Gas extraction method and system for downhole drilling

Abstract

The application provides a gas extraction method and system of a downward drilling hole, relates to the technical field of mine gas extraction, and comprises the following steps: first drilling construction, constructing a first drilling hole in a coal rock layer of a first recovery roadway towards a second recovery roadway, and making the hole mouth of the first drilling hole be at the lowest position of the first drilling hole; second drilling construction, constructing a second drilling hole in a panel main roadway of a coal rock layer, and connecting the lowest position of the second drilling hole at a position of the first drilling hole which is higher than the hole mouth of the first drilling hole, and performing segmented fracturing on the second drilling hole; second drilling hole drainage, accumulated water in the second drilling hole is drained into a mine drainage system through the first drilling hole; and second drilling hole extraction, a downhole extraction system is connected with the second drilling hole to perform gas extraction. The application is favorable for drilling hole drainage and residue removal, has high gas extraction operation efficiency, is low in cost, can realize continuous extraction operation on the drilling hole in a gas extraction depletion period, and improves the drilling hole gas extraction effect.

Description

Technical Field

[0001] This application relates to the field of mine gas extraction technology, and in particular to a gas extraction method and system for downhole drilling. Background Technology

[0002] Due to factors such as coal and rock strata occurrence, working face layout, and mining continuity, some mines have to construct long downward directional boreholes for gas drainage. However, ordinary long downward directional boreholes have low drainage efficiency, especially during the gas drainage depletion period. While staged fracturing technology can effectively improve the permeability of coal and rock strata, for long downward directional boreholes, a large amount of water will remain in the borehole after fracturing, which seriously affects the desorption of gas from the coal and rock strata. Furthermore, the water further softens the borehole wall, significantly increasing the risk of borehole collapse, and still fails to achieve the goal of promoting efficient gas drainage from the borehole. To ensure efficient gas extraction in long directional boreholes, many technologies employ a method of draining water from the borehole after fracturing using specialized drainage and slag removal devices to avoid the impact of water accumulation on gas extraction operations. However, this method adds the step of installing specialized drainage and slag removal devices within the borehole, making the operation cumbersome, affecting the efficiency of gas extraction operations, and resulting in high costs. Furthermore, it cannot enable continued gas extraction operations during the gas extraction depletion period, leading to low gas extraction efficiency. Summary of the Invention

[0003] The present invention aims to at least partially solve one of the technical problems in the related art.

[0004] Therefore, one embodiment of the present invention proposes a gas extraction method for down-drilling boreholes. This method is beneficial for borehole drainage and slag removal, has high gas extraction efficiency, and low cost. At the same time, it can enable continued extraction operations during the gas extraction depletion period of the borehole, thereby improving the gas extraction effect of the borehole.

[0005] Another embodiment of the present invention provides a gas extraction system for downhole drilling.

[0006] A gas extraction method for a downburst borehole according to an embodiment of the present invention includes the following steps:

[0007] The first borehole is constructed in the first mining roadway towards the second mining roadway, with the borehole opening at the lowest point of the first borehole.

[0008] The second borehole is constructed in the main roadway of the panel to drill the second borehole into the coal and rock strata, and the lowest position of the second borehole is connected to the position of the first borehole above the opening of the first borehole, and the second borehole is subjected to segmented fracturing.

[0009] The second borehole is used for drainage, and the water accumulated in the second borehole is discharged into the mine drainage system through the first borehole.

[0010] The second borehole is used for gas extraction, and the downhole extraction system is connected to the second borehole for gas extraction.

[0011] According to an embodiment of the present invention, a gas extraction method using a downhole borehole comprises a first borehole drilled in the coal and rock strata along the direction from the first mining roadway toward the second mining roadway, and a second borehole drilled in the main roadway of the panel, communicating with the first borehole. The opening of the first borehole is its lowest point, and the lowest point of the second borehole is connected to a position higher than the opening of the first borehole. The design of the first borehole opening connecting to the mine drainage system allows water accumulated in the second borehole to be discharged into the mine drainage system through the first borehole, thus constructing an automatic drainage system for the second borehole within the coal and rock strata. The second borehole is connected to the underground extraction system. If the two are connected, gas extraction from the coal and rock strata can be carried out through the second borehole. The combination of the two forms a gas extraction system in the coal and rock strata that integrates gas extraction and self-drainage in a downward borehole. Compared with related technologies, this application only requires the structural layout of the first and second boreholes to facilitate drainage and slag removal in the second borehole, effectively avoiding the impact of water accumulation on the gas extraction operation of the second borehole, thus ensuring the gas extraction effect of the second borehole. Moreover, since the process of installing a dedicated drainage and slag removal device in the second borehole is eliminated, the operation process is simplified, the efficiency of gas extraction operation can be guaranteed, and costs can be saved.

