中上扬子地区震旦系灯影组沉积特征及其对碳酸盐岩优质储层的影响

    Sedimentary characteristics of the Sinian Dengying Formation in the Middle-Upper Yangtze Region and their influence on high-quality carbonate reservoirs

    • 摘要: 中上扬子地区震旦系灯影组是油气勘查的优质储层,目前针对性勘探主要集中在四川盆地内部,盆地以外的探查程度较低。为了进一步厘清灯影组的沉积过程和储层特征,以中上扬子德阳—安岳海槽和鄂西海槽为重点解剖区,综合地表露头和钻井资料,分析其沉积过程和储层分布特征。研究表明: ①中上扬子地区的大部分灯影组可以分为4段,鄂西宜昌地区分别为蛤蟆井段、石板滩段、白马沱段和天柱山段; ②灯影组沉积时期的3幕桐湾构造运动对碳酸盐储层具有良好的改造作用,桐湾运动Ⅰ幕发育在灯二段顶部,桐湾运动Ⅱ幕发育在灯影组顶部,桐湾运动Ⅲ幕发育在上覆麦地坪组(岩家河组)顶部; ③中上扬子地区灯影组沉积时期具有“三台两槽”特征,拉张环境产生地堑-地垒式的台盆结构,海槽内填充下寒武统富有机质页岩,提供优质烃源岩; ④鄂西海槽和德阳—安岳海槽东西两侧形成陡坡,灯影组有利储层发育于台地高部位,分别位于台地边缘和台内滩; ⑤灯影组优质白云岩储层和下伏陡山沱组、上覆筇竹寺组(水井沱组)页岩形成“三明治”式油气成藏组合,保存条件是天然气藏形成的关键。研究成果可为灯影组油气勘探提供新的找矿方向和理论基础。

       

      Abstract: The Sinian Dengying Formation in the Middle-Upper Yangtze Region is a high-quality reservoir for oil and gas exploration. Current targeted exploration remains concentrated in Sichuan Basin, while investigations outside the basin are relatively underexplored. Deyang-Anyue trough and Western Hubei trough within the Middle-Upper Yangtze Region were selected as key areas to further clarify the sedimentary processes and reservoir characteristics of Dengying Formation. The sedimentary evolution and spatial distribution of reservoirs were analyzed by integrating the surface outcrop data with the drilling records. Key findings showed that Dengying Formation could be subdivided into four members in most of the Middle-Upper Yangtze region, specifically designated as Hamajing, Shibantan, Baimatuo, and Tianzhushan Members in Yichang area of the western Hubei Province. Three phases of Tongwan tectonic movement during Dengying deposition period significantly reshaped carbonate reservoirs. Phase Ⅰ occurred at the top of the second member, Phase Ⅱ occurred at the formation's upper boundary, and Phase Ⅲ occurred at the top of Maidiping (Yanjiahe) Formation. Dengying Formation of the Middle-Upper Yangtze was characterized by "three-platform-two-trough" paleogeographic framework. The extensional settings created graben-horst platform-basin structures, and organic-rich shales deposited in these troughs during the Early Cambrian, providing premium source rocks. Steep slopes formed along both flanks of Western Hubei and Deyang-Anyue troughs, and favorable reservoirs in Dengying Formation developed in the higher parts of the platform, which were platform margins and intra-platform shoals. Sandwich-style hydrocarbon assemblage formed in high-quality dolomitic reservoirs in Dengying Formation, underlying Doushantuo Formation shales and overlying Qiongzhusi (Shuijingtuo) Formation. The preservation conditions was critical for natural gas accumulation. These results could provide new theoretical foundations and exploratory directions for Dengying Formation oil and gas exploration.

       

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