Sand filling pipe slurry pollution experiment device and method

Abstract

The invention discloses a sand-filled pipe mud pollution experiment device and method, and belongs to the technical field of rock displacement experiments, the sand-filled pipe mud pollution experiment device comprises an invasion unit and a reverse discharge unit, the influence of mud on artificial sand-filled cracks can be simulated, the experiment is carried out through the device, the invasion and backflow rules of heavy mud in a sand-filled pipe are analyzed, and the sand-filled pipe mud pollution experiment device is used for simulating the artificial sand-filled cracks. The sand filling pipe, the measuring cylinder and the intermediate container are connected, the regular conclusion of invasion of low-density slurry and heavy slurry can be obtained by changing the particle size of the slurry, and the intermediate container is connected with the pressure meter for measuring the pressure of the intermediate container; the experimental device disclosed by the invention is simple in structure and convenient to operate, and can be used for quickly measuring rock parameters on site. According to the experimental method, various parameters such as permeability, invasion distance, flowback rate and the like can be simply obtained; and according to the method, the regular conclusion of invasion of low-density slurry and heavy slurry can be obtained by changing the particle size of the slurry.

Description

Technical Field

[0001] The invention belongs to the technical field of rock displacement experiments, and in particular relates to a sand-filled pipe mud pollution experimental device and method. Background Art

[0002] Well repair operations in some ultra-deep, ultra-high-pressure, and high-temperature gas reservoirs in a certain area during production after transformation caused serious reservoir contamination and loss of single well production. Focusing on the problem of mud contamination in some target blocks, experimental methods were used to study the invasion and flowback of heavy mud in artificial sand-filled fractures, and analyze the influence of mud on the permeability of sand-filled fractures.

[0003] Since the current research on mud pollution mainly focuses on the drilling process, less consideration is given to the working conditions of the fracturing process. For repeated transformation wells with mud pollution, sand-filled fractures are the main channels for mud loss and pollution. The existing technology lacks simulation experimental equipment and methods for the impact of mud on artificial sand-filled fractures, and cannot well derive the invasion and backflow rules of heavy mud in sand-filled pipes. Summary of the invention

[0004] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a sand-filled pipe mud pollution experimental device and method for simulating the influence of mud on artificial sand-filled cracks. Experiments were carried out through the device to analyze the intrusion and backflow rules of heavy mud in the sand-filled pipe.

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

[0006] A sand-filled pipe mud pollution experimental device comprises: an invasion unit and a backflow unit; the invasion unit and the backflow unit are used alternately, and the invasion unit comprises a sand-filled pipe, the inlet end of the sand-filled pipe is connected to an intermediate container, the intermediate container is sequentially connected to a pressure gauge and a high-pressure gas storage tank, and the outlet end of the sand-filled pipe is connected to a measuring cylinder.

[0007] Preferably, the reverse discharge unit includes a six-way valve, the six-way valve replaces the intermediate container, and the inlet and outlet ends of the sand filling pipe are swapped, the original outlet end is sequentially connected to the six-way valve, the pressure gauge and the high-pressure gas storage tank, and the original inlet end is connected to the measuring cylinder.

[0008] Preferably, nitrogen is stored in the high-pressure gas storage tank.

[0009] The present invention also discloses a sand-filled pipe mud pollution experimental method, comprising the following steps:

[0010] Place the mud in an intermediate container and connect the inlet end of the sand filling pipe to the intermediate container;

[0011] Adjust the high-pressure gas storage tank so that the pressure gauge reading reaches the set value and record the start time;

[0012] When there is no more liquid flowing out of the outlet of the sand-filled tube, record the amount of liquid flowing out of the measuring cylinder and the end time;

[0013] Close the gas source, release the pressure at the inlet of the sand filling pipe and calculate the intrusion permeability;

[0014] Replace the inlet and outlet ends of the sand filling pipe, connect the reverse discharge unit, repeat the above steps to simulate the reverse discharge and end the experiment.

[0015] Preferably, the mud invasion distance is calculated according to the liquid output in the measuring cylinder and the void volume in the sand filling tube; the calculation method is to divide the liquid output by the void volume in the sand filling tube and multiply by the length of the sand filling tube.

[0016] Preferably, the void volume calculation method in the sand-filled tube is:

[0017] Void volume = liquid output × (end time - start time).

