Thermoelastic fracturing and buoyancy-driven convection: Surprising sources of longevity for EGS circulation

Abstract: To maximize value from an EGS system, engineers need to optimize flow rate, well spacing, and well configuration. Numerical simulations yield interesting and surprising results regarding the effect of coupled processes on long term thermal performance. Thermoelastic fracture opening and propagation can have a significant negative effect on the uniformity of flow. On the other hand, interactions between fracture opening and buoyancy driven fluid circulation cause downward fracture propagation during long-term circulation that greatly improves the thermal longevity of the system. Passive inflow control design can significantly mitigate the negative effect of thermoelastic fracture opening on flow uniformity, while maintaining the positive effects of thermoelastic fracture opening and propagation on flow rate and thermal longevity. Overall, simulations suggest that an EGS doublet with 8000 ft laterals at 475' F, using inflow control at the production well, could sustain electricity generation rates of 8 to 10 MWe for more than 30 years. Without inflow control, 6 to 8 MWe over 30 years is possible; however, there is greater risk of uncontrolled thermal breakthrough.