The Role of Water Film on Dead-end Pore Walls in the Enhancement of Mass Transfer between Shielded Oil and Gas

Abstract

Water shielding happens in water-wet reservoirs after waterflooding, where water fills the throats of oil-bearing dead-end pores and prevents tertiary injected gas from direct contact with oil; however, diffusion takes place between gas and oil via dissolution of components in water, which causes the oil to gradually swell until it completely pushes away the water from the throat. None of the previous experimental and numerical studies on the water-shielded oil recovery from a single dead-end pore have considered the presence of the thin water film on the surface of water-wet rocks, whereas it considerably enhances the gas-oil mass transfer rate by extending the contact area between the oil ganglion and the surrounding water. In this study, a 2-D mathematical model was utilized to investigate the impact of the water film covering the pore walls on the time required for displacing of water barrier by oil. Four micromodel experiments were modeled with and without considering the presence of water film, and the estimated times were compared. The results showed that inclusion of water film in the model yielded highly more accurate results, inferring the necessity to take this phenomenon into account in order to obtain realistic results.