Capillary Desaturation in Unconsolidated Beads

Abstract

Abstract Glass beads have been surface treated with Dri-film to render them oil wetby n-octane to varying degrees, and capillary desaturation curves have beendetermined by the restored state method. The desaturation curves show aregularity of increasing displacement pressures as the oil wetness increases.This has been used to compute apparent contact angles between n-octane andwater on glass. The family of desaturation curves also shows a regularcrossover, such that the residual wetting liquid saturation values are inreverse order to the displacement pressures. A semi-logarithmic variation isshown between the apparent contact angle and the residual saturation. Thedesaturation data are interpreted to mean that the wetting liquid ceases to bea continuous phase within individual pores before the capillary pressure can beraised sufficiently to force out the wetting phase completely. The saturationof wetting liquid at which this break in liquid continuity occurs is higher asthe oil wetness decreases. Introduction The petroleum industry has for some time been using measurements ofcapillary pressures on porous media for research correlations and engineeringcalculations. It has been generally recognized that the capillary desaturationcurve reflects the character and arrangement of the pores within the media andthe distribution of fluids within the pores. Methods have been proposed forcomputing pore size distributions, tortuosity factors, and relativepermeabilities from capillary desaturation data. There is little doubt that the interactions between porous rocks and theircontained fluids resulting from surface forces play a dominant role indetermining the magnitude and direction of capillary pressure measurements.There have been attempts to introduce as variables two quantities - interfacialtension and contact angle - generally used to characterize surface forces, butin spite of the wide interest in these quantities as important variables, fewdefinite conclusions have been drawn concerning their qualitative orquantitative significance. Interfacial Tension The interfacial tension appears in a capillary pressure function given byLeverett for correlating capillary desaturation type curves. Use of theinterfacial tension in this function seems to be justified by other experimentsreported. Apparently, interfacial tensions have little bearing on wetting phaseresidual by desaturation. T.P. 3639