Determination of gas-diffusion and interface-mass-transfer coefficients in fracture-heavy oil saturated porous matrix system

For the modeling and simulation of oil recovery from naturally fractured reservoirs during the gas injection process, an accurate value of the molecular diffusion coefficient (MDC) of gases from a gas filled fracture into the oil matrix is essential. During the injection of miscible fluids with oil, transport of the injectant and oil are controlled by fracture and matrix properties. Diffusion is a significant-oil recovery mechanism between matrix and fracture. However, experimentally determined data concerning to gas transfer between fracture-matrix systems by diffusion mechanism are relatively rare. In this study the pressure-decay method is applied to obtain effective molecular diffusion coefficient of CO2 and CH4 in heavy oil saturated porous matrix media at different conditions of temperatures. Gas-diffusion and interface-mass-transfer coefficients are determined by applying a transient-state equilibrium diffusion model. The effect of porous media presence on these coefficients has also been investigated. It is expected that the experimental results will be useful in deriving the matrix-fracture transfer function by diffusion, which is required for simulation of recovery in naturally fractured reservoirs.