泥质重力流沉积研究进展及其页岩油气地质意义——以东营凹陷古近系沙河街组三段为例

摘要

页岩油气的勘探开发推动了泥页岩沉积机理研究的快速发展,使得细粒物质的搬运和沉积成为当今沉积学界和油气工业界共同关注的焦点.尽管海洋环境下的泥质重力流沉积研究成果频见报道,但有关我国新生代湖泊环境中的泥质重力流沉积尚未引起沉积学界的关注.故本文在国内外相关文献调研基础上,以岩芯观察和薄片鉴定为重点,分析了渤海湾盆地东营凹陷古近系沙河街组三段湖相泥质重力流沉积特征;探讨了湖相泥质重力流沉积的形成机制;以期为湖泊沉积学研究和陆相页岩油气开发提供参考.研究发现,东营凹陷古近系沙河街组三段发育泥质块体流、泥质碎屑流、泥质浊流及泥质异重流等多种重力流沉积类型;泥质滑塌岩、泥质碎屑岩、泥质浊积岩和泥质异重岩在时空上可以共生共存.认为泥质沉积物可以在动荡水体和较强水动力条件下沉淀;泥质重力流沉积在深水沉积区占有重要地位;泥质重力流对于泥页岩中的粗粒碎屑物质、有机质的搬运和沉积以及有机质的埋藏起到重要作用,因而具有重要的非常规油气地质意义.%With promotion of shale oil and gas development on intensive studies on depositional mechanisms of mudstone and shales, transportation and deposition of fine-grained sediment have currently become hot topics in both sedimentoligical studies and petroleum industries.However, muddy gravity flow deposits in the Cenozoic lacustrine environment have not yet arisen attentions of geologists, although literatures of gravity flow-generated muddy deposits in marine environments extensively existed.Based on extensive literature researches, detailed core examinations and thin section observations, this paper analyzes characteristics of gravity flow-generated fine-grained deposits in the 3rd oil-member of the Paleogene Shahejie Formation (E2s3), Dongying Sag, Bohai Bay Basin.Discussions on their forming mechanisms have theoretical significances on lacustrine sedimentary environment study and have practical meanings on developments of shale oil and gas.Results: 1) there are various gravity flow deposits, including muddy mass flows, muddy debris flows, muddy turbidity currents and muddy hyperpycnal flows exist in E2s3 in the Dongying Sag;2) muddy slumps, muddy debrites, muddy turbidites and muddy hyperpycnites co-generate and co-exist in spatio-temporal extents.Conclusions: 1) muddy sediments can deposit in turbulent waterbody and high hydrodynamic conditions;2) muddy gravity flow deposits play an important role in deep water sedimentary regions;3) muddy gravity flows are of great importance to transportation and deposition of coarse grains and organic matters, and so to preservation of organic matters;4) muddy gravity flow deposits have important geological significances on unconventional oil and gas.