The Impact of Common Reservoir Minerals and Temperature on the Low Salinity EOR-effect in Sandstone

The mechanism of the low salinity EOR process in Sandstone reservoirs has been debated in the literature for more than a decade. We recently proposed a chemical wettability alteration mechanism for the process, well founded in experimental observations. Even though this main chemical understanding is quite well described, there are parameters/factors that could disturb the main process. Combinations of certain minerals, temperature, and salinity/composition of formation water could have impact on the low salinity EOR process. Plagioclase, a polysilicate mineral, is often present in sandstone reservoir rocks, and could have a significant effect on the initial pH of the formation water, which will influence the initial wetting conditions. In this experimental work it is shown that Plagioclase in reservoir rock and outcrop material responded differently on the low salinity effect. It is also verified that enhanced dissolution of anhydrite, CaSO4, in the low saline fluid suppressed the increase in pH, which is an important parameter for observing tertiary low salinity effects. A combination of high reservoir temperature, Tres>100 oC and very high salinity of the formation water, >200 000 ppm, resulted in too water wet conditions for observing tertiary low salinity EOR effects, even though the clay content was high, ≈20 wt%. The experimental results are in line and discussed in relation to the previously published chemical mechanism for the low salinity EOR process.