In geothermal systems, networks of fractures provide main fluid pathways. Hydraulic stimulation of fractured geothermal reservoirs can increase the possibility of geothermal fluid to flow through the formation by causing sliding and dilation of preexisting fractures as well as fracture propagation. This represents a complex coupled process-structure interaction, where the fractured structure of the formation both dominates coupled fluid flow and rock deformation and conversely is altered because of these processes. A main result achieved in the project so far is a novel coupled thermo-hydro-mechanical simulation model for hydraulic stimulation of fractured porous rock, where slip, dilation and propagation of fractures result as a consequence of fluid injection.
Fundamental progress has also been made in the simulation of reactive thermal multi-phase flow in high-temperature geothermal systems. For the phase equilibrium problem, we have developed formulations that enables simultaneous determination of phase stability and splits for a wide range of subsurface conditions. The developed methodology provides a modular way to include and couple the local fluid phase equilibrium within compositional multi-phase flow simulations. This enables simulating injection into and production in high-enthalpy, including superhot geothermal systems. The combination of high salt content, boiling and condensation, and temperature‑ and pressure‑dependent mineral precipitation/dissolution requires specialised equations of state. These have been combined with mathematical models for reactive compositional multiphase flow with phase change.
Substantial work has also been performed on novel mathematical models for deformable fractured media, numerical solution strategies, and necessary software improvements in the open-source framework PorePy, much of which is central to prepare for the next phase of the project.
