Key parameters affecting the performance of fractured geothermal reservoirs: a sensitivity analysis by thermo-hydraulic-mechanical simulation

A discretely fractured reservoir has the capability to support and sustain long term geothermal energy extraction operations. The process of injecting cold water to extract hot water from a fracture reservoir results in thermal and poroelastic stresses in the rock matrix. Therefore, these thermo-hydro-mechanical (THM) mechanisms govern the efficiency of an enhanced geothermal system (EGS) operation. However, THM mechanisms are governed by various rock and fluid parameters as well as on the initial and boundary conditions of the model set-up. In this paper, we have identified and analyzed 22 such parameters. Due to this large number of involved parameters, it is difficult to accurately estimate the relative importance of individual parameters. To address this issue, we have performed an extensive sensitivity analysis for the purpose of the Horizon 2020 project, Multidisciplinary and multi-contact demonstration of EGS exploration and Exploitation Techniques and potentials (H2020 MEET) using the design of the experiment method and identified key parameters influencing three key outcomes of the simulation: thermal breakthrough time, mass flux, and overall energy recovery. We found that for a given discrete fracture network, the fracture aperture, the rock matrix permeability, and the wellbore radius are the most influential parameters controlling the thermal breakthrough time, mass flux, and overall energy recovery.