A visual simulation device and method for inhibiting coal powder migration from volume fracturing cracks to the wellbore

Abstract

The present invention discloses a visual simulation device and method for inhibiting the migration of coal dust in volume fracturing cracks into a wellbore. The box body is provided with an inlet and an outlet. The inlet of the box body is connected to a pumping device. The hollow visualization pipe string is provided with a sealed connection port that can be sealed with the outlet of the box body. The outlet of the box body is connected to a sealing interface and the angle of the box outlet is adjustable. The sealed connection port serves as the inlet of the hollow visualization pipe string. The hollow visualization pipe string is also provided with an outlet. The outlet of the hollow visualization pipe string is connected to the inlet of a separator. The separator is used for solid-liquid separation. The metering device is used to measure the mass of the solid separated by the separator. The box body is transparent. The visual monitoring device is used to capture images of the inner cavity of the box body in real time. The present invention can realize real-time monitoring and quantitative characterization of the migration of coal dust in volume fracturing cracks at different perforation angles in coal seams into the horizontal section wellbore of a horizontal well, provide technical support for fracturing perforation design, and improve coalbed methane recovery rate.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil and natural gas development, and is mainly used for visual simulation of inhibiting the migration of coal powder in volume fracturing cracks of coal seams to wellbores, and particularly relates to a visual simulation device and method for inhibiting the migration of coal powder in volume fracturing cracks to wellbores. Background Art

[0002] As conventional oil and gas resources enter the middle and late stages of development, unconventional reservoirs hold significant reserves, prompting the need for increased development of these resources. Coalbed methane (CBM) resources are abundant and offer significant development potential, making it a valuable alternative to clean energy. In recent years, CBM development wells have gradually shifted from vertical to horizontal wells. However, due to the low tensile and compressive strength, low elastic modulus, and Poisson's ratio of coal seams, they are susceptible to fracturing and collapse. Consequently, fracturing the reservoir produces significant amounts of coal dust. This sedimentation not only impacts fluid migration pathways and reduces permeability, but also accumulates and settles within the wellbore or enters the drainage system, leading to pump burial and sticking, necessitating frequent pump inspections and workovers, and severely impacting CBM well drainage and, ultimately, its production potential. Due to gravity, if the fractures in the coal seam are located at the top of the horizontal section, the coal dust in the fractures is more likely to sink into the wellbore, compromising stable CBM production. For the development of coalbed methane horizontal wells, directional perforation is carried out, and the length of the fracturing crack at the top of the horizontal section is one-third to one-half of the lower crack, which can reduce the migration of coal powder into the wellbore.

[0003] Therefore, simulating the migration of pulverized coal into the wellbore within volumetric fractures in coal seams is crucial for reducing the amount of pulverized coal migrating into the wellbore during actual coalbed methane (CBM) extraction, thereby maximizing CBM well productivity. Currently, methods for inhibiting the migration of pulverized coal into the wellbore within volumetric fractures include conducting geological analysis and geophysical interpretation of static geological factors influencing pulverized coal production, such as structure, hydrology, and coal body structure, during the CBM development and well placement phases to avoid areas and intervals prone to pulverized coal production; employing acid fracturing in coal seams with high inorganic mineral content to reduce the generation of secondary pulverized coal; and monitoring pulverized coal concentration in wells producing pulverized coal, generating warnings when the pulverized coal concentration reaches a set level. However, the predicted results of geological analysis and geophysical interpretation methods can differ from actual results; acid fracturing can easily damage the reservoir; and pulverized coal concentration monitoring cannot provide real-time monitoring. Therefore, there is an urgent need for an economical and practical visual simulation device and method for inhibiting the migration of pulverized coal into the wellbore within volumetric fractures. Summary of the Invention

[0004] In order to solve the above-mentioned problems, the purpose of the present invention is to provide a visual simulation device and method for inhibiting the migration of coal powder in volume fracturing cracks into the wellbore. The present invention can realize real-time monitoring and quantitative characterization of the migration of coal powder in volume fracturing cracks at different perforation angles in coal seams into the horizontal section of the horizontal wellbore, provide technical support for fracturing perforation design, and improve coalbed methane recovery rate.

