Eocene Sequence Architecture And Controls Of Sha 4 Member, In Southwest Dongying Depression, Bohai Bay Basin

Dongying Depression is a secondary basin of Jiyang Sag in Bohai Basin, which is alacustrine rift-subsidence basin. Extremely rich in oil and gas, Dongying Depressionis one of the famous hydrocarbon bearing basins in east China. Boxing area, managedby Shengli Petroleum Administration Bureau, is in southwest Dongying Depression.It's an important area for oil and gas exploration and development.This paper integrated the theory and method of high-resolution sequence stratigraphy,sedimentology, petroleum geology, and structural geology. Middle Eocene is a periodof early rifting. High-resolution sequence stratigraphy is based on high resolutiondatabases including closely wire-line well logs, mud loggings and 3-D seismicreflection data. One of the most important purposes of this paper is to recognize andcorrelate high resolution sequences by identified and correlated multi-level sequenceboundary. Es4 section can be divided into 2 third-order sequences, and 5-6fourth-order sequences. LST (low-standard systems tract) usually formed by 3-4fourth-order sequences, but HST (high-standard systems tract) and EST(lake-expanded systems tract) formed by 1-2 fourth-order sequences. The key inestablishing of high-resolution sequence framework is the identification andcorrelation of the fourth-order sequences. High-resolution sequence framework is apowerful and predictive tool for facies analysis and reservoir prediction.It is more objective to analysis sedimentary systems and to reveal its law of temporaland spatial evolution in isochronal sequence stratigraphic framework. The study hasthe following discoveries: the sediment supply of the study area came from southgentle slope, west Qingcheng convex and west steep slope. Main sedimentary systemsconsist of beach bar and delta.The study project has established a predictive sequence architecture pattern. There aremuch difference in south gentle slope, north and west steep slope, and Boxingfault-step belt, because of the difference of paleostructure and paleogeomorphology.LST and HST develops beach bar and delta sedimentary systems, EST is thedevelopment level of high quality hydrocarbon source rock. The study has beenrevealed sequence architecture controlled by the change of the paleogeology,paleostructure, paleoclimate and base level.The study section reservoir stratigraphic unit consists of beach bar and delta of LSTand late HST, and delta of early EST. Interbedding of siltstone and mudstone formedprofitable source-reservoir-caprock assemblage. Reservoir sand rocks developed inthe area of south gentle slope, southwest steep slope, and Boxing fault-step belt. Thedistribution of the profitable reservoir rock is controlled by paleostructure,paleoclimate and base level. It is significant to guide the exploration and developmentof reservoir of Es4, especially the lithologic and stratigraphic hydrocarbon reservoir.