195 / 2019-06-13 19:54:02

Sedimentary Evolution Characteristics of Nearshore Subaqueous Fans in the upper part of the fourth member of Shahejie Formation in Yan 22 area, Dongying sag

imaging logging data; lithofacies association; gravity flow; sedimentary evolution

In order to clarify the sedimentary characteristics and spatial evolution of near-shore subaqueous fans in the upper part of the fourth member of Shahejie Formation in Yan 22 area, Dongying sag, combined with FMI imaging logging data, core observation, logging data analysis and seismic data, the lithofacies association types, distribution characteristics and evolution pattern are analyzed in depth in the study area.The study shows that the near-shore subaqueous fans are developed in the upper part of the Es4 showing the multiple-superimposition development of the progradation fans and retrogradation fans. The progradation fan is mostly reverse rhythm, and the logging curves are obvious. Logging curves feature funnel type or toothed funnel type. The lithofacies association is characterized by pebbly sandstone facies—fine conglomerate facies— middle gravel-bearing fine conglomerate facies. The retrogradation fan’s logging curves are mainly box type. Seismic reflections are disordered. According to imaging logging and core observation, the retrogradation fan is developed three major types of lithofacies, including conglomerate facies, sandstone facies and mudstone facies, and subdivided into 12 subtypes, of which the positive rhythm is dominant. The lithofacies association are characterized by large set of matrix-supported fine conglomerate facies and particle-surpporting medium conglomerate facies—fine conglomerate facies—pebbly sandstone facies, indicating the characteristics of event gravity flow dominated by sandy debris flow. The retrogradation fan is well developed in the research area which can be recognized with massive bedding、scouring surface、spliting muddy clastics and horizontal bedding. In addition, the oriented gravels are also seen in the massive bedding pebbly sandstone, reflecting a certain traction current sedimentary structure which indicates the characteristics of multi-stage river channel superimposition. On the whole, the development of the near-shore subaqueous fan in the upper part of the fourth member of the Shahejie Formation in the northern part of the Dongying sag is controlled by event gravity flow, datum level change, source supply and boundary fault activity, showing the sedimentary evolution characteristics of a superimposition development of the progradation fans and retrogradation fans.