[0005] In order to achieve the above object, the technical solution of the present invention is as follows:

[0006] A visual simulation device for inhibiting the migration of coal powder in volume fracturing cracks into a wellbore, comprising a hollow visualization string, a box, a pumping device, a separator, a metering device and a visualization monitoring device, wherein the hollow visualization string is used to simulate the horizontal section of the wellbore of a horizontal well in coalbed methane mining, the box is used to simulate the cracks generated during volume fracturing, the box is provided with an inlet and an outlet, the inlet of the box is connected to the pumping device, the pumping device is used to pump a mixture of coal powder and liquid into the box, the hollow visualization string is provided with a sealing connection port that can be sealed to the outlet of the box, the outlet of the box is connected to the sealing interface and the angle of the box outlet is adjustable, the sealing connection port serves as the inlet of the hollow visualization string, the hollow visualization string is also provided with an outlet, the outlet of the hollow visualization string is connected to the inlet of the separator, the separator is used for solid-liquid separation, the metering device is used to measure the mass of the solid separated by the separator, the box is transparent, and the visualization monitoring device is used to capture images of the inner cavity of the box in real time.

[0007] Preferably, the box body is a rotating body with an outlet at one end and a smooth inner cavity surface, and the inlet of the box body is arranged in the middle or bottom of the box body.

[0008] Preferably, the box body is shaped like a large middle and small ends (e.g., a spindle, ellipsoid, or rugby ball). The inlet is located in the middle or at the bottom of one end, and the outlet is located at the other end. The box body can also be shaped like a wine bottle, with the box body transitioning smoothly to form the outlet. A smooth transition from the box body to the outlet is required, ensuring that there are no dead angles. This ensures that the coal dust in the box body can flow smoothly toward the outlet, and prevents the coal dust from being retained within the box due to the box body's shape.

[0009] Preferably, the sealing connection ports are provided on both the upper and lower sides of the hollow visualization tube column. When the outlet of the box is connected to one of the sealing connection ports on the hollow visualization tube column, the remaining sealing connection ports are closed by the sealing device.

[0010] Preferably, the sealing connection port of the hollow visualization pipe column has a rotating structure, the outlet of the box is connected to the sealing connection port of the hollow visualization pipe column through the rotating structure, the rotating structure has a circulation channel, the inlet of the circulation channel of the rotating structure is connected to the outlet of the box, and the outlet of the circulation channel of the rotating structure is connected to the inner cavity of the hollow visualization pipe column. The rotating structure can adjust the flow direction of the mixture of coal powder and liquid injected by the box into the inner cavity of the hollow visualization pipe column and realize the adjustment of the box outlet angle.

[0011] Preferably, the pumping device includes a coal powder box, a powder injection pipeline, a three-way valve, a liquid storage tank, a water injection pipeline, an injection pipeline and an injection pump. The coal powder box is connected to the first interface of the three-way valve through the powder injection pipeline, the liquid storage tank is connected to the second interface of the three-way valve through the water injection pipeline, the third interface of the three-way valve is connected to the inlet of the injection pump through the injection pipeline, the outlet of the injection pump is connected to the inlet of the box through a pipeline, and the first interface and the second interface of the three-way valve are both provided with flow regulating devices.

[0012] Preferably, the metering device includes a collecting bucket and a balance, the collecting bucket is arranged on the balance, the solid outlet of the separator is connected to a powder outlet pipeline, and the powder outlet pipeline extends into the inner cavity of the collecting bucket.

[0013] Preferably, the liquid outlet of the separator is connected to a vacuum pump via a first liquid outlet pipeline, the outlet of the vacuum pump is connected to a second liquid outlet pipeline, and the outlet of the second liquid outlet pipeline is connected to a waste liquid collection bucket;

[0014] The hollow visualization column and the box body are both arranged in the visualization glass plate box. The hollow visualization column includes a transparent cylinder and a first fixed body and a second fixed body respectively sealed and connected at both ends of the cylinder. The first fixed body and the second fixed body are both arranged in the inner cavity of the visualization glass plate box.

[0015] The visual monitoring device uses a high-precision camera.

[0016] Preferably, it further comprises a data receiving and control center, and the pumping device, vacuum pump, visual monitoring device and metering device are all connected to the data receiving and control center;

[0017] The data receiving and control center can control the start and stop of the pumping device. When it is necessary to pump a mixture of coal powder and liquid into the tank, the data receiving and control center controls the pumping device to start; when the tank cavity is blocked by coal powder, or when it is necessary to stop pumping the mixture of coal powder and liquid into the tank, the data receiving and control center can control the pumping device to stop;

[0018] The data receiving and control center can also receive and store the mass of solids separated by the separator measured by the metering device;

[0019] The data receiving and control center can also control the start and stop of the vacuum pump. When the vacuum pump needs to be started, the data receiving and control center controls the vacuum pump to start; when the vacuum pump needs to be stopped, the data receiving and control center controls the vacuum pump to stop.

