A self-degradable reservoir protection temporary plugging agent suitable for unconventional reservoirs, and its preparation method and application

Abstract

The present invention provides a temporary plugging agent for self-degradable reservoir protection in unconventional reservoirs, and its preparation method and application, which belongs to the field of reservoir protection in oil and gas field development. The preparation method of the temporary plugging agent comprises the following steps: (1) melt-blending a mixture of polylactic acid and polycaprolactone to obtain a molten phase; (2) adding a reinforcing agent to a silane coupling agent solution and performing ultrasonic treatment, filtering, washing, and drying to obtain a modified reinforcing agent; (3) adding a cross-linking agent to an ethanol aqueous solution and performing pre-hydrolysis to obtain a pre-hydrolyzed cross-linking agent solution; (4) sequentially adding the pre-hydrolyzed cross-linking agent solution, a modified reinforcing agent, an initiator, and a degradation agent to the obtained molten phase, stirring evenly; cooling, crushing, washing, and freeze-drying to obtain. The temporary plugging agent of the present invention has the advantages of easy availability of raw materials and a simple preparation process. The obtained temporary plugging agent can effectively plug fracture leakage. At the same time, after the temporary plugging agent is degraded, the reservoir permeability can be restored.

Description

Technical Field

[0001] The invention relates to a temporary plugging agent suitable for self-degrading reservoir protection in unconventional reservoirs, a preparation method and application thereof, and belongs to the field of reservoir protection in oil and gas field development. Background Art

[0002] Unconventional energy resources include shale oil and gas, coalbed methane, and natural gas hydrates. With the continuous deepening of oil and gas exploration and development, the development of unconventional oil and gas has gradually moved deeper, which can easily lead to fracture-induced leakage in unconventional reservoirs during extraction, affecting the stability of unconventional reservoirs and reducing extraction efficiency.

[0003] During oil and gas production, drilling operations directly impact the effective extraction of oil and gas resources from unconventional reservoirs. Drilling fluid intrusion into the reservoir is a major issue affecting unconventional reservoir damage. Once fracture-induced leakage occurs during drilling, drilling fluid loss occurs rapidly. If not controlled promptly, large amounts of drilling fluid can leak into the reservoir, causing reservoir damage, extending drilling and completion cycles, severely hindering oil and gas exploration and development, and increasing project costs. Therefore, resolving or preventing leakage is a pressing technical challenge. To address fracture-induced leakage in unconventional reservoirs, a common approach is to add temporary plugging agents to seal the fluid and mitigate the damage caused by fracture-induced leakage.

[0004] During the drilling and completion of oil and gas wells, temporary plugging agents are often used to seal off specific areas and fractures. Their performance is directly related to the well's subsequent production. If the temporary plugging agents are not promptly decomposed or removed, they can restrict the flow of oil and gas, preventing normal oil and gas penetration. Existing publicly available technologies for sealing reservoir fractures still have many shortcomings. For example, the reservoir protection formula for pre-supporting cracks and temporarily plugging deep fractured oil and gas layers disclosed in Chinese patent document CN116297098A is as follows: 4% LCC100-8-1+4% LCC100-8-2+2.8% GZD-A+4.3% GZD-B+2.2% GZD-C+3.7% GZD-D, which is mainly GZD series materials. Therefore, when it is dissolved in the later stage, 20% hydrochloric acid is needed to dissolve it and remove it in order to restore the seepage capacity of the reservoir fractures. High concentration of hydrochloric acid will chemically react with minerals in the rock, especially with calcium carbonate and other soluble minerals, change the pore structure and permeability of the rock, reduce the bearing capacity of the rock, increase the risk of formation collapse, and affect the stability of the formation. Chinese patent document CN107828010A discloses a polymer for preparing a temporary plugging agent and a preparation method of the temporary plugging agent, which mainly includes raw materials such as acrylamide and acrylic acid 2-acrylamide-2-methylpropanesulfonic acid, a metal ion crosslinker as the crosslinking agent, and a peroxide as the breaker. However, metal ions may react with clay minerals in the reservoir, causing clay mineral expansion and particle migration, thereby changing the pore structure, reducing permeability, and damaging the reservoir. In addition, peroxide is unstable during use, easily decomposes and generates pollutants that are incompatible with the formation, changing the chemical environment of the formation, causing formation damage, and thus prolonging the cycle of oil and gas field development. Chinese patent document CN115678521A provides a reservoir protection temporary plugging agent suitable for water-based drilling fluid. During preparation, biodegradable material particles polylactic acid are added as a temporary plugging material, and a non-water-soluble resin is used as a shell to protect the biodegradable material to prevent it from degrading too quickly. However, non-water-soluble resins are highly adhesive and non-degradable. This means that once deposited in a well or fracture, they form a persistent blockage that cannot be naturally decomposed or removed. This residual resin accumulates in the fractures, significantly reducing the permeability of the reservoir and hindering fluid flow, thus affecting the effective recovery of oil and gas.Chinese patent document CN113185960A discloses a temperature-responsive self-degradable temporary plugging agent, its preparation method, and its application in wellbore plugging. The preparation raw materials include: 4-6% monomer, 0.2-1% cross-linking agent, 0.02-0.06% initiator, 0.05-0.1% degradation catalyst, 0.01-0.05% chain transfer agent, and water as the balance. The temporary plugging agent provided is suitable for reservoirs with a reservoir temperature of 50-80°C. It cross-links to form a plug within 1-5 hours and can automatically degrade and hydrate within 3-7 days. However, the temporary plugging agent has a long automatic degradation cycle, the gel strength cannot meet the complex pressure differential environment of old oilfield production enhancement and reconstruction, and the gel strength duration is short. Chinese patent document CN118256201A provides a reservoir protective agent for oil-based drilling fluid, which comprises, by mass, 100 parts of solvent oil, 7 to 18 parts of emulsifier, 20 to 50 parts of surface-modified degradable nano-micron plugging agent, 6 to 17 parts of surface-modified acid-soluble nano-inert particles, and 3 to 5 parts of suspending dispersant. The surface-modified degradable nano-micron plugging agent is prepared by the following process: 100 parts of degradable polyester and 2 to 8 parts of chain extender are added to a blending extruder. The process involves heating the reaction vessel to 60-75°C and passing nitrogen at 0.5-0.7 MPa. The reaction is then heated to 170-190°C, and after completion, the reaction vessel is pressurized to extrude the reactants into granules. After the granules cool and form, they are frozen to -10-20°C and ground to nano-micron size. The nano-micron-sized particles are then added to an aqueous surfactant solution for surface modification, and then heated to 50-60°C for drying to obtain the surface-modified, degradable nano-micron plugging agent. However, the agent suffers from issues such as limited tolerance to high-temperature and high-pressure environments, uncontrollable plugging time, and significant fluctuations in plugging performance.

