A system and method for testing the porosity of in-situ coal using magnetic fluid

Abstract

The present invention discloses a system and method for testing the porosity of an in-situ coal body using a magnetic fluid. The system includes a supply subsystem and a test subsystem; using coal mine scrap iron to prepare medium and large particle size magnetic fluid through crushing, grinding and centrifugation processes, and preparing small particle size magnetic fluid through a vacuum evaporator; injecting small particle size magnetic fluid through a magnetic fluid delivery borehole, and starting the magnetic fluid targeted control electromagnetic rod in the borehole, and after the magnetic fluid is pulled to fill the coal body pores in the target test area, the electromagnetic rod in the magnetic fluid delivery borehole is started to recover the magnetic fluid; repeating the above steps, filling the target test area with medium and large particle size magnetic fluid and recovering it, and calculating the in-situ coal body porosity based on the two magnetic fluid injection volumes. The present invention uses magnetic fluid as a coal body pore nanoprobe to achieve low-loss and accurate testing of the porosity of the coal body under in-situ stress conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of mine gas extraction and utilization, and in particular to a system and method for testing the porosity of an in-situ coal body by using magnetic fluid. Background Art

[0002] Coalbed methane is an efficient and clean energy source, but it is also an important source of danger in the coal mine production process. Efficient extraction of coalbed methane can help achieve the country's "dual carbon" goals and effectively prevent the occurrence of mine gas disasters. Coal is a dual porous medium containing cracks and pores. The complex pore structure of coal serves as a gas storage space and migration channel. Accurate testing of coal body porosity and fracture rate is of great significance to understanding the storage form and migration status of coalbed methane.

[0003] Commonly used coal porosity testing methods include mercury injection, gas adsorption, nuclear magnetic resonance, etc., each of which has its own characteristics in terms of repeatability, sample size, test range, test accuracy, etc., and these testing methods are basically based on on-site sampling. Not only does the sampling process cause secondary disturbance and damage to the coal sample, destroying the original pore-crack structure of the coal body, causing the test results to deviate from the true value, but the sampling process also relieves the complex stress state of the coal sample. Even if the laboratory conditions take stress effects into account, it cannot truly describe the actual pore-crack structure of the coal body under the in-situ stress constraint conditions. Summary of the invention

[0004] In view of the above-mentioned technical deficiencies, the purpose of the present invention is to provide a system and method for testing the in-situ coal porosity using magnetic fluid, in which a sampling unit and a heating unit are arranged in a shell, and electric energy is provided by a battery pack to drive the motor inside the heating unit and the sampling unit to extract and heat the sampled asphalt, thereby ensuring the fluidity of the asphalt and facilitating manual operation and transportation.

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

[0006] The present invention provides a system for testing the porosity of an in-situ coal body by using magnetic fluid, comprising a supply subsystem and a test subsystem; the supply subsystem comprises a crusher for inputting coal mine scrap iron into a vacuum evaporator and a mill, a surfactant storage tank for inputting a surfactant into the vacuum evaporator and the mill, and a base carrier liquid storage tank for inputting a base carrier liquid into the vacuum evaporator and the mill; the outlet of the vacuum evaporator is connected to a small-particle-diameter magnetic fluid storage tank; the mill is also connected to a centrifuge, and the outlet of the centrifuge is connected to a medium- and large-particle-diameter magnetic fluid storage tank;

[0007] The test subsystem includes a plurality of magnetic fluid targeted control boreholes arranged in a circular array in the target coal seam, a magnetic fluid delivery borehole is opened in the center of the circular array; medium and large particle size magnetic fluid storage tanks and small particle size magnetic fluid storage tanks are connected to the magnetic fluid delivery boreholes and deliver fluid to them.

[0008] Preferably, the distance between the magnetic fluid targeted control borehole and the magnetic fluid transport borehole is less than or equal to 5m, and the number of the magnetic fluid targeted control boreholes is not less than 8.

[0009] Preferably, both the magnetic fluid targeted control drilling and the magnetic fluid conveying drilling are provided with an electromagnetic sealing device, and the electromagnetic sealing device comprises a hollow push rod and a high-power electromagnetic rod which are fixedly connected in sequence; the high-power electromagnetic rod is close to the bottom of the hole and its outer wall is sheathed with a protective rubber sleeve; the hollow push rod is fixed in the hole by two sealing plugs sheathed on the outer wall; a gas extraction pipe and a magnetic fluid conveying pipe are reserved on the sealing plug; a grouting orifice is reserved in the sealing section of the hollow push rod between the two sealing plugs.

