Plugging agent for oil-based drilling fluid, preparation method of plugging agent, plugging slurry and application of plugging slurry in oil-based drilling fluid

Abstract

The invention relates to the technical field of petroleum drilling plugging, in particular to a plugging agent for oil-based drilling fluid, a preparation method of the plugging agent, plugging slurry and application of the plugging slurry in the oil-based drilling fluid. The plugging agent comprises the following raw materials in parts by weight: 50-80 parts of a flaky material, 80-130 parts of a granular material and 60-100 parts of a fiber material, wherein the flaky material is flaky resin; the flaky material is formed by tabletting phenolic resin and epoxy resin; the thickness of the flaky material is 0.3 to 0.5 mm; the fiber material is selected from two or more of sepiolite fiber, asbestos wool or lignin fiber; the plugging agent is added into the oil-based drilling fluid and uniformly mixed to obtain the plugging slurry, and the plugging slurry is injected into a stratum through a conventional plugging process, so that a 3-5mm leakage crack can be plugged. The prepared plugging agent is high in plugging quality, capable of rapidly and effectively plugging cracks of 3-5 mm, high in pressure bearing capacity and small in leakage amount.

Description

Technical Field

[0001] The present invention relates to the technical field of oil drilling plugging, in particular to a plugging agent for oil-based drilling fluid, a preparation method thereof, a plugging slurry, and an application of the plugging slurry in oil-based drilling fluid. Background Art

[0002] During the drilling process, when drilling through high-permeability formations, especially formations with developed fractures or large holes, serious well leakage problems often occur. Well leakage is one of the common technical problems in drilling operations. It can lead to a large amount of loss of drilling fluid, not only increasing the drilling cost, but also damaging the oil and gas reservoirs, interfering with geological logging work, and even causing serious accidents such as stuck pipe, blowout, and well collapse. According to the morphology of the leakage channels, well leakage can be classified into porous leakage, fractured leakage, and cavernous leakage, among which fractured leakage is the main type of well leakage. In recent years, with the continuous progress of drilling technology and the in-depth exploration and development of oil and gas, the problem of oil-based drilling fluid leakage in fractured formations has become increasingly serious, seriously hindering the process of oil and gas resource exploration and development.

[0003] Currently, in the drilling plugging materials for oil and gas exploitation, they are roughly divided into two categories: water-based drilling fluid plugging and oil-based drilling fluid plugging. Most of the current drilling plugging materials are developed for water-based drilling fluid systems. There are many varieties of water-based drilling fluid plugging materials, such as lost circulation materials while drilling, composite plugging agents, bridge plugging agents, etc., with different particle sizes and materials. Commonly used materials include fiber products (such as paper, cottonseed hulls, etc.), particulate matter (such as nut shells), cellulose, plant gum, pentosan, etc.

[0004] With the continuous development of oil and gas exploitation, oil-based drilling fluid has advantages such as good lubricity, strong inhibition, good thermal stability, strong anti-invasion ability, and less damage to oil and gas reservoirs, and has great advantages in the application of deep wells, ultra-deep wells, offshore drilling, shale gas horizontal wells, and water-sensitive formations. However, compared with water-based drilling fluid, oil-based drilling fluid is more prone to leakage. Using plugging materials is currently the most common method to solve the problem of well leakage. Compared with the plugging materials for water-based drilling fluid, the types of plugging materials suitable for oil-based drilling fluid are still less. In on-site applications, the plugging materials for water-based drilling fluid are often used to solve the leakage problem of oil-based drilling fluid, and the plugging success rate is relatively low. Most conventional bridging materials are hydrophilic and have poor dispersibility in oil-based drilling fluid, resulting in poor plugging effect; water absorption and swelling materials and polymer gel materials cannot achieve sufficient swelling and gelation in oil-based drilling fluid and cannot effectively play a plugging role; there are problems such as contact pollution between conventional silicate cement slurry and oil-based drilling fluid. Due to the lack of oil-based drilling fluid plugging materials, and the problem of insufficient compatibility when water-based plugging agents are applied in oil-based drilling fluid systems, it is easy to damage the stability of oil-based drilling fluid, resulting in flocculation and precipitation of materials, affecting the plugging effect, and even blocking drilling equipment, increasing non-productive time.

[0005] Therefore, there is an urgent need to develop an oil-based plugging agent that has good compatibility with the oil-based drilling fluid system, strong dispersibility in the base oil, and good plugging effect. SUMMARY OF THE INVENTION

[0006] In view of the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide an oil-based plugging agent for oil-based drilling fluid, its preparation method, plugging slurry, and the application of the plugging slurry in the oil-based drilling fluid, which are used to solve the problems of poor compatibility between the plugging agent and the oil-based drilling fluid and poor plugging effect in the prior art.

