Effect of Wettability in Free-Fall and Controlled Gravity Drainage in Fractionally Wet Porous Media with Fractures

Wettability was found to significantly influence the oil recovery behavior in heterogeneous porous media in gravity drainage processes. Despite the considerable efforts conducted on this issue, there are still challenging aspects remaining. The objective of this study is to investigate the wettability effects in fractured and homogeneous porous media during free-fall gravity drainage (FFGD) and controlled gravity drainage (CGD) conditions. Different test fluids (water and Varsol oil) were employed for completely water-wet, completely oil-wet, and fractionally wet porous media in this research. This experimental work enabled us to capture important characteristics of gravity drainage processes such as the production performance, matrix fracture flow communication, and liquid production rate by the film-flow mechanism. It was concluded that the physical properties of the test fluids and the fractional wettability composition of the porous medium govern the fluid recovery mechanism during FFGD and CGD processes. The oil production rate by film flow was found to be appreciably affected by the packing composition when water-wet and oil-wet beads were randomly mixed. A percolation threshold of oil-wet beads was obtained at about 63%, after which no further change was experienced in the production rate magnitude when the film flow was a dominant recovery mechanism. Moreover, the results revealed that the wetting properties of the test fluid considerably affected the matrix-to-fracture transfer and the fluid saturation. The water-wet beads condition was favored in oil recovery for both FFGD and CGD processes. The oil-wet conditions provided greater film-flow rates and matrix-to-fracture transfer rates.