Temporary plugging and supporting microspheres, and preparation method and application thereof

Abstract

This invention relates to a temporary plugging-support microsphere, its preparation method, and its application. The temporary plugging-support microsphere has a core-shell composite structure, comprising a biodegradable temporary plugging shell and a support core completely encapsulated by the biodegradable temporary plugging shell. The biodegradable temporary plugging shell is made of a reservoir-environment-degradable polymer material and is used to bridge and seal opened fractures and redirect pressure during fracturing operations. It can also self-degrade under reservoir conditions to achieve unblocking. The support core is made of a propping material used in oil and gas fracturing and provides mechanical support to reservoir fractures and maintains fracture conductivity after the biodegradable temporary plugging shell degrades. This invention integrates temporary plugging and support functions into a single microsphere, enabling the sequential completion of temporary plugging, redirection, and support functions in a single injection. This completely eliminates the existing step-by-step injection mode, simplifies the construction process, shortens construction time, significantly reduces construction costs, and improves operational economy.

Description

Technical Field

[0001] This invention relates to the field of oil and gas reservoir development technology, and in particular to hydraulic fracturing temporary plugging and fracture support technology for oil and gas reservoirs, specifically to a temporary plugging-support microsphere, its preparation method, and its application. Background Technology

[0002] Hydraulic fracturing is a core production enhancement technology for unconventional oil and gas extraction. Its core principle is to inject fracturing fluid into the reservoir under high pressure, forming a complex and extensive fracture network within the reservoir, thereby increasing the reservoir stimulation volume and improving oil and gas recovery efficiency. With the continuous development of unconventional oil and gas extraction technologies, the use of temporary plugging and diversion fracturing technology for reservoir volume stimulation has gradually become the mainstream stimulation method in the industry. This technology uses a temporary plugging agent to form a bridge and seal in the already opened fractures, forcing subsequent fracturing fluid and energy to redirect to the insufficiently stimulated areas, thereby expanding and complicating the fracture network, effectively improving fracturing efficiency and single-well production.

[0003] Currently, temporary plugging and diversion operations generally adopt a step-by-step operation mode. This involves first injecting a plugging agent to temporarily seal the already opened fractures. After the fracturing fluid is diverted and opens new fractures or branch fractures, proppant is then injected to support the newly opened fractures and maintain their conductivity. However, this step-by-step operation mode has many shortcomings, seriously affecting the efficiency and effectiveness of fracturing operations:

[0004] Firstly, the operation procedure is cumbersome. The two injection processes not only increase the construction time but also significantly increase the construction cost and reduce the economic efficiency of the operation.

[0005] Secondly, existing temporary plugging agents (such as acid-soluble temporary plugging agents and gel-based temporary plugging agents) have the problem of incomplete degradation. The residual temporary plugging agents are very easy to remain in the fractures, blocking the oil and gas flow channels, significantly affecting the fracture conductivity, and thus reducing oil and gas production.

[0006] Third, in the step-by-step injection mode, it is impossible to accurately determine whether the proppant can enter the temporarily plugged crack area, making it difficult to guarantee the stability and reliability of the propping effect.

[0007] Furthermore, existing technologies disclose a core-shell structured microsphere that primarily seals high-permeability zones in reservoirs through water absorption and expansion, used for deep profile control and water shut-off operations. This core-shell microsphere lacks self-unblocking capabilities, and its design purpose is to seal reservoir pore throats, making it unsuitable for sealing fractures of varying sizes. This hinders its application in temporary plugging operations during hydraulic fracturing and fails to address the technical limitations of existing step-by-step operation methods.

[0008] Based on this, developing a material, its preparation method, and its application that can simultaneously achieve temporary plugging, steering, and support functions, simplify the construction process, avoid temporary plugging agent residue, ensure support effect, and be suitable for hydraulic fracturing operations in oil and gas reservoirs has become an urgent technical problem to be solved in this field. Summary of the Invention

[0009] In view of the shortcomings of the prior art, the main objective of this invention is to provide a temporary plugging-support microsphere, its preparation method and application, in order to solve the technical problems of the existing step-by-step operation mode of hydraulic fracturing in oil and gas reservoirs, such as complex procedures, high construction costs, low construction efficiency, easy residue of temporary plugging agent affecting fracture conductivity, and inability to guarantee the effect of proppant injection.

[0010] The technical solution of the present invention is as follows:

[0011] This invention proposes a temporary plugging-support microsphere for hydraulic fracturing of oil and gas reservoirs. The temporary plugging-support microsphere has a core-shell composite structure, comprising a biodegradable temporary plugging shell and a support core completely encapsulated by the biodegradable temporary plugging shell; wherein...

[0012] The biodegradable temporary plugging shell is made of a reservoir-environment-degradable polymer material. It is used to bridge and plug open fractures and redirect pressure during fracturing operations. It can also degrade on its own under reservoir conditions to achieve unblocking. The reservoir-environment-degradable polymer material includes at least one of polylactic acid, polyglycolic acid, polycaprolactone, polylactic acid-polyglycolic acid copolymer, gelatin, and sodium alginate.

[0013] The supporting core is made of a support material for oil and gas fracturing, and is used to provide mechanical support to reservoir fractures and maintain fracture conductivity after the biodegradable temporary plug shell degrades. The support material for oil and gas fracturing includes at least one of ceramsite, quartz sand, biodegradable ceramics, and high-strength polymers.

[0014] The temporary plugging-support microspheres can enter reservoir fractures through a single injection process. They are first plugged and redirected by the biodegradable temporary plugging shell, and then supported by the support core after the biodegradable temporary plugging shell degrades.

[0015] In some embodiments, the thickness of the biodegradable temporary plugging shell is 20-200 μm, and the degradation time of the biodegradable temporary plugging shell under reservoir conditions is 1-30 days.

[0016] In some embodiments, the particle size of the supporting core is 100-500 μm, and the compressive strength of the supporting core is not less than 35 MPa.

[0017] In some embodiments, the overall particle size of the temporary plugging-support microspheres is 150-800 μm; the mass of the biodegradable temporary plugging shell accounts for 20%-60% of the total mass of the microspheres, and the mass of the support core accounts for 40%-80% of the total mass of the microspheres.

[0018] In some embodiments, the biodegradable temporary plugging shell is made of polylactic acid, and the supporting core is made of ceramsite, forming a core-shell composite structure of ceramsite core and polylactic acid shell.