[0005] Therefore, it is of great significance to develop a temporary plugging agent that can effectively seal fracture leakage and is easily degradable and suitable for unconventional reservoirs. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention provides a self-degrading temporary plugging agent for unconventional reservoir protection, as well as its preparation method and application. The temporary plugging agent of the present invention has the advantages of readily available raw materials and a simple preparation process. The resulting temporary plugging agent can effectively seal fracture-induced leakage and, after degradation, can restore reservoir permeability.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing a self-degradable reservoir protection temporary plugging agent suitable for unconventional reservoirs comprises the following steps:

[0009] (1) melt-blending a mixture of polylactic acid and polycaprolactone to obtain a molten phase;

[0010] (2) adding the reinforcing agent to a silane coupling agent solution and performing ultrasonic treatment, followed by filtering, washing, and drying to obtain a modified reinforcing agent;

[0011] (3) adding the cross-linking agent to an ethanol aqueous solution for pre-hydrolysis to obtain a pre-hydrolyzed cross-linking agent solution;

[0012] (4) The pre-hydrolyzed cross-linking agent solution obtained in step (3), the modifier, enhancer, initiator and degradation agent obtained in step (2) are sequentially added to the molten phase obtained in step (1) and stirred evenly; after cooling, crushing, washing and freeze-drying, a temporary plugging agent suitable for self-degradable reservoir protection in unconventional reservoirs is obtained.

[0013] Preferably, according to the present invention, the molecular weight of the polylactic acid in step (1) is 50,000-100,000 g / mol, and the molecular weight of the polycaprolactone is 30,000-70,000 g / mol; and the mass ratio of the polylactic acid to the polycaprolactone is 30-40:20-30.

[0014] According to the preferred embodiment of the present invention, in step (1), the melting temperature is 140-180°C, more preferably 150-160°C, and the melting time is 4-5 hours.

[0015] According to the preferred embodiment of the present invention, the reinforcing agent in step (2) is glass fiber or polypropylene fiber; the diameter of the reinforcing agent is 5-15 μm and the length is 5-15 mm; the mass ratio of the reinforcing agent to polylactic acid is 1-2:30-40.

[0016] According to the present invention, preferably, the silane coupling agent in step (2) is γ-aminopropyltriethoxysilane (KH550), γ-glycidyloxypropyltrimethoxysilane (KH560) or methyltrimethoxysilane (KH540); the mass ratio of the silane coupling agent to the reinforcing agent is 1-2:10; the mass concentration of the silane coupling agent solution is 0.5-1.5wt%, and the silane coupling agent solution is obtained by dissolving the silane coupling agent in an ethanol aqueous solution, and the volume ratio of ethanol to water in the ethanol aqueous solution is 6-9:1.

[0017] According to the preferred embodiment of the present invention, the ultrasonic treatment time in step (2) is 20 to 40 minutes.

[0018] According to the preferred embodiment of the present invention, the washing in step (2) is washing with deionized water for 2 to 3 times; and the drying is drying at 80 to 120° C. to a constant weight.