[0020] The present invention also provides a visual simulation method for inhibiting the migration of coal dust in volumetric fractures into a wellbore. The method is performed using the visual simulation device for inhibiting the migration of coal dust in volumetric fractures into a wellbore as described above, and includes the following steps:

[0021] Adjust the angle between the box outlet and the axis of the hollow visualization column to a preset angle, and pump the mixture of coal powder and liquid into the box through the pumping device. A portion of the coal powder in the mixed liquid entering the box is deposited in the box, and the rest of the coal powder flows into the hollow visualization column with the liquid;

[0022] The mixture of coal powder and liquid in the hollow visualization column flows into the separator and undergoes solid-liquid separation. The coal powder separated by the separator is weighed by a metering device.

[0023] Calculate the ratio of the mass of pulverized coal transported to the hollow visualization column to the total mass of injected pulverized coal, where the total mass of injected pulverized coal is the mass of pulverized coal in the mixture of pulverized coal and liquid pumped into the box by the pumping device, and the mass of pulverized coal transported to the hollow visualization column is the difference between the total mass of injected pulverized coal and the mass of pulverized coal separated by the separator.

[0024] The present invention has the following beneficial effects:

[0025] In the visualization simulation device for inhibiting the migration of coal powder in volume fracturing cracks into the wellbore of the present invention, a box body can be used to simulate the cracks generated during the volume fracturing process, a pumping device can be used to pump a mixture of coal powder and liquid into the box body to simulate volume fracturing, and a hollow visualization pipe string can be used to simulate the horizontal section wellbore of a horizontal well in coalbed methane extraction. The outlet of the box body is connected to the sealing interface and the angle of the box outlet is adjustable. In this way, the coal powder in the volume fracturing cracks of the coal seam with different perforation angles can be realized to migrate into the horizontal section wellbore of the horizontal well. A separator can be used to separate the liquid and solid of the mixed liquid flowing out of the hollow visualization pipe string to separate the coal powder in the mixed liquid. A metering device can be used to measure the mass of the solid separated by the separator, and then the proportion of the weight of the coal powder migrated to the hollow visualization pipe string under this box placement method and angle to the total weight of the injected coal powder is obtained, providing technical support for fracturing perforation design and improving the coalbed methane recovery rate. The visual monitoring device can be used to capture images of the inner cavity of the box in real time to determine the distribution of coal powder in the box. If the coal powder is found to be blocked in the box, the mixture of coal powder and liquid will be immediately stopped from being pumped into the box to ensure the safety of the experiment. In addition, the coal powder separated by the separator can be recycled, and the collected coal powder can be reused, saving precious bottom hole cores. In addition, the use of the visual simulation device of the present invention can reduce the costs associated with the experiment, and the feasibility is high. The present invention only requires a small amount of bottom hole cores to be ground into coal powder and the required experimental liquid to realize the test. The experimental device itself is low in cost and is less affected by the environment, and the feasibility of the experiment is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic structural diagram of a visual simulation device for inhibiting coal powder from migrating into a wellbore within a volumetric fracturing crack according to the present invention.

[0027] Figure 2 Schematic diagram of perforation above the wellbore in an embodiment of the present invention.

[0028] Figure 3 Schematic diagram of perforating 30° below the wellbore in an embodiment of the present invention

[0029] In the figure, 1 is a coal powder box, 2 is a powder injection pipeline, 3 is a three-way valve, 4 is a liquid storage tank, 5 is a water injection pipeline, 6 is an injection pipeline, 7 is an injection pump, 8 is a first fixed body, 11 is a first sealed connection port, 12 is a second sealed connection port, 13 is a hollow visualization column, 14 is a box, 15 is a high-precision camera, 16 is a visualization glass plate box, 17 is a second fixed body, 18 is an outflow pipeline, 19 is a separator, 20 is a powder outlet pipeline, 21 is a collection bucket, 22 is a data transmission line of a high-precision camera, 23 is a balance, 24 is a data transmission line of a balance, 25 is a data transmission line, 26 is a first liquid outlet pipeline, 27 is a vacuum pump, 28 is a second liquid outlet pipeline, 29 is a waste liquid collection bucket, 30 is a data line, and 31 is a data receiving and control center. DETAILED DESCRIPTION

