Gaetano Garfi , Qingyang Lin, Steffen Berg, Cédric M. John , Sam Krevor

The wetting state is an important control on flow in subsurface multi fluid phase systems, e.g., carbon storage and oil production. Advances in X-ray imaging allow us to characterise the wetting state using imagery of fluid arrangement within the pores of rocks. We derived a model from equilibrium thermodynamics relating fluid coverage of rock surfaces to wettability and fluid saturation. The model reproduces the behaviour measured in a water-wet, nearly all-quartz, Bentheimer sandstone imaged during steady-state imbibition. A shift in fluid surface coverage is observed when the rock is altered to a new wetting state with crude oil. In two multi-mineralogical (Berea) samples, one water-wet and the other altered with crude oil, the analysis of fluid surface coverage after imbibition revealed mineral specific wetting preferences only in the altered system. Clays and calcite preferentially alter to an oil wet state, leading to mixed wettability in the rock.