Some Observations on the Capillary Pressure Hysteresis Using the Ultracentrifuge

ABSTRACT

The use of centrifuge technology for the determination of capillary pressure characteristics of reservoir rocks has received increasing attention in the recent decades. In recent experiments it has become evident that the hysteresis observed in the centrifuge experiments is different than the hysteresis observed in the traditional porous plate measurements. More specifically, the value of the “irreducible” wetting phase saturation seems to shift between the first drainage cycle and the second drainage cycle. This phenomenon was studied in some detail in our laboratory. Approximately sixty (60) core plugs were tested under a variety of conditions which included crude and refined oils at room and reservoir temperatures. The cores used were Berea sandstone, Baker dolomite and plugs from various carbonate pinnacle reefs of Western Canada. The tests were conducted using reservoir core that was in both native and restored state. It was found that the widest hysteresis occurred when crude oil was used. The hysteresis was more significant in carbonates than in sandstones. This can be only partially attributed to the fact that the carbonates have significantly smaller pore volumes (i.e. a higher expected experimental relative error). However, the trends on clean carbonates (Baker dolomite) are opposite to the ones of reservoir rock. Also, there seems to be no significance on the effect of saturation history (i.e. whether or not the displacement was single or multi step).

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