[0012] In some embodiments, the gas extraction method for downhole drilling further includes a step following the second borehole extraction operation:

[0013] In the second borehole suffocation, when the gas extraction volume Q1 of the second borehole is ≤0.25Q0, the downhole compressed air system is connected to the second borehole and gas is injected to suffocate the borehole, where Q0 is the initial gas extraction volume of the second borehole.

[0014] The first borehole is used for gas extraction, and the connection between the downhole extraction system and the second borehole is cut off. The downhole extraction system is connected to the first borehole for gas extraction.

[0015] Repeat the second borehole drilling and the first borehole extraction operation until the gas extraction of the coal and rock strata is completed.

[0016] In some embodiments, the duration of the gas injection puncture is t, where t ≥ 1 day.

[0017] In some embodiments, the first drilling operation specifically includes:

[0018] A directional drilling rig constructs the first borehole in the coal and rock strata along the direction from the first mining roadway toward the second mining roadway. Hydraulic cavitation is performed at set intervals along the extension direction of the first borehole to form cavities.

[0019] A first steel pipe is coaxially arranged in the first borehole. The outer circumferential surface of the first steel pipe and the inner circumferential surface of the first borehole are spaced apart and together define a first sealing channel. A first valve is installed at the end of the first steel pipe near the opening of the first borehole. The portion of the first steel pipe near the bottom of the first borehole is connected to the first borehole and used to transport water and gas.

[0020] Grouting is performed on the first sealing channel to form a first grouting section, the length of which is less than the length of the first sealing channel.

[0021] In some embodiments, the first sealing channel is sealed by grouting using a two-plug-one-injection method, and the length of the first grouting section is greater than or equal to 50 meters.

[0022] In some embodiments, the second drilling operation specifically includes:

[0023] The directional drilling rig constructs multiple second boreholes in the main roadway of the panel to drill multiple second boreholes in the coal and rock strata. The multiple second boreholes are arranged at intervals along the extension direction of the main roadway of the panel and correspond one-to-one with the holes and are directionally connected within a set distance from the first borehole.

[0024] The first valve is closed, and a segmented fracturing tool string is placed in the second borehole along the extension direction of the second borehole. The segmented fracturing tool string is connected to a high-pressure water pump. The high-pressure water pumped by the high-pressure water pumps the second borehole in segments and creates fracturing cracks on the peripheral wall surface of the second borehole.

[0025] Remove the segmented fracturing tool string, and coaxially arrange a second steel pipe in the second borehole. The outer circumferential surface of the second steel pipe and the inner circumferential surface of the second borehole are spaced apart and together define a second sealing channel. A second valve is installed at the end of the second steel pipe near the borehole opening of the second borehole. The portion of the second steel pipe near the bottom of the second borehole is connected to the second borehole and used to transport gas and water.

[0026] Grouting is performed on the second sealing channel to form a second grouting section, the length of which is less than the length of the second sealing channel.

[0027] In some embodiments, the second borehole has four or more fracturing stages.

[0028] The second sealing channel is sealed by grouting using a two-plug-one-injection method.

[0029] In some embodiments, the second borehole drainage operation specifically includes:

[0030] When the first valve is opened, the first borehole is connected to the mine drainage system, and the water accumulated in the second borehole is discharged into the mine drainage system through the first borehole to achieve initial drainage.

[0031] The second borehole is connected to the underground compressed air system through the second valve. Gas from the underground compressed air system is injected into the second borehole. The gas forces the water in the fracture and the cavity into the mine drainage system through the first borehole to achieve secondary drainage.

[0032] The first valve and the second valve are closed.

[0033] In some embodiments, the second borehole extraction operation specifically includes:

[0034] When the second valve is opened, the downhole extraction system is connected to the second borehole for gas extraction.

[0035] The first valve is opened periodically to drain water from the first and second boreholes.

[0036] A gas extraction system for downburst drilling according to an embodiment of the present invention includes a first mining roadway, a panel main roadway, a second mining roadway, a first borehole, and a second borehole.

[0037] The first mining roadway, the main roadway of the panel, and the second mining roadway are connected in sequence. One of the main roadway of the panel and the first mining roadway extends along the strike of the coal and rock strata, and the other extends along the dip of the coal and rock strata. The first mining roadway and the second mining roadway are arranged at intervals along the extension direction of the main roadway of the panel, and their extension directions are consistent.

[0038] Both the first borehole and the second borehole are located in the coal and rock strata. The first borehole extends from the first mining roadway toward the second mining roadway, and the second borehole extends from the main roadway of the panel toward the first borehole. The opening of the first borehole is the lowest point of the first borehole, and the lowest point of the second borehole is connected to the position of the first borehole that is higher than the opening of the first borehole.

