A study on the effect of the chemical composition of brine to improve oil recovery from carbonates

Abstract

ABSTRACTNowadays, brines are not simply regarded as tools for pressure support in reservoirs. Their chemical properties have also been taken into consideration. Chemicals in the brines can alter the rock brine and oil interactions in a favorable way to improve oil recovery. Studies have focused on the determination of such chemicals leading to wettability change and their proper compositions in brine samples. In this study, the properties of brine samples utilization, which can lead to improvement in oil recovery from carbonates, were tried to be determined using wettability measurements.Wettability of the oil/brine/limestone systems was measured applying the Modified Flotation Test (MFT) procedure. Many oil samples having different properties and thus having different reactivities toward the carbonate surface, formation brine samples having different salinities, seawater sample, modified seawater samples obtained by either increasing the sulfate concentration or removing NaCl, the brine samples including only Na2SO4 or MgSO4, and distilled water were used. In case of using the oil samples having a high base number and low acid number and the pure oil samples lacking heavy components, the utilization of seawater, modified seawater samples, and the brine sample containing only Na2SO4 generally resulted in higher water-wet fractions compared with the water-wet fractions obtained using the formation brine samples. On the other hand, the improvement achieved via sulfated brine utilization was not observed in case of using the oil sample having a high acid number but low base number. In addition, it was observed that the MgSO4 solution was less effective than the other sulfated brines and distilled water was not effective in increasing the water wettability.