An experimental study into rock dissolution mechanism during diluted seawater injection in carbonate rocks

Three decades has passed since the introduction of smart water injection in carbonate rocks; however, use of diluted seawater (dSW) and its associated mechanisms are not yet well understood. Several mechanisms have been introduced in the literature for increased productivity of low salinity water injection. In this study, coreflooding tests were conducted to analyze the importance of one of the contribution mechanisms, the so-called rock dissolution mechanism. We used seawater as the baseline injecting phase, along with two dSW solutions, 5- and 20-folds dilution ratios as the low salinity solutions. Several pore volumes of the displacing phase were injected into real reservoir core plugs to recover the oil content. The impact of rock dissolution on oil recovery was evaluated by measuring core plug permeabilities before and after the flood as well as the recovery factor (RF) as a function of time, along with monitoring pH of the displacing phase at the inlet and effluent. The interaction of rock and fluid was closely monitored and analyzed by studying the injection pressure profiles. It was obtained that diluting the seawater intensified the rock dissolution. This mechanism was absent when unprocessed seawater was used to recover the oil.