An Innovative Closed-Loop Geothermal Well Solution for Large-Scale District Cooling Projects

Abstract Typical geothermal district cooling projects are characterized by high upfront investment in drilling and have geological requirements which pose geographical limitations as to where a project can be executed. This paper introduces a new closed-loop horizontal geothermal well technology that helps harness the abundantly available lower enthalpy geothermal energy for direct use in district cooling projects at most locations using an absorption chiller. The new technology utilizes a single closed-loop horizontal well to replace the typical two wells in a standard hydrothermal solution (one producer and one injector) with specific geological requirements. This is achieved by using vacuumized pipe-in-pipe completion installed in a closed-loop horizontal geothermal well. By injecting return water from the district cooling network into the well in the annulus between the pipe-in-pipe completion and the outer casing/liner section along the geological formations in the horizontal section of the well, this working fluid is heated to reach the temperature of the geological formations. It then flows back to the surface inside the vacuumized pipe-in-pipe completion with minimal heat loss for direct use in district cooling grids by using an absorption chiller. Implementation of the technology shows significant upscaling potential both geographically, regarding the number of wells that can be completed, and the thermal energy output achieved. The well design depends on the local geothermal temperature gradient and the thermal conductivity needed to achieve the required thermal energy output. The very limited geological requirements enable harvesting the abundantly available geothermal energy in most places. As it is a closed-loop system, there is no need for reservoir stimulation, continuous depletion of underground water aquifers, well interventions, or downhole equipment maintenance, which minimizes operational costs. Simulations showed that the execution of 10 wells with a depth of 4 km each and 3-6 km horizontal sections could deliver about 20 MW of thermal energy with 90 °C – 100 °C fluids at the surface which will be diverted to an absorption chiller to provide 16 MW thermal plus with water at 6 °C ready for direct use in district cooling applications. This entire system is estimated to reliably work for 50+ years with minimal need for maintenance and almost no requirement for any well interventions. This paper introduces a thorough review of the breakthrough innovation in geothermal district cooling by introducing a closed-loop horizontal single-well system that can add significant value and, at the same time, mitigate the issues with conventional hydrothermal solutions.