Reservoir Characteristics and Seepage Mechanism of the Second Member of the Eocene Liushagang Formation, Southeast Flank of the Weixinan Depression, South China

In this study, the reservoir characteristics of the second member of Liushagang Formation in the southeast flank zone of Weixinan Sag were analysed using scanning electron microscopy (SEM), high‐pressure mercury intrusion (HPMI) and other experimental methods. The results show that the cementation and dissolution of the reservoir in the study area are weak, and the compaction is the main control factor of the reservoir quality. The analysis of the HPMI experiment data shows that the reservoir in the study area presents multi‐segment fractal characteristics. The fractal dimension is distributed in the range of 1.5959–2.9966, with an average of 2.6864. The dominant pore throat radius in the study area is R 25 (the pore throat radius corresponding to the mercury injection saturation of 25%), and different porosity‐permeability zones can be well distinguished by using the dominant pore throat radius. The results of the comparative study show that the pore size and spatial distribution are important factors affecting the seepage capacity of the reservoir, and six spatial distribution models are summarised, among which the local positive anomalous pore‐throat distribution model has a significant impact on the distribution of residual oil. The differences in microscopic pore structure are the main reasons for the difference in production capacity under the same permeability conditions in different oil fields. Under the same permeability conditions, the higher the macropore content, the more movable fluid content, the better the production capacity.