High-gas coal seam gas extraction drill hole sealing method

Abstract

The invention discloses a high-gas coal seam gas extraction drill hole sealing method which comprises the following steps: injecting a grouting material containing multiple types of microbiologic bacteria into a sealing space, on one hand, injecting the grouting material into a grouting space in a constant pressure injection mode, and filling hole cracks around a drill hole with slurry in a free seepage mode; then, the slurry diffusion range is enlarged in a pulse mode; on the other hand, the diagenesis effect of the aerobic bacteria and the anaerobic bacteria is utilized, generated carbonate can effectively block fractures around the extraction drill hole in the continuous extraction period, the activity of various microbiological bacteria is improved in a subsequent nutrient solution injection mode, different bacteria are matched with one another, and the effect of improving the extraction efficiency is achieved. Therefore, it is guaranteed that at least one kind of bacteria is in the active stage in each gas extraction period, the fracture plugging effect is improved and the air leakage probability is reduced by continuously generating new carbonate, finally, the hole sealing quality in the gas extraction process is effectively kept, and the gas extraction efficiency is improved.

Description

Technical Field

[0001] The invention relates to a method for sealing a borehole for gas extraction in a high-gas coal seam, and belongs to the technical field of reducing the air leakage rate of a borehole and efficiently extracting gas in a deep high-gas coal seam. Background Art

[0002] In order to ensure the safe mining of coal resources, gas extraction is currently mostly carried out by drilling a large number of holes in the coal seam. After drilling, the in-situ stress balance of the coal seam is destroyed, the free gas in the coal seam can flow into the borehole, and the adsorbed gas begins to desorb in large quantities and diffuse into the fracture structure, forming a certain gas flow field. However, in the subsequent gas extraction process, the continuously decreasing pore pressure may cause the closure of the coal matrix pore fracture structure around the borehole, and at the same time, the fracture circle around the extraction borehole will continue to expand under the action of ground stress.

[0003] The pore structure of the coal matrix around the gas extraction borehole will cause air leakage, which will eventually cause the negative pressure in the extraction borehole to be unstable, affecting the gas extraction effect. For this reason, technical methods such as secondary grouting of gas extraction boreholes have been proposed to seal the pore and fissure structure around the borehole, but the secondary grouting method often has the problem that the solidification of the primary grouting material hinders the flow of the secondary grouting slurry into the new fissures, thus failing to fundamentally solve the problem of air leakage in the borehole. In view of this, it is urgent to develop a new gas extraction borehole sealing method that can effectively maintain the sealing quality during the gas extraction process and thereby ensure the efficiency of gas extraction, which is the research direction required by the present invention. Summary of the invention

[0004] In view of the problems existing in the above-mentioned prior art, the present invention provides a method for sealing drilling holes for gas extraction in high-gas coal seams, which utilizes bacteria to produce carbonate to continuously accumulate and seal newly generated cracks, and can effectively maintain the sealing quality during the gas extraction process, thereby ensuring the efficiency of gas extraction.

[0005] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a method for sealing a drilling hole for gas extraction in a high-gas coal seam, the specific steps of which are:

[0006] A. Drill gas extraction holes to the designed depth in the air intake and return tunnels toward the target coal seam.

[0007] B. The gas extraction pipe is extended into the gas extraction borehole, and the first plugging device, the second plugging device and the third plugging device are installed on the outside of the gas extraction pipe, and the first plugging device is farthest from the hole opening, and the third plugging device is closest to the hole opening; then one end of the grouting pipe is passed through the third plugging device and the second plugging device in sequence from the hole opening to extend between the second plugging device and the first plugging device; the grouting pipe part between the second plugging device and the first plugging device is a pressure connecting pipe, which can be automatically disconnected when the pressure reaches P2; one end of the first return slurry pipe is passed through the third plugging device and the second plugging device in sequence from the hole opening to extend between the second plugging device and the first plugging device; one end of the second return slurry pipe is passed through the third plugging device from the hole opening to extend between the third plugging device and the second plugging device; both the first return slurry pipe and the second return slurry pipe are equipped with valves.

