Oil-soluble temporary plugging agent with multi-layer microcapsule and preparation method thereof

Abstract

The present application relates to an oil-soluble temporary plugging agent with multilayer microcapsules and a preparation method thereof, and belongs to the technical field of oil field chemical industry and downhole operation. The microcapsule comprises a microcapsule core and a hydrophilic protective film coated on the surface of the microcapsule core, the microcapsule core is composed of modified low-melting-point polypropylene, oil-soluble additives and capsule-type trigger agent, and the hydrophilic protective film is obtained by drying and solidifying carboxymethyl cellulose sodium / polyvinyl alcohol coating solution. The present application promotes the degradation of the temporary plugging agent through the embedded oil-soluble additives and capsule-type trigger agent, wherein the capsule-type trigger agent releases the degradation-promoting component in a slow-release manner, realizes timed automatic degradation, ensures that the plugging layer disappears completely at a predetermined time while effectively plugging downhole fluid, thereby restoring the permeability of the formation and ensuring subsequent downhole operation and production, achieves the dual requirements of stability and preset timed automatic unblocking of the temporary plugging agent, and solves the problems in the background art.

Description

Technical Field

[0001] This invention belongs to the field of oilfield chemical and downhole construction technology, and specifically relates to an oil-soluble temporary plugging agent with multi-layer microcapsules and its preparation method. Background Technology

[0002] In oilfield operations such as well completion, workover, fracturing, and water shut-off / profile modification, temporary plugging agents are widely used as a key oilfield chemical to prevent downhole fluid cross-flow, improve stratification effectiveness, and ensure production safety. Currently, publicly available technologies both domestically and internationally mainly fall into three categories: water-based temporary plugging agents, acid-soluble plugging agents, and oil-soluble plugging agents. However, new slow-release temporary plugging agents that have emerged in recent years cannot be simply categorized as water-based, acid-soluble, or oil-soluble. Water-based temporary plugging agents primarily rely on substances capable of forming gelled or settled plugging layers in aqueous systems, such as polymer colloids and water-soluble microparticles. Many oilfield service units have used related products, but these plugging agents are significantly affected by water quality (such as high salinity and pH changes), resulting in unstable plugging and unblocking efficiency. Furthermore, long-term use may cause formation damage. Acid-soluble plugging agents generally use salts or acid-catalyzed polymers soluble in acid solutions. These products gradually dissolve after injection, relying on downhole acid injection or the natural acidic environment. However, their disadvantages include the potential for formation corrosion from acidic substances and significant fluctuations in the unblocking time. Most of these technologies focus on immediate plugging, lacking precise control over the unblocking time. Regarding oil-soluble temporary plugging agents, oil-soluble resins achieve plugging and automatic unblocking in the oil phase. However, analysis shows that these technologies often use a single oil-soluble polymer or resin, primarily relying on the thermal dissolution and swelling of the polymer in the oil phase to degrade the plugging agent. Their structure is relatively simple, resulting in insufficient adaptability to changes in downhole temperature and crude oil composition. This type of technology focuses on using oil-soluble additives to promote plugging agent dissolution, making it difficult to simultaneously meet the high mechanical strength and timed unblocking requirements needed for downhole plugging.

[0003] Currently, the sustained-release temporary plugging agent technology generally has the following shortcomings:

[0004] When using a single oil-soluble polymer or resin, the temporary plugging agent has insufficient mechanical strength and compressive strength, making it difficult to form a stable and uniform plugging layer downhole;

[0005] It is sensitive to downhole temperature and crude oil, and the unblocking time is difficult to control precisely. It may unblock too quickly or too late, resulting in unsatisfactory sealing effect.

[0006] The lack of an overall design to address the synergistic effect of chemical degradation and physical expansion during the degradation process of plugging agents results in residual plugging agent particles being difficult to remove after degradation, affecting subsequent oil layer penetration.

[0007] Most publicly available technologies in the field of downhole temporary plugging agents are aqueous or acid-soluble technologies, primarily relying on modified polyolefins or petroleum resins as a single system. Under high-temperature, crude oil-involved downhole environments, these often suffer from insufficient sealing layer strength, unstable degradation rates, and residual plugging agent particles after unblocking. Existing temporary plugging agents, under high-temperature, high-pressure, and crude oil-involved conditions, often fail to form a stable plugging layer downhole due to their loose structure and insufficient mechanical properties (e.g., the oil-soluble temporary plugging agent disclosed in CN104831401A suffers from insufficient mechanical properties). This makes it difficult to precisely control the unblocking time, resulting in premature unblocking (e.g., the small-particle-size water-soluble temporary plugging agent disclosed in CN105482793A suffers from premature unblocking), while others leave residues in the well due to incomplete degradation, severely affecting formation permeability and subsequent production. Therefore, existing temporary plugging agents cannot simultaneously meet the dual requirements of stable sealing and pre-set timed automatic unblocking. Summary of the Invention

[0008] To address the above problems, this invention provides an oil-soluble temporary plugging agent with multilayer microcapsules and its preparation method.

[0009] The first objective of this invention is to provide an oil-soluble temporary plugging agent having multilayer microcapsules, wherein the microcapsules include a microcapsule core and a hydrophilic protective film coating the surface of the microcapsule core, the microcapsule core being composed of modified low-melting-point polypropylene, an oil-soluble additive, and a capsule-type triggering agent, and the hydrophilic protective film being obtained by drying and curing a sodium carboxymethyl cellulose / polyvinyl alcohol coating solution;

[0010] In this invention, the oil-soluble additive lowers the softening temperature of the modified low-melting-point polypropylene polymer matrix, improves the swelling performance of the modified low-melting-point polypropylene polymer in the oil phase, and accelerates the timed degradation of the temporary plugging agent in the crude oil environment. The capsule-type triggering agent slowly releases weak acid (or weak base) under downhole oil phase and high temperature conditions, promoting matrix softening and swelling, chain segment relaxation and disintegration, thereby accelerating the overall degradation of the plugging agent and achieving timed unblocking. Thus, the oil-soluble temporary plugging agent of this invention is an oil-soluble temporary plugging agent with a dual triggering degradation mechanism.