[0019] The present invention also proposes a method for preparing the temporary plugging-support microspheres according to the above-mentioned method, comprising the following steps:

[0020] Pretreatment of the surface of the propping material particles for oil and gas fracturing: First, the propping material for oil and gas fracturing is soaked in a first-type alcohol organic solvent and ultrasonically cleaned, then filtered and dried; then, a silane coupling agent treatment solution with a mass fraction of 0.1%-5% is prepared, and the dried propping material for oil and gas fracturing is immersed in the treatment solution and stirred, then filtered and dried again to obtain the pretreated propping material;

[0021] Preparation of coating solution of biodegradable polymer material in reservoir environment: Dissolve biodegradable polymer material in halogenated hydrocarbon, ketone or ester organic solvent to prepare coating solution with mass fraction of 5wt%-15wt%;

[0022] Preparation of coating suspension: The surface-pretreated support material is added to the coating solution and stirred to form a uniform suspension;

[0023] Preparation of biodegradable temporary plugging shell emulsion: Prepare a polyvinyl alcohol aqueous solution, add the suspension to the polyvinyl alcohol aqueous solution and subject it to high-speed shearing to form a stable emulsion;

[0024] Precipitation of biodegradable polymeric materials in the reservoir environment and formation of biodegradable temporary plugging shell: The emulsion is continuously stirred at room temperature to allow the halogenated hydrocarbons, ketones or esters to slowly evaporate, and the biodegradable polymeric materials in the reservoir environment precipitate and solidify on the surface of the support material to form a biodegradable temporary plugging shell covering the support material.

[0025] Temporarily plugged-supported microsphere formation: The coated emulsion is first centrifuged, then washed sequentially with water and a second alcohol organic solvent, and then spread in a petri dish to dry, thus obtaining the temporarily plugged-supported microspheres.

[0026] In some embodiments, the propping material for oil and gas fracturing is at least one of ceramsite, quartz sand, biodegradable ceramics, and high-strength polymers; and / or, the biodegradable polymer material for the reservoir environment is at least one of polylactic acid, polyglycolic acid, polycaprolactone, polylactic acid-polyglycolic acid copolymer, gelatin, and sodium alginate.

[0027] In some embodiments, the first alcoholic organic solvent is at least one of anhydrous ethanol, isopropanol, and ethylene glycol monobutyl ether, or an aqueous solution prepared using any one of anhydrous ethanol, isopropanol, and ethylene glycol monobutyl ether.

[0028] In some embodiments, the silane coupling agent in the silane coupling agent treatment solution is at least one of aminosilane, epoxysilane, methacryloxysilane, vinylsilane, and isocyanate-based silane.

[0029] The solvent in the silane coupling agent treatment solution is a mixture of organic solvent and water, or an anhydrous organic solvent; wherein the organic solvent is at least one of ethanol, isopropanol, methanol, and acetone.

[0030] In some embodiments, the halogenated hydrocarbon, ketone, or ester organic solvent is at least one of dichloromethane, chloroform, acetone, and ethyl acetate.

[0031] In some embodiments, the washing solvent is deionized water.

[0032] In some embodiments, the second alcoholic organic solvent is at least one of anhydrous ethanol, methanol, and isopropanol.

[0033] In some embodiments, the ultrasonic cleaning time is 10 minutes; and / or, the high-speed shearing time is 3 to 5 minutes.

[0034] The present invention also proposes an application of the above-mentioned temporary plugging-support microspheres in hydraulic fracturing of oil and gas reservoirs, wherein the temporary plugging-support microspheres are mixed with fracturing fluid and injected into the reservoir in a single operation to achieve integrated construction operations of temporary plugging, diversion and support.

[0035] The advantages of this invention over the prior art are:

[0036] (1) The temporary plugging-support microsphere of the present invention adopts a core-shell composite structure, which integrates the temporary plugging function and the support function into a single microsphere, so that the three functions of temporary plugging, steering and support can be completed in sequence with a single injection. This completely eliminates the existing step-by-step injection mode, simplifies the construction process, shortens the construction time, greatly reduces the construction cost, and improves the economic efficiency of operation.

[0037] (2) The biodegradable temporary plugging shell of the present invention is made of a reservoir environment biodegradable polymer material, which can be completely degraded after the temporary plugging is completed and there is no residue. This effectively avoids the problem of existing temporary plugging agents leaving residues that block cracks and affect the flow capacity, ensuring smooth oil and gas flow channels and improving oil and gas recovery efficiency.

[0038] (3) The support core of the present invention is made of high-strength oil and gas fracturing support material. After the shell degrades, it can stably support the fracture and maintain the fracture conductivity. Moreover, the microsphere can achieve temporary plugging and support at the same time with a single injection, which can accurately ensure that the proppant enters the target fracture area and improve the stability and reliability of the support effect.

[0039] (4) The microspheres of the present invention are specifically designed for the fracture operation scenario of hydraulic fracturing of oil and gas reservoirs. They can achieve bridging and sealing and deflection at the fracture, overcoming the defects of existing core-shell microspheres that do not have the function of unblocking and can only be adapted to pore throat sealing. They are more adaptable and have a wider range of applications.

[0040] (5) The preparation method of the present invention is simple, convenient to operate, and mild, and is easy to scale up for industrial production; the application method is simple, does not require modification of existing fracturing equipment, and is easy to promote and apply on site.

[0041] It should be understood that the description in the Summary of the Invention is not intended to limit the key or essential features of the embodiments of the present invention, nor is it intended to restrict the scope of the invention. Other features of the invention will become readily apparent from the following description. Furthermore, implementation of any embodiment of the present invention does not imply the simultaneous possession or achievement of multiple or all of the aforementioned beneficial effects. Attached Figure Description

[0042] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0043] The structures, proportions, sizes, etc. illustrated in this specification are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed herein, and are not intended to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportions, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention.

[0044] Figure 1 This is a schematic diagram of the temporary plugging-support microsphere structure according to some embodiments of the present invention;

[0045] Figure 2 This is a schematic diagram of the preparation process of temporary plugging-support microspheres according to a specific embodiment of the present invention;

[0046] Figure 3This is a schematic diagram illustrating the application process of temporary plugging-support microspheres in oil and gas reservoir temporary plugging and diversion fracturing operations according to some embodiments of the present invention.

[0047] Marked in the image:

[0048] 1- Supporting kernel;

[0049] 2- Biodegradable temporary plugging shell.

[0050] The same or corresponding marks in the diagram indicate the same or corresponding parts. Detailed Implementation

[0051] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. Here, the illustrative embodiments and descriptions of the present invention are used to explain the present invention, but are not intended to limit the present invention.

[0052] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0053] It should be understood that the terms "comprising / including," "consisting of," or any other variations are intended to cover non-exclusive inclusion, such that a product, apparatus, process, or method that comprises a list of elements includes not only those elements but may also include, where necessary, other elements not expressly listed, or elements inherent to such a product, apparatus, process, or method. Without further limitation, an element defined by the phrases "comprising / including," "consisting of," does not exclude the presence of additional identical elements in the product, apparatus, process, or method that includes said element.

