Experimental Study on Enhanced Oil Recovery by Low Salinity Water Flooding on the Fractured Dolomite Reservoir

Enhanced Oil Recovery from carbonate reservoirs is a major challenge especially in naturally fractured formations where spontaneous imbibition is a main driving force. The Low Salinity Water Injection (LSWI) method has been suggested as one of the promising methods for enhanced oil recovery. However, the literature suggests that LSWI method, due to high dependence on rock mineralogy, injected and formation water salt concentration and complexity of reactions is not a well-established technology in oil recovery from carbonate reservoirs. The underlying mechanism of LSWI is still not fully understood. Due to lack of LSWI study in free clay dolomite fractured reservoir, and to investigate of anhydrate composition effect on oil recovery in this type of reservoir, the main purpose is the experimental evaluation of oil recovery from one of the Iranian naturally fractured carbonated (dolomite containing anhydrate and free clay) reservoirs using LSWI. For this purpose, a set of experiments including spontaneous and forced imbibition is conducted. To obtain the optimum salt concentration for oil recovery, the secondary mode of the spontaneous imbibition tests is performed by seawater in various salt concentrations at the reservoir temperature (75°C). Also, the tertiary recovery mode is subsequently applied with optimum brine salinity. The lab results reveal that by decreasing the injected water salt concentration, oil production increases. Furthermore, in order to upscale the experimental results to the field scale, a more precise dimensionless-time correlation is used. Due to some inconsistencies over the influence of mechanisms on LSWI oil recovery, the mineral dissolution, pH-increase mechanisms, and wettability alteration are also studied. The results indicate that wettability alteration is the main mechanism and mineral dissolution may be the predominant mechanism of the improved oil recovery in the studied reservoir. It is noticed, the elevation of pH led to enhanced oil recovery when high dilution of low salinity water is implemented.