Dynamic sub-control ground gas extraction well system for multi-series goaf group

Abstract

The invention belongs to the technical field of coal mine gas ground extraction, and particularly relates to a dynamic sub-control ground gas extraction well system for a multi-layer system goaf group, which is characterized in that a vertical well section of a ground well is communicated with at least two horizontal branches, and a dynamic sub-control unit is mounted in a solid pipe of an inclination increasing section of each horizontal branch; and a horizontal section anti-blocking unit is arranged outside the stable inclination section screen pipe of each horizontal branch. The dynamic sub-control unit comprises a hydraulic control valve system, a methane concentration sensor and a gas pressure sensor; the dynamic sub-control unit realizes independent opening and closing of each horizontal branch through a hydraulic control valve system; the hydraulic control valve system has an opening and closing decision-making mechanism; the horizontal section anti-blocking unit adopts a gradient density anti-blocking filter screen, and the anti-blocking filter screen is coated with a polytetrafluoroethylene-nano silicon dioxide composite sparse pulverized coal coating. By means of the system, goaf gas large-scale dynamic sub-control ground extraction of non-communicated goaf groups at different extraction levels can be achieved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of coal mine gas ground extraction, and particularly relates to a dynamic sub-control ground gas extraction well system for a multi-layer system goaf group. BACKGROUND

[0002] The non-connected goaf group formed by multi-level mining of a coal mine constitutes a spatially discrete isolated gas-bearing system due to its geological isolation and difference in mining time sequence. Each goaf in such a system is dominated by the heterogeneity of the dilatation coefficient and the difference in gas supply dynamics, showing spatial and temporal differentiation of the methane concentration field and asynchrony of the extractable time window. The traditional ground vertical well is difficult to achieve extraction of non-connected goafs in the same level due to the constraint of a single target area. Although the ground horizontal well technology can realize physical connection of multi-level isolated goafs, it is easy to form long-term over-extraction of goaf gas with low methane concentration due to the lack of dynamic sub-control mechanism of the gas-bearing system of each connected goaf, leading to spontaneous combustion of the goaf coal seam and causing safety accidents. Therefore, the extraction of each goaf often needs to stop when the methane concentration decreases to a certain threshold. Due to the replenishment of gas from sources such as residual coal in the goaf and coal seams affected by mining, the goaf that stops extraction due to methane concentration decay often has the ability to gradually increase the methane concentration. Therefore, the gas extraction of each goaf should have reciprocity, which requires the ground horizontal well to have a dynamic sub-control function when extracting goaf gas. In addition, during the extraction process of the ground well, the extraction gas flow carries coal powder migration, and the mining-induced crack coal powder migration is driven by the Stokes-Darcy coupling effect, forming adhesion deposition at the screen interface. The traditional homogeneous screen causes exponential decay of the flow rate due to saturation of the interception capacity. In view of the above reasons, it is necessary to break through the geological adaptation-dynamic sub-control-interface anti-blocking triple technical bottleneck of non-connected goaf gas extraction. Therefore, the application provides a dynamic sub-control ground gas extraction well system for a multi-layer system goaf group, which completes the development of a ground horizontal well extraction system for a non-connected goaf group that integrates dynamic sub-control and long-term coal powder protection. SUMMARY

[0003] The purpose of the application is to provide a dynamic sub-control ground gas extraction well system for a multi-layer system goaf group, which is a key technical basis for realizing safe and efficient ground horizontal well extraction of multi-level non-connected goaf groups.

[0004] The technical scheme adopted by the application is as follows:

[0005] A dynamic sub-control ground gas extraction well system for a multi-layer system goaf group:

[0006] First, the well structure unit is set: the ground well vertical well section is located in the goaf and the adjacent unclosed area of the caving zone, and is completed drilling at 20m below the floor of the deepest goaf, and the vertical well section adopts two-opening structure; after the first opening drilling hole is completed drilling, the first opening drilling hole casing is lowered, and the well cementation is performed to the ground surface; after the second opening drilling hole is completed drilling, the second opening drilling hole casing is lowered, and the well cementation is performed to the ground surface; the vertical well section is connected with not less than two horizontal branches, which are distributed at the top of the mining fractured zone of the multiple non-communicating goafs and caving zones of different mining levels; the horizontal branches are 30±5m away from the roadway boundary; the build-up section of the horizontal branches adopts downward drilling, and after completion of drilling, the horizontal branch build-up section is lowered into the solid pipe, and the build-up section of the horizontal branch is lowered into the screen pipe;

[0007] Secondly, the dynamic control unit is installed: the dynamic control unit is installed in the solid pipe lowered in the build-up section of the horizontal branch; the dynamic control unit includes a hydraulic control valve system, a methane concentration sensor and a gas pressure sensor installed in sequence;

[0008] Finally, the horizontal section anti-blocking unit is set: the anti-blocking filter screen of the gradient density structure is installed outside the screen pipe lowered in the build-up section of the horizontal branch, and the anti-blocking filter screen adopts a near-vertical well end sixty-mesh screen to a far-end twenty-mesh screen.

