A numerical investigation into the use of directionally drilled wells for the extraction of geothermal energy from abandoned oil and gas wells

Geothermal energy is an ideal renewable resource for power production since it is not limited by the intermittency issues associated with other renewables like wind and solar. Despite its ability to provide a steady supply of electricity on demand, the adoption of geothermal is not widespread, largely due to the high cost of drilling. One way to mitigate this cost is to use abandoned oil and gas wells, which are abundant (with an estimated 2.3 million in the United States) but pose a potential hazard to the environment. Studies in the literature have proposed installing heat exchangers in vertical wells to solve this problem. Vertical designs, however, would undergo high friction and temperature losses due to the use of internal piping. Such designs also do not enable the use of the L-shaped directionally drilled wells which have greater contact with the ground at high temperatures. This paper proposes an approach for extracting geothermal energy from abandoned oil and gas wells by using directionally drilled wells, thereby improving upon the existing designs by eliminating internal piping and maximizing contact with high ground temperatures. Through additional drilling, two adjacent wells can be connected to create a continuous loop from which thermal energy can be collected for use in a power cycle. The proposed geometry was studied numerically to determine the outlet temperatures and heat extraction rates from the system for the prediction of thermal energy extraction and electrical power production. The results show that a system with 4000 m deep vertical wells and a 4800 m horizontal section could produce approximately 2 MW of thermal energy and 200 kW of power using an organic Rankine cycle. Moreover, these wells are capable of providing a heat source for electricity generation for several decades.