[0019] Preferably, according to the present invention, the cross-linking agent in step (3) is methyltrimethoxysilane or dimethyldimethoxysilane; and the mass ratio of the cross-linking agent to polylactic acid is 1-2:30-40.

[0020] Preferably, according to the present invention, the ethanol aqueous solution in step (3) is obtained by mixing ethanol and water in a volume ratio of 4 to 9:1.

[0021] Preferably, according to the present invention, the ratio of the mass of the cross-linking agent to the volume of the ethanol aqueous solution in step (3) is 1-5 g:100 mL.

[0022] According to the preferred embodiment of the present invention, the pre-hydrolysis time in step (3) is 20 to 40 minutes.

[0023] According to the preferred embodiment of the present invention, the initiator in step (4) is ammonium persulfate or potassium persulfate, and the mass ratio of the initiator to polylactic acid is 0.5-1:30-40.

[0024] Preferably, according to the present invention, the degradation agent in step (4) is poly-3-hydroxybutyrate or polybutylene terephthalate; the molecular weight of the poly-3-hydroxybutyrate is 50,000-200,000 g / mol, and the molecular weight of the polybutylene terephthalate is 30,000-200,000 g / mol; and the mass ratio of the degradation agent to polylactic acid is 5-10:30-40.

[0025] Preferably, according to the present invention, after adding the pre-hydrolyzed cross-linking agent solution in step (4), stirring is carried out at 140-180°C for 10-20 minutes; after adding the modifying enhancer, stirring is carried out at 140-180°C for 10-20 minutes; after adding the initiator, stirring is carried out at 120-150°C for 20-40 minutes; after adding the degradation agent, stirring is carried out at 120-150°C for 20-40 minutes.

[0026] According to the preferred embodiment of the present invention, the pre-hydrolyzed cross-linking agent solution, modifier, initiator and degradation agent in step (4) are all added under nitrogen protection and stirring conditions.

[0027] According to the preferred embodiment of the present invention, the washing in step (4) is performed using anhydrous ethanol for 2 to 3 times, the freeze-drying temperature is -60°C to -40°C, and the freeze-drying time is 45 to 50 hours.

[0028] The present invention also provides a temporary plugging agent for self-degrading reservoir protection applicable to unconventional reservoirs, which is prepared by the above-mentioned preparation method.

[0029] According to the present invention, the above-mentioned self-degradable reservoir protection temporary plugging agent suitable for unconventional reservoirs is used to seal cracks and prevent drilling fluid loss during the drilling process of unconventional reservoirs; the unconventional reservoirs include but are not limited to shale oil and gas reservoirs, coalbed methane reservoirs, and natural gas hydrate reservoirs.

[0030] The technical features and beneficial effects of the present invention are as follows:

[0031] 1. The present invention uses polylactic acid (PLA) and polycaprolactone (PCL) as raw materials. PCL is a semi-crystalline polymer. When the two are blended, it can act as a nucleating agent to induce the crystallization of amorphous PLA, thereby increasing the crystallinity and crystallization rate of PLA. At the same time, PCL has good toughness but poor strength, while PLA has high strength but poor impact resistance. Mixing the two can achieve complementary toughness and strength. The degradation rate of PCL is slow, while the degradation rate of PLA is fast. By mixing these two materials, the degradation rate of the temporary plugging agent can be controlled. PLA is a new type of biodegradable material made from renewable plant resources. After use, it can be completely degraded by microorganisms to produce carbon dioxide and water, without polluting the environment. PCL can also be degraded into carbon dioxide and water. Both are environmentally friendly materials.

[0032] 2. The temporary plugging agent of the present invention increases the strength of the material by adding a reinforcing agent. Both glass fiber and polypropylene fiber have good high temperature resistance. Their addition can enable the temporary plugging agent to maintain good structural stability even at high temperatures. The high tensile strength of the fiber can provide good mechanical properties for the temporary plugging agent, fill the gaps in the temporary plugging agent, increase the overall strength of the temporary plugging agent, and improve the compressive, tensile and shear strengths, so that it can still maintain structural integrity under higher external pressures and stresses. Improving the stability of the temporary plugging agent helps the temporary plugging agent maintain good performance under different pressures, temperatures and chemical environments, prolongs the life of the plugging agent, and ensures the reliability and durability of the plugging process.

