鄂尔多斯盆地麻黄山西区块北部中侏罗统延安组延一段沉积特征

摘要

Abstract: The compositions, sedimentary structures, grain size distribution and sedimentary facies types are examined on the basis of cores, well logs and grain size data of the rocks from the 1st member of the Middle Jurassic Yanan Formation in western Mahuangshan, Ordos Basin. The 1st member of the Yanan Formation is built up of the fluvial sedimentary system in which the braided and meandering stream deposits are developed. Two sedimentary subfacies have been distinguished including the riverbed and overbank subfacies which may be subdivided into the riverbed lag, channel bar, point bar, overbank, backswamp and crevasse-splay microfacies. During the deposition of the Yan-10 oil measures, the 1st member of the Yanan Formation was occupied by the braided stream deposits with well-developed channel bars and wider channels. The palaeocurrents were oriented NW to SE. Influenced by the lake-level rising during the deposition of the Yan-9 oil measures, the study area was prevailed over by the meandering stream deposits with the point bar deposits.%本文通过岩心观察、录测井及岩心粒度资料,对鄂尔多斯盆地麻黄山西区块北部中侏罗统延安组延一段的岩石组分、结构构造、粒度分布等特征进行分析,确定其沉积相类型.结果表明:延安组延一段属河流沉积体系,发育辫状河和曲流河两种沉积类型,主要包括河床和河漫两个亚相,可进一步识别出河床滞留、心滩、边滩、河漫滩、河漫沼泽、决口扇等微相.延一段延10油层组沉积时期,研究区以辫状河沉积为主,心滩发育,河道较宽,平面上摆动宽度为2~8km,主水流方向由西北至东南;延一段延9油层组沉积时期,受鄂尔多斯盆地湖水面整体抬升的影响,河道分布范围逐渐缩小,研究区以曲流河沉积为主,发育两条曲流河,平面上摆动宽度约2~4km,河道凸岸发育边滩沉积.