Architectural characteristics, evolutionary stages, and sedimentary models of clastic beach bars

Abstract

Beach bars are important reservoirs and have good exploration potential in several petroliferous basins globally. At present, we urgently need to make a further study on beach bars based on previous studies to promote the process of oil and gas exploration and development, regardless of modern or ancient sedimentation. Using satellite maps, research achievements of predecessors and theoretical analysis as our references, we selected four typical areas of beach bars. Based on field surveys and core observations, we tried to divide beach-bars into three types, corresponding to five architectural units. We applied manual and machine learning recognition to categorize the architectural units observed in the study areas. Based on the sedimentary and environmental characteristics of architectural units, we summarized the sedimentary evolution stages and established the sedimentary models of each beach bar. The results indicated that the beach bars could be divided into shore beaches, submerged beaches and bars, based on different sedimentary and environmental characteristics. The shore beach includes the backshore and part of the foreshore (swash zone). The submerged beach has a swamp, part of the foreshore (except the swash zone) and the shoreface. Bars may appear anywhere on the shore-shallow sea/lake. The architectural units of beach bars were divided into five subtypes, corresponding to four evolutionary stages based on hydrodynamic traits and the sedimentary environment. Additionally, a discrimination standard was established based on principal component analysis and Bayesian discrimination on the Shahejie Formation of the Dongying Depression while using fine-scale recognition to verify the units. The coincidence between manual recognition and machine recognition results was 94.8%. We hope that our methodology and models will help address the limitations in previous studies on beach bar reservoirs and will help promote improvements in the related theories and optimization of their exploration and development.