[0054] It should also be understood that the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device, component or structure referred to must have a specific orientation, be constructed or operated in a specific orientation, and should not be construed as a limitation of the present invention.

[0055] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0056] The implementation of the present invention will be described in detail below with reference to preferred embodiments.

[0057] like Figure 1 As shown, this invention proposes a temporary plugging-support microsphere for hydraulic fracturing of oil and gas reservoirs. The overall structure is a core-shell composite structure, mainly composed of two parts: a biodegradable temporary plugging shell 1 and a support core 2 completely covered by the biodegradable temporary plugging shell 1.

[0058] The biodegradable temporary plugging shell 1 is made of a polymer material that can be hydrolyzed or biodegraded under reservoir temperature, pressure, and fluid environment. In this embodiment, the polymer material may be polylactic acid (PLA), polyglycolic acid (PGA), polycaprolactone (PCL), polylactic acid-polyglycolic acid copolymer (PLGA), gelatin, or sodium alginate.

[0059] In this invention, based on the solubility of various polymers and the differences in the microsphere preparation process of this invention, the above-mentioned polymers are mainly divided into two categories: synthetic polyesters and natural polymers.

[0060] Specifically, synthetic polyester materials suitable for organic solvent dissolution-solvent evaporation processes include polylactic acid (PLA), polycaprolactone (PCL), and polylactic acid-polyglycolic acid copolymer (PLGA). These materials are typically fed in granular or powder form, are soluble in volatile organic solvents such as dichloromethane and chloroform, and are suitable for preparing a uniform and dense outer shell layer via solvent evaporation. Under reservoir conditions, the ester bonds in the polymer chains gradually hydrolyze and break, and the long-chain molecules decompose into small-molecule oligomers or monomers, which are ultimately carried away by formation fluids or metabolized by microorganisms, achieving complete degradation and residue-free unblocking.

[0061] Among them, PLA has a moderate degradation cycle and is suitable for routine temporary blocking and turning operations; PCL has a longer degradation cycle and is suitable for scenarios requiring long-term sealing; PLGA can precisely control the degradation rate within the range of several days to several months by adjusting the copolymerization ratio of lactic acid and glycolic acid.

[0062] Degradable polymeric materials suitable for aqueous dissolution-crosslinking curing or other specialized processes in natural reservoir environments include gelatin and sodium alginate. These materials are typically fed in granular or powder form, are insoluble in common organic solvents, but soluble in water or hot water. When preparing the outer shell, aqueous dissolution combined with crosslinking agents such as glutaraldehyde or calcium chloride is required for curing. Under reservoir conditions, gelatin is primarily degraded into amino acids or peptides through enzymatic hydrolysis; sodium alginate can be gradually degraded through hydrolysis or enzymatic hydrolysis, and the degradation products are non-toxic and harmless.

[0063] Additionally, for polyglycolic acid (PGA), which also belongs to the synthetic polyester family: PGA is fed in the form of white crystalline powder or granules and has an extremely fast degradation rate, but high molecular weight PGA is almost insoluble in common organic solvents. When solvent evaporation is required to prepare the shell, PGA is usually copolymerized with PLA to form PLGA, or applied through melt coating processes.

[0064] During fracturing operations, the biodegradable temporary plugging shell 1 can be the first to enter and bridge open high-permeability fractures, forming an effective physical barrier. This forces subsequent fracturing fluid to deflect and open areas in the reservoir that have not been adequately modified, thereby expanding and complicating the fracture network. After completing its temporary plugging and deflection function, the biodegradable temporary plugging shell 1 can decompose and disappear on its own under reservoir conditions through the aforementioned hydrolysis or biodegradation processes, achieving complete unblocking. This fundamentally avoids the problem of traditional plugging agents (such as acid-soluble plugging agents and gel-based plugging agents) remaining in the fractures due to incomplete degradation, blocking oil and gas channels, and affecting conductivity.

[0065] In some embodiments, the thickness of the biodegradable temporary plugging shell 1 is controlled between 20 and 200 μm. This thickness range can ensure the structural strength of the shell and the performance of crack bridging and plugging, while also taking into account the needs of subsequent reservoir fluid infiltration and degradation.

[0066] Based on the design mechanism of the temporary plugging material, the core design idea of ​​the core-shell encapsulation structure is to delay the premature dissolution and degradation of the temporary plugging material during transportation by using the encapsulation and protection function of the outer shell, so as to ensure that the microspheres are stably transported to the crack location before playing a plugging role.

[0067] Existing research shows that polylactic acid / polyglycolic acid blends can achieve controlled degradation in reservoir environments at 90°C for several hours to several days, while polylactic acid / ethyl cellulose blends can achieve a degradation rate of over 90% in formation water environments at 90°C and pH=9 within 15 days. The controlled degradation characteristics of these reservoir-degradable polymer materials can well meet the time requirements of fracturing and temporary plugging operations.

[0068] Existing engineering research and industrial applications have confirmed that the structural design of using an outer shell to delay degradation can effectively balance the plugging time and subsequent unblocking performance of the temporary plugging agent, achieving effective plugging in the short term and complete degradation in the later stage. At the same time, reservoir temperature and salinity can regulate the degradation rate of polymers, with high temperature accelerating hydrolysis and high salinity environment inhibiting degradation, providing adjustable space for on-site adaptation to different construction cycles.

[0069] Meanwhile, the thickness of the outer shell directly determines the mechanical plugging performance of the microspheres. Existing experimental studies have confirmed that surface coating modification can significantly improve the pressure-bearing capacity of temporary plugging particles, and the coating structure can improve the pressure-bearing performance of the temporary plugging agent by more than 36.1%.

[0070] Under the same operating conditions and a solid-liquid ratio of 150:1, the breakthrough pressures of three reservoir-degradable polymer materials—polylactic acid (PLA), polyglycolic acid (PGA), and polybutylene terephthalate adipate (PBAT)—were 11.7 MPa, 10.9 MPa, and 7.5 MPa, respectively. Among them, the polylactic acid substrate exhibited the best high-pressure plugging capability.

[0071] Based on the aforementioned degradation characteristics and mechanical performance test patterns, this invention limits the shell thickness to 20–200 μm. This thickness range ensures sufficient structural strength of the shell through the coating reinforcement effect, enabling the PLA-based shell to stably withstand a fracture breakthrough pressure of ≥11.7 MPa, meeting the requirements for bridging and sealing deep high-pressure fractures. Simultaneously, it avoids the problem of impeded media permeation caused by excessively thick shells, ensuring that reservoir fluids can smoothly penetrate into the shell after construction, allowing for efficient and thorough degradation of the microspheres and preventing residual blockage of reservoir pores.

