四级层序格架内浊流沉积特征及演化模式——以鄂尔多斯盆地镇泾地区三叠系延长组7段为例  

Sedimentary characteristics and evolution model of turbidites within a fourth-order sequence stratigraphic framework:A case study of the Triassic Chang 7 Member in Zhenjing area,Ordos Basin

作　　者：冯烁 李胜利[1] 于兴河[1] 何发岐[2] 李顺利[1] 齐荣[2] Feng Shuo;Li Shengli;Yu Xinghe;He Faqi;Li Shunli;Qi Rong(China University of Geosciences(Beijing),Beijing 100083,China;North China Petroleum Bureau,SINOPEC,Zhengzhou,Henan 450006,China)

机构地区：[1]中国地质大学(北京),北京100083 [2]中国石化华北油气分公司,河南郑州450006

出　　处：《石油与天然气地质》2022年第4期859-876,共18页Oil & Gas Geology

基　　金：国家自然科学基金项目(421721112);国家油气重大专项(2017ZX05001-002-003)。

摘　　要：沉积期鄂尔多斯盆地西南缘镇泾地区延长组7段(长7段)既是优质烃源岩发育层段,也是浊流沉积发育的重要储集层段。镇泾地区长7段沉积期为湖盆鼎盛时期,发育深湖-半深湖向三角洲过渡的沉积体系。随镇泾地区油气勘探开发的不断深入,尤其是细粒沉积与页岩油气日益受到重视,长7段浊流沉积特征也备受关注。基于露头、岩心与测井资料,结合层序地层与沉积学研究方法,开展了四级层序格架内的浊流沉积演化与沉积模式研究。结果表明:长7段自下而上可分为MSC1,MSC2和MSC3共3个四级层序;长7段总体以细粒沉积为主,表现出前三角洲与湖相背景下的浊流沉积特征,其中前三角洲亚相主要发育在MSC3层序和MSC2层序;MSC1层序主要发育湖相沉积,三角洲不发育;浊流在3个四级旋回中的发育特征不同。结合研究区沉积演化特点,利用湖平面相对位置代表基准面变化(V_(a))、去压实后的平均地层厚度表征沉积物供给速率(V_(s)),对可容纳空间增加速率(ΔV_(a))及沉积物供给速率(ΔV_(s))的比值变化进行研究,建立了3种浊流沉积演化模式:湖侵泥质型、高位早期砂-泥混合型和高位晚期砂质型,其中高位晚期砂质型浊流砂体应是今后油气勘探的重点目标。The 7th member of Yanchang Formation(Chang 7 Member)in Zhenjing area at the southwestern margin of Ordos Basin,features development of both high-quality source rocks and turbidite reservoirs.The Chang 7 Member is deposited in a period of maximum lake depth of the Ordos Basin,with its sedimentary system transitioning from deepsemi-deep lacustrine facies to deltaic facies.As the oil/gas exploration and development has been progressing in the study area,more and more attention has been paid to fine-grained deposits and shale oil/gas reservoirs,especially the sedimentary characteristics of turbidites therein.An integration of outcrop,core and logging data is applied to study sedimentary evolution and depositional patterns of the turbidites within a fourth-order sequence stratigraphic framework,in which sequence stratigraphy and sedimentology methods are adopted.The results show that the Chang 7 Member can be divided into three fourth-order sequences from bottom to top,namely MSC1,MSC2 and MSC3.The member in general is dominated by fine-grained deposits and exhibits signs of turbidite deposition in a pre-deltaic and lacustrine setting.Among others,the pre-deltaic subfacies is widely seen in MSC3 and MSC2;while the lacustrine facies predominates in MSC1 with underdeveloped deltas facies.The three fourth-order sequences feature diverse kinds of turbidite development.Three sedimentary evolution models are established for the turbidites:the lacustrine transgressive muddy type,early highstand mixed sandy and muddy type,and late highstand sandy type,with the last type being the major target for future exploration.In the process,the sedimentary evolution characteristics in the study area are considered;the relative position of lake level is taken as the proxy of the base level fluctuation(V_(a)),and the mean decompacted thickness serves to reflect the sediment supply rate(V_(s)).Besides,the variation of the ratio of the increase rate in accommodation space(ΔV_(a))to the sediment supply rate(ΔV_(s))is also taken into accoun

关 键 词：可容纳空间 沉积物供给速率 四级层序 浊流沉积演化模式 沉积体系 延长组7段 镇泾地区 鄂尔多斯盆地 

分 类 号：TE121.3[石油与天然气工程—油气勘探]