[0039] The technical advantages of the gas extraction system for downhole drilling according to the embodiments of the present invention are the same as those of the gas extraction method for downhole drilling described above, and will not be repeated here.

[0040] In some embodiments, the height of the central axis of the first borehole to the bottom of the coal and rock stratum gradually increases along the direction from the first mining roadway toward the second mining roadway, the height of the central axis of the second borehole to the bottom of the coal and rock stratum gradually decreases along the direction from the main roadway of the panel toward the first borehole, and the length of the second borehole is greater than the length of the first borehole.

[0041] In some embodiments, a first grouting section is provided in the first borehole, the length of the first grouting section being less than the length of the first borehole; and a second grouting section is provided in the second borehole, the length of the second grouting section being less than the length of the second borehole.

[0042] The gas extraction system for the downhole borehole also includes a first steel pipe, a first valve, a mine drainage system, a second steel pipe, a second valve, and an underground extraction system.

[0043] Wherein, at least a portion of the first steel pipe is fitted into the first grouting section and extends axially along the first borehole, the portion of the first steel pipe near the bottom of the first borehole is connected to the first borehole, the first valve is installed at the end of the first steel pipe near the opening of the first borehole, the first borehole has a drainage mode and a first extraction mode, and the first valve is connected to the mine drainage system in the drainage mode.

[0044] In this configuration, at least a portion of the second steel pipe is fitted into the second grouting section and extends axially along the second borehole. The portion of the second steel pipe adjacent to the bottom of the second borehole is connected to the second borehole. The second valve is installed at the end of the second steel pipe adjacent to the opening of the second borehole. The second borehole has a second extraction mode. In the first extraction mode, the first valve is connected to the downhole extraction system and the second valve is closed. In the second extraction mode, the first valve is closed and the second valve is connected to the downhole extraction system.

[0045] In some embodiments, the gas extraction system of the downhole borehole further includes a downhole compressed air system, the second borehole also has a dammed mode, the second valve is connected to the downhole compressed air system in both the drainage mode and the dammed mode, and the first valve is closed in the dammed mode.

[0046] In some embodiments, the gas extraction system of the downhole borehole further includes a cavity, which is disposed at the intersection of the first borehole and the second borehole, and the diameter of the cavity is larger than the diameter of the first borehole and the second borehole.

[0047] The second boreholes are multiple and spaced apart along the extension direction of the main roadway of the panel, and the holes are multiple and spaced apart along the extension direction of the first boreholes, with each hole corresponding to one of the second boreholes.

[0048] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of the structure of a gas extraction system for a downhole borehole according to an embodiment of the present invention.

[0050] Figure 2 This is a schematic diagram of the connection between the second borehole and the cavity in the coal and rock strata in a gas extraction system of a downhole borehole according to an embodiment of the present invention.

[0051] Figure 3 yes Figure 2 A schematic diagram of the segmented fracturing structure of the second borehole.

[0052] Figure 4 This is a schematic diagram of the cross-sectional structure of the first borehole and cavity in the coal and rock strata in a gas extraction system with a downhole borehole according to an embodiment of the present invention.

[0053] Attached reference numerals: 1. First borehole, 2. First mining roadway, 3. Coal and rock strata, 4. Second mining roadway, 5. Second borehole, 6. Main roadway of the panel, 7. Hole, 8. Pressure fracture. Detailed Implementation

[0054] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0055] like Figures 1 to 4 As shown, a gas extraction method for downburst drilling according to an embodiment of the present invention includes the following steps:

[0056] The first borehole 1 is constructed in the direction of the coal and rock layer 3 towards the second mining roadway 4 in the first mining roadway 2, and the opening of the first borehole 1 is at the lowest position of the first borehole 1.

[0057] Construction of the second borehole 5: The second borehole 5 is constructed in the main roadway 6 of the panel area, connecting the lowest position of the second borehole 5 to the position of the first borehole 1 above the opening of the first borehole 1, and the second borehole 5 is subjected to segmented fracturing.

[0058] The second borehole 5 is used for drainage, and the accumulated water in the second borehole 5 is discharged into the mine drainage system through the first borehole 1.

[0059] The second borehole 5 is used for gas extraction. The downhole extraction system is connected to the second borehole 5 for gas extraction.