[0018] Preferably, the intrusion permeability is calculated according to the start time, the end time, the liquid output and the pressure gauge reading, and the calculation method of the intrusion permeability is as follows:

[0019]

[0020] Where: K 1 is the invasion permeability; Δp is the pressure difference before and after the fluid passes through the sand body, Q 1 is the amount of fluid flowing through the sand body under the action of the intrusion pressure difference, μ is the viscosity of the fluid passing through the sand body, L is the length of the sand body, and A is the cross-sectional area of ​​the sand body perpendicular to the flow direction.

[0021] Preferably, when the reverse discharge unit is turned on to simulate reverse discharge, the six-way valve replaces the intermediate container, and the inlet and outlet ends of the sand filling pipe are exchanged.

[0022] Preferably, turning on the reverse discharge unit to simulate reverse discharge specifically includes the following steps:

[0023] The inlet and outlet ends of the sand filling pipe are swapped, the original outlet end is connected to the six-way valve, pressure gauge and high-pressure gas storage tank in sequence, and the original inlet end is connected to the measuring cylinder;

[0024] Adjust the high-pressure gas storage tank so that the pressure gauge reading reaches the set value and record the start time;

[0025] When no more liquid flows out from one end of the measuring cylinder, record the amount of liquid flowing out and the end time; close the high-pressure gas storage tank and calculate the backflow rate.

[0026] Preferably, the backflow rate is calculated according to the liquid output before and after the inlet and outlet ends of the sand filling pipe are replaced, and the calculation method is as follows:

[0027]

[0028] Where: K2 is the back discharge rate; Q 2 is the amount of liquid discharged through the sand body under the action of the backflow pressure difference, Q 1 It is the amount of liquid discharged through the sand body under the action of the intrusion pressure difference.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The invention discloses a sand-filled pipe mud pollution experimental device, which comprises an invasion unit and a backflow unit, and can simulate the influence of mud on artificial sand-filled fractures. Experiments are carried out through the device, and the invasion and backflow rules of heavy mud in the sand-filled pipe are analyzed and obtained. The sand-filled pipe, a measuring cylinder and an intermediate container are connected, and the regularity conclusion of the invasion of low-density mud and heavy mud can be obtained by changing the mud particle size. The intermediate container is connected to a pressure gauge for measuring its pressure; a high-pressure gas storage tank is used to provide nitrogen. The experimental device of the invention has a simple structure and is easy to operate, and can quickly realize the determination of rock parameters on site.

[0031] The invention discloses a sand-filled pipe mud pollution experimental method, which can relatively simply obtain various parameters: permeability, invasion distance, flowback rate, etc.; and the method can obtain regularity conclusions on the invasion of low-density mud and heavy mud by changing the mud particle size. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of the intrusion unit structure of the experimental device of the present invention.

[0033] Figure 2 It is a schematic diagram of the structure of the reverse discharge unit of the experimental device of the present invention.

[0034] Figure 3 Schematic diagram of the relationship between the displacement pressure of mud with different particle sizes and the mud invasion depth in an embodiment of the present invention.

[0035] Figure 4 Schematic diagram of the return flow rate of mud with different particle sizes in an embodiment of the present invention.

[0036] Figure 5 Schematic diagram of dimensionless permeability relationship under different conditions in an embodiment of the present invention.

[0037] In the figure: 1- measuring cylinder, 2- sand filling tube, 3- pressure gauge, 41- intermediate container, 42- six-way valve, 5- high-pressure gas storage tank. DETAILED DESCRIPTION

[0038] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0039] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0040] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0041] Therefore, this study designed a sand-filled pipe mud pollution experimental device and experimental method to simulate the influence of mud on artificial sand-filled fractures. Experiments were carried out using this device, and the invasion and backflow rules of heavy mud in sand-filled pipes were analyzed.

[0042] See also Figure 1 , Figure 2 The present application discloses a sand-filled pipe mud pollution experimental device, characterized in that it includes: an invasion unit and a backflow unit; the invasion unit and the backflow unit are used alternately, and the invasion unit includes a sand-filled pipe 2, the inlet end of the sand-filled pipe 2 is connected to an intermediate container 41, the intermediate container 41 is connected to a pressure gauge 3 and a high-pressure gas storage tank 5 in sequence, and the outlet end of the sand-filled pipe 2 is connected to a measuring cylinder 1. The use of the invasion unit and the backflow unit can simulate the influence of mud on artificial sand-filled fractures. Through the device, experiments are carried out, and the invasion and backflow rules of heavy mud in the sand-filled pipe are analyzed. The sand-filled pipe 2, the measuring cylinder 1 and the intermediate container 41 are connected, and the regularity of the invasion of low-density mud and heavy mud can be obtained by changing the mud particle size. The intermediate container 41 is connected to a pressure gauge 3 for measuring its pressure; the high-pressure gas storage tank 5 is used to provide nitrogen. The experimental device of the present invention has a simple structure and is easy to operate, and can quickly realize the determination of rock parameters on site.

