Hydrocarbon liquid production from carbonate formations should be increased in order to meet the global growing demand of fossil fuels. Conventional water flooding application in these reservoirs are not very effective mainly due to the oil-wet nature of carbonate reservoirs. Special attention has been recently directed on changing ions composition of the injected water to improve the oil recovery which is referred to smart water flooding. Different studies showed that the adjusted water altered the rock wettability to preferentially more water wet which improves the ultimate oil recovery.

A major problem in this approach is to adjust the ions composition of the huge volume of the injected brine. In this research, we introduced a novel, more practical approach as Smart Water Shock Injection (SWSI) to reduce the pore volume size of the injection. This approach is applied to an Omani carbonate field. Since smart water is injected within a short period of time, called shock, governing parameters such as brine salinity and active ions have to be optimized to achieve the highest oil recovery. Analytical methods such as contact angle measurement, pH measurement, brine analysis, SEM-EDS, and zeta potential measurement were also utilized to provide comprehensive analyses of the performance of the proposed method.

The results verified that increasing the concentration of sulfate ions and magnesium ions in the injected diluted brine turned the oil-wet carbonate surface to a water-wet surface which affects the oil production by a shock injection. The new sequence of the SWSI makes the low salinity water flooding method more practical and cheaper. Core flooding experiment showed that SWSI as the tertiary oil recovery approach improves the oil recovery by 4.3 %. Diagnostic tests showed that, carbonate dissolution and multi ion exchange (MIE) are dominant mechanisms to alter the wettability and improve the oil recovery in our approach.

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