A plugging agent and its preparation method

Abstract

The present invention discloses a plugging agent and its preparation method. The raw materials, by weight, include at least 10-20 parts of special fiber, 5-10 parts of inert bridging material, 3-5 parts of viscosity enhancer, 1-5 parts of fluid loss additive, 1-3 parts of coagulant, and 5-10 parts of water. The plugging agent has high pressure and temperature resistance and is suitable for both thin and heavy oil wells. It also exhibits excellent plugging performance, a simple process, short application time, and maintains full bore diameter without affecting subsequent operations.

Description

Technical Field

[0001] The present invention relates to the technical field of oilfield chemistry, in particular to the field of IPC C09, and more specifically to a plugging agent and a preparation method thereof. Background Art

[0002] During oilfield construction and development, casing leaks can occur due to a variety of factors. These include quality defects during casing manufacturing; wear and tear during drilling, loose fastening, or poor cementing quality; formation movement damaging the casing; and corrosion of metal materials in chemical environments, all of which can cause casing damage and leaks. Common repair methods currently include casing patching, hanging isolation, and chemical plugging. Chemical plugging offers the advantage of effectively restoring the casing's diameter, but conventional chemical plugging agents cannot withstand high-pressure applications and offer limited safety and reliability.

[0003] CN106281272B discloses a bridging plugging agent for fractured reservoirs. The plugging agent comprises a large amount of bridging material and calcium carbonate, with a small amount of asphalt powder and fiber added. When used, the plugging agent can seal cracks within a width of 5 mm, has an acid solubility rate of over 70%, and does not harm the oil and gas formations. However, the pressure bearing capacity after use is only above 15 MPa, and the pressure bearing level is limited. Summary of the Invention

[0004] In order to solve the above problems, the first aspect of the present invention provides a plugging agent, the raw materials of which include at least 10-20 parts of special fibers, 5-10 parts of inert bridging materials, 3-5 parts of viscosity enhancers, 1-5 parts of fluid loss additives, 1-3 parts of coagulant, and 5-10 parts of water, in parts by weight.

[0005] Preferably, the special fiber is at least one of polyolefin fiber, polyester fiber, and polyvinyl chloride fiber.

[0006] Preferably, the special fiber is a mixture of polyester fiber and polyvinyl chloride fiber, and the mass ratio of the polyester fiber to the polyvinyl chloride fiber is (0.5-2):1.

[0007] Preferably, the mass ratio of the polyester fiber to the polyvinyl chloride fiber is 1:1.

[0008] Preferably, the fluid loss reducer is at least one of silica, calcium carbonate, sulfonated starch and lignite.

[0009] Preferably, the fluid loss additive is a mixture of silicon dioxide and calcium carbonate, and the mass ratio of silicon dioxide to calcium carbonate is (2-8):(1-3).

[0010] Preferably, the mass ratio of silicon dioxide to calcium carbonate is 4:1.

[0011] This application uses a silica to calcium carbonate mass ratio of 4:1 as a fluid loss reducer, effectively utilizing silica to temporarily plug micropores and microcracks in the formation, thereby reducing the loss of special fibers and inert bridging materials in the plugging agent, causing them to aggregate at abnormal connection points to the near-wellbore area, adsorbing on the soil surface to form an adsorption layer to prevent clay particles from flocculating and growing larger. Furthermore, the use of calcium carbonate and silica for compounding can stabilize the fine particles disassembled by the mud circulation system during stirring through adsorption, preventing them from sticking together into large particles, thereby completely plugging the near-wellbore position. There is no need to find leaks, no coagulation at non-leak points, simple construction, and the product produced by the plugging agent is a plastic material with high pressure resistance.

[0012] Preferably, the viscosity increasing agent is at least one of xanthan gum, hydroxypropyl guar gum, and carboxymethyl cellulose sodium salt.

[0013] Preferably, the viscosity enhancer is a mixture of xanthan gum and sodium carboxymethyl cellulose, and the mass ratio of xanthan gum to sodium carboxymethyl cellulose is (2-5):(3-6).