[0009] Preferably, the multiple-layer goaf group includes multiple-layered mining coal seams and non-coal strata, the second opening drilling hole is directly drilled into the multiple-layered mining coal seams and non-coal strata, and multiple goafs and caving zones are located in the mining coal seams and non-coal strata.

[0010] Preferably, at least two horizontal branches are located in the goafs and caving zones and the top of the mining fractured zone of different mining levels, and the horizontal branches are positioned 25-35m away from the roadway boundary.

[0011] Preferably, the pre-installed glass steel casing is lowered at the designed horizontal branch opening position, and the casing is windowed at the glass steel casing position at the corresponding depth to form the horizontal branch.

[0012] Preferably, the anti-blocking filter screen surface is coated with a polytetrafluoroethylene-nano silicon dioxide composite coal dust-repellent coating, the nano SiO2 mass ratio in the composite coating is 18%-22%, and the coating thickness is 50-200um.

[0013] Preferably, the dynamic control unit realizes independent opening and closing of each horizontal branch through the hydraulic control valve system, the methane concentration sensor monitors the methane concentration in each horizontal branch in real time, and the gas pressure sensor monitors the gas pressure of each horizontal branch in real time.

[0014] Preferably, the decision mechanism for closing the hydraulic control valve system is to automatically close the hydraulic control valve system when the sensor detects that the methane concentration is < 25% and lasts > 30 min; the decision mechanism for restarting the closed hydraulic control valve system is:

[0015] (I) The horizontal branch is stopped when the methane concentration is ≥ 40% and lasts ≥ 72 h;

[0016] (II) The gas pressure in the branch is > the initial gas pressure when the branch is stopped;

[0017] (III) Artificial confirmation and triggering of remote instruction triggering.

[0018] The technical effects achieved by the present application are:

[0019] The system of the present application is provided with at least two horizontal branches in the vertical well section of the ground well, and the horizontal branches are respectively located at the top of the isolated goaf fracture zone at different mining levels. The dynamic control unit is installed in the actual pipe of the build-up section of each horizontal branch, and the horizontal segment anti-blocking unit is installed outside the screen pipe of the stable inclination section of each horizontal branch. The dynamic control unit includes a hydraulic control valve system, a methane concentration sensor and a gas pressure sensor; the dynamic control unit realizes the independent opening and closing of each horizontal branch through the hydraulic control valve system; the hydraulic control valve system has a decision mechanism for opening and closing; the decision for closing the hydraulic control valve system is to automatically close the hydraulic control valve system when the sensor detects that the methane concentration is < 25% and lasts > 30 min, so as to realize the shutdown of the current horizontal branch; the decision for restarting the closed hydraulic control valve system is: the methane concentration of the stopped horizontal branch is ≥ 40% and lasts ≥ 72 h; the gas pressure in the branch is > the initial gas pressure when the branch is stopped; artificial confirmation and triggering of remote instruction triggering. The horizontal segment anti-blocking unit adopts a gradient density anti-blocking filter screen, and a polytetrafluoroethylene-nano silicon dioxide composite coal dust prevention coating is coated on the anti-blocking filter screen. The system can realize the dynamic control of the goaf gas scale of the non-connected goaf group at different mining levels. BRIEF DESCRIPTION OF DRAWINGS

[0020] Fig. 1 is a schematic diagram of a dynamic control ground gas extraction well system for a multi-layer goaf group according to the present application;

[0021] Fig. 2 is a schematic diagram of the profile of the dynamic control unit in the present application;

[0022] Fig. 3 is a schematic diagram of the overall structure of the anti-blocking filter screen in the present application.