[0072] The support core 2 is made of high-strength proppant material (proppant particles) used for oil and gas fracturing. In this embodiment, the proppant material can be selected from ceramsite, quartz sand, biodegradable ceramics, high-strength polymers, or other materials with high compressive strength.

[0073] Specifically, the expanded clay is artificial expanded clay or sintered bauxite with a compressive strength of 52-103 MPa; the quartz sand has a compressive strength of 35-50 MPa; the biodegradable ceramic is calcium phosphate-based ceramic with adjustable compressive strength; and the high-strength polymer is polyetheretherketone or polyphenylene sulfide.

[0074] The main function of the supporting core 2 is that after the outer biodegradable temporary plugging shell 1 degrades and disappears in the reservoir environment, it can remain stably in the fracture channel, providing continuous mechanical support for the reservoir fracture, preventing the fracture from closing, thereby maintaining the high conductivity of the fracture for a long time and ensuring the efficient production of oil and gas.

[0075] In some embodiments, the overall particle size of the supporting core 2 is controlled within the range of 100–500 μm. Simultaneously, the mechanical properties of the supporting core 2 are limited, with its compressive strength set at no less than 35 MPa. This allows it to effectively withstand reservoir formation pressure and fracture closure stress, withstand long-term compaction without easily breaking, and continuously provide stable mechanical support to reservoir fractures, ensuring long-term fracture conductivity.

[0076] It should be understood that the industry typically uses the breakage rate under a specific closure pressure as the evaluation standard for proppant strength. This performance indicator is a basic entry requirement for fracturing operations in deep, high-pressure, and other high-closure-stress reservoirs. Industry-standard technical specifications require that the breakage rate of high-strength ceramic proppant be less than 10% under a closure pressure of 35 MPa. Extensive experimental data has verified the material compatibility at this pressure level. Specifically, the measured breakage rate of red mud ceramic proppant under a 35 MPa closure pressure is only 7.5%, fully meeting the strength requirements for high-pressure reservoir propping operations.

[0077] In some embodiments, the overall particle size of the temporary plugging-support microspheres is controlled within the range of 150–800 μm. This particle size scale can adapt to the pore size distribution characteristics of reservoir fractures, facilitating the transport of the microspheres into the fracture interior along with the fracturing fluid, and successfully achieving bridging, deposition, and sealing. Simultaneously, the mass ratio of each component of the microspheres is rationally designed, with the supporting core accounting for 40%–80% of the total mass of the microspheres, and the biodegradable temporary plugging shell accounting for 20%–60% of the total mass of the microspheres.

[0078] In this invention, the particle size parameter is defined based on the mature theory of fracture bridging and plugging in oil and gas reservoirs, and has sufficient theoretical and engineering practice support.

[0079] Currently, the industry has established a complete theory for bridging and sealing based on the quantitative matching of temporary plugging agent particle size and crack width. The mainstream matching principle is that when the particle size of the bridging particles is 1 / 3 to 2 / 3 of the crack width, a stable bridging and sealing structure can be formed inside the crack. Other studies have confirmed that when the particle size of the bridging particles matches 80% to 100% of the average crack opening degree, efficient and stable bridging and sealing can also be achieved.

[0080] Meanwhile, the fracturing operation conditions directly affect the sealing effect. The higher the viscosity of the carrying fluid and the larger the discharge volume, the more difficult it is to form the sealing layer. Appropriately increasing the particle size of the temporary plugging particles and increasing the particle concentration can significantly optimize the crack sealing effect and ensure the stability of the sealing layer formation.

[0081] Numerous studies on crack sealing mechanisms have shown that the bridging and sealing distance of temporary plugging agents within cracks increases with the crack width. When the crack width at the end reaches 4 mm, temporary plugging particles in the 212–850 μm particle size range are difficult to effectively form a sealing segment.

[0082] Based on the above principles, this invention sets the upper limit of the overall particle size of the microspheres to 800μm, which can accurately match the upper limit of the width of conventional hydraulic fracturing fractures, cover most reservoir fracture plugging conditions, and effectively avoid the problem that microspheres cannot bridge and plug large-size fractures.

[0083] From the perspective of technical solution differentiation, existing core-shell structured plugging microspheres mostly focus on plugging reservoir micro- and nano-scale pore throats. The particle size of these plugging agents is generally controlled between 0.1 and 20 μm, and they are only suitable for plugging and modifying small pore throats. In contrast, this invention targets the macroscopic fracture plugging scenario after hydraulic fracturing in oil and gas reservoirs, setting the overall particle size of the microspheres to 150–800 μm, forming a clear scale distinction from pore throat plugging microspheres. The parameter design is highly targeted, accurately adaptable to the scenario, and the technical rationality is significant.

[0084] Furthermore, the present invention specifies that the mass ratio of the biodegradable temporary plugging shell of the microspheres is 20% to 60%. This parameter range is also designed based on mature industry applications and research results in similar fields, and has excellent functional adaptability.

[0085] The core design logic of core-shell structured temporary plugging agents is to rely on the outer biodegradable shell to achieve the protective function, delay the premature degradation and failure of the core material during transportation, and ensure that the microspheres accurately reach the target crack location to play a temporary plugging role. To achieve this core function, the shell mass ratio of core-shell temporary plugging products adapted to the industry is generally not less than 20%.

[0086] Meanwhile, the mature research on core-shell microspheres in the field of drug sustained release can provide evidence for the design of shell parameters in this invention: the shell thickness, proportion and structural characteristics can precisely control the action sequence and failure rate of the core material, and the core-shell composite structure can improve the particle aggregation and blocking effect through electrical adaptation.

[0087] Based on the above theory, the shell mass ratio of 20% to 60% in this invention can ensure that the shell has sufficient structural thickness and mechanical strength, effectively control the overall degradation sequence of the microspheres and avoid early failure, and also ensure that the supporting core occupies the main mass ratio. After the shell degrades and unblocks, the core can give full play to the long-term support function of the cracks, perfectly taking into account the multiple functions of temporary blocking, controllable degradation and later crack support.

[0088] In addition, existing research indicates that single-size temporary plugging agents have poor sealing effects and are difficult to form a tight sealing layer within fractures (Journal of Jianghan Petroleum Staff University, 2022). On the other hand, sealing tests of fractured-vuggy reservoirs have confirmed that when the particle size and fracture width are matched at a ratio of approximately 1:1, and when combined with rigid bridging particles and deformable particles, a tight sealing layer can be rapidly constructed, achieving a sealing efficiency of 99.9999% and a pressure bearing capacity of no less than 12 MPa (Petroleum Drilling Technology, 2012).

