塔里木盆地东部地区天然气地球化学特征及成因探讨(之一)

Geochemical Characteristics and Origin of Natural Gas in the Eastern Tarim Basin(I)

塔里木盆地是世界上勘探程度较低的大型盆地之一。近年来在该盆地中进行了大规模的油气勘探 ,发现了一系列的油、气田 ,其油、气资源量近似 1∶1,说明在该盆地中天然气资源非常丰富。该盆地已发现的天然气主要分布在塔里木盆地东部地区的塔北隆起、塔中隆起和库车拗陷。天然气主要与凝析油及原油伴生。该盆地天然气组分分析表明 ,已发现的天然气藏绝大多数烃类气体含量大于 6 5 % ;非烃气体CO2 含量小于 5 % ,N2 含量小于 10 %。一些天然气中N2 含量达 2 5 %到 35 %。在塔北隆起油气藏中天然气的干湿指数 (C1/C2 +比值 )具有从东到西降低的趋势 ,天然气中N2 含量具有从东到西升高的趋势 ,天然气甲烷的碳同位素组成也具有由东到西变轻的趋势 ,结合该区的地质背景可知造成这一趋势的主要因素可能是由于该区下古生界烃源岩热演化程度具有东高西低的特征。

Tarim Basin, located in the northwest China, is one of the largest basins in the world, which has not been well explored. In recent years the large scale of petroleum exploration in the basin has led to the discovery of a series of oil and gas fields, with an approximate 1∶1 ratio of oil to gas resource. This means that the natural gas resource is very important for the hydrocarbon resource in the Tarim basin. In this basin most of the discovered gases are condensate associated gas and oil associated gas. It is show by chemical components analysis that the content of hydrocarbon of the natural gases from this basin is mostly higher than 65%. The content of CO 2 is mostly less than 5%. The content of N 2 is mostly less than 10% and the N 2 in some gases reaches 25% to 35%. The C 1/C 2+ ratios of gases from Tabei area show a generally decreasing trend from east to west.The content of N 2 in gases shows generally Qincreasing trend from east to west.The carbon isotopic composition of methane becomes gradually lighter from east to west. All these may be responsible to the low palaeozoic source rock,of which maturity is generally becoming lower from east to west.