A slug design method to improve the anti-dilution ability of plugging agents in cracks

Abstract

The present invention provides a segment plug design method for improving the anti-dilution ability of a plugging agent in a fracture, and belongs to the field of oilfield chemistry in tertiary oil recovery technology. A segment plug design method for improving the anti-dilution ability of a plugging agent in a fracture, mainly through regulating the viscosity of the front segment plug, the plugging agent and the rear segment plug, testing the anti-dilution ability of the plugging agent in the fracture under different segment plug combinations, so as to select the best segment plug combination design. The experimental results show that when the viscosity relationship between the front segment plug, the plugging agent and the rear segment plug satisfies: the viscosity of the front segment plug> the viscosity of the plugging agent> the viscosity of the rear segment plug, the anti-dilution ability of the plugging agent in the fracture is the best. A segment plug design method for improving the anti-dilution ability of a plugging agent in a fracture, the main purpose of which is to select the best combination of the viscosity of the front segment plug, the viscosity of the plugging agent and the viscosity of the rear segment plug, and improve the anti-dilution ability of the plugging agent in the fracture. This method has important guiding significance for the on-site profile adjustment process design of fractured oil reservoirs.

Description

Technical Field

[0001] The invention belongs to the field of oilfield chemistry in tertiary oil recovery technology, and particularly relates to a slug design method for improving the anti-dilution ability of a plugging agent in a fracture. Background Art

[0002] Fractured tight oil reservoirs are a key research area for increasing oil reserves and production in the 21st century. Widely distributed across major oil and gas fields and basins across China, they hold a crucial position in my country's petroleum industry. However, due to the low permeability of the reservoir matrix and the presence of associated fractures, injected water rapidly flows along large fractures during waterflooding, resulting in ineffective water injection. This ultimately leads to low crude oil utilization in these reservoirs, with recovery factors generally less than 10%, resulting in unsatisfactory development results and poor economic benefits. Further enhancing crude oil recovery through water shutoff is urgently needed.

[0003] Profile control in fractured tight oil reservoirs is based on formation characteristics: low matrix permeability, large displacement pressure gradients, and low formation breakdown pressures. This dictates the need for small, deep plugging. Therefore, a crucial property of plugging agents is dilution resistance. Therefore, a slug design method that enhances the dilution resistance of plugging agents in fractures is urgently needed to provide guidance for the design of on-site profile control processes. Summary of the Invention

[0004] The present invention primarily overcomes the shortcomings of the prior art and aims to provide a slug design method that improves the dilution resistance of plugging agents in fractures. Using a visual flat plate model, the present invention controls the viscosity of the pre-protection slug, the plugging agent, and the post-protection slug injected into the model to test the dilution resistance of the plugging agent in fractures using different slug combinations. Ultimately, a slug design method for improving the dilution resistance of the plugging agent in fractures is developed, allowing the optimal slug combination to be selected.

[0005] In order to achieve the above technical objectives, the present invention adopts the following technical solutions:

[0006] A slug design method for improving the anti-dilution capability of a plugging agent in a fracture, the method comprising the following steps:

[0007] S1: Dye the clean water blue, the plugging agent black, and the protection slug red. Then use a Brookfield viscometer to test the viscosity of the front protection slug, plugging agent, and rear protection slug at room temperature (25°C) and record the values. Then use a multifunctional core flooding device ( Figure 2) Add 1000 ml of blue water to multifunctional core displacement device No. 1, add 1000 ml of black plugging agent to multifunctional core displacement device No. 2, add 1000 ml of red pre-protection slug solution to multifunctional core displacement device No. 3 (after injecting the pre-protection slug solution, clean multifunctional core displacement device No. 3 and add the post-protection slug solution), and connect the experimental device at the same time.

