection pressure gradually increased, reaching a test point and breaking through. The injection pressure at this test point was considered the maximum temporary plugging pressure of the temporary plugging agent, and the measured crack plugging strength of the temporary plugging agent was 30 MPa.

[0070] A temporary plugging agent was evenly applied at a thickness of 2 mm within the fractures of a simulated core (sandstone core matrix permeability: 10 mD). The temperature was set at 170°C, and the tracking confining pressure was adjusted to always exceed the injection pressure by 2 MPa. Simulated formation water was injected at a constant flow rate through the inlet section. When the injection pressure reached 10 MPa, the injection was switched to a constant pressure injection. During this period, no liquid was injected at the outlet. After 6 hours, the temporary plugging section was breached. Formation water was then injected at a constant flow rate of 5 mL / min, and the permeability of the gel-coated temporary plugging agent after degradation was measured to be 177 mD.

[0071] Comparative Example 1 The gel-coated temporary plugging agent was prepared in the same manner as in Example 1, except that: In step (3), the “acrylic acid (0.4 kg), 2-acrylamide-2-methylpropanesulfonic acid (0.8 kg), polyethylene glycol diacrylate (0.8 kg), surfactant (0.015 kg), initiator (0.01 kg) and balance water are mixed to form a solution” in Example 1 is replaced with “acrylic acid (0.4 kg), n-butyl acrylate (0.75 kg), polyethylene glycol diacrylate (0.8 kg), surfactant (0.015 kg), initiator (0.01 kg) and balance water are mixed to form a solution”.

[0072] The gel-coated temporary plugging agent includes a proppant core and a degradable gel shell coated on the outer surface of the proppant core, wherein the average particle diameter of the proppant core is 281µm; the average thickness of the degradable gel shell is 15µm; and the volume ratio of the gel-coated temporary plugging agent to the proppant core is 0.05:1.

[0073] The temporary plugging experiment of fractures was carried out by the same method as in Example 1. When the pressure was increased to 1 MPa, simulated formation water was injected at the same flow rate. The results showed that the plugging strength of the temporary plugging agent was 1.7 MPa.

[0074] The temporary plugging agent was evenly applied in a simulated core fracture at a thickness of 5 mm. After 5 hours, the temporary plugging section broke through. The gel-coated temporary plugging agent was then injected at a constant flow rate of 5 mL / min, and the permeability after degradation was measured to be 80 mD.

[0075] Since the small molecule comonomer used in Comparative Example 1 is n-butyl acrylate, the same experiment shows that the coating effect is poor, and the sealing and crack support and diversion performances are not good.

[0076] Comparative Example 2 The gel-coated temporary plugging agent was prepared in the same manner as in Example 1, except that in step (3), the “acrylic acid (0.4 kg), 2-acrylamide-2-methylpropanesulfonic acid (0.8 kg), polyethylene glycol diacrylate (0.8 kg)” in Example 1 was replaced with “acrylic acid (0.4 kg), 2-acrylamide-2-methylpropanesulfonic acid (0.8 kg), polyethyleneimine (molecular weight 300) (0.8 kg)”.

[0077] Comparative Example 2 uses polyethyleneimine, but no coating can be formed, and the obtained product does not form an obvious gel-coated proppant structure.

[0078] Comparative Example 3 The gel-coated temporary plugging agent was prepared in the same manner as in Example 1, except that in step (2), the "solid phase proppant modification: 0.6 kg of vinyl trimethoxysilane (effective content > 98%)" in Example 1 was replaced with "solid phase proppant modification: 0.45 kg of γ-glycidyloxypropyl trimethoxysilane" was used.

[0079] In Comparative Example 3, only the type of silane coupling agent was modified, and no coating was formed. The obtained product did not form an obvious gel-coated support structure.

[0080] Comparative Example 4 The gel-coated temporary plugging agent was prepared in the same manner as in Example 1, except that in step (2), the temperature in Example 1 was replaced by the temperature rise rate of 5°C / min to 110°C and the pot rotation speed was set at 200 rpm, with the temperature rise rate of 5°C / min to 50°C and the pot rotation speed was set at 40 rpm.

[0081] The gel-coated temporary plugging agent includes a proppant core and a degradable gel shell coated on the outer surface of the proppant core, wherein the average particle diameter of the proppant core is 265µm; the average thickness of the degradable gel shell is 20µm; and the volume ratio of the gel-coated temporary plugging agent to the proppant core is 0.07:1.

[0082] The temporary plugging experiment of fractures was carried out using the same method as in Example 1. When the pressure was increased to 1 MPa, simulated formation water was injected at the same flow rate. The results showed that the plugging strength of the temporary plugging agent was 1.4 MPa.

[0083] The temporary plugging agent was evenly applied to a simulated core fracture at a thickness of 5 mm. After 0.5 hours, the temporary plugging section broke through. The gel-coated temporary plugging agent was then injected at a constant flow rate of 5 mL / min, and the permeability after degradation was measured to be 77 mD.

