Studying the effect of wettability heterogeneity on the capillary pressure curves using the centrifuge technique

Wettability heterogeneity and its effect on fluid flow properties has been the subject of several papers in the past few years. This effect is usually studied by using composite cores made up of blocks of different wettability. In this work, wettability heterogeneity is created in the core by partial filling of the pore space with oil, which creates parts of different wetting in the core. The part accessed with oil will change its wettability while the rest will stay water-wet, which creates a core plug of heterogeneous wettability. The effect of heterogeneous wettability on the capillary pressure is studied in a systematic way using the centrifuge technique in combination with numerical simulation of the experimental data. perimental procedure consists of the following steps: (1) the core plug is fully saturated with brine and subsequently, a drainage experiment is performed targeting initial oil saturation, Soi, (2) after aging, the oil is displaced by water to residual oil saturation, Sor, and finally (3) oil is injected, targeting higher initial oil saturation. This procedure was repeated several times on the same plugs, each time targeting higher initial oil saturation. eresting feature that has been observed is a discontinuity (step) in the capillary pressure curve when oil from a wettability-altered part accesses an unaltered (water-wet) part of the core. This step is believed to be due to wettability contrast between the two parts, the higher the contrast, the larger the observed step. Moreover, the size of this step allows for systematic study of the effect of aging and initial oil saturation on wettability alteration on pore scale. The results of this study show that aging a core sample at low oil saturation introduces significant wettability alteration in the pores filled with oil, while the rest of the core is not affected. This wettability alteration on the pore scale is difficult to capture by simple Amott index measurement. The results also suggest that aging time to restore wettability may decrease as oil saturation increases.