Pressure Relief Method and Application for Remaining Coal Pillars in Upper Goaf Based on Controllable Shock Waves

Abstract

The present invention discloses a method for pressure relief of remaining coal pillars in the upper gob area based on controllable shock waves and its application. The method first analyzes the stress distribution law of the coal pillar floor to determine the influence area of the coal pillar stress on the mining of the lower coal seam; then arranges a plurality of electromagnetic radiation monitoring points in the roadways of the coal pillar influence area and the non-coal pillar influence area to monitor the real-time change of the electromagnetic radiation energy of the roadway surrounding rock; then drills holes from the ground surface to conduct controllable shock wave pre-splitting in the coal pillar and its roof rock stratum; finally, injects acetone solution to weaken the strength of the coal and rock strata in the pre-splitting range until it is monitored that the stress of the roadway surrounding rock in the coal pillar influence area is equal to or lower than the stress of the surrounding rock in the non-coal pillar influence area. In addition, this method is applied to extract the gas in the gob area. The present invention not only avoids the influence of stress concentration on the mining of the lower coal seam, but also has important significance for gas prevention and utilization.

Description

Technical Field

[0001] The present invention relates to the technical field of mine safety production, and particularly relates to a method and application for pressure relief of residual coal pillars in the upper goaf based on controllable shock waves. Background Art

[0002] Existing technologies all adopt methods such as borehole pressure relief and roof pre-splitting blasting for the lower coal seam, and do not fundamentally solve the influence of residual coal pillars on the mining of the lower coal seam. It is necessary to reduce the influence of coal pillars on the mining of the lower coal seam from the perspective of weakening the upper residual coal pillars. Summary of the Invention

[0003] Aiming at the deficiencies of the above-mentioned existing technologies, the present invention provides a method and application for pressure relief of residual coal pillars in the upper goaf based on controllable shock waves.

[0004] To solve the above technical problems, the technical solution adopted by the present invention is: A method for pressure relief of residual coal pillars in the upper goaf based on controllable shock waves, comprising the following steps:

[0005] Step 1: Analyze the stress distribution law of the coal pillar floor, and determine the influence area of the coal pillar stress on the mining of the lower coal seam. The process is as follows:

[0006] Step 1.1: Take the lower boundary of the coal pillar as the x-axis, the direction perpendicular to the coal pillar downward as the y-axis, and the center position or the left boundary point of the lower boundary of the coal pillar as the coordinate origin to establish a rectangular coordinate system;

[0007] Step 1.2: Obtain the coal pillar load distribution function q(x) by means of on-site measurement or theoretical analysis;

[0008] Step 1.3: Take a micro-segment with a distance of from the coordinate origin and a width of for research, where is any point in the coal and rock mass around the coal pillar floor, and x and y are the horizontal and vertical coordinates of this point in the rectangular coordinate system respectively; According to the semi-plane body theory, combined with formula (1), the vertical stress at any point M under the action of the load distribution function q(x) is obtained:

[0009] (1)

[0010] where a and b are the coordinate values of the two side boundary points of the coal pillar in the x direction respectively;

[0011] Step 1.4: Establish a mechanical model for stress transfer of the coal pillar floor, input the vertical stress formula (1), the load distribution function q(x), and the calculation range of the coal pillar floor into the model, and simulate through a mechanical analysis software to obtain the vertical stress distribution nephogram of the coal pillar floor, so as to determine the stress influence range of the upper coal pillar floor on the lower coal seam;

[0012] Step 1.5: If the stress at the floor of the coal pillar does not transfer to the lower coal seam to be mined, the coal pillar is not weakened; if the stress at the floor of the coal pillar affects the lower coal seam to be mined, then proceed to Step 2.