[0084] In Comparative Example 4, the temperature and the mixer speed were lowered during the coating process, but the coating effect was also poor.

[0085] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A gel-coated temporary plugging agent, characterized in that: The gel-coated temporary plugging agent includes a proppant core and a degradable gel shell coated on the outer surface of the proppant core, wherein the degradable gel shell is formed by a gel shell gel solution, and the gel shell gel solution includes a small molecule comonomer and a degradable cross-linking agent, wherein the small molecule comonomer includes one or more of acrylamide, N,N-dimethylacrylamide, acrylic acid, hydroxyethyl acrylate, benzyl acrylate, 2-propyl acrylic acid, 2-acrylamide-2-methylpropanesulfonic acid, and N-vinyl pyrrolidone.

2. The gel-coated temporary plugging agent according to claim 1, wherein: The gel shell forming solution also includes an initiator, a surfactant and water; Preferably, based on the total weight of the gel shell gel solution, the content of the small molecule monomer is 10-24 weight percent, the content of the degradable cross-linking agent is 5-16 weight percent, the content of the initiator is 0.05-0.25 weight percent, the content of the surfactant is 0.1-0.5 weight percent, and the balance is water; Preferably, the pH value of the gel shell gel solution is 7-8.

3. The gel-coated temporary plugging agent according to claim 2, wherein: The degradable cross-linking agent includes one or more of polyethylene glycol diacrylate, triethylene glycol diacrylate, neopentyl glycol diacrylate, 1,5-pentanediol diacrylate, ethoxylated trimethylolpropane triacrylate, and ditrimethylolpropane tetraacrylate, more preferably polyethylene glycol diacrylate; And / or, the initiator includes one or more of ammonium persulfate, potassium persulfate, a mixture of potassium persulfate and sodium bisulfite, azobisisobutylamidine hydrochloride, azobiscyanovaleric acid, and sodium azobisisopropylbenzenesulfonate, preferably azobisisobutylamidine hydrochloride; And / or, the surfactant includes one or more of Triton X-100, coconut oil diethanolamide, coconut oil amidopropyl betaine, octadecyl dimethyl betaine, sodium dodecylbenzenesulfonate, and sodium alkylphenol polyoxyethylene ether carboxylate-10, more preferably Triton X-100.

4. The gel-coated temporary plugging agent according to claim 1, wherein: The proppant core includes one or more of ceramsite, quartz sand and high-purity calcium carbonate; Preferably, the proppant core is modified using a proppant modifier; Preferably, the proppant modifier has a structure shown in formula (1), , formula (1); Wherein, R is one or more C1-C5 alkylene groups; Mt is -NH2, -CH3, -Cl, 、 One or more of; Preferably, the proppant modifier includes one or more of vinyltriethoxysilane, vinyltrimethoxysilane, vinyltri(2-methoxyethoxy)silane, trichlorohexylsilane, 3-aminopropyltrimethoxysilane, 3-(methacryloyloxy)propyltrimethoxysilane, methacryloxypropyltri(trimethylsiloxy)silane, and octyltrimethoxysilane, more preferably vinyltrimethoxysilane.

5. The gel-coated temporary plugging agent according to any one of claims 1 to 4, wherein: The average particle diameter of the proppant core is 150-380 μm; and / or, the average thickness of the degradable gel shell is 245-432 µm; And / or, the volume ratio of the gel-coated temporary plugging agent to the proppant core is (0.7-1.6):

1.

6. A method for preparing the gel-coated temporary plugging agent according to any one of claims 1 to 5, characterized in that: The preparation method comprises: (S1) spraying the gel shell gel solution onto the outer surface of the proppant core to polymerize it in situ to obtain a reaction product; (S2) washing, dehydrating, vibrating screening, and drying the reaction product to obtain a gel-coated temporary plugging agent.

7. The preparation method according to claim 6, wherein The weight ratio of the gel shell gel solution to the proppant core is (1.5-2.5): 1; And / or, the spraying method includes a high-pressure spraying method. Preferably, the conditions of the high-pressure spraying method include: a pressure of 5-10 MPa; And / or, the spraying method includes: the temperature is 95-130° C., and the pot rotation speed is set in a mixer at 200-600 rpm.

8. The preparation method according to claim 6 or 7, wherein The preparation method further comprises: before step (S1), modifying the proppant core: (S1-1) hydroxylating the surface of the proppant core; (S1-2) In an organic alcohol solvent, the product obtained in step (S1-1) is contacted with a proppant modifier for modification to obtain a modified proppant.

9. The preparation method according to claim 8, wherein In step (S1-1), the conditions of the hydroxylation treatment include: pH = 7-8, temperature 20-25°C, and time 2-4h; And / or, in step (S1-2), the modification treatment conditions include: pH value of 8-10, reaction temperature of 40-60°C, and reaction time of 2-4h.

10. Use of the gel-coated temporary plugging agent according to any one of claims 1 to 5 in temporary plugging and diversion fracturing of deep / ultra-deep formations.

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