title: Comparison of residual oil cluster size distribution, morphology and saturation in oil-wet and water-wet sandstone.
abstract: We imaged an oil-wet sandstone at residual oil saturation (S(or)) conditions using X-ray micro-tomography with a nominal voxel size of (9 μm)(3) and monochromatic light from a synchrotron source. The sandstone was rendered oil-wet by ageing with a North Sea crude oil to represent a typical wettability encountered in hydrocarbon reservoirs. We measured a significantly lower S(or) for the oil-wet core (18.8%) than for an analogue water-wet core (35%). We analysed the residual oil cluster size distribution and find consistency with percolation theory that predicts a power-law cluster size distribution. We measure a power-law exponent τ=2.12 for the oil-wet core which is higher than τ for the water-wet system (τ=2.05), indicating fewer large clusters in the oil-wet case. The clusters are rough and sheet-like consistent with connectivity established through layers in the pore space and occupancy of the smaller pores; in contrast the clusters for water-wet media occupy the centres of the larger pores. These results imply less trapping of oil, but with a greater surface area for dissolution. In carbon storage applications, this suggests that in CO(2)-wet systems, capillary trapping is less significant, but that there is a large surface area for dissolution and reaction.
authors.affiliation: Curtin University, Department of Petroleum Engineering, Kensington, Australia. stefan.iglauer@curtin.edu.au
authors.forename: S
authors.initials: S
authors.lastname: Iglauer
authors.forename: M A
authors.initials: MA
authors.lastname: Fernø
authors.forename: P
authors.initials: P
authors.lastname: Shearing
authors.forename: M J
authors.initials: MJ
authors.lastname: Blunt