Intermediate wettability by chemical treatment

To study the effect of wettability on recovery, we used a chemical additive that changes the surface properties of natural rock samples while keeping interfacial tension and viscosity constant. The wettability change is weaker than for other chemical treatments (e.g., silane) and is therefore closer to reservoir cases. The chemical additive is a potassium methyl siliconate that is soluble in water. A polymerization of the adsorbed layer on the pore surface is obtained when the pH is lowered near neutral. Outcrop sandstone samples were treated either with or without the presence of oil (at Swirr) using carbon dioxide as a neutralizer. Efficiency of the treatment is determined mainly by comparing centrifuge (negative) imbibition capillary pressure curve on treated and untreated samples. Micropore membrane technique was also applied to measure the positive imbibition capillary pressure curve. The main results are (1) the final oil saturation (Sor) is reduced from 0.4 to 0.3 and 0.1 depending on how the treatment was performed; (2) there are only minor modifications on the primary drainage capillary pressure curve; and (3) water relative permeability at Sor measured after centrifuge forced imbibition is not modified by the treatment.