[0011] Modified low-melting-point polypropylene serves as the main framework of the plugging agent, providing excellent physical sealing properties. It gradually softens, swells, and degrades in the downhole oil phase at 60–90°C, achieving automatic unplugging after temporary plugging.

[0012] Sodium carboxymethyl cellulose / polyvinyl alcohol coating solution is used to form a uniform and dense hydrophilic protective film on the surface of the microcapsule core, so that the resulting temporary plugging agent particles are stably suspended in the water-based medium. After being injected downhole, the film is quickly broken due to oil, releasing the core and promoting degradation.

[0013] The role of modified fillers: to be uniformly dispersed in the polymer matrix, improve the mechanical hardness, compressive strength and fatigue resistance of the temporary plugging agent particles, ensure the stability of the downhole plugging layer, and effectively prevent particle breakage under high pressure.

[0014] In a specific embodiment of the present invention, the oil-soluble temporary plugging agent is prepared from the following raw materials by weight percentage:

[0015] Modified low-melting-point polypropylene: 50–60 wt%

[0016] Oil-soluble additives: 15–25 wt%

[0017] Capsule-type trigger: 3–10 wt%

[0018] Sodium carboxymethyl cellulose / polyvinyl alcohol coating solution: 5–15 wt%

[0019] Modified filler: 5-15 wt%

[0020] The total percentage of each raw material is 100 wt%.

[0021] In a specific embodiment of the present invention, the oil-soluble temporary plugging agent is prepared from the following raw materials by weight percentage:

[0022] Modified low-melting-point polypropylene: 55 wt%

[0023] Oil-soluble additive: 19 wt%;

[0024] Capsule-type trigger: 6 wt%

[0025] Sodium carboxymethyl cellulose / polyvinyl alcohol coating solution: 10 wt%

[0026] Modified filler: 10wt%.

[0027] In a specific embodiment of the present invention, the oil-soluble temporary plugging agent is prepared from the following raw materials by weight percentage:

[0028] Modified low-melting-point polypropylene: 55 wt%

[0029] Oil-soluble additive: 20 wt%

[0030] Capsule-type trigger: 6 wt%

[0031] Sodium carboxymethyl cellulose / polyvinyl alcohol coating solution: 9 wt%;

[0032] Modified filler: 10wt%.

[0033] In a specific embodiment of the present invention, the oil-soluble temporary plugging agent is prepared from the following raw materials by weight percentage:

[0034] Modified low-melting-point polypropylene: 55 wt%

[0035] Oil-soluble additive: 19 wt%;

[0036] Capsule-type trigger: 7 wt%

[0037] Sodium carboxymethyl cellulose / polyvinyl alcohol coating solution: 9 wt%

[0038] Modified filler: 10wt%.

[0039] In a specific embodiment of the present invention, the oil-soluble additive is diisooctyl dioctanoate, which not only functions as an oil-soluble additive but also as a plasticizer, improving the plasticity of the microcapsule core.

[0040] In a specific embodiment of the present invention, the capsule-type trigger is a maleic anhydride-modified polymer microcapsule, which can achieve timed unblocking of oil-soluble temporary plugging agents in 3 to 7 days.

[0041] In a specific embodiment of the present invention, the coated maleic anhydride-modified polymer microcapsules comprise the following components by weight percentage:

[0042] Maleic anhydride-grafted polypropylene: 50–65 wt%

[0043] Toluene diisocyanate: 10–15 wt%

[0044] Ethylenediamine: 3–8 wt%

[0045] First surfactant: 0.5-3%;

[0046] First organic solvent: 15–25 wt%

[0047] Inorganic filler: 0.2–0.5 wt%.

[0048] In a specific embodiment of the present invention, the first surfactant is one or a mixture of several nonionic and anionic surfactants, such as polyoxyethylene castor oil, polysorbate surfactants, sodium dodecyl sulfate, Tween 80, Span 80, etc.

[0049] In a specific embodiment of the present invention, the first surfactant is a mixture of Tween 80 and Span 80 in any ratio.

[0050] Preferably, in the first surfactant at a weight percentage of 0.5 to 3%, the weight percentage of Tween is 1 to 2 wt%, and the weight percentage of Span80 is 0.5 to 1 wt%.

[0051] In a specific embodiment of the present invention, the first organic solvent is one of halogenated hydrocarbons, organic esters and ketone solvents, such as dichloromethane, ethyl acetate, acetone, n-hexane, etc.

[0052] Preferably, the first organic solvent is dichloromethane.

[0053] In a specific embodiment of the present invention, the inorganic filler is one of nano-to-submicron grade nano-silica, nano-talc, nano-alumina, nano-montmorillonite, or nano-titanium dioxide, or one of nano-to-submicron grade aluminosilicate fillers.

[0054] Preferably, the inorganic filler is nano-silica.

[0055] In a specific embodiment of the present invention, the sodium carboxymethyl cellulose / polyvinyl alcohol coating solution includes a solid component and a solvent component;

[0056] The solid component comprises the following components by weight percentage:

[0057] Sodium carboxymethyl cellulose: 60–80 wt% of the solids;

[0058] Polyvinyl alcohol: 18–35 wt% of the solids component;

[0059] Second surfactant: accounting for 0.5 to 6 wt% of the solid component.

[0060] In a specific embodiment of the present invention, the mass concentration of the sodium carboxymethyl cellulose / polyvinyl alcohol coating solution is 3-10 wt%.

[0061] In a specific embodiment of the present invention, the solvent component includes water.

[0062] In a specific embodiment of the present invention, the solvent component further includes an auxiliary solvent.

[0063] In a specific embodiment of the present invention, the mass ratio of the auxiliary solvent to the solvent component is 1 to 3:100.

[0064] The auxiliary solvent is a second organic solvent miscible with water, preferably ethanol.

[0065] In a specific embodiment of the present invention, the second surfactant is one or a mixture of several nonionic and anionic surfactants, such as polyoxyethylene castor oil, polysorbate surfactants, sodium dodecyl sulfate, Tween 80, Span 80, etc. Preferably, the second surfactant is Tween 80.