[0008] S2: 1.0 PV of blue water was injected into the visual flat plate model at a certain rate. Subsequently, 0.3 PV of pre-protection slug solution (viscosity 83.12 mPa·s) was injected into the visual flat plate model at the same rate. Then, 0.3 PV of plugging agent (viscosity 83.12 mPa·s) was injected into the visual flat plate model at the same rate. Subsequently, the multifunctional core displacement device No. 3 was cleaned, the post-protection slug solution was added, the experimental device was connected, and 0.3 PV of post-protection slug solution (viscosity 83.12 mPa·s) was injected into the visual flat plate model again to observe the dilution of the plugging agent.

[0009] S3: 1.0 PV of blue water was injected into the visual flat plate model at a certain rate. Subsequently, 0.3 PV of pre-protection slug solution (viscosity 83.12 mPa·s) was injected into the visual flat plate model at the same rate. Then, 0.3 PV of plugging agent (viscosity 55.36 mPa·s) was injected into the visual flat plate model at the same rate. Subsequently, the multifunctional core displacement device No. 3 was cleaned, the post-protection slug solution was added, the experimental device was connected, and 0.3 PV of post-protection slug solution (viscosity 83.12 mPa·s) was injected into the visual flat plate model again to observe the dilution of the plugging agent.

[0010] S4: Inject 1.0 PV of blue water into the visual flat plate model at a certain rate, then inject 0.3 PV of pre-protection slug solution (viscosity 83.12 mPa·s) into the visual flat plate model at the same rate, and then inject 0.3 PV of plugging agent (viscosity 55.36 mPa·s) into the visual flat plate model at the same rate. Then clean the multifunctional core displacement device No. 3, add the post-protection slug solution, connect the experimental device, and inject 0.3 PV of post-protection slug solution (viscosity 55.36 mPa·s) into the visual flat plate model again to observe the dilution of the plugging agent.

[0011] S5: Inject 1.0 PV of blue water into the visualization flat plate model at a certain rate, then inject 0.3 PV of pre-protection slug solution (viscosity 83.12 mPa·s) into the visualization flat plate model at the same rate, and then inject 0.3 PV of plugging agent (viscosity 106.5 mPa·s) into the visualization flat plate model at the same rate. Then clean the multifunctional core displacement device No. 3, add the post-protection slug solution, connect the experimental device, and inject 0.3 PV of post-protection slug solution (viscosity 106.5 mPa·s) into the visualization flat plate model again to observe the dilution of the plugging agent.

[0012] S6: Inject 1.0 PV of blue water into the visualization flat plate model at a certain rate, then inject 0.3 PV of pre-protection slug solution (viscosity 83.12 mPa·s) into the visualization flat plate model at the same rate, and then inject 0.3 PV of plugging agent (viscosity 106.5 mPa·s) into the visualization flat plate model at the same rate. Then clean the multifunctional core displacement device No. 3, add the post-protection slug solution, connect the experimental device, and inject 0.3 PV of post-protection slug solution (viscosity 106.5 mPa·s) into the visualization flat plate model again to observe the dilution of the plugging agent.

[0013] S7: Inject 1.0 PV of blue water into the visualized flat plate model at a certain rate. Then, inject 0.3 PV of pre-protection slug solution (viscosity 55.36 mPa·s) into the visualized flat plate model at the same rate. Then, inject 0.3 PV of plugging agent (viscosity 83.12 mPa·s) into the visualized flat plate model at the same rate. Then, clean the multifunctional core displacement device No. 3, add the post-protection slug solution, connect the experimental device, and inject 0.3 PV of post-protection slug solution (viscosity 106.5 mPa·s) into the visualized flat plate model again to observe the dilution of the plugging agent. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 To visualize the structure of the flat plate model;

[0015] Figure 2 This is the flow chart of the anti-dilution plate experiment;

[0016] Figure 3 This is a plan view of the plugging agent injection process when the viscosity of the front slug, the plugging agent, and the viscosity of the rear slug are all 83.12 mPa·s;

[0017] Figure 4 This is a plan view of the plugging agent injection process when the viscosity of the front slug and the viscosity of the rear slug are both 83.12 mPa·s and the viscosity of the plugging agent is 55.36 mPa·s;

