渤海湾盆地石炭—二叠系含煤岩系沉积环境及其展布规律

Sedimentary environment and distribution law of Carboniferous-Permian coal-bearing series in Bohai Bay Basin

在对渤海湾盆地内各坳陷区上百口钻井研究的基础上,结合岩芯、测录井及地震等资料,探讨了渤海湾盆地石炭—二叠系含煤岩系沉积环境,建立了含煤岩系沉积模式,揭示了含煤岩系的残余地层展布规律。渤海湾盆地石炭—二叠系含煤岩系主要发育在太原组及山西组,岩石类型包括煤岩及暗色泥岩(包括炭质泥岩)。其中,太原组含煤岩系沉积环境以陆表海堡岛沉积体系下泥炭坪为特征,沉积物泥炭的显微组分以腐殖组为主,普遍富硫,且矿物质含量较高,成煤后以镜质组为特点,壳质组相对丰富;山西组由于受物源区碎屑物质供给能力增强及大规模海退的影响,各类泥炭坪等主要成煤环境随时间推移由北向南发展,并逐渐被浅水三角洲平原泥炭沼泽聚煤环境取代,该类泥炭沼泽形成煤层厚度较大,但受分流河道冲刷作用,因此横向厚度变化较大,结构复杂,硫含量一般较低,灰分含量高。根据华北晚古生代含煤岩系及成煤环境的特点,可将其划分为堡后泥炭坪、潮坪泥炭坪、潟湖泥炭坪、潮汐三角洲泥炭坪及浅水三角洲平原泥炭沼泽5种模式类型,它们各具不同的沉积岩相组合及成煤特点,多种成煤模式可同时共存且相互演化。通过研究认为,渤海湾盆地石炭—二叠系含煤岩系残留厚度较大,分布广泛,但受中新生代构造断裂影响,部分地区遭受剥蚀。通过对渤海湾盆地石炭—二叠系含煤岩系有机质丰度等烃源岩指标的分析,结合不同类型的测井曲线,估算了渤海湾盆地石炭—二叠系有效煤系烃源岩的厚度。其中渤海湾盆地石炭—二叠系有效煤系烃源岩在黄骅坳陷南部、冀中坳陷的苏桥—文安地区分布较厚,有效煤系烃源岩厚度在150~200 m,最厚可达250 m以上;临清坳陷及东濮坳陷中东部有效煤系烃源岩厚度普遍在50~100 m;济阳坳陷有效煤系烃源岩呈零星分布,在各次级凹陷中均有小面积累厚较大的煤系烃源岩发育。

Based on more than 100 drilling wells of various depressions in Bohai Bay Basin,combined with drill cores,logging and seismic data,this paper discussed coal-bearing series sedimentary environment of Carboniferous and Permian,established sedimentary model of coal-bearing series,revealed the distribution law of residual coal measure strata.Coal-bearing series of Carboniferous and Permian in Bohai Bay Basin mainly developed in Taiyuan Formation and Shanxi Formation.Rock types are coal and rock and dark mudstone(including carbonaceous mudstone).The sedimentary environment of coal-bearing series in Taiyuan Formation is characterized by peat flat under epeiric sea barrier sedimentary system.Sedimentary peat is mainly composed of humus group,which is generally rich in sulfur and minerals.After coal formation is characterized by vitrinite group,and chitinite group is relatively abundant.Shanxi Formation is affected by the increasing supply of detrital materials and the large-scale regression,mainly coal-forming environment such as all kinds of peat flat developed from north to south over time,and is gradually replaced by peat bog of shallow water delta plain.The thickness of coal seam formed by this kind of peat swamp is large,but it is subject to the scour action of distributary channel,so the lateral thickness changes greatly,the structure is complex,the sulfur content is generally low,and the ash content is high.According to the characteristics of coal-bearing series and coal-forming environment in north China late Paleozoic,peat flats can be divided into peat flat after barrier island,tidal flat peat flat,lagoon peat flat,tidal delta peat flat and shallow water delta plain peat bog.They have different lithofacies combination and coal-forming characteristics.The variety of coal-forming model can coexist and mutual evolve at the same time.According to the study,the carboniferous Permian coal-bearing rock series in Bohai bay basin has a large residual thickness and a wide distribution,but some areas suffer from denudation due to the influence of Mesozoic and Cenozoic tectonic faults.Through the analysis of carboniferous Permian coal-bearing rock series organic matter abundance and other hydrocarbon source rock indexes in Bohai bay basin,combined with different types of logging curves,the thickness of carboniferous Permian hydrocarbon source rocks in Bohai bay basin is estimated.It is considered that the effective coal source rocks of Carboniferous and Permian in Bohai Bay Basin is thicker in southern Huanghua Depression and Suqiao-Wen’an area of Jizhong Depression,and the thickness of the effective coal source rocks is 150-200 m,the maximum thickness can be up to 250 m.The thickness of the effective coal source rocks of Linqing Depression and Dongpu Depression is generally 50-100 m.Effective coal source rocks in Jiyang Depression are scattered,coal source rocks with a large thickness are developed in each secondary sag.