云桂铁路老石山隧道浅层天然气成因模式研究

摘要

Focused on the emission and burning of natural gas in the Laoshishan tunnel on the Kunming-Nanning passenger dedicated line, which passes through a non-coal stratum, the formation mode of natural gas was researched regarding the causes of tunnel hazards and natural gas sources. Based on the geological conditions of the emission area, the characteristics of the oil-gas generation layer, the reservoir layer, and the bearing layer were analyzed, proving that: 1) the anticline structure at the tunnel's exit is the affected area for oil and gas migration;2) a series of underlying generation layers have the capacity to generate oil and gas;and 3) the shallow accumulation of oil and gas is possible via the fault structure. According to a comparison of gas concentrations before and after tunnel excavation, it is determined that shallow natural gas mainly comes from deep rock below the tunnel floor, and the rock around the tunnel body may have already been affected by accumulation at individual sections. The causes of shallow natural gas in the Laoshishan tunnel are obtained by analyzing gas distribution characteristics and the gas formation mode: namely, the gas comes from the shale of the Qiongzhusi formations of the deep Silurian system and the Cambrian system with migration along the Longquansi fault zone.%云桂铁路老石山隧道在穿越非煤层系地层施工时，发生了天然气溢出及燃烧现象。文章针对该隧道病害形成原因及天然气来源，对天然气的成因模式进行了研究；在收集区域油气地质背景的基础上，从生油气层、油气储层和油气层构造三方面进行分析得出，隧道出口的背斜构造是油气运移的指向区和逸散浸染带，隧道下伏的多套生油气地层均存在一定的生油气能力，油气有通过断裂构造向上运移至浅部富集的可能性；结合隧道开挖前后天然气浓度检测结果分析表明，浅层天然气主要来源于隧道底板下深部岩层，而隧道洞身岩层可能已受油气浸染，在个别地段有富集的可能；最后通过对天然气分布特征及形成模式的分析研究得出，老石山隧道浅层天然气的成因模式，即气体来源于深部志留系和寒武系筇竹寺组的页岩天然气，沿龙泉寺断裂带向上运移至隧道溢出。