Outburst prevention measures in coal seam gas pre

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Outburst prevention measures for coal seam gas pre extraction area by drilling along the seam in the mining face

I. purpose and significance of coal seam gas pre extraction in the mining face

according to the comprehensive gas management system, in order to improve the extraction rate, reduce the gas content, eliminate the blank zone in the mining face, achieve the purpose of outburst elimination, practically realize "no outburst", and fundamentally ensure the safe production of the mine, the gas control scheme in the mining face area is specially designed

II. The occurrence of coal seam II 1 in Pingyu No.4 coal mine

according to the work arrangement of safety production in No.4 coal mine and the deployment of gas regional governance of the group company, the occurrence of coal seams in the mine field was statistically analyzed. Since our mine only exploits the No.21 coal seam at present, according to the actual disclosure in the original production process and the relevant drilling data, we have analyzed and studied the No.21 coal seam, and learned its distribution law, distribution range, area, coal seam thickness change and other basic conditions in detail. Now it is described as follows:

from the drilling data and actual disclosure of the No.4 coal mine, the thickness of the No.21 coal seam in the No.4 coal mine varies and the occurrence is unstable

III. basic situation of 12190 mining face

12190 mining face is located in the east wing of the downhill of mining area II, adjacent to 11090 mining face and 11100 mining face waterproof coal pillars in the north, 12210 mining face (not excavated) in the south, and connected to the East Ι The hanging wall of the fault in the mining area breaks the coal intersection, and it is close to the protective coal pillar of the track down the mountain in the lower mining area II in the West. The elevation of the mining face is -314.20m ~ -364.121m, and the corresponding ground elevation is 240.8m ~ 259M. The coal seam No.21 is mined in this mining face. According to the exposure of the fan and fan tunnels, the coal seam in this mining face is unstable. The thickness of the coal seam gradually thickens from west to East, with a thickness of 1.8 ~ 7.3m. From the perspective of tendency, the thickness of the coal seam gradually thickens from north to south, with a thickness of 1.2m ~ 3.5. The thickness of the eastern coal seam is between 3.5m ~ 6.5m, with an average thickness of 4m

the design length and strike length of the mining face are 980m, the minable strike length is 720m, the mining length is 170m, and the minable reserves are 520000 tons. At present, the machine lane has been constructed to the design position, with a total length of 978 meters, and the remaining quantities of cutting holes are 170 meters

IV. design scheme of regional measures

1. Design scheme of pre drainage strip coal seam gas

12190 cutting hole high drainage roadway is designed to be arranged with a horizontal distance of 20 meters outside the 12190 cutting hole, which is located in the Dachang sandstone with a vertical distance of 10 meters above the coal seam roof. The design length of the high drainage roadway is 170m. After the construction is completed, the stable drainage drilling rig is used to drill through layer boreholes in the high drainage roadway, and the through layer boreholes are used to pre bleed the gas in the coal roadway. The design cross-section shape of high extraction roadway is semicircular arch, with a net cross-sectional area of 8.3m2; The net width of the roadway is 3.0m, the wall height is 1.4m, and the arch height is 1.5m. The support form is bolt and anchor support

during the construction of high extraction roadway, geophysical exploration and drilling are combined, and the measures to prevent accidental coal exposure are prepared to detect the coal seam horizon and the geological structure in front of the excavation head. At the same time, the geological survey department draws the expected profile of the high extraction roadway from the coal seam according to the detection, so as to grasp the horizon in time and reasonably adjust the drilling angle through the seam

use the high drainage roadway to drill through the layer to the construction position of the coal roadway, and use the hydraulic fracturing technology to carry out hydraulic fracturing on the coal seam, increase the permeability coefficient of the coal seam, improve the drainage effect of the through layer hole, timely conduct joint drainage on the constructed boreholes, achieve pre drainage of gas in advance, and ensure that the high drainage roadway is 100m ahead of the coal roadway, so as to achieve the purpose of outburst elimination before the construction of the coal roadway

