The Influence of the Formation Water Salinity on the Low Salinity EOR-effect in Sandstone at High Temperature

Abstract

The low salinity EOR process mechanism in sandstone reservoirs has been debated in the literature during last decade. Based on our recently proposed chemical wettability alteration mechanism, well founded in experimental observations, temperature, formation water salinity/composition, etc. could have impact on the EOR process by affecting: (1) The initial wetting condition; (2) The wettability alteration process when high salinity formation water is displaced by low salinity water. It has been experimentally observed the low salinity EOR effect decreases as the reservoir temperature increases. The present paper discusses the low salinity EOR effect at high temperatures, Tres>100 °C, and high formation water salinities, close to 200 000 ppm. In general, the adsorption of active polar components onto clay minerals decreases as the temperature and salinity of the formation water increases. As a result the rock became more water wet, and low salinity EOR potential decreases. Oil recovery tests at 110 °C with high salinity did not show any low salinity effect. However, when the formation water salinity was reduced to ~23000 ppm, a low salinity effect was observed. The combination of high reservoir temperature and high formation water salinity is most likely not favourable for observing low salinity EOR effects.