Evaluation of seismic activity and fault reactivation for Enhanced Geothermal Systems

Abstract

Growth in energy demand from developing nations necessitates the utilization of all available sources of energy. Primarily due to their environmental benefits, clean and renewable energy resources are of particular interest. Moreover, since renewable energy is gathered from naturally replenished sources, it is widely available around the world. Origins of renewable energy include sunlight, rain, wind, waves, and geothermal heat. Of these, geothermal heat is the area of focus in this research. The main goal of geothermal energy technology is to find a way to transfer the thermal energy to the surface where it can be used for heating and generating electricity. All geothermal technologies are based on this principle. The process of geothermal energy extraction can take place in both shallow and deep layers of crust. Among the commonly available energy extraction technologies, Enhanced Geothermal System (EGS) is of particular interest in this research. Through EGS, a cold fluid is injected into the ground and extracted heat energy is delivered through a process called “hydraulic stimulation”. The target of this research is to develop a model to investigate the geomechanical issues of a deep EGS set-up in addition to the influence of the “hydraulic stimulation” process on the geologic medium, particularly the problem of induced seismicity in a pre-existing fault which exists in the system. A 2D numerical finite element code is developed to iv analyze the behavior of porous subsurface in terms of displacement, stress, fluid pressure distribution, and temperature through a coupled thermo-hydro-mechanical (THM) approach using the corresponding mathematical governing equations. After modeling an EGS setup and stimulation program, an efficient approach is introduced along the concept of Mohr-Coulomb diagram which enables studying the seismic risk potential in an EGS using the final stress state of the geologic medium obtained from the THM approach.