Thermodynamics-related processes during the migration of acid gases and methane in deep sedimentary formations

TMGAS, an equation of state module of TOUGH2 V.2.0 reservoir simulator, was used to model the migration of CO2, H2S, and CH4 in a deep sedimentary formation. The scope is the improvement of the description of non-condensable gas (NCG) migration within modeling studies of sedimentary basins' evolution. Different scenarios have been simulated with NCG migration taking place in a large sedimentary formation discretized with a full 3D Voronoi approach by using specifically improved versions of the pre- and post-processing tools for TOUGH2 developed at the University of Bologna. Simulated reference scenarios are related to the migration of CO2, H2S, and CH4 generated at constant rate for 1 × 106 years in a fresh water aquifer. Additional scenarios are simulated with NCG migration taking place in the same formation but saturated with brine. The effects of pressure-temperature-composition (PTX) conditions on thermodynamic equilibria, phase composition, phase thermo-physical properties and, consequently, on the migration features of different NCGs are modeled and discussed.