祁连山冻土区天然气水合物岩心顶空气组分与同位素的指示意义——以DK-9孔为例

通过对祁连山冻土区天然气水合物DK-9孔不同深度岩心顶空气中的烃类气体组分及甲烷、乙烷的C同位素分析测试,对比分析了岩心顶空气组分含量变化与天然气水合物及其异常层段、油气显示层段、断层或破碎带分布之间的空间关系,探讨了顶空气组分对天然气水合物及其异常现象、油气显示现象、烃类气体运移作用及顶空气同位素对气体成因的指示意义。结果显示,岩心顶空气中烃类气体含量高的深度段180.26~308.50m、356.45~399.32m、458.55~508.65m与天然气水合物及其异常层段、油气显示层段具有较好的对应关系,其高值区间可作为天然气水合物、油气显示的一种指示。距断层或破碎带产出位置不同的岩心顶空气组分含量变化显示,不同级次的断裂系统为烃类气体向上运移提供了通道,部分可为天然气水合物提供一定的赋存空间;甲烷、乙烷C同位素数据显示气体以热解成因为主,部分为混合成因。

The indicative significance of gas composition and isotopes of headspace gases from the gas hydrate drilling core in the Qilian Mountain permafrost: A case study of well DK-9

Based on an analysis of hydrocarbon gas components and carbon isotopes of methane and ethane at different depths in headspace gases from the core in well DK-9 in Qilian Mountain permafrost, this paper discusses the spatial relationship of the variation of core headspace gas content with gas hydrate and its anomalous sections, oil-gas showing sections, and fault or fracture zones, and indicated the origin of the hydrocarbon in headspace gases. The results show that the sections of 180.26~308.50m, 356.45~399.32m, 458.55~508.65m with gas component content anomalies are comparable with gas hydrate and its major anomalous layer as well as oil and gas showing layer; the anomalous section can be used as an indication of gas hydrate and its major anomalies and oil and gas shows. The relationship between variation of hydrocarbon gas content in headspace gases and the location of fault or fracture zones suggests that different levels of the fault system from the depth can provide a channel for deep hydrocarbon gas migration or the space for the formation of gas hydrate. Methane and ethane carbon isotopes suggest that the hydrocarbon gas in headspace gases is genetically mainly composed of pyrolysis gas, with the mixture of some hybrid genetic gas and biogenetic gas.