[0023] In the drawings, the component list represented by each reference numeral is as follows:

[0024] 1. Horizontal branch; 2. Goaf and caving zone; 3. Mined coal seam; 4. Non-coal strata; 5. 60-mesh mesh; 6. 20-mesh mesh; 7. Screen pipe; 8. Anti-clogging filter; 9. Pressure sensor; 10. Methane concentration sensor; 11. Hydraulic control valve system; 12. Solid pipe; 13. Annular cement ring; 14. First-stage borehole casing; 15. Second-stage borehole casing; 16. Fiberglass casing. Detailed Implementation

[0025] To make the objectives and advantages of this invention clearer, the invention will be specifically described below with reference to embodiments. It should be understood that the following text is merely used to describe one or more specific embodiments of the invention and does not strictly limit the scope of protection specifically claimed by the invention.

[0026] like Figs. 1-3 As shown, a dynamic, controlled surface gas extraction well system for multi-layered goaf clusters is described:

[0027] First, the well body structure unit is set up: the vertical section of the surface well is located in the unmined area adjacent to the goaf and caving zone 2, and is completed 20m below the bottom plate of the deepest goaf. The vertical section adopts a two-stage structure. After the first stage of drilling is completed, the first stage casing 14 is run in and cemented to the surface. After the second stage of drilling is completed, the second stage casing 15 is run in and cemented to the surface. The vertical section is connected to no less than two horizontal branches 1. The horizontal branches 1 are distributed at the top of the mining fracture zone of multiple non-connected goafs and caving zone 2 at different mining levels. The horizontal branches 1 are 30±5m away from the roadway boundary. The stabilization section of the horizontal branches 1 adopts a downward drilling method. After completion, the inclination-increasing section of the horizontal branches 1 is drilled with a solid pipe 12, and the stabilization section of the horizontal branches 1 is drilled with a screen pipe 7.

[0028] Next, the dynamic control unit is installed: the dynamic control unit is installed in the solid pipe 12 that is lowered into the inclined section of the horizontal branch 1; the dynamic control unit includes a pressure sensor 9, a methane concentration sensor 10 and a hydraulic control valve system 11 installed in sequence;

[0029] Finally, the anti-clogging unit is set up in the horizontal section: the anti-clogging filter 8 with a gradient density structure is installed outside the screen pipe 7 that is lowered into the stabilizing section of the horizontal branch 1. The anti-clogging filter 8 adopts a 60-mesh mesh 5 at the near vertical well end and a 20-mesh mesh 6 at the far end.

[0030] Preferably, the multi-layered goaf group includes multi-layered coal seams 3 and non-coal strata 4. The second-stage drilling casing 15 is directly drilled into the multi-layered coal seams 3 and non-coal strata 4. Multiple goafs and collapse zones 2 are located in the coal seams 3 and non-coal strata 4.

[0031] Preferably, at least two horizontal branches 1 are located at the top of the goaf and the mining fracture zone 2 at different mining levels, and the horizontal branches 1 are positioned 25 to 35m from the roadway boundary.

[0032] Preferably, a pre-installed fiberglass sleeve 16 is inserted at the designed opening position of the horizontal branch 1 so that a sleeve window can be opened at the corresponding depth position of the fiberglass sleeve 16 to form the horizontal branch 1.

[0033] Preferably, the surface of the anti-clogging filter 8 is coated with a polytetrafluoroethylene-nano silica composite coal powder coating, wherein the mass percentage of nano-SiO2 in the composite coating is 18% to 22%, and the coating thickness is 50-200 μm.

[0034] Preferably, the dynamic sub-control unit realizes the independent opening and closing of each horizontal branch 1 through the hydraulic control valve system 11, the methane concentration sensor 10 monitors the methane concentration in each horizontal branch 1 in real time, and the gas pressure sensor 9 monitors the gas pressure in each horizontal branch 1 in real time.

[0035] Preferably, the decision mechanism for shutting down the hydraulic control valve system 11 is to automatically shut down the hydraulic control valve system 11 when the sensor detects a methane concentration of <25% for >30 minutes; the decision mechanism for restarting the shut-down hydraulic control valve system 11 is as follows:

[0036] (I): Shut down horizontal branch 1 with methane concentration ≥40% for ≥72 hours;

[0037] (ii): The air pressure inside the branch is greater than the initial air pressure when the branch was shut down;

[0038] (iii): Manual confirmation and triggering of remote command.

[0039] like Figs. 1-3 As shown, in an actual engineering example of this invention, in the Baode mining area of ​​Shanxi:

[0040] Target strata: From top to bottom, the target strata are: No. 8 coal seam and No. 11 coal seam. Among them, No. 8 coal seam is buried at a depth of 380m and has a thickness of 6.02m; No. 11 coal seam is buried at a depth of 470m and has a thickness of 4.0m.

