Author Description

Wettability reversal during the displacement processes encountered in hydrocarbon reservoirs has gained significant attention in recent years owing to its critical role in the success/failure of water-based enhanced oil recovery (EOR) schemes. Regardless of different designations used for these technologies, e.g., low-salinity waterflooding (LSWF), smart water injection, or engineered water injection, manipulating the ionic compositions and concentrations of the aqueous solutions to trigger the wettability reversal process is the shared objective. Despite the encouraging application potentials, the mechanisms that govern the wettability reversal and how it affects the displacement efficiency are still poorly understood, particularly in oil-wet carbonates. Therefore, in this work, multi-scale experiments were carefully designed and conducted to probe the impacts of rock wettability and its reversal, induced through brine chemistry manipulation, on oil recovery performance. We first investigated the adsorption-controlled calcite substrate wettability using a HPHT interfacial tension/contact angle measurement apparatus. The results were then further examined in natural rock samples through miniature core-flooding experiments. A high-resolution X-ray micro-CT scanner was used with a multiphase fluid delivery system to conduct the flow tests. Prior to each waterflooding experiment, an equilibrium wettability state was established in the core sample. This study reveals that wettability reversal, caused by adsorption/desorption of the polar components present in crude oil, is the principal factor responsible for the changes in oil recovery trend during LSWF. Dynamic contact angles measured on calcite substrates indicated that adsorption of the polar components controlled the surface wettability. Higher concentrations of Ca2/SO42− can facilitate/obstruct the adsorption of polar components thus increase/decrease the dynamic contact angle values. A similar wetting strength se