[0018] Figure 5 This is a plan view of the plugging agent injection process when the viscosity of the front protection slug is 83.12 mPa·s and the viscosity of the rear protection slug and the plugging agent are both 55.36 mPa·s;

[0019] Figure 6 This is a plan view of the plugging agent injection process when the viscosity of the front protection slug and the rear protection slug are both 83.12 mPa·s and the viscosity of the plugging agent is 106.5 mPa·s;

[0020] Figure 7 This is a plan view of the plugging agent injection process when the viscosity of the front protection slug is 83.12 mPa·s and the viscosity of the plugging agent and the rear protection slug are both 106.5 mPa·s;

[0021] Figure 8 This is a plan view of the plugging agent injection process when the viscosity of the front protection plug is 83.12 mPa·s, the viscosity of the plugging agent is 83.12 mPa·s, and the viscosity of the rear protection plug is 106.5 mPa·s. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0023] Example:

[0024] A slug design method for improving the anti-dilution capability of a plugging agent in a fracture, the method comprising the following steps:

[0025] S1: Dye the clean water blue, the plugging agent black, and the protection slug red. Then use a Brookfield viscometer to test the viscosity of the front protection slug, plugging agent, and rear protection slug at room temperature (25°C) and record the values. Then use a multifunctional core flooding device ( Figure 2 ) Add 1000 ml of blue water to multifunctional core displacement device No. 1, add 1000 ml of black plugging agent to multifunctional core displacement device No. 2, add 1000 ml of red pre-protection slug solution to multifunctional core displacement device No. 3 (after injecting the pre-protection slug solution, clean multifunctional core displacement device No. 3 and add the post-protection slug solution), and connect the experimental device at the same time.

[0026] S2: 1.0 PV of blue water was injected into the visual flat plate model at a certain rate. Subsequently, 0.3 PV of pre-protection slug solution (viscosity 83.12 mPa·s) was injected into the visual flat plate model at the same rate. Then, 0.3 PV of plugging agent (viscosity 83.12 mPa·s) was injected into the visual flat plate model at the same rate. Subsequently, the multifunctional core displacement device No. 3 was cleaned, the post-protection slug solution was added, the experimental device was connected, and 0.3 PV of post-protection slug solution (viscosity 83.12 mPa·s) was injected into the visual flat plate model again to observe the dilution of the plugging agent.

[0027] S3: 1.0 PV of blue water was injected into the visual flat plate model at a certain rate. Subsequently, 0.3 PV of pre-protection slug solution (viscosity 83.12 mPa·s) was injected into the visual flat plate model at the same rate. Then, 0.3 PV of plugging agent (viscosity 55.36 mPa·s) was injected into the visual flat plate model at the same rate. Subsequently, the multifunctional core displacement device No. 3 was cleaned, the post-protection slug solution was added, the experimental device was connected, and 0.3 PV of post-protection slug solution (viscosity 83.12 mPa·s) was injected into the visual flat plate model again to observe the dilution of the plugging agent.

[0028] S4: Inject 1.0 PV of blue water into the visual flat plate model at a certain rate, then inject 0.3 PV of pre-protection slug solution (viscosity 83.12 mPa·s) into the visual flat plate model at the same rate, and then inject 0.3 PV of plugging agent (viscosity 55.36 mPa·s) into the visual flat plate model at the same rate. Then clean the multifunctional core displacement device No. 3, add the post-protection slug solution, connect the experimental device, and inject 0.3 PV of post-protection slug solution (viscosity 55.36 mPa·s) into the visual flat plate model again to observe the dilution of the plugging agent.

[0029] S5: Inject 1.0 PV of blue water into the visualization flat plate model at a certain rate, then inject 0.3 PV of pre-protection slug solution (viscosity 83.12 mPa·s) into the visualization flat plate model at the same rate, and then inject 0.3 PV of plugging agent (viscosity 106.5 mPa·s) into the visualization flat plate model at the same rate. Then clean the multifunctional core displacement device No. 3, add the post-protection slug solution, connect the experimental device, and inject 0.3 PV of post-protection slug solution (viscosity 106.5 mPa·s) into the visualization flat plate model again to observe the dilution of the plugging agent.