[0066] In a specific embodiment of the present invention, the modified filler is one of modified nano-silica, modified nano-talc, modified nano-alumina, modified nano-montmorillonite, and modified nano-titanium dioxide. Preferably, the modified filler is modified nano-silica.

[0067] In a specific embodiment of the present invention, the particle size of the modified filler is 10-100 nm.

[0068] In a specific embodiment of the present invention, the particle size of the oil-soluble temporary plugging agent is 100–300 μm. Preferably, the particle size of the oil-soluble temporary plugging agent is 100–200 μm.

[0069] A second objective of this invention is to provide a method for preparing an oil-soluble temporary plugging agent having multilayer microcapsules, comprising:

[0070] The dried modified low-melting-point polypropylene, oil-soluble additives, capsule-type triggering agents, and modified fillers are mixed together.

[0071] The resulting molten mixture is dissolved in a third organic solvent and then granulated by spray molding to obtain microcapsule cores.

[0072] The microcapsule core was sprayed with a sodium carboxymethyl cellulose / polyvinyl alcohol coating solution, dried and solidified to obtain an oil-soluble temporary plugging agent.

[0073] In a specific embodiment of the present invention, the preparation of the encapsulated trigger is as follows:

[0074] Maleic anhydride-grafted polypropylene, a first surfactant, and a first organic solvent are used to prepare an oil phase;

[0075] The oil phase is added to an aqueous solution containing ethylenediamine and stirred to obtain a water-in-oil emulsion with a diameter of 5-50 μm.

[0076] Toluene diisocyanate was added dropwise to a water-in-oil emulsion. The mixture was stirred and reacted at a first preset temperature for 1–2 hours. The temperature was then raised to a second preset temperature and maintained for 0.5–1 hours. The mixture was centrifuged, the precipitate was collected, washed, and dried to obtain a capsule-type trigger.

[0077] In a specific embodiment of the present invention, the first preset temperature is 30-60°C, and the second preset temperature is 60-70°C.

[0078] In a specific embodiment of the present invention, the mixing temperature is 120-160°C, the mixing time is 5-10 min, and the mixing shear rate is 100-200 rpm.

[0079] In a specific embodiment of the present invention, the preparation of the sodium carboxymethyl cellulose / polyvinyl alcohol coating solution includes:

[0080] Sodium carboxymethyl cellulose and solvent components are mixed evenly to obtain a sodium carboxymethyl cellulose solution;

[0081] Add sodium carboxymethyl cellulose solution to polyvinyl alcohol while stirring until polyvinyl alcohol dissolves. Add a second surfactant, stir until homogeneous, filter, and adjust the total solids content to obtain sodium carboxymethyl cellulose / polyvinyl alcohol coated solution.

[0082] In a specific embodiment of the present invention, the third organic solvent is one of the volatile organic solvents, such as cyclohexane.

[0083] In a specific embodiment of the present invention, the particle size of the microcapsule core is 100-200 μm.

[0084] The beneficial effects of this invention are:

[0085] This invention discloses an oil-soluble temporary plugging agent with multi-layer microcapsules and its preparation method. The oil-soluble temporary plugging agent is an oil-soluble temporary plugging agent with a dual-trigger degradation mechanism. Both the embedded oil-soluble additive and the capsule-type trigger can promote the degradation of the temporary plugging agent. The capsule-type trigger slowly releases the degradation-promoting components, achieving automatic degradation at a set time (5-10 days). This ensures that the plugging layer effectively seals downhole fluids while completely disappearing within a predetermined time, thereby restoring formation permeability and guaranteeing subsequent downhole operations and production. This achieves the dual requirements of stability and pre-set timed automatic unblocking of the temporary plugging agent, solving the problems in the prior art.

[0086] The oil-soluble temporary plugging agent of the present invention can achieve at least 95% automatic dissolution within 3 to 7 days after the addition of the oil phase in a downhole environment of 60 to 90°C, as demonstrated by laboratory simulation tests. This ensures that the downhole passage can be restored on time after temporary plugging. This unblocking timing is about 20%–30% smaller than the unblocking fluctuation range of traditional single oil-soluble materials.

[0087] Because of the microcapsule core and outer hydrophilic membrane used in this invention, the temporary plugging agent particles achieve uniform dispersion and long-term stability in the injected water-based liquid. After the sealing layer is formed, it is well bonded to the pore wall through the bridging effect. Experimental data show that in the standard pressure test, the compressive strength of the sealing layer composed of this plugging agent is increased by about 15%–20%, which is significantly better than the prior art.

[0088] By employing a dual mechanism of embedded capsule-type triggering agent and oil-soluble additive, and through the combined action of temperature and crude oil, the plugging agent not only ensures the sealing effect downhole, but also leaves less than 5% of solid particles when unplugging, effectively avoiding long-term production losses caused by residual plugging agent downhole.

[0089] This invention utilizes modified fillers as reinforcing fillers to regulate the overall hardness and compressive strength of the particles, ensuring that they are not easily broken under high pressure. The results of downhole fluid pressure peak simulation tests show that the pressure limit of the plugging agent system can be increased by about 15%–25% compared with the unfilled product.

[0090] In summary, the oil-soluble temporary plugging agent of the present invention has the advantages of better mechanical properties of the plugging layer, more controllable unplugging time, and better adaptability to the downhole environment in solving the problems of unstable plugging, unplugging time, and residual plugging agent affecting downhole production in the prior art. It provides an efficient, economical and reliable technical solution for realizing temporary plugging and automatic unplugging in oilfields.

[0091] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description and claims. Detailed Implementation

[0092] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0093] The modified low-melting-point polypropylene used in the following examples is sourced from: Recommended manufacturer: Dow Chemical (China) Co., Ltd., model: Dowlex 2120 (in some examples, it may be replaced with an equivalent industrial-grade product).

[0094] Diisooctyl dioctanoate (oil-soluble additive) key parameters: viscosity at room temperature approximately 20–100 mPa·s, good thermal stability, and excellent compatibility with polypropylene. Recommended manufacturer: BASF (China) Co., Ltd., model: DI-65, or equivalent industrial grade product;

[0095] Key parameters of modified nano-silica: average particle size approximately 12 nm; specific surface area approximately 200 m². 2 / g, modified to enhance compatibility with the matrix. Recommended manufacturer: Evonik Specialty Chemicals (Shanghai) Co., Ltd., model: Aerosil 200, or an equivalent industrial-grade product.