[0007] To achieve the above-mentioned purpose and other related purposes, the present invention is obtained through the following technical solutions.

[0008] The first aspect of the present invention is to provide an oil-based plugging agent for oil-based drilling fluid, which comprises the following raw materials in parts by weight: 50 - 80 parts of sheet materials, 80 - 130 parts of granular materials, and 60 - 100 parts of fiber materials. The sheet material is a sheet resin; the sheet material is formed by pressing phenolic resin and epoxy resin; the thickness of the sheet material is 0.3 - 0.5 mm; the fiber material is selected from two or more of sepiolite fiber, asbestos wool, or lignin fiber.

[0009] The second aspect of the present invention is to provide a preparation method of an oil-based plugging agent for oil-based drilling fluid, which comprises the following steps: mixing the sheet material, granular material, and fiber material to obtain the plugging agent.

[0010] The third aspect of the present invention provides a plugging slurry, which comprises the above-mentioned plugging agent; preferably, the plugging slurry is composed of the above-mentioned plugging agent and the oil-based drilling fluid in a weight-to-volume ratio of 190 - 310 g:1 L.

[0011] The fourth aspect of the present invention is to provide the application of the above-mentioned plugging slurry or the oil-based plugging agent for oil-based drilling fluid in the field of plugging formation leakage cracks.

[0012] As described above, an oil-based plugging agent for oil-based drilling fluid, its preparation method, plugging slurry, and the application of the plugging slurry in the oil-based drilling fluid of the present invention have the following beneficial effects:

[0013] (1) The oil-based plugging agent of the present invention selects three components: sheet material, granular material, and fiber material, and adjusts and optimizes the ratio of the three components, so that the plugging agent has higher plugging quality, can quickly and effectively plug cracks of 3 - 5 mm, has high pressure-bearing capacity and small leakage volume.

[0014] (2) Each component of the lost circulation material for oil-based drilling fluid of the present invention selects inert materials with good lipophilicity, which is more suitable for oil-based drilling fluid and has good compatibility with the drilling fluid. It will not undergo physical or chemical reactions, does not affect the performance of the lost circulation slurry, and avoids safety problems in on-site lost circulation operations. At the same time, the selected materials are all natural or renewable resources, and no harmful substances are emitted during the preparation process, meeting the environmental protection requirements.

[0015] (3) Compared with traditional lost circulation materials, the materials used in this lost circulation material have lower costs, and the preparation process is simple, which helps to reduce production costs. At the same time, the selected materials are all natural or renewable resources, and no harmful substances are emitted during the preparation process, meeting the environmental protection requirements.

[0016] (4) The preparation method and application process of the lost circulation material for oil-based drilling fluid of the present invention are simple. The existing bridging lost circulation technology can be used to effectively control the lost circulation problem of oil-based drilling fluid, which is easy to operate and control, helps to reduce production costs and improve production efficiency. Specific embodiments

[0017] In order to make the invention purpose, technical solution and beneficial technical effects of the present invention clearer, the present invention will be further described in detail below with reference to embodiments. Those familiar with this technology can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0018] The first aspect of the present invention is to provide a lost circulation material for oil-based drilling fluid, including the following raw materials in parts by weight: 50 - 80 parts of sheet materials, 80 - 130 parts of granular materials, and 60 - 100 parts of fiber materials. The sheet materials are sheet resins; the sheet materials are formed by pressing phenolic resin and epoxy resin; the thickness of the sheet materials is 0.3 - 0.5 mm; the fiber materials are selected from two or more of sepiolite fiber, asbestos wool or lignin fiber.

[0019] Through the systematic action of the above-mentioned sheet materials, granular materials and fiber materials, the present invention can effectively block lost circulation cracks of 3 - 5 mm. In the lost circulation material provided by the present invention, the characteristics of the three materials complement each other. The sheet materials form the main supporting framework of a stable sealing layer. The granular materials fill the gaps between the sheet materials, improving the tightness and pressure-bearing capacity of the seal. The fiber materials are intertwined around the sheet and granular materials, enhancing the toughness and stability of the overall structure, preventing them from loosening or shifting under complex formation stresses, and jointly constituting a stable three-dimensional sealing structure, enabling the sealing layer formed by the lost circulation slurry to simultaneously have high strength, toughness and tightness, and improving the sealing quality.

[0020] The sheet material of the present invention plays a bridging role when plugging cracks, thereby improving the strength of plugging, requiring the sheet material to have a certain strength. When the sheet material is a sheet resin, the strength is better and the plugging effect is better. Independent sheet epoxy resin or phenolic resin cannot fully meet the requirements of the present application in terms of strength. The material compounded by epoxy resin and phenolic resin has obvious advantages in heat resistance, chemical corrosion resistance and mechanical strength, is more suitable for the oil industry, and has low cost. If materials such as mica or rice husk are used, due to the poor strength of mica or rice husk, the material strength is low, thereby causing insufficient pressure bearing capacity of plugging.

