Effects of pressure and wettability on residual phase saturation in sandstone rock

Abstract

The nature of fluid distribution in porous media is among the least understood mechanisms when describing porous media statics and dynamics. Particularly for a three-phase flow, this is far from a revealed field of science. Because of unfavourable water injectivity, several reservoirs in the North Sea have been waterflooded while maintaining production pressure below the bubble point. One crucial parameter for this process is the critical gas saturation which has a great impact on the oil production. Both production pressure and fluid mobility control the amount and distribution of free gas in the system. Two-phase waterfloods and three-phase waterfloods with simultaneous pressure depletion were performed. The rock material was Berea sandstone and the fluids used were a recombined C 1/nC 5-mixture and brine and the experiments were performed at laboratory temperature and pressures ranging from 10–20 bar. To evaluate the effect of wettability on recovery, both water-wet and intermediate-wet cores, prepared by silanisation, were used. For the three-phase experiments, each core was waterflooded and simultaneously depleted by a fixed depletion rate to a unique constant back pressure below the initial bubble point of the binary mixture. The data analysis show that the recovery is dependent on the amount of gas liberated, and also on the wetting preferences of the core. The intermediate-wet cores give a higher recovery and the results indicate higher critical and residual gas saturation for intermediate-wet cores.