Sedimentary characteristics and formation mechanisms of large-scale braided river deltas in the second member of the Enping Formation in the Shunde North Sag

The second member of the Enping Formation is the most important exploration sequence in the Shunde North Sag. However, due to the late start of exploration in this area, there is an urgent need to strengthen the research on the basic petroleum geological conditions such as the characteristics and formation mechanisms of large-scale reservoir bodies. Based on the data of drilling lithology, sedimentary structures, grain size characteristics, logging curves and 3D seismic data, this paper conducts a study on the characteristics, development conditions, distribution patterns and development models of the braided river delta in the second member of the Enping Formation in the Shunde North Sag. The study shows that in the second member of the Enping Formation around the Shunde North Sag, a braided river delta sedimentary system is developed, which is sourced from the Shenhu Uplift and the Shunde Low Uplift. It is clarified that the multi-level wide and gentle geomorphology lays the topographic foundation for the development of large-scale braided river deltas. Sufficient provenance supply controls the scale of large-scale braided river deltas. The planar distribution and activity of faults control the injection position and advancing distance of the braided river deltas. The multi-stage lake level changes control the vertical evolution of large-scale braided river deltas. It is pointed out that controlled by the two major provenance areas, namely the Shenhu Uplift in the north and the Shunde Low Uplift in the south, three braided river delta sedimentary systems, namely the northern, southern and western ones, are formed in the Shunde North Sag. As a whole, it has the characteristics that the braided river deltas in the short axis direction are more developed than those in the long axis direction, the braided river deltas in the north are larger in scale than those in the south. Vertically, it can be divided into three stages, with multi-inheritance development, and the scale in the early stage is larger than that in the late stage. Based on this, three development models of braided river deltas are established, namely the fault sand accumulation in the large provenance area in the north, the paleo-gully sand accumulation on the gentle slope in the south, and the fault trough sand accumulation along the long axis of the sag. It is pointed out that the fault sand accumulation in the large provenance area in the north and the fault trough sand accumulation along the long axis of the sag are favorable development models for large-scale braided river deltas. It is clear that the braided river delta sourced from the northern large provenance area represents the most favorable direction for exploration breakthroughs in the Shunde north sag.