Simultaneous Determination of Residual Saturation and Capillary Pressure Curves Utilizing the Ultracentrifuge

Abstract

ABSTRACT Residual saturation and capillary pressure curves are important for modelling reservoir and laboratory processes. Knowledge of the residual saturation curve is necessary to determine the ultimate production from a tertiary recovery process Capillary pressure is required to interpret laboratory core floods and to describe multi-phase reservoir fluid flow. The ultracentrifuge provides a rapid means of determining capillary pressure and residual saturation relationships. It is non-destructive, uses small samples, and is capable of attaining both high capillary pressures and extremely low residual saturations. The effects of variation in residual saturation with Bond number are not included in the traditional Hassler-Brunner analysis for capillary pressure. Such desaturation effects can explain the anomalous experimental saturation distributions reported at high rotation rates [1,2]. The current work generalizes the Hassler-Brunner analysis to include desaturation and also to include the variation in centripetal acceleration through the core. The analysis also provides for the determination of residual saturation as a function of Bond number (kΔρg/σ). Laboratory ultracentrifuge data is analyzed and both capillary pressure and Bond number residual saturation curves are obtained. The conversion of Bond number residual saturation curves to capillary number (µv/σ) curves may be performed by comparison with residual saturation curves obtained from core floods. In general, the ultracentrifuge residual saturation curves greatly extend those measured during conventional, non-destructive core floods; close to 100% oil recovery has been observed with the ultracentrifuge.