[0021] The components of the plugging agent of the present invention have good compatibility with the oil-based drilling fluid: the oil-based drilling fluid can be effectively suspended, no physical and chemical reactions occur, and the electrical stability of the oil-based drilling fluid is less affected; the material has good resistance to high-temperature aging: after high-temperature aging, the strength, particle size and other properties of the material change little or remain unchanged.

[0022] In some embodiments of the present invention, the plugging agent comprises the following raw materials in parts by weight: 50-80 parts of flaky material, 80-130 parts of granular material, and 60-100 parts of fibrous material.

[0023] In some embodiments of the present invention, the plugging agent comprises the following raw materials in parts by weight: 50-65 parts of flaky material, 80-110 parts of granular material, and 60-80 parts of fibrous material.

[0024] In some embodiments of the present invention, the plugging agent comprises the following raw materials in parts by weight: 65-80 parts of flaky material, 110-130 parts of granular material, and 80-100 parts of fibrous material.

[0025] In some embodiments of the present invention, the plugging agent includes the following raw materials in parts by weight: 50 parts of flaky material, 80 parts of granular material, and 60 parts of fibrous material.

[0026] In some embodiments of the present invention, the plugging agent includes the following raw materials in parts by weight: 65 parts of flaky material, 110 parts of granular material, and 80 parts of fibrous material.

[0027] In some embodiments of the present invention, the plugging agent includes the following raw materials in parts by weight: 80 parts of flaky material, 130 parts of granular material, and 100 parts of fibrous material.

[0028] In some embodiments of the present invention, the sheet material is formed by pressing a phenolic resin and an epoxy resin. The present invention has no requirements for the selection of the phenolic resin, and any phenolic resin can be used. The present invention has no requirements for the source of the phenolic resin, and commercially available products of phenolic resins commonly used by those skilled in the art can be used. Specifically, the phenolic resin can be a thermoplastic phenolic resin or a thermosetting phenolic resin. The present invention has no requirements for the selection of the epoxy resin, and any epoxy resin can be used. The present invention has no requirements for the source of the epoxy resin, and commercially available products of epoxy resins commonly used by those skilled in the art can be used. Specifically, the epoxy resin can be one or more of bisphenol A epoxy resin, bisphenol F epoxy resin, polyphenol type glycidyl ether epoxy resin, aliphatic glycidyl ether epoxy resin, and glycidyl ester type epoxy resin.

[0029] In some embodiments of the present invention, the mass ratio of the phenolic resin to the epoxy resin is 1-5:1-5. Specifically, the mass ratio of the phenolic resin to the epoxy resin can be 1-3:3-5 or 3-5:1-3. Typically but not restrictively, for example, it can be 1:3, 3:5, 5:3, or 3:1.

[0030] In some embodiments of the present invention, the thickness of the sheet material is 0.3-0.5 mm, and the particle size of the sheet material is 4-6 mesh. Specifically, the thickness of the sheet material can be 0.3-0.4 mm or 0.4-0.5 mm. Typically but not restrictively, for example, it can be 0.3 mm, 0.4 mm, or 0.5 mm.

[0031] In some embodiments of the present invention, the pressure for pressing is 15-18 MPa; the time for pressing is 25-40 min; the temperature for pressing is 175-195 °C. Specifically, the pressure for pressing can be 15-16 MPa or 16-18 MPa. Typically but not restrictively, for example, it can be 15 MPa, 16 MPa, or 18 MPa; the time for pressing can be 25-35 min or 35-40 min. Typically but not restrictively, for example, it can be 25 min, 35 min, or 40 min; the temperature for pressing can be 175-185 °C or 185-195 °C. Typically but not restrictively, for example, it can be 175 °C, 185 °C, or 195 °C.

[0032] In some embodiments of the present invention, the particulate material only needs to meet the following requirements, that is, the particulate material has good compatibility with the oil-based drilling fluid: it can be effectively suspended in the oil-based drilling fluid (density adaptability), does not undergo physical or chemical reactions (inertness), and has little influence on the electrical stability of the oil-based drilling fluid; (2) the particulate material has good high-temperature aging resistance: after high-temperature aging, the properties such as the strength and particle size of the material change little or remain unchanged. Specifically, the particulate material is selected from one or more of walnut shells or sepiolite powder; preferably, the particulate material is walnut shells. The walnut shells are carbonized and modified walnut shells. The carbonized and modified walnut shells can be self-made or commercially available; the carbonized and modified walnut shells of the present invention are commercially available, and the present invention has no special requirements for the source of the carbonized and modified walnut shells, and commercially available manufacturers of carbonized and modified walnut shells commonly used in the art can be adopted. Specifically, the manufacturer of the carbonized and modified walnut shells of the present invention is Xinjiang Grid Petroleum Technology Co., Ltd. The preparation method of the carbonized and modified walnut shells of the present invention includes the following steps: carbonizing the walnut shells at a temperature of 220-250°C for 45-60 minutes, and then cooling to obtain the carbonized and modified walnut shells.