[0096] Example 1: The purpose is to provide an oil-soluble temporary plugging agent:

[0097] The main components and their weight contents of the oil-soluble temporary plugging agent are shown below:

[0098] Modified low-melting-point polypropylene: 55 wt%; diisooctyl dioctanoate: 19 wt%; maleic anhydride-modified polymer microcapsules: 6 wt%; sodium carboxymethyl cellulose / polyvinyl alcohol coating solution (containing Tween-80): 10 wt%; modified nano-silica: 10 wt%.

[0099] The preparation components, proportions, and preparation process of the maleic anhydride-modified polymer microcapsules (trigger component) are described below:

[0100] Maleic anhydride-grafted polypropylene: 60 wt%; Toluene diisocyanate (TDI): 12 wt%; Ethylenediamine (EDA): 6 wt%; Tween 80: 1.5 wt%; Span 80: 0.7 wt%; Dichloromethane: 19.5 wt%; Nano silica: 0.3 wt%

[0101] Preparation process:

[0102] Step 1: Raw material pretreatment:

[0103] Maleic anhydride-grafted polypropylene, ethylenediamine, modified nano-silica, and other solid components were dried at 60°C for 2 hours to remove moisture; dichloromethane, Tween 80, and Span 80 were prepared in advance to ensure they were uniformly usable at room temperature.

[0104] Step 2: Oil phase preparation:

[0105] Maleic anhydride-grafted polypropylene, Tween 80, and Span 80 were added to dichloromethane to prepare a uniform oil phase dispersion. The mixture was stirred at a temperature controlled between 40 and 60 °C to form a uniform oil phase suspension.

[0106] Step 3: Emulsion formation:

[0107] The oil phase is slowly added dropwise to a deionized aqueous solution containing ethylenediamine at a weight concentration of approximately 5%. An appropriate amount of emulsifier may be added to the aqueous phase (if applicable), such as 0.5 wt% of an emulsifier, such as sodium dodecyl sulfate (SDS). Using a high-speed homogenizer, emulsify for 10 minutes at 5000 rpm to form a water-in-oil emulsion with an average particle size of 5–50 μm.

[0108] Step 4: Interface aggregation and capsule wall formation:

[0109] In the emulsion, TDI is added slowly dropwise while the system temperature is maintained at 50°C, allowing ethylenediamine and TDI to undergo polyureaization or polyamidization reactions at the oil-water interface; the reaction continues for 1.5 hours until a dense and uniform capsule wall forms on the surface of the oil droplets, encapsulating the core material.

[0110] Step 5: Curing, washing and drying:

[0111] After the reaction was completed, the emulsion temperature was slowly raised to 50°C and the capsule wall was solidified for 50 minutes. The residual reactants and dichloromethane were removed by centrifugation and multiple water washing. Finally, the microcapsules were dried under vacuum at 55°C for 1.5 hours until the water content was less than 3%.

[0112] Step 6: Screening and Packaging

[0113] The dried microcapsules are graded using a vibrating sieve, and the required particle size range can be controlled within 20–150 μm. The qualified products are then packed into multi-layer aluminum foil bags or sealed containers, vacuum-packed, and stored at dry room temperature to ensure product stability and long shelf life (6–12 months).

[0114] The components and proportions of the sodium carboxymethyl cellulose / polyvinyl alcohol coating solution are as follows:

[0115] Sodium carboxymethyl cellulose, accounting for 70 wt% of the solids; polyvinyl alcohol, accounting for 29 wt% of the solids; Tween-80, accounting for 1 wt% of the solids.

[0116] The preparation process uses other solvents such as water and ethanol, but these are not included in the proportion of solid components.

[0117] The total solids content in sodium carboxymethyl cellulose / polyvinyl alcohol coated solution (containing Tween 80) is generally controlled at 3-10 wt%.

[0118] Preparation process of sodium carboxymethyl cellulose / polyvinyl alcohol coated solution (containing Tween 80):

[0119] Step 1: Dissolving stage:

[0120] In a suitable reaction vessel, add a certain amount of deionized water and heat to 55°C; slowly add a predetermined proportion of sodium carboxymethyl cellulose and stir at a medium speed (about 300 rpm) until the sodium carboxymethyl cellulose is completely dissolved to form a homogeneous high-viscosity solution.

[0121] Step 2: Mixing stage:

[0122] When the sodium carboxymethyl cellulose solution is cooled to 45°C, polyvinyl alcohol is gradually added while stirring to ensure that the polyvinyl alcohol is fully dissolved. After the system is stirred evenly, Tween-80 is added while stirring is maintained to ensure that Tween-80 is fully dispersed and helps to form a stable emulsion. If necessary, 2 wt% ethanol can be added as an auxiliary solvent to improve the flowability of the solution and control the viscosity of the solution.

[0123] Step 3: Filtration and Detection Stage

[0124] After thorough stirring, the solution is filtered through a fine-pore filter to remove insoluble impurities and ensure that the coating solution is transparent and uniform. The total solids content is checked and adjusted to the target range (5 wt%). If necessary, it is diluted or concentrated to adjust the solution. Finally, a uniform, transparent coating solution with appropriate viscosity is obtained.

[0125] The final preparation process of oil-soluble temporary plugging agent:

[0126] Step 1: Raw material pretreatment:

[0127] The modified low-melting-point polypropylene, diisooctyl dioctanoate, maleic anhydride-coated polymer microcapsules, and modified nano-silica were first dried. Drying conditions: drying at 55℃ for 2 hours to ensure that the moisture content of each component was below 1%, avoiding the influence of moisture on the melt blending effect during mixing.

[0128] Step 2: Melt blending:

[0129] The pretreated components are added to a mixing device (e.g., a twin-screw extruder) in a predetermined ratio and melt-mixed at a temperature of 140°C. Using a twin-screw extruder, the shear rate is controlled at 150 rpm and the mixing time is 8 minutes to ensure that all components are fully and uniformly dispersed and that the integrity of the microcapsules is maintained.