[0013] Step 2: According to the influence area of the coal pillar stress on the mining of the lower coal seam, arrange an electromagnetic radiation monitoring point every 5 m in the roadways of the coal pillar influence area and the non - coal pillar influence area, and use an electromagnetic radiation monitor to monitor the change of electromagnetic radiation energy of the surrounding rock of the roadway in real - time. The higher the stress on the coal and rock mass, the stronger the electromagnetic radiation signal of the coal and rock mass;

[0014] Step 3: Drill a hole from the ground surface and conduct controllable shock wave pre - splitting in the coal pillar and its roof rock layer. The process is as follows:

[0015] Step 3.1: Use a drill pipe to send the shock wave equipment to the first shock wave operation point at the bottom of the hole, that is, the position of the coal pillar, inject clear water into the hole, seal the hole mouth, and then turn on the power supply to conduct 4 - 8 times of shock wave operations on the shock wave operation point;

[0016] Step 3.2: Use a directional drill to retract the shock wave equipment to the second shock wave operation point in the hole, that is, 3 - 6 m above the coal pillar, and repeat Step 3.1 to complete the permeability - increasing operation of the second shock wave operation point.

[0017] Step 4: Withdraw the shock wave generating equipment, install an automatic hole - sealing device connected with a liquid injection rubber hose above the coal pillar in the drill hole, and connect the liquid injection rubber hose to the liquid injection system on the ground; after hole - sealing, inject acetone solution into the liquid injection pipeline to make the acetone solution produce physical and chemical reactions with the mineral crystals and cements of the coal body, thereby weakening the strength of the coal and rock layers in the pre - splitting range; until the stress of the surrounding rock of the roadway in the coal pillar influence area is equal to or lower than the stress of the surrounding rock in the non - coal pillar influence area through electromagnetic radiation monitoring. The process is as follows:

[0018] Step 4.1: Withdraw the shock wave generating equipment, install an automatic hole - sealing device connected with a liquid injection rubber hose above the coal pillar in the drill hole, and connect the liquid injection rubber hose to the liquid injection system on the ground; after hole - sealing, inject acetone solution into the liquid injection pipeline to make the acetone solution produce physical and chemical reactions with the mineral crystals and cements of the coal body, form several defects inside the coal seam, and thereby weaken the strength of the coal and rock layers in the pre - splitting range;

[0019] Step 4.2: Adopt the electromagnetic radiation monitoring method to inversely obtain the stress change situation under the coal pillar through the electromagnetic radiation intensity value;

[0020] Step 4.3: Monitor the stress change situation in the area under the coal pillar after being weakened by the acetone solution until the stress of the surrounding rock of the roadway under the coal pillar is equal to or lower than the stress of the surrounding rock in the non - coal pillar area.

[0021] Further, the mass concentration of the acetone solution is 2% - 5%.

[0022] On the other hand, the present invention also provides an application of the above - mentioned method for relieving pressure on the remaining coal pillars in the upper gob area based on controllable shock waves in the gas drainage of the gob area, which is specifically as follows:

[0023] After being treated by the method for relieving pressure on the remaining coal pillars in the upper gob area based on controllable shock waves, under the action of the controllable shock waves and the acetone solution, the pores and fissures in the coal pillars and the roof and floor rock strata develop; by using the method of hydraulic fracturing, the fissures are further promoted to develop until the fissures are connected with the gob area, creating conditions for gas evacuation; after the hydraulic fracturing is completed, under the action of the ground drainage negative pressure, gas is extracted through the boreholes.

[0024] Further, the process of extracting gas through boreholes under the action of the ground drainage negative pressure is as follows:

[0025] S1: After the hydraulic fracturing is completed, drain the liquid in the hole, install the gas drainage pipeline. Under the action of the ground drainage negative pressure, the gas gathers towards the borehole area along the fissures in the coal pillars and the roof rock strata, and the gas in the gob area is extracted through the gas extraction pipeline.

[0026] S2: If it is found that the gas drainage effect is not good, continue to use hydraulic fracturing or inject acetone solution to further improve the gas permeability of the coal pillars and the roof rock strata.