[0033] In some embodiments of the present invention, the particle size gradation of the walnut shells and / or carbonized and modified walnut shells of the present invention. Specifically, the walnut shells or carbonized and modified walnut shells are obtained by grading particles with particle sizes of 4-6 mesh, 10-20 mesh, and 60-100 mesh; preferably, the walnut shells or carbonized and modified walnut shells are composed of particles with particle sizes of 4-6 mesh, 10-20 mesh, and 60-100 mesh in a mass ratio of 1-2:2-4:5-10. The mass ratio of the walnut shells with particle sizes of 4-6 mesh, 10-20 mesh, and 60-100 mesh can be 1-2:2-3:5-8, 1-2:3-4:8-10; typically but not restrictively, for example, 1:2:5, 2:3:10, 1:4:10. Compared with conventional mineral-based (calcite, basalt) plugging materials, the walnut shells have a smaller density, which is beneficial to dispersion in the oil-based drilling fluid and can avoid problems such as uneven distribution of the plugging agent in the drilling fluid caused by factors such as gravity segregation and affect the plugging quality; at the same time, the walnut shells have good compatibility with the oil-based drilling fluid and have little influence on the physical and chemical properties of the oil-based drilling fluid. The carbonized and modified walnut shells have higher hardness and wear resistance and can play a role in filling and supporting in the cracks. Filling walnut shells with different particle sizes can adapt to voids of different shapes and sizes, making the plugging agent more evenly distributed in the cracks microscopically, improving the tightness of the plugging, and at the same time can also assist the sheet material to bear a certain formation pressure and enhance the plugging effect.

[0034] In some embodiments of the present invention, the fiber material includes sepiolite fiber, asbestos wool, and lignin fiber; preferably, the fiber material is composed of sepiolite fiber, asbestos wool, and lignin fiber in a mass ratio of 1-3:3-9:2-4; specifically, the mass ratio of the sepiolite fiber, asbestos wool, and lignin fiber can be 1-2:3-6:2-3, 2-3:6-9:3-4; typically but not restrictively, for example, 1:3:2, 2:6:3, 3:9:4. Sepiolite fiber has lipophilicity and strong adaptability in oil-based drilling fluids; asbestos wool has certain high-temperature resistance, and in the complex high-temperature environment downhole, it can ensure that the performance of the plugging agent will not deteriorate severely due to high temperature; lignin fiber has good flexibility and can interweave with each other in the plugging slurry, playing a role in enhancing the toughness and integrity of the plugging slurry. Sepiolite fiber can extend in larger crack gaps, asbestos wool fills the tiny gaps between sepiolite fibers and tightly winds around other materials, and lignin fiber further strengthens the overall network structure, forming a multi-level network from macro to micro, improving the overall stability and plugging effect of the plugging slurry.

[0035] In some embodiments of the present invention, the length of the fiber material is 0.1-12 mm; the diameter is 80-150 μm. Specifically, the length of the fiber material can be 0.1-3 mm, 3-8 mm, 8-12 mm; the diameter of the fiber material can be 80-100 μm, 100-150 μm.

[0036] In some embodiments of the present invention, the length of the sepiolite fiber is 0.1-0.5 mm; specifically, the length of the sepiolite fiber can be 0.1-0.3 mm, 0.3-0.5 mm; the length of the asbestos wool is 1-3 mm; specifically, the length of the asbestos wool can be 0.1-0.2 mm, 0.2-0.3 mm; the length of the lignin fiber is 5-12 mm; specifically, the length of the lignin fiber can be 5-8 mm, 8-12 mm.

[0037] In some embodiments of the present invention, there are no special requirements for the source of sepiolite fiber, and the commercially available manufacturers of sepiolite fiber commonly used in the art can be adopted. There are no special requirements for the source of asbestos wool, and the commercially available manufacturers of asbestos wool commonly used in the art can be adopted. There are no special requirements for the source of lignin fiber, and the commercially available manufacturers of lignin fiber commonly used in the art can be adopted.

[0038] The second aspect of the present invention lies in providing a preparation method of a plugging agent for oil-based drilling fluids, including the following steps: mixing sheet materials, particulate materials, and fiber materials to obtain a plugging agent.

[0039] The third aspect of the present invention lies in providing a plugging slurry, which comprises the plugging agent described above; preferably, the plugging slurry is composed of the plugging agent described above and an oil-based drilling fluid in a weight-to-volume ratio of 190-310 g:1 L.

