In situ surfactant generation via saponification in alkali-assisted steam flooding for heavy oil recovery

This study explores alkali-assisted steam flooding as an effective approach for enhancing oil recovery in heavy oil reservoirs with high acid content. This method eliminates the need for costly surfactants by generating soap in situ. The research identifies naphthenic acids as the dominant acidic components in crude oil, with a double bond equivalent value of 3 or 4. Upon reacting with the sodium hydroxide (NaOH) solution, the interfacial tension decreased to ∼10−2 mN/m, and the acid–base reaction produced soap, altering the rock's wettability from oil-wet to water-wet. The emulsion viscosity was reduced with NaOH at an oil–water ratio of 3:7. Alkali-assisted steam flooding demonstrated that after the first alkali injection, the water cut was controlled, leading to a more than 10% increase in oil recovery. Alternating steam and alkali injections further improved the saponification reaction, resulting in a noticeable reduction in emulsion droplet diameter in the recovered oil samples, with most droplets concentrated in the 4–10 μm range. The shift in droplet diameter distribution indicates a transition from an initially thermally dominated emulsification process to a more stable emulsification system driven by alkali-induced interfacial activity. This study provides valuable insights into the mechanisms of alkali-assisted steam flooding for enhancing recovery in high-acid heavy oil reservoirs.