A novel physics-based numerical model is proposed to simulate the orientation and effective confining pressure dependent permeability of anisotropic rock. In the two-dimensional discrete element model, presence of anisotropy is explicitly represented by inserting a set of smooth joints. Based on the experimentally obtained effective stress law at sample scale, a physics-based relation is deduced to describe the reduction of pipe aperture upon the normal contact force at grain scale. Darcy test is conducted to validate the model by comparing the flow rate and pressure distributions with analytical solutions. Different parameters are assigned to represent the difference in flow capacity of rock matrix and beddings. Fluid flow tests performed on the isotropic model and anisotropic models with horizontal and vertical beddings reveal that the macro permeability decreases with increasing effective stress, following the same effective stress law. The initial aperture dominates the intrinsic permeability while the reduction of permeability is due to the closure of pipe aperture. Permeability anisotropy is caused by the different apertures assigned to the rock matrix and the bedding while the force sensitivity factors determine the stress-dependence of the permeability anisotropy. Simulations of the stress concentration and fluid dissipation around borehole confirm the capacity of the model in capturing the hydro-mechanical coupled responses of anisotropic rock formation. This study provides a fluid flow model for the exploration of mechanisms underlying the orientation and stress dependent permeability of anisotropic rocks and for the simulation of their engineering responses subjected to hydro-mechanical coupling.

提出了一种新的基于物理的数值模型来模拟各向异性岩石的方向和有效围压相关渗透率。在二维离散元模型中，各向异性的存在通过插入一组平滑的关节来明确表示。根据实验获得的样品尺度有效应力定律，推导出了一个基于物理的关系来描述晶粒尺度法向接触力下管道孔径的减小。通过将流量和压力分布与解析解进行比较，进行达西测试以验证模型。分配不同的参数来表示岩石基质流动能力的差异和床上用品。对具有水平和垂直层理的各向同性模型和各向异性模型进行的流体流动测试表明，宏观渗透率随着有效应力的增加而降低，遵循相同的有效应力规律。初始孔隙主导着固有渗透率，而渗透率的降低是由于管道孔隙的关闭。渗透率各向异性是由分配给岩石基质和层理的不同孔径引起的，而力敏感因子决定了渗透率各向异性的应力依赖性。模拟周围的应力集中和流体耗散钻孔证实了模型在捕捉各向异性岩层的流体力学耦合响应方面的能力。本研究提供了一种流体流动模型，用于探索各向异性岩石的取向和应力相关渗透率的潜在机制，以及模拟它们在水力-机械耦合下的工程响应。