Study On The Sedimentary System Of Beach And Bar In The Upper Fourth Member Of Shahejie Formation Of The Paleogene In The Western Dongying Sag

Based on the analysis of the seismic, core and well logs data and by using the theories of sedmentology, sequence stratigraphy and logging geology , this paper studied types, sedimentatary features, plane distribution, vertical evolution and controlling factors of beach and bar in the Upper Fourth Member of the Shahejie Formation of the Palaogene in the western Dongying Sag, and established the depositional model and the quantitative predicting model of beach and bar . The main achievements are as follows:(1) The Upper Fourth Member of the Shahejie Formation in the Dongying Sag is divided into one sequence with three systems tracts (lowstand systems tract, transgressive systems tract and highstand systems tract), and further subdivided into seven parasequence sets .(2) The beach and bar in the three parasequence sets of lowstand systems tract are well developed but poorly developed in transgressive systems tract and highstand systems tract .(3) The beach single sand layer is relatively thin and the mudstone interbedded is well developed. The main sedimentary structures are wave-microwave beddings, wave mixed beddings, low angle wedgelike beddings, swash cross beddings, veinlike beddings, lenticular beddings, wave-formed sand ripples beddings and so on. The main bedding surface sedimentary structures are wave-formed ripples, interference ripples, decorated ripples and shallow water microwave ripples and so on. Well log features of the beach are thinly finger crowd association curve, thinly finger or sticker-shape curve with high-middle amplitude .(4) The bar distributes in the beach, the single sand layer is relatively thick and the mudstone interbedded is poorly developed. The main sedimentary structures are wave beddings, wave mixed beddings, wedgelike beddings, parallel beddings and massive beddings and so on. The main bedding surface sedimentary structures are wave-formed ripples, parting lineations and so on. Well log features of the bar are wide amplitude finger, jagged infundibuliform or jagged box form .(5) The system of'paleoclimate-provenance-basin'controlling beach-bar model is established. In this model, the distribution areas of beach-bar are divided into three zones, namely the northern steep slope leeward zone, the center shaking zone and the southern gentle slope windward zone. In these zones, its features in hydrodynamic, provenance, sedimentation and reservoir are different, and have been analysed in detail in this study.(6) In this paper, the author proposes the beach-bar on the southern gentle slope in the Boxing sag is controlled by different hydrodynamic zones, namely the surfing- backflowing zone controls the pebbly beach-bar and inshore beach-bar, the breaker zone controls nearshore beach-bar and the broken zone controls infralittoral shore beach-bar. The quantitative predicting model of the beach-bar is also built up. The thickness, width and length of the sandy bar in different hydrodynamic zones are quantitatively predicted. By using statistics of single bar sandy layer thickness and well tie correlation of sandbodies, the predicted results are tested and proved to be reliable and effective. This method is the first time using sedmentology, and is an improvement and supplement for thin sandbodies quantitative prediction, and also provides a new insight on the prediction of thin sandbodies .