[0027] The beneficial effects of adopting the above - mentioned technical solutions are as follows:

[0028] 1. The method provided by the present invention conducts controllable shock wave pre - fracturing on the remaining upper coal pillars and a certain range of rock strata of their roof and floor, and uses acetone solution to further weaken the coal rock mass. The stress concentration degree at the bottom of the coal pillar is significantly reduced, avoiding the influence of stress concentration on the mining of the lower coal seam.

[0029] 2. After adopting the present invention, when the lower working face is mined to the area affected by the coal pillar, on the one hand, it can reduce the superposition effect of the coal pillar stress and the advanced abutment pressure of the working face, and reduce the stress concentration degree of the advanced abutment stress; on the other hand, it can avoid the accident of coal pillar roof cutting and support pressing when the working face is mined to the boundary of the coal pillar. For the special - condition mining under the upper coal pillar, the strata pressure behavior in the working face and the advanced area is well controlled.

[0030] 3. The present invention also provides an application of the method for relieving pressure on the remaining coal pillars in the upper gob area based on controllable shock waves in the gas drainage of the gob area. After the coal pillar is pre - fractured and pressure - relieved by the controllable shock wave borehole, it can also be used for gas drainage in the upper coal seam gob area, which is of great significance for gas prevention and utilization. Description of the Drawings

[0031] Figure 1Flow chart of the method for relieving pressure on the remaining coal pillars in the upper goaf based on controllable shock waves in the embodiments of the present invention;

[0032] Figure 2 Plan view of the relative position relationship among the upper coal pillar, the goaf and the lower working face in the embodiments of the present invention;

[0033] Figure 3 Schematic diagram of the pre - splitting situation of controllable shock waves in the embodiments of the present invention;

[0034] Figure 4 Mechanical model of stress transfer at the bottom of the coal pillar in the embodiments of the present invention.

[0035] Among them, 1 - coal pillar in the upper coal seam; 2 - goaf in the upper coal seam; 3 - roadway for coal mining in the lower coal seam; 4 - borehole for controllable shock waves; 5 - fissures generated by controllable shock waves; 6 - boundary of the stress influence range at the bottom of the upper coal seam. Specific implementation manners

[0036] The following further describes the specific implementation manners of the present invention in detail with reference to the drawings and embodiments. The following embodiments are used to illustrate the present invention, but do not limit the scope of the present invention.

[0037] Taking the multi - seam mining of a certain coal mine as an example, the specific implementation process of the method of the present invention is clarified. The depth of the coal seam in a certain coal mine is 500 m, and the average coal thickness is 4.8 m. The dip length of the 8101 working face is 200 m, and the strike length is 1000 m. The fully - mechanized full - thickness coal mining method is used for mining. There are two goafs perpendicular to it above the working face. The direct overlying of the goaf is a 40 - m sectional coal pillar. The relative position relationship is as Figure 2 and Figure 3 shown. The remaining coal pillars in the upper part can have an important impact on the mining of the lower coal seam.

[0038] As Figure 1 shown, the method for relieving pressure on the remaining coal pillars in the upper goaf based on controllable shock waves in this embodiment is as follows.

[0039] Step 1: Analyze the stress distribution law at the bottom of the coal pillar, and determine the influence area of the coal pillar stress on the mining of the lower coal seam. The process is as follows:

[0040] Step 1.1: Take the lower boundary of the coal pillar as the x - axis, the direction perpendicular to the coal pillar downward as the y - axis, and the center position or the left - hand boundary point of the lower boundary of the coal pillar as the coordinate origin to establish a rectangular coordinate system;

[0041] Step 1.2: Use the method of on - site measurement or theoretical analysis to obtain the coal pillar load distribution function q(x);

[0042] In this embodiment, the coal pillar load shows a "double - peak" distribution. As Figure 4 shown, take the horizontal direction of the coal seam floor as The shaft, with the vertical direction being the shaft, taking the center position of the coal seam floor as the coordinate origin, a rectangular coordinate system is established. At this time, the width of the sectional coal pillar is relatively large, and the load distribution function q(x) is as follows:

[0043]

[0044] Wherein, — The load distribution function when the width of the sectional coal pillar is relatively large; — The stress concentration coefficient at the peak stress of the coal pillar, with a value of 4; — The unit weight of the rock, 2500 Kg / m 3 ; — The burial depth is 300 m; — The distance between the peak stress point of the coal pillar and the center of the coal pillar is 7 m; — The distances from the two boundaries of the stable stress area in the middle of the coal pillar to the center of the coal pillar are 9 m; — The distances from the two boundaries of the coal pillar to the center of the coal pillar are 10 m; is the stress concentration coefficient of the stable stress area in the middle of the coal pillar when the width of the sectional coal pillar is relatively large, with a value of 2.

[0045] Step 1.3: Take a micro-segment with a distance of from the coordinate origin and a width of for research, where is any point in the coal and rock mass around the coal pillar floor, and x and y are the horizontal and vertical coordinates of this point in the rectangular coordinate system respectively; according to the semi-plane body theory, combined with formula (1), the vertical stress at any point M under the action of the load distribution function q(x) is obtained:

[0046] (1)

[0047] Wherein, a and b are the coordinate values of the two boundary points on the coal pillar in the x direction respectively;

[0048] Step 1.4: Establish a mechanical model for the stress transfer of the coal pillar floor, input the vertical stress formula (1), the load distribution function q(x), and the calculation range of the coal pillar floor into the model, and through mechanical analysis software, simulate to obtain the vertical stress distribution nephogram of the coal pillar floor, so as to determine the stress influence range of the upper coal pillar floor on the lower coal seam;

[0049] Step 1.5: If the stress of the coal pillar floor does not transfer to the lower coal seam to be mined, the coal pillar is not weakened; if the stress of the coal pillar floor affects the lower coal seam to be mined, then step 2 is executed.

[0050] Step 2: According to the influence area of the coal pillar stress on the extraction of the lower coal seam, electromagnetic radiation monitoring points are arranged every 5 m in the roadways of the coal pillar influence area and the non-coal pillar influence area, and an electromagnetic radiation monitor is used to monitor the change of electromagnetic radiation energy of the surrounding rock of the roadway in real time. The higher the stress on the coal and rock mass, the stronger the electromagnetic radiation signal of the coal and rock mass;

[0051] Step 3: Drill holes from the ground surface, and conduct controllable shock wave pre-splitting in the coal pillar and its roof rock stratum. The pre-splitting situation is as Figure 3 shown, and the process is as follows:

[0052] Step 3.1: Use a drill pipe to send the shock wave equipment to the first shock wave operation point at the bottom of the hole, that is, the coal pillar position, inject clear water into the hole, seal the hole mouth, and then turn on the power supply to conduct 8 shock wave operations on the shock wave operation point;

[0053] Step 3.2: Use a directional drill to retract the shock wave equipment to the second shock wave operation point in the hole, that is, 5 m above the coal pillar, and repeat Step 3.1 to complete the permeability enhancement operation of the second shock wave operation point.

[0054] Step 4: Withdraw the shock wave generating equipment, install an automatic hole sealer connected with a liquid injection rubber hose above the coal pillar in the drill hole, and connect the liquid injection rubber hose to the liquid injection system on the ground; after hole sealing, inject acetone solution into the liquid injection pipeline to make the acetone solution produce physical and chemical reactions with the mineral crystals and cements of the coal body, so as to weaken the strength of the coal and rock strata in the pre-splitting range; until the stress of the surrounding rock of the roadway in the coal pillar influence area is equal to or lower than the stress of the surrounding rock in the non-coal pillar influence area through electromagnetic radiation monitoring. The process is as follows:

[0055] Step 4.1: Withdraw the shock wave generating equipment, install an automatic hole sealer connected with a liquid injection rubber hose above the coal pillar in the drill hole, and connect the liquid injection rubber hose to the liquid injection system on the ground; after hole sealing, inject acetone solution into the liquid injection pipeline to make the acetone solution produce physical and chemical reactions with the mineral crystals and cements of the coal body, form several defects inside the coal seam, and thus weaken the strength of the coal and rock strata in the pre-splitting range;

[0056] Step 4.2: Adopt the electromagnetic radiation monitoring method to inversely obtain the stress change situation under the coal pillar through the electromagnetic radiation intensity value;

[0057] Step 4.3: Monitor the stress change situation in the area under the coal pillar after being weakened by the acetone solution until the stress of the surrounding rock of the roadway under the coal pillar is equal to or lower than the stress of the surrounding rock in the non-coal pillar area.

[0058] Further, the mass concentration of the acetone solution is 2%.

[0059] On the other hand, this embodiment also provides an application of a method for relieving pressure on the remaining coal pillars in the upper goaf based on controllable shock waves in the gas drainage from the goaf, which is specifically as follows:

[0060] After being treated by the method for relieving pressure on the remaining coal pillars in the upper goaf based on controllable shock waves, under the action of the controllable shock waves and acetone solution, the pores and fissures in the coal pillars and the roof and floor rock strata develop; the hydraulic fracturing method is adopted to promote the further development of the fissures until the fissures are connected with the goaf, creating conditions for gas evacuation; after the hydraulic fracturing is completed, under the action of the ground drainage negative pressure, gas is extracted through the boreholes.

[0061] Furthermore, the process of extracting gas through boreholes under the action of the ground drainage negative pressure is as follows:

[0062] S1: After the hydraulic fracturing is completed, drain the liquid in the borehole, install the gas drainage pipeline. Under the action of the ground drainage negative pressure, the gas accumulates in the borehole area along the fissures in the coal pillars and the roof rock strata, and the gas in the goaf is extracted through the gas drainage pipeline;

[0063] S2: If it is found that the gas drainage effect is not good, continue to use hydraulic fracturing or inject acetone solution to further improve the gas permeability of the coal pillars and the roof rock strata.

Claims

1. A method for pressure relief of remaining coal pillars in the upper gob area based on controllable shock waves, characterized in that, It includes the following steps: Step 1: Analyze the stress distribution law of the coal pillar floor, and determine the influence area of the coal pillar stress on the mining of the lower coal seam; Step 1.1: Take the lower boundary of the coal pillar as the x-axis, the direction vertically downward of the coal pillar as the y-axis, and the center position of the lower boundary of the coal pillar or the left boundary point as the coordinate origin to establish a rectangular coordinate system; Step 1.2: Use the method of on-site measurement or theoretical analysis to obtain the coal pillar load distribution function q(x); Step 1.3: Take a micro-segment with a distance of from the coordinate origin and a width of for research, where is an arbitrary point in the coal and rock mass around the coal pillar floor, and x and y are the horizontal and vertical coordinates of this point in the rectangular coordinate system respectively; according to the semi-plane body theory, the vertical stress at any point M under the action of the load distribution function q(x) is obtained by combining formula (1): (1) where a and b are the coordinate values of the two side boundary points of the coal pillar in the x direction respectively; Step 1.4: Establish a mechanical model for the stress transfer of the coal pillar floor, input the vertical stress formula (1), the load distribution function q(x), and the calculation range of the coal pillar floor into the model, and simulate through a mechanical analysis software to obtain the vertical stress distribution nephogram of the coal pillar floor, so as to determine the stress influence range of the upper coal pillar floor on the lower coal seam; Step 1.5: If the stress of the coal pillar floor does not transfer to the lower coal seam to be mined, the coal pillar is not weakened; if the stress of the coal pillar floor affects the lower coal seam to be mined, then execute Step 2; Step 2: According to the influence area of the coal pillar stress on the mining of the lower coal seam, arrange an electromagnetic radiation monitoring point every 5 m in the roadways of the coal pillar influence area and the non-coal pillar influence area, and use an electromagnetic radiation monitor to monitor the change of the electromagnetic radiation energy of the roadway surrounding rock in real time. The higher the stress on the coal and rock mass, the stronger the electromagnetic radiation signal of the coal and rock mass; Step 3: Drill holes from the ground surface and conduct controlled shock wave pre-fracturing in the coal pillar and its roof rock strata; Step 4: Withdraw the shock wave generating equipment, install an automatic hole sealer connected with a liquid injection rubber tube above the coal pillar in the drill hole, and connect the liquid injection rubber tube with the ground liquid injection system; after sealing the hole, inject acetone solution into the liquid injection pipeline, so that the acetone solution produces physical and chemical effects with the mineral crystals and cements of the coal body, thereby weakening the strength of the coal and rock strata in the pre-fractured range; until the stress of the roadway surrounding rock in the coal pillar influence area is equal to or lower than the stress of the surrounding rock in the non-coal pillar influence area monitored by electromagnetic radiation; Step 4.1: Withdraw the shock wave generating equipment, install an automatic hole sealer connected with a liquid injection rubber tube above the coal pillar in the drill hole, and connect the liquid injection rubber tube with the ground liquid injection system; after sealing the hole, inject acetone solution into the liquid injection pipeline, so that the acetone solution produces physical and chemical effects with the mineral crystals and cements of the coal body, forming several defects inside the coal seam, thereby weakening the strength of the coal and rock strata in the pre-fractured range; Step 4.2: Adopt the electromagnetic radiation monitoring method, and inversely obtain the stress change situation under the coal pillar through the electromagnetic radiation intensity value; Step 4.3: Monitor the stress change situation in the area under the coal pillar after being weakened by the acetone solution until the stress of the roadway surrounding rock under the coal pillar is equal to or lower than the stress of the surrounding rock in the non-coal pillar influence area.

