Simulating Complex Fracture Systems in Geothermal Reservoirs Using an Explicitly Coupled Hydro-Geomechanical Model

Low permeability geothermal reservoirs can be stimulated by hydraulic fracturing to create Enhanced (or Engineered) Geothermal Systems (EGS) with higher permeability and improved heat transfer to increase heat production. In this paper, we document our effort to develop a numerical simulator with explicit geomechanics-discrete flow network coupling by utilizing and further advancing the simulation capabilities of the Livermore Distinct Element Code (LDEC). The important modules of the simulator include an explicit finite element solid solver, a finite volume method flow solver, a joint model using the combined FEM-DEM capability of LDEC, and an adaptive remeshing module. The numerical implementation is verified against the classical KGD model. The interaction between two fractures with simple geometry and the stimulation of a relatively complex existing fracture network under different in-situ stress conditions are studied with the simulator.

低渗透性地热储层可通过水力压裂进行刺激，以创建具有更高渗透率和改进的热传递性能的增强型（或工程化）地热系统（EGS），从而提高热能产出。在本文中，我们记录了我们开发一个数值模拟器的过程，该模拟器通过利用并进一步扩展利弗莫尔离散单元代码（LDEC）的模拟能力，实现了显式地学力学-离散流动网络耦合。模拟器的重要模块包括显式有限元固体求解器、有限体积法流动求解器、利用LDEC的FEM-DEM综合能力的联合模型以及自适应重网格模块。该数值实现经过经典KGD模型的验证。使用该模拟器，我们研究了具有简单几何形状的两个裂缝之间的相互作用以及在不同原位应力条件下对相对复杂的现有裂缝网络的刺激作用。