[0033] 3. The temporary plugging agent of this invention incorporates a degradation agent, poly-3-hydroxybutyrate (PHB) or polybutylene terephthalate (PBT), to achieve reversibility of the plugging agent's effect. The degradation of PHB and PBT is primarily due to the ester bond (-COO-) in their molecular structure. Ester bonds break down through hydrolysis in water or environments with high moisture content. Furthermore, many microorganisms possess enzymes, such as lipase, that catalyze the hydrolysis of ester bonds. Through microbial degradation, PHB or PBT can be broken down into small molecules, which can ultimately be metabolized or converted into harmless environmental substances such as water and carbon dioxide. The addition of a degradation agent can control the duration of the plugging agent's effect. By adjusting the degradation agent concentration and reaction conditions, the degradation rate of the plugging agent can be controlled, ensuring effective operation within a specific plugging period. Furthermore, the addition of a degradation agent can control the plugging agent's degradation rate, allowing the plugging agent to rapidly degrade, dissolve, or decompose when the plugging is needed, restoring the reservoir's original channels or permeability. This reversible plugging is crucial for systems that require frequent operations or periodic maintenance. In addition, self-degradable materials are environmentally friendly, reducing the long-term negative impact of residual pollutants on the formation, reducing cleaning and costs in operational projects, and reducing environmental pollution, which is in line with modern green and environmentally friendly production concepts.

[0034] 4. The temporary plugging agent of the present invention incorporates a crosslinking agent, methyltrimethoxysilane or dimethyldimethoxysilane. By introducing chemical bonds between polymer chains, a three-dimensional crosslinked network is formed, significantly enhancing the temporary plugging agent's mechanical strength, thermal stability, and corrosion resistance, enabling it to maintain structural integrity in complex downhole environments such as high temperature, high pressure, and severe shear. Furthermore, the functional groups (Si-OR) contained in the crosslinking agent, methyltrimethoxysilane or dimethyldimethoxysilane, react with hydroxyl groups on the surface of the reinforcing agent after hydrolysis, thereby achieving good interfacial bonding between the reinforcing components, such as inorganic glass fiber, and the organic matrix. This improves the composite material's dispersibility and adhesion, preventing delamination between components or degradation of mechanical properties.

[0035] 5. The plugging agent of the present invention can be applied to the fracture leakage phenomenon caused by the drilling process of unconventional reservoirs. After adding the temporary plugging agent, the fractures can be effectively blocked to prevent the drilling fluid from leaking into the formation and causing reservoir damage. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is the infrared spectrum of the self-degradable reservoir protection temporary plugging agent suitable for unconventional reservoirs prepared in Example 1. DETAILED DESCRIPTION

[0037] The present invention will be described in detail below with reference to the following embodiments, but the present invention is not limited to the following embodiments.

[0038] Meanwhile, the experimental methods described in the following examples, unless otherwise specified, are conventional methods; the reagents and materials, unless otherwise specified, can be obtained from conventional commercial channels.

[0039] The molecular weight of the polylactic acid used in the examples is 100,000 g / mol, the molecular weight of the polycaprolactone is 50,000 g / mol, the molecular weight of the poly-3-hydroxybutyrate is 100,000 g / mol, and the molecular weight of the polybutylene terephthalate is 100,000 g / mol.

[0040] The diameter of the glass fiber and the polypropylene fiber were 10 μm and the length was 10 mm.

[0041] The “parts” described in the following examples and comparative examples are all parts by weight.

[0042] Example 1

[0043] A method for preparing a self-degradable reservoir protection temporary plugging agent suitable for unconventional reservoirs comprises the following steps:

[0044] (1) Weigh 30 parts of polylactic acid and 30 parts of polycaprolactone, melt blend at 150°C for 5 hours to obtain a molten phase;

[0045] (2) Two parts of reinforcing glass fiber were placed in 20 parts of a 1 wt% KH550 ethanol aqueous solution (the volume ratio of ethanol to water was 6:1) and ultrasonicated for 30 min. The mixture was filtered, washed three times with deionized water, and dried at 100 °C to constant weight to obtain a modified reinforcing agent.

[0046] (3) Mix 2 parts of a crosslinker, methyltrimethoxysilane, with an ethanol aqueous solution (the volume ratio of ethanol to water in the ethanol aqueous solution is 6:1), with the mass ratio of the crosslinker to the volume of the ethanol aqueous solution being 2 g:100 mL, and stir and hydrolyze for 30 minutes to obtain a pre-hydrolyzed crosslinker solution;

[0047] (4) Add the pre-hydrolyzed cross-linking agent solution obtained in step (3) to the molten phase obtained in step (1), and stir at 150°C for 15 minutes; then add the modified reinforcing agent obtained in step (2), and stir at 150°C for 15 minutes; then add 1 part of initiator ammonium persulfate, and stir at 130°C for 30 minutes; finally, add 10 parts of degradation agent poly-3-hydroxybutyrate, and stir at 130°C for 30 minutes to disperse evenly;

[0048] (5) Pour out the reactants from step (4) and cool them down. After cooling, crush them using a crusher and sieve out particles with a size of 500 mesh.

[0049] (6) The particles obtained in step (5) were washed twice with anhydrous ethanol to remove free crosslinkers and oligomers, and freeze-dried at -50°C for 48 hours to obtain a self-degradable reservoir protection temporary plugging agent suitable for unconventional reservoirs.

