Spatial Correlation of Contact Angle and Curvature in Pore-Space Images

We study the in situ distributions of contact angle and oil/brine interface curvature measured within millimeter-sized rock samples from a producing hydrocarbon carbonate reservoir imaged after waterflooding using X-ray microtomography. We analyze their spatial correlation combining automated methods for measuring contact angles and interfacial curvature (AlRatrout et al., 2017, https://doi.org/10.1016/j.advwatres.2017.07.018), with a recently developed method for pore-network extraction (Raeini et al., 2017, https://doi.org/10.1103/PhysRevE.96.013312). The automated methods allow us to study image volumes of diameter approximately 1.9 mm and 1.2 mm long, obtaining hundreds of thousands of values from a data set with 435 million voxels. We calculate the capillary pressure based on the mode oil/brine interface curvature value and associate this value with a nearby throat in the pore space. We demonstrate the capability of our methods to distinguish different wettability states in the samples studied: water-wet, weakly oil-wet, and mixed-wet. The contact angle and oil/brine interface curvature are spatially correlated over approximately the scale of an average pore. There is a wide distribution of contact angles within a single pore. A range of local oil/brine interface curvature is found with both positive and negative values. There is a correlation between interfacial curvature and contact angle in trapped ganglia, with ganglia in water-wet patches tending to have a positive curvature and oil-wet regions seeing negative curvature. We observed a weak correlation between average contact angle and pore size, with the larger pores tending to be more oil-wet. Plain Language Summary This research article concerns the pore-scale characterization of wettability. A novel method has been developed to automatically extract contact angles and fluid/fluid interface curvature from pore-space images (AlRatrout et al., 2017). The method has been successfully tested on benchmark synthetic images for which the contact angle and curvature are known analytically and has been applied to a real rock data set. Both a water-wet and a mixed-wet rock have been analyzed. Further, the method has been utilized to study the spatial correlation of the in situ measured distributions of contact angles and oil/brine interface curvatures within the reservoir rock samples at subsurface conditions used in Alhammadi et al. (2017, ). We relate the measurements of contact angle and interfacial curvature (capillary pressure) to individual trapped ganglia of oil and to the pore sizes extracted by a generalized pore-network modeling approach (Raeini et al., 2017). Our findings and analysis could potentially have implications for pore-scale modeling of multiphase flow, in which methods using local curvature measurements could be directly used to calculate capillary pressures for displacement.