Experimental Measurements of Capillary Pressure and Relative Permeability Hysteresis (original) (raw)
Capillary pressure and relative permeability hysteresis have been investigated on core samples with different wetting characteristics. The relative permeability and capillary pressure curves depend on the direction of saturation changes and on the maximum and minimum achieved saturations. A conceptual model to explain the hysteresis trends in both the relative permeability and capillary pressure is presented. The model attributes hysteresis to a combination of 1) trapping of one phase by another, 2) contact angle hysteresis and 3) the wettability change of parts of the pore space after contact with crude oil. In the literature there is a lack of a complete and consistent physical model to describe the hysteresis phenomenon due mainly to the fact that experimental data is rather scarce. Most of the available data is for water-wet systems. Therefore, there is a need for measurements done on non-water-wet systems. The data presented in this paper is measured on core samples of different wettability, i.e., water-wet and non-water-wet core samples. The measurements have been carried out on both carbonate and sandstone core material using Centrifuge, Steady State, CAPRICI and Pc-probe techniques. The experimental data show that there is significant hysteresis in the capillary pressure between primary drainage, primary imbibition and secondary drainage curves especially for non-water-wet samples. Moreover, for non-water wet samples, the bounding imbibition (i.e., primary imbibition) and secondary drainage P c curves do not form a closed hysteresis loop. This is observed in both the bounding and scanning curves. We also found that water relative permeability curves exhibited either very little or no hysteresis at all except when considerable part of the pore space became oil-wet. On the other hand, oil relative permeability curves showed strong hysteresis between the primary drainage and primary imbibition curves for all wetting status, with very little hysteresis thereafter except for mixed to oil-wet plugs. Experimental data suggests that while contact angle hysteresis has a profound effect on capillary pressure hysteresis, it hardly affects relative permeability hysteresis.
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