煤层水力压裂影响因素数值模拟研究

Numerical Simulation Study on Influencing Factors of Hydraulic Fracturing of Coal Seam

水力压裂技术是目前煤层气增产的主要措施之一,它可有效地造成裂缝网络,增大气体渗流通道面积,减少煤粉的生成。为研究煤层压裂裂缝扩展的影响因素,针对目前现场对煤层压裂效果认识不清晰的问题,本文基于线弹性traction-separation准则,利用黏聚力单元模拟裂缝起裂和地层损伤,建立了水平井煤层水力裂缝计算模型;运用单因素控制方法利用该模型研究了射孔相位角、地应力差值以及弹性模量对水力裂缝的影响。计算结果表明射孔相位角越小,地层起裂压力越大,随着相位角的变化,地层起裂压力增幅可达32.5%;弹性模量为6 GPa时,地层起裂压力最低为23.77 MPa,高弹模地层容易形成长窄缝,低弹模地层容易形成短宽缝。最终利用该模型优化了煤层水平井水力压裂施工参数,为水力压裂方案的设计提供了参考和指导。

Hydraulic fracturing technology is one of the main measures to enhance CBM production at present.Hydraulic fracturing can effectively connect natural fractures in the reservoir to form a fracture network,and reduce the generation of pulverized coal.In order to study the influence factors of coal seam hydraulic fracturing fracture,a horizontal coal seam fracture model was established.The model was theoretically based on the linear elastic traction-separation rule.The effects of perforating phase angle,horizontal principal stress difference and elastic modulus on hydraulic fractures were studied by using this model.The results show that the perforation phase angle and elastic modulus are the main factors affecting fracture propagation.The smaller the perforation phase angle is,the greater the formation fracturing pressure will be.With the change of the phase angle,the formation fracturing pressure will increase by 32.5%.When the elastic modulus is 6 GPa,the formation crack initiation pressure is 23.77 MPa at the minimum.The formation with high elastic modulus is easy to form long and narrow cracks,while the formation with low elastic modulus is easy to form short and wide cracks.The hydraulic fracturing parameters of horizontal well in coal seam are optimized by this model,which provides reference and guidance for the design of hydraulic fracturing scheme.