[0010] Preferably, the insulated wire connected to the high-power electromagnetic rod passes through the hollow push rod and is electrically connected to the controller.

[0011] The present invention also provides a method for using a system for testing the porosity of an in-situ coal body using magnetic fluid, comprising the following steps:

[0012] S1, putting coal mine scrap iron into the crusher, putting the tailings into the vacuum evaporator and the mill, and simultaneously adding surfactant and base carrier liquid into the vacuum evaporator and the mill respectively through the surfactant storage tank and the base carrier liquid storage tank;

[0013] S2, start the vacuum evaporator and the mill, wherein the vacuum evaporator produces small-particle magnetic fluid and stores it in a small-particle magnetic fluid storage tank, the medium- and large-particle magnetic fluid crude liquid produced by the mill is transported to a centrifuge to obtain medium- and large-particle magnetic fluid and stores it in a medium- and large-particle magnetic fluid storage tank, and the large-particle magnetic fluid centrifuged is transported to the mill for re-milling;

[0014] S3. Construct magnetic fluid targeted control boreholes and magnetic fluid delivery boreholes in the target coal seam, seal each borehole in the rock layer section, and connect the gas extraction pipes in each borehole to the gas extraction pipeline to pre-extract gas from the coal seam;

[0015] S4, when the gas flow rate in the borehole changes steadily, close the gas extraction pipe in the magnetic fluid delivery borehole, open the magnetic fluid delivery pipe in the magnetic fluid delivery borehole, and inject small-particle magnetic fluid into the target test area through the small-particle magnetic fluid storage tank; at the same time, start the magnetic fluid targeted control high-power electromagnetic rod in the borehole to target and pull the small-particle magnetic fluid to fill the target test area, and record the cumulative injection volume V1;

[0016] S5, when magnetic fluid flows out of the gas extraction pipe and the magnetic fluid delivery pipe in the magnetic fluid targeted control borehole, the gas extraction pipe in the magnetic fluid targeted control borehole is closed, and the high-power electromagnetic rod in the magnetic fluid delivery borehole is started to recover the small-particle magnetic fluid to the small-particle magnetic fluid storage tank;

[0017] S6. Repeat steps S4-S5, inject medium and large particle size magnetic fluid into the target test area through the medium and large particle size magnetic fluid storage tank and recover it, and record the cumulative injection volume V2, and calculate the in-situ coal body porosity based on the two magnetic fluid injection volumes.

[0018] Preferably, in step S1, the base liquid is water and the surfactant is oleic acid.

[0019] Preferably, the volume fraction of iron particles contained in the medium-large particle size magnetic fluid and the small particle size magnetic fluid is greater than or equal to 30%, the volume fraction of surfactant is greater than or equal to 20%, and the remaining components are base carrier fluid.

[0020] Preferably, the particle size of the iron particles in the small-particle-size magnetic fluid is less than or equal to 100 nm, and the particle size of the iron particles in the medium- and large-particle-size magnetic fluid is greater than or equal to 100 nm.

[0021] Preferably, the calculation formula of the in-situ coal body pores in step S6 is:

[0022]

[0023] Where: φ is the total porosity of coal, φ f is the coal body fracture ratio, φ m is the coal matrix porosity, r is the circle diameter of the target test area, and H is the average coal seam thickness.

[0024] The beneficial effects of the present invention are as follows: the present invention utilizes the characteristics of magnetic fluid with low viscosity, strong controllability under electric field and controllable particle size as a nanoscale probe in the porosity testing process, so as to realize the full-scale porosity testing of diffusion pores and seepage fractures of coal in situ; utilizes electromagnet targeted traction magnetic fluid to fill the pores and fractures of coal, so as to avoid the problem of traditional high-pressure fluid injection destroying the pore and fracture structure, so as to realize the low-loss and precise testing of the full-scale porosity of diffusion pores and seepage fractures under complex in-situ stress conditions of coal, and solves the problem of secondary destruction of the original pore-crack structure of coal induced by existing testing methods during on-site sampling and testing; it is difficult to reproduce the complex load stress of coal in-situ conditions under laboratory testing conditions, resulting in the pores and fractures in the coal body being separated from the constraint stress, and the porosity test results cannot represent the actual situation on site; therefore, the porosity testing of coal porosity under in-situ stress conditions is realized, which ensures the reliability, practicality and authenticity of the porosity test results in providing reference for engineering practice. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0026] Figure 1 A schematic diagram of the connection relationship of a system for testing the in-situ coal porosity using magnetic fluid provided in an embodiment of the present invention.

