鄂尔多斯盆地清涧-宜川地区上石炭统本溪组混积特征及沉积演化

Hybrid sediments characteristics and sedimentary evolution of Upper Carboniferous Benxi Formation in Qingjian⁃Yichuan area of Ordos Basin

鄂尔多斯盆地清涧-宜川地区上石炭统本溪组为一套潮坪-障壁岛-陆棚沉积体系,发育陆源碎屑岩与碳酸盐岩的混积层序,为了提高混积储层预测的准确度,在分析沉积演化背景基础上,综合野外露头、岩心、录井、测井等多方面资料,探讨混积发育的特征及沉积相类型,并对混积和混积层系进行沉积演化分析。结果表明:本溪组沉积类型主要为相缘混积,发育在潮间带、潮下带、潟湖和障壁岛的向陆一侧,大型混积层系发育规模较小;本溪组可以划分为SQ1、SQ2共2个三级沉积层序,其中SQ1和SQ2均可识别出低位体系域(LST)、海侵体系域(TST)和高位体系域(HST),SQ2还可以识别出下降期体系域(FSST);相缘混积主要发育在海侵体系域和高位体系域早期的浅水区内,发育规模相对较小,主要发育在潮坪与潟湖、潟湖与障壁坪的过渡区域内,与潮坪砂岩和障壁砂岩相伴生,相缘混积与上覆的砂泥岩地层形成混积层系。研究成果可为混积储层预测提供借鉴。

Upper Carboniferous Benxi Formation of Qingjian-Yichuan area in Ordos Basin is a set of tidal flat-barrier island-shelf sedimentary system,developing hybrid sediments sequences of terrigenous clastic rocks and carbonate rocks.In order to improve sediments reservoirs prediction accuracy,based on analysis of sedimentary evolution background,hybrid sedimentary development characteristics and sedimentary facies types are studied by comprehensively analyzing field outcrop,core,mud logging and electric logging data,and sedimentary evolution of hybrid sediments and hybrid strata series are analyzed.The results show that sedimentary type of Benxi Formation is mainly facies-marginal hybrid sediments,which develops in intertidal zone,subtidal zone,lagoon and landward side of barrier island.Large hybrid sediment sequences have small-scale development.Benxi Formation is divided into 2 third-order sedimentary sequences of SQ1 and SQ2,both with lowstand system tract(LST),transgressive system tract(TST)and highstand system tract(HST)identified,and SQ2 has also falling stage system tract(FSST)identified.Facies-marginal hybrid sediments mainly develop in early shallow water areas of TST and HST with relatively small development scale.They mainly develop in transition areas between tidal flats and lagoons and between lagoons and barrier flats,coexisting with tidal flat sandstones and barrier sandstones and forming hybrid sediments strata series with overlying sand-mudstone layers.The research provides reference for prediction of hybrid sediments reservoirs.