2. The method for pressure relief of remaining coal pillars in the upper gob area based on controllable shock waves according to claim 1, characterized in that The process of Step 3 is as follows: Step 3.1: Use a drill rod to send the shock wave equipment to the first shock wave operation point at the bottom of the hole, that is, the coal pillar position, inject clear water into the hole, seal the hole mouth, and then turn on the power supply to conduct 4 - 8 times of shock wave operations on the shock wave operation point; Step 3.2: Use the directional drilling rig to retract the shock wave device to the second shock wave operation point in the hole, that is, 3 - 6 m above the coal pillar, and repeat Step 3.1 to complete the permeability enhancement operation at the second shock wave operation point.

3. The method for pressure relief of remaining coal pillars in the upper gob area based on controllable shock waves according to claim 1, characterized in that The mass concentration of the acetone solution is 2% - 5%.

4. Application of the method for pressure relief of remaining coal pillars in the upper goaf based on controllable shock waves according to any one of claims 1 to 3 in the gas drainage in the goaf, characterized in that: After treatment by the method of pressure relief of the remaining coal pillar in the upper goaf based on controllable shock waves, under the action of the controllable shock waves and the acetone solution, the pores and fractures of the coal pillar and the roof rock formation develop; the hydraulic fracturing method is adopted to promote the further development of the fractures until the fractures are connected with the goaf, creating conditions for gas evacuation; after the hydraulic fracturing is completed, under the action of the ground drainage negative pressure, gas is extracted by using boreholes.

5. The application according to claim 4, characterized in that Under the action of the ground drainage negative pressure, the process of gas extraction by using boreholes is as follows: S1: After the hydraulic fracturing is completed, drain the liquid in the hole, install the gas drainage pipeline. Under the action of the ground drainage negative pressure, gas accumulates from the fractures of the coal pillar and the roof rock formation to the borehole area, and the gas in the goaf is extracted through the gas extraction pipeline. S2: If it is found that the gas drainage effect is not good, continue to use hydraulic fracturing or inject acetone solution to further improve the gas permeability of the coal pillar and the roof rock formation.

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