[0060] According to an embodiment of the present invention, a gas extraction method using a downhole borehole comprises a first borehole 1 drilled in the coal and rock stratum 3 along the direction from the first mining roadway 2 toward the second mining roadway 4, and a second borehole 5 drilled in the main roadway 6 of the panel, communicating with the first borehole 1. The opening of the first borehole 1 is its lowest point, and the lowest point of the second borehole 5 is connected to a position higher than the opening of the first borehole 1. The design of the opening of the first borehole 1 communicating with the mine drainage system allows water accumulated in the second borehole 5 to be discharged into the mine drainage system through the first borehole 1, thus constructing an automatic drainage system for the second borehole 5 in the coal and rock stratum 3. The second borehole 5 and the mine drainage system are interconnected. When the lower extraction system is connected, gas extraction from the coal and rock stratum 3 can be carried out through the second borehole 5. The combination of the two forms a gas extraction system in the coal and rock stratum 3 that integrates gas extraction and self-drainage through a downward borehole. Compared with related technologies, this application only requires the structural layout of the first borehole 1 and the second borehole 5 to facilitate drainage and slag removal in the second borehole 5, effectively avoiding the impact of water accumulation on the gas extraction operation of the second borehole 5, thus ensuring the gas extraction effect of the second borehole 5. Furthermore, since the process of installing a dedicated drainage and slag removal device in the second borehole 5 is eliminated, the operation process is simplified, the efficiency of gas extraction operation can be guaranteed, and costs can be saved.

[0061] It is understandable that, in order to facilitate the drainage of water accumulated in the second borehole 5 through the first borehole 1, the first borehole 1 can be a horizontal borehole or an upward borehole. Preferably, the first borehole 1 is an upward borehole, that is, the height of the central axis of the first borehole 1 to the bottom of the coal and rock stratum 3 gradually increases along the direction from the first mining roadway 2 toward the second mining roadway 4. In addition, since the first borehole 1 is mainly used to assist in the drainage of water accumulated in the second borehole 5, the first borehole 1 can be a joint borehole, that is, the first borehole 1 is constructed along the coal seam in the coal and rock stratum 3 to improve construction efficiency and reduce construction costs.

[0062] It should be noted that the second borehole 5 is primarily a downward borehole, meaning that the height from the centerline of the second borehole 5 to the bottom of the coal seam 3 gradually decreases along the direction from the main roadway 6 in the panel towards the first borehole 1. Because downward boreholes are easily affected by their own orientation, a large amount of water will accumulate inside the borehole after fracturing, severely affecting gas desorption from the coal seam 3; therefore, drainage operations are necessary. This application applies to gas extraction from downward boreholes with a length of 300 meters or more (i.e., the length of the second borehole 5 is not less than 300 meters). The length of the second borehole 5 is much greater than the length of the first borehole 1, which is a short borehole.

[0063] like Figures 1 to 3As shown, in some embodiments, the gas extraction method for the downhole drilling also includes a step following the extraction operation of the second borehole 5:

[0064] When the gas extraction volume Q1 of the second borehole 5 is less than or equal to 0.25Q0, the downhole compressed air system is connected to the second borehole 5 and gas is injected to dam the borehole. Here, Q0 is the initial gas extraction volume of the second borehole 5.

[0065] The first borehole 1 is used for gas extraction. The connection between the downhole extraction system and the second borehole 5 is cut off. The downhole extraction system is then connected to the first borehole 1 for gas extraction.

[0066] Repeat the second borehole 5 drilling and the first borehole 1 extraction operation until the gas extraction of coal and rock strata 3 is completed.

[0067] By injecting air into the second borehole 5 through the underground compressed air system, the fracturing degree of the second borehole 5 at the fracturing location can be further expanded, thereby increasing the permeability of the coal and rock stratum 3 and promoting the desorption of gas in the coal and rock stratum 3. At the same time, the gas extraction volume along the entire borehole axis gradually decreases with the increase of its own length. Therefore, switching the underground extraction system to be connected to the first borehole 1 makes it easier for the gas in the second borehole 5 away from its orifice to be extracted by the underground extraction system through the first borehole 1, thereby realizing the continued extraction operation of the second borehole 5 during the gas extraction depletion period and improving the gas extraction effect.

[0068] Understandably, compared to related technologies that can only extract gas from the opening of the second borehole 5, when the second borehole 5 enters the gas extraction depletion period, the portion near the bottom of the borehole is not effectively extracted, resulting in low gas extraction efficiency for the entire second borehole 5. This application, however, can extract gas from the portion near the bottom of the second borehole 5 by cooperating with the first borehole 1, which is located near the bottom of the second borehole 5, through a downhole extraction system connected to the first borehole 1. This allows the first borehole 1 to simultaneously assist in drainage of the second borehole 5 and promote continued extraction of gas from the second borehole 5 during the gas extraction depletion period.

[0069] It should be noted that the gas extraction volume along the entire borehole axis gradually decreases with the increase of its length. This is because the extraction pressure of the underground extraction system gradually weakens from the borehole opening towards the bottom of the borehole, resulting in a decrease in the gas extraction volume along the depth of the borehole. The length of the bottom of the first borehole 1 adjacent to the second borehole 5 is much shorter than that of the second borehole 5. That is, the length from the opening of the first borehole 1 to the bottom of the second borehole 5 is shorter than the length from the opening of the second borehole 5 to the bottom of the second borehole 5. Therefore, the extraction pressure provided by the underground extraction system from the first borehole 1 to the bottom of the second borehole 5 is greater, which can fully extract the gas in the coal and rock strata 3 adjacent to this part.