[0030] S6: Inject 1.0 PV of blue water into the visualization flat plate model at a certain rate, then inject 0.3 PV of pre-protection slug solution (viscosity 83.12 mPa·s) into the visualization flat plate model at the same rate, and then inject 0.3 PV of plugging agent (viscosity 106.5 mPa·s) into the visualization flat plate model at the same rate. Then clean the multifunctional core displacement device No. 3, add the post-protection slug solution, connect the experimental device, and inject 0.3 PV of post-protection slug solution (viscosity 106.5 mPa·s) into the visualization flat plate model again to observe the dilution of the plugging agent.

[0031] S7: Inject 1.0 PV of blue water into the visualized flat plate model at a certain rate. Then, inject 0.3 PV of pre-protection slug solution (viscosity 55.36 mPa·s) into the visualized flat plate model at the same rate. Then, inject 0.3 PV of plugging agent (viscosity 83.12 mPa·s) into the visualized flat plate model at the same rate. Then, clean the multifunctional core displacement device No. 3, add the post-protection slug solution, connect the experimental device, and inject 0.3 PV of post-protection slug solution (viscosity 106.5 mPa·s) into the visualized flat plate model again to observe the dilution of the plugging agent.

[0032] Example 1:

[0033] This example experimentally tests a plug design method for improving the dilution resistance of a plugging agent in a fracture. The method controls the injection volume of the pre-protection plug, the plugging agent, and the post-protection plug into a visual flat-plate model to 0.3 PV, and the injection rate of each of the pre-protection plug, the plugging agent, and the post-protection plug to 8 ml / min. By adjusting the viscosity of the pre-protection plug, the plugging agent, and the post-protection plug injected into the visual flat-plate model, the effects of different plug combinations on the plugging agent's dilution resistance are observed, and the strength of the plugging agent's dilution resistance is determined. The measurement method follows S1 and S2, with the viscosity of the pre-protection plug, the plugging agent, and the post-protection plug all set to 83.12 mPa·s.

[0034] From the plane diagram of the visual flat plate model during the injection of plugging agent ( Figure 3 ) It can be seen that during the entire injection process of the front protection slug, the plugging agent, and the rear protection slug, after the front protection slug is injected, the plugging agent cannot be pushed forward smoothly in the visualized flat plate model during the entire injection process of the plugging agent. During the advancement process, part of the plugging agent is diluted. After the plugging agent is injected, during the entire injection process of the rear protection slug, the rear protection slug cannot completely push the plugging agent forward smoothly. During the advancement process, part of the plugging agent is diluted, and its anti-dilution ability is poor.

[0035] Example 2:

[0036] This example experimentally tests a plug design method for improving the dilution resistance of a plugging agent in a fracture. The method controls the injection volume of the pre-protection plug, the plugging agent, and the post-protection plug into a visual flat-plate model to 0.3 PV, and the injection rate of the pre-protection plug, the plugging agent, and the post-protection plug to 8 ml / min. By adjusting the viscosity of the pre-protection plug, the plugging agent, and the post-protection plug injected into the visual flat-plate model, the effects of different plug combinations on the plugging agent's dilution resistance are observed, and the strength of the plugging agent's dilution resistance is determined. The measurement method follows S1 and S3, with the viscosity of the pre-protection plug and the post-protection plug being 83.12 mPa·s, and the viscosity of the plugging agent being 55.36 mPa·s.