[0130] Step 3: Granulation and Sieving

[0131] The molten mixture is dispersed in a suitable volatile organic solvent (such as cyclohexane), pre-dispersed under high shear, and then atomized and dried at 80°C using a spray drying device to obtain preliminary granular masterbatch.

[0132] Crushing and sieving:

[0133] To further optimize the particle size distribution, the masterbatch was granulated using a low-temperature ball mill or air jet mill, and then the particle size was controlled and collected using a vibrating sieve. The target particle size was controlled within the range of 100–300 μm, with a preferred particle size of 100–200 μm.

[0134] 4. Coating with a hydrophilic protective film:

[0135] Sodium carboxymethyl cellulose / polyvinyl alcohol coated solution (containing Tween 80), with a solution concentration of approximately 6 wt%.

[0136] The sieved particles are placed in a fluidized bed coating machine and sprayed with coating liquid. Coating conditions: the inlet air temperature is controlled at 55℃; the spray pressure and flow rate are adjusted to ensure that the particle surface is uniformly covered with a liquid film, and the coating time is generally 20 minutes. The purpose is to form a uniform and dense hydrophilic protective film on the particle surface.

[0137] The coated granules were dried at 55°C for 1.5 hours to ensure that the coating film was completely cured and the final product had a moisture content of less than 1%.

[0138] If necessary, 0.1–0.5 wt% of an anti-caking agent (such as modified silica micro powder) can be added during or after the drying process to prevent caking.

[0139] The final particle size distribution of the product is determined by vibrating sieving. After reaching the requirement of 100-300μm, the product is packaged in multi-layer aluminum foil bags or sealed metal drums with nitrogen filling or vacuum filling. It is stored in dry, room temperature conditions to ensure a shelf life of 6-12 months.

[0140] Example 2: The purpose is to provide an oil-soluble temporary plugging agent:

[0141] The main components and their weight contents of the oil-soluble temporary plugging agent are shown below:

[0142] Modified low-melting-point polypropylene: 55 wt%; diisooctyl dioctanoate: 20 wt%; maleic anhydride-modified polymer microcapsules: 6 wt%; sodium carboxymethyl cellulose / polyvinyl alcohol coating solution (containing Tween-80): 9 wt%; modified nano-silica: 10 wt%

[0143] Maleic anhydride-modified polymer microcapsules (trigger component):

[0144] Main function: Slowly releases weak acid (or weak alkali) under downhole oil phase and high temperature conditions, promotes matrix softening and swelling, chain segment relaxation and disintegration, thereby accelerating the overall degradation of the plugging agent and achieving timed unblocking in 3 to 7 days.

[0145] The preparation components, proportions, and preparation process are described below:

[0146] Maleic anhydride-grafted polypropylene: 63 wt%; Toluene diisocyanate (TDI): 12 wt%; Ethylenediamine (EDA): 6 wt%; Tween 80: 1.5 wt%; Span 80: 0.7 wt%; Dichloromethane: 16.5 wt%; Nano silica: 0.3 wt%.

[0147] Preparation process:

[0148] Step 1: Raw material pretreatment:

[0149] Maleic anhydride-grafted polypropylene, ethylenediamine, modified nano-silica, and other solid components were dried at 60°C for 2 hours to remove moisture; dichloromethane, Tween 80, and Span 80 were prepared in advance to ensure they were uniformly usable at room temperature.

[0150] Step 2: Oil phase preparation:

[0151] Maleic anhydride-grafted polypropylene, Tween 80, and Span 80 were added to dichloromethane to prepare a uniform oil phase dispersion. The mixture was stirred at a temperature controlled between 40 and 60 °C to form a uniform oil phase suspension.

[0152] Step 3: Emulsion formation:

[0153] The oil phase is slowly added dropwise to a deionized aqueous solution containing ethylenediamine at a weight concentration of approximately 5%. An appropriate amount of emulsifier may be added to the aqueous phase (if applicable), such as 0.5 wt% of an emulsifier, such as sodium dodecyl sulfate (SDS). Using a high-speed homogenizer, emulsify for 10 minutes at 5000 rpm to form a water-in-oil emulsion with an average particle size of 5–50 μm.

[0154] Step 4: Interface aggregation and capsule wall formation:

[0155] In the emulsion, TDI is added slowly dropwise while the system temperature is maintained at 50°C, allowing ethylenediamine and TDI to undergo polyureaization or polyamidization reactions at the oil-water interface; the reaction continues for 1.5 hours until a dense and uniform capsule wall forms on the surface of the oil droplets, encapsulating the core material.

[0156] Step 5: Curing, washing and drying:

[0157] After the reaction was completed, the emulsion temperature was slowly raised to 50°C and the capsule wall was solidified for 50 minutes. The residual reactants and dichloromethane were removed by centrifugation and multiple water washing. Finally, the microcapsules were dried under vacuum at 55°C for 1.5 hours until the water content was less than 3%.

[0158] Step 6: Screening and Packaging

[0159] The dried microcapsules are graded using a vibrating sieve, and the required particle size range can be controlled within 20–150 μm. The qualified products are then packed into multi-layer aluminum foil bags or sealed containers, vacuum-packed, and stored at dry room temperature to ensure product stability and long shelf life (6–12 months).

[0160] Sodium carboxymethyl cellulose / polyvinyl alcohol coated solution (containing Tween 80):

[0161] The components and proportions of the sodium carboxymethyl cellulose / polyvinyl alcohol coating solution (containing Tween 80) are as follows:

[0162] Sodium carboxymethyl cellulose, accounting for 71 wt% of the solids; polyvinyl alcohol, accounting for 28 wt% of the solids; Tween-80, accounting for 1 wt% of the three components: sodium carboxymethyl cellulose, polyvinyl alcohol, and Tween-80.

[0163] The preparation process uses other solvents such as water and ethanol, but these are not included in the proportion of solid components.

[0164] The total solids content (sodium carboxymethyl cellulose / polyvinyl alcohol content) in sodium carboxymethyl cellulose / polyvinyl alcohol coated solution (containing Tween 80) is generally controlled at 3-10 wt%.

