Intelligent fluid flow management for enhanced geothermal system in fractured horizontal wells

Abstract

The presence of thermal short-circuiting impedes the further development of enhanced geothermal systems (EGSs) with horizontal wells. The objective of this research is to explore the effectiveness of a new technique, i.e., tunable fracture conductivity, in the control of thermal short-circuiting in EGSs with horizontal wells. The core idea of tunable fracture conductivity is to adjust the hydraulic conductivity of fractures according to the surrounding temperature at any point and seal any dominant flow path with a low temperature that may short-circuit the fluid flow. By utilizing this technique, thermal shortcuts between the wells can be effectively suppressed, and uniform heat extraction from each flow path can be expected. The performance of tunable fracture conductivity is investigated based on numerical simulations. According to the simulation results, tunable fracture conductivity can significantly improve heat sweeping between the injection and production well. After 50 years of operation, this technique increases production temperature by approximately 50 K, from 358.71 K to 410.32 K, which significantly elongates the effective period of operation in an EGS. Furthermore, using temperature-adaptive fracture conductivity improves heat extraction efficiency by 113.2 % which can be translated as an extra reduction in greenhouse gas (GHG) emission for 1.15 – 3.21 Mt with only one pair of wells. Besides, smaller fracture half-length and fracture spacing can also help the tunable fracture conductivity to better control the thermal short-circuiting and maintain the high-efficient EGS operation. This study provides a new method to achieve cleaner, more profitable, and highly efficient geothermal systems in the future.