  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.
