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川西北地区泥盆系观雾山组紫红色白云岩成因初探
郝毅,李文正,苑保国,姚倩颖,戴鑫,熊绍云
0
(1. 中国石油杭州地质研究院, 浙江 杭州 310023;
2. 中国石油天然气集团公司碳酸盐岩储层重点实验室, 浙江 杭州 310023;
3. 中国石油西南油气田公司勘探开发研究院, 四川 成都 610041)
摘要:
川西北地区泥盆系观雾山组是新发现的重要天然气产层。在青川何家梁以及葛底坝等地区,泥盆系观雾山组存在一种特殊紫红色调的白云岩,目前对该白云岩成因及形成环境的研究较为薄弱。本次研究采用宏观与微观、矿物学与地球化学相结合的方式对该白云岩进行了系统分析。该类白云岩呈紫红、肉红等色调,单层厚度3~50cm,显微镜下岩石本身呈晶粒结构。对其成因初步分析认为:白云岩中的紫红色、肉红色是一种次生色,是铁元素富集后被氧化的颜色;白云岩存在暴露、岩溶、垮塌现象,指示其形成于古地貌相对较高的局限蒸发环境;只有白云石核心变色,说明其形成时间较早,应为准同生期在相对局限的环境下,颗粒被富含铁元素的水体浸泡侵染所致,随后颗粒外继续形成白云石胶结物将其包裹。紫红色白云岩相对发育的地层往往白云岩的储层厚度大,物性好,岩溶现象发育,储集空间类型多样,是该地区油气勘探的一种重要指示标志。
关键词:  川西北  泥盆系  观雾山组  紫红色白云岩  成因
DOI:10.19826/j.cnki.1009-3850.2019.10001
投稿时间:2019-10-11修订日期:2020-08-03
基金项目:中国石油重大科技专项(课题编号:2016E-0601);十三五国家专项(课题编号:2016ZX05004-002,2017ZX05008-005);中国石油重大科技项目(课题编号2018A-0103,2018A-0105)
The genesis of the purplish-red dolostone in the Middle Devonian Guanwushan Formation, Northwest Sichuan Basin
Hao Yi, Li Wenzheng, Yuan Baoguo, YAO Qianying, DAI Xin, XIONG Shaoyun
(1. Hangzhou Institute of Petroleum Geology, PetroChina, Hangzhou, 310023, Zhejiang;
2. Key Laboratory of Carbonate Reservoir, CNPC, Hangzhou 310023, Zhejiang;
3. Research Institute of Exploration and Development, PetroChina Southwest Oil&Gas Field Company, Chengdu 610041, Sichuan)
Abstract:
The Devonian Guanwushan Formation in northwest Sichuan Basin is a newly discovered important stratigraphic horizon for exploration of gas. The dolostone of the Middle Devonian Guanwushan Formation in Hejialiang and Gediba areas is with purplish-red or yellow-brown colors. Previously, the research on the genesis and forming environment of the dolostone is relatively weak. Based on studies of mineralogy, geochemistry, lithology and experimental analysis data of field samples, the genesis of the dolostone with purplish-red or yellow-brown colors is detailedly analyzed in this paper. The single layer thickness of dolostone with purplish-red or flesh-red colors is between 3cm and 50cm. It has obvious grain structure under microscopes. The preliminary analysis of its genesis is as follow:1) The purplish-red color showed in the dolostone is a secondary color, which was caused by the oxidation of the ferric element;2) Exposure, karst and collapse were common in this kind of dolostone, meaning it was formed in a limited evaporation environment with relatively high paleogeomorphology;3) Only the cores of the dolomite are with different colors, indicating that they were formed earlier than their cement outsides. It is believed that during the contemporaneous period, carbonate grains were dyed by enriched irons in a relatively confined environment, then, they were wrapped by cement outsides. Dolostone with purplish-red, flesh-red or yellow-brown colors is usually with large thickness, good reservoir, developed karst phenomenon and various reservoir space types. It is one of important indications for oil-gas exploration in the region.
Key words:  northwest Sichuan Basin  Devonian  the Guanwushan Formation  purplish-red dolostone  genesis

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