Favorable attributes of low salinity water aided alkaline on crude oil-brine-carbonate rock system

Abstract

Although low-salinity water flooding (LSWF) is an enhanced oil recovery (EOR) method, it does not target weakly water-wet situation (which is the best situation for the EOR process) for carbonate rocks. Also, this method does not show a significant reduction in the oil-water interfacial tension (IFT). Despite the ability of alkaline flooding to alter the rock wettability to the desirable range as well as a signification reduction in IFT, the need for a high amount of alkaline makes the approach economically unjustified. In the current study, favorable attributes of low salinity water aided alkaline (LSWA) approach on a crude oil/brine/carbonate rock (CBR) system are presented in terms of IFT reduction and contact angle (CA) alteration. To this end, three solutions with different alkalinity (weak (NaHCO3), intermediate (Na2CO3), and strong (NaOH)) degrees are used in combination with different LSW. The results show that LSWA achieves the target wettability range (75-85°). Also, the reaction between divalent ions with an alkaline solution is an unfavorable factor on the rock surface. As a considerable achievement, the LSWA approach resulted in a significant reduction in IFT, which was reduced from 13.2 mN/m to 1.1 mN/m in the LSW approach by adding 4000 ppm of NaOH. Therefore, using the LSWA flooding in enhancing oil recovery (EOR) from carbonate reservoirs is highly recommended to get a higher efficiency at a lower concentration of alkaline, which leads to a decrease in costs.