[0050] The infrared spectrum of the self-degradable temporary plugging agent for unconventional reservoir protection prepared in Example 1 is as follows: Figure 1 As shown by Figure 1 It can be seen that 3300cm -1 The broad -OH peak near 1750 cm indicates the presence of residual hydroxyl groups during the hydrolysis of KH550. -1 The C=O stretching vibration of the ester group in polylactic acid, polycaprolactone and poly-3-hydroxybutyrate was detected at 1250 cm -1 -1050cm -1 The COC stretching was detected at 1020 cm -1 -1100cm -1 Si-O-Si and Si-OC stretching vibrations were detected, indicating that the cross-linking agent was cross-linked with the hydroxyl groups in the system after hydrolysis, indicating that the target temporary plugging agent material was successfully constructed.

[0051] Example 2

[0052] A method for preparing a self-degradable temporary plugging agent for protecting unconventional reservoirs is as described in Example 1, except that the weight parts of the raw materials are as follows:

[0053] 30 parts of polylactic acid, 30 parts of polycaprolactone, 2 parts of reinforcing agent glass fiber, 1 part of cross-linking agent methyltrimethoxysilane, 1 part of initiator ammonium persulfate, and 10 parts of degradation agent poly-3-hydroxybutyrate;

[0054] In step (2), 2 parts of reinforcing glass fibers are placed in 20 parts of a 1 wt% KH550 ethanol aqueous solution (the volume ratio of ethanol to water is 6:1). Other conditions and steps are the same as in Example 1.

[0055] Example 3

[0056] A method for preparing a self-degradable temporary plugging agent for protecting unconventional reservoirs is as described in Example 1, except that the weight parts of the raw materials are as follows:

[0057] 30 parts of polylactic acid, 30 parts of polycaprolactone, 1 part of reinforcing agent glass fiber, 2 parts of cross-linking agent methyltrimethoxysilane, 1 part of initiator ammonium persulfate, and 10 parts of degradation agent poly-3-hydroxybutyrate;

[0058] In step (2), 1 part of reinforcing glass fiber is placed in 10 parts of a 1 wt% KH550 ethanol aqueous solution (the volume ratio of ethanol to water is 6:1). Other conditions and steps are the same as those in Example 1.

[0059] Example 4

[0060] A method for preparing a self-degradable temporary plugging agent for protecting unconventional reservoirs is as described in Example 1, except that the weight parts of the raw materials are as follows:

[0061] 30 parts of polylactic acid, 30 parts of polycaprolactone, 2 parts of reinforcing agent glass fiber, 2 parts of cross-linking agent methyltrimethoxysilane, 1 part of initiator ammonium persulfate, and 5 parts of degradation agent poly-3-hydroxybutyrate;

[0062] In step (2), 2 parts of reinforcing glass fibers are placed in 20 parts of a 1 wt% KH550 ethanol aqueous solution (the volume ratio of ethanol to water is 6:1). Other conditions and steps are the same as in Example 1.

[0063] Example 5

[0064] A method for preparing a self-degradable temporary plugging agent for protecting unconventional reservoirs is as described in Example 1, except that the weight parts of the raw materials are as follows:

[0065] 30 parts of polylactic acid, 30 parts of polycaprolactone, 2 parts of reinforcing agent glass fiber, 2 parts of cross-linking agent methyltrimethoxysilane, 1 part of initiator ammonium persulfate, and 10 parts of degradation agent polybutylene terephthalate;

[0066] In step (2), 2 parts of reinforcing glass fibers are placed in 20 parts of a 1 wt% KH550 ethanol aqueous solution (the volume ratio of ethanol to water is 6:1). Other conditions and steps are the same as in Example 1.

[0067] Example 6

[0068] A method for preparing a self-degradable temporary plugging agent for protecting unconventional reservoirs is as described in Example 1, except that the weight parts of the raw materials are as follows:

[0069] 30 parts of polylactic acid, 30 parts of polycaprolactone, 2 parts of reinforcing agent glass fiber, 2 parts of cross-linking agent methyltrimethoxysilane, 0.5 parts of initiator ammonium persulfate, and 10 parts of degradation agent poly-3-hydroxybutyrate;

[0070] In step (2), 2 parts of reinforcing glass fibers are placed in 20 parts of a 1 wt% KH550 ethanol aqueous solution (the volume ratio of ethanol to water is 6:1). Other conditions and steps are the same as in Example 1.

[0071] Example 7

[0072] A method for preparing a self-degradable temporary plugging agent for protecting unconventional reservoirs is as described in Example 1, except that the weight parts of the raw materials are as follows:

[0073] 30 parts of polylactic acid, 30 parts of polycaprolactone, 2 parts of reinforcing agent glass fiber, 2 parts of cross-linking agent methyltrimethoxysilane, 1 part of initiator potassium persulfate, and 10 parts of degradation agent poly-3-hydroxybutyrate;

[0074] In step (2), 2 parts of reinforcing glass fibers are placed in 20 parts of a 1 wt% KH550 ethanol aqueous solution (the volume ratio of ethanol to water is 6:1). Other conditions and steps are the same as in Example 1.

