鄂尔多斯盆地靖西地区下古生界奥陶系天然气成因研究

Origin of natural gas in Ordovician in the west of Jingbian Gasfield,Ordos Basin

随着靖西地区奥陶系中组合天然气勘探的突破,判识天然气成因类型、明确其主要来源成为有效指引勘探方向的关键问题。以天然气地球化学特征分析为基础,通过气—气、气—源对比、源—储—盖空间组合分析等方法,在深化高—过成熟天然气成因判别认知的同时,探讨靖西地区奥陶系天然气的主要来源。研究表明,靖西地区下古生界奥陶系天然气以煤成气为主,局部存在自生自储的油型气;对于高演化干气的成因判识,适宜选取甲烷碳同位素为主要依据。此外,本文对天然气组分碳同位素序列倒转现象提出了新的解释思路。

With the break-through of natural gas exploration of the middle array of Ordovician Majiagou Formation in the west of Jingbian Gasfield,the determination of the origin of natural gases becomes a key issue of the gas exploration direction.Based on the analysis of the geochemical characteristics of natural gas,deepening the understanding of distinguishing the origin of high-over mature gas,the paper investigated the primary source of the natural gas of Ordovician in the west of Jingbian Gasfield by the correlation of gas-gas and gas-source and the analysis of the spacial combination of source-reservoir-cap rocks.The results show that the Ordovician natural gas in the west of Jingbian Gasfield mainly belongs to coal-formed gas and there is some oil-type gas which is characterized by self-generation and self-preservation in local areas.According to the research,the genetic discrimination of highly matured dry gas should take the methane carbon isotope as a main basis.In addition,a kind of new interpretation about the phenomenon that the δ^13C2 is apparently low and even lower than δ^13C1 has been put forward in this paper.