[0030] The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0031] See also Figure 1-Figure 3 The present invention provides a visual simulation device for inhibiting the migration of coal powder in volume fracturing cracks into a wellbore, comprising a hollow visualization string 13, a box 14, a pumping device, a separator 19, a metering device and a visual monitoring device. The hollow visualization string 13 is used to simulate the horizontal wellbore of a horizontal well in coalbed methane mining, and the box 14 is used to simulate the cracks generated during volume fracturing. The box 14 is provided with an inlet and an outlet. The inlet of the box 14 is connected to the pumping device, which is used to pump a mixture of coal powder and liquid into the box 14. The hollow visualization string 13 is provided with a There is a sealed connection port that can be sealed with the outlet of the box body 14. The outlet of the box body 14 is connected to the sealed interface and the angle of the outlet of the box body 14 is adjustable. The sealed connection port serves as the inlet of the hollow visualization column 13. The hollow visualization column 13 is also provided with an outlet. The outlet of the hollow visualization column 13 is connected to the inlet of the separator 19. The separator 19 is used for solid-liquid separation. The metering device is used to measure the mass of the solid separated by the separator 19. The box body 14 is transparent, and the visual monitoring device is used to capture the image of the inner cavity of the box body 14 in real time.

[0032] The working process of the above-mentioned visual simulation device of the present invention includes:

[0033] Adjust the angle between the outlet of the box 14 and the axis of the hollow visualization column 13 to a preset angle, and pump the mixture of coal powder and liquid into the box 14 through the pumping device. A portion of the coal powder in the mixture entering the box 14 is deposited in the box 14, and the remaining coal powder flows into the hollow visualization column 13 along with the liquid;

[0034] The mixture of coal powder and liquid in the hollow visualization column 13 flows into the separator 19 and undergoes solid-liquid separation. The coal powder separated by the separator 19 is weighed by a metering device.

[0035] Calculate the ratio of the mass of coal powder transported to the hollow visualization column 13 to the total mass of the injected coal powder, where the total mass of the injected coal powder is the mass of the coal powder in the mixture of coal powder and liquid pumped into the box 14 by the pumping device, and the mass of the coal powder transported to the hollow visualization column 13 is the difference between the total mass of the injected coal powder and the mass of the coal powder separated by the separator 19.

[0036] See also Figure 1-Figure 3 The box body 14 of the present invention adopts a rotating body with an outlet at one end and a smooth inner cavity surface. The inlet of the box body 14 is set in the middle or bottom of the box body 14, so that the coal powder in the mixed liquid can smoothly enter the hollow visualization pipe column 13, which is conducive to the movement of the coal powder.

[0037] The housing 14 of the present invention typically has a large center and small ends, such as a spindle, ellipsoid, or rugby ball shape. The inlet of the housing 14 is located in the center or at the bottom of one end, and the outlet is located at the other end. The housing can also be shaped like a wine bottle, with the housing body transitioning smoothly to form the outlet. A smooth transition from the housing body to the outlet is essential, ensuring that there are no dead angles. This ensures that the pulverized coal in the housing flows smoothly toward the outlet, and prevents the pulverized coal from being trapped within the housing due to the housing's shape.

[0038] See also Figure 2 and Figure 3 To simulate perforations at different locations in a horizontal well, the hollow visualization string 13 of the present invention is provided with sealed connections on both its upper and lower sides, respectively, for simulating perforations at the top and bottom of the horizontal well section. When the inlet of the housing 14 is connected to one of the sealed connections on the hollow visualization string 13, the remaining sealed connections are sealed by a sealing device. The sealing device can be a sealing plug or sealing bolt compatible with the sealing connection, ensuring that the seal does not leak or release pressure.

[0039] The sealed connection port of the hollow visualization column 13 of the present invention has a rotating structure, and the outlet of the box 14 is connected to the sealed connection port of the hollow visualization column 13 through the rotating structure. The interior of the rotating structure has a circulation channel, and the inlet of the circulation channel of the rotating structure is connected to the outlet of the box 14, and the outlet of the circulation channel of the rotating structure is connected to the inner cavity of the hollow visualization column 13. The rotating structure can adjust the flow direction of the mixture of coal powder and liquid injected into the inner cavity of the hollow visualization column 13 by the box 14, and realize the adjustment of the outlet angle of the box 14. The rotating structure can adopt a ball head type universal connection structure.

