Hydraulic fracturing-enhanced drainage in Xinjing Mine, Yangquan City
Introduction
Xinjing coal mine is located in Yangquan City, Shanxi Province, with gas emission of 330m3/min and more than 150 coal and gas outbursts. The test coal seam is No. 3 coal seam of Shanxi Formation of Lower Permian, with a buried depth of about 600m and a thickness of 2.4m. The gas content of coal seam 3 is 12.87～15.95m3/t, with an average of 14.41 m3/t, and the gas pressure of coal seam is 2.26 MPa. Mine gas extraction concentration is low, flow is small, gas extraction time is long, effect is poor, gas control cost is high.
Treatment solution
According to the development plan and mining replacement plan of Xinjing coal mine, a floor through layer drilling was arranged in the south of the extraction roadway. After the drilling passed through the strata and entered the coal seam, the hole diameter was 120mm. The whole hydraulic fracturing technology was adopted to carry out one-time whole hydraulic fracturing construction in the boreholes, so as to increase the permeability of coal seam and improve the efficiency of gas drainage.
Drilling equipment (zdy12000 directional drilling machine)
Hydraulic fracturing equipment (byw65 / 400 underground fracturing pumps)
Work situation
The opening point of fracturing drilling was located in the floor rock roadway of No.3 coal seam, with a total drilling footage of 495m, including 188m in rocks and 307m in coal seam. The secondary hole body structure was adopted for drilling: the primary hole diameter was 193mm, the hole length was 35m, the φ146mm seamless steel casing was put in and cement slurry was injected to fix the hole; the secondary hole diameter was 120mm. After fracturing drilling from coal seam floor to coal seam 3, the borehole was drilled along the middle and upper part of the coal seam as a whole.
In the hydraulic fracturing test, the capsule expander was used to seal the hole. The packer was mainly composed of capsule packer, guide shoe, single flow valve, sliding sleeve, high pressure string and orifice safety joint. BYW65/400 underground high-pressure pump was used to inject water into the fracturing borehole for fracturing. The cumulative injected water volume of the borehole was 1510m3, the injection time was 51.11h, the maximum displacement was 56.45m3/h, and the maximum injection pressure was 26.09MPa.
Schematic diagram of field test
Achieved accomplishment
After the completion of fracturing, the monitoring and drainage data were for 230 days, and the drilling gas extraction concentration was 49.38% ～ 83.70%, with an average of 64.30%. The net amount of extracted methane was 1395～2810m3/d, with an average of 2173m3/d, and the cumulative net amount of extracted methane was 508000 m3.
Borehole gas drainage curves
The maximum influence radius of borehole fracturing was 58m. The permeability of coal seam was 2.677 times higher than that before fracturing, and the attenuation coefficient of gas flow in borehole was 45.1% of that before fracturing.
Distribution of influence radius of hydraulic fracturing
The research results of the project won the second prize of China Coal Industry Association.
Project award certificate
1. FAQ
(1) What is the impact of the implementation of the project on the mine gas prevention and control.
Hydraulic fracturing technology plays a positive role in enhanced gas extraction in coal mines. After the implementation of the project, the participating units further realized the potential of the technology. In order to further improve the relevant process parameters, the following experimental studies were carried out in different areas of the mine, and the overall effect was relatively ideal.
(2) This technology can be used in the field of the enhanced gas drainage and also used in other fields, and what is the effect?
Hydraulic fracturing technology is essentially to make the stratum produce fractures. At present, the technology is applied in the enhanced gas drainage in the coal mines, but also in the control of the surrounding rocks of the working faces. At present, the application effect is good in Shendong mining area, effectively solves the problems existing in the mining of the working faces.
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