Experimental studies on oil imbibition in mixed-wetting porous medium
Qi Yukai1, Luo Xiaorong1, He Yonghong2, Dang Hailong2, Liu Naigui1, Lei Yuhong1, Zhang likuan1
1. Key Laboratory of Petroleum Resource Research, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029;
2. Research Institute of Yanchang Petroleum (Group) Co. Ltd., Xi'an 710075
Mixed wetting phenomena are widely observed in porous medium. Multiple-phase expulsions in such medium are complicated. However, studies on such mixed wettability are still very rare even it is important for hydrocarbon migration and accumulation, as well as residual oil distributions in reservoirs. In this study, oil imbibition experiments were systematically conducted using glass tubes filled with mixed-wetting glass beans. The multiple-phase flowing behaviors in mixed-wetting porous medium with different proportion of oil wetting glass beans were observed. Experiment results show that the threshold of oil imbibition seems to be related to the proportion of oil-wetting beans in the medium. It is deduced that the pore throat may behaves as oil-wetting or water wetting, depending on the number of oil wetting grains the pore throat contains. When the grains which comprise the throat are dominated by oil-wetting grains, the throat may behave as oil-wetting, and vice versa. And oil can continuously imbibe into the medium only when the wetting throats connect each other to form a complete pathway through the medium. When oil-wetting and water-wetting grains distribute randomly within the medium, the occurrence of oil imbibition and corresponding oil saturation in the mixed wetting medium depends largely on the proportion of oil-wetting grains.