[0040] A typical structure of the pumping device of the present invention is as follows Figure 1 As shown, it includes a coal powder box 1, a powder injection pipeline 2, a three-way valve 3, a liquid storage tank 4, a water injection pipeline 5, an injection pipeline 6 and an injection pump 7. The coal powder box 1 is connected to the first interface of the three-way valve 3 through the powder injection pipeline 2, the liquid storage tank 4 is connected to the second interface of the three-way valve 3 through the water injection pipeline 5, the third interface of the three-way valve 3 is connected to the inlet of the injection pump 7 through the injection pipeline 6, and the outlet of the injection pump 7 is connected to the inlet of the box 14 through a pipeline. The first interface and the second interface of the three-way valve 3 are both provided with flow regulating devices. The flow of coal powder and the flow of liquid can be adjusted respectively by using these two flow regulating devices, thereby ensuring the ratio of coal powder to liquid in the mixed liquid. After the injection pump 7 is working, the coal powder in the coal powder box 1 and the liquid in the liquid storage tank 4 are sucked into the three-way valve 3. The coal powder and liquid are mixed in the three-way valve 3 to form a mixed liquid and are pumped into the box 14 by the injection pump 7.

[0041] A typical structure of the metering device of the present invention is as follows Figure 1 As shown, it includes a collecting bucket 21 and a balance 23. The collecting bucket 21 is set on the balance 23. The solid outlet of the separator 19 is connected to the powder outlet pipeline 20, which extends into the inner cavity of the collecting bucket 21. The powder outlet pipeline 20 only extends into the collecting bucket 21, and the two are not hard-connected to ensure that the balance 23 can measure the quality of the coal powder separated by the separator 19 in real time and accurately.

[0042] The liquid outlet of the separator 19 of the present invention is connected to a vacuum pump 27 through a first liquid outlet pipeline 26, the outlet of the vacuum pump 27 is connected to a second liquid outlet pipeline 28, and the outlet of the second liquid outlet pipeline 28 is connected to a waste liquid collection bucket 29; before and after the start of the experiment, the negative pressure of the vacuum pump 27 can be used to clean the pipelines of the entire simulation device to avoid affecting the accuracy of the experiment.

[0043] The hollow visualization tube column 13 and the box body 14 are both arranged in a visualization glass plate box 16. The visualization glass plate box 16, the hollow visualization tube column 13 includes a transparent cylinder and a first fixed body 8 and a second fixed body 17 sealed at both ends of the cylinder. The first fixed body 8 and the second fixed body 17 are both arranged in the inner cavity of the visualization glass plate box 16; the visualization glass plate box 16 can support the hollow visualization tube column 13 and the box body 14, and can also serve as a protective cover to prevent the hollow visualization tube column 13 and the box body 14 from being damaged during the test, resulting in the integrity of the test bench and protecting the safety of the test personnel.

[0044] The visual monitoring device adopts a high-precision camera 15, which can achieve high-definition photography, so that the test personnel can understand the distribution status of the coal powder in the box 14 in real time.

[0045] In order to realize automation, the present invention further provides a data receiving and control center 31, to which the injection pump 7, vacuum pump 27, high-precision camera 15 and balance 23 of the pumping device are all connected;

[0046] The data receiving and control center 31 can control the start and stop of the injection pump 7. When it is necessary to pump the mixture of pulverized coal and liquid into the tank 14, the data receiving and control center 31 controls the injection pump 7 to start; when the inner cavity of the tank 14 is blocked by pulverized coal, or when it is necessary to stop pumping the mixture of pulverized coal and liquid into the tank 14, the data receiving and control center 31 can control the injection pump 7 to stop;

[0047] The data receiving and control center 31 is also capable of receiving and storing the mass of the solid separated by the separator 19 as measured by the balance 23;

[0048] The data receiving and control center 31 can also control the start and stop of the vacuum pump 27. When the vacuum pump 27 needs to be turned on, the data receiving and control center 31 controls the vacuum pump 27 to be turned on; when the vacuum pump 27 needs to be stopped, the data receiving and control center 31 controls the vacuum pump 27 to be stopped.

[0049] Example

[0050] The specific structure of the visual simulation device for inhibiting the migration of coal powder from volume fracturing cracks to the wellbore in this embodiment is as follows: Figure 1-Figure 3 As shown, it mainly includes a pumping device, a pulverized coal movement visualization device, a vacuum device and a metering device;

[0051] The pumping device includes a coal powder box 1, a powder injection pipeline 2, a three-way valve 3, a liquid storage tank 4, a water injection pipeline 5, an injection pipeline 6 and an injection pump 7. The coal powder box 1 is connected to the first interface of the three-way valve 3 through the powder injection pipeline 2, the liquid storage tank 4 is connected to the second interface of the three-way valve 3 through the water injection pipeline 5, the third interface of the three-way valve 3 is connected to the inlet of the injection pump 7 through the injection pipeline 6, and the outlet of the injection pump 7 is connected to the inlet of the box 14 through a pipeline. The first interface and the second interface of the three-way valve 3 are both provided with a flow regulating device. The injection pump 7 sucks the coal powder in the coal powder box 1 and the liquid in the liquid storage tank 4 through the powder injection pipeline 2, the water injection pipeline 5 and the injection pipeline 6. The coal powder and the liquid are mixed under the control of the three-way valve 3 and then enter the box 14, providing coal powder and liquid for the migration of coal powder in the simulated volume fracturing crack into the wellbore.

