Surface well partition gas extraction technology system and engineering practice

In order to effectively reduce the gas content of coal seam, realize the efficient utilization of gas resources and reduce the difficulty of underground gas management, combined with the geological characteristics of Shoushan I mine site, we built a surface well zoning gas extraction technology, aiming to realize the systemization of gas management in the mine area. Based on the spatial and temporal distribution characteristics of mining activities, the mine field was divided into unmined area, mined area and vacant area, and different surface wells were established for gas extraction in zoning, so as to realize the change from gas management to gas utilization. The systematic gas management technology includes four parts: scientific arrangement of surface wells, well structure and construction design, reservoir fracturing and permeability enhancement in unmined area, and drainage and gathering engineering. The selection of surface well locations is based on the spatial stratification, coal seam characteristics, surface location, coal seam recovery and gas storage conditions. In the mining area, based on the height of the collapse zone and fissure zone after coal seam retrieval, the straight wells and L-type wells in the mining area were designed to be located in the middle and upper part of the fissure zone, so that the gas can be extracted efficiently from multiple coal seams in the area with the effect of pressure relief of this coal seam retrieval. The L-shaped well body in the unmined area, the straight well body in the mined area, the L-shaped well body in the mined area and the straight well body in the mined area were designed. Hydraulic fracturing of the coal seam in the unmined area to achieve coal seam penetration increase, the composite fracturing process of directional injection & pumped bridge plug type light casing fracturing was selected to fracture the coal seam, deep penetration reinforcing bullet was used for injection operation, and 20/40 mesh quartz sand was used as proppant. In Shoushan No.1 Mine, the engineering practice of surface well zoned gas extraction technology was carried out, and the statistics of gas extraction from different types of surface wells in the mine area showed that: the maximum daily gas production from a single well in the mining area can exceed 40 000 m³, and the accumulated gas extraction from a single well is up to 2 597 000 m³, and 11 wells are currently being drilled for extraction in the well field area, with an accumulated extraction of up to 14 252 000 m³. Field effect test showed that the implementation of surface wells zoned gas extraction technology can achieve efficient gas extraction, forming a gas management model of “mining one layer to treat multiple layers”.