A method for drilling a gas extraction borehole through a layer without sealing

Abstract

The application discloses a method for drilling a gas extraction hole in a drilling field without sealing and with high gas concentration, three air bag sealing walls are used to form an overall communication space, a first pressure buffer space and a second pressure buffer space, and when the gas is extracted, the negative pressure of the overall communication space is continuously greater than that of the first pressure buffer space, and the negative pressure of the first pressure buffer space is continuously greater than that of the second pressure buffer space, so that a stepped pressure buffer sealing is formed, the three air bag sealing walls can be sealed more and more tightly under the action of respective pressure differences during the extraction process, meanwhile, the stepped pressure buffer sealing can ensure that the pressure difference on both sides of each air bag sealing wall is lower than the maximum bearing pressure of the air bag sealing wall, and deformation of the air bag sealing wall is prevented to cause sealing failure, and finally, the gas extraction can be carried out under the premise of high negative pressure and large flow, the continuous sealing during the gas extraction is ensured, the possibility of external air entering the extraction pipeline is reduced, and the gas extraction concentration is ensured.

Description

Technical Field

[0001] This invention relates to a method for extracting high-concentration methane, and more particularly to a method for extracting high-concentration methane without sealing through boreholes in drilling sites. Background Technology

[0002] Pre-drainage of coal seam gas through cross-bureau boreholes is one of the main measures taken to prevent coal and gas outbursts. The drainage cycle for pre-drainage of coal seam gas through cross-bureau boreholes is generally 1-3 years. Due to the excessively long drainage cycle, the mine's mining and excavation succession becomes strained, and each cross-bureau borehole needs to be sealed before drainage can begin. During the gas drainage cycle, each cross-bureau borehole is affected by in-situ stress. After being subjected to in-situ stress for a long time, fissures will form around the cross-bureau boreholes, which will develop, expand, and connect. Ultimately, under the negative pressure of drainage, outside air can easily enter the cross-bureau borehole through these fissure leakage channels, resulting in a decrease in gas drainage concentration, shortening the effective drainage life of the cross-bureau borehole, and reducing the utilization rate of the borehole. For the reasons mentioned above, in order to shorten the cycle of pre-drainage of coal seam gas through cross-burrows, most outburst-prone mines mainly adopt high negative pressure and high flow rate drainage systems. Although this can speed up the gas drainage process, the high negative pressure and high flow rate of the internal drainage can make the sealing effect of the cross-burrows more prone to failure. That is, under a certain external atmospheric pressure, the greater the negative pressure inside the borehole, the greater the pressure exerted on it by the external air pressure. This increases the possibility of deformation of the cross-burrow under pressure. Once the sealing fails, it will cause an increase in gas leakage, resulting in a decrease in the gas drainage concentration. In the end, instead of shortening the gas drainage cycle and alleviating the problem of tight mining succession, the gas drainage pump station's drainage concentration is lower than 30%, affecting the utilization of gas.

[0003] Therefore, one of the research directions in this industry is to provide a new method that can effectively shorten the gas extraction cycle while ensuring the sealing of the gas extraction pipeline, reducing the possibility of external air entering the extraction pipeline, thereby ensuring the gas extraction concentration, and eliminating the need to seal each cross-layer borehole separately, thus simplifying the construction process. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a method for high-concentration gas extraction through cross-layer drilling without sealing. This method can effectively shorten the gas extraction cycle while ensuring the sealing of the gas extraction process, reducing the possibility of external air entering the extraction pipeline, thereby ensuring the gas extraction concentration. In addition, it eliminates the need to seal each cross-layer borehole separately, simplifying the construction process.