[0089] Those skilled in the art therefore recognize that precise matching of the temporary plugging agent particle size to the crack size is the key to ensuring the plugging effect, while multi-particle-size compounding or multi-functional structural combination is an effective way to improve the temporary plugging performance.

[0090] This invention preferably uses polylactic acid (PLA) as the outer shell and ceramic particles as the core to prepare core-shell structured temporary plugging-support microspheres. The plugging performance is tested in accordance with the temporary plugging and leakage evaluation test method published in "Petroleum Drilling Technology" in 2012. Under the condition of simulating a fracture width of 400-600 μm, the forming time of the plugging layer is ≤5 min, and the effective pressure resistance can reach 8-12 MPa. All performances meet the engineering use standards for fracturing temporary plugging and diversion.

[0091] It is worth noting that existing industrialized core-shell biodegradable temporary plugging products rely on an outer biodegradable shell to block formation fluids, preventing premature degradation and failure of the inner core material during transportation, and ensuring targeted plugging of the agent. These products have been applied in multiple wells, increasing the construction pressure by 2-8 MPa and significantly increasing production in the application blocks. These engineering examples demonstrate the technical advantages of the core-shell coating structure in targeted control, providing an engineering basis for the structural design of this invention.

[0092] Relevant degradation test results show that after the polylactic acid outer shell is completely degraded in the formation temperature environment, the core permeability recovery rate can reach more than 90% (Acta Petrolei Sinica, 2022). Based on the characteristics of this material, after the microspheres of this invention complete the temporary plugging operation, the outer shell gradually hydrolyzes and dissipates, while the ceramic core remains inside the fracture to achieve long-term support, effectively restoring the reservoir conductivity and avoiding the retention of solid residues that could damage the reservoir.

[0093] Furthermore, the biodegradable temporary plugging shell 2 is made of polylactic acid (PLA), and the supporting core 1 is made of ceramsite, forming a core-shell composite structure of ceramsite core and PLA shell. To optimize the overall service performance of the microspheres, improve their high-pressure plugging capability, long-term crack support effect, and controllable shell degradation, this invention, through multiple sets of performance comparison tests, has optimized the above-mentioned combination of ceramsite and PLA. Relevant experimental data and industry research conclusions fully demonstrate the scientific nature and technological superiority of this material selection scheme.

[0094] Existing research on the properties of polyester-based temporary plugging agents confirms that the overall ultimate pressure bearing capacity of the temporary plugging microspheres is determined by the strength of the supporting core material itself, and the two are positively correlated. The higher the mechanical properties of the core material, the higher the upper limit of the plugging pressure bearing capacity of the microspheres under high-pressure environments in the formation. The polymer material used for the biodegradable shell directly determines the structural strength and rupture resistance of the shell itself.

[0095] Under the standardized plugging evaluation test conditions of 150:1 solid-liquid ratio, when only the outer shell polyester material is changed and the core material is kept the same, the pressure breakthrough pressure of different polyester preparation samples is ranked as follows: PLA (11.7MPa) > PGA (10.9MPa) > PBAT (7.5MPa).

[0096] Therefore, under the same core support conditions, PLA material has higher shell structure strength and better pressure resistance, making it more suitable as a substrate for temporary plugging shells in high-pressure reservoirs.

[0097] Based on the determination of the optimal outer shell material, in order to further match the long-term support requirements of deep high-stress reservoirs, it is necessary to select high-strength, high-fracture-resistance, and high-conductivity support materials for core oil and gas fracturing.

[0098] From the perspective of the pressure-bearing and conductivity performance of proppant materials used in oil and gas fracturing, the conductivity test results of different proppants under varying closure pressure show that the conductivity performance of various proppant materials used in oil and gas fracturing differs significantly under different formation stress conditions:

[0099] When the closure pressure is below 15MPa, ceramsite, quartz sand, and film-modified proppant materials for oil and gas fracturing can all maintain good conductivity.

[0100] When the closure pressure is in the range of 15 to 25 MPa, quartz sand is easily broken under pressure and its conductivity decreases significantly, while ceramsite and coated modified propping materials for oil and gas fracturing can still maintain stable conductivity.

[0101] In deep, high-stress environments with closure pressures exceeding 25 MPa, only ceramsite, with its excellent anti-fracture properties, can maintain high conductivity in cracks over the long term.

[0102] For medium-high closure stress reservoirs of 25-35 MPa, the test proved that a 50% ceramsite content in the system can meet the engineering requirements for long-term fracture conductivity. Under the same closure stress conditions, the field construction method of pre-injection of quartz sand and post-injection of ceramsite has a better conductivity than the injection scheme of pre-mixed uniform quartz sand and ceramsite.

[0103] According to the material selection conventions in the oil and gas field fracturing industry, quartz sand is preferred for reservoirs with a depth of less than 600m, while ceramsite or proppant for oil and gas fracturing can be used for wells with a depth of 600-1000m. For deep oil and gas wells with a depth exceeding 1000m, due to higher ground stress, ceramsite must be used. Ceramsite, with its high hardness, high sphericity, and resistance to acid and alkali corrosion, has a higher overall cost and better economic benefits than quartz sand in the long-term development of deep, low-permeability oil reservoirs.

[0104] Under the premise of selecting materials with optimal rigidity performance for the core and outer shell, the biodegradable outer shell must also take into account the controllable degradation characteristics that are compatible with the formation, so as to meet the core requirements of fracturing construction: "stable sealing and complete unblocking in the later stage".

[0105] Analysis of polymer hydrolysis characteristics reveals a clear distinction in degradation rates among commonly used biodegradable aliphatic polyesters in oilfields: PGA exhibits strong hydrophilicity and degrades extremely rapidly in neutral and alkaline formation water environments; high-quality PGA products can completely decompose into carbon dioxide and water within 3-5 days, providing thorough unblocking without residue. However, this rapid degradation rate leads to premature product failure during storage and a short shelf life, hindering industrial-scale application. PCL, on the other hand, has high crystallinity and stable molecular chains, resulting in a long degradation cycle. It is primarily used in long-lasting medical implants and cannot meet the short-term requirements of fracturing applications. The PLA meets the construction requirements of temporary plugging and timely unplugging after operation; the PLA side chain has methyl groups, and its hydrophilicity and crystallinity are moderate. Its degradation rate is between that of PGA and PCL. Hydrolysis is slow and controllable within the conventional formation temperature range of 50-120℃. During the construction phase, the shell structure can be maintained. The core-shell structure is used to achieve fracture bridging and plugging and pressure diversion. After the temporary plugging operation is completed, it can be gradually hydrolyzed and dissolved. Related tests show that the core permeability recovery rate can reach more than 90% after the PLA shell is completely degraded, effectively avoiding the retention of solid residues that damage the reservoir.

