柴达木盆地天然气的碳同位素地球化学特征及成因分析

依据天然气碳同位素中δ13C1、δ13C2、δ13C3的组成与划分标准，将柴达木盆地天然气划分为煤型气、裂解气、油型气与生物气四种类型，通过对天然气同位素中的δ13C1、δ13C2-δ13C1、δ13C3-δ13C2值的差异分析以及与对应的烃源岩干酪根碳同位素进行对比分析，探讨了柴达木盆地不同地区天然气的成因以及影响因素，这对于探索柴达木盆地的成气规律以及在不同地区天然气勘探的目标选择都有着现实意义。

Characteristics of Carbon Isotope and Origin of Natural Gas in Qaidam Basin

δ13C1，δ13C2,δ13C3，δ13C4 of〖KG*2〗natural gas isotopic composition are various in different parts of Qaidam Basin. The average〖KG*2〗of them are －23.1‰,－24.1‰,－22.7‰ and〖KG*2〗－23.6‰ in Sanhu area around; －29.8‰,－24.7‰,－23.1‰ and〖KG*2〗－22.9‰ in Chaibeiyuan area;〖KG*2〗－39.2‰,－26.8‰,－23‰ and〖KG*2〗－23‰ in Chaixi area;〖KG*2〗－67.8‰,－39.2‰，－32.3‰ and lack of〖KG*2〗δ13C4 in Sanhu area. δ13C4>δ13C3〖KG*2〗>δ13C2〖KG*2〗>δ13C1 exist between〖KG*2〗component of most natural〖KG*2〗gas isotope, and reversion〖KG*2〗of minor heavy carbon isotopic composition exist. Reginally,δ13C1，δ13C2,δ13C3，δ13C4 of〖KG*2〗natural gas isotopic composition〖KG*2〗decrease gradually from〖KG*2〗Sanhu area around,〖KG*2〗Chaibeiyuan area and Chaixi area to Sanhu area.〖KG*2〗δ13C2-δ13C1〖KG*2〗andδ13C3-δ13C2 of〖KG*2〗natural gas isotopic composition increase gradually from〖KG*2〗Sanhu area around,〖KG*2〗Chaibeiyuan area and Chaixi area to Sanhu area, the average〖KG*2〗of them are －0.8‰ and〖KG*2〗－0.9‰ in〖KG*2〗Sanhu area around, 5.1‰ and 1.3‰ in Chaibeiyuan area，14.5‰ and 2.3‰ in Chaixi area， 27.9‰ and 12.5‰ in Sanhu area. δ13C4>δ13C3〖KG*2〗>δ13C2〖KG*2〗>δ13C1 exist between〖KG*2〗component of most natural〖KG*2〗gas isotope because natural〖KG*2〗gas of organic geneses are derived from the similar process of thermodynamic action, and reversion〖KG*2〗of minor heavy carbon isotopic composition exist because of the mixed action of natural gas from the different derivation or the difference of duration, temperatures and pressures〖KG*2〗in developing hydrocarbon process from the same source rock. The difference between δ13C2-δ13C1〖KG*2〗and δ13C3-δ13C2〖KG*2〗in different area depend on duration, temperatures and pressures〖KG*2〗of source rock evolution, the higher temperatures and pressures〖KG*2〗and the longer duration of source rock evolution, the more uniform〖KG*2〗δ13C distribution between natural〖KG*2〗gas component. In the meantime, bacteria and types of kerogen have an effect on δ13C2-δ13C1〖KG*2〗andδ13C3-δ13C2 to some extent. The study on carbon isotope geochemical characteristic. can not only divide types of natural〖KG*2〗gas and discuss〖KG*2〗their geneses in theory, but also guide the exploration of natural〖KG*2〗gas.