[0041] Construction process:

[0042] First drilling: Drill to the bedrock stable section using a Φ406.4mm drill bit, run in a Φ339.7mm first drilling casing 14, and cement the well to form an annular cement sheath 13 to the surface.

[0043] Second-stage drilling: Drilling was carried out using a Φ311.1mm drill bit. Drilling was completed 20m below the bottom plate of the deepest target coal seam, No. 11 coal seam, with a burial depth of approximately 490m. Then, a Φ244.5mm second-stage borehole casing 15 was run in. At the designed opening position of horizontal branch 1, a pre-installed fiberglass casing 16 was run in, and cementing was performed to form an annular cement sheath 13.

[0044] Horizontal branch 1 construction: Φ215.9mm drill bit is used. First, the deepest target coal seam, i.e. 11# coal, is constructed, and the glass steel sleeve 16 position at the corresponding depth is cased and windowed. The MWD / LWD system is used for geological steering to ensure that the horizontal section extends along the designed trajectory, and the build-up section precisely lands on the 5-8m hard rock layer above the top boundary of the fracture zone. The horizontal branch 1 is 30±5m away from the 11# coal seam roadway boundary. After drilling, well washing is completed, and well logging is used to confirm the wellbore condition.

[0045] The polytetrafluoroethylene-nano-silicon dioxide composite anti-powder coating is customized, and the mass fraction of nano-SiO2 in the coating is 18%-22%. The anti-blocking filter screen 8 is customized, and the anti-blocking filter screen 8 adopts a near sixty-mesh screen 5 to a twenty-mesh screen 6 gradient change grid. The anti-blocking filter screen 8 is coated with a polytetrafluoroethylene-nano-silicon dioxide composite anti-powder coating, and the coating thickness is 50-200um.

[0046] The screen pipe 7 of the anti-blocking unit Φ139.7mm is lowered into the build-up section of the horizontal branch 1, the Φ139.7mm solid pipe 12 is lowered into the build-up section of the horizontal branch 1, and the build-up section of the horizontal branch 1 is cemented.

[0047] Then, well washing and electrical measurement of the horizontal branch 1 are completed.

[0048] The above steps are repeated to construct the 8# coal horizontal branch 1.

[0049] The electro-hydraulic proportional servo valve, i.e. the hydraulic control valve system 11, the methane concentration sensor 10 accuracy (±0.1% vol) and the air pressure sensor 9 (range -1Mpa-1MPa) are preferred.

[0050] From bottom to top, the dynamic control unit of the branch, i.e. the hydraulic control valve system 11, the methane concentration sensor 10 and the air pressure sensor 9 are installed.

[0051] System connection and debugging: connect the hydraulic lines and signal lines of all dynamic control units to the ground control system, test the on-off of each branch control valve, calibrate each branch methane sensor and air pressure sensor. Debug the dynamic control decision system.

[0052] Connect the extraction pump station and start gas extraction. Real-time monitoring of each branch methane concentration, flow, valve state, system total extraction parameters, etc. Verify the response of the dynamic control unit.

[0053] The ground well starts continuous extraction.

[0054] In summary, the system of the present application comprises: a ground well vertical well section at least communicating two horizontal branches 1, the horizontal branches 1 being respectively located at the top of isolated goaf 2 mining fissure zones of different mining levels, and a dynamic control unit being installed in the real pipe 12 of the build-up section of each horizontal branch 1, and a horizontal section anti-blocking unit being installed outside the screen pipe 7 of each horizontal branch 1. The dynamic control unit comprises a hydraulic control valve system 11, a methane concentration sensor 10 and a gas pressure sensor 9; the dynamic control unit realizes independent opening and closing of each horizontal branch through the hydraulic control valve system 11; the hydraulic control valve system 11 has a decision mechanism for opening and closing; the decision for closing the hydraulic control valve system 11 is that when the sensor detects that the methane concentration is < 25% and lasts for > 30 min, the hydraulic control valve system 11 is automatically closed to realize the shutdown of the current horizontal branch 1; the decision for restarting the closed hydraulic control valve system 11 is: 1) the methane concentration of the shutdown horizontal branch is ≥ 40% and lasts for ≥ 72 h; 2) the gas pressure in the branch is > the initial gas pressure of the shutdown branch; 3) manual confirmation and triggering of remote instructions. The horizontal section anti-blocking unit adopts a gradient density anti-blocking filter screen 8, and the anti-blocking filter screen 8 is coated with a polytetrafluoroethylene-nano silicon dioxide composite coal dust repellent coating. The system can realize the scale dynamic control of goaf gas of non-communicating goaf groups of different mining levels.

