LAMOUREUX-VAR, V., S. WOLF, F. SCHNEIDER, I. CHARLETTE, and A. PRINZHOFER
Institut Francais du Petrole, Rueil-Malmaison, France

Abstract: Advanced Physics For Modeling Solubilization And Diffusion Of Gas At Basin Scale

In the past few years, the idea has grown up that molecular diffusion of gas in petroleum systems is a non-negligible process for quantifying gas migration, particularly for methane. In order to quantify gas migration and leakage, a 3D compositional basin model has been developed, integrating multiphase flow, solubilization and advection/diffusion of gas.

The gas diffusion in sediments is controlled by the diffusivity y which strongly depends on the structural properties of the porous medium. This coefficient is not yet well determined, so a preliminary study has been performed to understand it. Both experimental measurements and a theoretical approach have shown that the evolution of diffusivity y as a function of porosity f can be described for sandstones by an explicit relationship.

In basin models, the cell size (generally several hundreds of meters) generates upscaling artefacts. In our case, this concerns the diffusivity and the coupling between solubilization and diffusion. As diffusivity is very similar to permeability, we can use previous abundant works on permeability upscaling. One main problem remains: as diffusion is quite a slow process, we cannot assume that the water phase is at thermodynamic equilibrium with the other phases in all the cell. This non-equilibrium can be accounted for by introducing a time dependant term, which is a function of the cell size, in the solubilization law.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas