大别造山带铁路隧道气体燃烧的地质意义

目前合肥盆地的油气勘探工作主要沿用中国东部盆地的勘探成功经验,工作重点以"中新生代盆地系统"为主,迄今尚无实质性的油气突破。大别造山带和合肥盆地是紧密相连的2个构造单元,在形成和时空演化上具有密切的关系。在大别造山带内发现的可燃天然气和发生燃烧的隧道具有明显的区域性,集中分布于磨子潭—晓天断裂以南的北大别杂岩带和信阳—舒城断裂附近的早石炭世变质石英片岩中。通过对大别山区隧道燃烧现象的系统分析,结合大别造山带、合肥盆地的演化特征和海相烃源岩发育状况,结论认为:磨子潭—晓天断裂和信阳—舒城断裂是连通深部的气源通道断裂;推覆体之下的寒武系凤台组和北淮阳型石炭系2套海相烃源岩是隧道可燃天然气的主力气源岩,且其均已进入热演化的过成熟阶段。因此,下一步勘探重心应从"中新生代盆地系统"转移到"深部海相层系",以寻找"古生古储"或"古生新储"类型油气藏为主。

Geologic significance of gas combustion in railway tunnels in the Dabie orogenic belt

Current petroleum exploration in the Hefei Basin mainly draws on the experiences of exploration in the petroliferous basins in eastern China and focuses on the Meso Cenozoic basins. However, no significant discoveries have been made till now. The Dabie orogenic belt and the Hefei Basin are two closely connected tectonic units and are closely related in respect of origin as well as temporal and spatial evolution. The combustible gas and railway tunnels with gas combustion in the Dabie orogenic belt are regionally distributed and mainly occur in the complex to the south of the Mozitan Xiaotian fault and in the Early Carboniferous metamorphosed quartz schist near the Xinyang Shucheng fault. Based on a systematic analysis of gas combustion in railway tunnels in the Dabie Mountain and in combination with the evolutionary features and the development of marine source rocks in the Dabie orogenic belt and the Hefei Basin, it is believed that the Mozitan Xiaotian and Xinyang Shucheng faults are deep rooted and act as pathways for the migration of deep gas. The combustible gas in the railway tunnels are mainly sourced from the marine source rocks in the Cambrian Fengtai Formation underlying the thrust nappe and that in the Cretaceous Beihuaiyang Formation, both of which are overmature. The timing of hydrocarbon generation and trap formation is the focus of study. Therefore, the focus of future exploration should be shifted from the Meso Cenozoic strata to the deep marine sequences to search for pools with old source rocks and old reservoirs or pools with old source rocks but young reservoirs.