الملخص الإنجليزي
Carbonate reservoirs, which are complex and heterogeneous, contain the majority of the world's reserves. Since the mineral surface of carbonate rocks has a positive charge that draws acidic oil compounds to it, most of these reservoirs are mixed-wet to oil-wet. Owing to their characteristics, carbonate reservoirs exhibit relatively low spontaneous imbibition of water, which leads to inadequate oil recovery using traditional water floods. Surfactant flooding can alter the wettability of these reservoirs and improve oil displacement through interfacial tension (IFT) reduction. However, the economic viability of surfactant flooding severely restricts its application. Anionic carboxylate surfactants are cheap and have a lot of promise in harsh reservoir environments with high salinity and high temperature. A flexible alkyl ether carboxylate (AEC) is produced by synthesizing carboxylate surfactant with varying amounts of ethylene oxide (EO) and/or propylene oxide (PO) units and variable alkyl chain lengths. Previous studies confirmed the positive effect of surfactants on enhancing oil recovery by spontaneous imbibition. Therefore, the objective of this study was to investigate the effect of AEC surfactant structures, rock permeability, and temperature in spontaneous imbibition dynamics in oil-wet carbonate and to provide better understanding of forces controlling spontaneous imbibition dynamics under different conditions. The experimental approach included the following: IFT, contact angle (CA), and spontaneous imbibition tests. These tests were conducted at four different temperatures (25℃, 50℃, 75℃, and 100℃) and for three rock permeability ranges (low permeability: 2-10 mD, medium permeability: 45-150 mD, and high permeability: >200 mD). The minimum IFT in the order of 10−2mN/m was achieved by surfactant with a long alkyl chain and low hydrophilicity. CA measurements revealed that the surfactant which has best IFT reduction properties was able only to alter wettability toward neutral or weak oil-wet. While, the other surfactant can alter the wettability from strong oil-wet to strong water-wet with final CA of around 35°. This surfactant had the shortest alkyl chain and highest hydrophilicity. These surfactants were considered then for spontaneous imbibition tests. Surfactant with the long alkyl obtained higher oil recovery than the surfactant with
short alkyl at all conditions, except at low permeability and low temperatures (25℃ and 50℃). High permeability yielded higher oil recovery for both surfactant at all temperatures, except for the surfactant with the short alkyl chain at low temperature (25℃) at which low permeability yielded the highest oil recovery. Temperature was found to have a positive effect on oil recovery at all conditions. The findings of this study show that IFT reduction leads to fastest and highest oil recovery in spontaneous imbibition compared to wettability alteration mechanism except at low temperatures (≤ 50℃) and low permeability. In regard to the forces affecting spontaneous imbibition dynamics, results show that at early time spontaneous imbibition capillary force is dominant. While late time spontaneous imbibition is controlled mainly by viscous and gravity forces.
