Including seismic risk mitigation measures into the Levelized Cost Of Electricity in enhanced geothermal systems for optimal siting

Abstract

The seismic risk associated with deep fluid injection in Enhanced Geothermal Systems can be mitigated by stopping reservoir stimulation when the seismic risk becomes unacceptable or by reducing production flow rates when seismicity occurs during the operational phase. So far, none of these mitigation measures have been included in the Levelized Cost Of Electricity. A meta-model is introduced that estimates the optimal price of electricity, based on an analytical geothermal energy model, and updates this cost to include the outlay for mandatory seismic risk mitigation measures. The proposed energy model computes both electricity production and heat credit. The costs added during reservoir stimulation are based on the probability of abandoning an injection well, based on a traffic-light system, defined as the ratio of scenarios that exceed a given seismic safety threshold in the risk space. In the production phase, the net energy generated is reduced by clipping the production flow rate so that the reservoir's overpressure does not exceed the regional minimum effective stress. Based on a generic geothermal triplet, we investigate the trade-off between heat credit and seismic risk mitigation cost. The added cost, mostly due to financial risk aversion, shifts the optimal site for a plant from between a few kilometres to tens of kilometres away from populated areas, for increasingly vulnerable building stocks. Finally, using a simple yet realistic optimisation strategy, we study the role that a seismic safety standard plays for determining the number of EGS plants that can be sited in a given region.