沁水盆地南部煤储层水力压裂裂缝发育特征的数值模拟研究

以沁水盆地南部为研究区,以山西组3号煤储层为目标层位,根据该区的地应力场特征以及晋城市寺河矿煤样的三轴压缩实验结果,利用大型有限元软件ANSYS建立了该区3号煤储层的地质模型,模拟水力压裂过程中地应力场和储层弹性模量对裂缝起裂压力和裂缝扩展形态的影响。结果表明:裂缝的起裂压力与最大水平主应力无关,随最小水平主应力的增大而线性增大,变化范围为10～25 MPa;裂缝的最大缝长和最大缝宽不随最大水平主应力的变化而变化,随最小水平主应力和煤岩弹性模量的增大而减小,其中最大缝长介于36～83 m范围内的概率最高。模拟结果和现场数据基本吻合,说明该模型具有一定的合理性,研究成果对于沁水盆地南部地区煤层气井水力压裂设计具有重要的参考价值。

Numerical Simulation Research on Propagation of Hydraulic Fractures of Coal Reservoir in South Qinshui Basin

Taking the south Qinshui basin as researching area and the 3# coal bed as the researching target,a geological model of this area was set up on the base of the characteristics of the field stress and the triaxial stress test results of coal samples from Sihe coal mine in Jincheng.Using finite element software ANSYS as the platform,this research simulated the changing law that the geological factors including ground stress and Young’s modulus of coal reservoirs influence on the initiation pressure and propagation of the fracture.The results show that the initiation pressure keeps constant when the maximum horizontal principal stress changes,but increases with the minimum horizontal principal stress increasing,and the variation range is between 10 MPa and 25 MPa.The maximum fracture length and the maximum fracture width keep unchanged with the increasing of the maximum horizontal principal stress,but decrease with the rising of the minimum horizontal principal stress and Young’s modulus.The maximum fracture length has the highest probability to range between 36 m and 83 m.The results coincide well with the field data.This achievement would provide a reference for hydrofracturing design of coalbed methane well in south Qinshui basin.