[0043] In some embodiments, the backflow unit includes a six-way valve 42, which replaces the intermediate container 41, and the inlet and outlet ends of the sand filling pipe 2 are swapped, the original outlet end is connected to the six-way valve 42, the pressure gauge 3 and the high-pressure gas storage tank 5 in sequence, and the original inlet end is connected to the measuring cylinder 1; after the six-way valve 42 replaces the intermediate container 41, it is connected to the sand filling pipe 2 and the measuring cylinder 1 to simulate the mud backflow situation, and the regularity of the backflow of low-density mud and heavy mud can be obtained by changing the mud particle size.

[0044] Preferably, nitrogen is stored in the high-pressure gas storage tank 5 .

[0045] An experimental method for a sand-filled pipe mud pollution experimental device comprises the following steps:

[0046] S1: placing mud in an intermediate container 41 and connecting the inlet end of the sand filling pipe 2 to the intermediate container 41;

[0047] S2: Adjust the high-pressure gas storage tank 5 so that the pressure gauge 3 reading reaches the set value and record the start time;

[0048] S3: No more liquid flows out from the outlet of the sand tube 2 to be filled, and the amount of liquid in the measuring cylinder 1 is recorded, and the end time is recorded;

[0049] S4: Turn off the gas source, release the pressure at the inlet end of the sand filling pipe 2 and calculate the intrusion permeability;

[0050] S5: Replace the inlet and outlet ends of the sand filling pipe 2, connect the reverse discharge unit, repeat the above steps to simulate the reverse discharge and end the experiment.

[0051] This method can easily obtain various parameters: invasion permeability, invasion distance, return flow rate, etc.; and this method can obtain regularity conclusions on the invasion of low-density mud and heavy mud by changing the mud particle size.

[0052] In some embodiments, the mud invasion distance is calculated according to the liquid output in the measuring cylinder 1 and the void volume in the sand filling tube; the calculation method is to divide the liquid output by the void volume in the sand filling tube and then multiply by the length of the sand filling tube.

[0053] In some embodiments, the void volume in the sand-filled tube is calculated as follows:

[0054] Void volume = liquid output × end time - start time.

[0055] In some embodiments, the intrusion permeability is calculated according to the start time, the end time, the liquid output and the pressure gauge reading, and the calculation method of the intrusion permeability is as follows:

[0056]

[0057] Where: K 1is the invasion permeability; Δp is the pressure difference before and after the fluid passes through the sand body, Q 1 is the amount of fluid flowing through the sand body under the action of the intrusion pressure difference, μ is the viscosity of the fluid passing through the sand body, L is the length of the sand body, and A is the cross-sectional area of ​​the sand body perpendicular to the flow direction.

[0058] In some embodiments, when the reverse discharge unit is turned on to simulate reverse discharge, the six-way valve 42 replaces the intermediate container 41, and the inlet and outlet ends of the sand filling pipe 2 are swapped.

[0059] In some embodiments, turning on the reverse discharge unit to simulate reverse discharge specifically includes the following steps:

[0060] S6: The inlet and outlet ends of the sand filling pipe 2 are exchanged, the original outlet end is connected to the six-way valve 42, the pressure gauge 3 and the high-pressure gas storage tank 5 in sequence, and the original inlet end is connected to the measuring cylinder 1;

[0061] S7: Adjust the high-pressure gas storage tank 5 so that the pressure gauge 3 reading reaches the set value, and record the start time;

[0062] S8: When no more liquid flows out from one end of the measuring cylinder 1, record the liquid output and the end time; close the high-pressure gas storage tank 5 and calculate the backflow rate.

[0063] In some embodiments, the backflow rate is calculated based on the liquid output before and after the inlet and outlet ends of the sand filling tube 2 are replaced, and the calculation method is as follows:

[0064]

[0065] Where: K 2 is the back discharge rate; Q 2 is the amount of liquid discharged through the sand body under the action of the backflow pressure difference, Q 1 It is the amount of liquid discharged through the sand body under the action of the intrusion pressure difference.