[0070] To ensure the pore-blocking effect of the second borehole 5, in some embodiments, the pore-blocking time for gas injection is t, where t ≥ 1 day.

[0071] like Figure 1 and Figure 4 As shown, in some embodiments, the construction operation of the first borehole 1 specifically includes:

[0072] The directional drilling rig constructs the first borehole 1 in the coal and rock stratum 3 along the direction from the first mining roadway 2 toward the second mining roadway 4. Hydraulic cavitation is performed in the first borehole 1 at set intervals along the extension direction of the first borehole 1 to form cavities 7.

[0073] A first steel pipe is coaxially arranged in the first borehole 1. The outer circumferential surface of the first steel pipe and the inner circumferential surface of the first borehole 1 are separated and together define the first sealing channel. A first valve is installed at the end of the first steel pipe near the opening of the first borehole 1. The part of the first steel pipe near the bottom of the first borehole 1 is connected to the first borehole 1 and used to transport water and gas.

[0074] Grouting is performed on the first sealing channel to form a first grouting section, the length of which is less than the length of the first sealing channel.

[0075] The cavity 7 in the first borehole 1 can release the stress and gas pressure of the coal body around the first borehole 1, thereby relieving the pressure on the coal seam and increasing the permeability of the coal seam, so as to effectively improve the gas extraction efficiency and extraction volume. The first grouting section enables the first steel pipe to be reliably installed in the first borehole 1, thereby sealing the first borehole 1 and ensuring the smooth operation of water accumulation and gas transportation by the first steel pipe in the later stage.

[0076] Specifically, during hydraulic cavity creation, the coordinates of the cavity creation point can be recorded simultaneously. The first steel pipe is a pressure-resistant steel pipe. The first steel pipe and the first valve are threaded together, so that the thread structure can form a large axial locking force between them, reducing the impact of the high-pressure medium in the first steel pipe on the reliability of the connection between them. The first valve is a high-pressure resistant valve. The first sealing channel is sealed by grouting using a two-plug-one-injection method. To ensure the sealing effect, the length of the first grouting section is greater than or equal to 50 meters.

[0077] like Figures 1 to 3 As shown, in some embodiments, the construction operation of the second borehole 5 is specifically as follows:

[0078] The directional drilling rig constructs multiple second boreholes 5 in the main roadway 6 of the panel and the coal and rock strata 3. The multiple second boreholes 5 are arranged at intervals along the extension direction of the main roadway 6 of the panel and correspond one-to-one with the holes 7 within a set range from the first borehole 1 and are directionally connected.

[0079] To ensure the segmented fracturing operation of the second borehole 5, the first valve is closed before the fracturing is completed. A segmented fracturing tool string is placed in the second borehole 5 along the extension direction of the second borehole 5. The segmented fracturing tool string is connected to a high-pressure water pump. The high-pressure water pump supplies high-pressure water to segmentally fracture the second borehole 5 and create fracturing fractures 8 on the peripheral wall of the second borehole 5.

[0080] Remove the segmented fracturing tool string, and coaxially arrange the second steel pipe in the second borehole 5. The outer circumferential surface of the second steel pipe is separated from the inner circumferential surface of the second borehole 5 and together define the second sealing channel. A second valve is installed at the end of the second steel pipe near the opening of the second borehole 5. The part of the second steel pipe near the bottom of the second borehole 5 is connected to the second borehole 5 and used to transport gas and water.

[0081] Grouting is performed on the second sealing channel to form a second grouting section, the length of which is less than the length of the second sealing channel.

[0082] The cavity 7 facilitates the connection between the second borehole 5 and the first borehole 1 during construction. The hydraulic fractures 8 formed by the segmented fracturing of the second borehole 5 can effectively improve the permeability of the coal seam. At the same time, since the bottom part of the second borehole 5 is adjacent to the cavity 7, the stress and gas pressure of the coal body around the second borehole 5 can be released to a certain extent, the coal seam can be depressurized, the permeability of the coal seam can be increased, and the gas extraction efficiency and extraction volume can be effectively improved. The second grouting section allows the second steel pipe to be reliably installed in the second borehole 5, realizing the sealing of the second borehole 5.

[0083] Specifically, the second borehole 5 has at least four fracturing stages. The second steel pipe is made of pressure-resistant steel, specifically 50 steel. The second steel pipe is threaded into the second valve. The second valve is a high-pressure resistant valve. The second sealing channel is sealed using a two-plug-one-injection grouting method.

