Sedimentary hydrodynamic study of sand bodies in the upper subsection of the 4th Member of the Paleogene Shahejie Formation the eastern Dongying Depression, China

摘要

Petroleum is produced from a beach-bar sand reservoir in the upper subsection of the 4th member of the Paleogene Shahejie Formation (Es_(4)~(s)) in the eastern Dongying Depression, penetrated by many wells in the Guangli-Qingnan area and this subsection still has further exploration potential. Using drilling and logging data, we analyzed the sand body types, emphasizing the sedimentary characteristics of the beach-bar sand bodies. Combining these data with the concepts of lacustrine and oceanic hydrodynamics, we explain the formation and distribution of the beach-bar sands in the eastern Dongying Depression. The connectivity between beach-bar sand bodies within each individual hydrodynamic zone is better than that between sand bodies in any two adjacent zones. The tempestite sand bodies developed in this area are characterized by typical storm deposits and are located at the bottoms of the beach-bar sand bodies. They grade upward to normal shore and shallow-lacustrine beaches and bars. We also propose a new simple method to estimate the paleo-water depth using the thicknesses of the bar sand bodies in parasequences combined with the principle of hydrodynamic zonation. Based on the distribution of the beach-bar sands in parasequence set 3, we infer that the paleo-wind direction was from the north with an average paleo-wind force of 6 when the major beach-bar sand bodies formed.