Dynamic Interactions between Matrix and Fracture during Miscible Gravity Drainage in Naturally Fractured Reservoirs

Miscible gas or solvent injection has received increasing attention in recent years as an efficient method for improving oil recovery from naturally fractured reservoirs. Because of the large permeability difference between fracture and matrix, the success of this method depends to a large extent on the degree of enhancement of the mass-exchange rate between the solvent flowing through the fracture and the oil residing in the matrix. In this study, a series of experiments were conducted to investigate the mass-transfer rate between the fracture and the matrix when a solvent is injected through the fracture system. The effects of injection rate, fracture aperture, water saturation, matrix wettability, and fluid properties on the recovery behavior were examined. The interaction between the matrix and fracture was visualized for solvent injection by means of computed tomography (CT) scanning, which can be used to validate theories of enhanced transfer in fractured media. The results obtained with a simulation model, which takes diffusive, gravitational, and convective forces into account, showed good agreement with the experimental results within an acceptable range of accuracy.