[0014] Preferably, the mass ratio of xanthan gum to sodium carboxymethyl cellulose is 3:5.

[0015] Preferably, the coagulant is at least one of potassium persulfate, aluminum sulfate, and potassium silicate.

[0016] Preferably, the coagulant is potassium persulfate.

[0017] Preferably, the inert bridging material is at least one of polytetrafluoroethylene, polybutylene, and perfluoroalkoxyalkane polymer.

[0018] Preferably, the inert bridging material is polytetrafluoroethylene.

[0019] The second aspect of the present invention provides a method for preparing the plugging agent as described above, characterized in that it comprises at least the following steps: (1) mixing the special fiber, the viscosity enhancer and the water in proportion and stirring them uniformly; (2) continuously adding the inert bridging material, the fluid loss reducer and the coagulant and stirring them uniformly to obtain the plugging agent.

[0020] Beneficial effects:

[0021] 1. The present application provides a plugging agent with high pressure bearing capacity and high temperature resistance, which is applicable to both thin oil and heavy oil wells, and has good plugging performance, simple process, short construction time, retains full bore, and does not affect subsequent operations.

[0022] 2. This application uses a silica to calcium carbonate mass ratio of 4:1 as a filtration loss reducer, which can effectively utilize silica to temporarily plug the micropores and microcracks in the formation, thereby reducing the filtration loss of special fibers and inert bridging materials in the plugging agent, causing them to accumulate at abnormal connection points to the near-wellbore area, and adsorb on the soil surface to form an adsorption layer to prevent clay particles from flocculating and growing larger.

[0023] 3. The present application uses a compound of calcium carbonate and silicon dioxide to stabilize the fine particles dispersed by the stirring of the mud circulation system through adsorption, so that they no longer stick together into large particles, thereby sealing the entire near-well position without the need for leak detection and simple construction.

[0024] 4. The plugging agent provided in this application can also make the fracture have a higher conductivity after unblocking, and can prevent the fracture from closing during production operations, so that the plugging operation also has the effect of reservoir transformation, thereby increasing the production of fractured reservoirs.

[0025] 5. The plugging agent provided in this application uses an inert bridging material that can solidify quickly after being subjected to a pressure difference, does not deteriorate in acids, alkalis, and salts, and has a long-lasting effect. DETAILED DESCRIPTION

[0026] Example

[0027] Example 1:

[0028] Example 1 provides a plugging agent, the raw materials of which are, by weight, 15 parts of special fiber, 8 parts of inert bridging material, 4 parts of viscosity enhancer, 3 parts of fluid loss additive, 2 parts of coagulant, and 8 parts of water.

[0029] The special fiber is a mixture of polyester fiber and polyvinyl chloride fiber, and the mass ratio of polyester fiber to polyvinyl chloride fiber is 1:1.

[0030] The fluid loss additive is a mixture of silica and calcium carbonate, with the mass ratio of silica to calcium carbonate being 4:1.

[0031] The viscosity enhancer is a mixture of xanthan gum and sodium carboxymethyl cellulose, and the mass ratio of the xanthan gum to sodium carboxymethyl cellulose is 3:5.

[0032] The coagulant is potassium persulfate.

[0033] Inert bridging material: PTFE.

[0034] The preparation method of the plugging agent as described above is characterized by comprising the following steps: (1) mixing the special fiber, the viscosity enhancer and the water in proportion and stirring them uniformly; (2) continuously adding the inert bridging material, the fluid loss reducer and the coagulant and stirring them uniformly to obtain the plugging agent.

[0035] Example 2

[0036] Example 2 provides a plugging agent, and its specific implementation method is the same as that of Example 1, except that, in parts by weight, the raw materials include 10 parts of special fiber, 6 parts of inert bridging material, 3 parts of viscosity enhancer, 2 parts of fluid loss reducer, 3 parts of coagulant, and 6 parts of water.

