黔东北地区铁丝坳组—大塘坡组细粒沉积岩高精度层序地层特征和充填演化模式

High-resolution sequence stratigraphic characteristics and organic matter enrichment mechanism of fine-grained sedimentary rocks in the Tiesiao Datangpo Formations in northeastern Guizhou

南华系大塘坡组是一套优质烃源岩和潜在非常规油气储层,具有重要的地史研究和油气勘探意义,然而关于其沉积过程及高精度层序地层方面的研究还较为薄弱。作者以黔东北ZK513井岩心描述及薄片观察为主要研究手段,运用了新的细粒沉积物的分类标准,精细划分识别了以石英砂岩、含砾泥质砂岩、灰色泥岩、灰色含砾砂质泥岩、灰色泥质砂岩、黑色炭质–硅质砂质泥岩、黑色含砾炭质–硅质泥质砂岩、灰色石英砂岩、黑色锰质泥岩、黑色泥质粉砂岩、黑灰色泥质粉砂岩、灰黑色泥质粉砂岩、灰色粉砂质泥岩、灰白色泥岩为代表的14种岩相。并根据岩相组合特征识别了陆棚内盆地、深水陆棚、浅水陆棚3种沉积相,以及前滨、冰海浅水陆棚、陆棚内富锰盆地、陆棚内深水盆地、陆棚内盆地边缘、深水陆棚、浅水陆棚7种沉积亚相。据岩相、沉积相分析,认为陆棚内盆地相内LF9黑色锰质泥岩、LF10黑色泥质粉砂岩为烃源岩的有利相区和层段。通过对岩相、沉积相的研究,识别出5个三级层序SQ1—SQ5,以及4个三级层序界面SB1—SB4;在三级层序内部,根据岩相叠加样式并结合沉积构造定量化统计,总结出4种典型的准层序类型,根据准层序的叠加形式识别了三级层序内部若干准层序组,进而识别出5个海侵(TST)—高位(HST)体系域旋回及内部的5次最大海泛面MFS1—MFS5,进而建立单井层序地层格架。综合ZK513井和研究区其他井岩相、沉积相、层序等资料,通过连井对比,建立了黔东北大塘坡组一段沉积期充填演化模式,预测了研究区内有利相区陆棚内盆地的分布,以及相区内富有机质层段LF9—LF10的展布模式。

The Datangpo Formation of the Nanhua System is a set of high-quality source rocks and potential unconventional oil and gas reservoirs,which has important geological historical research and oil and gas exploration significance.However,research on its sedimentary process and high-precision sequence stratigraphy remains relatively limited.The current study,using the core description and thin section observation from Well ZK513 in northeast Guizhou as the primary research methods,employed updated classification criteria for fine-grained sediments to meticulously classify and identify 14 distinct lithofacies,including quartz sandstone,pebbly argillaceous sandstone,grey mudstone,grey pebbly sandy mudstone,grey argillaceous sandstone,black carbonaceous-siliceous sandy mudstone,black pebbly carbonaceous-siliceous argillaceous sandstone,grey quartz sandstone,black manganese mudstone,black argillaceous siltstone,black grey argillaceous siltstone,grey-black argillaceous siltstone,grey silty mudstone and grey-white mudstone.Based on the characteristics of lithofacies combination,three sedimentary facies—intra-shelf basin,deep-water shelf and shallow-water shelf—were identified.These three facies were subsequently subdivided into seven sedimentary subfacies:foreshore,ice sea shallow continental shelf,manganese-rich basin in continental shelf,deep-water basin in continental shelf,margin of basin in continental shelf,deep-water continental shelf and shallow-water continental shelf.Based on the analysis of lithofacies and sedimentary facies,it is considered that LF9 black manganese mudstone and LF10 black argillaceous siltstone in the continental intra-shelf basin facies are favorable facies and intervals for hydrocarbon source rocks.Through the study of lithofacies and sedimentary facies,five third-order sequences SQ1-SQ5 and four third-order sequence boundaries SB1-SB4 were identified.According to the lithofacies superposition pattern and quantitative statistics of sedimentary structure,four typical parasequence types were summarized in the third-order sequence.Based on the superposition form of parasequence,several parasequence sets in the third-order sequence were identified,and then five transgressive(TST)-highstand system tract(HST)cycles and five internal maximum flooding surfaces MFS1-MFS5 were identified,and then the single well sequence stratigraphic framework was established.Based on the data of lithofacies,sedimentary facies and sequence of Well ZK513 and other wells in the study area,the filling evolution model of the sedimentary period of Datangpo 1 member in northeast Guizhou was established by well comparison.The distribution of the basin in the continental shelf of the favorable facies area in the study area and the distribution pattern of the organic-rich interval LF9-LF10 in the facies area were predicted.