[0005] To achieve the above objectives, the technical solution adopted by this invention is: a method for high-concentration gas extraction without sealing in cross-layer drilling at a drilling site, the specific steps of which are as follows:

[0006] Step 1: Deploy the gas drainage drilling site: The drilling site is deployed along the roadway direction in the underlying coal seam floor roadway. The drilling site has a trapezoidal cross-section, with the smallest end located at the deepest point of the floor roadway. Inside the drilling site, from the inside out, a minimum-sized airbag sealing wall, an intermediate-sized airbag sealing wall, and a maximum-sized airbag sealing wall are sequentially installed. This creates a drainage sealing space between the smallest end of the drilling site and the minimum-sized airbag sealing wall, a first pressure buffer sealing space between the minimum-sized and intermediate-sized airbag sealing walls, and a second pressure buffer sealing space between the intermediate-sized and maximum-sized airbag sealing walls. The gas collection pipe... One end of the pipeline passes through the largest-sized airbag sealing wall, the middle-sized airbag sealing wall, and the smallest-sized airbag sealing wall in sequence and extends into the extraction sealing space. One end of the first pipeline passes through the largest-sized airbag sealing wall and the middle-sized airbag sealing wall in sequence and extends into the first pressure buffer sealing space. One end of the second pipeline passes through the largest-sized airbag sealing wall and extends into the second pressure buffer sealing space. The other ends of the gas collection pipe, the first pipeline, and the second pipeline are all connected to the main gas extraction pipeline. The gas collection pipe is equipped with a second control valve, the first pipeline is equipped with a first control valve, and the second pipeline is equipped with a third control valve, thus completing the gas extraction drilling site layout.

[0007] Step 2: Drilling through-layer boreholes: Drill multiple through-layer boreholes into the coal seam inside the extraction sealing space in Step 1. Each through-layer borehole and the extraction sealing space form an integrated connected space. After completion, insert extraction pipes slightly longer than the depth of the through-layer boreholes into each through-layer borehole. After fixing, they are all connected to the gas collection pipe in the extraction sealing space through connecting pipes.

[0008] Step 3: High Negative Pressure and High Flow Rate Gas Extraction: At the start of gas extraction, the main gas extraction pipeline is under negative pressure. Open the first, second, and third control valves, ensuring the second control valve is opened more fully than the first, and vice versa. The main gas extraction pipeline extracts gas from the overall connected space, the first pressure buffer space, and the second pressure buffer space through the gas manifold, the first pipeline, and the second pipeline, respectively. At this time, the amount of gas extracted from the overall connected space per unit time is greater than that from the first pressure buffer space. The amount of gas extracted is greater in the first pressure buffer space than in the second pressure buffer space. This results in the negative pressure in the overall connected space being consistently greater than that in the first pressure buffer space, and vice versa. This creates a stepped pressure buffer seal, which in turn creates pressure differences on both sides of the smallest size airbag sealing wall, the middle size airbag sealing wall, and the largest size airbag sealing wall. These pressure differences ensure the sealing effect of the three airbag sealing walls, enabling high negative pressure and high flow rate gas extraction.

[0009] Furthermore, the smallest size airbag sealing wall is placed at a drilling depth of 0.4 to 0.5 times from the inside out of the drilling site, the middle size airbag sealing wall is placed at a drilling depth of 0.55 to 0.65 times from the inside out of the drilling site, and the largest size airbag sealing wall is placed at a drilling depth of 0.7 to 0.8 times from the inside out of the drilling site.

[0010] Furthermore, at the start of gas extraction, the second control valve is opened to a greater degree than the first control valve, and the first control valve is opened to a greater degree than the third control valve. This configuration ensures that, initially, there is a difference in the gas flow rate extracted from the gas manifold, the first pipeline, and the second pipeline.

[0011] Furthermore, the gas collection pipe, the first pipeline, and the second pipeline have the same diameter. Using the same diameter facilitates installation.

[0012] Furthermore, the smallest, medium-sized, and largest-sized airbag sealing walls are all made of Hypalon adhesive tape and can withstand air pressure of 0.2–0.3 MPa. This ensures that the required pressure resistance of each airbag sealing wall meets the requirements.

[0013] Furthermore, the extraction pipe consists of a solid pipe and a screen pipe, with the solid pipe located in the rock strata and the screen pipe located in the coal seam. This structure facilitates the extraction of gas from the coal seam.