[0106] In summary, among various optional raw material options, this embodiment preferably uses ceramsite as the supporting core and polylactic acid as the biodegradable outer shell. The resulting core-shell microspheres possess excellent high-pressure plugging performance, long-term fracture support performance, and controllable degradation performance, making them precisely suitable for the field conditions of hydraulic fracturing and temporary plugging and diversion in deep, high-stress oil and gas reservoirs.

[0107] The temporary plugging-support microspheres of this invention adopt a core-shell integrated composite structure design, which organically integrates the three major functions of temporary plugging, pressure diversion and crack support into a single particle system, achieving a reasonable functional layout and precise matching of working sequence.

[0108] More precisely, the microspheres can be injected into the reservoir fracture system along with fracturing fluid in a single injection process. The operation process works step by step according to a preset sequence: First, the outer biodegradable temporary plugging shell 1 forms an effective bridging and sealing within the opened fracture, constructing a sealed barrier structure to achieve pressure diversion and fracture reversal. After the temporary plugging and reversal operation and reservoir stimulation are completed, the biodegradable temporary plugging shell 1 gradually degrades and disappears in the reservoir environment, and the internal high-strength support core 2 is fully exposed and remains in the fracture, continuously forming a rigid support constraint on the fracture wall, effectively inhibiting fracture closure and compaction, maintaining fracture opening and seepage channel connectivity for a long time, and finally constructing a stable and unobstructed high-efficiency oil and gas flow channel inside the reservoir, significantly improving the reservoir stimulation effect and single-well productivity.

[0109] This invention also proposes a method for preparing the above-mentioned temporary plugging-support microspheres, specifically including the following process steps:

[0110] Surface pretreatment of proppant particles for oil and gas fracturing: The proppant particles for oil and gas fracturing that form the proppant core 2 are subjected to surface pretreatment modification to improve the interfacial compatibility with biodegradable polymer materials in the reservoir environment. Specifically, the proppant particles are first soaked in a first alcohol-based organic solvent and ultrasonically cleaned. After filtration and drying, a silane coupling agent treatment solution with a mass fraction of 0.1%-5% is prepared. The dried proppant particles for oil and gas fracturing are then immersed in the silane coupling agent treatment solution and thoroughly stirred for modification. After filtration and drying again, the pretreated proppant particles are obtained.

[0111] Preparation of a coating solution for biodegradable polymer materials in the reservoir environment: Polylactic acid particles used to prepare biodegradable temporary plugging shell 1 are dissolved in halogenated hydrocarbons, ketones or esters in organic solvents and stirred thoroughly until completely dissolved to prepare a coating solution with a mass fraction of 5wt% to 15wt% and uniform and stable composition.

[0112] Preparation of the coating suspension: The surface-pretreated support material is added to the above coating solution and continuously stirred and mixed to make the support core particles uniformly dispersed, forming a suspension with uniform component distribution.

[0113] Preparation of biodegradable temporary plugging shell emulsion: Prepare a polyvinyl alcohol aqueous solution in advance, and then slowly add the prepared suspension to the polyvinyl alcohol aqueous solution system. Emulsification and dispersion are carried out through high-speed shearing to form a uniform and stable emulsion.

[0114] Degradable polymer material precipitation and degradable temporary plugging shell formation in reservoir environment: The obtained emulsion is continuously stirred at room temperature to promote the slow and uniform evaporation of halogenated hydrocarbons, ketones or esters in the system that can dissolve the polymer. The dissolved degradable polymer (polylactic acid particles) gradually precipitates and solidifies on the surface of the support material, and uniformly deposits and coats it, eventually forming a complete degradable temporary plugging shell 1 that completely encapsulates the outer layer of the support material.

[0115] Temporarily plugged-supported microsphere formation: After the core-shell structure is coated and formed, the microsphere suspension system obtained after coating is centrifuged and separated. It is then thoroughly washed with water and a second alcohol organic solvent to remove residual impurities and solvents on the surface. Subsequently, it is laid flat in a petri dish for drying, and finally, temporary plugged-supported microspheres with complete structure, dense coating and uniform performance are obtained.

[0116] In the above preparation process, the propping material for oil and gas fracturing is at least one of ceramsite, quartz sand, biodegradable ceramics, and high-strength polymer.

[0117] Furthermore, the reservoir environment degradable polymeric material is at least one of polylactic acid, polyglycolic acid, polycaprolactone, polylactic acid-polyglycolic acid copolymer, gelatin, and sodium alginate.

[0118] Furthermore, the first alcohol-based organic solvent can be at least one of anhydrous ethanol, isopropanol, and ethylene glycol monobutyl ether, or an aqueous solution prepared from any one of anhydrous ethanol, isopropanol, and ethylene glycol monobutyl ether.

[0119] Preferably, the ultrasonic cleaning time after immersion in anhydrous ethanol is set to 10 minutes, which can fully remove dust and impurities from the surface of the support material used for oil and gas fracturing.

[0120] Furthermore, the silane coupling agent may be at least one selected from aminosilane, epoxysilane, methacryloxysilane, vinylsilane, and isocyanate-based silane. The preferred embodiment of this invention is γ-aminopropyltriethoxysilane (KH-550).

[0121] The solvent for the silane coupling agent treatment solution can be a mixture of organic solvent and water or an anhydrous organic solvent. The organic solvent can be at least one of ethanol, isopropanol, methanol, and acetone.

[0122] Specifically, there are two optional solvent systems for preparing the coupling agent treatment solution: one is a mixed solvent of at least one organic solvent selected from ethanol, isopropanol, methanol, and acetone and water, with the volume ratio of organic solvent to water controlled between 90:10 and 99:1, preferably 95:5.

[0123] The second is an anhydrous organic solvent. Taking KH-550 as an example, its mass percentage concentration in the treatment solution is in the range of 0.1% to 5%, preferably 0.5% to 2%, or even more preferably 0.8% to 1.2%. Within this preferred concentration range, a structurally complete silane coating film can be generated on the substrate surface, maximizing the improvement of the interfacial adhesion between the supporting substrate and the polymer shell and enhancing the mechanical properties of the composite system.

[0124] Furthermore, the halogenated hydrocarbon, ketone, or ester organic solvent that can dissolve the polymer is selected from at least one of the halogenated hydrocarbon, ketone, or ester solvents such as dichloromethane, trichloromethane, acetone, and ethyl acetate.

[0125] Furthermore, when preparing the coating solution, it is preferable to set the mass fraction of the coating solution to 10 wt%, which is more conducive to the stable dissolution of biodegradable polymer materials in the reservoir environment and their subsequent uniform precipitation and coating on the surface of the supporting core 2.

