扬子陆块下古生界页岩气保存条件分析

Shale gas preservation conditions in the Lower Paleozoic,Yangtze block

早古生代扬子陆块主要发育有下寒武统牛蹄塘组与上奥陶—下志留统五峰—龙马溪组2套富有机质页岩。受多期造山与多期成盆事件影响，2套页岩在经历广西、印支、燕山与喜马拉雅4期造山事件改造后，上扬子区及中扬子西部改造相对较弱、变形叠加期次最少（2～3期），页岩气保存条件最好、页岩气含量最高、最有资源前景；中扬子东部及下扬子区西部改造强度与变形叠加期次其次（3～4期），页岩气保存条件相对较差、页岩气含量相对较高、资源前景较好；下扬子区东部及扬子陆块周缘山前改造最强、变形叠加期次最多（4期），页岩气保存条件最差、页岩气含量较低、资源前景有限；陆块内部总体以残留复向斜区页岩气保存条件最好。

Two sets of organic-rich shale developed in the Yangtze block during the Early Paleozoic. The first set was in the Lower Cambrian Niutitang Formation, while the second set was in the Upper Ordovician Wufeng Formation and the Lower Silurian Longmaxi Formation. The shales experienced four stages of orogenic events, in-cluding the Guangxi, Indosinian, Yanshanian and Himalayan. Shales are well-preserved in the Upper Yangtze region and to the west of the middle Yangtze region, where only two or three phases of deformation took place. The shale gas content is high, showing a good potential for exploration. In the east of the middle Yangtze region and the west of the lower Yangtze region, shale gas preservation conditions are poorer due to three or four phases of deformation. As a result, the shale gas content is lower as is the exploration potential. In the east of the lower Yangtze region and in the periphery orogenic front of the Yangtze block, four phases of deformation took place, which led to the poorest preservation conditions for shale gas. As to the whole Yangtze block, the residual synclines are most favorable for shale gas preservation.