塔里木盆地塔中奥陶系天然气的非烃成因及其成藏意义

Non-hydrocarbon origin of Ordovician natural gas in Tazhong of Tarim Basin and its implications for non-hydrocarbon accumulation

塔里木盆地塔中北部斜坡带奥陶系海相碳酸盐岩油气勘探取得了重大突破,发现了台缘坡折带礁滩复合体大型凝析气藏和台内岩溶风化壳大型油气藏。利用有机地化指标与构造沉积演化紧密结合对有效烃源岩及成藏过程的研究取得了较好成果,但随着勘探的纵深发展,流体分布复杂的问题日趋突出,通过天然气组分以及相关同位素等分析化验数据,进行塔中北部斜坡带奥陶系油气成藏研究,建立了"三期成藏、两期调整,早期成油、晚期注气,复式聚集、普遍含油"成藏模式,明确了塔中天然气以原油裂解气为主,强调晚期气侵是形成塔中大型天然气田的关键。

In the north of the Tazhong Area in Tarim Basin, a large condensate pool of reef-fiat facies and a large karst weathering crustal oil-gas field have beert discovered, which demonstrates a breakthrough in the oil- gas exploration in carbonate rocks of Ordovician marine facies. By using organo-geochemical indexes combined with the analysis of the evolution of tectonic-sedimentation some good results have been achieved in the study of the effective hydrocarbon source rock and the accumulation process, But as the exploration depth increases, the complexity of fluid distribution becomes a more and more prominent problem. Through the research on the Ordovician oil-gas accumulation in the north of the Tazhong Area by dating and analysing the natural gas components and their isotopes, we could sum up the mode of pool formation in Tazhong as follows： There were three periods of formation and two periods of adjustment; oil-charging occurred in the early stage and gas-injection occurred in the later stage; oil-gas accumulated in multi-fashion and oil-bearing rocks were widespread. It is confirmed that the natural gas is mainly the oil-cracked gas in the Tazhong Area and it is emphasized that the gas-injection in the later stage is the key to the formation of the large-scale gas field in Tazhong.