Quantum mechanics

Scale (ratio)

Mathematics education

Residual oil

Engineering

Flooding (psychology)

Metallurgy

Materials science

Brine

Displacement (psychology)

Petroleum engineering

Salinity

Chemical engineering

Carbonate

Geology

Oil field

Porosity

Oceanography

Physics

Organic chemistry

Psychology

Mathematics

Microstructure

Psychotherapist

Water flooding

Environmental science

Porous medium

Composite material

Microscale chemistry

Enhanced oil recovery

Chemistry

Wetting

Seawater

Micromodel

Energy & Fuels

Previous macroscopic core flooding tests have shown that injecting low-salinity water improves oil recovery in sandstone and carbonate reservoirs through wettability alteration. However, consistent mechanistic clarification of the underlying physicochemical mechanisms involved in oil wettability at the pore-scale level is not fully understood. In this work, a microfluidic approach is used to provide in situ visualization of oil–brine flow to give an indication of the micromechanisms affecting oil sweep efficiency. The potential of enhancing oil recovery by low-salinity flooding at the microscale is also investigated, which would help in predicting a reservoir's performance before committing to production processes at a large field scale. Two types of crude oils with various acid numbers were used, and hydrophilic and hydrophobic physical microstructures were used to mimic sandstones and carbonates. The results revealed a reduction by 7–10% in the residual oil for the water-wet microstructure when the seawater was diluted twice from its original concentration, apparently due to a decrease in the attractive forces. There is no change in the recovery factor for the oil-wet micromodel for the two kinds of crude oils examined. Tertiary low-salinity flooding did not show any effect on the initial wetting state of the hydrophobic surface, rendering it with a strongly oil-wet condition. It is also observed that flow dynamics of the two microstructures examined are different, as the snap-off–coalesce phenomenon dominants the flow in the water-wet system, while oil moved by a piston-like displacement with a stable or irregular front in the hydrophobic system. In contrast to some of the published macroscopic results, our pore-scale displacement shows that low-salinity flooding seems to be an unsuitable choice for enhanced oil recovery for strongly oil-wet reservoirs.

Pore-Scale Displacement Efficiency during Different Salinity Water Flooding in Hydrophilic and Hydrophobic Microstructures