Residual Saturation of Water-Wet Sandstones: Experiments, Correlations and Pore-Scale Modeling

Abstract

Displacement experiments using the porous plate method were conducted on water-wet sandstones to measure the capillary trapping of oil by waterflooding as a function of its saturation after primary drainage. Three sandstone samples ranging in porosity from 12.2% to 22.1% were considered. Experiments on two samples were conducted at an elevated temperature and back-pressure of 343K and 9MPa respectively; experiments on the third sample were conducted at ambient conditions (292 to 297K and 0.06 to 0.17MPa). Residual oil saturation increases monotonically, but with a decreasing gradient, as initial saturation increases.The dependence of residual saturation on initial saturation is accurately predicted by a two-phase pore-network simulator when a uniform distribution of intrinsic contact angles between 35° and 65° is assumed. The networks were extracted from Xray microtomography images of small samples of the same rock as those used in the experiments. The laboratory measurements are also accurately described by trapping models proposed by Land (1968) and Spiteri et al. (2008). The residual saturations we measured were higher than in previous displacement experiments, suggesting, for example, that capillary trapping may be an effective way to store substantial quantities of carbon dioxide in aquifers.