[0027] Figure 2 A schematic structural diagram of an electromagnetic sealing device provided in an embodiment of the present invention.

[0028] In the figure: 1-coal mine scrap iron, 2-surfactant storage tank, 3-base carrier storage tank, 4-vacuum evaporator, 5-crusher, 6-mill, 7-centrifuge, 8-medium and large particle size magnetic fluid storage tank, 9-small particle size magnetic fluid storage tank, 10-target coal seam, 11-magnetic fluid targeted control drilling, 12-target test area, 13-magnetic fluid conveying drilling, 14-rock layer, 15-gas extraction pipe, 16-magnetic fluid conveying pipe, 17-insulated wire, 18-grouting hole, 19-sealing plug, 20-hollow push rod, 21-protective rubber sleeve, 22-high power electromagnetic rod. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions 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 are within the scope of protection of the present invention.

[0030] like Figure 1 to Figure 2 As shown, a system for testing the porosity of an in-situ coal body using a magnetic fluid comprises a multi-grade particle size magnetic fluid supply subsystem and an in-situ coal body porosity testing subsystem, hereinafter referred to as the supply subsystem and the testing subsystem;

[0031] The supply subsystem includes a crusher 5 for inputting coal mine scrap 1 to the vacuum evaporator 4 and the mill 6, a surfactant storage tank 2 for inputting surfactant to the vacuum evaporator 4 and the mill 6, and a base carrier liquid storage tank 3 for inputting base carrier liquid to the vacuum evaporator 4 and the mill 6; the outlet of the vacuum evaporator 4 is connected to a small-particle-size magnetic liquid storage tank 9; the mill 6 is also connected to a centrifuge 7, and the outlet of the centrifuge 7 is connected to a medium-large-particle-size magnetic liquid storage tank 8;

[0032] The test subsystem includes a plurality of magnetic fluid targeted control boreholes 11 arranged in a circular array in the target coal seam 10, and a magnetic fluid delivery borehole 13 is opened in the center of the circular array; medium and large particle size magnetic fluid storage tanks 8 and small particle size magnetic fluid storage tanks 9 are connected to the magnetic fluid delivery borehole 13 and deliver fluid to them.

[0033] The distance between the magnetic fluid targeted control borehole 11 and the magnetic fluid delivery borehole 13 is less than or equal to 5m, and the number of the magnetic fluid targeted control boreholes 11 is not less than 8.

[0034] The magnetic fluid targeted control borehole 11 and the magnetic fluid delivery borehole 13 are both provided with an electromagnetic sealing device, which includes a hollow push rod 20 and a high-power electromagnetic rod 22 which are fixedly connected in sequence; the high-power electromagnetic rod 22 is close to the bottom of the hole and its outer wall is sheathed with a protective rubber sleeve 21; the hollow push rod 20 is fixed in the hole by two sealing plugs 19 sheathed on the outer wall; the sealing plug 19 is reserved with a gas extraction pipe 15 and a magnetic fluid delivery pipe 16; the hollow push rod 20 is reserved with a grouting orifice 18 in the sealing section between the two sealing plugs 19.

[0035] The insulated wire 17 connected to the high-power electromagnetic rod 22 passes through the hollow push rod 20 and is electrically connected to the controller.

[0036] The embodiment of the present invention also provides a method for using a system for testing the porosity of an in-situ coal body using a magnetic fluid, comprising the following steps:

[0037] S1, putting coal mine scrap 1 into the crusher 5, putting the tailings into the vacuum evaporator 4 and the mill 6, and simultaneously adding surfactant and base carrier liquid into the vacuum evaporator 4 and the mill 6 through the surfactant storage tank 2 and the base carrier liquid storage tank 3 respectively;

[0038] S2, start the vacuum evaporator 4 and the grinding mill 6, wherein the vacuum evaporator 4 produces small-particle magnetic fluid and stores it in the small-particle magnetic fluid storage tank 9, the medium-large particle magnetic fluid crude liquid produced by the grinding mill 6 is transported to the centrifuge 7 for centrifugation to obtain medium-large particle magnetic fluid and store it in the medium-large particle magnetic fluid storage tank 8, and the large particle magnetic fluid centrifuged is transported to the grinding mill 6 for re-grinding;

[0039] S3, constructing a magnetic fluid targeted control borehole 11 and a magnetic fluid delivery borehole 13 in the target coal seam 10, sealing each borehole in the rock layer 14, and connecting the gas extraction pipe 15 in each borehole to the gas extraction pipeline to pre-extract gas from the coal seam;

