Fluid Surface Coverage Showing the Controls of Rock Mineralogy on the Wetting State

Abstract

The wetting state is an important control on flow in subsurface multi-fluid phase systems, for example, carbon storage and oil production. Advances in X-ray imaging allow us to characterize 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 behavior 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 multimineralogical (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.