Wettability determination of core samples through visual rock and fluid imaging during fluid injection

Reservoir rock wettability is a key factor in oil recovery, as it controls the location, flow, and distribution of reservoir fluids. However, proper assessment of wettability is not an easy task and provides a number of challenges. Wettability is in parts determined by the history of the oil reservoir through mechanisms such as aging and fouling. Hence direct measurements on freshly exposed rock surfaces (e.g. on core plugs) are critical and might not represent the true wettability within the sample. We present a new and fast method for wettability determination based on the optical observation of injected fluids, which allows for wettability determination independent from the surface wettability state of the sample. Fluid behavior within the boundaries of the capillary regime is driven by capillary forces and thus by wettability, which is exploited for our method. We show that a combined optical white-light and fluorescence imaging technique provides excellent contrast for reliable observations. Based on this imaging technique, we successfully distinguish core samples with different internal wettability, independent of their surface state.