[0126] Furthermore, the high-speed shearing time after mixing the suspension with the polyvinyl alcohol aqueous solution is preferably controlled to be 3 to 5 minutes. This ensures excellent surface impurity removal for the support material used in oil and gas fracturing, while also making the emulsion emulsification more uniform and stable, which is conducive to forming a regular core-shell structure of microspheres and a uniform coating effect.

[0127] Furthermore, the washing solvent should be deionized. The second alcoholic organic solvent can be at least one of anhydrous ethanol, methanol, and isopropanol.

[0128] The preparation method of the temporary plugging-support microspheres of the present invention has a simple and clear process flow, mild and controllable process conditions, and can be completed entirely at room temperature and normal pressure. It does not require high temperature, high pressure and complex special equipment, and is easy to operate, implement and mass-produce in the industrial. At the same time, by performing silane coupling agent surface modification treatment on the support material for oil and gas fracturing, the interfacial bonding force between the support core and the biodegradable polymer shell is effectively enhanced, so that the core and shell structure is tightly covered and not easy to fall off. The microspheres have a regular overall structure, uniform particle size distribution and good product stability.

[0129] This method employs a solvent evaporation precipitation coating molding process; and the process parameters are easy to control. It can be flexibly adapted to the preparation of temporary plugging-support microspheres with different particle sizes, shell thicknesses, and core-shell ratios according to actual application needs. It has strong versatility and can well meet the usage requirements of different working conditions in hydraulic fracturing of oil and gas reservoirs.

[0130] Compared with existing conventional processes, this invention relies on the coordinated control of multiple parameters such as shearing time, coating solution concentration, and substrate pretreatment. While retaining the advantages of the mild preparation method using solvent evaporation, it effectively improves the controllability of microsphere morphology and particle size, reduces the formation of hollow impurity spheres, and achieves a balance between production cost and product molding quality.

[0131] In one specific embodiment, see Figure 2 The preparation method of the temporary plugging-support microspheres of the present invention is carried out according to the following process parameters and operation steps:

[0132] Accurately weigh 10g of ceramsite as the supporting core material, soak it thoroughly in anhydrous ethanol, and ultrasonically clean it for 10 minutes. After removing impurities from the surface, filter and dry it for later use.

[0133] A 1 wt% ethanol solution of silane coupling agent KH-550 was prepared separately. The dried ceramsite was completely immersed in the solution and stirred thoroughly for modification. After modification, it was filtered and dried again to obtain pretreated ceramsite particles.

[0134] Accurately weigh 2g of PLA (polylactic acid) particles, add them to 20ml of dichloromethane solvent, place them on a magnetic stirrer and stir continuously at room temperature until the PLA particles are completely dissolved, to prepare a PLA transparent solution with a mass fraction of 10wt%.

[0135] The surface-pretreated ceramic particles are added to the above-mentioned PLA transparent solution and stirred continuously to make the ceramic particles evenly dispersed and form a stable suspension.

[0136] Accurately weigh 4g of PVA polyvinyl alcohol particles, add them to 200ml of deionized water, heat and stir until the PVA is completely dissolved, and let it cool naturally to room temperature; then slowly add the prepared suspension to the PVA aqueous solution system and perform high-speed shear emulsification for 3-5 minutes to obtain a uniformly dispersed and stable emulsion system.

[0137] After emulsification, the emulsion was transferred to a beaker and placed on a magnetic stirrer. The mixture was stirred continuously at low speed at room temperature to allow the dichloromethane organic solvent in the system to evaporate slowly and steadily. The PLA polymer gradually precipitated and deposited uniformly on the surface of the ceramic particles, solidifying to form a dense and complete biodegradable temporary plugging shell 1.

[0138] After the organic solvent has fully evaporated and the core-shell structure has been fully formed, the microsphere suspension after standing is centrifuged. The microsphere sample is then washed multiple times with deionized water and anhydrous ethanol to remove residual solvent and impurities from the surface. Finally, the washed microspheres are laid flat in a petri dish for drying to obtain the finished temporary plugging-support microspheres.

[0139] The temporary plugging-support microsphere prepared by this invention integrates the functions of temporary plugging, pressure diversion and fracture support. It can complete all the steps of the traditional process in a single injection, which greatly simplifies the on-site fracturing operation process, effectively shortens the construction cycle and reduces the construction and operation costs.

[0140] Simultaneously, the microspheres enter the target fracture area along with the fracturing fluid, ensuring clear positioning of the support core and precise control of its supporting effect. This completely solves the drawback of the inability to determine the positioning effect of the proppant in traditional processes.

[0141] In addition, the biodegradable temporary plugging shell of the microspheres can achieve time-controlled degradation according to reservoir conditions. The degradation reaction is thorough and complete, with no solid residue remaining inside the fractures. This can significantly reduce the secondary damage caused by reagent residues to the reservoir and fracture channels, and maintain the effective opening and conductivity of the fractures for a long time, which is conducive to improving the reservoir stimulation effect and the single-well oil and gas recovery capacity.

[0142] In some embodiments, see Figure 3 This invention also proposes an application of the aforementioned temporary plugging-support microspheres in hydraulic fracturing of oil and gas reservoirs. This application method is simple to operate, adaptable to existing conventional fracturing equipment and processes, requires no additional modification to the on-site construction process, and can be directly embedded into existing fracturing construction procedures. Its complete application process is as follows:

[0143] First, following the conventional fracturing operation process, the reservoir is initially fractured by pre-fracturing fluid to form an initial fracture channel. Then, the temporary plugging-support microspheres prepared in this invention are thoroughly mixed with the proppant-carrying fracturing fluid in a reasonable ratio and stirred evenly to form a stable fracturing fluid-microsphere mixture system. This mixture system is then pumped into the oil and gas reservoir through a single injection process.

[0144] Microspheres are transported along with the fracturing fluid and enter the entrance or space of an already opened fracture. Through the accumulation and bridging effect between particles in the fracture channel, they quickly form a physical sealing barrier, temporarily plugging the high-permeability fractures. This forces the subsequent fracturing fluid to depressurize and extend into areas of the reservoir that have not been fully modified, thereby opening new fractures or branch fractures, significantly expanding the reservoir modification volume, and constructing a more complex fracture network.

[0145] After the temporary plugging and diversion function is completed, the microspheres enter the reservoir fracture. Under the triggering of formation temperature, pressure and fluid environment, the outer biodegradable temporary plug shell 1 gradually undergoes hydrolysis and degradation and disappears completely. The high-strength support core 2 wrapped inside is released and remains in situ in the fracture channel, continuously providing rigid mechanical support to the fracture wall, preventing the fracture from closing and compacting, maintaining the fracture opening and conductivity for a long time, and providing a stable and smooth seepage channel for subsequent oil and gas production.