[0066] [Example]

[0067] like Figure 1 and Figure 2 As shown, a sand-filled pipe mud pollution experimental device includes a sand-filled pipe 2, the outlet end of the sand-filled pipe 2 is connected to a measuring cylinder 1, and the inlet end is connected to an intermediate container 41 or a six-way valve 42; the intermediate container 41 or the six-way valve 42 is connected to a pressure gauge 3 for measuring its pressure; and also includes a high-pressure gas storage tank 5 for providing nitrogen.

[0068] When simulating mud invasion, the inlet end of the sand filling pipe 2 is connected to the intermediate container 41, the intermediate container 41 is connected to the pressure gauge 3 and the high-pressure gas storage tank 5 in sequence, and the outlet end of the sand filling pipe 2 is connected to the measuring cylinder 1;

[0069] When simulating mud backflow, the inlet and outlet ends of the sand filling pipe 2 are swapped, the six-way valve 42 replaces the intermediate container 41, the original outlet end is connected to the six-way valve 42, the pressure gauge 3 and the high-pressure gas storage tank 5 in sequence, and the original inlet end is connected to the measuring cylinder 1.

[0070] The experimental method using the above-mentioned sand-filled pipe mud pollution experimental device includes the following steps:

[0071] Step 1: The inlet end of the sand filling pipe 2 is connected to the intermediate container 41, and the mud is placed in the intermediate container 41;

[0072] Step 2: Adjust the high-pressure gas storage tank 5 so that the pressure gauge 3 reading reaches the set value and start recording the time;

[0073] Step 3: When no more liquid flows out of the outlet, record the liquid volume at the outlet and the time at this time;

[0074] Step 4: Turn off the gas source and release the pressure at the inlet end;

[0075] Step 5: Clean the measuring cylinder 1, swap the inlet and outlet ends of the sand filling tube 2, and connect the inlet end to the six-way valve 42; the inlet end in step 1 is used as the outlet end to connect the measuring cylinder 1;

[0076] Step 6: Adjust the high-pressure gas storage tank 5 so that the pressure gauge 3 reading reaches the set value;

[0077] Step 7: When no more liquid flows out of the outlet, record the amount of liquid flowing out; close the high-pressure gas storage tank 5, and the experiment is completed. After the experiment is completed, remove the pressure at the inlet end, disassemble the pipeline, remove and clean the sand filling tube 2 and the measuring cylinder 1.

[0078] The void volume in the sand filling tube 2 is calculated according to the pressure gauge readings obtained in steps 1 to 4, the liquid volume at the outlet and the corresponding time; the calculation method is flow rate multiplied by time, that is, the liquid volume at the outlet corresponds to the volume.

[0079] Calculate the permeability K based on the pressure gauge readings, outlet liquid volume and corresponding time obtained in steps 1 to 4; the calculation method is as follows:

[0080]

[0081] Wherein: Δp is the pressure difference before and after the fluid passes through the sand body (the pressure difference is the pressure value measured by the pressure gauge 3), Q is the flow rate through the sand body under the action of the pressure difference, μ is the viscosity of the fluid passing through the sand body, L is the length of the sand body, and A is the cross-sectional area of ​​the sand body perpendicular to the flow direction.

[0082] The permeability test is carried out according to Darcy's law. When water passes through the sand-filled pipe 2, the flow rate Q is proportional to the cross-sectional area of ​​the sand body in the sand-filled pipe 2 and the inlet and outlet pressure difference, and inversely proportional to the length of the sand body.

[0083] The mud invasion distance is calculated according to the liquid volume at the outlet end obtained in step 3 and the void volume in the sand filling tube 2; the calculation method is to divide the liquid volume at the outlet end by the void volume in the sand filling tube 2 and then multiply it by the length of the sand filling tube 2.

[0084] The flowback rate is calculated based on the liquid volume at the outlet obtained in step 3 and the liquid volume at the outlet obtained in step 7. The calculation method is that the flowback rate is the ratio of the liquid volume at the outlet obtained in step 7 to the liquid volume at the outlet obtained in step 3.

[0085] The experimental method of the present invention is used to carry out invasion experiments of ceramsite with different particle sizes in low-density mud and ceramsite with different particle sizes in high-density mud under different displacement pressures; the particle sizes of the ceramsite are selected to be 20 / 40, 30 / 50, and 40 / 70 meshes respectively.

