Effect of Trapped Gas on Relative Permeability and Residual Oil Saturation in an Oil-Wet Sandstone

Abstract

Abstract A comprehensive set of experimental data from preserved reservoir sandstone is used to demonstrate features important to oil-wet systems not usually included in water-wet three-phase relative permeability models. The data are described by a generalized version of the relative permeability model developed by Jerauld (1997). The impact of these features on immiscible and miscible water-alternating-gas performance is estimated with type pattern simulations. The sandstone reservoir studied shows large amounts of spontaneous imbibition of oil and traps water during secondary drainage. Oil relative permeability is almost a function of oil saturation alone while water relative permeability is significantly lower in the presence of trapped gas. Unlike most systems, the trapped gas saturation depends on the relative amounts of oil and water. While two-phase trapped gas values are consistent with values in the literature for similar sandstones, three-phase trapped gas levels are approximately a factor of two lower. The residual oil saturations for waterflooding and gasflooding followed by waterflooding are the same. Furthermore, the incremental oil production during the waterflood following gasflooding was minimal. Two different lithologies show the same general behavior. Experiments run with different pressure drops demonstrate that the low trapped gas saturations are not due to capillary desaturation. CT scans show that little redistribution of gas occurs during trapping.