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Waterflooding and Water-Alternating-CO2 Injection: Effect of Injected Brine Salinity
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Over the past fifty years, Improved Oil Recovery (IOR)/Enhanced Oil Recovery (EOR) technologies have been modified to include the effects of salinity of injected brine on oil recovery. Water-Alternating-Gas (WAG) is one such EOR process in the field. It improves the synergy of various individual mechanisms underlying EOR processes, such as ion exchange, wettability alteration, and mobility control. This process has matured over the years, but the alteration of the salinity of injected brine during WAG has not been extensively tested. This work investigates the effect of injected brine salinity during water-alternating-CO2 injection and compares its performance with stand-alone brine injection, using 20 in. length outcrop Grey Berea sandstone cores. The water-alternating-CO2 process was done under immiscible conditions. This work also studies the effect of aging of cores on oil recovery during the waterflooding process. In the present work, six coreflood experiments were performed: four experiments before aging the cores and two experiments after aging the cores. The temperature was set at 149 °F (65 °C) for all the experiments. This work evaluated the oil recovery and pressure drop for each coreflood. The effect of salinity on rock wettability during waterflooding and water-alternating-CO2 processes was studied using axisymmetric contact angle measurements. The effect of salinity on the waterflooding process, as well as the water-alternating-CO2 injection process, was observed throughout the coreflood experiments. Low-salinity brine yielded the highest recovery during the waterflooding process in aged cores, and seawater brine yielded the highest recovery during the water-alternating-CO2 injection process. Wettability alteration toward a more water-wet state improved the oil recovery during the low-salinity brine injection process. The lower solubility of CO2 in seawater brine, compared to the solubility of CO2 in low-salinity brine, resulted in higher oil recovery by seawater brine during the water-alternating-CO2 injection process. Fines migration was observed during the low-salinity brine-alternating-CO2 injection process. Aging the cores improved the oil recovery during the waterflooding process. The salinity of brine affected the contact angle measurements of the Grey Berea sandstone rock. The rock was strongly water-wet in the presence of low-salinity brine. Seawater brine made the rock more oil-wet due to the ion binding nature of the divalent ions in seawater brine. The aging of the cores increased the contact angle of the rock, thereby making the rock more oil-wet. These findings provide a basis for optimizing the salinity of injected brine during the waterflooding and water-alternating-CO2 injection.
Ramanathan, Raja S. (2015). Waterflooding and Water-Alternating-CO2 Injection: Effect of Injected Brine Salinity. Master's thesis, Texas A & M University. Available electronically from