Abstract Two-phase flow in fractured and karstified porous media subject to coupled hydro-mechanical conditions is an important issue for oil recovery in carbonate reservoirs. However, due to the co-existence of porous media flow, fracture flow and free flow, as well as their couplings with geomechanical deformation, modeling the behavior of fractured karst systems remains challenging. In this work, a novel coupled hydro-mechanical model for simulating the complex behavior of fractured and karstified porous media is developed. Two-phase Darcy's equation is used to describe fluid flow in both matrix and fractures, while the free flow in cavities is considered based on an assumption of phase instantaneous gravity segregation. A modified Barton-Bandis's constitutive model is used to mimic the nonlinear fracture deformation. The cavity deformation is solved based on the fluid pressure on the cavity boundaries. A mixed finite volume-finite element method and a fixed-stress iterative splitting method are adopted to numerically solve the coupled system of equations. The model is then applied to a series of 2D and 3D problems to unravel the impacts of fractures and cavities on two-phase flow and geomechanical deformation in fractured karst systems. The results indicate that cavities hinder water breakthrough due to storage effects, while water may quickly migrate through highly conductive fractures. Cavities tend to dominate the flow and mechanical processes even though fractures are present as well. Significant stress concentration is observed around cavities. Furthermore, the results of 3D cases imply that phase gravity segregation in cavities leads to lower water saturation in the area above cavities and delays water breakthrough.

中文翻译：

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基于流体力学耦合模型模拟裂缝性岩溶储层两相流和地质力学变形

摘要 流体力学耦合条件下裂缝和岩溶多孔介质中的两相流是碳酸盐岩油藏采油的一个重要问题。然而，由于多孔介质流、裂缝流和自由流的共存，以及它们与地质力学变形的耦合，对裂缝岩溶系统的行为进行建模仍然具有挑战性。在这项工作中，开发了一种新的流体力学耦合模型，用于模拟断裂和岩溶多孔介质的复杂行为。两相达西方程用于描述基质和裂缝中的流体流动，而空腔中的自由流动是基于相瞬时重力分离的假设来考虑的。修改后的 Barton-Bandis 本构模型用于模拟非线性断裂变形。基于腔边界上的流体压力求解腔变形。采用混合有限体积有限元法和固定应力迭代分裂法对耦合方程组进行数值求解。然后将该模型应用于一系列 2D 和 3D 问题，以阐明裂缝和空洞对断裂岩溶系统中两相流和地质力学变形的影响。结果表明，由于储存效应，空腔阻碍了水的突破，而水可能会通过高导电裂缝快速迁移。即使也存在裂缝，腔体也倾向于主导流动和机械过程。在空腔周围观察到显着的应力集中。此外，