[0052] The coal powder migration visualization device includes a first fixed body 8, a hollow visualization pipe column 13, a box body 14, a high-precision camera 15, a visualization glass plate box 16 and a second fixed body 17. The hollow visualization pipe column 13 is fixed in the visualization glass plate box 16 by the first fixed body 8 and the second fixed body 17, and the box body 14 is located in the visualization glass plate box 16; a first sealed connection port 11 and a second sealed connection port 12 are respectively provided on both sides of the foot of the left end of the hollow visualization pipe column 13. Both the first sealed connection port 11 and the second sealed connection port 12 can be sealed and connected to the box body 14 at different angles; the high-precision camera 15 can monitor the distribution of coal powder in the box body 14. If coal powder blockage is found, the data will be transmitted to the data receiving and control center 31 through the high-precision camera data transmission line 22, thereby pausing the simulation.

[0053] The vacuum pump 27 is used as the vacuum device. Before the experiment begins, the vacuum pump 27 is turned on to evacuate the dust in the hollow visualization column 13 and the box 14 or the coal powder that was not cleaned in time after the last experiment, so as not to affect the accuracy of the experiment.

[0054] The metering device includes a collecting bucket 21 and a balance 23. The collecting bucket 21 is set on the balance 23. Part of the coal powder injected into the box 14 by the injection pump 7 is deposited at the bottom of the box 14 due to gravity, and part of it is carried out from the hollow visualization column 13 by the injected liquid. After separation by the separator 19, the liquid flows into the waste liquid collection bucket 29 through the first liquid outlet pipeline 26 and the second liquid outlet pipeline 28, and the coal powder flows into the collecting bucket 21 through the powder outlet pipeline 20. The balance 23 can continuously record the mass of the coal powder collection bucket 21 and transmit the data in real time to the data receiving and control center 31 through the balance data transmission line 24.

[0055] The hollow visualization string 13, the box 14, and the visualization glass plate box 16 are all made of visualization glass. The hollow visualization string 13 simulates the horizontal section of the horizontal well in coalbed methane mining, and the box 14 simulates the cracks generated during the volume fracturing process.

[0056] The method for using the visual simulation device for inhibiting coal dust migration from volume fracturing cracks to the wellbore in this embodiment includes the following steps:

[0057] Step (1) Turn on the vacuum pump 27 to evacuate the dust in the hollow visualization column 13 and the box 14 or the coal powder that was not cleaned in time after the last experiment, so as not to affect the accuracy of this experiment.

[0058] Step (2) takes the coal powder in the simulated fracture and transports the coal seam bottom core to the wellbore, processes it into 50-100 mesh coal powder, weighs 400g with an electronic balance and puts it into the coal powder box 1, and records the weight of the weighed coal powder in the data receiving and control center 31.

[0059] In step (3), the box body 14 is connected to the hollow visualization column 13 at a preset angle. The data receiving and control center 31 starts the injection pump 7 to mix the coal powder in the coal powder box 1 and the liquid in the liquid storage tank 4, and then injects the liquid mixed with the coal powder into the box body 14. After a part of the coal powder enters the box body 14, it will be deposited at the bottom of the box body 14 due to gravity, and the remaining coal powder will enter the hollow visualization column 13 with the liquid and then be discharged into the separator 19 through the outflow pipeline 18.

[0060] In step (4), after the coal powder and liquid enter the box 14, the high-precision camera 15 can constantly monitor the distribution of the coal powder in the box 14. If coal powder blockage is found, the data will be transmitted to the data receiving and control center 31 through the high-precision camera data transmission line 22, thereby suspending the experiment.

[0061] In step (5), separator 19 separates the incoming pulverized coal from the liquid. The separated pulverized coal flows through a pulverized coal outlet line 20 to a collection tank 21, where the weight of the collected pulverized coal is displayed on a scale 23. The separated liquid flows through a first liquid outlet line 26 and a second liquid outlet line 28 to a waste liquid collection tank 29.

