裂缝性页岩储层水力压裂多簇裂缝扩展的FEM-DFN数值模拟

Numerical simulation of multi-cluster fractures propagation in naturally fractured shale reservoir based on finite element method-discrete fracture network

为有效模拟裂缝性页岩储层中水力裂缝的随机扩展并准确描述其拉张、剪切和混合损伤行为,建立渗流-应力-损伤耦合的裂缝扩展有限元-离散裂缝网络模型,并通过黏性主导的解析模型进行验证。研究不同天然裂缝逼近角、簇间距、水平应力差和压裂泵注排量下的多簇裂缝扩展数值模拟,探讨天然裂缝对水力裂缝扩展的影响机制。研究表明:(1)水力裂缝与天然裂缝主要存在水力裂缝穿过天然裂缝、水力裂缝开启天然裂缝和水力裂缝被天然裂缝阻止3种相互作用机制;(2)随逼近角越大,天然裂缝越容易使水力裂缝扩展方向发生偏转甚至阻止水力裂缝扩展;(3)簇间距、水平应力差和泵注排量的提高均能在一定程度上促进多簇裂缝扩展的均匀程度。本文模型能更加准确地描述水力压裂多簇裂缝的扩展行为,可为裂缝性页岩储层的水力压裂数值模拟提供新手段。

To effectively simulate the random propagation of hydraulic fractures and accurately describe the tensile,shear and mixed damage behaviour in naturally fractured shale reservoirs,a finite element method-discrete fracture network model coupled with seepage-stress-damage is established.The viscosity-dominated analytical model is utilized to verify the accuracy of the model.The effect of the approach angle,cluster spacing,horizontal stress difference and pumping rate on multi-cluster fractures propagation is investigated and the interaction mechanism between hydraulic and natural fractures is discussed.The results show that:(1)There are three main interaction mechanisms between hydraulic fracture and natural fracture:crossing through natural fracture,opening natural fracture and arrested by natural fracture;(2)With the increase of the approach angle,the natural fracture is easier to deflect the propagation direction of hydraulic fracture and even prevent the propagation of hydraulic fracture;(3)The increase of cluster spacing,horizontal stress difference and pumping rate can promote the uniform growth of multi-cluster fractures to a certain extent.The model can more accurately describe the propagation behaviour of multi-cluster fractures,and provide a new method for numerical simulation of hydraulic fracturing in naturally fractured shale reservoir.