Stratigraphic base-level cycles and sedimentary microfacies of Es_2-7 Formation in the Shengtuo Oilfield

Abstract：Combining borehole data with dynamic data from the oil development area of Es_2-7 Formation in the Shengtuo Oilfield, the authors studied the features of the high resolution sequence stratigraphy and the sedimentary microfacies in different base-level cycles. The results show that the hierarchical base-level cycles are well developed and composed of one long-term cycle, two middle-term cycles and nine short-term cycles, indicating the hierarchical change of the accommodation space to sediment supply ratios (A/S) in a vertical direction. Several smaller cycles with decreasing-increasing A/S ratios were observed on a general decreasing A/S background. With the descending-fluctuating-ascending of base-level cycles, the microfacies change from the sheet pattern of relict distributary channel at the bottom to the combined pattern of mouth bar at the top of the 7th Formation. A/S ratios control the sedimentary microfacies types and distribution pattern, suggesting that the relationship between the sedimentation characteristics and the base-level cycles has a very important guiding significance in precise reservoir characterization and well pattern optimization.