[0040] In some embodiments of the present invention, the weight-to-volume ratio of the plugging agent described above and the oil-based drilling fluid can be 190-230 g:1 L, 230-270 g:1 L, 270-310 g:1 L; typically but not restrictively, for example, it can be 190 g:1 L, 230 g:1 L, 270 g:1 L, 310 g:1 L.

[0041] In some embodiments of the present invention, there are no special requirements for the source of the oil-based drilling fluid, and commercially available products of the oil-based drilling fluid commonly used in the art can be used. The oil-based drilling fluid of the present invention can also be prepared by using existing technologies including but not limited to the preparation methods described in patents and papers.

[0042] Specifically, the oil-based drilling fluid of the present invention is the oil-based drilling fluid used on-site in a well in the Haixihu Sag, and the oil-based drilling fluid comprises the following raw materials in weight percentages: white oil, calcium chloride solution, emulsifier 2-3%, filtration reducer 2-3%, calcium oxide 2.5-4%, flow pattern regulator 2.5-3%, density regulator, and the density regulator is used to adjust the density of the oil-based drilling fluid to 1.32 g / cm 3 。

[0043] In some embodiments of the present invention, the volume ratio of the white oil and the calcium chloride solution is 4:1; the mass percentages of the emulsifier, filtration reducer, calcium oxide, and flow pattern regulator are based on the total of the white oil and the calcium chloride solution.

[0044] In some embodiments of the present invention, there are no special limitations on the source of the oil, and commercially available products of the oil commonly used by those skilled in the art can be used. Preferably, the oil of the present invention is No. 3 white oil.

[0045] In some embodiments of the present invention, there are no special requirements for the selection of the emulsifier, and the emulsifier commonly used in the art can be used. The emulsifier subsequently used in the present invention is Span-80.

[0046] In some embodiments of the present invention, there are no special requirements for the selection of the calcium chloride aqueous solution, and the calcium chloride aqueous solution commonly used in the art can be used. Specifically, the mass percentage of the calcium chloride aqueous solution of the present invention includes but is not limited to 26%.

[0047] In some embodiments of the present invention, there are no special requirements for the selection of the filtration reducer, and the filtration reducers commonly used in the art can be adopted. The filtration reducer subsequently used in the present invention is sulfonated asphalt. The present invention does not specifically limit the source of the sulfonated asphalt, and commercially available products of sulfonated asphalt commonly used by those skilled in the art can be adopted.

[0048] In some embodiments of the present invention, there are no special requirements for the selection of the flow pattern regulator, and the flow pattern regulators commonly used in the art can be adopted. The flow pattern regulator subsequently used in the present invention is organobentonite. The present invention does not specifically limit the source of the organobentonite, and commercially available products of organobentonite commonly used by those skilled in the art can be adopted.

[0049] In some embodiments of the present invention, there are no special requirements for the selection of the density regulator, and the density regulators commonly used in the art can be adopted. The density regulator subsequently used in the present invention is barite. The present invention does not specifically limit the source of the barite, and commercially available products of barite commonly used by those skilled in the art can be adopted. The particle size of the barite is 600 mesh. Since there are differences between the density of barite produced by manufacturers on the market and the theoretical density, the method of adding while measuring is adopted during actual application until the designed density is reached.

[0050] In some embodiments of the present invention, the density of the oil-based drilling fluid is 1.3 - 1.7 g / cm 3 , and pH = 9.3 - 9.5. Specifically, the density of the oil-based drilling fluid can be 1.29 - 1.31 g / cm 3 , 1.31 - 1.51 g / cm 3 , 1.51 - 1.7 g / cm 3 ; typically but not restrictively, for example, it is 1.29 g / cm 3 , 1.31 g / cm 3 , 1.33 g / cm 3 .

[0051] The fourth aspect of the present invention lies in providing the application of the plugging slurry as described above or the plugging agent for oil-based drilling fluid as described above in the field of plugging formation leakage fractures.

[0052] In some embodiments of the present invention, the width of the fracture is 3 - 5 mm. Specifically, the width of the fracture can be 3 - 4 mm, 4 - 5 mm; typically but not restrictively, for example, it is 3 mm, 4 mm, 5 mm.

[0053] In some embodiments of the present invention, the using method of the plugging slurry of the present invention is to inject the plugging slurry into the formation according to the conventional plugging process, thereby plugging the leakage fracture. The plugging process of the present invention is the plugging process commonly used in the art.

