COMPARATIVE STUDY OF DEEP CO-AXIAL CLOSED LOOP AND U-SHAPED WELLBORE GEOTHERMAL SYSTEMS

Abstract

Until recently, geothermal energy has been limited to regions with favorable subsurface conditions. Most installed geothermal systems are open, using two wells for fluid injection and extraction. Closed-loop systems have historically been used in low-depth installations as ground source heat pumps. However, climate changes and energy market volatility have catalyzed the development of deep-borehole heat exchangers (DBHE) - a potentially cost-competitive technology for direct heat applications and electricity generation. The closed-loop systems can be built in any area with a sustainable geothermal gradient, while millions of abandoned wells worldwide offer low-cost repurposing as closed-loop DBHEs, producing revenue without the large cost linked with drilling. This study provides a technical assessment of coaxial and U-shaped DBHE systems, with a primary focus on the effects of pipe insulation. Results indicate that the installation of proper insulation is a vital part of the system, with a particular emphasis on the return line insulation of U-shaped systems.