[0075] Example 8

[0076] A method for preparing a self-degradable reservoir protection temporary plugging agent suitable for unconventional reservoirs is as described in Example 1, except that the reinforcing agent is polypropylene fiber.

[0077] Example 9

[0078] A method for preparing a self-degradable reservoir protection temporary plugging agent suitable for unconventional reservoirs is as described in Example 1, except that the cross-linking agent is dimethyldimethoxysilane.

[0079] Example 10

[0080] A method for preparing a self-degradable reservoir protection temporary plugging agent suitable for unconventional reservoirs is as described in Example 1, except that an equal mass of KH560 is used instead of KH550 in step (2).

[0081] Example 11

[0082] A method for preparing a self-degradable reservoir protection temporary plugging agent suitable for unconventional reservoirs is as described in Example 1, except that an equal mass of KH540 is used instead of KH550 in step (2).

[0083] Comparative Example 1

[0084] A method for preparing a self-degradable reservoir protection temporary plugging agent suitable for unconventional reservoirs is as described in Example 1, except that polycaprolactone is not added. The mass parts of the raw materials are as follows:

[0085] 30 parts of polylactic acid, 2 parts of reinforcing agent glass fiber, 2 parts of cross-linking agent methyltrimethoxysilane, 1 part of initiator ammonium persulfate, and 10 parts of degradation agent poly-3-hydroxybutyrate.

[0086] Comparative Example 2

[0087] A method for preparing a self-degradable reservoir protection temporary plugging agent suitable for unconventional reservoirs is as described in Example 1, except that polylactic acid is not added. The weight parts of the raw materials are as follows:

[0088] 30 parts of polycaprolactone, 2 parts of reinforcing agent glass fiber, 2 parts of crosslinking agent methyltrimethoxysilane, 1 part of initiator ammonium persulfate, and 10 parts of degradation agent poly-3-hydroxybutyrate.

[0089] Comparative Example 3

[0090] A method for preparing a self-degradable reservoir protection temporary plugging agent suitable for unconventional reservoirs is as described in Example 1, except that no reinforcing agent is added. The weight parts of the raw materials are as follows:

[0091] 30 parts of polylactic acid, 30 parts of polycaprolactone, 2 parts of crosslinking agent methyltrimethoxysilane, 1 part of initiator ammonium persulfate, and 10 parts of degradation agent poly-3-hydroxybutyrate.

[0092] Comparative Example 4

[0093] A method for preparing a self-degradable temporary plugging agent for protecting unconventional reservoirs is as described in Example 1, except that no cross-linking agent is added. The weight parts of the raw materials are as follows:

[0094] 30 parts of polylactic acid, 30 parts of polycaprolactone, 2 parts of reinforcing agent glass fiber, 1 part of initiator ammonium persulfate, and 10 parts of degradation agent poly-3-hydroxybutyrate.

[0095] Comparative Example 5

[0096] A method for preparing a self-degradable temporary plugging agent for protecting unconventional reservoirs is as described in Example 1, except that the cross-linking agent is not pre-hydrolyzed. The specific steps are as follows:

[0097] (1) Weigh 30 parts of polylactic acid and 30 parts of polycaprolactone, melt blend at 150°C for 5 hours to obtain a molten phase;

[0098] (2) Two parts of reinforcing glass fiber were placed in 20 parts of a 1 wt% KH550 ethanol aqueous solution (the volume ratio of ethanol to water was 6:1) and ultrasonicated for 30 min. The mixture was filtered, washed three times with deionized water, and dried at 100 °C to constant weight to obtain a modified reinforcing agent.

[0099] (3) Add 2 parts of crosslinking agent methyltrimethoxysilane to the molten phase obtained in step (1) and stir at 150°C for 15 minutes; then add the modifier obtained in step (2) and stir at 150°C for 15 minutes; then add 1 part of initiator ammonium persulfate and stir at 130°C for 30 minutes; finally add 10 parts of degradation agent poly-3-hydroxybutyrate and stir at 130°C for 30 minutes to disperse evenly;

[0100] (4) Pour out the reactants from step (3) and cool them down. After cooling, crush them using a crusher and sieve out particles with a size of 500 mesh.

[0101] (5) The particles obtained in step (4) were washed twice with anhydrous ethanol to remove free crosslinkers and oligomers, and freeze-dried at -50°C for 48 hours to obtain a self-degradable reservoir protection temporary plugging agent suitable for unconventional reservoirs.

