一种不具煤系气标志的煤系气——四川盆地南部上二叠统天然气成生分析

A COAL GAS WITHOUT COAL GAS INDICATORS

本文针对四川盆地南部地区上二叠统(P_(2L))天然气不具一般煤系气的地球化学标志,但同层“瓦斯”又具有与陆相煤系气的标志雷同的表征。通过地质、地化的综合分析,认为虽是煤系(Ⅲ型)气经运移与长兴组储层形成的(Ⅲ_1型)气混合,并经历了高成熟阶段的演化和改造,导致现今上二叠统天然气不具煤系气表征,但实际上又主要源自煤系地层,并受控于地质、地球化学条件,此乃潮坪含煤建造,碳酸盐岩生、储油条件及其高热演化的天然气所具有的特征。据此还提出了有利于天然气形成和富集的地区。

This paper discusses the upper permian natural gas which is absent of common geochemical indicators of coal gas in the southern part of Sichuan Basin,but with In—situ gas similar to coal gas (Type Ⅲ)was mixed with the gas (Type Ⅱ) generated from Chang Xin formation reservoir. So present natural gas of P_(21) does not have characteristics of coal gas due to undergoing evolution and remaking in high maturity period. In fact, it mainly generated under coal formation geologic and geochemical condition. These are the features of natural gas of tidal construction with coal,condition for oil generated and preserved in carbonate rock and high heat evolution. Depending on these features, areas favourable for gas generation and accumulation are suggested.