[0054] In some embodiments of the present invention, the method for using the lost circulation material for oil-based drilling fluids of the present invention is to add the above-mentioned lost circulation material into the oil-based drilling fluid to form a lost circulation slurry, and then inject it into the formation according to the conventional lost circulation technology, thereby plugging the lost circulation fractures. The lost circulation technology of the present invention is the lost circulation technology commonly used in the art. The present invention has no special requirements for the source of the oil-based drilling fluid, and commercially available products of the oil-based drilling fluid commonly used in the art can be used. The oil-based drilling fluid of the present invention can also be prepared by using existing technologies including, but not limited to, the preparation methods described in patents and papers.

[0055] The present invention will be further illustrated by the following examples, but the scope of the present invention is not limited thereby.

[0056] When numerical ranges are given in the examples, it should be understood that unless otherwise specified in the present invention, any numerical value between the two endpoints of each numerical range and the two endpoints can be selected. Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those skilled in the art of this technology. For those conditions not specified in the examples, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. All reagents or instruments without indicating the manufacturer are conventional products that can be obtained through commercial purchase. Except for the specific methods, equipment, and materials used in the examples, according to the knowledge of those skilled in the art of this technology and the description of the present invention, any methods, equipment, and materials of the prior art similar or equivalent to those described in the embodiments of the present invention can also be used to implement the present invention.

[0057] The oil-based drilling fluid used in the present invention comprises the following raw materials in weight percentages: 800 mL of No. 3 white oil, 200 mL of 26% CaCl₂ solution, 2% emulsifier, 2% filtration reducer, 2.5% calcium oxide, 2.5% flow pattern regulator, and density regulator to 1.32 g / cm 3 ; the emulsifier is Span-80; the filtration reducer is sulfonated asphalt; the flow pattern regulator is organobentonite; the density regulator is barite with 600 mesh, and the density regulator is used to adjust the density of the oil-based drilling fluid to 1.32 g / cm 3 . The density of the oil-based drilling fluid is 1.32 g / cm 3 , and the pH of the oil-based drilling fluid is 9.3.

[0058] Example

[0059] Example 1

[0060] This embodiment provides a plugging agent for oil-based drilling fluid, which comprises raw materials with the following weights: 80 g of flaky material, 130 g of granular material, and 100 g of fibrous material; The preparation method of the flaky material comprises the following steps: mixing phenolic resin and epoxy resin in a mass ratio of 1:1, pressing the mixed resin at 15 MPa and 180 °C for 30 min to form a sheet, ensuring the thickness is 0.3 - 0.5 mm, and then crushing it to a particle size of 4 - 6 mesh; The granular material is carbonized modified walnut shell, and the carbonized modified walnut shell is composed of particle sizes of 4 - 6 mesh, 10 - 20 mesh, and 60 - 100 mesh in a mass ratio of 1:2:5; The fibrous material is composed of sepiolite fiber, asbestos wool, and lignin fiber in a mass ratio of 1:3:2.

[0061] This embodiment provides a preparation method of a plugging agent for oil-based drilling fluid, which comprises the following steps: mixing the flaky material, granular material, and fibrous material for 30 min to obtain the plugging agent.

[0062] This embodiment provides a plugging slurry, which comprises raw materials with the following weight-volume ratio: 1 L of oil-based drilling fluid and 310 g of plugging agent.

[0063] The application method of the plugging agent for oil-based drilling fluid in the field of plugging formation leakage cracks comprises the following steps: adding the plugging agent into the oil-based drilling fluid and mixing evenly to obtain the plugging slurry, and injecting the plugging slurry into the formation through the conventional plugging process, then the leakage cracks of 3 - 5 mm can be effectively plugged.

[0064] Example 2

[0065] This embodiment provides a plugging agent for oil-based drilling fluid, which comprises raw materials with the following weights: 50 g of flaky material, 80 g of granular material, and 60 g of fibrous material; The others are exactly the same as those in Example 1.

[0066] This embodiment provides a plugging slurry, which comprises raw materials with the following weight-volume ratio: 1 L of oil-based drilling fluid and 190 g of plugging agent.

[0067] Comparative Example

[0068] Comparative Example 1

[0069] This comparative example provides a plugging agent for oil-based drilling fluid, which comprises raw materials with the following weights: 120 g of granular material and 100 g of fibrous material; The others are exactly the same as those in Example 1.

[0070] This comparative example provides a plugging slurry, which comprises raw materials with the following weight-volume ratio: 1 L of oil-based drilling fluid and 220 g of plugging agent.

[0071] Comparative Example 2

[0072] This comparative example provides a plugging agent for oil-based drilling fluids, which comprises raw materials with the following weights: 150 g of sheet material, 200 g of granular material, and 160 g of fiber material; the others are exactly the same as those in Example 1.

[0073] This comparative example provides a plugging slurry, which comprises raw materials with the following weight-to-volume ratio: 1 L of oil-based drilling fluid and 350 g of plugging agent.

[0074] Comparative Example 3

[0075] This comparative example provides a plugging agent for oil-based drilling fluids, which comprises raw materials with the following weights: 40 g of sheet material, 60 g of granular material, and 50 g of fiber material; the others are exactly the same as those in Example 1.

