Effects of Monovalent Ions on Low Salinity Waterflooding in Shaly-sandstone Reservoir

Abstract

Multi-component Ion Exchange (MIE) was proved to be a major mechanism occurred during Low Salinity Waterflooding (LSWF). Reduction of both total salinity and concentration of divalent ions of injected water together with a presence of monovalent ion results in dissolution of divalent ions linking between rock surface and oil. As a consequence, oil is liberated from rock surface.

This study aims to study effects of monovalent ions in MIE mechanism. Stirring test is performed and results show that ion with less hydration radius tends to be more active in MIE; hence, potassium ion and cesium ion illustrate potential in oil recovery mechanism. Then, the best three water formulations can be selected to perform imbibition and coreflood tests and both tests show results in the same direction. Pure cesium ion is very fast in MIE mechanism while pure potassium ion with a few water molecules can also function well in oil recovery. However, its mobility is less than cesium ion. The combination of cesium-sodium-calcium at 20-40-40 tends to be similar results of pure potassium ion. In comparision, Pure cesium ion is the best water formulation enhacing recovery factor up to 0.26. However, complexometric titration result shows remarkable contrast to the stirring test that both cesium ion and potassium ion tend to displace magnesium ion better than calcium ion. In conslusion, this study has already proved the theory regarding the hydrate of monovalent ion.