Depositional evolution and lithologic reservoir exploration in Jizhong depression

Based on analyses of a large amount of drilling data,logging curves,seismic information and paleontologic fossils,the sequence framework and depositional evolution of paleogene in Jizhong depression were studied.The results show that the strata of paleogene can be divided into one first-order sequence,three second-order sequences and thirteen third-order sequences.The depositional evolution of paleogene has experienced five filling types and made a vertical filling series from fault-subsidence to depression period.Moreover,the relationships between three oil-bearing groups in upper,middle and lower parts of vertical section and distribution of lithologic reservoir were investigated.According to three geological key elements including structural setting,sequence types and sedimentary systems,four types and twenty kinds of structure-petrographical,zonations are summarized in different zones,such as steep slope,sub-sag area,gentle slope and central uplift.For different oil-bearing groups,comprehensive evaluation for favorable exploration zones from shallow to deep strata was conducted.Fourteen types of structure-petrographical zonations were finally selected as favorable exploration zones.The work can provide reference for exploration of lithologic reservoir effectively.