Investigating Imbibition Rate and Oil Recovery Mechanisms from Fractured Formations by Hybrid EOR Approaches

Abstract Enhanced Oil Recovery (EOR) methods play a crucial role in producing significant volumes of trapped hydrocarbons within fractured oil-wet reservoirs. These methods aim to modify the fluid-rock interactions, reduce interfacial tension, and alter the wettability of the reservoir to increase the total oil recovery. Imbibition is the fundamental mechanism for fluid transport between matrix and fracture within fractured formations. Different EOR mechanisms affect the imbibition by altering capillary-related parameters such as wettability and interfacial tension. The rate of spontaneous imbibition is different during different EOR techniques, such as surfactant flooding, low salinity water injection, and hybrid methods. The effect of the type of capillary modifications on the imbibition rate was studied in this work. This study delves into a series of spontaneous imbibition tests aimed at scrutinizing imbibition rates across diverse EOR strategies: low salinity water flooding, surfactant flooding, and hybrid EOR approaches for fractured reservoirs. The effect of parameters such as pH was also investigated. The oil recovery due to the alteration in capillary force during the spontaneous imbibition was recorded, and the imbibition rate was analyzed based on recovery/square root of time data. Furthermore, an array of parameters, including interfacial tension, ion composition, and pH, were measured and studied to investigate the mechanisms behind varied imbibition rates. The impact of imbibition rates on the forced imbibition process was also assessed, striving for a comprehensive understanding of imbibition dynamics during EOR strategies. The results showed a significant difference in imbibition rates between standalone low salinity water flooding imbibition and surfactant solutions. Our studies demonstrated that the rate of capillary pressure alteration due to changes in interfacial tension surpasses the rate of alteration caused by shifts in the wettability state. Application of the hybrid method enhances the imbibition rate, which affects the oil recovery from a fractured formation. Under high pH conditions, the imbibition rate exhibited a low initial rate, followed by substantial increases by the injected water dilution. Conversely, under acidic conditions, the trend was reversed due to the activation of different low salinity water-related recovery mechanisms. The significance of this investigation goes beyond the laboratory setting, extending its impact to the practical realm of designing processes within fractured reservoirs. By illuminating the complicated interplay between pH, water salinity, capillary, and imbibition rates, this study serves as a vital base for designing hybrid approaches that optimize EOR techniques tailored to fractured reservoirs’ complexities.