Abstract
Natural fractures and artificial fractures in a tight rock matrix of an enhanced geothermal system make flow and heat transfer become seriously anisotropic. In this paper, a field-scale fractured heterogeneous geothermal reservoir model is built to study the heat transfer process. Based on an equivalent continuum method and local thermal non-equilibrium model, an equivalent permeability tensor is mapped from discrete fractures and a coupled thermal-hydraulic-mechanical mathematical model is adopted in which logarithmic stress sensitivity model is used to couple effective stress and permeability. From numerical simulation results at different injection rates, the contour results show the heterogeneity of flow, heat transfer and stress sensitivity are dominated by fractures distribution. Temperature contours reveal that the heat convection between water and rock in a fracture is more intense than the heat conduction between rock under different temperatures. The predicted power generation of a geothermal plant reveals the adverse effect on heat conversion efficiency, which is caused by the temperature drop at high injection rates.
Highlights
Geothermal is one of the promising renewable energy resources around the world
The assessment report published by the MIT-led interdisciplinary panel forecast an enhanced geothermal system (EGS) could provide 100 GW electricity or more of cost-competitive generating capacity in the 50 years in USA [1]
Xu et al [4] proposed a simplified approach to simulate the coupled hydro-thermal system for EGS, capable of providing a detailed prediction of fluid flow and heat transfer in a geothermal reservoir based on an equivalent pipe network model
Summary
Geothermal is one of the promising renewable energy resources around the world. Hot dry rock (HDR) has great possibility to provide large amounts of energy due to the extensive distribution of the heat resource. Xu et al [4] proposed a simplified approach to simulate the coupled hydro-thermal system for EGS, capable of providing a detailed prediction of fluid flow and heat transfer in a geothermal reservoir based on an equivalent pipe network model. Developed a numerical program to simulate the heat extraction from naturally fractured geothermal systems by coupling fluid flow with heat transfer between the rock matrix and circulating fluid This provides a dynamic treatment of the characteristic properties (aperture, length and orientation) of individual fractures. To utilize a THM coupling model in field-scale cases, a numerical method which fully integrates the anisotropy of fractures and heat transfer between water and rock should be developed to investigate the actual performance of EGS. This model can better reflect the anisotropy of a fractured reservoir and the simulation results can provide a better representation of the real operational status of a geothermal reservoir compared with simplified conceptual model
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