[0037] From the plane diagram of the visual flat plate model during the injection of plugging agent ( Figure 4 ) It can be seen that during the entire injection process of the front protection slug, the plugging agent, and the rear protection slug, after the front protection slug is injected, during the entire injection process of the plugging agent, the plugging agent directly breaks through the front protection slug and cannot be pushed forward smoothly in the visualized flat plate model. During the advancement process, part of the plugging agent is diluted. After the plugging agent is injected, during the entire injection process of the rear protection slug, the rear protection slug cannot completely push the plugging agent forward smoothly. During the advancement process, part of the plugging agent is diluted, and its anti-dilution ability is poor.

[0038] Example 3:

[0039] This example experimentally tests a plug design method for improving the dilution resistance of a plugging agent in a fracture. The method controls the injection volume of the pre-protection plug, the plugging agent, and the post-protection plug into a visual flat-plate model to 0.3 PV, and the injection rate of the pre-protection plug, the plugging agent, and the post-protection plug to 8 ml / min. By adjusting the viscosity of the pre-protection plug, the plugging agent, and the post-protection plug injected into the visual flat-plate model, the effects of different plug combinations on the plugging agent's dilution resistance are observed, and the strength of the plugging agent's dilution resistance is determined. The measurement method follows S1 and S4, with the pre-protection plug's viscosity being 83.12 mPa·s, and the post-protection plug and the plugging agent both having a viscosity of 55.36 mPa·s.

[0040] From the plane diagram of the visual flat plate model during the injection of plugging agent ( Figure 5) It can be seen that during the entire injection process of the front protection slug, the plugging agent, and the rear protection slug, after the front protection slug is injected, during the entire injection process of the plugging agent, the plugging agent directly breaks through the front protection slug and cannot be pushed forward smoothly in the visualized flat plate model. During the advancement process, part of the plugging agent is diluted. After the plugging agent is injected, during the entire injection process of the rear protection slug, the rear protection slug cannot completely push the plugging agent forward smoothly. During the advancement process, part of the plugging agent is diluted, and its anti-dilution ability is poor.

[0041] Example 4:

[0042] This example experimentally tests a plug design method for improving the dilution resistance of a plugging agent in a fracture. The method controls the injection volume of the pre-protection plug, the plugging agent, and the post-protection plug into a visual flat-plate model to 0.3 PV, and the injection rate of the pre-protection plug, the plugging agent, and the post-protection plug to 8 ml / min. By adjusting the viscosity of the pre-protection plug, the plugging agent, and the post-protection plug injected into the visual flat-plate model, the effects of different plug combinations on the plugging agent's dilution resistance are observed, and the strength of the plugging agent's dilution resistance is determined. The measurement method follows S1 and S5, with the viscosity of the pre-protection plug and the post-protection plug both being 83.12 mPa·s, and the viscosity of the plugging agent being 106.5 mPa·s.

[0043] From the plane diagram of the visual flat plate model during the injection of plugging agent ( Figure 6 ) It can be seen that during the entire injection process of the front protection slug, the plugging agent, and the rear protection slug, after the front protection slug is injected, the plugging agent cannot be pushed forward smoothly in the visualized flat plate model during the entire injection process of the plugging agent. During the advancement process, part of the plugging agent is diluted. After the plugging agent is injected, during the entire injection process of the rear protection slug, the rear protection slug cannot completely push the plugging agent forward smoothly. During the advancement process, part of the plugging agent is diluted, and its anti-dilution ability is poor.

[0044] Example 5:

[0045] This example experimentally tests a plug design method for improving the dilution resistance of a plugging agent in a fracture. The method controls the injection volume of the pre-protection plug, the plugging agent, and the post-protection plug into a visual flat-plate model to 0.3 PV, and the injection rate of the pre-protection plug, the plugging agent, and the post-protection plug to 8 ml / min. By adjusting the viscosity of the pre-protection plug, the plugging agent, and the post-protection plug injected into the visual flat-plate model, the effects of different plug combinations on the plugging agent's dilution resistance are observed, and the strength of the plugging agent's dilution resistance is determined. The measurement method follows S1 and S6, with the pre-protection plug's viscosity being 83.12 mPa·s, and the plugging agent and post-protection plug's viscosity both being 106.5 mPa·s.