[0165] Preparation process of sodium carboxymethyl cellulose / polyvinyl alcohol coated solution (containing Tween 80):

[0166] Step 1: Dissolving stage:

[0167] In a suitable reaction vessel, add a certain amount of deionized water and heat to 55°C; slowly add a predetermined proportion of sodium carboxymethyl cellulose and stir at a medium speed (about 300 rpm) until the sodium carboxymethyl cellulose is completely dissolved to form a homogeneous high-viscosity solution.

[0168] Step 2: Mixing stage:

[0169] When the sodium carboxymethyl cellulose solution is cooled to 45°C, polyvinyl alcohol is gradually added while stirring to ensure that the polyvinyl alcohol is fully dissolved. After the system is stirred evenly, Tween-80 is added while stirring is maintained to ensure that Tween-80 is fully dispersed and helps to form a stable emulsion. If necessary, 2 wt% ethanol can be added as an auxiliary solvent to improve the flowability of the solution and control the viscosity of the solution.

[0170] Step 3: Filtration and Detection Stage

[0171] After thorough stirring, the solution is filtered through a fine-pore filter to remove insoluble impurities and ensure that the coating solution is transparent and uniform. The total solids content is checked and adjusted to the target range (5 wt%). If necessary, it is diluted or concentrated to adjust the solution. Finally, a uniform, transparent coating solution with appropriate viscosity is obtained.

[0172] The final preparation process of oil-soluble temporary plugging agent:

[0173] Step 1: Raw material pretreatment:

[0174] The modified low-melting-point polypropylene, diisooctyl dioctanoate, maleic anhydride-coated polymer microcapsules, and modified nano-silica were first dried. Drying conditions: drying at 55℃ for 2 hours to ensure that the moisture content of each component was below 1%, avoiding the influence of moisture on the melt blending effect during mixing.

[0175] Step 2: Melt blending:

[0176] The pretreated components are added to a mixing device (e.g., a twin-screw extruder) in a predetermined ratio and melt-mixed at a temperature of 140°C. Using a twin-screw extruder, the shear rate is controlled at 150 rpm and the mixing time is 8 minutes to ensure that all components are fully and uniformly dispersed and that the integrity of the microcapsules is maintained.

[0177] Step 3: Granulation and Sieving

[0178] The molten mixture is diluted in a suitable volatile organic solvent (such as cyclohexane), pre-dispersed under high shear, and then atomized and dried at 90°C using a spray drying device to obtain preliminary granular masterbatch.

[0179] Crushing and sieving:

[0180] To further optimize the particle size distribution, the masterbatch is granulated using a low-temperature ball mill or air jet mill, and then the particle size is controlled and collected using a vibrating sieve. The target particle size is controlled within the range of 100–300 μm, preferably 100–200 μm. This step is used to eliminate agglomerates or large particles formed during spray drying, ensuring that the final temporary plugging agent particle size meets the injection requirements.

[0181] Step 4: Coat with a hydrophilic protective film:

[0182] Sodium carboxymethyl cellulose / polyvinyl alcohol coated solution (containing Tween 80), with a solution concentration of approximately 6 wt%.

[0183] The sieved particles are placed in a fluidized bed coating machine and sprayed with coating liquid. Coating conditions: the inlet air temperature is controlled at 55℃; the spray pressure and flow rate are adjusted to ensure that the particle surface is uniformly covered with a liquid film, and the coating time is generally 20 minutes. The purpose is to form a uniform and dense hydrophilic protective film on the particle surface.

[0184] The coated granules were dried at 55°C for 1.5 hours to ensure that the coating film was completely cured and the final product had a moisture content of less than 1%.

[0185] If necessary, 0.1–0.5 wt% of an anti-caking agent (such as modified silica micro powder) can be added during or after the drying process to prevent caking.

[0186] The final particle size distribution of the product is determined by vibrating sieving. After reaching the requirement of 100-300 μm, it is packaged in multi-layer aluminum foil bags or sealed metal drums with nitrogen filling or vacuum filling. It is stored in dry, room temperature conditions to ensure a shelf life of 6-12 months.

[0187] Example 3: The purpose is to provide an oil-soluble temporary plugging agent:

[0188] The main components and their weight contents of the oil-soluble temporary plugging agent are shown below:

[0189] Modified low-melting-point polypropylene: 55 wt%; diisooctyl dioctanoate: 19 wt%; maleic anhydride-modified polymer microcapsules: 7 wt%; sodium carboxymethyl cellulose / polyvinyl alcohol coating solution (containing Tween-80): 9 wt%; modified nano-silica: 10 wt%

[0190] Maleic anhydride-modified polymer microcapsules (trigger component):

[0191] The preparation components, proportions, and preparation process are described below:

[0192] Maleic anhydride-grafted polypropylene: 58 wt%; Toluene diisocyanate (TDI): 12 wt%; Ethylenediamine (EDA): 6 wt%; Tween 80: 1.5 wt%; Span 80: 0.7 wt%; Dichloromethane: 21.5 wt%; Nano silica: 0.3 wt%

[0193] Preparation process:

[0194] Step 1: Raw material pretreatment:

[0195] Maleic anhydride-grafted polypropylene, ethylenediamine, modified nano-silica, and other solid components were dried at 60°C for 2 hours to remove moisture; dichloromethane, Tween 80, and Span 80 were prepared in advance to ensure they were uniformly usable at room temperature.

[0196] Step 2: Oil phase preparation:

[0197] Maleic anhydride-grafted polypropylene, Tween 80, and Span 80 were added to dichloromethane to prepare a uniform oil phase dispersion. The mixture was stirred at a temperature controlled between 40 and 60 °C to form a uniform oil phase suspension.

[0198] Step 3: Emulsion formation:

[0199] The oil phase is slowly added dropwise to a deionized aqueous solution containing ethylenediamine at a weight concentration of approximately 5%. An appropriate amount of emulsifier may be added to the aqueous phase (if applicable), such as 0.5 wt% of an emulsifier, such as sodium dodecyl sulfate (SDS). Using a high-speed homogenizer, emulsify for 10 minutes at 5000 rpm to form a water-in-oil emulsion with an average particle size of 5–50 μm.

