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

Chemically tuned water flooding can significantly enhance oil recovery in carbonate reservoirs, with potential increases of up to 40% of original oil in place (OOIP). This finding stems from a mechanistic model that elucidates how sulfate ions (SO₄²⁻) replace adsorbed carboxylic groups on rock surfaces, altering wettability from oil-wet or mixed-wet to more water-wet conditions. The model, tuned using experimental data from Stevns Klint chalk, demonstrates that optimal brine formulations for chalk reservoirs contain abundant sulfate (0.096 mol/kg water), moderate cation concentrations, and low salinity (<0.2 mol/kg water). While cations like Ca²⁺ have a minor effect on recovery (~5% OOIP), physical parameters such as rock surface area and diffusion coefficient influence the rate but not the final oil recovery. This research provides a robust tool for predicting improved oil recovery (IOR) under varying conditions, offering practical insights for field applications in carbonate reservoirs.

Qiao, C., Li, L., Johns, R. T., & Xu, J. (2014). A Mechanistic Model for Wettability Alteration by Chemically Tuned Water Flooding in Carbonate Reservoirs. SPE Annual Technical Conference and Exhibition. https://doi.org/10.2118/170966-ms