Alteration of wetting of mica surfaces

Models of the complex interactions among crude oils, brines, and reservoir rocks are needed to facilitate studies of oil reservoir wettability. Sandstone reservoir minerals are usually represented by crystalline quartz or by various glass surfaces, but links between wetting alteration on these mineral surfaces and wetting effects in sandstone cores are difficult to establish. Mica is an alternative that is attractive for several reasons. It is relatively easy to reproduce fresh, molecularly smooth surfaces that are ideal for contact angle measurements. Surface chemistry can be varied by ion exchange. While sandstones may be composed primarily of quartz, pore surfaces may be better represented by high-surface-area clays. Muscovite mica has a similar surface structure to illite, a common clay mineral. Mica itself may be a more common component of reservoir rocks than has generally been recognized. Interactions have been tested with two varieties of mica and compared to previous studies on glass surfaces with the same brines and crude oils. Results are consistent with respect to the water film-stability concepts developed in studies using glass surfaces. The principal difference between mica and glass is the effect of temperature on crude oil/brine/solid interactions.