天然裂缝对页岩储层水力裂缝扩展影响数值模拟研究

Study on numerical simulation of effect on natural fractures to hydraulic fracture propagation in shale reservoirs

页岩储层中存在大量的天然裂缝,对水力压裂过程中裂缝扩展影响作用显著。为探究天然裂缝对水力裂缝扩展规律的影响,考虑岩石储层变形与裂缝内的流体流动之间的耦合作用以及天然裂缝与水力裂缝的相互作用建立了页岩储层二维流固耦合水力压裂裂缝相交扩展模型,通过与经典KGD模型和室内试验结果的对比,验证了模型的正确性。在此基础上研究了水平应力差、天然裂缝相交角和长度对水力裂缝与天然裂缝相交扩展的影响。研究结果表明:随着水平应力差的线性增加,裂缝起裂注水压力呈线性增大趋势,最大水平主应力对水力裂缝与天然裂缝相交后的裂缝扩展路径有诱导作用;水力裂缝与天然裂缝相交时,注水点水压出现骤降现象,裂缝相交点处易出现应力集中区,裂缝相交处宽度出现间断现象;天然裂缝相交角越大,间断现象越明显,压裂裂缝长度越短,压裂裂缝面积越小;天然裂缝长度对压裂裂缝长度影响较小,但对压裂裂缝的宽度和面积影响明显。研究结论对优化页岩气水力压裂设计有一定的指导作用。

There are a large number of natural fractures in shale reservoirs,which have a significant effect on fracture propagation during hydraulic fracturing.In order to explore the influence of natural fractures on the propagation law of hydraulic fractures,considering the coupling effect between rock reservoir deformation and fluid flow in fractures and the interaction between natural fractures and hydraulic fractures,a two-dimensional fluid-solid coupling hydraulic fracturing fracture intersection propagation model for shale reservoirs is established.The correctness of the model was verified by comparing the results with the classical KGD model and the laboratory test results.The research shows that with the linear increase of horizontal stress difference,the water injection pressure of fracture initiation increases linearly.The maximum horizontal principal stress induces the propagation path of hydraulic fracture and natural fracture.When the hydraulic fracture intersects with the natural fracture,the water pressure at the water injection point drops sharply.The stress concentration area is prone to occur at the fracture intersection,and the width at the fracture intersection is discontinuous.The larger the intersection angle of natural fractures,the more obvious the discontinuity of fracture width.At the same time,the shorter the fracture length,the smaller the area.Natural fracture length has little effect on fracture length,but has obvious effect on fracture width and area.However,natural fracture length has little effect on fracture length,but has obvious effect on fracture width and area.The research can provide reference for the design of hydraulic fracturing during actual shale reservoir.