2. Technical design scheme for pre drainage of strip coal seam gas through layer drilling

according to Article 4, section 6, Chapter VIII of the code for coal mine gas drainage, when the drilling volume of pre drainage of coal seam gas adopts through layer hole drainage, the spacing of coal spots in the drilling can be referred to: the coal seam is easy to be drained by 15 ~ 20 meters, the coal seam can be drained by 10 ~ 15 meters, and the coal seam is difficult to be drained by 8 ~ 10 meters. The permeability of coal seam No. 21 in our mine is poor, ranging from 0.0292 m2/(mpa2.d) ~ 0.0956 m2/(mpa2.d), which is a coal seam that is difficult to be pumped. The spacing of coal spots in boreholes should be controlled below 8 meters. At the same time, according to the actual situation of our mine, in order to effectively achieve the pumping effect, combined with the pumping half diameter (1 meter), and referring to the current Ping 5, through independent research and development and technological innovation, the hydraulic fracturing effect of coal mine No. 10 and coal mine No. 13, The coal breakthrough interval of 12190 cutting hole high extraction roadway through layer extraction borehole is determined to be 4 meters. Hydraulic fracturing should be carried out in advance before drilling through the layer in the high extraction roadway, so as to increase the drainage radius and improve the permeability of the coal seam, which can effectively improve the drainage effect

(1) drill holes are arranged below 1.3 meters from the roadway floor in the west side of 12190 and eye height extraction roadway. A group is arranged every 4 meters along the roadway excavation direction, with 7 holes in each group. The drill holes are perpendicular to the excavation direction of high extraction roadway. The bottom position controls that the left and right sides of the cut coal roadway are 15m respectively, and the total control width range is 34 meters (the designed clear width of the cut is 4.0 meters). The depression angle and length of the seven boreholes, the coal penetration point and the length of the coal seam are calculated and designed according to different bottoming positions. For details, see the design profile of the cross layer boreholes. After the coal is found in the borehole, it penetrates the whole coal seam and enters the coal seam floor for 0.3m

(2) the cross layer pumping and releasing drill is wrongly arranged, and it is not allowed to drill through and heavy, otherwise it will be regarded as invalid

(3) pumping

joint pumping shall be carried out after the completion of drilling construction, and one joint must be made to adhere to the continuity of pumping; See the attached table for the layout and design of boreholes

3. Hydraulic fracturing measures for 12190 cut hole high drainage roadway

in order to increase the permeability of the coal seam and increase the gas drainage effect of the coal seam, the area in the high drainage roadway where there is no construction of through-layer boreholes is first subject to hydraulic fracturing, and then the through-layer boreholes are constructed according to the original design, and the through-layer boreholes are jointly pumped, so as to improve the outburst prevention effect

(1) fracturing drilling arrangement

12190 cut hole high pumping roadway design and construction 170m, considering the 12190 machine roadway protruding point hole, the No. 1 hole is 132M away from the lower opening of the high pumping roadway, and the No. 2 hole is 8m away from the upper opening of the high pumping roadway, a total of 2 through laminar fracturing holes are designed and constructed. See the drilling layout for details

the drilling hole is located at the west side of 12190 cut hole high extraction roadway, and the construction drilling hole is below the middle waist line, which is perpendicular to the upper side of the roadway, 0.4m away from the roadway floor, with a depression angle of 270, using Ф 50mm drill pipe with Ф The 89mm drill bit drilled through the coal seam and entered the floor for 0.3m

(2) borehole depth

the fracturing object is the 12190 cut coal seam section fracturing. The borehole enters the coal seam section by 7.0m and the rock section by 18.6m, and the total depth of the fracturing hole is 25.9m. The fracturing borehole bottoming position is within the construction outline of 12190 air roadway and coal roadway. (see the figure below)

(3) fracturing hole sealing depth

this test selects the sealing depth of 18.6m, requiring the fracturing pipe to enter the coal seam for 1m, and seal the hole from the coal rock interface. The length of the rock sealing section is the whole rock section, and the hole is sealed with cement mortar

