鄂尔多斯盆地东胜地区延安组砂岩漂白蚀变特征及成因机制  

Alteration characteristics and genetic mechanisms of Yan'an Formation sandstone bleaching in Dongsheng area

作　　者：谭玉涵 王建强[2] 高丹 何羽飞 韩鹏[3] 

机构地区：[1]中国石油集团测井有限公司油气评价中心 [2]大陆动力学国家重点实验室.西北大学 [3]中国石油长庆油田公司勘探开发研究院

出　　处：《天然气勘探与开发》2017年第4期17-24,共8页Natural Gas Exploration and Development

基　　金：国家自然科学重点基金项目"坳陷型富烃凹陷的主要特征和形成的动力学环境--以鄂尔多斯盆地为例"(编号:41330315)

摘　　要：鄂尔多斯盆地东北部中侏罗统延安组顶部广泛发育砂岩的漂白现象,其漂白蚀变特征及形成机制仍是迄今研究较薄弱的重要问题。在前人研究成果的基础上,以东胜市神山沟地区的典型剖面为解剖对象,开展了漂白砂岩岩石矿物组成与填隙物特征、主量元素与微量元素等地球化学指标、砂岩包裹体特征等测试分析研究,初步揭示了延安组顶部岩石漂白蚀变特征及形成机制。研究结果表明:(1)延安组漂白砂岩矿物碎屑以石英为主,长石含量少、溶蚀强烈,填隙物以高岭石为主,高岭石填隙物是砂岩呈现白色调的主因;(2)延安组漂白砂岩经历了黏土化并发生了铁离子的迁移,黏土化和铁离子的流失是砂岩发生漂白蚀变的内在因素;(3)漂白砂岩包裹体中存在有以CH_4为主的气态烃类流体,表明该区曾发生过还原性酸性有机流体作用,改变了pH值、氧化—还原电位,引起了砂岩高岭石化和铁离子的迁移,促使砂岩漂白蚀变;(4)延安组漂白砂岩的形成与该区早白垩世末自盆地西南向北东发生大规模天然气逸散存在密切的联系。The bleaching phenomenon of sandstone is widely developed at the top of Middle Jurassic Yan＇an Formation in northeast- ern Ordos Basin. So far, however, its alteration characteristics and formation mechanisms have been less researched. In this paper, the typical section of Shenshangou in Dongsheng area was taken the study object. Based on the previous research results, the bleached sandstones were tested and analyzed from aspects of mineral texture characteristics, geochemical characteristics and sandstone inclu- sion characteristics, and the alteration characteristics and formation mechanisms of sandstone bleaching at the top of Yan＇an Formation was revealed preliminarily. The following research results were obtained. First, the mineral clastics in Yah＇an Formation bleached sandstones are mainly composed of quartz with a little feldspar, and they are strongly dissolved. Kaolinite is the main interstitial ma- terial and it is the main reason for the white color of sandstones. Second, Yan＇an Formation bleached sandstones suffer clayzation and ferric ion migration, and clayzation and ferric ion loss are the internal causes of bleaching and alteration of sandstones. Third, there is gas hydrocarbon with CH4 as the dominant component in the inclusion of bleached sandstone. It is indicated that reducing acid organic fluidization once occurred in this area, and it changes pH value and oxidation/reduction potential, leading to the kaolinization of sand- stones and the migration of ferric ion and promoting the bleaching and alteration of sandstones. And fourth, the formation of Yah＇an Formation bleached sandstones is in close relation with the large-scale escaping of natural gas from the southwest to the northeast of the Ordos Basin at the end of Early Cretaceous. This understanding can be used as the reference for the exploration in this area.

关 键 词：鄂尔多斯盆地 中侏罗世 延安组 砂岩漂白 蚀变特征 成因机制 高岭石化 离子迁移 包裹体 

分 类 号：P618.13[天文地球—矿床学]