[0014] Compared with the prior art, the present invention has the following advantages:

[0015] 1. After completing each cross-layer borehole, this invention eliminates the need to seal each borehole, allowing all boreholes to connect with the extraction sealing space to form a unified connected space. During subsequent gas extraction, the negative pressure in each gas extraction main pipeline is transmitted to each cross-layer borehole via the gas collection pipe, connecting pipe, and extraction pipe, enabling gas extraction from each borehole. Simultaneously, since each cross-layer borehole is connected to the extraction sealing space, it facilitates the transmission of extraction negative pressure from each borehole to the extraction sealing space, achieving negative pressure gas extraction from the entire connected space. This not only eliminates the need for sealing but also utilizes the mine's existing extraction system for high-negative-pressure, high-flow-rate gas extraction from the coal seam, effectively shortening the gas extraction cycle.

[0016] 2. This invention forms an overall connected space, a first pressure buffer space, and a second pressure buffer space through a minimum-sized airbag sealing wall, a medium-sized airbag sealing wall, and a maximum-sized airbag sealing wall, respectively. During high-negative-pressure, high-flow-rate gas extraction, negative pressure extraction is performed on the overall connected space, the first pressure buffer space, and the second pressure buffer space through the gas collecting pipe, the first pipeline, and the second pipeline, respectively. By setting different opening degrees, the negative pressure in the overall connected space is consistently greater than the negative pressure in the first pressure buffer space, and the negative pressure in the first pressure buffer space is consistently greater than the negative pressure in the second pressure buffer space, forming a stepped pressure buffer seal. That is, the negative pressure in each space decreases sequentially, achieving a stepped pressure buffer seal. This method creates pressure differentials on both sides of the smallest, middle, and largest gasbag sealing walls during gas extraction. Because the drilling site is arranged in a trapezoidal pattern, the sealing tightness of these walls increases progressively under the pressure differentials. Simultaneously, the stepped pressure buffer seal ensures that the pressure differential on both sides of each gasbag sealing wall remains below its maximum withstand pressure, preventing deformation and sealing failure. By gradually reducing and buffering the pressure, continuous sealing is maintained during gas extraction under high negative pressure and high flow rates, reducing the possibility of external air entering the extraction pipeline and thus ensuring the gas extraction concentration. Attached Figure Description

[0017] Figure 1 This is a perspective view of the layout position of the present invention.

[0018] Figure 2 yes Figure 1 Cross-sectional view along the AA direction.

[0019] Figure 3 This is a schematic diagram of the extraction tube in this invention.

[0020] In the diagram: 1. Extraction pipe; 2. Connecting pipe; 3. Minimum end of the drilling site; 4. Maximum end of the drilling site; 5. First pipeline; 6. Gas collection pipe; 7. Second pipeline; 8. Maximum size airbag sealing wall; 9. Intermediate size airbag sealing wall; 10. Minimum size airbag sealing wall; 11. Coal seam; 12. Cross-seam borehole; 13. Extraction sealing space; 14. Main gas extraction pipeline; 15. First control valve; 16. Second control valve; 17. Third control valve. Detailed Implementation

[0021] The present invention will be further described below.

[0022] like Figure 1 As shown, the specific steps of this invention are as follows:

