A Mechanistic Model for Wettability Alteration by Chemically Tuned Waterflooding in Carbonate Reservoirs

A novel mechanistic model demonstrates that chemically tuned waterflooding can enhance oil recovery by up to 40% original oil in place (OOIP) in carbonate reservoirs, such as Stevns Klint chalk. The model reveals that sulfate ions (SO₄²⁻) play a pivotal role in altering rock wettability from oil-wet or mixed-wet to more water-wet conditions by replacing adsorbed carboxylic groups on the rock surface, while cations like Ca²⁺ and Mg²⁺ have a minor effect. The study integrates multiphase flow, multicomponent surface complexation, and wettability alteration, showing that optimal brine formulations for chalk contain abundant sulfate (0.096 mol/kg water), moderate cation concentrations, and low salinity (<0.2 mol/kg water). This work provides the first mechanistic coupling of these processes to predict improved oil recovery under varying conditions, offering a powerful tool for optimizing chemically tuned waterflooding in carbonate reservoirs.

Qiao, C., Li, L., Johns, R. T. T., & Xu, J. (2015). A Mechanistic Model for Wettability Alteration by Chemically Tuned Waterflooding in Carbonate Reservoirs. SPE Journal, 20(04), 767–783. https://doi.org/10.2118/170966-pa