[0008] C. Inject high-pressure water into the first plugging device, the second plugging device and the third plugging device respectively to make them expand and deform and squeeze the gas extraction borehole, thereby forming a first grouting space between the first plugging device and the second plugging device, and a second grouting space between the second plugging device and the third plugging device.

[0009] D. Start the grouting pump and inject the sealing material mixed with bacteria into the first grouting space through the grouting pipe in a static high-pressure manner and let it flow into the cracks around the borehole. The injection pressure is P1, and P1 is less than P2. When the sealing material flows out from the other end of the first return grouting pipe, close the valve of the first return grouting pipe and adjust the grouting pump to the pulse injection mode. Continue the pulse injection at the injection pressure of P1 for 2 hours and then stop the pulse injection.

[0010] E. Increase the power of the grouting pump to increase the grouting pressure to above P2. At this time, the pressure connecting pipe is disconnected under pressure, and then the grouting pressure is adjusted to P1. At this time, the sealing material mixed with bacteria is injected into the second grouting space from the disconnection point and flows into the cracks around the borehole; when the sealing material flows out of the second return slurry pipe, close the valve of the second return slurry pipe, and adjust the grouting pump to the pulse injection mode, and continue the pulse injection at the injection pressure of P1 for 2 hours and then stop the pulse injection.

[0011] F. After completion, connect the gas extraction pipe to the underground gas extraction network for networked extraction.

[0012] G. During the gas extraction process, the carbonates produced by the bacteria in the first grouting space and the second grouting space during metabolism can continue to accumulate in the cracks to fill and block the cracks. If new cracks are generated around the borehole due to ground stress, the bacteria will flow into the new cracks with the slurry and continue to produce carbonates in the current cracks to fill and block the new cracks, thereby continuously maintaining the sealing quality of the borehole and achieving efficient gas extraction.

[0013] Furthermore, the sealing material mixed with bacteria has a flexible sealing material as a matrix and is provided with a nutrient solution suitable for bacterial life, wherein the bacteria include aerobic bacteria and anaerobic bacteria.

[0014] Furthermore, after the sealing material mixed with bacteria is injected into the borehole, in the initial sealing stage, due to the high amount of oxygen inside the borehole, the aerobic bacteria are more active and continue to metabolize to produce carbonates; as the gas extraction time continues, the oxygen concentration in the borehole continues to decrease, and the anaerobic bacteria are more active and continue to metabolize to produce carbonates. The longer the extraction time, the stronger the activity of the anaerobic bacteria, thereby achieving adaptive filling and sealing of cracks throughout the gas extraction process.

[0015] Furthermore, the gas extraction borehole is a through-layer borehole, and its length in the coal seam is at least 40m.

[0016] Furthermore, the maximum expansion pressure of the first plugging device, the second plugging device and the third plugging device is 15 MPa.

[0017] Furthermore, the first plugging device, the second plugging device and the third plugging device are respectively located at a distance of 10m, 6m and 2m from the opening of the gas extraction borehole.

[0018] Furthermore, the injection pressure P1 is 1.5-2 MPa, the pulse frequency during pulse injection is 500-800 Hz, and the injection pressure P2 is 1.5 times of P1.

[0019] Furthermore, in the initial stage of gas extraction, if the negative pressure in the gas extraction borehole is lower than 20% of the set negative pressure, the nutrient solution required for aerobic bacteria is injected into the first grouting space and the second grouting space through the grouting pipe; in the middle and late stages of gas extraction, if the negative pressure in the gas extraction borehole is lower than 30% of the set negative pressure, the nutrient solution required for anaerobic bacteria is injected into the first grouting space and the second grouting space through the grouting pipe, thereby ensuring that at least one bacterium is in an active stage in each period of gas extraction.

