  Porosity and permeability alteration due to the thermo-poro-elastic stress
field disturbance from the cold fluid injection is a deciding factor for
longer, economic and safer heat extraction from an enhanced geothermal system
(EGS). In the Soultz-sous-For\^ets geothermal system, faulted zones are the
main flow paths and the resulting porosity-permeability development over time
due to stress reorientation is more sensitive in comparison with the regions
without faulted zones. Available operational and field data are combined
through a validated numerical simulation model to examine the mechanical impact
on the pressure and temperature evolution. Results shows that near the
injection wellbore zones, permeability and porosity values are strongly
affected by the stress field changes and the permeability changes will affect
the overall temperature and pressure of the system demonstrating a fully
coupled phenomenon. In some regions inside the faulted zones and close to the
injection wellbores, the porosity doubles whereas permeability may enhance up
to 30 times. From the sensitivity analysis on the two unknown parameters from
the mechanical aspect is performed and results shows that only one of the
parameters impacts significantly on the porosity-permeability changes. Further
experimental and field works on this parameter will help to model the heat
extraction from the Soultz-sous-For\^ets and elsewhere more precisely than
before.