[0102] Comparative Example 6

[0103] A method for preparing a self-degradable temporary plugging agent for protecting unconventional reservoirs is as described in Example 1, except that the reinforcing agent is not modified. The specific steps are as follows:

[0104] (1) Weigh 30 parts of polylactic acid and 30 parts of polycaprolactone, melt blend at 150°C for 5 hours to obtain a molten phase;

[0105] (2) Mix 2 parts of a crosslinker, methyltrimethoxysilane, with an ethanol aqueous solution (the volume ratio of ethanol to water in the ethanol aqueous solution is 6:1), with the mass ratio of the crosslinker to the volume of the ethanol aqueous solution being 2 g:100 mL, and stir and hydrolyze for 30 minutes to obtain a pre-hydrolyzed crosslinker solution;

[0106] (3) Add the pre-hydrolyzed crosslinker solution obtained in step (2) to the molten phase obtained in step (1), and stir at 150°C for 15 minutes; then add 2 parts of reinforcing glass fiber, and stir at 150°C for 15 minutes; then add 1 part of initiator ammonium persulfate, and stir at 130°C for 30 minutes; then add 10 parts of degradation agent poly-3-hydroxybutyrate, and stir at 130°C for 30 minutes to disperse evenly;

[0107] (4) Pour out the reactants from step (3) and cool them down. After cooling, crush them using a crusher and sieve out particles with a size of 500 mesh.

[0108] (5) The particles obtained in step (4) were washed twice with anhydrous ethanol to remove free crosslinkers and oligomers, and freeze-dried at -50°C for 48 hours to obtain a self-degradable reservoir protection temporary plugging agent suitable for unconventional reservoirs.

[0109] Test Example 1

[0110] 10 g of the temporary plugging agent prepared in Example 1 was mixed with 100 mL of deionized water and placed in a sealed container. The sealed container was placed in a constant temperature water bath at 100°C for 10 hours. The remaining solid mass was weighed and the degradation rate was calculated.

[0111] 10 g of the temporary plugging agent prepared in Example 1 was mixed with 100 mL of deionized water and placed in a sealed container. The sealed container was placed in a constant temperature water bath at 100° C. for 24 hours. The remaining solid mass was weighed and the degradation rate was calculated.

[0112] 10 g of the temporary plugging agent prepared in Example 1 was mixed with 100 mL of deionized water and placed in a sealed container. The sealed container was placed in a constant temperature water bath at 100° C. for 48 h. The remaining solid mass was weighed and the degradation rate was calculated.

[0113] The above operation was repeated for the remaining embodiments and comparative examples.

[0114] The degradation rates of the self-degradable temporary plugging agents prepared in different embodiments are calculated and shown in Table 1.

[0115] Table 1 Degradation rate of temporary plugging agent

[0116]

[0117] From the experimental data in the above table, it can be seen that the temporary plugging agent prepared by the present invention can be degraded by more than 80% in 24 hours and more than 87% in 48 hours, indicating that the temporary plugging agent has excellent degradation performance, low pollution, and can effectively restore reservoir permeability.

[0118] Test Example 2

[0119] A pressure displacement test was carried out using a multifunctional core displacement device. The displacement pressure was set to 30.0 MPa and water was injected into the core at a rate of 1 mL / min. Water was driven until the water content of the output water was 98%. The solid temporary plugging agent particles were configured into a uniformly dispersed suspension with a mass concentration of 3.0 wt%. 500 mL of the temporary plugging agent suspension was injected. After the pumping was completed, it was placed at 50 ° C for 8 hours, its permeability was measured, and the plugging rate was calculated.

[0120] Calculation of plugging rate: Plugging rate = (initial permeability - permeability after plugging) / initial permeability × 100%.

[0121] The plugging performance of the self-degradable temporary plugging agents prepared in different comparative examples is shown in Table 2.

[0122] Table 2 Plugging rate of temporary plugging agent

[0123]

[0124] As can be seen from the above table, the temporary plugging agent prepared in the embodiment of the present invention has a plugging rate of up to 96% or more, indicating that the temporary plugging agent of the present invention can not only effectively prevent leakage of drilling fluid, but also has an excellent plugging effect, thereby avoiding the problem of wellbore stability caused by leakage.

[0125] Test Example 3

[0126] The pressure-bearing capacity of a simulated sandfill was tested using a multifunctional core flooding device. First, a uniformly dispersed suspension of solid temporary plugging agent particles at a mass concentration of 3.0 wt% was injected into the sandfill. The suspension was then left at 80°C for 12 hours to simulate the consolidation process of the temporary plugging agent in a real-world formation environment. Water flooding was then applied, and pressure was slowly increased at a constant injection rate (1 mL / min). The moment when liquid seepage began at the outlet was monitored in real time, and the corresponding displacement pressure was recorded. The test results are shown in Table 3.

[0127] Table 3 Pressure bearing strength of temporary plugging agent

[0128]

[0129] The data in the table show that the temporary plugging agent prepared in the examples of the present invention exhibits superior compressive strength, with the highest compressive strength reaching 30.44 MPa, significantly higher than that of the samples in the comparative examples. This result demonstrates that the prepared temporary plugging agent possesses excellent mechanical strength and compactness, effectively withstanding high-pressure downhole environments and meeting the pressure requirements of unconventional reservoir plugging operations.

