青海南部陆域冻土区钻孔岩芯地球化学特征及其水合物指示意义

为探讨青海南部陆域冻土区烃源岩地球化学异常成因及气源条件，通过分析青海开心岭冻土区TK- 1钻孔岩芯样品中酸解烃、荧光光谱、甲烷碳同位素含量及垂向迁移变化特征，解析其烃类地球化学异常成因，剖析岩芯中烃类异常与裂隙或破碎带、水合物稳定带、烃类运聚成藏过程的响应关系，研究其对天然气水合物及烃类运聚的地球化学指示意义。结果显示：钻孔岩芯中烃类在62~80 m、112~119 m、150~169 m和254~350 m深度段出现明显的地球化学异常富集特征，钻孔岩芯酸解烃中烃类组成、参数比值(C1/ΣC1- 5、C1/ΣC2- 5、C1/ΣC2- 3、iC4/nC4等)、甲烷碳同位素(δ13CPDB)显示烃类以热解成因为主，包括油型裂解气、凝析油伴生气、煤成气和少量的无机成因气。二叠系那益雄组煤系烃源岩处于高—过成熟阶段，其热演化过程中的生排烃气可能是形成水合物所需气体的重要来源。冻土带的封盖“挡板效应”，在冻土层下方形成烃类地球化学强异常，可作为天然气水合物及烃类运聚等异常现象的指示。裂隙或破碎带内岩芯酸解烃组分含量相对较高，随着深度变化，烃类组分呈现明显的“色层效应”，显示裂隙或破碎带对烃类的运移、聚集具有一定控制作用。

Geochemical characteristics of the drill core and its hydrate indications in permafrost region of southern Qinghai, China

In order to explore thegenesis of hydrocarbon geochemical anomalies and gas source conditions of hydrocarbon source rocks in the permafrost region of southern Qinghai, we analyze the content of acidolysis hydrocarbon, fluorescence spectrum, and methane carbon isotope of core samples from the TK- 1 borehole in the Kaixinling permafrost region. We also examine the vertical migration characteristics of these samples and discuss the causes of hydrocarbon geochemical anomalies. Our research delves into the relationship between hydrocarbon anomalies and the fractures or fracture zones, hydrate stability zones, and the process of hydrocarbon formation. By analyzing this relationship, we aim to understand the significance of geochemical anomalies in hydrocarbon migration and accumulation. The results show significant geochemical anomaly enrichment of hydrocarbons at depths of 62~80 m, 112~119 m, 150~169 m, and 254~350 m. Based on the hydrocarbon composition, parameter ratio (C1/ΣC1- 5, C1/ΣC2- 5, C1/ΣC2- 3, iC4/nC4, etc.), and methane carbon isotope (δ13CPDB) characteristics, we conclude that the hydrocarbons are mainly pyrolytic in nature. This includes oil- type cracking gas, condensate- associated gas, coal- derived gas, and a small amount of inorganic gas. Furthermore, the coal series source rocks of the Permian Nayixiong Formation have reached the high- to- over- mature stage. The hydrocarbon generation and expulsion of gas during thermal evolution might be an important source of gas for hydrate formation. The “baffle effect” of the permafrost zone forms a strong geochemical anomaly of hydrocarbons beneath the permafrost layer, which can be used as an indicator of natural gas hydrates and abnormal phenomena. Additionally, the content of acidolysis hydrocarbon components in the fractures or fracture zones is relatively high. With the change of depth, hydrocarbon components show an obvious “color layer effect” indicating that the fractures or fracture zones exert a certain control effect over the migration and accumulation of hydrocarbons.