塔里木盆地天然气成因类型与分布规律

Genetic type and distribution of natural gas in Tarim Basin

塔里木盆地发育寒武—奥陶系腐泥型和三叠—侏罗系腐殖型两套烃源岩,由此决定了塔里木盆地存在来自腐殖型母质的煤型气和来自腐泥型母质的油型气。通过对塔里木盆地天然气组分和碳同位素组成分析,发现塔里木盆地不同类型的天然气分布受寒武系—奥陶系的腐泥型和三叠系—侏罗系腐殖型烃源岩分布范围和热演化程度的影响。煤型气主要分布在塔里木盆地的四周,主要包括库车坳陷、塔西南坳陷和塔东南坳陷,而油型气主要分布在塔北隆起、北部坳陷、中央隆起和塔西南坳陷的北部。塔里木盆地油型气又可分为干酪根裂解气和原油裂解气两种。在满东地区、和田河地区和塔中地区,原油可以达到二次油气裂解程度,向塔北隆起的轮南方向原油裂解程度呈减弱趋势。

There are two sets of effective source rocks in Tarim Basin, including Cambrian-Ordovician sapropelic matters and Triassic- Jurassic humics. The spatial distribution and the thermal maturity of two sets of effective source rocks controlled the genetic type and regional distribution of natural gas. Two genetic types of natural gas in the basin can be clearly identified according to the carbon iso- tope composition of methane and its homologue, namely oil type gas and coal-type gas. Generally, the coal-type gas is derived from the humic matters, whereas the oil type gas stems from the sapropelics. The coal-type gas is preserved in the traps along the margin of the basin, including Kuqa Depression, Southwest Depression and Southeast Depression, while the oil-type gas is mainly distributed in Tabei Uplift, North Depression, Central Uplift and the northern part of Southwest Depression. Based on the theoretical and empirical carbon isotope fractionation patterns, the oil-type gas can be further divided into the primary gas and oil-cracking gas. The primary gas geographically limits in Tabei Uplift, while oil accumulated in Lunnan, Mandong, Hetianhe and Tazhong attributes to the secondary cracking. The distribution of different oil-type gas greatly depends on the thermal maturity of the sapropelic matter.