[0200] Step 4: Interface aggregation and capsule wall formation:

[0201] In the emulsion, TDI is added slowly dropwise while the system temperature is maintained at 50°C, allowing ethylenediamine and TDI to undergo polyureaization or polyamidization reactions at the oil-water interface; the reaction continues for 1.5 hours until a dense and uniform capsule wall forms on the surface of the oil droplets, encapsulating the core material.

[0202] Step 5: Curing, washing and drying:

[0203] After the reaction was completed, the emulsion temperature was slowly raised to 50°C and the capsule wall was solidified for 50 minutes. The residual reactants and dichloromethane were removed by centrifugation and multiple water washing. Finally, the microcapsules were dried under vacuum at 55°C for 1.5 hours until the water content was less than 3%.

[0204] Step 6: Screening and Packaging

[0205] The dried microcapsules are graded using a vibrating sieve, and the required particle size range can be controlled within 20–150 μm. The qualified products are then packed into multi-layer aluminum foil bags or sealed containers, vacuum-packed, and stored at dry room temperature to ensure product stability and long shelf life (6–12 months).

[0206] The components and proportions of the sodium carboxymethyl cellulose / polyvinyl alcohol coating solution are as follows:

[0207] Sodium carboxymethyl cellulose, accounting for 68 wt% of the solids; polyvinyl alcohol, accounting for 31 wt% of the solids.

[0208] Tween-80: 1 wt% of the solids component;

[0209] The preparation process uses other solvents such as water and ethanol, but these are not included in the proportion of solid components.

[0210] Preparation process of sodium carboxymethyl cellulose / polyvinyl alcohol coated solution (containing Tween 80):

[0211] Step 1: Dissolving stage:

[0212] In a suitable reaction vessel, add a certain amount of deionized water and heat to 55°C; slowly add a predetermined proportion of sodium carboxymethyl cellulose and stir at a medium speed (about 300 rpm) until the sodium carboxymethyl cellulose is completely dissolved to form a homogeneous high-viscosity solution.

[0213] Step 2: Mixing stage:

[0214] When the sodium carboxymethyl cellulose solution is cooled to 45°C, polyvinyl alcohol is gradually added while stirring to ensure that the polyvinyl alcohol is fully dissolved. After the system is stirred evenly, Tween-80 is added while stirring is maintained to ensure that Tween-80 is fully dispersed and helps to form a stable emulsion. If necessary, 2 wt% ethanol can be added as an auxiliary solvent to improve the flowability of the solution and control the viscosity of the solution.

[0215] Step 3: Filtration and Detection Stage

[0216] After thorough stirring, the solution is filtered through a fine-pore filter to remove insoluble impurities and ensure that the coating solution is transparent and uniform. The total solids content is checked and adjusted to the target range (5 wt%). If necessary, it is diluted or concentrated to adjust the solution. Finally, a uniform, transparent coating solution with appropriate viscosity is obtained.

[0217] The final preparation process of oil-soluble temporary plugging agent:

[0218] Step 1: Raw material pretreatment:

[0219] The modified low-melting-point polypropylene, diisooctyl dioctanoate, maleic anhydride-coated polymer microcapsules, and modified nano-silica were first dried. Drying conditions: drying at 55℃ for 2 hours to ensure that the moisture content of each component was below 1%, avoiding the influence of moisture on the melt blending effect during mixing.

[0220] Step 2: Melt blending:

[0221] The pretreated components are added to a mixing device (e.g., a twin-screw extruder) in a predetermined ratio and melt-mixed at a temperature of 140°C. Using a twin-screw extruder, the shear rate is controlled at 150 rpm and the mixing time is 8 minutes to ensure that all components are fully and uniformly dispersed and that the integrity of the microcapsules is maintained.

[0222] Step 3: Granulation and Sieving

[0223] The molten mixture is diluted in a suitable volatile organic solvent (such as cyclohexane), pre-dispersed under high shear, and then atomized and dried at 100°C using a spray drying device to obtain preliminary granular masterbatch.

[0224] Crushing and sieving:

[0225] To further optimize the particle size distribution, the masterbatch is granulated using a low-temperature ball mill or air jet mill, and then the particle size is controlled and collected using a vibrating sieve. The target particle size is controlled within the range of 100–300 μm, preferably 100–200 μm. This step is used to eliminate agglomerates or large particles formed during spray drying, ensuring that the final temporary plugging agent particle size meets the injection requirements.

[0226] 4: Hydrophilic protective film:

[0227] Sodium carboxymethyl cellulose / polyvinyl alcohol coated solution (containing Tween 80), with a solution concentration of approximately 6 wt%.

[0228] The sieved particles are placed in a fluidized bed coating machine and sprayed with coating liquid. Coating conditions: the inlet air temperature is controlled at 55℃; the spray pressure and flow rate are adjusted to ensure that the particle surface is uniformly covered with a liquid film, and the coating time is generally 20 minutes. The purpose is to form a uniform and dense hydrophilic protective film on the particle surface.

[0229] The coated granules were dried at 55°C for 1.5 hours to ensure that the coating film was completely cured and the final product had a moisture content of less than 1%.

[0230] If necessary, 0.1–0.5 wt% of an anti-caking agent (such as modified silica micro powder) can be added during or after the drying process to prevent caking.

[0231] The final particle size distribution of the product is determined by vibrating sieving. After reaching the requirement of 100-300 μm, it is packaged in multi-layer aluminum foil bags or sealed metal drums with nitrogen filling or vacuum filling. It is stored in dry, room temperature conditions to ensure a shelf life of 6-12 months.

[0232] Comparative Example 1: The purpose is to provide a temporary plugging agent.

[0233] Compared to Example 1, the capsule-type trigger in the formulation was replaced with an equal amount of modified polypropylene, while the rest remained the same.

[0234] Comparative Example 2: The purpose is to provide a temporary plugging agent:

[0235] Compared to Example 1, the oil-soluble additive in the formulation was replaced with an equal amount of modified polypropylene, while the rest remained the same.

[0236] To further verify the influence of the key components of the oil-soluble temporary plugging agent on the performance of the present invention, laboratory simulation tests were conducted on the temporary plugging agent samples prepared in Examples 1-3 and Comparative Examples 1-2.

