An experimental investigation of smart-water wettability alteration in carbonate rocks - oil recovery and temperature effects

The smart water flooding has found tremendous applications in the oil recovery sector. This technique is designed by changing the concentrations of cations - mainly SO4 (2-), Ca2+, and Mg2+ - in the synthetic water mixtures being injected. The complexity of the underlying reaction mechanism, compared to the sandstone counterparts, calls for substantial research in this field. The present article lists an experimental investigation of wettability alteration in carbonate rocks by focusing on the role of individual ions for the fluid-solid interactions. The oil recovery results are reported for five synthetic smart waters, as well as the real formation water in the temperature range between 25 and 70 Celsius. A chemical-based mechanism is proposed - supported by zeta-potential data - to render the role of ions in the wettability alteration process. The smart-water samples are designed to hold the same level of total dissolved solids as the seawater of the Persian Gulf. The increase in the concentration of SO4 (2-) ion is found to accelerate the rate of reaction in the crude oil-brine-rock (CBR) system, resulting in more wettability alteration. In addition, the Mg2+ ion is rendered more effective in the wettability change process than the Ca2+ ion. The seawater enriched with sulfate ions (two/four-fold) has yielded the highest recovery, with essential increase in higher temperatures. The elevation of temperature to 70 degrees C has yielded an impressive outcome on the recovery - approximately 17.20% - for the best smart-water samples evaluated.