[0086] The penetration depth is calculated according to the above method. The result is as follows: Figure 3 As shown in the figure, it can be seen that the invasion depth of low-density mud increases significantly with the increase of displacement pressure at 20 / 40 and 30 / 50 particle sizes. At the same time, the invasion depth increases the most at displacement pressures of 3MPa to 5MPa. The invasion depth of high-density mud does not change with displacement pressure. As the proppant particle size increases, the pore space in the sand-filling pipe increases, the space for fluid flow increases, the mud is easier to flow in the sand-filling pipe, and the mud invasion depth increases.

[0087] The mud return rate is calculated according to the above method, and the result is as follows: Figure 4 As shown in the figure, it can be seen that the high-density mud + 20 / 40 mesh ceramsite group shows that the mud continuously flows out of the sand filling pipe, and its invasion depth cannot be calculated. The low-density mud + 30 / 50 mesh ceramsite group and the low-density mud + 20 / 40 mesh ceramsite group mud pass through the sand filling pipe at displacement pressures of 5MPa and 3MPa, respectively. However, liquid flows out only within a few seconds after the pressure is increased.

[0088] As can be seen from the figure, when the proppant particle size is larger, the flow resistance of the mud in the sand-filled pipe is smaller, the heavy mud intrusion is larger, and it is difficult to discharge the mud intruding into the sand-filled pipe during nitrogen displacement. According to statistics, the mud return rate in the sand-filled pipe filled with 20 / 40 mesh ceramsite and 30 / 50 mesh ceramsite is 15% to 30%. A large amount of mud is retained in the cracks, causing serious damage to the permeability of the sand-filled pipe.

[0089] According to the above method, the dimensionless permeability under different conditions is calculated, and the results are as follows: Figure 5 As shown in the figure, under the particle size of 30 / 50, the residual permeability after mud contamination is 2.2% to 3.0% of the original permeability, and the mud damage rate to the permeability of the sand filling pipe is 97%. Compared with high-density mud, low-density mud has less damage, but the difference is only 0.3% to 0.7%.

[0090] Table 1 shows the change in permeability of the sand-filled pipe before and after mud pollution, and Table 2 shows the mud invasion volume and flowback rate. The above change rules can also be seen from the following tables.

[0091] Table 1. Changes in permeability of sand-filled pipes before and after mud pollution

[0092]

[0093] Table 2. Mud invasion volume and flowback rate

[0094]

[0095] The experimental device of the present invention has a simple structure and is easy to operate. It can quickly measure rock parameters on site. The experimental method can easily obtain various parameters: permeability, invasion distance, return flow rate, etc. It can be seen from the above embodiments that under 20 / 40 and 30 / 50 particle sizes, the invasion depth of low-density mud increases significantly with the increase of displacement pressure. At the same time, under 3MPa to 5MPa displacement pressure, the invasion depth increases the most. The invasion depth of high-density mud does not change with the displacement pressure. As the proppant particle size increases, the pore space in the sand filling pipe increases, the space for fluid flow increases, the mud is easier to flow in the sand filling pipe, and the mud invasion depth increases. When the proppant particle size is larger, the flow resistance of the mud in the sand filling pipe is smaller, the invasion amount of heavy mud is larger, and it is difficult to remove the mud invading the sand filling pipe during nitrogen reverse displacement. The mud return rate in the sand-filled pipe filled with 20 / 40 mesh ceramsite and 30 / 50 mesh ceramsite is 15%-30%. A large amount of mud is retained in the cracks, causing serious damage to the permeability of the sand-filled pipe. Under the particle size of 30 / 50, the residual permeability after mud contamination is 2.2%-3.0% of the original permeability, and the mud damage rate to the permeability of the sand-filled pipe is 97%. Compared with high-density mud, low-density mud has less damage, but the difference is only 0.3%-0.7%.

[0096] In summary, the sand-filled pipe mud pollution experimental device disclosed in the present application includes an invasion unit and a backflow unit, which can simulate the influence of mud on artificial sand-filled fractures. Experiments were carried out through the device, and the invasion and backflow laws of heavy mud in the sand-filled pipe were analyzed. The sand-filled pipe, the measuring cylinder and the intermediate container are connected, and the regularity of the invasion of low-density mud and heavy mud can be obtained by changing the mud particle size. The intermediate container is connected to a pressure gauge for measuring its pressure; the high-pressure gas tank is used to provide nitrogen. The experimental device of the present invention has a simple structure and is easy to operate, and can quickly realize the determination of rock parameters on site.

[0097] The invention discloses a sand-filled pipe mud pollution experimental method, which can relatively simply obtain various parameters: permeability, invasion distance, flowback rate, etc.; and the method can obtain regularity conclusions on the invasion of low-density mud and heavy mud by changing the mud particle size.

