Assessing geothermal risk prior to drilling

Abstract

The planning phase of geothermal projects involves diverse levels of uncertainty. Consequently, risk remains high prior to exploration drilling. Generating a qualitative risk matrix, supported by numerical results can aid the decision-making process during the planning phase of a geothermal installation.
A discrete parameter analysis can be employed to rank the relative influence of these uncertainties. In this setting, uncertainty is classified in three main categories, namely: initial subsurface conditions (pressure, gas saturation), geological and geophysical properties (permeability and fault seal) and lastly operational parameters (flow rate and re-injection temperature). By populating the uncertainty classes with discrete values and simulating all combinations, a qualitative and quantitative risk assessment can be performed.
Using the case study of the envisioned Groningen geothermal doublet, we present a workflow that integrates seismic, petrophysical and reservoir data. The generated risk matrix identifies pressure depletion as a major project risk. Furthermore, power generation can be maintained beyond 60 years, while similar power output can be achieved with different combinations of flow rate and re-injection temperature.