摘要
基于鄂尔多斯盆地西南部三叠系延长组长73亚段页岩油勘探实践进展,综合野外露头、钻井、测井、岩心、地球化学等资料,以及水槽实验模拟等技术手段,开展陆相湖盆细粒沉积古环境、岩相组合和分布、沉积成因及页岩油储集特征的系统研究。结果表明:①长73亚段沉积期研究区古环境整体表现为温暖湿润、梅雨事件频发、水体深度较大的淡水湖盆特征,古地貌呈现西南陡、东北缓的不对称型,可进一步细分为湖底深洼、古沟道、湖底古脊等微古地貌单元。②长73亚段发育一套极细砂岩、粉砂岩、泥页岩、凝灰岩等细粒沉积,垂向多呈薄互层—纹层组合分布,砂岩粒径大多小于62.5μm,单层厚度为0.05~0.64 m,含完整植物碎片,发育波状层理、逆粒序-正粒序组合、爬升沙纹层理等沉积构造,揭示异重流沉积成因。③环形水槽模拟实验再现了异重流搬运过程及沉积特征,主要表现为初期的密度流速差造成头部较厚且粒径较大,上部较薄且粒径偏小的特征;中期滑水作用促使流体头部抬升并向前快速搬运,由此产生的多个“新前端”促使粉砂岩、泥质粉砂岩等细粒砂岩向湖盆中部长距离搬运。④明确了盆地西南部细粒砂质岩以异重流成因为主,指出频繁发育的洪水事件、西南部陡坡地形是异重流发育的主控因素。⑤长73亚段砂岩、泥页岩发育微纳米孔喉系统,不同岩性均含油,但可动油含量差异大,砂岩中可动油含量最大。⑥明确了长73亚段多期异重流砂岩与泥页岩形成的细粒沉积复合体具有“整体含油、差异储集”特征,低TOC泥岩与粉砂岩组合为目前最有利的勘探目标。
Based on recent advancements in shale oil exploration within the Ordos Basin,this study presents a comprehensive investigation of the paleoenvironment,lithofacies assemblages and distribution,depositional mechanisms,and reservoir characteristics of shale oil of fine-grained sediment deposition in continental freshwater lacustrine basins,with a focus on the Chang 73 sub-member of Triassic Yanchang Formation.The research integrates a variety of exploration data,including field outcrops,drilling,logging,core samples,geochemical analyses,and flume simulation.The study indicates that:(1)The paleoenvironment of the Chang 73 deposition is characterized by a warm and humid climate,frequent monsoon events,and a large water depth of freshwater lacustrine basin.The paleogeomorphology exhibits an asymmetrical pattern,with steep slopes in the southwest and gentle slopes in the northeast,which can be subdivided into microgeomorphological units,including depressions and ridges in lakebed,as well as ancient channels.(2)The Chang 73 sub-member is characterized by a diverse array of fine-grained sediments,including very fine sandstone,siltstone,mudstone and tuff.These sediments are primarily distributed in thin interbedded and laminated arrangements vertically.The overall grain size of the sandstone predominantly falls below 62.5μm,with individual layer thicknesses of 0.05–0.64 m.The deposits contain intact plant fragments and display various sedimentary structure,such as wavy bedding,inverse-to-normal grading sequence,and climbing ripple bedding,which indicating a depositional origin associated with density flows.(3)Flume simulation experiments have successfully replicated the transport processes and sedimentary characteristics associated with density flows.The initial phase is characterized by a density-velocity differential,resulting in a thicker,coarser sediment layer at the flow front,while the upper layers are thinner and finer in grain size.During the mid-phase,sliding water effects cause the fluid front to rise and facilitate rapid forward transport.This process generates multiple“new fronts”,enabling the long-distance transport of fine-grained sandstones,such as siltstone and argillaceous siltstone,into the center of the lake basin.(4)A sedimentary model primarily controlled by density flows was established for the southwestern part of the basin,highlighting that the frequent occurrence of flood events and the steep slope topography in this area are primary controlling factors for the development of hyperpynal flows.(5)Sandstone and mudstone in the Chang 73 sub-member exhibit micro-and nano-scale pore-throat systems,shale oil is present in various lithologies,while the content of movable oil varies considerably,with sandstone exhibiting the highest content of movable oil.(6)The fine-grained sediment complexes formed by multiple episodes of sandstones and mudstones associated with density flow in the Chang 73 formation exhibit characteristics of“overall oil-bearing with differential storage capacity”.The combination of mudstone with low total organic carbon content(TOC)and siltstone is identified as the most favorable exploration target at present.
作者
刘显阳
刘江艳
王秀娟
郭芪恒
吕奇奇
杨智
张岩
张忠义
张文选
LIU Xianyang;LIU Jiangyan;WANG Xiujuan;GUO Qiheng;LYU Qiqi;YANG Zhi;ZHANG Yan;ZHANG Zhongyi;ZHANG Wenxuan(PetroChina Changqing Oilfield Company,Xi’an 710018,China;National Engineering Laboratory for Exploration and Development of Low-Permeability Oil&Gas Fields,Xi’an 710018,China;Yangtze University,Wuhan 430100,China;PetroChina Research Institute of Petroleum Exploration&Development,Beijing 100083,China)
出处
《石油勘探与开发》
北大核心
2025年第1期84-98,共15页
Petroleum Exploration and Development
基金
中国石油天然气集团有限公司前瞻性基础性研究科技重大项目“鄂尔多斯盆地页岩油勘探开发理论与关键技术研究”(2021DJ1806)。
关键词
细粒沉积
异重流
水槽模拟实验
储集特征
长7_(3)亚段
三叠系延长组
页岩油
鄂尔多斯盆地
fine-grained sedimentation
density flow mode
flume simulation experiments
reservoir characteristics
Chang 7_(3)sub-member
Triassic Yanchang Formation
shale oil
Ordos Basin
