Towards fully coupled Thermo-Hydro-Mechanical-Chemical (THMC) modelling in advanced reservoir engineering: GOLEM-PHREEQC

Abstract. Effective geothermal resource development requires sophisticated computational tools integrating different physical and chemical processes. This work describes a novel coupling of GOLEM, an open source simulator for thermal-hydraulic-mechanical modeling based on the MOOSE multiphysics framework, with the PHREEQC geochemical solver. GOLEM solves coupled partial differential equations governing subsurface fluid flow, heat transfer, conservative mass transport, and mechanical deformation in complex geological environments. PHREEQC is a proven and widely adopted geochemical simulator in the scientific community. The coupling to GOLEM is achieved leveraging an efficient and original wrapper based on the IPhreeqc module. The newly developed coupling of flow, transport and geochemical reactions is validated against standalone PHREEQC by means of 1D RTM benchmarks including both equilibrium and kinetic mineral reactions. A further demonstration of the capabilities of the GOLEM-PHREEQC coupling is shown, on a 2D domain with three distinct geochemical zones.