LAUSR

Abstract Imbibition of water, as wetting phase in oil-wet fractured carbonate reservoirs, plays a key role in fluid flow between matrix and fracture system. The type of injected seawater and its chemistry would profoundly influence the imbibition process. In this study, the impact of smart water (a brine that its ions have been adjusted to facilitate oil recovery) and low salinity water on co- and counter-current imbibition processes for oil-wet carbonate cores has been experimentally investigated. The results show an increase of about 10% in oil recovery for co- and counter currents for smart seawater imbibition compared to that of low salinity seawater. In addition, as a result of the influence of co- and counter current on each other, by co-current removal from one core face, the counter current in the other face would be intensified by as much as about 75%. A close examination of different lengths (5, 7 and 9 cm) of carbonate cores with the same permeability revealed that by decreasing porous medium length, the amount of counter current producing oil would be decreased so that in the 5 cm core, counter current oil production will not happen. For similar core lengths by increasing permeability, the share of counter current flow would be decreased approximately 18% since the capillary pressure could not overcome non-wetting phase viscous forces. Considering the role of matrix length along with a modified brine (which is designed according to the matrix mixture) strengthen the relevant mechanisms to have more oil production so that the higher thickness of matrix causes the higher amount of co-current oil producing and consequently more total recovery.