[0146] Once the above procedures are completed, subsequent fracturing section construction can proceed or the process can directly transition to the runoff and production stage.

[0147] This application method eliminates the need for stepwise injection of temporary plugging agents and proppants. A single injection can simultaneously achieve integrated construction operations of temporary plugging, diversion, and propping, significantly simplifying the construction process, shortening the construction cycle, and effectively reducing operating costs. At the same time, the propping core 2 is precisely positioned, the propping effect is controllable, and the outer shell degrades completely without residue, avoiding secondary damage to the reservoir. This significantly improves the reservoir stimulation effect and single-well oil and gas production, and is especially suitable for volumetric fracturing stimulation operations in unconventional oil and gas reservoirs, with broad application prospects.

[0148] It will be readily understood by those skilled in the art that, without conflict, the above-mentioned preferred solutions can be freely combined and superimposed.

[0149] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A temporary plugging-support microsphere for hydraulic fracturing of oil and gas reservoirs, characterized in that, The temporary plugging-support microsphere has a core-shell composite structure, including a biodegradable temporary plugging shell and a support core completely covered by the biodegradable temporary plugging shell; in The biodegradable temporary plugging shell is made of a reservoir-environment-degradable polymer material. It is used to bridge and plug open fractures and redirect pressure during fracturing operations. It can also degrade on its own under reservoir conditions to achieve unblocking. The reservoir-environment-degradable polymer material includes at least one of polylactic acid, polyglycolic acid, polycaprolactone, polylactic acid-polyglycolic acid copolymer, gelatin, and sodium alginate. The supporting core is made of a support material for oil and gas fracturing, and is used to provide mechanical support to reservoir fractures and maintain fracture conductivity after the biodegradable temporary plug shell degrades. The support material for oil and gas fracturing includes at least one of ceramsite, quartz sand, biodegradable ceramics, and high-strength polymers. The temporary plugging-support microspheres can enter reservoir fractures through a single injection process. They are first plugged and redirected by the biodegradable temporary plugging shell, and then supported by the support core after the biodegradable temporary plugging shell degrades.

2. The temporary plugging-support microsphere according to claim 1, characterized in that, The thickness of the biodegradable temporary plugging shell is 20-200 μm, and the degradation time of the biodegradable temporary plugging shell under reservoir conditions is 1-30 days.

3. The temporary plugging-support microsphere according to claim 1, characterized in that, The particle size of the supporting core is 100-500μm, and the compressive strength of the supporting core is not less than 35MPa.

4. The temporary plugging-support microsphere according to claim 1, characterized in that, The overall particle size of the temporary plugging-support microspheres is 150-800 μm; the mass of the biodegradable temporary plugging shell accounts for 20%-60% of the total mass of the microspheres, and the mass of the support core accounts for 40%-80% of the total mass of the microspheres.

5. The temporary plugging-support microsphere according to claim 1, characterized in that, The biodegradable temporary plugging shell is made of polylactic acid, and the supporting core is made of ceramic particles, forming a core-shell composite structure of ceramic particle core and polylactic acid shell.

6. A method for preparing temporary plugging-support microspheres according to any one of claims 1 to 5, characterized in that, Includes the following steps: Pretreatment of the surface of the propping material particles for oil and gas fracturing: First, the propping material for oil and gas fracturing is soaked in a first-type alcohol organic solvent and ultrasonically cleaned, then filtered and dried; then, a silane coupling agent treatment solution with a mass fraction of 0.1%-5% is prepared, and the dried propping material for oil and gas fracturing is immersed in the treatment solution and stirred, then filtered and dried again to obtain the pretreated propping material; Preparation of coating solution of biodegradable polymer material in reservoir environment: Dissolve biodegradable polymer material in halogenated hydrocarbon, ketone or ester organic solvent to prepare coating solution with mass fraction of 5wt%-15wt%; Preparation of coating suspension: The surface-pretreated support material is added to the coating solution and stirred to form a uniform suspension; Preparation of biodegradable temporary plugging shell emulsion: Prepare a polyvinyl alcohol aqueous solution, add the suspension to the polyvinyl alcohol aqueous solution and subject it to high-speed shearing to form a stable emulsion; Precipitation of biodegradable polymeric materials in the reservoir environment and formation of biodegradable temporary plugging shell: The emulsion is continuously stirred at room temperature to allow the halogenated hydrocarbons, ketones or esters to slowly evaporate, and the biodegradable polymeric materials in the reservoir environment precipitate and solidify on the surface of the support material to form a biodegradable temporary plugging shell covering the support material. Temporarily plugged-supported microsphere formation: The coated emulsion is first centrifuged, then washed sequentially with water and a second alcohol organic solvent, and then spread in a petri dish to dry, thus obtaining the temporarily plugged-supported microspheres.

7. The method according to claim 6, characterized in that, The propping material for oil and gas fracturing is at least one of ceramsite, quartz sand, biodegradable ceramics, and high-strength polymers; and / or, the biodegradable polymer material for the reservoir environment is at least one of polylactic acid, polyglycolic acid, polycaprolactone, polylactic acid-polyglycolic acid copolymer, gelatin, and sodium alginate.

8. The method according to claim 6, characterized in that, The first alcoholic organic solvent is at least one of anhydrous ethanol, isopropanol, and ethylene glycol monobutyl ether, or an aqueous solution prepared using any one of anhydrous ethanol, isopropanol, and ethylene glycol monobutyl ether; and / or, The silane coupling agent in the silane coupling agent treatment solution is at least one selected from aminosilane, epoxysilane, methacryloxysilane, vinylsilane, and isocyanate silane; and / or, The solvent in the silane coupling agent treatment solution is a mixture of an organic solvent and water, or an anhydrous organic solvent; wherein the organic solvent is at least one selected from ethanol, isopropanol, methanol, and acetone; and / or, The halogenated hydrocarbon, ketone, or ester organic solvent is at least one selected from dichloromethane, chloroform, acetone, and ethyl acetate; and / or, The washing solvent is deionized water; and / or, The second alcoholic organic solvent is at least one of anhydrous ethanol, methanol, and isopropanol.

9. The method according to claim 6, characterized in that, The ultrasonic cleaning time is 10 minutes; and / or the high-speed shearing time is 3 to 5 minutes.

10. An application of the temporary plugging-support microsphere according to any one of claims 1-5 in hydraulic fracturing of oil and gas reservoirs, characterized in that, The temporary plugging-support microspheres are mixed with fracturing fluid and injected into the reservoir in a single operation to achieve integrated construction of temporary plugging, diversion and support.

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