[0023] Step 1: Deploy the gas extraction drilling site: such as Figure 2 As shown, a drilling site is set up along the roadway direction in the underlying floor roadway of coal seam 11. The drilling site has a trapezoidal cross-section, with the smallest end 3 located at the deepest point of the floor roadway. Inside the drilling site, from the inside out, a minimum-sized airbag sealing wall 10, a middle-sized airbag sealing wall 9, and a maximum-sized airbag sealing wall 8 are sequentially arranged. The minimum-sized airbag sealing wall 10 is placed at 0.4 to 0.5 times the drilling depth from the inside out, the middle-sized airbag sealing wall 9 is placed at 0.55 to 0.65 times the drilling depth from the inside out, and the maximum-sized airbag sealing wall 8 is placed at 0.7 to 0.8 times the drilling depth from the inside out. This creates a sealing space 13 between the smallest end 3 and the minimum-sized airbag sealing wall 10, and a first pressure buffer sealing space between the minimum-sized airbag sealing wall 10 and the middle-sized airbag sealing wall 9. A second pressure buffer sealing space is formed between the gas collection pipe 9 and the largest size airbag sealing wall 8. One end of the gas collection pipe 6 passes through the largest size airbag sealing wall 8, the middle size airbag sealing wall 9, and the smallest size airbag sealing wall 10 in sequence and extends into the extraction sealing space 13. One end of the first pipeline 5 passes through the largest size airbag sealing wall 8 and the middle size airbag sealing wall 9 in sequence and extends into the first pressure buffer sealing space. One end of the second pipeline 7 passes through the largest size airbag sealing wall 8 and extends into the second pressure buffer sealing space. The other ends of the gas collection pipe 6, the first pipeline 5, and the second pipeline 7 are all connected to the main gas extraction pipeline 14. The gas collection pipe 6 is equipped with a second control valve 16, the first pipeline 5 is equipped with a first control valve 15, and the second pipeline 7 is equipped with a third control valve 17, thus completing the gas extraction drilling site layout. The gas collection pipe 6, the first pipeline 5, and the second pipeline 7 have the same diameter.

[0024] Step 2: Drilling through-seam boreholes 12: Multiple through-seam boreholes 12 are drilled into the coal seam 11 inside the extraction sealing space 13 established in Step 1. Each through-seam borehole 12 forms a unified, interconnected space with the extraction sealing space 13. After completion, extraction pipes 1, slightly longer than the depth of the through-seam boreholes 12, are inserted into each through-seam borehole 12 and fixed. All are then connected to the gas collection pipe 6 within the extraction sealing space 13 via connecting pipes 2. Figure 3 As shown, the extraction pipe 1 consists of a solid pipe and a screen pipe, wherein the solid pipe is located in the rock stratum and the screen pipe is located in the coal seam 11. This structure facilitates the extraction of gas from the coal seam.

[0025] Step 3, High Negative Pressure and High Flow Rate Gas Extraction: When gas extraction begins, the main gas extraction pipeline 14 is under negative pressure. The first control valve 15, the second control valve 16, and the third control valve 17 are opened, with the second control valve 16 opening to a greater extent than the first control valve 15, and the first control valve 15 opening to a greater extent than the third control valve 17. This setup ensures that initially, the gas flow rate difference between the gas collection pipe 6, the first pipeline 5, and the second pipeline 7 is maintained. The main gas extraction pipeline 14 extracts gas from the overall connected space, the first pressure buffer space, and the second pressure buffer space through the gas collection pipe 6, the first pipeline 5, and the second pipeline 7, respectively. At this time, the amount of gas extracted from the overall connected space per unit time is greater than the amount of gas extracted from the first pressure buffer space, and the amount of gas extracted from the first pressure buffer space is greater than the amount of gas extracted from the second pressure buffer space. This results in the negative pressure in the overall connected space being continuously greater than the negative pressure in the first pressure buffer space, and the negative pressure in the first pressure buffer space being continuously greater than the negative pressure in the second pressure buffer space, forming a stepped pressure buffer seal. Consequently, pressure differences are formed on both sides of the smallest size airbag sealing wall 10, both sides of the middle size airbag sealing wall 9, and both sides of the largest size airbag sealing wall 8. Due to the pressure difference, the sealing effect of the three airbag sealing walls is guaranteed, achieving high negative pressure and high flow rate gas extraction.

[0026] As an improvement of the present invention, the minimum-sized airbag sealing wall 10, the intermediate-sized airbag sealing wall 9, and the maximum-sized airbag sealing wall 8 are all made of Hypalon adhesive tape material and can withstand air pressure of 0.2-0.3 MPa. This ensures the sealing performance of the minimum-sized airbag sealing wall 10, the intermediate-sized airbag sealing wall 9, and the maximum-sized airbag sealing wall 8, preventing deformation and failure of the airbag sealing walls due to excessive pressure differential.

