摘要
通过野外宏观地质特征观察、显微岩石学鉴定、全岩主要元素分析,揭示了漂白蚀变岩石的岩石学判识标志。结合蚀变岩石及围岩方解石胶结物碳氧同位素分析、流体包裹体研究、有机质分析,进一步阐明了漂白蚀变岩石形成的流体环境,这些特征反过来又对研究区烃类的运移及散失具有重要的指示意义。研究结果表明,漂白蚀变砂岩与红色原岩相伴而生,其颜色变化趋势、裂隙铁质充填特征、显微岩石学、地球化学特征指示研究区曾经历过化学还原性流体作用。方解石胶结物碳氧同位素分析表明,其δ13C较轻,大部分小于-10‰,指示存在有机碳源供给;流体包裹体特征显示,主要以气态烃及气液烃包裹体为主,成分主要为CO2和CH4,表明研究区经历过天然气作用;漂白砂岩及围岩有机质抽提特征显示,有机质成熟度高,而研究区煤系Ro小于0.5%,成熟度低,显然不是来自本地;盆地东北部天然气逸散表明,其与研究区延安组顶部漂白蚀变砂岩关系密切。综合分析表明,漂白蚀变砂岩形成是上古生界天然气逸散后与近地表围岩发生流体-岩石相互作用的结果,该研究对厘定近地表烃类运散、特别是天然气的逸散提供了新的判识方法,可作为指示油气运散的间接标志。
The petrologic identification marks of the bleached altered sandstone in the studied area are demonstrated according to the observation of field macro-geological characteristics,microscopic petrology identification and main element whole rock analysis. The fluid environment under which the bleached altered sandstone were formed is revealed based on the carbon and oxygen isotope analysis of the calcite cements,the study of the fluid inclusions and the analysis of the organic matters in the bleached altered sandstone and its adjacent rock,which are of important indicative significance to the migration and escaping of hydrocarbons in the studied area. It is shown that the bleached altered sandstone is accompanied by the red original rock,and the variation trend of the rock color,the ferruginous infilling features in cracks,the microscopic petrologic features and the geochemical features all show that the studied area experienced the action of reducing fluid. The carbon and oxygen isotope analysis of the calcite cements show that the δ13C value of the most of samples is less than- 10‰,which indicates that there is the supply of organic carbon. The fluid inclusion features show that there are mainly gaseous hydrocarbon and gas-liquid hydrocarbon inclusions,whose composition is mainly CO2and CH4,which indicates that the studied area experienced the action of natural gas. The organic extraction features of the bleached altered sandstone and its adjacent rock show that the organic matter in the area is high maturity,but the vitrinite reflectance( Ro) of local coal-bearing strata is lower than 0. 5%,which indicates the organic matter of high maturity is not local. The escaping of the natural gas in northeastern Ordos Basin shows that the gas escaping is closely related to the bleached altered sandstone on the top of Yan'an Formation in the studied area. All the results show that the formation of the bleached altered sandstone in the studied area is due to the fluid- rock interaction of the natural gas escaping from Upper Paleozoic with near-surface rock. The research results in this paper provide a new method for the identification of the migration and escaping of near-surface hydrocarbons,especially the escaping of natural gas.
出处
《西安石油大学学报（自然科学版）》
CAS
北大核心
2014年第2期37-42,49,共7页
Journal of Xi’an Shiyou University（Natural Science Edition）
基金
国家自然科学基金项目(编号:40902042
90814005)
国家重点基础研究发展规划"973"项目(编号:2003CB214607)
关键词
鄂尔多斯盆地
延安组
流一岩作用
岩石学记录
烃类运散
Ordos Basin
Yan'an Formation
fluid-rock interaction
petrologic record
migration and escaping of hydrocarbons
作者简介
马艳萍（1976-），女，博士，讲师，主要从事天然气地质学和地球化学的研究。E-mail：bye9@sohu．com