[0237] The testing process is as follows: Each sample is added to a simulated oil phase and heated continuously at 60-90℃ in a constant temperature oil bath. Samples are taken and weighed at regular intervals, and the time T (unit: days) required for the temporary plugging agent sample to lose 95% of its mass is recorded to characterize its auto-dissolution ability.

[0238] The test results are shown in Table 1 (Comparison of solubility and stability in water of oil-soluble temporary plugging agents):

[0239] Table 1

[0240]

[0241] As shown in Table 1, within the set temperature range, the oil-soluble temporary plugging agents prepared in Examples 1-3 can all achieve ≥95% auto-dissolution within the predetermined 3-7 days, meeting the requirements for timely restoration of channels after temporary sealing in engineering projects. However, Comparative Examples 1 and 2, lacking key components (triggering agents or oil-soluble additives), failed to achieve 95% dissolution even after 180 hours under the same conditions, indicating that they do not possess the timed and controllable degradation capability required by this invention. This also verifies that the capsule-type triggering agent and the oil-soluble additive have a synergistic promoting effect on the oil solubility of the temporary plugging agent.

[0242] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that various modifications or equivalent substitutions can be made to these embodiments without departing from the spirit and essence of the present invention, and all such modifications or substitutions should be covered within the protection scope of the present invention.

Claims

1. An oil-soluble temporary plugging agent having multilayer microcapsules, characterized in that, The microcapsule comprises a microcapsule core and a hydrophilic protective membrane coating the surface of the microcapsule core. The microcapsule core is composed of modified low-melting-point polypropylene, oil-soluble additives, and a capsule-type triggering agent. The hydrophilic protective membrane is obtained by drying and curing a sodium carboxymethyl cellulose / polyvinyl alcohol coating solution. The oil-soluble temporary plugging agent is prepared from the following raw materials by weight percentage: Modified low-melting-point polypropylene: 50–60 wt% Oil-soluble additives: 15–25 wt% Capsule-type trigger: 3–10 wt% Sodium carboxymethyl cellulose / polyvinyl alcohol coating solution: 5–15 wt% Modified filler: 5-15 wt% The sum of the proportions of each raw material is 100 wt%; The oil-soluble additive is diisooctyl dioctanoate; The capsule-type trigger is a maleic anhydride-modified polymer microcapsule, comprising the following components by weight percentage: Maleic anhydride-grafted polypropylene: 50–65 wt% Toluene diisocyanate: 10–15 wt% Ethylenediamine: 3–8 wt% First surfactant: 0.5-3%; First organic solvent: 15–25 wt% Inorganic filler: 0.2–0.5 wt% The preparation of the capsule-type trigger includes: Maleic anhydride-grafted polypropylene, a first surfactant, and a first organic solvent are used to prepare an oil phase; The oil phase is added to an aqueous solution containing ethylenediamine and stirred to obtain a water-in-oil emulsion with a diameter of 5-50 μm. Toluene diisocyanate was added dropwise to a water-in-oil emulsion. The mixture was stirred and reacted at a first preset temperature for 1–2 hours. The temperature was then raised to a second preset temperature and maintained for 0.5–1 hours. The mixture was centrifuged, the precipitate was collected, washed, and dried to obtain a capsule-type trigger.

2. The oil-soluble temporary plugging agent with multilayer microcapsules according to claim 1, characterized in that, The first surfactant is one or a mixture of several nonionic and anionic surfactants; the first organic solvent is one of halogenated hydrocarbons, organic esters and ketones; the inorganic filler is one of nano silica, nano talc, nano alumina, nano montmorillonite and nano titanium dioxide.

3. The oil-soluble temporary plugging agent with multilayer microcapsules according to claim 1, characterized in that, The sodium carboxymethyl cellulose / polyvinyl alcohol coating solution includes solid components and solvent components; The solid component comprises the following components by weight percentage: Sodium carboxymethyl cellulose: 60–80 wt% of the solids; Polyvinyl alcohol: 18–35 wt% of the solids component; Second surfactant: accounting for 0.5 to 6 wt% of the solid component.

4. The oil-soluble temporary plugging agent with multilayer microcapsules according to claim 3, characterized in that, The mass concentration of the sodium carboxymethyl cellulose / polyvinyl alcohol coating solution is 3-10 wt%. The solvent component includes water.

5. The oil-soluble temporary plugging agent with multilayer microcapsules according to claim 3, characterized in that, The solvent components include water and auxiliary solvents; The mass ratio of the auxiliary solvent to the solvent component is 1 to 3:100; the auxiliary solvent is a second organic solvent miscible with water.

6. The oil-soluble temporary plugging agent with multilayer microcapsules according to claim 3, characterized in that, The second surfactant is one or a mixture of several nonionic and anionic surfactants.

7. An oil-soluble temporary plugging agent with multilayer microcapsules according to any one of claims 1-6, characterized in that, The modified filler is one of modified nano-silica, modified nano-talc, modified nano-alumina, modified nano-montmorillonite, and modified nano-titanium dioxide; the oil-soluble temporary plugging agent has a particle size of 100-300 μm.

8. A method for preparing an oil-soluble temporary plugging agent with multilayer microcapsules according to any one of claims 1-7, characterized in that, include: The dried modified low-melting-point polypropylene, oil-soluble additives, capsule-type triggering agents, and modified fillers are mixed together. The resulting molten mixture is dispersed in a third organic solvent and then spray-granulated to obtain microcapsule cores. The microcapsule core was sprayed with a sodium carboxymethyl cellulose / polyvinyl alcohol coating solution, dried and solidified to obtain an oil-soluble temporary plugging agent.

9. A method for preparing an oil-soluble temporary plugging agent with multilayer microcapsules according to claim 8, characterized in that, The mixing temperature is 120–160°C, the mixing time is 5–10 min, and the mixing shear rate is 100–200 rpm.

10. A method for preparing an oil-soluble temporary plugging agent with multilayer microcapsules according to any one of claims 8-9, characterized in that, The third organic solvent is cyclohexane; the particle size of the microcapsule core is 100-200 μm.

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