Study Of Sequence Architecture And Depositional Systems Of Dongying Formation In Liaozhong Depression

In recent years, with the development of structural hydrocarbon reservoir exploration, the amount of discovered large-scale petroleum fields has been reduced significantly in Liaozhong Depression, Bohai area. Looking for litho-stratigraphic accumulation is becoming the new exploration direction. This raised the question that the current second- and third-order sequence frameworks cannot fulfill the exploration needs. To solve this problem and provide important exploration references, this dissertation tries to find smaller-scale depositional cycles and build a more detailed chronostratigraphic framework to investigate the model of litho-stratigraphic traps in the rift lacustrine basin by using a new generation of sequence stratigraphy theory and basin analysis methods.In the study based on sequence stratigraphy, the characteristics of different order sequence boundaries and their configurations have been clarified. It is the first time to propose using easier identified and traced regressive surfaces to bound fourth-order sequences. A more detailed high-resolution sequence framework of study area has been established, and this provides new reference and basis for the prediction of litho-stratigraphic traps.Combining the analysis of seismic facies, well logs, and cores, six types of sedimentary facies have been recognized in study area. This study focuses on sublacustrine fan deposits by studying their depositional composition and seismic sedimentological features within fourth-order sequences, and suggests identification feature for sand-rich sublascutrine fans, which could be useful for the exploration of litho-stratigraphic traps. Meanwhile, this study has revealed the depositional composition of systems tracts within sequences of rift basin, and has established sequence stratigraphic models for deep-water lacustrine basin. A new depositional composition model of fourth-order sequences in rift basin has been proposed, including two types: sublacustrine fan, and sublacustrine fan plus delta. In this study, a falling-stage systems tract has been recognized firstly in the rift basin. The development and distribution of low-stand systems tract, transgressive systems tract, high-stand systems tract, and falling-stage systems tract have been revealed together with their sedimentary facies.This study also conducts the research on paleo-structures, paleo-geomorphology, paleo-climate, and sand dispersing systems. The constructing pattern of depositional sequences and the controlling factors of sand-rich depositional systems in the rift basin have been deeply discussed. It reveals that the balance between tectonic subsidence and sediment supply defines the type of basin fill. Episodic tectonic movement controls the development of third-order sequences. Fluctuation of lake level resulted from high-frequency climate cycle might control the development of fourth-order sequences. Provenance system and paleo-structural geomorphology are responsible for the way of sand body gathering and the degree of its abundance.At last, combining the paleo-structural setting of this basin, the development and distribution of depositional systems, and the distribution pattern of oil and gas in study area, a model of litho-stratigraphic traps within sequence framework has been built. The favorable zones also have been predicted regarding different structural units.