[0027] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for high-concentration methane extraction through cross-layer drilling without sealing, characterized in that, The specific steps are as follows: Step 1: Deploy the gas drainage drilling site: The drilling site is deployed along the roadway direction in the underlying coal seam floor roadway. The drilling site has a trapezoidal cross-section, with the smallest end located at the deepest point of the floor roadway. Inside the drilling site, from the inside out, a minimum-sized airbag sealing wall, an intermediate-sized airbag sealing wall, and a maximum-sized airbag sealing wall are sequentially installed. This creates a drainage sealing space between the smallest end of the drilling site and the minimum-sized airbag sealing wall, a first pressure buffer sealing space between the minimum-sized and intermediate-sized airbag sealing walls, and a second pressure buffer sealing space between the intermediate-sized and maximum-sized airbag sealing walls. The gas collection pipe... One end of the pipeline passes through the largest-sized airbag sealing wall, the middle-sized airbag sealing wall, and the smallest-sized airbag sealing wall in sequence and extends into the extraction sealing space. One end of the first pipeline passes through the largest-sized airbag sealing wall and the middle-sized airbag sealing wall in sequence and extends into the first pressure buffer sealing space. One end of the second pipeline passes through the largest-sized airbag sealing wall and extends into the second pressure buffer sealing space. The other ends of the gas collection pipe, the first pipeline, and the second pipeline are all connected to the main gas extraction pipeline. The gas collection pipe is equipped with a second control valve, the first pipeline is equipped with a first control valve, and the second pipeline is equipped with a third control valve, thus completing the gas extraction drilling site layout. Step 2: Drilling through-layer boreholes: Drill multiple through-layer boreholes into the coal seam inside the extraction sealing space in Step 1. Each through-layer borehole and the extraction sealing space form an integrated connected space. After completion, insert extraction pipes slightly longer than the depth of the through-layer boreholes into each through-layer borehole. After fixing, they are all connected to the gas collection pipe in the extraction sealing space through connecting pipes. Step 3: High Negative Pressure and High Flow Rate Gas Extraction: At the start of gas extraction, the main gas extraction pipeline is under negative pressure. The first, second, and third control valves are opened, with the second control valve opening more fully than the first, and the first control valve opening more fully than the third. The main gas extraction pipeline extracts gas from the overall connected space, the first pressure buffer space, and the second pressure buffer space through the gas manifold, the first pipeline, and the second pipeline, respectively. At this time, the amount of gas extracted from the overall connected space per unit time is greater than that from the first pressure buffer space. The amount of gas extracted is greater in the first pressure buffer space than in the second pressure buffer space. This results in the negative pressure in the overall connected space being consistently greater than that in the first pressure buffer space, and vice versa. This creates a stepped pressure buffer seal, which in turn creates pressure differences on both sides of the smallest size airbag sealing wall, the middle size airbag sealing wall, and the largest size airbag sealing wall. These pressure differences ensure the sealing effect of the three airbag sealing walls, enabling high negative pressure and high flow rate gas extraction.

2. The method for high-concentration gas extraction without sealing in cross-layer drilling according to claim 1, characterized in that, The smallest size airbag sealing wall is placed at a drilling depth of 0.4 to 0.5 times from the inside out of the drilling site, the medium size airbag sealing wall is placed at a drilling depth of 0.55 to 0.65 times from the inside out of the drilling site, and the largest size airbag sealing wall is placed at a drilling depth of 0.7 to 0.8 times from the inside out of the drilling site.

3. The method for high-concentration gas extraction without sealing in cross-layer drilling according to claim 1, characterized in that, The gas collection pipe, the first pipeline, and the second pipeline have the same diameter.

4. The method for high-concentration gas extraction without sealing in cross-layer drilling according to claim 1, characterized in that, The minimum size airbag sealing wall, the intermediate size airbag sealing wall, and the maximum size airbag sealing wall are all made of Hypalon adhesive tape material and can withstand air pressure of 0.2 to 0.3 MPa.

5. The method for high-concentration gas extraction without sealing in cross-layer drilling according to claim 1, characterized in that, The extraction pipe consists of a solid pipe and a screen pipe, wherein the solid pipe is located in the rock stratum and the screen pipe is located in the coal seam.

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