[0055] The above description is only the preferred embodiments of the present application, and it should be pointed out that for ordinary skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, and these improvements and refinements should be considered as the protection scope of the present application. The structures, devices and operation methods not specifically described and explained in the present application, such as without special description and limitation, are implemented according to the conventional means in the art.

Claims

1. A dynamic, controlled surface gas extraction well system for multi-layered goaf clusters, characterized in that: First, the well body structure unit is set up: the vertical well section of the surface well is located in the unmined area adjacent to the goaf and caving zone (2), and is completed 20m below the bottom plate of the deepest goaf. The vertical well section adopts a two-stage structure; after the first stage borehole is completed, the first stage borehole casing (14) is installed and cemented to the surface; after the second stage borehole is completed, the second stage borehole casing (15) is installed and cemented to the surface; the vertical well section is connected to no less than two horizontal branches (1), and the horizontal branches (1) are distributed at the top of the mining fracture zone of multiple non-connected goaf and caving zone (2) at different mining levels; the horizontal branches (1) are 30±5m away from the roadway boundary; the stabilizing section of the horizontal branch (1) adopts a downward drilling method. After completion, the increasing section of the horizontal branch (1) is installed with a solid pipe (12), and the stabilizing section of the horizontal branch (1) is installed with a screen pipe (7). Next, the dynamic control unit is installed: the dynamic control unit is installed in the solid pipe (12) inserted into the inclined section of the horizontal branch (1); the dynamic control unit includes a hydraulic control valve system (11), a methane concentration sensor (10) and a gas pressure sensor (9) installed in sequence. Finally, the anti-clogging unit of the horizontal section is set up as follows: an anti-clogging filter (8) with a gradient density structure is installed outside the screen pipe (7) that is lowered into the stabilizing section of the horizontal branch (1). The anti-clogging filter (8) adopts a 60-mesh mesh (5) at the near vertical well end to a 20-mesh mesh (6) at the far end.

2. The dynamic control surface gas extraction well system for multi-layer goaf groups according to claim 1, characterized in that: The multi-layered goaf group includes multi-layered coal seams (3) and non-coal strata (4). The second borehole is directly drilled into the multi-layered coal seams (3) and non-coal strata (4). Multiple goafs and caving zones (2) are located in the coal seams (3) and non-coal strata (4).

3. A dynamic controlled surface gas extraction well system for multi-layered goaf groups according to claim 2, characterized in that: At least two of the horizontal branches (1) are located at the top of the goaf and caving zone (2) at different mining levels, and the horizontal branches (1) are located 25 to 35 m from the roadway boundary.

4. A dynamic controlled surface gas extraction well system for multi-layered goaf groups according to claim 3, characterized in that: A pre-installed fiberglass sleeve (16) is inserted at the opening position of the designed horizontal branch (1), and a window is made in the sleeve at the corresponding depth position of the fiberglass sleeve (16) to form the horizontal branch (1).

5. A dynamic controlled surface gas extraction well system for multi-layered goaf groups according to claim 4, characterized in that: The horizontal branch (1) is 30±5m from the roadway boundary.

6. A dynamic controlled surface gas extraction well system for multi-layered goaf groups according to claim 5, characterized in that: The surface of the anti-clogging filter (8) is coated with a polytetrafluoroethylene-nano silica composite coal powder coating, wherein the mass ratio of nano-SiO2 in the composite coating is 18% to 22% and the coating thickness is 50-200 μm.

7. A dynamic controlled surface gas extraction well system for multi-layered goaf groups according to claim 6, characterized in that: The dynamic sub-control unit realizes the independent opening and closing of each horizontal branch (1) through the hydraulic control valve system (11), the methane concentration sensor (10) monitors the methane concentration in each horizontal branch (1) in real time, and the gas pressure sensor (9) monitors the gas pressure in each horizontal branch (1) in real time.

8. A dynamic controlled surface gas extraction well system for multi-layered goaf groups according to claim 7, characterized in that: The decision mechanism for shutting down the hydraulic control valve system (11) is to automatically shut down the hydraulic control valve system (11) when the sensor detects a methane concentration of <25% for >30 minutes; the decision mechanism for restarting the shut-down hydraulic control valve system (11) is as follows: (I) Shut down horizontal branches (1) Methane concentration ≥40% and lasting ≥72h; (ii) The air pressure within the branch is greater than the initial air pressure at which the branch was shut down; (iii) Manual confirmation and triggering of remote command.

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