上、下扬子区古生界页岩气形成和保存的构造背景对比分析

Comparative Study of the Tectonic Setting on the Formation and Preservation of Paleozoic Shale Gas between the Upper Yangtze and the Lower Yangtze Platforms

地质历史中构造相对较稳定的扬子地台是中国最符合页岩气富集赋存的区域之一,但由于地台东西跨度较大,西部的上扬子区与东部的下扬子区构造背景差异明显,对页岩气的形成和保存有重要影响。对比分析了上扬子区与下扬子区古生代的沉积—构造演化过程,结合目前泥页岩的储层特征,认为上扬子区与下扬子区沉积构造演化过程较相似,都具有良好的页岩气形成条件;对比分析古生代以来上扬子区和下扬子区构造活动特征,认为上扬子区自中生代以来一直处于挤压构造背景中,有利于页岩气的保存,下扬子区印支期处于挤压构造环境,燕山期以来发生构造反转,处于伸展构造环境中,对页岩气的保存有重要破坏作用,因此上扬子区比下扬子区具有更大的页岩气勘探潜力。

The Yangtze platform is relatively stable in the geological history,so it is one of the most possible regions for the accumulation of shale gas.Because of large lateral span of Yangtze platform,the tectonic settings between the Upper Yangtze platform on the west and the Lower Yangtze on the east are rather different,which is of obvious significance for the formation and preservation of the shale gas.The comparative analysis on the Paleozoic sedimentary-tectonic evolution of the Upper and Lower Yangtze platforms,combined with the recent reservoir properties,indicate that sedimentary-tectonic evolution progresses between the two platforms are similar,and have good conditions for shale gas formation.The comparation on the tectonic activities since the Paleozoic show that the Upper Yangtze platform has been in a background of compression since the Mesozoic,and is conducive to the preservation of shale gas,while the Lower Yangtze platform has been in compression since Indosinian,and tectonic inversion took place in Yanshanian and was in an extensional environment,which is destructive for the reservoirs of shale gas.So,the Upper Yangtze platform has greater potential for shale gas exploration and development than the Lower Yangtze region.