[0040] S4, when the gas flow rate in the borehole changes steadily, close the gas extraction pipe 15 in the magnetic fluid delivery borehole 13, open the magnetic fluid delivery pipe 16 in the magnetic fluid delivery borehole 13, and inject small-particle magnetic fluid into the target test area 12 in the annular array through the small-particle magnetic fluid storage tank 9; at the same time, start the high-power electromagnetic rod 22 in the magnetic fluid targeted control borehole 11 to target and pull the small-particle magnetic fluid to fill the target test area 12, and record the cumulative injection volume V1;

[0041] S5, when magnetic fluid flows out of the gas extraction pipe 15 and the magnetic fluid delivery pipe 16 in the magnetic fluid targeted control borehole 11, the gas extraction pipe 15 in the magnetic fluid targeted control borehole 11 is closed, and the high-power electromagnetic rod 22 in the magnetic fluid delivery borehole 13 is started to recover the small-particle-size magnetic fluid to the small-particle-size magnetic fluid storage tank 9;

[0042] S6. Repeat steps S4-S5, inject medium-large particle size magnetic fluid into the target test area 12 through the medium-large particle size magnetic fluid storage tank 8 and recover it, and record the cumulative injection volume V2, and calculate the in-situ coal body porosity based on the two magnetic fluid injection volumes.

[0043] In step S1, water is used as the base liquid and oleic acid is used as the surfactant.

[0044] The volume fraction of iron particles contained in the medium-large particle size magnetic fluid and the small particle size magnetic fluid is greater than or equal to 30%, the volume fraction of surfactant is greater than or equal to 20%, and the remaining components are base carrier fluid.

[0045] The particle size of the iron particles in the small-particle magnetic fluid is less than or equal to 100 nm, and the particle size of the iron particles in the medium-large particle magnetic fluid is greater than or equal to 100 nm.

[0046] The calculation formula of the in-situ coal body pores in step S6 is:

[0047]

[0048] Where: φ is the total porosity of coal, φ f is the coal body fracture ratio, φ m is the coal matrix porosity, r is the circle diameter of the target test area, and H is the average coal seam thickness.

[0049] The present invention utilizes the characteristics of magnetic fluid with low viscosity, strong controllability under electric field and controllable particle size as a nanoprobe for the porosity testing process; it realizes low-loss and precise testing of porosity and fracture rate under in-situ stress conditions of coal body, and ensures the reliability, practicality and authenticity of the porosity test results in providing reference for engineering practice.

[0050] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A system for testing the porosity of an in-situ coal body using magnetic fluid, characterized in that: The invention comprises a supply subsystem and a test subsystem; the supply subsystem comprises a crusher (5) for inputting coal mine scrap iron (1) into a vacuum evaporator (4) and a grinding mill (6), a surfactant storage tank (2) for inputting surfactant into the vacuum evaporator (4) and the grinding mill (6), and a base carrier liquid storage tank (3) for inputting base carrier liquid into the vacuum evaporator (4) and the grinding mill (6); the outlet of the vacuum evaporator (4) is connected to a small-particle-diameter magnetic liquid storage tank (9); the grinding mill (6) is also connected to a centrifuge (7), and the outlet of the centrifuge (7) is connected to a medium-large-particle-diameter magnetic liquid storage tank (8); The test subsystem comprises a plurality of magnetic fluid targeted control boreholes (11) arranged in an annular array in the target coal seam (10), wherein a magnetic fluid delivery borehole (13) is opened in the center of the annular array; a medium-large particle size magnetic fluid storage tank (8) and a small particle size magnetic fluid storage tank (9) are connected to the magnetic fluid delivery borehole (13) and deliver fluid thereto; The distance between the magnetic fluid targeted control borehole (11) and the magnetic fluid transport borehole (13) is less than or equal to 5 m, and the number of the magnetic fluid targeted control boreholes (11) is not less than 8; The magnetic fluid targeted control borehole (11) and the magnetic fluid delivery borehole (13) are both provided with an electromagnetic sealing device, and the electromagnetic sealing device comprises a hollow push rod (20) and a high-power electromagnetic rod (22) which are fixedly connected in sequence; the high-power electromagnetic rod (22) is close to the bottom of the hole and its outer wall is sheathed with a protective rubber sleeve (21); the hollow push rod (20) is fixed in the hole by two sealing plugs (19) sheathed on the outer wall; the sealing plug (19) is reserved with a gas extraction pipe (15) and a magnetic fluid delivery pipe (16); the hollow push rod (20) is reserved with a grouting orifice (18) in the sealing section between the two sealing plugs (19).

