| Abstract |
We develop a novel three-dimensional transient model to investigate the subsurface heat exchange process in EGS. This model adopts the thought of single-porosity model and treats the porous heat reservoir as an equivalent porous medium of a single porosity. However, it considers local thermal non-equilibrium between solid rock matrix and fluid flowing in the apertures and employs two energy conservation equations to describe heat transfer in the rock matrix and in the apertures, respectively, enabling the modeling and analyses of convective heat exchange in the heat reservoir. Another salient feature of this model is its capability of simulating the complete subsurface heat exchange process in EGS. The EGS subsurface geometry of interest physically consists of multiple domains: open channels for injection and production wells, the artificial heat reservoir, and the base and cap rocks enclosing the heat reservoir, while computationally we treat it as a single-domain of multiple sub-regions associated with different sets of characteristic properties (porosity and permeability, etc.). This circumvents typical difficulties about matching boundary conditions between sub-domains in traditional multi-domain approaches and facilitates numerical implementation and simulation of the complete subsurface heat exchange process. With this new model, we perform a comprehensive parametric study with respect to an imaginary doublet EGS. Effects of several parameters, including the permeability of heat reservoir, heat exchange coefficient in the heat reservoir, the specific area of apertures in the heat reservoir, and mass flow rate of heat transmission fluid, on the heat extraction efficiency and EGS lifetime are analyzed |