Experimental Investigation of the Presence of Anhydrite on the Effectiveness of Low Salinity Water Injection in a Carbonate Reservoir

Low salinity water injection (LSWI) is an emerging and effective enhanced oil recovery (EOR) technique because of its recovery performance, low cost, and environmentally friendly compared to other EOR approaches. However, low salinity water effects and their governing mechanisms in carbonates were not fully understood. According to the literature, the present of anhydrite mineral can play a positive role in low salinity in carbonates. In this study, to investigate the present of anhydrite mineral, the wettability alteration was measured in a wide range of salinity by flotation technique. The flotation results show that the wettability modified toward a more water-wet state by decreasing salinity and in-active ions.  Rock wettability was slightly altered by deionized water that could be due to dissolution of anhydrite that provide SO4-2 ions consequently electrical charge reduction of the rock surface. It was then aimed to examine the effectiveness of the low salinity brines in core flood experiments. The results of core flooding experiments indicated that 25 times diluted sea water extracted 4.9 % extra oil production in tertiary mode following by formation water, sea water, and 10 times diluted sea water. This brine in secondary mode produced 2.3 % of OOIP more than sequentially injection of brines. Based chemical element analysis using ICP-OES method, multi-component ion exchange and mineral dissolution are responsible for wettability alteration to more water-wet.