[0076] This comparative example provides a plugging slurry, which comprises raw materials with the following weight-to-volume ratio: 1 L of oil-based drilling fluid and 150 g of plugging agent.

[0077] Comparative Example 4

[0078] This comparative example provides a plugging agent for oil-based drilling fluids, which is different from that in Example 1 in that: the preparation method of the sheet material comprises the following steps: pressing phenolic resin at 15 MPa and 180 °C for 30 min to form a sheet, ensuring the thickness is 0.3 - 0.5 mm, and then crushing it to a particle size of 4 - 6 mesh; the others are exactly the same as those in Example 1.

[0079] Comparative Example 5

[0080] This comparative example provides a plugging agent for oil-based drilling fluids, which is different from that in Example 1 in that: the granular material is walnut shell; the others are exactly the same as those in Example 1.

[0081] Comparative Example 6

[0082] This comparative example provides a plugging agent for oil-based drilling fluids, which is different from that in Example 1 in that: the fiber material is lignin fiber; the others are exactly the same as those in Example 1.

[0083] Comparative Example 7

[0084] This comparative example provides a plugging agent for oil-based drilling fluids, which is different from that in Example 1 in that: the thickness of the sheet material is 0.8 - 1 mm; the others are exactly the same as those in Example 1.

[0085] Comparative Example 8

[0086] This comparative example provides a plugging agent for oil-based drilling fluids, which is different from that in Example 1 in that: polypropylene fiber is used to replace sepiolite fiber; the others are exactly the same as those in Example 1.

[0087] Comparative Example 9

[0088] This comparative example provides a plugging agent for oil-based drilling fluids, which is different from Example 1 in that: the sheet material is mica flakes, and the others are exactly the same as in Example 1.

[0089] Performance Test

[0090] 1. Particle Size Analysis of Plugging Agent for Oil-Based Drilling Fluids

[0091] The plugging agents for oil-based drilling fluids prepared in Examples 1-2 were subjected to particle size analysis using the sieving method, and the results are shown in Table 1.

[0092] Table 1 Particle Size Distribution of Plugging Agents for Oil-Based Drilling Fluids Prepared in Examples 1-2

[0093]

[0094]

[0095] Combining Example 1 and Example 2, and combining the data in Table 1, it can be seen that the particle sizes of the components of the plugging agents in Example 1 and Example 2 are concentrated below 4 mesh (4.75 mm), showing a gradual distribution. The particle size distribution of each level is moderate, and the particle size distribution coverage range is relatively wide, which is beneficial to plugging leakage cracks of 3-5 mm.

[0096] 2. Compatibility Test of Plugging Agent for Oil-Based Drilling Fluid with Drilling Fluid

[0097] The plugging agents for oil-based drilling fluids prepared in Examples 1-2 and Comparative Example 5 were added to the oil-based drilling fluid to obtain a plugging slurry. According to the detection method in GB / T 16783.2-2012 "Petroleum and Natural Gas Industry - Drilling Fluid Field Testing - Part 2: Oil-Based Drilling Fluid", the influence of the plugging agent on the electrical stability of the oil-based drilling fluid was tested, and the changes in the system after adding the plugging material to the oil-based drilling fluid for 3 h were observed. The test results are shown in Table 2.

[0098] Table 2 Compatibility Test Results of Plugging Agents for Oil-Based Drilling Fluids in Examples 1-2 and Comparative Example 5 with Oil-Based Drilling Fluid

[0099]

[0100] Combining Examples 1-2 and Comparative Example 5, and combining the data in Table 2, it can be seen that after adding the plugging agent for oil-based drilling fluid prepared in the present invention to the oil-based drilling fluid, the performance of the obtained plugging slurry has not changed significantly compared with the oil-based drilling fluid. The demulsification voltage is stable, and there are no phenomena such as delamination, precipitation, bubbles, and agglomeration after standing for 3 h. The slurry is stable, indicating that the plugging agent has good compatibility with the oil-based drilling fluid.