[0046] From the plane diagram of the visual flat plate model during the injection of plugging agent ( Figure 7 ) It can be seen that during the entire injection process of the front protection slug, the plugging agent, and the rear protection slug, after the front protection slug is injected, the plugging agent is basically pushed forward smoothly in the visualized flat plate model during the entire injection process of the plugging agent. During the advancement process, a small part of the plugging agent is diluted. After the plugging agent is injected, during the entire injection process of the rear protection slug, the rear protection slug cannot completely push the plugging agent forward smoothly. During the advancement process, a part of the plugging agent is diluted, and its anti-dilution ability is poor.

[0047] Example 6:

[0048] This example experimentally tests a plug design method for improving the dilution resistance of a plugging agent in a fracture. The method controls the injection volume of the pre-protection plug, the plugging agent, and the post-protection plug into a visual flat-plate model to 0.3 PV, and the injection rate of the pre-protection plug, the plugging agent, and the post-protection plug to 8 ml / min. By adjusting the viscosity of the pre-protection plug, the plugging agent, and the post-protection plug injected into the visual flat-plate model, the effects of different plug combinations on the plugging agent's dilution resistance are observed, and the strength of the plugging agent's dilution resistance is determined. The measurement method follows S1 and S7, with the pre-protection plug's viscosity being 55.36 mPa·s, the plugging agent's viscosity being 83.12 mPa·s, and the post-protection plug's viscosity being 106.5 mPa·s.

[0049] From the plane diagram of the visual flat plate model during the injection of plugging agent ( Figure 8) It can be seen that during the entire injection process of the front protection slug, the plugging agent, and the rear protection slug, after the front protection slug is injected, during the entire injection process of the plugging agent, the plugging agent can be pushed forward smoothly in the visualized flat plate model, and the plugging agent is basically not diluted during the advancement process; after the plugging agent is injected, during the entire injection process of the rear protection slug, the rear protection slug can completely push the plugging agent forward smoothly, and during the advancement process, the plugging agent is almost not diluted, and its anti-dilution performance is very good.

[0050] From the above experiments, it can be seen that by adjusting the viscosity of the front protection slug, the viscosity of the plugging agent, and the viscosity of the rear protection slug, and observing the dilution of the plugging agent under six different slug combinations, it is found that the anti-dilution ability of the plugging agent is best when the viscosity of the front protection slug is lower than that of the plugging agent, and the viscosity of the plugging agent is lower than that of the rear protection slug.

[0051] The above description is merely a specific experimental example of the present invention and does not constitute any form of limitation to the present invention. Any person skilled in the art may, without departing from the scope of the technical solution of the present invention, make slight changes or modifications to the above-described technical contents to form equivalent embodiments with equivalent variations. However, any simple modifications, equivalent variations, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the content of the technical solution of the present invention, shall still fall within the scope of the technical solution of the present invention.

Claims

1. A method for testing the anti-dilution ability of a plugging agent in a crack, characterized in that By adjusting the viscosity of the front protection slug, the viscosity of the plugging agent, and the viscosity of the rear protection slug, the anti-dilution ability of the plugging agent in the fracture under different slug combinations is tested, including the following steps: S1: Dye the clean water blue, the plugging agent black, and the protection slug red. Then, use a viscometer to test the viscosity of the front protection slug, plugging agent, and rear protection slug at room temperature and record the values. Then, add 1000ml of blue-dyed water to the multifunctional core displacement device No. 1, 1000ml of black plugging agent to the multifunctional core displacement device No. 2, and 1000ml of red front protection slug solution to the multifunctional core displacement device No.