[0130] The above description is merely a few preferred embodiments of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing a self-degradable temporary plugging agent for protecting unconventional reservoirs, characterized in that: The steps are as follows: (1) melt-blending a mixture of polylactic acid and polycaprolactone to obtain a molten phase; the mass ratio of the polylactic acid to the polycaprolactone is 30-40:20-30; (2) adding a reinforcing agent to a silane coupling agent solution and performing ultrasonic treatment, and then filtering, washing, and drying to obtain a modified reinforcing agent; the reinforcing agent is glass fiber or polypropylene fiber; the mass ratio of the reinforcing agent to polylactic acid is 1-2:30-40; the silane coupling agent is γ-aminopropyltriethoxysilane, γ-glycidyloxypropyltrimethoxysilane or methyltrimethoxysilane; the mass ratio of the silane coupling agent to the reinforcing agent is 1-2:10; (3) adding a cross-linking agent to an ethanol aqueous solution for pre-hydrolysis to obtain a pre-hydrolyzed cross-linking agent solution; the cross-linking agent is methyltrimethoxysilane or dimethyldimethoxysilane; and the mass ratio of the cross-linking agent to the polylactic acid is 1-2:30-40; (4) The pre-hydrolyzed cross-linking agent solution obtained in step (3), the modifying enhancer obtained in step (2), the initiator and the degradation agent are sequentially added to the molten phase obtained in step (1) and stirred evenly; after cooling, crushing, washing and freeze-drying, a temporary plugging agent suitable for self-degradation reservoir protection of unconventional reservoirs is obtained; the initiator is ammonium persulfate or potassium persulfate, and the mass ratio of the initiator to the polylactic acid is 0.5-1:30-40; the degradation agent is poly-3-hydroxybutyrate or polybutylene terephthalate, and the mass ratio of the degradation agent to the polylactic acid is 5-10:30-40.

2. The method for preparing the self-degradable temporary plugging agent for protecting unconventional reservoirs according to claim 1, characterized in that: The molecular weight of the polylactic acid in step (1) is 50,000-100,000 g / mol, and the molecular weight of the polycaprolactone is 30,000-70,000 g / mol.

3. The method for preparing the self-degradable temporary plugging agent for protecting unconventional reservoirs according to claim 1, characterized in that: In step (1), the melting temperature is 140-180°C, and the melting time is 4-5 hours.

4. The method for preparing the self-degradable reservoir protection temporary plugging agent suitable for unconventional reservoirs according to claim 1, characterized in that: The diameter of the reinforcing agent in step (2) is 5-15 μm, and the length is 5-15 mm; the mass concentration of the silane coupling agent solution is 0.5-1.5 wt %, and the silane coupling agent solution is obtained by dissolving the silane coupling agent in an ethanol aqueous solution, wherein the volume ratio of ethanol to water in the ethanol aqueous solution is 6-9:1; the time of the ultrasonic treatment is 20-40 min; the washing is performed by washing with deionized water 2-3 times; and the drying is performed at 80-120° C. to constant weight.

5. The method for preparing the self-degradable temporary plugging agent for protecting unconventional reservoirs according to claim 1, characterized in that: The ethanol aqueous solution in step (3) is obtained by mixing ethanol and water in a volume ratio of 4 to 9:1; the ratio of the mass of the cross-linking agent to the volume of the ethanol aqueous solution is 1 to 5 g:100 mL; and the pre-hydrolysis time is 20 to 40 min.

6. The method for preparing the self-degradable temporary plugging agent for protecting unconventional reservoirs according to claim 1, characterized in that: The molecular weight of the poly-3-hydroxybutyrate in step (4) is 50,000-200,000 g / mol, and the molecular weight of the polybutylene terephthalate is 30,000-200,000 g / mol.

7. The method for preparing the self-degradable temporary plugging agent for protecting unconventional reservoirs according to claim 1, characterized in that: After adding the pre-hydrolyzed cross-linking agent solution in step (4), stirring is carried out at 140-180°C for 10-20 minutes; after adding the modifying enhancer, stirring is carried out at 140-180°C for 10-20 minutes; after adding the initiator, stirring is carried out at 120-150°C for 20-40 minutes; after adding the degradation agent, stirring is carried out at 120-150°C for 20-40 minutes.

8. The method for preparing the self-degradable temporary plugging agent for protecting unconventional reservoirs according to claim 1, characterized in that: The pre-hydrolyzed cross-linking agent solution, modifier, initiator and degradation agent in step (4) are added and stirred under nitrogen protection; the washing is performed using anhydrous ethanol for 2 to 3 times, the freeze-drying temperature is -60°C to -40°C, and the freeze-drying time is 45 to 50 hours.

9. A self-degradable reservoir protection temporary plugging agent suitable for unconventional reservoirs, characterized by: The preparation method is described in any one of claims 1 to 8.

10. The use of the self-degradable temporary plugging agent for unconventional reservoir protection according to claim 9, characterized in that: It is used to seal cracks and prevent drilling fluid loss during drilling in unconventional reservoirs; the unconventional reservoirs include shale oil and gas reservoirs, coalbed methane reservoirs, and natural gas hydrate reservoirs.

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