Origin analysis of Es sand body in Caofeidian 14-5 area of Shanan Depression in Bohai Bay Basin

Shahejie formation is thick layer in west sub-depression of Shanan depression in Bohai Bay Basin. From Es_3m to Es₁ the basin undergoes rifting Ⅲ phase and rifting IV phase, between them there is T5 uncomformity. The regional formations first undertake subsidence and then uplift, and at last subsidence phase, so there are three three-order sequences. And every sequence developed with different sedimentary systems. So under control of central fault, north supply and south supply, and then break belt on the north area developed. In Es_3m phase, semi-deep lacustrine, deep lacustrine, and mud-rich sublacustrine fan with weak hydrodynamic developed in Caofeidian 14-5 area. In Es_3u phase, semi-deep lacustrine, deep lacustrine, and sand-rich sublacustrine fan and volcanic sediments developed in the north with partial strong hydrodynamic. In Es₁₂ phase, kinds of sedimentary systems developed including semi-deep lacustrine and deep lacustrine, delta front, slope fan, slump, sublacustrine fan and volcanic. Traction current and gravity current sediments existed together in the study area, and gravity current sediments were the main body. Through above sedimentary evolution, exploration focuses on lithologic trap and construction-lothologic trap in the west sub-depression, especially good matching of faults and sand body in space leads to trap exploration success. Therefore, regional exploration should focus on finding different types of sand in thick mud.