Heat extraction through conductive proppants

Abstract

The absence of direct contact between the working fluid and the geothermal formation in closed-loop geothermal system (CLGS) limits its application to direct heating. Enhancing the CLGS heat extraction performance could lead to an effective utilization of CLGS for power generation purposes. Optimizing CLGS performance is still an active area of research. In this paper, we propose a fractured closed-loop geothermal system (FCLGS) with a conductive plug installed downhole and a fracture propped with conductive proppants to improve heat exchange performance of CLGS. Using an integrated numerical approach, we first explore the potential to improve the thermal conductivity of common types of proppants by applying metallic coatings. Applying a thick layer of copper coating to Aluminum Nitride proppants yields a thermal conductivity of 44.91 W/(mK), 24 times larger than that of uncoated sand. The proppant/coating with largest thermal conductivity is used for field-scale simulations. Heat extraction performance of FCLGS is evaluated at the field-scale under different parameter combinations. Numerical results show that incorporating a conductive plug into a fractured CLGS improves net power output by 30.60 %. Conductive plug shape and size play an important role in heat extraction in FCGLS. In addition, a circulation velocity of 2 m/s is observed to yield the highest increase in net power output.