[0062] Step (6) The real-time data of the balance 23 is transmitted to the data receiving and control center 31 via the balance data transmission line 24 and the data transmission line 25. After all the pulverized coal in the pulverized coal box 1 is injected into the box body 14, the injection pump 7 is turned off.

[0063] After the experiment in step (7) is completed, the receiving and control center 31 can use the weight of the coal powder used recorded before the experiment and the weight of the collected coal powder weighed by the final balance 23 to determine the proportion of the weight of the coal powder transferred to the hollow visualization column 13 under this placement and angle of the box 14 to the total weight of the injected coal powder.

[0064] Step (8) simulates perforating at the top of the horizontal well section by adjusting the box 14 to be perpendicular to the horizontal direction at the top of the wellbore, such as Figure 2 As shown, steps (1) to (7) are repeated to obtain the ratio of the weight of the coal powder moved to the hollow visualization pipe string 13 to the total weight of the injected coal powder when the box 14 is at the upper part of the wellbore.

[0065] Step (9) is to adjust the box 14 to be 30° from the vertical direction at the bottom of the wellbore to simulate the 30° perforation at the bottom of the horizontal well section, such as Figure 3 As shown, repeat steps (1) to (7) to obtain the ratio of the weight of the coal powder moved to the hollow visualization pipe string 13 to the total weight of the injected coal powder when the box 14 is at 30 degrees in the lower part of the wellbore.

[0066] In step (10), the data receiving and control center 31 determines that when the box is at the bottom, 30° below, and top of the hollow visualization string 13, in this embodiment, the weight of the coal powder transferred to the hollow visualization string 13 accounts for 23%, 34%, and 86% of the total weight of the injected coal powder, respectively. This indicates that when performing directional perforation in coalbed methane horizontal well development, the length of the fracture at the top of the horizontal section is shorter than the length of the fracture at the bottom, which can reduce the migration of coal powder into the wellbore.

Claims

1. A visual simulation device for inhibiting the migration of coal powder from volume fracturing cracks into the wellbore, characterized in that: The invention comprises a hollow visualization pipe string (13), a box (14), a pumping device, a separator (19), a metering device and a visualization monitoring device, wherein the hollow visualization pipe string (13) is used to simulate the horizontal section of a horizontal well in coalbed methane mining, the box (14) is used to simulate the cracks generated during the volume fracturing process, an inlet and an outlet are provided on the box (14), the inlet of the box (14) is connected to the pumping device, the pumping device is used to pump a mixture of coal powder and liquid into the box (14), and the hollow visualization pipe string (13) is provided with a sealable connection with the outlet of the box (14). The sealing connection port is connected to the outlet of the box (14) and the angle of the outlet of the box (14) is adjustable. The sealing connection port serves as the inlet of the hollow visualization column (13). The hollow visualization column (13) is also provided with an outlet. The outlet of the hollow visualization column (13) is connected to the inlet of the separator (19). The separator (19) is used for solid-liquid separation. The metering device is used to measure the mass of the solid separated by the separator (19). The box (14) is transparent. The visual monitoring device is used to take real-time images of the inner cavity of the box (14); The box body (14) is a rotating body with an outlet at one end and a smooth inner cavity surface, and the inlet of the box body (14) is arranged in the middle or bottom of the box body (14); The box body (14) is shaped to be large in the middle and small at both ends, the inlet of the box body (14) is arranged at the middle of the box body (14) or the bottom of one end, and the outlet of the box body (14) is located at the end of the other end of the box body (14); The sealed connection port is provided at one end of the hollow visualization tube column (13), and the outlet of the hollow visualization tube column (13) is provided at the other end of the hollow visualization tube column (13); The upper and lower sides of the hollow visualization tube column (13) are both provided with the sealing connection ports. When the outlet of the box (14) is connected to one of the sealing connection ports on the hollow visualization tube column (13), the remaining sealing connection ports are all sealed by the sealing device. The sealing connection port of the hollow visualization pipe column (13) has a rotating structure, and the outlet of the box (14) is connected to the sealing connection port of the hollow visualization pipe column (13) through the rotating structure. The rotating structure has a circulation channel, and the inlet of the circulation channel of the rotating structure is connected to the outlet of the box (14), and the outlet of the circulation channel of the rotating structure is connected to the inner cavity of the hollow visualization pipe column (13). The rotating structure can adjust the flow direction of the mixed liquid of coal powder and liquid injected into the inner cavity of the hollow visualization pipe column (13) by the box (14) and realize the adjustment of the outlet angle of the box (14).

