水力裂缝在煤岩界面处穿层扩展规律的数值模拟

Numerical simulation of layer-crossing propagation behavior of hydraulic fractures at coal-rock interface

为研究水力压裂裂缝在煤层与顶板界面处的穿层扩展规律,在分析煤岩界面性质的基础上,应用有限元法研究煤岩界面处裂缝从顶板起裂后的延伸情况,探讨了相关地质参数和施工参数对裂缝跨界面穿层扩展的影响。结果表明:地质因素中的地应力、煤岩界面强度为煤岩界面处裂缝能否穿层扩展的主要影响因素,垂向应力差异系数越大、界面抗剪切强度越大,越有利于裂缝穿层扩展沟通煤层;煤层与顶板间的弹性模量差异、抗拉强度差异是裂缝从顶板穿层进入煤层的有利因素;现场压裂施工应根据地层情况选择合适的施工参数(排量、注入点与界面的距离)以促进裂缝穿层扩展。研究成果能够为煤层顶板分段压裂水平井地面煤层气高效抽采技术的应用提供参考。

Based on the analysis of coal-rock interface,the vertical propagation behavior of hydraulic fractures at coal-roof interface was studied by using finite element method.The influence of some geological and engineering factors on fracture layer-crossing behavior was analyzed.Results have shown that in-situ stress and shear strength of coal-rock interface are the two main factors affecting the fracture propagation at the coal-rock interface.Greater vertical stress difference coefficient and interfacial shear strength make fractures more easier for crossing the interface.Meanwhile,the difference of elastic modulus and tensile strength between coal and rock has less effect on the fracture vertical propagation behavior.Besides,proper engineering parameters(mainly pump rate and the distance between injection point and interface)can promote fracture to cross the interface.Research results can provide a reference for the application of"multi-stage hydraulic fracturing horizontal well in roof"technology in surface CBM extraction.