基于嵌入式离散裂缝和扩展有限元的裂缝性页岩油藏流固耦合高效数值模拟方法

通过耦合嵌入式离散裂缝模型和扩展有限元建立了一种适用于裂缝性页岩油藏的流固耦合高效数值模拟方法。该方法创新性在于:通过对裂缝进行显式降维处理,可以准确刻画水力裂缝对渗流场和应力场的影响,同时可以模拟水力裂缝开度的动态变化过程以及水力裂缝内流体压力对裂缝变形的影响;在划分网格时仅需对基岩系统进行正交网格剖分,不必考虑裂缝的几何形态,渗流场和应力场均选取一套网格,使得网格划分时的复杂度大幅降低。对于渗流方程求解采取模拟有限差分方法,满足局部质量守恒并且可以有效处理全张量形式渗透率;对于岩石力学方程求解采取扩展有限元方法,可以准确处理裂缝两侧的位移间断性。通过算例分析,本文方法的正确性与优势得以验证。

Hydro-Mechanical Coupling Model of Fractured Shale Oil Reservoir Based on Embedded Discrete Fracture Model and Extended Finite Element Method

An efficient numerical simulation method has been developed to simulate the coupled processes of fluid flow and geomechanics in fractured shale oil reservoir by coupling the embedded discrete fracture model and extended finite element method. The innovation of the proposed method is that the effect of hydraulic fracture on seepage field and stress field can be accurately described by explicit dimensionality reduction. At the same time, the dynamic change process of hydraulic fracture aperture and the influence of fluid pressure in hydraulic fracture on fracture deformation can be simulated. When meshing, it is only necessary to perform orthogonal meshing on the bedrock system, regardless of the geometry of the fracture, and a set of meshes is selected for both the seepage field and the stress field, so that the complexity of meshing is greatly reduced. In the proposed method, the flow equations were solved by the mimetic finite difference method which can ensure the local mass conservation and deal with the full-tensor permeability, the geomechanics equations were solved by the extended finite element method which can be used to simulate the displacement discontinuity between the fracture surfaces. Lastly, several numerical examples have been performed to show the accuracy and applicability of the proposed method.