Pre-Operational Risk Study in Deep Geothermal Modeling: Insights from a Dual Medium Synthetic Model

Abstract

A common form of geothermal extraction involves extracting hot water from an aquifer from a production well and re-injecting cooled water in a second injection well within the same aquifer. As the operation takes place, a cooled water zone will spread over time from the injection well, eventually reaching the production well, which may have significant consequences for the overall sustainability of the project. The development of geothermal energy generation is closely linked to thermal and hydrogeological knowledge of the subsurface aquifers. Numerical modeling here appears as a tool to delineate development risks induced by limited geological data at great depths. Reservoir numerical modeling is used to investigate coupled transient hydraulic and thermal responses of geothermal operation on a deep sloped reservoir. Selected dual medium approach accounts for fractured reservoirs through the modeling of exchange mechanisms between matrix and fractures. The geothermal synthetic system, consisting of a fully saturated reservoir, overburden and underburden, is assumed to be part of a typical deep sedimentary basin. A thorough screening of uncertainties on a given range of input parameters allows the identification of key reservoir simulation outputs due to their respective influence on hydraulic and thermal performances of the geothermal system. This qualitative step is used to organize the main characteristics of the mining reservoir and the associated geothermal operation into a hierarchy in order to discard minor parameters from further analysis. This reduced set of parameters is subsequently used to carry out the uncertainty analysis that enables quantifying parameter impacts on modeled pressures, temperatures and complex output variables. The use of response surface method allows simulating thousands of automated scenarios. The stochastic method would allow determining the settings for input factors that meet technical feasibility constraints, resulting in the prediction probabilities of success of the overall project. This research is carried out in the REFLET-Geodenergies project handled by FONROCHE Géothermie