摘要
鄂尔多斯盆地南部三叠系长6—7段深水重力流砂岩毗邻烃源岩,前人普遍认为沉积时期大气淡水难以进入,沉积后又无表生暴露,其中发育的溶蚀孔隙是在有机酸作用下形成的。但是在该深湖致密砂岩沉积中发现大量的溶蚀孔隙,很难用传统有机酸溶蚀理论解释。通过薄片观察、CT扫描、恒速压汞等手段进行孔隙结构识别,并利用阴极发光观察、地球化学分析结合区域地质背景资料综合判断。结果表明:①研究区中除了成岩晚期的有机酸溶蚀外,还发育早期大气淡水溶蚀;②早期淡水溶蚀孔隙主要表现为高岭石含量较低,孔隙结构较差,喉道半径小,束缚水含量较高等特点;③早期溶蚀孔的形成,改善了成岩晚期酸性溶液在岩石中的渗流条件,从而提高了酸性溶液的溶蚀效率,可对早期孔隙溶蚀扩大和产生新的溶蚀孔隙。结论认为:在深湖环境中受重力流事件的影响,淡水也能大量进入湖盆,深湖沉积物中也可能形成大面积的早期淡水溶蚀,如果这些孔隙得以保存,则能够在这种深水砂岩中形成良好的储层。
Some deepwater gravity flow sandstone in the Triassic Yanchang 6 and 7 members, southern Ordos Basin, is adjacent to source rock. Previously, it was universally recognized that meteoric water could hardly flow into this area during deposition, no supergene exposure occurred after deposition, and developed dissolution pores might be formed by organic acid. However, a great number of dissolution pores have been found among these deposits of deeper lacustrine tight sandstone. And this phenomenon is hardly explained with the help of a traditional theory of dissolution by organic acid. So, pore structure was distinguished by means of thin-section identification, CT scanning, and constant-rate mercury penetration. In addition, a comprehensive judgment was carried out by virtue of cathode luminescence observation, geochemical analysis, and regional geological data. Results show that, in the study area,(1) early meteoritic water dissolution is developed besides organic acid dissolution during late diagenesis;(2) pores formed in the early stage by water dissolution are mainly characterized by low kaolinite content, poor pore structure, small throat radius, and high bound-water content;(3) to generate early dissolution pores improves flowing conditions of acid solution in rock during late diagenesis, so as to increase dissolution efficiency of acid solution, and thus these early pores can be dissolved and enlarged and new dissolution pores can be generated. In conclusion, under an effect of gravity flow in deeper lacustrine setting, plenty of meteoritic water can flow into lacustrine basin, and extensive water dissolution pores may be formed in deepwater sediments. If these pores are preserved, good reservoirs can be formed in this kind of deepwater sandstone.
作者
刘曦翔
张宇
蒲柏宇
徐会林
丁晓琪
Liu Xixiang;Zhang Yu;Pu Boyu;Xu Huilin;Ding Xiaoqi(Exploration and Development Research Institute, PetroChina Southwest Oil & Gasfield Company, Chengdu, Sichuan 610041,China;Southwest Petroleum University, Chengdu, Sichuan 610500,China;Exploration Division, PetroChina Southwest Oil & Gasfield Company, Chengdu, Sichuan 610041,China;Southern Sichuan Gas District, PetroChina Southwest Oil & Gasfield Company, Luzhou,Sichuan 646001,China;College of Energy Resources, Chengdu University of Technology, Chengdu, Sichuan 610059,China)
出处
《天然气勘探与开发》
2019年第2期48-55,共8页
Natural Gas Exploration and Development
基金
国家自然科学青年基金项目“大气淡水在碎屑岩次生孔隙形成中的作用”(编号:41302115)
关键词
鄂尔多斯盆地
晚三叠世
重力流
致密砂岩
淡水溶蚀
成因与意义
Ordos basin
Late Triassic
Gravity flow
Tight sandstone
Meteoric water dissolution
Genesis and significance
