北羌塘坳陷古风化壳地质特征及意义

发布时间：2018-06-14 10:07

本文选题：北羌塘坳陷 + 古风化壳　；参考：《成都理工大学》2017年硕士论文

【摘要】：羌塘盆地是我国最大的陆域海相含油气沉积盆地,其以中生代地层为主要出露,位处全球油气资源宝库特提斯域构造带东段,盆内烃源岩层丰富,从古生代-中生代均有出露,虽然该区拥有异常丰富的烃源岩,但储集层相对致密且缺乏是该区形成优质油藏的一个难题,而肖茶卡组与那底岗日组之间的古风化壳的发现无疑为解决这个难题提供了一个契机。近年来我国已经发现了大量与古风化壳有关的油气藏,如四川盆地高石1井、双探2井,又或者是鄂尔多斯盆地马家沟组、松辽盆地营城组等,都显示出了古风化壳之于油气成藏的重要意义,但针对碳酸盐岩古风化壳而言,其非均质性很强,分布规律异常复杂,这无疑增加了对风化壳油气成藏研究的难度。本次研究依据北羌塘坳陷构造演化特征,以野外地质勘测为主,结合地质学、地层学、岩相学、矿相学,并辅以储层地质学对北羌塘坳陷古风化壳进行多学科综合研究,结果表明:研究区古风化壳受区域性分带发育影响常呈正凸起直接超覆于任意地层之上(区内主要以肖茶卡地层为主),岩溶垮塌角砾岩为壳体剖面识别的重要标志;研究区风化作用呈现出北强南弱,西强东弱的特点,地化特征上表现为Ce轻微负异常、Eu明显负异常,说明壳体在形成过程中受当时氧化环境影响,元素产生分异。此外,古风化壳作为潜在储层主要发育有丰富的溶蚀孔洞,其中以大型溶蚀洞穴为埋藏期尚未暴露的壳体中潜在的优质储集空间,大量缝隙发育为古风化壳下渗流体提供了良好的运移通道,一定程度上保证了埋藏期壳体溶蚀孔洞系统的发育,对古风化壳形成时代来说,目前并未有较好的办法能予以测定,仅凭其上下地层时代厘定其上限年龄,至于其下限年龄还有待进一步研究。
[Abstract]:Qiangtang basin is the largest marine sedimentary basin in China. It is mainly exposed in Mesozoic strata, located in the eastern segment of the Tethys tectonic belt, a treasure house of global oil and gas resources, and rich in hydrocarbon source rocks in the basin, which is exposed from Paleozoic to Mesozoic. Although there are abundant hydrocarbon source rocks in this area, the relatively dense reservoir and lack of reservoir is a difficult problem to form high-quality reservoirs in this area. The discovery of paleo-weathering crust between Xiao Chaka formation and Nadigang Ri formation provides an opportunity to solve this problem. In recent years, a large number of oil and gas reservoirs related to paleo-weathering crusts have been discovered in China, such as Gaoshi 1 well, Shuangtang 2 well in Sichuan Basin, or Majiagou formation in Ordos Basin, Yingcheng formation in Songliao Basin, etc. Both show the importance of paleo-weathering crust in hydrocarbon accumulation, but for carbonate paleo-weathering crust, its heterogeneity is very strong and its distribution law is very complicated, which undoubtedly increases the difficulty of studying hydrocarbon accumulation in weathered crust. Based on the structural evolution characteristics of the North Qiangtang Depression and the field geological survey, this study combined with geology, stratigraphy, lithology, mineralogy and reservoir geology to study the paleo-weathered crust of the North Qiangtang Depression. The results show that the paleo-weathering crust in the study area is usually directly overlying on any stratum by the influence of regional zonation development (the main strata in the study area are Xiaocha formation and the karst collapse breccia is an important mark for the identification of shell profile; The weathering in the study area shows the characteristics of north strong, south weak, west strong and east weak. The geochemical characteristics show that ce is slightly negative anomaly and EU is obviously negative anomaly, which indicates that the shell is affected by the oxidation environment at that time and the elements are different during the formation process. In addition, the paleo-weathered crust as a potential reservoir has abundant dissolution pores, in which the large dissolution cave is regarded as the potential high quality reservoir space in the shell that has not been exposed in the burial period. A large number of gaps provide a good migration channel for the osmotic fluid in the paleo-weathered crust, which to some extent ensures the development of the cave system in the shell during the burial period. There is no good method to measure the formation of the paleo-weathered crust at present. The upper limit age is determined only by its upper and lower stratigraphic age, and the lower limit age needs further study.
【学位授予单位】：成都理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P618.13

【参考文献】