[0098] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A sand-filled pipe mud pollution experimental device, characterized in that: include: An invasion unit and a backflow unit; the invasion unit and the backflow unit are used alternately, and the invasion unit comprises a sand filling pipe (2), the inlet end of the sand filling pipe (2) is connected to an intermediate container (41), the intermediate container (41) is connected in sequence to a pressure gauge (3) and a high-pressure gas storage tank (5), and the outlet end of the sand filling pipe (2) is connected to a measuring cylinder (1).

2. The sand-filled pipe mud pollution experimental device according to claim 1 is characterized in that: The reverse discharge unit comprises a six-way valve (42), the six-way valve (42) replaces the intermediate container (41), and the inlet and outlet ends of the sand filling pipe (2) are exchanged, the original outlet end is connected to the six-way valve (42), the pressure gauge (3) and the high-pressure gas storage tank (5) in sequence, and the original inlet end is connected to the measuring cylinder (1).

3. The sand-filled pipe mud pollution experimental device according to claim 1 is characterized in that: Nitrogen is stored in the high-pressure gas storage tank (5).

4. An experimental method based on the sand-filled pipe mud pollution experimental device according to any one of claims 1 to 3, characterized in that: The following steps are involved: Placing the mud in an intermediate container (41) and connecting the inlet end of the sand filling pipe (2) to the intermediate container (41); Adjust the high-pressure gas storage tank (5) so that the pressure gauge (3) reading reaches the set value, and record the start time; When no more liquid flows out of the outlet of the sand-filled tube (2), the amount of liquid flowing out of the measuring cylinder (1) is recorded, and the end time is recorded; Turn off the gas source, release the pressure at the inlet end of the sand filling pipe (2) and calculate the intrusion permeability; The inlet and outlet ends of the sand filling pipe (2) are replaced, the reverse discharge unit is connected, and the above steps are repeated to simulate the reverse discharge and then the experiment is ended.

5. A shear self-supporting fracture mud contamination test method according to claim 4, characterized in that: The mud invasion distance is calculated according to the liquid output in the measuring cylinder (1) and the void volume in the sand filling pipe; the calculation method is to divide the liquid output by the void volume in the sand filling pipe and then multiply by the length of the sand filling pipe.

6. A shear self-supporting fracture mud contamination test method according to claim 5, characterized in that: The void volume calculation method in the sand-filled tube is: Void volume = liquid output × (end time - start time).

7. A shear self-supporting fracture mud contamination test method according to claim 4, characterized in that: The intrusion permeability is calculated according to the start time, the end time, the liquid output and the pressure gauge reading. The calculation method of the intrusion permeability is as follows: Where: K1 is the invasion permeability; Δp is the pressure difference before and after the fluid passes through the sand body, Q1 is the fluid output through the sand body under the action of the invasion pressure difference, μ is the viscosity of the fluid passing through the sand body, L is the length of the sand body, and A is the cross-sectional area of ​​the sand body perpendicular to the flow direction.

8. A shear self-supporting fracture mud contamination test method according to claim 4, characterized in that: When the reverse discharge unit is turned on to simulate reverse discharge, the six-way valve (42) replaces the intermediate container (41), and the inlet and outlet ends of the sand filling pipe (2) are exchanged.

9. A shear self-supporting fracture mud contamination test method according to claim 8, characterized in that: Connecting the reverse discharge unit to simulate reverse discharge specifically includes the following steps: The inlet and outlet ends of the sand filling pipe (2) are exchanged, the original outlet end is connected to the six-way valve (42), the pressure gauge (3) and the high-pressure gas storage tank (5) in sequence, and the original inlet end is connected to the measuring cylinder (1); Adjust the high-pressure gas storage tank (5) so that the pressure gauge (3) reading reaches the set value, and record the start time; When no more liquid flows out from one end of the measuring cylinder (1), the liquid output and the end time are recorded; the high-pressure gas storage tank (5) is closed and the backflow rate is calculated.

10. A shear self-supporting fracture mud contamination test method according to claim 9, characterized in that: The backflow rate is calculated based on the liquid output before and after the inlet and outlet ends of the sand filling pipe (2) are replaced. The calculation method is as follows: Where: K2 is the backflow rate; Q2 is the amount of liquid passing through the sand body under the action of the backflow pressure difference; Q1 is the amount of liquid passing through the sand body under the action of the intrusion pressure difference.

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