3. After injecting the front protection slug solution, clean the multifunctional core displacement device No. 3, add the rear protection slug solution, and connect the experimental device. S2: 1.0 PV of blue water was injected into the visual flat plate model at a certain speed. Subsequently, 0.3 PV of pre-protection slug solution with a viscosity of 83.12 mPa·s was injected into the visual flat plate model at the same speed. Then, 0.3 PV of plugging agent with a viscosity of 83.12 mPa·s was injected into the visual flat plate model at the same speed. Subsequently, the multifunctional core displacement device No. 3 was cleaned, and the post-protection slug solution was added. After the experimental device was connected, 0.3 PV of post-protection slug solution with a viscosity of 83.12 mPa·s was injected into the visual flat plate model again to observe the dilution of the plugging agent. S3: 1.0 PV of blue water was injected into the visualized flat plate model at a certain speed. Subsequently, 0.3 PV of pre-protection slug solution with a viscosity of 83.12 mPa·s was injected into the visualized flat plate model at the same speed. Then, 0.3 PV of plugging agent with a viscosity of 55.36 mPa·s was injected into the visualized flat plate model at the same speed. Subsequently, the multifunctional core displacement device No. 3 was cleaned, and the post-protection slug solution was added. After the experimental device was connected, 0.3 PV of post-protection slug solution with a viscosity of 83.12 mPa·s was injected into the visualized flat plate model again to observe the dilution of the plugging agent. S4: 1.0 PV of blue water was injected into the visualized flat plate model at a certain speed. Subsequently, 0.3 PV of pre-protection slug solution with a viscosity of 83.12 mPa·s was injected into the visualized flat plate model at the same speed. Then, 0.3 PV of plugging agent with a viscosity of 55.36 mPa·s was injected into the visualized flat plate model at the same speed. Subsequently, the multifunctional core displacement device No. 3 was cleaned, and the post-protection slug solution was added. After the experimental device was connected, 0.3 PV of post-protection slug solution with a viscosity of 55.36 mPa·s was injected into the visualized flat plate model again to observe the dilution of the plugging agent. S5: 1.0 PV of blue water was injected into the visualized flat plate model at a certain speed. Subsequently, 0.3 PV of pre-protection slug solution with a viscosity of 83.12 mPa·s was injected into the visualized flat plate model at the same speed. Then, 0.3 PV of plugging agent with a viscosity of 106.5 mPa·s was injected into the visualized flat plate model at the same speed. Subsequently, the multifunctional core displacement device No. 3 was cleaned, and the post-protection slug solution was added. After the experimental device was connected, 0.3 PV of post-protection slug solution with a viscosity of 106.5 mPa·s was injected into the visualized flat plate model again to observe the dilution of the plugging agent. S6: 1.0 PV of blue water was injected into the visualized flat plate model at a certain speed. Subsequently, 0.3 PV of pre-protection slug solution with a viscosity of 55.36 mPa·s was injected into the visualized flat plate model at the same speed. Then, 0.3 PV of plugging agent with a viscosity of 83.12 mPa·s was injected into the visualized flat plate model at the same speed. Subsequently, the multifunctional core displacement device No. 3 was cleaned, and the post-protection slug solution was added. After the experimental device was connected, 0.3 PV of post-protection slug solution with a viscosity of 106.5 mPa·s was injected into the visualized flat plate model again to observe the dilution of the plugging agent. S7: By observing the dilution of the plugging agent under five slug combinations, it was found that the plugging agent's anti-dilution ability reached its highest level when the viscosity of the leading protection slug (55.36 mPa·s) was lower than the viscosity of the plugging agent (83.12 mPa·s), and the viscosity of the plugging agent (83.12 mPa·s) was lower than the viscosity of the trailing protection slug (106.5 mPa·s). This viscosity gradient relationship should be used in slug design.

2. A method for testing the anti-dilution ability of a plugging agent in a crack according to claim 1, characterized in that: The visual flat plate model is used to simulate the distribution of complex underground fracture networks. The model is made of two visual flat plates. The outer dimensions of the flat plate model are 1000×200 mm, the inner dimensions of the crack are 940×140 mm, and the surrounding 30 mm is a sealing area. The height of the crack is 1 mm, and the total volume of the crack is 131.6 cm 3 .

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