ILLITE SURFACE CHEMISTRY AND SHALE OIL RESERVOIRS

Illite clay is a large component of unconventional shale reservoirs such as the Eagle Ford, Bakken, Marcellus Shale, Utica Shale, and Rhine Street Shale. Because of illite’s high surface area, illite-oil adhesion is a potential control over oil production. Here we develop a surface complexation model of illite-oil interaction and use it to consider the impact of frack water, flowback, and connate water chemistry on potential oil adhesion mechanisms. Key model inputs are illite edge vs. basal plane exposure, illite surface complexation constants, ambient water chemistry and oil acid and base numbers. The model also accounts for the impacts of secondary mineral equilibria (e.g. calcite) and variable salinity on illite and oil surface charge and electrostatic attraction. Key uncertainties are the surface acidity of shale oils and the reversibility of adhesion mechanisms.