雪峰山隆起北缘热历史及其对牛蹄塘组生烃作用的影响

对于复杂构造带的古老- 深层页岩，烃类的生成过程可能是多阶段的。准确恢复页岩的成熟演化过程是研究页岩气富集机理的先决条件。本文依托雪峰山隆起北缘新钻探的地质调查井，恢复雪峰山北缘古生代以来的热历史，从热演化的角度讨论牛蹄塘组页岩的生烃潜力。元素分析显示，热液活动对牛蹄塘组黑色页岩有机质的富集产生了积极影响，特别是下部页岩热液指示指标异常高、显著的Ce负异常、Eu正异常和Y正异常，都证明了牛蹄塘组早期受热液作用的影响。古温标联合反演结果显示，雪峰山北缘自古生代以来先后经历了三次升温—降温过程。三次热演化高峰依次出现在晚奥陶世末期、中三叠世末期和早白垩世末期，所达到的最高温度依次降低。三次升温过程分别受到早古生代拉张作用和岩浆活动、晚古生代—早中生代快速沉降作用和早白垩世岩浆活动的控制。受沉积埋藏作用和早期热事件的影响，牛蹄塘组页岩在寒武纪—早志留世快速经历了生油高峰、原油裂解高峰等生烃关键时期，在晚奥陶世达到过成熟阶段。随后第一次的抬升剥蚀作用，破坏了页岩及上覆盖层的封闭性，形成有利于气体扩散的裂缝或断层通道，使得早期形成的烃类散失。

Thermal history of the northern margin of the Xuefeng Mountains and its effect on hydrocarbon generation in the Lower Cambrian shale

Hydrocarbon generation may occur in multiple stages in ancient, complex, deep shale tectonic belts. The accurate reconstruction of the maturity evolution of shale is a prerequisite for the study of the shale gas accumulation mechanism. In this study, the thermal history of the northern margin of the Xuefeng Mountains since the Paleozoic was reconstructed based on a new well drilled by the Geological Survey. The hydrocarbon generation potential of the Lower Cambrian shale is discussed from the perspective of thermal evolution. The results of the inversion of the multiple geologic paleothermometers show that the northern margin of the Xuefeng Mountains had experienced three heating and cooling processes since the Paleozoic. Three thermal evolution peaks successively occurred at the end of the Late Ordovician, late Middle Triassic, and late Early Cretaceous. The maximum temperature decreased over time. The three heating processes were controlled by Early Paleozoic tension and magmatism, Late Paleozoic- Early Mesozoic rapid subsidence, and Early Cretaceous magmatism, respectively. Affected by burial and early thermal events, the shale of the Niutitang Formation experienced peaks in oil generation and cracking in the Cambrian and Early Silurian and reached the mature stage in the Late Ordovician. Subsequently, the first uplift- denudation destroyed the sealing properties of the overburden. This led to the formation of fractures or fault channels, which are conducive to gas diffusion, resulting in the loss of early formed hydrocarbon.