塔里木盆地阿克1气藏天然气的地球化学特征和成因

GEOCHEMICAL CHARACTERISTICS AND ORIGIN OF NATURAL GAS FROM AKE-1 GAS POOL IN THE TARIM BASIN

阿克1气藏是在塔里木盆地西南坳陷喀什凹陷油气勘探中发现的工业性气藏,这是该区天然气勘探的重大突破。根据天然气组分的含量、甲烷和乙烷碳同位素值及稀有气体同位素数据,分析了阿克1气藏天然气的地球化学特征。阿克1气藏天然气为典型干气,甲烷占优势(占80%～91%),重烃含量极低(不超过0.3%),非烃含量高(一般为20%左右),甲烷和乙烷碳同位素重(分别为-25.2‰～-24.7‰和-21.9‰～-21.1‰),稀有气体同位素比值高(3He/4He值达8.34×10-7、40Ar/36Ar值为1438)。结合地质背景,应用碳同位素动力学模拟计算结果,探讨了阿克1气藏天然气的成熟度和气源,为天然气成因评价提供了新思路。认为阿克1气藏天然气是烃源岩过成熟演化阶段的产物,其RO范围为2.0%～3.6%,属于混源气。

Ake-1 is a commercial gas pool that has made great breakthrough for oil & gas exploration in the Kashi Sag of the Southwestern Depression, Tarim Basin. On the basis of the component content of natural gas, carbon isotope ratios of methane and ethane, and isotope composition of rare gas, the geochemical characteristics of Ake-1 gas pool were studied in this paper. Natural gas of Ake-1 gas pool belongs to the typical dry gas. It has predominance methane (80%～91%), low content heavy hydrocarbon (<0.3%) and high content non-hydrocarbon (generally about 20%). There are heavy carbon isotope ratios of methane (-25.2‰～-24.7‰) and ethane (-21.9‰～-21.1‰), and relatively high isotope ratios of rare gases (()^(3)He/()^(4)He=8.34×10^(-7), ()^(40)Ar/()^(36)Ar=1 438). Combined with the geological background, the maturity and source of natural gas from Ake-1 gas pool were discussed by using the results of carbon isotope kinetic modelling. This provided a new thought for evaluating the origin of natural gas. It's suggested that natural gas of Ake-1 gas pool was the evolution product of over-matured source Rocks, with the maturity of 2.0%～3.6% R_O, and belonged to the mixed gas.