[0084] It should be noted that, based on the coordinates of the hole-making point recorded during the construction of the hole 7 in the first borehole 1, the initial construction position of the second borehole 5 on the main roadway 6 of the panel can be determined, so as to facilitate the construction of multiple second boreholes 5.

[0085] like Figure 1 and Figure 3 As shown, in some embodiments, the drainage operation of the second borehole 5 specifically involves:

[0086] The first valve is opened, and the first borehole 1 is connected to the mine drainage system. The water accumulated in the second borehole 5 is discharged into the mine drainage system through the first borehole 1, thus achieving initial drainage.

[0087] The second borehole 5 is connected to the underground compressed air system through the second valve. The gas from the underground compressed air system is injected into the second borehole 5. The gas pressurizes the water in the fracture 8 and the cavity 7 into the mine drainage system through the first borehole 1 to achieve secondary drainage.

[0088] The first and second valves are closed.

[0089] The second borehole 5, the first borehole 1, and the mine drainage system are connected to form a primary active drainage system for the second borehole 5. The underground compressed air system, the second borehole 5, the first borehole 1, and the mine drainage system are connected to form a secondary passive drainage system for the second borehole 5. The combination of the two drainage systems can achieve more thorough drainage and slag removal treatment for the second borehole 5, thereby promoting efficient gas extraction from the second borehole 5.

[0090] like Figure 1 As shown, in some embodiments, the extraction operation of the second borehole 5 specifically involves:

[0091] The second valve is opened, and the downhole extraction system is connected to the second borehole 5 to extract gas.

[0092] The first valve is opened periodically, and drainage is carried out in the first borehole 1 and the second borehole 5.

[0093] Compared to related technologies that require the installation of a dedicated drainage and slag removal device in the second borehole 5 to allow gas extraction and drainage / slag removal to be carried out separately without interference, or that require interrupting gas extraction after fracturing the second borehole 5 and when drainage / slag removal is needed to remove accumulated water, thus affecting gas extraction efficiency, this application, through the cooperation of the structures of the first borehole 1 and the second borehole 5, allows for periodic drainage throughout the entire gas extraction process, ensuring the continuity of gas extraction operations in the second borehole 5 and improving gas extraction efficiency.

[0094] Specifically, the downhole extraction system is connected to the second steel pipe via a second valve.

[0095] like Figures 1 to 4 As shown, a gas extraction system for a downhole borehole according to an embodiment of the present invention includes a first mining roadway 2, a panel main roadway 6, a second mining roadway 4, a first borehole 1, and a second borehole 5.

[0096] Among them, the first mining roadway 2, the main roadway 6 of the panel area, and the second mining roadway 4 are connected in sequence. One of the main roadway 6 of the panel area and the first mining roadway 2 extends along the strike of the coal and rock stratum 3, and the other extends along the dip of the coal and rock stratum 3. The first mining roadway 2 and the second mining roadway 4 are arranged alternately along the extension direction of the main roadway 6 of the panel area, and their extension directions are consistent.

[0097] The first borehole 1 and the second borehole 5 are both located in the coal and rock stratum 3. The first borehole 1 extends from the first mining roadway 2 toward the second mining roadway 4, and the second borehole 5 extends from the main roadway 6 of the panel toward the first borehole 1. The opening of the first borehole 1 is the lowest position of the first borehole 1, and the lowest position of the second borehole 5 is connected to the position of the first borehole 1 that is higher than the opening of the first borehole 1.

[0098] The technical advantages of the gas extraction system for downhole drilling according to the embodiments of the present invention are the same as those of the gas extraction method for downhole drilling described above, and will not be repeated here.

[0099] like Figures 1 to 4 As shown, in some embodiments, the height of the central axis of the first borehole 1 to the bottom of the coal and rock layer 3 gradually increases along the direction from the first mining roadway 2 to the second mining roadway 4, the height of the central axis of the second borehole 5 to the bottom of the coal and rock layer 3 gradually decreases along the direction from the main roadway 6 of the panel to the first borehole 1, and the length of the second borehole 5 is greater than the length of the first borehole 1.

[0100] The second borehole 5 is a downward borehole, while the first borehole 1 is designed as an upward borehole. The opening of the first borehole 1 is its lowest point. The lowest point of the second borehole 5 connects to a structure located above the opening of the first borehole 1. This allows water accumulated in the second borehole 5 to flow into the first borehole 1 under gravity and then along the first borehole 1 to its opening for discharge. Furthermore, because the length of the second borehole 5 is greater than the length of the first borehole 1, this combined structural design allows for the use of a shorter borehole to replace a dedicated drainage and slag removal device for draining long boreholes, reducing drainage and slag removal costs and construction difficulty.