2. A system for testing the porosity of an in-situ coal body using magnetic fluid as claimed in claim 1, characterized in that: The insulated wire (17) connected to the high-power electromagnetic rod (22) passes through the hollow push rod (20) and is electrically connected to the controller.

3. A method for using the system for testing the in-situ coal porosity using magnetic fluid as claimed in claim 1, characterized in that: The following steps are involved: S1, putting coal mine scrap iron (1) into a crusher (5), putting the tailings into a vacuum evaporator (4) and a grinding mill (6), and simultaneously adding a surfactant and a base carrier liquid into the vacuum evaporator (4) and the grinding mill (6) respectively through a surfactant storage tank (2) and a base carrier liquid storage tank (3); S2, starting the vacuum evaporator (4) and the grinding mill (6), wherein the vacuum evaporator (4) produces small-particle magnetic fluid and stores it in the small-particle magnetic fluid storage tank (9), the medium-large particle magnetic fluid crude liquid produced by the grinding mill (6) is transported to the centrifuge (7) for centrifugation to obtain medium-large particle magnetic fluid and store it in the medium-large particle magnetic fluid storage tank (8), and the large particle magnetic fluid obtained by centrifugation is transported to the grinding mill (6) for re-grinding; S3, constructing a magnetic fluid targeted control borehole (11) and a magnetic fluid transport borehole (13) in the target coal seam (10), sealing each borehole in the rock layer (14), and connecting the gas extraction pipe (15) in each borehole to the gas extraction pipeline to pre-extract gas from the coal seam; S4, when the gas flow rate in the borehole changes stably, the gas extraction pipe (15) in the magnetic fluid delivery borehole (13) is closed, and the magnetic fluid delivery pipe (16) in the magnetic fluid delivery borehole (13) is opened, and small-particle magnetic fluid is injected into the target test area (12) in the annular array through the small-particle magnetic fluid storage tank (9); at the same time, the high-power electromagnetic rod (22) in the magnetic fluid targeted control borehole (11) is started to target and pull the small-particle magnetic fluid to fill the target test area (12), and the cumulative injection volume V1 is recorded; S5, when magnetic fluid flows out of the gas extraction pipe (15) and the magnetic fluid delivery pipe (16) in the magnetic fluid targeted control borehole (11), the gas extraction pipe (15) in the magnetic fluid targeted control borehole (11) is closed, and the high-power electromagnetic rod (22) in the magnetic fluid delivery borehole (13) is started to recover the small-particle-size magnetic fluid to the small-particle-size magnetic fluid storage tank (9); S6, closing the gas extraction pipe (15) in the magnetic fluid delivery borehole (13), opening the magnetic fluid delivery pipe (16) in the magnetic fluid delivery borehole (13), and injecting medium and large particle size magnetic fluid into the target test area (12) through the medium and large particle size magnetic fluid storage tank (8); at the same time, starting the high power electromagnetic rod (22) in the magnetic fluid targeted control borehole (11) to target and pull the medium and large particle size magnetic fluid to fill the target test area (12), and recording the cumulative injection volume V2; S7, when magnetic fluid flows out of the gas extraction pipe (15) and the magnetic fluid delivery pipe (16) in the magnetic fluid targeted control borehole (11), the gas extraction pipe (15) in the magnetic fluid targeted control borehole (11) is closed, and the high-power electromagnetic rod (22) in the magnetic fluid delivery borehole (13) is started to recover the medium and large particle size magnetic fluid to the medium and large particle size magnetic fluid storage tank (8); S8. Calculate the in-situ coal porosity based on the small-size magnetic hydraulic injection volume V1 and the medium-large-size magnetic hydraulic injection volume V2.

4. The method of use according to claim 3, characterized in that: In step S1, water is used as the base liquid and oleic acid is used as the surfactant.

5. The method of use according to claim 4, characterized in that: The volume fraction of iron particles contained in the medium-large particle size magnetic fluid and the small particle size magnetic fluid is greater than or equal to 30%, the volume fraction of surfactant is greater than or equal to 20%, and the remaining components are base carrier fluid.

6. The method of use according to claim 5, characterized in that: The particle size of the iron particles in the small-particle magnetic fluid is less than or equal to 100 nm, and the particle size of the iron particles in the medium-large particle magnetic fluid is greater than or equal to 100 nm.

7. The method of use according to claim 6, characterized in that: The calculation formula of the in-situ coal body pores in step S8 is: Where: is the total porosity of the coal body, is the coal body fracture ratio, is the coal matrix porosity, r is the circle diameter of the target test area, and H is the average coal seam thickness.

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