Dewetting dynamics of heavy crude oil droplet in low-salinity fluids at elevated pressures and temperatures

Improved oil recovery by low-salinity injection correlates to the optimal brine concentration to achieve maximum dewetting of oil droplets on rock surfaces. While interfacial tension and electrical double layer forces are often cited as being determinant properties, we hypothesize that other structural/interfacial forces are more prominent in governing the system behavior.

The sessile droplet technique was used to study the receding dynamics of oil droplets from flat hydrophilic substrates in brines of different salt type (NaCl and CaCl₂) and concentration, and were studied at both low and elevated temperatures (60 and 140 °C) and pressures (1, 10, 100 and 200 bar).

At 1 bar and 60 °C, the minimum oil droplet-substrate adhesion force (F_A) was determined at 34 mM NaCl and 225 mM CaCl₂. For NaCl this strongly correlated to strengthening hydration forces, which for CaCl₂ were diminished by long-range hydrophobic forces. These results highlight the importance of other non-DLVO forces governing the dewetting dynamics of heavy crude oil droplets. At 140 °C and 200 bar, the optimal brine concentrations were found to be much higher (1027 mM NaCl and 541 mM CaCl₂), with higher concentrations likely attributed to weakening hydration forces at elevated temperatures.