[0101] like Figures 1 to 4 As shown, in some embodiments, a first grouting section (not shown in the figure) is provided in the first borehole 1, the length of which is less than the length of the first borehole 1. A second grouting section (not shown in the figure) is provided in the second borehole 5, the length of which is less than the length of the second borehole 5. This not only seals the first borehole 1 and the second borehole 5, but also enhances their pressure resistance and structural stability.

[0102] The gas extraction system for the downhole drilling also includes a first steel pipe, a first valve, a mine drainage system, a second steel pipe, a second valve, and an underground extraction system (not shown in the figure).

[0103] In this system, at least a portion of the first steel pipe is fitted into the first grouting section and extends axially along the first borehole 1. The portion of the first steel pipe near the bottom of the first borehole 1 is connected to the first borehole 1. A first valve is installed at the end of the first steel pipe near the opening of the first borehole 1. The first borehole 1 has a drainage mode and a extraction mode. In the drainage mode, the first valve is connected to the mine drainage system. The first borehole 1 has two functions: assisting the drainage of the second borehole 5 and promoting the continued extraction of gas from the second borehole 5 during the gas extraction depletion period. While ensuring the gas extraction effect of the second borehole 5, it simplifies the overall structure of the gas extraction system of the descending borehole.

[0104] In this configuration, at least a portion of the second steel pipe is fitted into the second grouting section and extends axially along the second borehole 5. The portion of the second steel pipe adjacent to the bottom of the second borehole 5 is connected to the second borehole 5. A second valve is installed at the end of the second steel pipe adjacent to the opening of the second borehole 5. The second borehole 5 has a second extraction mode. In the first extraction mode, the first valve is connected to the downhole extraction system and the second valve is closed. In the second extraction mode, the first valve is closed and the second valve is connected to the downhole extraction system.

[0105] like Figures 1 to 3 As shown, in some embodiments, the gas extraction system of the downhole borehole also includes a downhole compressed air system (not shown in the figure), the second borehole 5 also has a dammed mode, the second valve is connected to the downhole compressed air system in both the drainage mode and the dammed mode, and the first valve is closed in the dammed mode.

[0106] like Figure 1 As shown, in some embodiments, the gas extraction system of the downhole borehole also includes a cavity 7, which is located at the intersection of the first borehole 1 and the second borehole 5. The diameter of the cavity 7 is larger than the diameter of the first borehole 1 and the second borehole 5, which reduces the accuracy requirements for the docking construction of the first borehole 1 and the second borehole 5 and facilitates the docking between the two.

[0107] There are multiple second boreholes 5, which are spaced apart along the extension direction of the main roadway 6 in the panel area. There are multiple holes 7, which are spaced apart along the extension direction of the first borehole 1. The holes 7 correspond one-to-one with the second boreholes 5.

[0108] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0109] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0110] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0111] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0112] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0113] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for gas extraction in a downburst borehole, characterized in that, Includes the following steps: The first borehole is constructed in the first mining roadway towards the second mining roadway, with the borehole opening at the lowest point of the first borehole. The second borehole is constructed in the main roadway of the panel to drill the second borehole into the coal and rock strata, and the lowest position of the second borehole is connected to the position of the first borehole above the opening of the first borehole, and the second borehole is subjected to segmented fracturing. The second borehole is used for drainage, and the water accumulated in the second borehole is discharged into the mine drainage system through the first borehole. The second borehole is used for gas extraction; the downhole extraction system is connected to the second borehole for gas extraction. The gas extraction method for the downhole also includes a step following the second borehole extraction operation: The second borehole was blocked, and the gas extraction volume in the second borehole was... ≤0.25 At that time, the downhole compressed air system is connected to the second borehole and gas is injected to plug the hole, wherein, This is the initial gas extraction rate of the second borehole; The first borehole is used for gas extraction, and the connection between the downhole extraction system and the second borehole is cut off. The downhole extraction system is connected to the first borehole for gas extraction. Repeat the second borehole slugging and the first borehole extraction operation until the gas extraction of the coal and rock strata is completed. The first drilling operation is as follows: A directional drilling rig constructs the first borehole in the coal and rock strata along the direction from the first mining roadway toward the second mining roadway. Hydraulic cavitation is performed at set intervals along the extension direction of the first borehole to form cavities. A first steel pipe is coaxially arranged in the first borehole. The outer circumferential surface of the first steel pipe and the inner circumferential surface of the first borehole are spaced apart and together define a first sealing channel. A first valve is installed at the end of the first steel pipe near the opening of the first borehole. The portion of the first steel pipe near the bottom of the first borehole is connected to the first borehole and used to transport water and gas. Grouting is performed on the first sealing channel to form a first grouting section, the length of which is less than the length of the first sealing channel.

