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

摘要： 渤海湾盆地沾化凹陷沙河街组二段(沙二段)历经60余年的勘探,已形成“广覆含油、多点突破”的勘探局面。目前,由于沙二段发育于断陷向坳陷转化阶段(断—坳转换期),在复杂盆地结构影响下,滩坝的沉积特征、主控因素和勘探潜力仍不够明确。基于钻井、测井和取心等地质资料,对沾化凹陷沙二段滩坝的沉积特征、沉积相展布规律、主控因素和勘探潜力开展了研究。研究结果表明:①沾化凹陷沙二段发育砂岩滩坝、碳酸盐岩滩坝和混积滩坝3种沉积相类型。纵向上,由沙二段4砂组至1砂组,砂岩滩坝、碳酸盐岩滩坝和混积滩坝的规模逐渐增大;横向上,砂岩滩坝分布于湖岸线附近,碳酸盐岩滩坝分布于渤南洼陷的鼻状构造带附近,混积滩坝分布于渤南洼陷的鼻状构造带及其两翼。②滩坝受风场、物源和盆地结构控制。由风场决定的湖盆水动力区控制了滩坝的类型、走向和分布位置,其中,砂岩滩坝发育于水动力最强的破浪带,碳酸盐岩滩坝和混积滩坝发育于水体能量较强的碎浪带;物源控制了滩坝的发育程度和类型,其中,物源充足区发育规模较大的砂岩滩坝,而物源匮乏区则发育碳酸盐岩滩坝和混积滩坝;断—坳转换期产生的独特盆地结构控制了滩坝的类型和分布位置,并在构造高部位发育砂岩滩坝、碳酸盐岩滩坝和混积滩坝。③沾化凹陷沙二段储层整体具有高孔、低渗的特征,砂体单层厚度为2~6 m的储层是勘探开发的有利目标,共识别出28个有利砂体,预测有利勘探面积为300.24 km²。研究成果以期为同类地质背景的油气勘探提供理论依据。

关键词: 沾化凹陷, 沙二段, 滩坝, 沉积特征, 控制因素, 勘探潜力