煤岩缝网改造关键因素分析及应用研究

Analysis and applied study on key factors of coal and rock crack network reconstruction

为提高低渗煤层瓦斯抽采效率,在分析页岩气"缝网压裂"基础上,提出了煤矿井下煤岩储层缝网压裂的技术思路。通过分析影响缝网形成的关键因素,采用Mshale模拟水力压裂脆性指数-泊松比-单一水力裂缝体积三者关系,判断天然裂缝发生张性断裂和剪切断裂的力学条件,试验模拟不同地应力差水力裂缝特征。研究表明:在注入量一定条件下,随着脆性指数增加,单一水力裂缝体积减小,水力裂缝数量增加;随着主应力差的增大,试样破裂面表面积增加且渐为粗糙,裂缝张开度减小;水力裂缝和天然裂缝相交角越小,水力裂缝越易沿天然裂缝剪切破坏;主应力差较小时,水力裂缝易出现转向、分叉等。在鹤壁中泰矿业有限公司进行了缝网压裂试验,压裂有效面积达21 666 m2,钻孔日抽采量是缝网压裂前的13倍,是常规水力压裂的2.6倍,采用CYT探测了水平剖面和垂直剖面视电阻率的变化,证实了水力压裂缝网的存在。

In order to improve the gas drainage efficiency of low permeable seam, based on an analysis on a ＂crack network fracturing＂ of shale gas, fracturing technical idea of a crack network in the coal and rock reservoir of an underground coal mine was provided.With an a- nalysis on the key factors affected to the crack network formation, the Mshale was applied to simulate the three relationship of the hydraulic fracturing fragility index-Poisson＇ s ratio-single section hydraulic crack volume, the mechanics conditions of the tensile breakdown caused by the natural cracks were judged and the study was conducted on the experiment simulation of the hydraulic fracturing features with differ- ent geostress difference.All above showed that under the certain condition of the injection volume, with the fragility index increased, the single section hydraulic fracturing volume would be decreased and the number of the hydraulic fractures would be increased.With the main stress difference increased, the surface area of the sample breaking surface would be increased and would be steadily rough and the frac- ture opening would be decreased.The smaller intersectional angle between the hydraulic fracture and the natural fractures was, the more easy of the hydraulic fractures would be sheared and damaged along the natural fractures.When the main stress difference was small, the hydraulic fractures would easily have the turn off, bifurcation and other conclusion.Finally, a fracturing experiment of the crack network was conducted in Hebi Zhongtai Mining Company Limited.The effective scope of the fracturing was 21 666 mE, the daily gas drainage vol- ume of a borehole was 13 times higher than before the fracturing of the crack network and was 2.6 times higher thane the conventional hy- draulic fracturing.CYT was applied to detect the apparent resistivity variation of the horizontal cross section and the vertical cross sectionand to confirm the existenee of the hydraulic fractured crack network.