关键词: 沾化凹陷, 沙二段, 滩坝, 沉积特征, 控制因素, 勘探潜力

Abstract: After more than 60 years of exploration, the Member 2 of Shahejie Formation in Zhanhua sag of Bohai Bay Basin, has formed an exploration situation of "widely containing oil and making breakthroughs in many aspects". At present, due to the Member 2 of Shahejie Formation developed in a transitional stage from rift to depression (rift-depression transition period), under the influence of complex basin structure, the sedimentary characteristics, main controlling factors, and exploration potential of beach- bars are still unclear. Based on geological data of drilling, logging and coring, the paper investigates the depositional features, sedimentary facies distribution patterns, controlling factors, and exploration potential of beach-bars in the Member 2 of Shahejie Formation of Zhanhua sag. The research results show as follows. (1)Three types of sedimentary facies, i.e., sandstone beach-bar, carbonate beach-bar, as well as mix beach-bar, have been identified in the Member 2 of Shahejie Formation. Vertically, the scale of all three beach-bar types gradually increases from the fourth sand group to the first sand group. Laterally, sandstone beach-bar facies are distributed near the lake shoreline, carbonate beach-bar facies are adjacet to the plunging structural belt in Bonan subsag, and the mix beach-bar facies are distributed across both the plunging structural belt and its flanks in Bonan subsag. (2)The development of beach-bar is mainly controlled by windfield, sediment source, and basin structure. Specifically, the windfield-controlled hydrodynamic zones of lake basin play a role in controlling the types, orientation and location of beach-bar. Sandstone beach-bar is developed in the breaker zone with the strongest hydrodynamic energy, while both carbonate and mix beach-bars are developed in the surfzone with strong water body energy. The sediment source influences the development scale and type of beach-bar. Large-scale sandstone beach-bar is developed in the area with sufficient provenance, while carbonate and mix beach-bars are developed in the area with poor provenance. The unique basin structure formed during the transition period has a controlling effect on the types and distributions of beach-bars. Sandstone, carbonate, and mix beach-bars are developed in structural high. (3)The Member 2 of Shahejie Formation reservoir exhibits high porosity and low permeability. The sand bodies with the layer thicknesses of 2 m to 6 m are favorable exploration targets in the study area. A total of 28 favorable sand bodies have been identified, and the favorable exploration area is predicted to be 300.24 km². The research results are expected to provide a theoretical basis for oil and gas exploration under similar geological backgrounds.

Key words: Zhanhua sag, Member 2 of Shahejie Formation, beach-bar, sedimentary characteristics, control factors, exploration potential