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 weake r 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 po re surface is obtained when the pH is lowered near neutral. Outcrop sandsto ne samples were treated either with or without the presence of oil (at Swir r) using carbon dioxide as a neutralizer. Efficiency of the treatment is de termined mainly by comparing centrifuge (negative) imbibition capillary pre ssure curve on treated and untreated samples. Micropore membrane technique was also applied to measure the positive imbibition capillary pressure curv e. 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 cur ve; and (3) water relative permeability at Sor measured after centrifuge fo rced imbibition is not modified by the treatment. (C) 1999 Elsevier Science B.V. All rights reserved.