The power generation potential of enhanced geothermal systems in ductile crust at >15 km depth

This study explores the power generation potential of enhanced geothermal systems (EGS) at depths of >15 km, where continental crust typically exhibits ductile behavior at temperatures above 400 °C. We employed a numerical model to evaluate the response of such deep crustal rock to fluid injection-induced pressurization and cooling. Our simulations indicate that circulating 80 kg/s of water through rock initially at 425 °C could yield ~100-120 MWth (approximately 20 MWe) for two decades. Even after a century of fluid circulation, fluid temperatures at the production wells exceed 250 °C and thermal energy output exceeds 40 MWth. However, achieving effective permeability in the stimulated volume is crucial to developing an exploitable resource; our model suggests that bulk permeability values between ~10^-15 and 10^-14 m² in a rock volume of 0.1 km³ are optimal. This range balances the need to avoid excessive injection pressures and the risk of rapid thermal depletion. As the reservoir cools, the transition from ductile to brittle behavior in rock is assumed, reducing fluid pressures but increasing the risk of fluid pathway short-circuiting, a common challenge in EGS operations. Our theoretical investigation underscores the importance of geological (e.g., rock temperature and permeability) and operational (e.g., injection rate) factors in harnessing the energy potential of the ductile crust. However, practical implementation hinges on revolutionary advancements in deep drilling technology and a better understanding of rock behavior under high temperature and pressure conditions.