[0020] Compared with the prior art, the present invention injects grouting materials containing multiple types of microorganisms into the plugging space. On the one hand, the grouting material is injected into the grouting space by a conventional pressure injection method, and the slurry is filled into the cracks around the borehole by a free seepage method, and then the slurry diffusion range is increased by a pulse method; on the other hand, the diagenesis of aerobic bacteria and anaerobic bacteria is respectively utilized, and the carbonate produced can effectively plug the cracks around the extraction borehole under a continuous extraction cycle, wherein the aerobic bacteria are more active due to more oxygen in the early stage of extraction, and the anaerobic bacteria are more active due to less oxygen in the middle and late stages of extraction, and the activity of multiple microorganisms is increased by a subsequent nutrient solution injection method, and the two bacteria cooperate with each other to ensure that at least one bacterium is in an active stage in each period of gas extraction, and the crack plugging effect is improved and the probability of air leakage is reduced by continuously producing new carbonates, and finally the sealing quality of the gas extraction process is effectively maintained, and the gas extraction efficiency is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the construction layout of the present invention.

[0022] In the figure: 1-target coal seam, 2-gas extraction borehole, 3-third plugging device, 4-second plugging device, 5-first plugging device, 6-grouting pipe, 7-second slurry return pipe, 8-first slurry return pipe, 9-gas extraction pipe, 10-first grouting space, 11-pressure connecting pipe. DETAILED DESCRIPTION

[0023] The present invention will be further described below.

[0024] like Figure 1 As shown, the specific steps of the present invention are:

[0025] A. Construct gas extraction borehole 2 in the air intake and return tunnels toward the target coal seam 1 to the designed depth.

[0026] B. The gas extraction pipe is extended into the gas extraction borehole 2, and the first plugging device 5, the second plugging device 4 and the third plugging device 3 are installed outside the gas extraction pipe 2, and the first plugging device 5 is farthest from the hole, and the third plugging device 3 is closest to the hole; then one end of the grouting pipe 6 is passed through the third plugging device 3 and the second plugging device 4 from the hole in sequence and extended between the second plugging device 4 and the first plugging device 5; the part of the grouting pipe 6 between the second plugging device 4 and the first plugging device 5 is a pressure connecting pipe 11, which can be automatically disconnected when the pressure reaches P2; one end of the first return slurry pipe 8 is passed through the third plugging device 3 and the second plugging device 4 from the hole in sequence and extended between the second plugging device 4 and the first plugging device 5; one end of the second return slurry pipe 7 is passed through the third plugging device 3 from the hole in sequence and extended between the third plugging device 3 and the second plugging device 4; the first return slurry pipe 8 and the second return slurry pipe 7 are both equipped with valves.

[0027] C. Inject high-pressure water into the first plugging device 5, the second plugging device 4 and the third plugging device 3 respectively to make them expand and deform and squeeze the gas extraction borehole 2, thereby forming a first grouting space 10 between the first plugging device 5 and the second plugging device 4, and a second grouting space between the second plugging device 4 and the third plugging device 3; the maximum expansion pressure of the first plugging device 5, the second plugging device 4 and the third plugging device 3 is 15MPa.

[0028] D. Start the grouting pump, and inject the sealing material mixed with bacteria into the first grouting space 10 through the grouting pipe 6 in a static high-pressure manner, and let it flow into the cracks around the borehole. The injection pressure is P1, and P1 is less than P2. When the sealing material flows out from the other end of the first return slurry pipe 8, close the valve of the first return slurry pipe 8, and adjust the grouting pump to a pulse injection mode, and continue the pulse injection at an injection pressure of P1 for 2 hours, and then stop the pulse injection.