[0037] Comparative Example 1

[0038] Comparative Example 1 provides a plugging agent, and its specific implementation is the same as that of Example 1, except that the special fiber is polyester fiber.

[0039] Comparative Example 2

[0040] Comparative Example 2 provides a plugging agent, and its specific implementation method is the same as that of Example 1, except that the special fiber is a mixture of polyester fiber and polyvinyl chloride fiber, and the mass ratio of polyester fiber to polyvinyl chloride fiber is 1:3.

[0041] Comparative Example 3

[0042] Comparative Example 3 provides a plugging agent, and its specific implementation is the same as that of Example 1, except that the fluid loss agent is silica.

[0043] Comparative Example 4

[0044] Comparative Example 4 provides a plugging agent, and its specific implementation is the same as that of Example 1, except that the fluid loss reducer is a mixture of silica and calcium carbonate, and the mass ratio of silica to calcium carbonate is 1:3.

[0045] Performance testing:

[0046] 1. Pressure Bearing Capacity Test: The pressure bearing capacity of the plugging agents prepared in Examples 1-2 of the present invention and Comparative Examples 1-4 was determined. The test method was as follows: gravel-filled tubes were filled with gravel of different particle sizes to simulate the irregular pore structure (pore size 1.5 cm) formed after perforation. The plugging agent was slowly injected from one end of the filling tube while observing the injection pressure changes. Whenever the pressure increased by 5.0 MPa, the pressure was maintained for 10 minutes and injection was continued until the injection pressure reached the design pressure. When no liquid flowed out of the other end of the filling tube, the pressure was maintained and held for 240 minutes to allow the plugging agent, solidified by the pressure differential, to fully solidify in the gravel pores and form an integrated embedded network structure.

[0047] 2. Sample slurry leakage: The base slurry leakage of the plugging agents prepared in Examples 1-2 of the present invention and Comparative Examples 1-4 was measured. The test method was as follows: after stirring the base slurry for 30 minutes, the base slurry leakage was tested using a plugging instrument. After adding 300 g of the plugging agent to the base slurry and stirring for 30 minutes, the sample slurry leakage was tested using a plugging instrument.

[0048] Table 1

[0049] Pressure after plugging / MPa Sample slurry leakage / mL Example 1 173.2 297 Example 2 170.5 305 Comparative Example 1 157.1 326 Comparative Example 2 162.6 323 Comparative Example 3 158.4 331 Comparative Example 4 165.3 335

Claims

1. A plugging agent, characterized in that: The raw materials include at least 10-20 parts of special fiber, 5-10 parts of inert bridging material, 3-5 parts of viscosity enhancer, 1-5 parts of fluid loss reducer, 1-3 parts of coagulant, and 5-10 parts of water in parts by weight; The inert bridging material is polytetrafluoroethylene; the special fiber is a mixture of polyester fiber and polyvinyl chloride fiber, and the mass ratio of the polyester fiber to the polyvinyl chloride fiber is (0.5-2):1; the fluid loss reducer is a mixture of silica and calcium carbonate, and the mass ratio of the silica to calcium carbonate is (2-8):(1-3); and the coagulant is potassium persulfate.

2. The plugging agent according to claim 1, characterized in that The viscosity enhancer is at least one of xanthan gum, hydroxypropyl guar gum, and carboxymethyl cellulose sodium salt.

3. The plugging agent according to claim 1, characterized in that The viscosity enhancer is a mixture of xanthan gum and sodium carboxymethyl cellulose, and the mass ratio of the xanthan gum to sodium carboxymethyl cellulose is (2-5):(3-6).

4. A method for preparing the plugging agent according to any one of claims 1 to 3, characterized in that: The method comprises at least the following steps: (1) mixing the special fiber, the viscosity enhancer and the water in proportion and stirring them uniformly; (2) continuously adding the inert bridging material, the fluid loss reducer and the coagulant and stirring them uniformly to obtain the product.