An Improved Mathematical Model for Mass Transfer in Fractured Reservoirduring Gas Injection Process

Abstract

In fractured reservoirswith relativelylow matrix permeability, i.e. small matrix block size with respect to capillary threshold height, diffusionbecomes an important recovery mechanism. In this work, we have attemptedto model the mass transfer between matrix and fracture by considering afractured porous media as a single matrix block with an adjacent fracture.An appropriate model should be applicable in the case of the matrix being saturated with both saturated and undersaturated oils. The proposed model presents such versatility.The model is a modification for the formulation ofJamili et al.(SPE132622)which suffered from several drawbacks such as use of classical Fick's law, use of Hua and Whitson (SPE21893)to calculate diffusion mass transfer coefficients between fracture and matrix and use of Darcy's law to model convection mass transfer between fracture and matrix. In this work we surveyed these drawbacks and amended them. Subsequently, the improved model has been validated through a gas injection experiment. Following model validation, the effects of matrix permeability, initial gas saturation and injection rate on the recovery rate are investigated. The numerical analysis showed that the effect of gas injection rate on the recovery rate is considerable.