[0029] E. Increase the power of the grouting pump to increase the grouting pressure to above P2. At this time, the pressure connecting pipe 11 is disconnected under pressure, and then the grouting pressure is adjusted to P1. At this time, the sealing material mixed with bacteria is injected into the second grouting space from the disconnection point and flows into the cracks around the borehole; when the sealing material flows out of the second return slurry pipe 7, close the valve of the second return slurry pipe 7, and adjust the grouting pump to a pulse injection mode, and continue the pulse injection at an injection pressure of P1 for 2 hours and then stop the pulse injection; the sealing material mixed with bacteria is based on a flexible sealing material and is provided with a nutrient solution suitable for bacterial life, and the bacteria include aerobic bacteria and anaerobic bacteria. After the sealing material mixed with bacteria is injected into the borehole, in the initial sealing stage, due to the high amount of oxygen inside the borehole, aerobic bacteria are more active and continue to metabolize to produce carbonates. As the gas extraction time continues, the oxygen concentration in the borehole continues to decrease, and anaerobic bacteria are more active and continue to metabolize to produce carbonates. The longer the extraction time, the stronger the activity of the anaerobic bacteria, thereby achieving adaptive filling and sealing of cracks throughout the gas extraction process.

[0030] F. After completion, the gas extraction pipe 9 is connected to the underground gas extraction pipe network for networked extraction.

[0031] G. During the gas extraction process, the carbonates produced by the bacteria in the first grouting space 10 and the second grouting space during metabolism can continue to accumulate in the cracks to fill and block the cracks. If new cracks are generated around the borehole due to ground stress, the bacteria will flow into the new cracks with the slurry and continue to produce carbonates in the current cracks to fill and block the new cracks, thereby continuously maintaining the sealing quality of the borehole and achieving efficient gas extraction.

[0032] As an improvement of the present invention, the gas extraction borehole 2 is a through-layer borehole, and its length in the coal seam is at least 40m. The distances between the first plugging device 5, the second plugging device 4 and the third plugging device 3 and the orifice of the gas extraction borehole 2 are 10m, 6m and 2m respectively. The injection pressure P1 is 1.5-2MPa, the pulse frequency during pulse injection is 500-800Hz, and the injection pressure P2 is 1.5 times P1.

[0033] As another improvement of the present invention, in the initial stage of gas extraction, if the negative pressure in the gas extraction borehole 2 is lower than 20% of the set negative pressure, the nutrient solution required for aerobic bacteria is injected into the first grouting space 10 and the second grouting space through the grouting pipe 6; in the middle and late stages of gas extraction, if the negative pressure in the gas extraction borehole 2 is lower than 30% of the set negative pressure, the nutrient solution required for anaerobic bacteria is injected into the first grouting space 10 and the second grouting space through the grouting pipe 6, thereby ensuring that at least one bacterium is in an active stage in each period of gas extraction.

[0034] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for sealing a borehole for gas extraction in a high-gas coal seam, characterized in that: The specific steps are: A. Drill gas extraction holes to the designed depth in the air intake and return tunnels toward the target coal seam; B. The gas extraction pipe is extended into the gas extraction borehole, and the first plugging device, the second plugging device and the third plugging device are installed on the outside of the gas extraction pipe, and the first plugging device is farthest from the hole, and the third plugging device is closest to the hole; then one end of the grouting pipe is passed through the third plugging device and the second plugging device from the hole in sequence and extended between the second plugging device and the first plugging device; the grouting pipe part between the second plugging device and the first plugging device is a pressure connecting pipe, which can be automatically disconnected when the pressure reaches P2; one end of the first slurry return pipe is passed through the third plugging device and the second plugging device from the hole in sequence and extended between the second plugging device and the first plugging device; one end of the second slurry return pipe is passed through the third plugging device from the hole in sequence and extended between the third plugging device and the second plugging device; valves are installed on the first slurry return pipe and the second slurry return pipe; C. Injecting high-pressure water into the first plugging device, the second plugging device and the third plugging device respectively to make them expand and deform and squeeze the gas extraction borehole, thereby forming a first grouting space between the first plugging device and the second plugging device, and forming a second grouting space between the second plugging device and the third plugging device; D. Start the grouting pump, and inject the sealing material mixed with bacteria into the first grouting space through the grouting pipe in a static high-pressure manner and flow it into the cracks around the borehole. The injection pressure is P1, and P1 is less than P2. When the sealing material flows out from the other end of the first return grouting pipe, close the valve of the first return grouting pipe, and adjust the grouting pump to a pulse injection mode, and continue the pulse injection at the injection pressure of P1 for 2 hours and then stop the pulse injection. E. Increase the power of the grouting pump to increase the grouting pressure to above P2. At this time, the pressure connecting pipe is disconnected under pressure, and then the grouting pressure is adjusted to P1. At this time, the sealing material mixed with bacteria is injected into the second grouting space from the disconnection point and flows into the cracks around the borehole; when the sealing material flows out of the second return grouting pipe, close the valve of the second return grouting pipe, and adjust the grouting pump to the pulse injection mode, and continue the pulse injection at the injection pressure of P1 for 2 hours before stopping the pulse injection; F. After completion, the gas extraction pipe is connected to the underground gas extraction pipe network for network extraction; G. During the gas extraction process, the carbonates produced by the bacteria in the first grouting space and the second grouting space during metabolism can continue to accumulate in the cracks to fill and block the cracks. If new cracks are generated around the borehole due to ground stress, the bacteria will flow into the new cracks with the slurry and continue to produce carbonates in the current cracks to fill and block the new cracks, thereby continuously maintaining the sealing quality of the borehole and achieving efficient gas extraction.

2. The method for sealing a borehole for gas extraction in a high-gas coal seam according to claim 1, characterized in that: The sealing material mixed with bacteria takes a flexible sealing material as a matrix and is provided with a nutrient solution suitable for bacterial life, wherein the bacteria include aerobic bacteria and anaerobic bacteria.

3. The method for sealing a borehole for gas extraction in a high-gas coal seam according to claim 2, characterized in that: After the sealing material mixed with bacteria is injected into the borehole, in the initial sealing stage, due to the high amount of oxygen inside the borehole, aerobic bacteria are more active and continue to metabolize to produce carbonates. As the gas extraction time continues, the oxygen concentration in the borehole continues to decrease, and anaerobic bacteria are more active and continue to metabolize to produce carbonates. The longer the extraction time, the stronger the activity of the anaerobic bacteria, thereby achieving adaptive filling and sealing of cracks throughout the gas extraction process.

4. The method for sealing a borehole for gas extraction in a high-gas coal seam according to claim 1, characterized in that: The gas extraction borehole is a through-layer borehole, and its length in the coal seam is at least 40m.

5. The method for sealing a borehole for gas extraction in a high-gas coal seam according to claim 1, characterized in that: The maximum value of the expansion pressure of the first plugging device, the second plugging device and the third plugging device is 15 MPa.

6. The method for sealing a borehole for gas extraction in a high-gas coal seam according to claim 1, characterized in that: The first plugging device, the second plugging device and the third plugging device are respectively located at a distance of 10m, 6m and 2m from the opening of the gas extraction borehole.

7. The method for sealing a borehole for gas extraction in a high-gas coal seam according to claim 1, characterized in that: The injection pressure P1 is 1.5-2 MPa, the pulse frequency during pulse injection is 500-800 Hz, and the injection pressure P2 is 1.5 times of P1.

8. The method for sealing a borehole for gas extraction in a high-gas coal seam according to claim 1, characterized in that: In the early stage of gas extraction, if the negative pressure in the gas extraction borehole is lower than 20% of the set negative pressure, the nutrient solution required by aerobic bacteria is injected into the first grouting space and the second grouting space through the grouting pipe; in the middle and late stages of gas extraction, if the negative pressure in the gas extraction borehole is lower than 30% of the set negative pressure, the nutrient solution required by anaerobic bacteria is injected into the first grouting space and the second grouting space through the grouting pipe, thereby ensuring that at least one bacterium is in an active stage in each period of gas extraction.

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