沉积环境对渤海金西A洼烃源岩的控制作用

Sedimentary Environment Control Effect on Source Rocks in Jinxi A Subsag,Bohai

以沙三段为烃源岩,以沙三段、沙二段为主要目的层,在金西A洼实施钻探一直未取得商业突破,且多数井未见油气显示。在洼陷中央钻穿沙三段,泥岩中有机质丰度低,不具备生烃条件,该洼陷勘探潜力存在较大争议。在充分利用地震、钻井及区域地质资料的基础上,类比分析了渤海湾盆地不同类型凹(洼)陷油气地质条件,开展金西A洼具体特征研究。研究结果表明:凹(洼)陷的位置、陆源碎屑的供给量控制了其烃源岩的形成与分布,根据它们之间的关系,将凹(洼)陷分成持续近源型、断续近源型和持续远源型三类;金西A洼属于断续近源型,孔店组—沙四段时期发育有效烃源岩,沙三段时期不发育烃源岩;基于地化相—有机相—沉积相—地震相较好对应关系,预测金西A洼烃源岩仅分布在沙四段—孔店组洼陷的中心位置,其烃源岩具有一定厚度、有机质丰度高、类型好,邻近沙四段—孔店组烃源岩的近源构造是该区有利勘探方向。

With the Es_3(the Third member of Shahejie Formation)source rock and the Es_(3) and Es_2(the Second member of Shahejie Formation) serving as the primary target formations,early explorations in Jinxi A subsag have not resulted in commercial breakthroughs,and most wells have not shown oil and gas displays.The mudstone in Es_(3) has a low abundance of organic matter and does not have the conditions necessary for hydrocarbon generation in the center of the subsag.There is still considerable controversy over the exploration potential of this region.This study used seismic,drilling,and regional geological data to conduct an analogous examination on the oil and gas geological conditions of different types of sags(subsags) in Bohai Bay Basin,and analyzed the specific characteristics of Jinxi A subsag.The results suggest that the formation and distribution of source rocks are controlled by the position of the subsag/sag and the supply of terrigenous clastics.Each sag/subsag can be classified into one of three types based on their relationships:continuous near-source,intermittent near-source,and continuous distant-source.The intermittent nearsource type characterizes Jinxi A subsag.Effective source rocks were developed during the deposition of Es_(4) and Ek,but no source rocks were developed during the deposition of Es3.Based on the correlation between geochemical,organic,sedimentary,and seismic facies,the source rocks are predicted to be solely distributed in the center of the subsag during the deposition of Es_4(the Fourth member of Shahejie Formation) and Ek(Kongdian Formation),and those source rocks have a certain thickness,high abundance,and good types.The near-source structure adjacent to the source rocks in Es_(4) and Ek is a favorable exploration direction in this area.