Numerical simulation of a comparative study on heat extraction from Soultz-sous-For\^ets geothermal field using supercritical carbon dioxide and water as a working fluid

TL;DR

This study uses numerical simulations to compare heat extraction from Soultz-sous-Forêts geothermal reservoir using supercritical CO2 and water, revealing CO2's advantages in efficiency and thermal stability over 50 years.

Contribution

It develops a field-scale hydro-thermal model to evaluate and compare the long-term heat extraction potential of CO2 versus water as working fluids in geothermal reservoirs.

Findings

CO2 maintains higher temperature levels over 50 years.

Lower injection temperatures improve heat extraction efficiency.

Wellbore effects significantly influence reservoir temperature response.

Abstract

Geothermal energy is an infinite energy source for the present human society. Energy extraction from the deep subsurface requires engineering using a working fluid that circulates between well doublet. Due to its thermal properties, CO2 is an ideal option as a heat transfer fluid. By using CO2, working fluid loss is an advantage compared to other working fluids. This study developed a field-scale hydro-thermal model to examine the heat extraction potential from Soultz-sous-For\^ets with CO2 as the working fluid. Results are compared for the same scenario with water as the working fluid. A better understanding of the heat extraction mechanism is established by considering the reservoir response and the wellbore heat exchange. Sensitivity analyses are performed for different injection temperatures and flow rates for 50 years. Results show that the wellbore effect is multiple times higher than the reservoir response to the production temperature. Furthermore, lowering the injection temperature eventuates to a smaller temperature reduction at the subsurface, enhancing the overall heat extraction potential with a minor impact on thermal breakthrough. The cold region developed around the injection wellbore may affect the production fluid temperature due to its proximity to the production wellbore. To reach higher heat extraction efficiency, it is essential to use sufficient wellbore spacing. CO2 can be used as working fluid for over 50 years as it does not show significant thermal breakthrough and temperature plume evolution in the reservoir under studied conditions. CO2 shows lower temperature reduction for all injection rates and temperatures for 50 years of operation.