A Fully Coupled Hydro-Mechanical-Gas Model Based on Mixture Coupling Theory

The interactions of gas migration, water transport and mechanical deformation of rocks are significant for geoenergy industry (e.g. Carbon Capture and Storage, radioactive waste disposal); however, the hydro-mechanical-gas coupled model remains a challenge due to the gap between multiple disciplines (e.g. Geomechanics and Geoenergy). This work presents a novel hydro-mechanical framework model of fully coupled two-phase fluid transport in a deformable porous media through extending mixture coupling theory which is based on non-equilibrium thermodynamics. The main difference between the mixture coupling theory approach and other approaches (ex., mechanic's approach) is that the mixture coupling theory uses energy and entropy analysis by utilizing the unbalanced thermodynamics, while the mechanic's approach analyses the stress-strain tensors. The gas free energy has been included in the Helmholtz free energy balance equation. Three main governing equations have been obtained for solid, liquid and gas phases. Benchmark experiments and modelling based on classical continuum mechanics approaches are used to validate the model by comparing the measured data to the simulation results. The results have a good agreement with experimental data, demonstrating that gas migration has a great influence on water transport and deformation of the solids. The novelty of this study is that it is providing a new approach to study the multiphase flow coupling in porous media rather than the classic mechanic's approach.