Technology and application of directional hydraulic fracturing with guide slot to enhance permeability and gas extraction in coal seam
Aiming at the difficulty of gas pre-extraction in low permeability and high gas coal seam,the technology of directional hydraulic fracturing of coal seam with guide slot was proposed.The distribution of plastic zone after reaming in coal seam was calculated by theoretical derivation,and the initiation and propagation of hydraulic fractures in coal seam of cross-seam drilling were analyzed to reveal the mechanical mechanism of directional hydraulic fracturing of coal seam with guide slot.The permeability-increasing equipment for directional hydraulic fracturing of coal seam with guide slot was developed and applied in Shanxi Zhongxing Coal Mine.The results show that after the water jet reaming of cross-layer borehole in coal seam section,an approximately cylindrical hole is generated in the coal body.The radius of the plastic zone of the surrounding rock of the cross-layer borehole is positively related to the radius of the borehole.Drilling reaming is an effective method to increase the range of the plastic zone,which significantly promotes the development of cracks,and improves the gas extraction effect.A complete set of equipment for directional hydraulic fracturing and outburst prevention of guide slot was developed.The main components are mobile high-pressure hydraulic pumping station,sprayer,nozzle,orifice blowout preventer,spiral assisted slag discharge water jet high-pressure drill pipe and high-pressure rotary joint,combining with remote monitoring and control of underground hydraulic operation.The field monitoring results show that the average gas concentration and the mixing amount of gas extraction increased to 2.75 times and 1.81 times of that of the conventional hole by the method of permeability-increasing drilling,which indicates that the permeability-increasing effect of the proposed technology is remarkable.
water jet reamingguide slotdirectional hydraulic fracturingcoal seam permeability enhancementgas extraction
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