2. The gas extraction method for downburst drilling according to claim 1, characterized in that, The second drilling operation is as follows: The directional drilling rig constructs multiple second boreholes in the main roadway of the panel to drill multiple second boreholes in the coal and rock strata. The multiple second boreholes are arranged at intervals along the extension direction of the main roadway of the panel and correspond one-to-one with the holes and are directionally connected within a set distance from the first borehole. The first valve is closed, and a segmented fracturing tool string is placed in the second borehole along the extension direction of the second borehole. The segmented fracturing tool string is connected to a high-pressure water pump. The high-pressure water pumped by the high-pressure water pumps the second borehole in segments and creates fracturing cracks on the peripheral wall surface of the second borehole. Remove the segmented fracturing tool string, and coaxially arrange a second steel pipe in the second borehole. The outer circumferential surface of the second steel pipe and the inner circumferential surface of the second borehole are spaced apart and together define a second sealing channel. A second valve is installed at the end of the second steel pipe near the borehole opening of the second borehole. The portion of the second steel pipe near the bottom of the second borehole is connected to the second borehole and used to transport gas and water. Grouting is performed on the second sealing channel to form a second grouting section, the length of which is less than the length of the second sealing channel.

3. The gas extraction method for downburst drilling according to claim 2, characterized in that, The second borehole drainage operation is as follows: When the first valve is opened, the first borehole is connected to the mine drainage system, and the water accumulated in the second borehole is discharged into the mine drainage system through the first borehole to achieve initial drainage. The second borehole is connected to the underground compressed air system through the second valve. Gas from the underground compressed air system is injected into the second borehole. The gas forces the water in the fracture and the cavity into the mine drainage system through the first borehole to achieve secondary drainage. The first valve and the second valve are closed.

4. The gas extraction method for downburst drilling according to claim 2 or 3, characterized in that, The second borehole extraction operation is as follows: When the second valve is opened, the downhole extraction system is connected to the second borehole for gas extraction. The first valve is opened periodically to drain water from the first and second boreholes.

5. A gas extraction system for downburst drilling, characterized in that, include: The first mining roadway, the main roadway of the panel, and the second mining roadway are connected sequentially. One of the main roadway and the first mining roadway extends along the strike of the coal and rock strata, and the other extends along the dip of the coal and rock strata. The first mining roadway and the second mining roadway are spaced apart along the extension direction of the main roadway, and their extension directions are consistent. The first borehole and the second borehole are both located in the coal and rock strata. The first borehole extends from the first mining roadway toward the second mining roadway, and the second borehole extends from the main roadway of the panel toward the first borehole. The opening of the first borehole is the lowest point of the first borehole, and the lowest point of the second borehole is connected to the position of the first borehole that is higher than the opening of the first borehole.

6. The gas extraction system for downburst drilling according to claim 5, characterized in that, The height of the centerline of the first borehole to the bottom of the coal and rock stratum gradually increases along the direction from the first mining roadway to the second mining roadway, and the height of the centerline of the second borehole to the bottom of the coal and rock stratum gradually decreases along the direction from the main roadway of the panel to the first borehole. The length of the second borehole is greater than the length of the first borehole.

7. The gas extraction system for downburst drilling according to claim 5, characterized in that, The first borehole is provided with a first grouting section, the length of which is less than the length of the first borehole; the second borehole is provided with a second grouting section, the length of which is less than the length of the second borehole. The gas extraction system for the downhole drilling also includes: A first steel pipe, a first valve, and a mine drainage system, wherein at least a portion of the first steel pipe is fitted into the first grouting section and extends axially along the first borehole; a portion of the first steel pipe adjacent to the bottom of the first borehole communicates with the first borehole; the first valve is installed at the end of the first steel pipe adjacent to the orifice of the first borehole; the first borehole has a drainage mode and a first extraction mode; and the first valve communicates with the mine drainage system in the drainage mode. A second steel pipe, a second valve, and a downhole extraction system are provided. At least a portion of the second steel pipe is fitted into the second grouting section and extends axially along the second borehole. The portion of the second steel pipe adjacent to the bottom of the second borehole is connected to the second borehole. The second valve is installed at the end of the second steel pipe adjacent to the orifice of the second borehole. The second borehole has a second extraction mode. In the first extraction mode, the first valve is connected to the downhole extraction system and the second valve is closed. In the second extraction mode, the first valve is closed and the second valve is connected to the downhole extraction system.

8. The gas extraction system for a downburst borehole according to any one of claims 5-7, characterized in that, The gas extraction system of the downhole also includes a cavity, which is located at the intersection of the first borehole and the second borehole, and the diameter of the cavity is larger than the diameter of the first borehole and the second borehole. The second boreholes are multiple and spaced apart along the extension direction of the main roadway of the panel, and the holes are multiple and spaced apart along the extension direction of the first boreholes, with each hole corresponding to one of the second boreholes.

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