Evaluation of Water-Based Enhanced Oil Recovery (EOR) by Wettability Alteration in a Low-Permeable Fractured Limestone Oil Reservoir

This paper introduces a comprehensive method on how to evaluate wetting properties and oil recovery potential by spontaneous imbibition of "smart water" Into a low-permeable limestone reservoir (approximate to 1 mD) The reservoir temperature was 110 degrees C, and the salinity of the formation water was high (similar to 208 000 ppm) Crude oils from different possible source rocks were characterized for acid and base numbers, asphaltene viscosity, and density The potential of water-based enhanced oil recovery (EOR) was evaluated on the basis of the following studies (1) The wetting potential of crude oils toward carbonate surface was investigated (2) The presence of capillary forces in the core material was tested by spontaneous imbibition (3) The initial wetting condition was determined by the chromatographic wettability test on mildly cleaned cores (4) The surface reactivity of limestone core toward Ca2+, Mg2+, and SO42- was evaluated, when exposed to seawater at different temperatures (70-150 degrees C) (5) The presence of anhydrite CaSO4(s) in the limestone core material was confirmed, which will affect the initial wetting conditions (6) The potential of smart water to enhance oil recovery from limestone cores containing crude oil and formation water at 110 degrees C was evaluated by imbibition of seawater and modified seawater Because of the low content of acidic material in the crude oils and the presence of anhydrite in core material, the limestone cores were expected to be preferentially water wet, which was confirmed by the chromatographic wettability test About 40% of original oil in place (OOIP) was recovered in a spontaneous imbibition process at 110 degrees C using formation water In a tertiary imbibition process with seawater and modified seawater, the oil recovery increased to similar to 50% of OOIP