南堡凹陷2号构造带天然气成因分析

南堡凹陷2号构造带天然气成因研究薄弱，采用地质地球化学途径对深、浅层天然气特征及其形成机制进行了研究。分析表明，该构造带天然气以烃类气体为主，非烃组分以CO₂、N₂和H₂S为主，且主要集中在深部潜山天然气中；天然气的干燥系数(C₁/C_1-5)为0.68~0.94，具有典型的湿气特征，其中南堡280断块天然气相对偏干；天然气碳同位素整体上具有正碳同位素系列趋势，少量样品出现碳同位素部分倒转。依据母质类型和成熟度的分析，将该构造带天然气划分为3种类型：成熟阶段早期形成的混合气(东一段、馆陶组)、成熟阶段晚期形成的混合气(老堡南1断块)、高成熟阶段形成的煤型热解气(南堡280断块)。综合分析认为，第三系浅层东一段和馆陶组天然气来自于东三+沙一段烃源岩，潜山天然气主要来源于沙三段偏腐殖型烃源岩，沿断层和不整合运移到储集层中。这个研究对南堡油田深浅层天然气勘探具有重要参考价值。

Genetic Analysis of Natural Gas in No.2 Structural Belt of Nanpu Depression

The origin of natural gas in No.2 structural belt of Nanpu depression is still unclear. Geological and geochemical approaches are utilized to reveal the characteristics and genetic mechanisms of deep and shallow natural gas. The results show that the components of natural gas in No.2 structural belt are dominated by hydrocarbon gas with non-hydrocarbon mainly composed of CO₂, N₂ and H₂S, which are mainly found in buried hill reservoirs. The dry coefficient of natural gas varies from 0.68 to 0.94, indicating mainly a wet gas. Carbon isotopes of natural gas are relatively heavy, showing a tendency of normal order, but some samples display a partially reversed isotopic order with δ¹³C₃>δ¹³C₄. There are three types of natural gas in No.2 structural belt with the analysis of organic matter type and maturity: the mixture gas generated during early phase of mature stage (gas within Ed₁ and Ng), the mixture gas generated during late phase of mature stage (gas within LPN1 fault block) and coal-based pyrolysis gas generated during high mature stage (gas within NP280 fault block). The comprehensive analysis indicates that the natural gas within Ed₁ and Ng formations of Tertiary is mainly generated from Ed₃ and E_s1 source rocks, while natural gas within buried hill is mainly derived from humic type organic matter in E_s3 Member. Faults and unconformities are the main paths for hydrocarbon migration. This research should be helpful to further exploration of deep and shallow natural gas in Nanpu depression.