Experimental investigations of the wettability of clays and shales

Abstract

Wettability in argillaceous materials is poorly understood, yet it is critical to hydrocarbon recovery in clay-rich reservoirs and capillary seal capacity in both caprocks and fault gouges. The hydrophobic or hydrophilic nature of clay-bearing soils and sediments also controls to a large degree the movement of spilled nonaqueous phase liquids in the subsurface and the options available for remediation of these pollutants. In this paper the wettability of hydrocarbons contacting shales in their natural state and the tendencies for wettability alteration were examined. Water-wet, oil-wet, and mixed-wet shales from wells in Australia were investigated and were compared with simplified model shales (single and mixed minerals) artificially treated in crude oil. The intact natural shale samples (preserved with their original water content) were characterized petrophysically by dielectric spectroscopy and nuclear magnetic resonance, plus scanning electron, optical and fluorescence microscopy. Wettability alteration was studied using spontaneous imbibition, pigment extraction, and the sessile drop method for contact angle measurement. The mineralogy and chemical compositions of the shales were determined by standard methods. By studying pure minerals and natural shales in parallel, a correlation between the petrophysical properties, and wetting behavior was observed. These correlations may potentially be used to assess wettability in downhole measurements. Copyright 2009 by the American Geophysical Union.