塔里木盆地西部阿克莫木气田形成初探

A PRELIMINARY STUDY ON FORMATION OF AKEMO GAS FIELD IN THE KASHI SAG, TARIM BASIN

塔里木盆地西部阿克莫木气田天然气为非烃组份含量较高的干气,干燥系数高达99 7%;天然气δ13C1和δ13C2值明显偏重,δ13C1为- 25 2‰~ - 21. 9,δ13C2为-21. 2 ^-20 .2‰,如果按传统的观点该天然气应为过成熟煤成气。但是综合气源对比研究表明阿克莫木气田天然气主要源自石炭系Ⅱ型烃源岩,成藏过程研究表明该气田主要聚集了石炭系烃源岩在Ro为1. 5%~1. 8%之后生成的天然气,具有晚期阶段聚气的特征,这是造成阿克1井天然气组份很“干”、碳同位素很重的主要原因。

The natural gas of Akemo gas pool was characterized with very “dry” gas, with a dry coefficient (bulk ratio of methane to total hydrocarbons) over 0.997, and containing much high non-hydrocarbon components. The δ 13C 1 value (methane carbon isotopic ratio) and the δ 13C 2 value (ethane carbon isotopic ratio) of the gas were obviously heavy, the former having values from -25.2 ‰ to -21.9 ‰ and the latter values from -21.2 ‰ to -20.2 ‰. According to the data, the traditional interpretation might think that the gas could derived from the measure strata source rocks. But, based on kerogen carbon isotope, maturity, generating history of Carboniferous source rocks, it was considered that the gas was mainly derived from Carboniferous source rocks of Ⅱ type. The filling process of the pool expressed that the pool accumulated and the gas generated by Carboniferous source rocks after R o value being 1.5%～1.8%. The main cause for the gas being “dry” and bearing heavier isotope composition should be the gas accumulated in later period.