Surfactant-aided wettability alteration in low-temperature low-salinity carbonate reservoirs




Almansouri, Mohammed A.

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Carbonate reservoirs tend to be oil-wet/mixed-wet and heterogeneous, which makes wettability alteration a key method for increasing oil recovery. Carbonate reservoirs are often fractured, especially with increased dolomitization. Changing wettability to a water-wet state aids water imbibition into the matrix, thereby sweeping bypassed oil. The objective of this study is to improve oil recovery in low-temperature dolomite reservoirs using low-salinity surfactant solutions. This work evaluates the potential of using surfactants in a low-temperature carbonate formation with a formation brine salinity of 10,887 ppm. The reservoir has a high dolomite concentration with a high density of fractures and an intermediate to oil-wet wettability. Brine composition was optimized using zeta potential and contact angle measurements. Surfactants were screened based on their aqueous stability under reservoir conditions and were further screened using contact angle experiments. Experiments of spontaneous imbibition upon exposure to surfactants on carbonate rocks have been conducted using various surfactant types and concentrations. Also, a coreflood was completed to evaluate recovery due to wettability alteration. Additionally, changing water salinity was performed to assess the impact on the wettability of carbonate surfaces. The effects of surfactant formulations and observations are discussed. Optimized surfactant formulations were found to increase oil recovery to up to 10.4% from conventional waterflooding


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