Ultra-short-term Base Level Cycle and Its Control on the Reservoir in Oil Series L60 in Oilfield P, Bohai

Oil series L60 in Guantao Formation in Block 1 of Oilfield P, Bohai consists of multi-stage stacking braided river sandstones. Based on the theory of high resolution sequence stratigraphy, the authors divided the ultra-short-term base level cycles into two unsymmetrical cycles i.e. upward-deepening in low accommodation and upward-deepening in high accommodation. According to the classification and correlation of sandstone bodies in the study interval, together with the change of A/S, the channel sand bodies are divided into three types:cutting type, stacking type and single type. On this basis, the characteristics of sedimentary micro-facies under ultra-short-term base level cycles are carefully described, and the distribution and development rules of interbedded layers under different ultra-short-term base level cycles in different periods are discussed. The flooded characteristics of the sand reservoir demonstrate that in the early ascent period of ultra-short-term base level, the argillaceous interlayers distributed locally, the blocking effect of percolation was weak and the remaining oil distributed in the upper part of the sand bodies. With the gradual increase of the ultra-short-term base level, however, the argillaceous interlayers were thickened locally. To the late period, the argillaceous interlayers distributed extensively and can be laterally correlated, the blocking effect of percolation was relatively strong and the remaining oil distributed in the sand bodies in the form of segment.