低渗煤层液态CO_2相变定向射孔致裂增透技术及应用

如何实现深部煤层瓦斯的高效抽采是保障我国煤炭企业安全生产的重要问题,而低透气性煤层瓦斯储层增产改造则是其中的核心技术和热点问题。为解决低透气性煤层瓦斯高效抽采技术难题,研究提出了地应力条件下优势射孔致裂方向的确定方法及低渗煤层液态CO_2相变定向射孔致裂增透技术,现场试验及应用研究形成了液态CO_2相变定向射孔致裂增透网格式瓦斯抽采方法。研究表明:孔壁破裂压力受钻孔方位角、倾角影响具有明显的方向性,并确定了试验区液态CO_2相变定向射孔优势致裂方向;该技术可有效增加煤样孔隙度、孔径、比表面积、可见孔比例等,改善煤岩体内孔隙结构及渗流能力,提高瓦斯抽采纯流量9~12倍,降低煤层瓦斯抽采流量衰减系数92%;现场试验及PFC2D数值模拟研究确定了该技术的影响半径为9~13 m;应用表明液态CO_2相变定向射孔致裂增透网格式瓦斯抽采方法,可有效预防低透气高突煤层巷道掘进期间的瓦斯超限问题,提高巷道掘进速度4~5倍。

Research and application on technology of increased permeability by liquid CO2 phase change directional jet fracturing in low-permeability coal seam

How to achieve an efficient extraction of deep coal seam gas has been a main challenge facing China’s energy security while the technology to increase the permeability of coal bed gas has been the focus of recent studies.In order to solve the technical problem of high efficiency gas drainage in deep low permeability coal seam,in this study,the method of advantageous direction of jet fracturing under the condition of in-suit stress are put forward based on theoretical analysis.A novel technology for cracking and increasing permeability in low permeability coal seam namely LCO2 phase change directional jet fracturing has been proposed and experimented.And a mesh drilling coal seam gas drainage method is proposed based on LCO2 phase change directional jet fracturing technology.The results show that the fracture pressure of the borehole wall is affected by the azimuth,inclination of borehole and has obvious directionality.The advantageous direction interval of the LCO2 phase change directional jet fracturing is determined in the test area.LCO2 phase change directional jet fracturing technology can effectively increase the total porosity,pore size,surface area,the ratio of visible pores of coal sample,improve the pore structure and seepage capacity within the coal matrix to effectively increase the pure flow rate of gas drainage in coal seams by 9 to 12 times,which reduces the flow attenuation coefficient of gas drainage in coal seam by 92%.The variation law of on-site gas drainage parameters and the results of PFC2D particle flow program show that the technology’s influence radius is 9-13 m.The mesh drilling coal seam gas drainage method of deep and low-permeability coal seam is based on LCO2 phase change directional jet fracturing technology,which can effectively prevent gas over alarm value during the roadway drivage with low permeability and high outburst coal seam,and improve drivage speed by 4-5 times.