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Geothermal energy; The Netherlands; induced seismicity; numerical modelling; slip tendency analysis
Abstract:
Geothermal energy is one of the most viable sources of renewable heat. However, the potential
risk of induced seismicity associated with geothermal operations may slow down the growth of
the geothermal sector. Previous research has led to significant progress in understanding fluidinjection-
induced seismicity in geothermal reservoirs. However, an in-depth assessment of
thermal effects on the seismic risk was generally considered to be of secondary importance. This
study aims to investigate the relative influence of temperature and key geological and
operational parameters on the slip tendency of pre-existing faults. This is done through coupled
thermo-hydro-mechanical simulations of the injection and production processes in synthetic
geothermal reservoir models of the most utilized and potentially exploitable Dutch geothermal
reservoir formations: Slochteren sandstone, Delft sandstone and Dinantian limestone.
In our study, changes in the slip tendency of a fault can largely be attributed to thermo-elastic
effects, which confirms the findings of recent studies linking thermal stresses to induced
seismicity. While the direct pore pressure effect on slip tendency tends to dominate over the
early phase of the operations, once pore pressure equilibrium is established in a doublet system,
it is the additional stress change associated with the growing cold-water front around the
injection well that has the greatest influence. Therefore, the most significant increase in the slip
tendency was observed when this low-temperature front reached the fault zone. The distance
between an injection well and a pre-existing fault thus plays a pivotal role in determining the
mechanical stability of a fault. A careful selection of a suitable target formation together with an
appropriate planning of the operational parameters is also crucial to mitigate the risk of induced
seismicity. Besides the well-known relevance of the in situ stress field and local fault geometry,
rock-mechanical properties and operation conditions exert a major influence on induced stress
changes and therefore on the fault (re)activation potential during geothermal operations.