[0101] 3. Plugging Pressure Bearing Capacity Test of Plugging Agent for Oil-Based Drilling Fluid

[0102] The lost circulation agents prepared in Examples 1-2 and Comparative Examples 1-9 were added to the oil-based drilling fluid to prepare a lost circulation slurry, and the lost circulation slurry was tested for its plugging pressure-bearing capacity. The test results of the plugging pressure-bearing capacity are shown in Table 3. The method for testing the plugging pressure-bearing capacity includes the following steps: placing a steel rock sample with a slit width of 3-5 mm in a holder, applying a confining pressure up to 30 MPa; preparing the lost circulation slurry according to the examples and adding it to the working fluid kettle of the lost circulation instrument, checking and connecting the experimental instruments; adjusting the experimental pressure to 1 MPa, and after 5 minutes, opening the pressure regulating valve at the inlet end of the kettle and the valve at the outlet end of the core holder, and measuring the initial leakage rate; after the initial leakage rate is stable, gradually increasing the pressure in the kettle at intervals of 2.0 MPa, maintaining each pressure point for 10 minutes, and respectively measuring the cumulative leakage rate at each pressure point; when the pressure in the kettle reaches a certain pressure point, the cumulative leakage rate increases rapidly, the pressure in the kettle drops sharply, and does not recover, then it is considered that the crack plugging fails, stop the experiment, and record the previous pressure point as the pressure-bearing capacity of the plugging layer.

[0103] Table 3 Test results of the plugging pressure-bearing capacity of the lost circulation slurry prepared from the lost circulation agents for oil-based drilling fluid prepared in Examples 1-2 and Comparative Examples 1-9

[0104] Sample Name Plugging Pressure Bearing Capacity / MPa Initial Leakage Volume / mL Accumulative Leakage Volume / mL Example 1 ≥20 25 45 Example 2 ≥20 40 85 Comparative Example 1 13 120 340 Comparative Example 2 ≥20 20 50 Comparative Example 3 9 80 170 Comparative Example 4 17 50 120 Comparative Example 5 17 30 90 Comparative Example 6 15 50 160 Comparative Example 7 ≥20 80 210 Comparative Example 8 19 50 95 Comparative Example 9 7 80 150

[0105] Combining Examples 1-2 and Comparative Examples 1-9, and combining the data in Table 3, it can be seen that the lost circulation agent provided by the present invention can effectively plug cracks with a width of 3-5 mm, has a high plugging pressure-bearing capacity and a very small leakage rate; after changing the components of the lost circulation agent, there will be a phenomenon of reduced pressure-bearing capacity or increased leakage rate.

[0106] The above embodiments are only illustrative of the principles and effects of the present invention, and are not used to limit the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes completed by those with ordinary knowledge in the technical field without departing from the spirit and technical ideas disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A plugging agent for oil-based drilling fluid, characterized in that: The invention comprises the following raw materials in parts by weight: 50-80 parts of sheet material, 80-130 parts of granular material and 60-100 parts of fiber material, wherein the sheet material is sheet resin; the sheet material is formed by pressing phenolic resin and epoxy resin into sheets; the thickness of the sheet material is 0.3-0.5 mm; the fiber material is selected from two or more of sepiolite fiber, asbestos wool or lignin fiber.

2. The plugging agent for oil-based drilling fluid according to claim 1, characterized in that: The mass ratio of the phenolic resin to the epoxy resin is 1-5:1-5.

3. The plugging agent for oil-based drilling fluid according to claim 1, characterized in that: Also includes one or more of the following characteristics: A1) the particle size of the flaky material is 4-6 mesh; A2) The tabletting pressure is 15-18 MPa; the tabletting time is 25-40 min; the tabletting temperature is 175-195°C.

4. The plugging agent for oil-based drilling fluid according to claim 1, characterized in that: Also includes one or more of the following characteristics: A3) the granular material is selected from one or more of walnut shells or sepiolite powder; preferably, the granular material is walnut shells; A4) the fiber material comprises sepiolite fiber, asbestos wool and lignin fiber; preferably, the fiber material comprises sepiolite fiber, asbestos wool and lignin fiber in a mass ratio of 1-3:3-9:2-4; A5) The fiber material has a length of 0.1-12 mm and a diameter of 80-150 μm.

5. A plugging agent for oil-based drilling fluid according to claim 4, characterized in that: The walnut shell is a carbonized modified walnut shell.

6. The plugging agent for oil-based drilling fluid according to claim 4, characterized in that: The walnut shells are obtained by grading particles of 4-6 mesh, 10-20 mesh and 60-100 mesh; preferably, the walnut shells are composed of particles of 4-6 mesh, 10-20 mesh and 60-100 mesh in a mass ratio of 1-2:2-4:5-10.

7. A method for preparing a plugging agent for oil-based drilling fluid according to any one of claims 1 to 6, characterized in that: The method comprises the following steps: mixing flaky materials, granular materials and fiber materials to obtain a plugging agent.

8. A plugging slurry, characterized in that: It comprises the plugging agent according to any one of claims 1-6; preferably, the plugging slurry is composed of the plugging agent according to any one of claims 1-6 and oil-based drilling fluid in a weight volume ratio of 190-310g:1L.

9. Use of the plugging slurry according to claim 8 or the plugging agent for oil-based drilling fluid according to any one of claims 1 to 6 in the field of plugging formation leakage cracks.

10. The use according to claim 9, characterized in that: The width of the crack is 3-5 mm.

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