Approaches to Studying of Associated Gas Diffusion in Oil Saturated Shale Core Samples

Diffusion is a key mechanism controlling the transport of hydrocarbons between fractures and matrix in low permeable shales in associated gas EOR. Diffusion in shales plays more important role than in conventional reservoirs, however low reservoir properties are the reasons for emerging issues in understanding and modelling of multiphase flows. Furthermore, literature does not provide reliable data on gas diffusion inside oil saturated shale core samples under reservoir conditions. Following this, laboratory modelling of associated gas diffusion and calculation of diffusion coefficient inside shale core samples will decrease the uncertainty in production modelling. Traditional ways of diffusion measurements are not applicable in shales because of low permeability values. NMR and CT scanning are promising technologies for such type of shale core analysis. The NMR measurements are based on recalculation of NMR relaxation signals to saturations, and as a result, to concentrations, which allows to determine diffusion coefficients based on Fick`s law. The principle of measurements in CT is based on tracking the difference in CT numbers dependent on oil and gas densities inside the core within the gas diffusion process. The received CT data can be recalculated to saturations and used in numerical model for gas diffusion coefficient estimation.