鄂尔多斯盆地陇东地区长7油层组深水水道型重力流沉积特征及沉积模式

Sedimentary characteristics and sedimentary model of deepwater channel-induced gravity flow of Chang 7 oil layer group in Longdong Area of the Ordos Basin

综合利用钻井岩心、测井和分析测试等资料,结合湖盆重力流沉积学理论和相关研究成果,研究鄂尔多斯盆地陇东地区长7油层组深水重力流的沉积特征、分布特征和演化,并建立研究区沉积模式。结果表明:研究区发育块状层理细砂岩相、正粒序层理粉(细)砂岩相、平行层理粉砂岩相、波纹交错层理粉砂岩相、水平层理泥质粉砂岩相、暗色泥岩相、富有机质页岩相、凝灰岩相8种岩相类型,代表砂质碎屑流沉积、浊流沉积、半深湖—深湖原地沉积、火山碎屑沉积成因类型;陇东地区长7油层组发育深水重力流沉积,可划分为限制性水道沉积、非限制性水道沉积、天然堤沉积、水道间沉积、朵叶体沉积和半深湖—深湖泥沉积6种沉积微相,从斜坡区到湖盆中心,依次发育限制性水道沉积、非限制性水道沉积、朵叶体沉积;长7_3沉积时期多发育朵叶体沉积,长7_2沉积时期多发育(非)限制性水道沉积、天然堤沉积、朵叶体沉积,长7_1沉积时期多发育(非)限制性水道沉积和天然堤沉积;自长7_3至长7_1沉积时期,湖盆面积逐渐萎缩,湖岸线向盆地中心推进,且受物源影响,重力流砂体的发育规模变大,并不断向湖盆中心推进。该研究结果为深水油气勘探提供依据。

By using drilling core,logging and analytical test data,and combining with the theory of gravity flow sedimentology in lake basin and related research results,the sedimentary characteristics,distribution characteristics and evolution law of deepwater gravity flow in Chang 7 oil layer group in Longdong Area of Ordos Basin were systematically studied,and the sedimentary model of the study area was established.The results show that there are eight lithofacies types,including massive bedding fine sandstone,normal graded bedding siltstone(fine)sandstone,parallel bedding siltstone,corrugated cross bedding siltstone,horizontal bedding muddy siltstone,dark mudstone,horizontal lamina shale,and tuff,which represent the genetic types of sandy debris flow deposits,turbidity current deposits,semi-deep lake and deep lake autochthonous deposits and volcanic debris deposits.Deepwater gravity flow deposits are developed in Chang 7 oil layer group in Longdong Area.Chang 7 oil layer group is divided into six sedimentary microfacies,including restricted channel,poorly restricted channel deposits,levee deposits,interchannel deposits,lobes deposits and semi-deep lake to deep lake mud.The restricted channel deposits,the poorly restricted channel deposits and the lobe deposits are successively developed from the slope area to the center of the lake basin.During the Chang 73 period,lobes deposits was mostly developed;During the Chang 72 period,(poorly)restricted channel deposits,levee deposits,lobes deposits were mostly developed;(poorly)restricted channel deposits,levee deposits developed in the Chang 71 period.The lake area gradually decreased,and the lake shoreline was closed to the center of the basin from Chang 73 period to Chang 71 period.Due to the influence of provenance,the development scale of gravity flow sand body becomes larger,and the gravity flow deposits continued to advance to the center of the lake basin.The research results supply a theoretical foundation for deepwater oil and gas exploration.