(4) type selection of water injection pump and pipeline

select P hong4 phase 2 project with rated pressure of 20MPa and rated flow of 80L. The estimated investment of the project is 4.94 billion yuan rb5a-80/20 emulsion pump for coal mine. In order to facilitate operation and control, the water injection pump is equipped with accessories such as pressure gauge, water meter and pressure relief valve, and the volume of the water tank is 2m3. Yhy60 (b) mine intrinsic safety digital pressure gauge is used as the pressure gauge

(5) the setting position of the fracturing pump

the fracturing pump is placed 100m outside the lower opening of the 12190 high pumping roadway. It is confirmed that the roadway has no ponding and the support form is good, which is convenient for personnel operation

but we should not consider too high and too low prices as much as possible

(6) fracturing parameters

adopt dynamic pressure water injection. It takes about 4 hours from the beginning of water injection to the end of hydraulic fracturing measures. The initial pressure is initially set at 10MPa, the pressure is increased by 2 MPa every 5min, and the pump pressure reaches about 20 MPa. After stabilizing for a period of time, the pressure drops rapidly, and the pressure does not rise significantly when continuously pressurized, and the gas concentration rises significantly. At this time, the pump can be stopped, the pressure relief valve can be closed, and the fracturing procedure is over

during the implementation of fracturing measures, the technician of the outburst prevention department will continuously record the water injection pressure and flow. According to the actual situation on site, the fracturing parameters can be adjusted in time after being reported to the downhole commander in chief and approved by the surface general manager

during the implementation of fracturing measures, the technician of the outburst prevention department will continuously record the water injection pressure and flow. According to the actual situation on site, the fracturing parameters can be adjusted timely after being reported to the downhole commander in chief and approved by the surface chief engineer

v. outburst prevention effect test of regional gas control measures

according to Article 55, section 4, Chapter III of the provisions on the prevention and control of coal and gas outburst, when the effect test of coal seam gas outburst prevention measures in the pre drainage section of the through hole is carried out, at least one inspection and test point is arranged at an interval of m in each coal roadway strip. According to the actual situation of our mine, an inspection and test point borehole is arranged every 50m in the 12190 cut high drainage roadway to test the residual gas pressure of the borehole. The specific hole layout requirements of the test holes: the test holes are arranged in the form of three holes. The No. 1 hole falls at the center of the coal roadway excavation face, the No. 2 hole falls at the top 13m of the coal roadway contour line, and the No. 3 hole falls at the bottom 13m of the coal roadway contour line. The spacing of the test holes is 50m, staggered layout, and full square testing

when the measured gas content of the residual coal seam is less than 0.74mpa, it indicates that the measure is effective. If not, it is considered that the measure is invalid, or the drill yard is densified within 100m around the front and back, and the through hole is constructed according to the design requirements and the joint drainage is carried out until the outburst hazard is eliminated. For details, please refer to the schematic diagram of 12190 cut hole high extraction pressure drill but dark and matte hole

layout plan of pressure measurement drill

v. safety technical measures for drilling through holes

(I) safety technical measures for power supply and electromechanical equipment management

1. The drill must undergo explosion-proof inspection before entering the well to ensure that the drill and supporting electrical equipment are in good condition without explosion

2. The power connection of the drilling rig should be approved by the mechanical and electrical department and contacted with the construction unit before it can be connected

3. The wiring process, joint and exposed length shall be strictly in accordance with the regulations, and the phenomenon of "chicken claw, sheep tail, open joint" and other deflagration shall be avoided

4. The cable shall be hung neatly, and the cable hook, switch and other electrical equipment shall be put on the shelf

5. During underground operation, it is not allowed to carry out live maintenance and relocation of electrical equipment. The equipment is chartered to people to prevent explosion loss

6. Pay attention to moisture-proof for electrical equipment such as motors and switches, and put desiccant regularly

7. Regularly measure the insulation of motor switches and cables; The electrical equipment should be overhauled regularly to ensure that the equipment is in good condition, and the explosion-proof inspection should be strengthened to prevent electrical explosion

8. When washing dust, do not wash dust against motor switches, cables and other electrical equipment

9. Wind power and gas power locking devices must be installed to ensure normal use

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