The quantitative prognosis of thin interbedded beach-bar sandbodies: a case study of the upper 4th submember of the Paleogene Shahejie Formation in Dongying Sag

Abstract：The quantitative prognosis of thin interbedded sandbodies is one of the difficulties in sedimentological research. The beach-bar is a typically thin interbedded sand body in shore-shallow lake whose prediction and exploration are very difficult. Based on the study of sedimentary characteristics, plane distribution and controlling factors of beach-bar in the upper 4th submember of the Paleogene Shahejie Formation in Dongying Sag, the authors consider that the development and distribution of beach-bar are mainly controlled by different wave zones, i.e., the surfing-backflowing zone controls pebble beach-bar and longshore beach-bar, the breaker zone controls nearshore beach-bar and the broken zone controls infralittoral shore beach-bar. Based on the wind-dynamic sandbodies distribution model and the analysis of wave parametric variation in different zones, the authors established the quantitative prognostic models of the sand body in the broken zone and the breaker zone, and calculated the thickness and width of sandy bar distribution in nearshore and infralittoral shore. In addition, using wind-dynamic mixed microtopography recovering technique, the authors obtained the extension length of the sandy. By employing statistics of single layer bar thickness and well connecting correlation, the authors examined the predicted results and proved them to be reliable and reasonable. It is demonstrated that the 6-8 wind scale is favorable for the development of the beach-bar. This method provides a new insight for the prediction of thin sand body and is useful to the exploration of subtle reservoirs; nevertheless, it is not suitable for the prediction of the thin sand body mainly controlled by the provenance.