Hydraulic stimulation is a critical process for increasing the permeability of fractured geothermal reservoirs. This technique relies on coupled hydromechanical processes induced by reservoir stimulation through pressurized fluid injection into the rock formation. The injection of fluids causes poromechanical stress changes that can lead to the dilation of fractures due to fracture slip and to tensile fracture opening and propagation, so-called mixed-mechanism stimulation. The effective permeability of the rock is particularly enhanced when new fractures connect with pre-existing fractures. Mixed-mechanism stimulation can significantly improve the productivity of geothermal reservoirs, and the technique is especially important in reservoirs where the natural permeability of the rock is insufficient to allow for commercial flow rates. This paper presents a modeling approach for simulating the deformation and expansion of fracture networks in porous media under the influence of anisotropic stress and fluid injection. It utilizes a coupled hydromechanical model for poroelastic, fractured media. Fractures are governed by contact mechanics and allowed to grow and connect through a fracture propagation model. To conduct numerical simulations, we employ a twolevel approach, combining a finite volume method for poroelasticity with a finite element method for fracture propagation. The study investigates the impact of injection rate, matrix permeability, and stress anisotropy on stimulation outcomes. By analyzing these factors, we can better understand the behavior of fractured geothermal reservoirs under mixedmechanism stimulation.

翻译：水力激励是提升裂缝性地热储层渗透率的关键过程。该技术依赖于通过向岩层高压注液引起的储层激励所驱动的流固耦合力学过程。流体注入导致孔隙力学应力变化，可引发裂缝滑动引起的剪胀以及拉伸裂缝的开启和扩展，即所谓混合机制激励。当新生裂缝与既有裂缝连通时，岩石的有效渗透率会显著增强。混合机制激励能大幅提升地热储层产能，尤其适用于天然渗透率不足以支撑商业流量规模的储层。本文提出一种模拟各向异性应力与流体注入作用下多孔介质中裂缝网络变形与扩展的建模方法。该方法采用针对孔隙弹性裂隙介质的流固耦合力学模型，其中裂缝由接触力学控制，并允许通过裂缝扩展模型实现生长与连通。数值模拟采用双层策略：将孔隙弹性问题的有限体积法与裂缝扩展的有限元法相结合。本研究分析了注入速率、基质渗透率及应力各向异性对激励效果的影响。通过解析这些因素，可更深入理解混合机制激励下裂缝性地热储层的行为特征。