Enhanced Oil Recovery from a Carbonate Reservoir During Low Salinity Water Flooding: Spontaneous Imbibition and Core-Flood Methods

Spontaneous imbibition and core flooding investigations were carried out on limestone core plug samples using different low salinity water (LSW) and smart brines at temperatures of 110 and 50 degrees C, respectively. To demonstrate further the potential of low salinity water injection (LSWI) as an agent for enhanced oil recovery (EOR) studies, the interfacial tension (IFT), contact angle (CA), and zeta potential (ZP) were measured. The recovery factor values provided from spontaneous imbibition experiments investigated by formation water (FW), seawater (SW), dilution versions of SW (i.e., 1/2SW, 1/10SW) were 10.07, 15.11, 18.05, and 16.04%, respectively. However, the secondary LSW flooding produced more oil, i.e., a higher recovery factor (37.3, 55, and 61% for FW, SW, and 1/10SW, respectively). The recovery factor obtained from LSW flooding at the tertiary state for SW, 1/2SW, and 1/10SW brines increased up to 11.86, 12.67, and zero, respectively. The main conclusions of the work were as follows. (1) The results of secondary spontaneous imbibition tests showed that LSWI had a significant potential to mobilize the trapped oil. (2) During secondary and tertiary core flooding, the maximum oil recovery (78% of OOIP) was achieved during smart water flooding when the amount of SO42- ion was increased and inactive ions (Na+ and Cl-) were eliminated. (3) LSWI and smart water showed significant effects on relative permeability curves, which are indicative of wettability alteration. (4) The main driving mechanism for oil mobilization was found to be wettability alteration, which was supported by the analyses of CA and ZP.

Automated summary

The study found that low salinity water injection has a significant effect on releasing trapped oil, and smart water flooding achieves the maximum oil recovery. Low salinity water and smart water have a significant impact on relative permeability curves, indicating wettability alteration.