2. A visual simulation device for inhibiting coal dust migration from volume fracturing cracks to a wellbore according to claim 1, characterized in that: The pumping device comprises a coal powder box (1), a powder injection pipeline (2), a three-way valve (3), a liquid storage tank (4), a water injection pipeline (5), an injection pipeline (6) and an injection pump (7); the coal powder box (1) is connected to a first interface of the three-way valve (3) via the powder injection pipeline (2); the liquid storage tank (4) is connected to a second interface of the three-way valve (3) via the water injection pipeline (5); the third interface of the three-way valve (3) is connected to an inlet of the injection pump (7) via the injection pipeline (6); the outlet of the injection pump (7) is connected to an inlet of the box (14) via a pipeline; and the first interface and the second interface of the three-way valve (3) are both provided with flow regulating devices.

3. The visual simulation device for inhibiting coal dust migration from volume fracturing cracks to the wellbore according to claim 1, characterized in that: The metering device comprises a collecting barrel (21) and a balance (23), wherein the collecting barrel (21) is arranged on the balance (23), and the solid outlet of the separator (19) is connected to a powder outlet pipeline (20), which extends into the inner cavity of the collecting barrel (21).

4. The visual simulation device for inhibiting coal dust migration from volume fracturing cracks to the wellbore according to claim 1, characterized in that: The liquid outlet of the separator (19) is connected to a vacuum pump (27) via a first liquid outlet pipeline (26), the outlet of the vacuum pump (27) is connected to a second liquid outlet pipeline (28), and the outlet of the second liquid outlet pipeline (28) is connected to a waste liquid collection bucket (29); The hollow visualization column (13) and the box body (14) are both arranged in the visualization glass plate box (16); the hollow visualization column (13) comprises a transparent cylinder and a first fixing body (8) and a second fixing body (17) respectively connected at both ends of the cylinder in a sealed manner; the first fixing body (8) and the second fixing body (17) are both arranged in the inner cavity of the visualization glass plate box (16); The visual monitoring device uses a high-precision camera (15).

5. A visual simulation device for inhibiting coal dust migration from volume fracturing cracks to a wellbore according to claim 4, characterized in that: It also includes a data receiving and control center (31), and the pumping device, vacuum pump (27), visual monitoring device and metering device are all connected to the data receiving and control center (31); The data receiving and control center (31) can control the start and stop of the pumping device. When it is necessary to pump the mixture of coal powder and liquid into the box (14), the data receiving and control center (31) controls the pumping device to start; when the inner cavity of the box (14) is blocked by coal powder, or it is necessary to stop pumping the mixture of coal powder and liquid into the box (14), the data receiving and control center (31) can control the pumping device to stop; The data receiving and control center (31) is also capable of receiving and storing the mass of the solid separated by the separator (19) measured by the metering device; The data receiving and control center (31) can also control the start and stop of the vacuum pump (27). When the vacuum pump (27) needs to be turned on, the data receiving and control center (31) controls the vacuum pump (27) to be turned on; when the vacuum pump (27) needs to be stopped, the data receiving and control center (31) controls the vacuum pump (27) to be stopped.

6. A visual simulation method for inhibiting the migration of coal dust from volume fracturing cracks to the wellbore, characterized in that: The method is performed using the visual simulation device for inhibiting the migration of coal powder from a volume fracturing crack into a wellbore as described in any one of claims 1 to 5, and includes the following steps: The angle between the outlet of the box (14) and the axis line of the hollow visualization pipe column (13) is adjusted to a preset angle, and the mixture of coal powder and liquid is pumped into the box (14) through the pumping device, so that a portion of the coal powder in the mixture entering the box (14) is deposited in the box (14), and the remaining coal powder flows into the hollow visualization pipe column (13) along with the liquid; The mixture of coal powder and liquid in the hollow visualization column (13) flows into the separator (19) and undergoes solid-liquid separation, and the coal powder separated by the separator (19) is weighed by a metering device; The proportion of the mass of the pulverized coal transported to the hollow visualization column (13) to the total mass of the injected pulverized coal is calculated, wherein the total mass of the injected pulverized coal is the mass of the pulverized coal in the mixture of pulverized coal and liquid pumped into the box (14) by the pumping device, and the mass of the pulverized coal transported to the hollow visualization column (13) is the difference between the total mass of the injected pulverized coal and the mass of the pulverized coal separated by the separator (19).

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