Wettability alternation and interface tension modification for enhanced oil recovery in oil-wet carbonates: A comparative study of different surfactants

Abstract

With the ever-growing demand for oil and gas today, and the increasing difficulty of recovering hydrocarbons from carbonate reservoirs, it is vital to apply enhanced oil recovery (EOR) techniques. Carbonate reservoirs typically have natural fractures and are found to have oil-wet matrixes natively, making EOR in these reservoirs more challenging. Wettability alteration is a viable mechanism in this scenario. However, there is an ambiguity about which chemical solutions perform better in carbonate reservoirs. This study assessed the capabilities of various surfactants and their ability to alter wettability and interfacial tension under surface and reservoir conditions. Fifty-six surfactants from four different chemical groups (cationic, anionic, zwitterionic/amphoteric, and nonionic) were screened for their stability and emulsification. Then, spontaneous imbibition experiments were performed on an Indiana limestone outcrop to assess the impact of wettability and interfacial tension on oil recovery for both aged and non-aged cores. Results show that six out of the eleven successful surfactants were nonionic. Furthermore, we found that, for oil-wet rocks, wettability alteration increases production in the early stages of imbibition, while the reduction in interfacial tension increases the recovery in the later stages by unlocking trapped oil in the pore matrix. Exploratory data analysis showed that IFT is the most correlated parameter with the recovery from the aged cores, while contact angle was highly correlated with both aged and non-aged cores. Finally, a generalized automated spontaneous imbibition model was derived based on the dimensionless exponential and hyperbolic functions. The fitting results show that both the exponential and hyperbolic models complied with the trend of spontaneous imbibition. However, the exponential model better matches the surfactant imbibition data. The results from this work help unlock the potential of carbonate reservoirs and maximize the oil recovery to solve the current global energy challenge.