四川盆地水溶气碳同位素组成特征及地质意义

在四川盆地川中、蜀南、川西北矿区天然气开发井产层三叠系须家河组、雷口坡组、嘉陵江组和二叠系茅口组取气层气钢瓶样品和气田水样品各22个,对比研究气层气与水溶气碳同位素组成的差异及其地质意义。气层气样品组分和碳同位素组成呈正常的有机成因气特征,而气田水脱溶气比气层气碳同位素组成明显偏重,说明气田水对天然气碳同位素组成有明显的分馏作用。在天然气成藏过程中,如果有较多的天然气从地层水中释放出来混入到气层气中,可能使气藏中天然气碳同位素组成偏重。水溶气碳同位素组成特征为天然气的成因及成藏机理研究提供了新的思路,地层水脱溶气的混入可能是塔里木盆地库车坳陷、四川盆地九龙山地区和威远气田、松辽盆地火山岩气藏天然气碳同位素异常的原因。

Stable carbon isotopic compositions and its significance of water-soluble gases

Twenty two gas and 22 water samples had been got from development wells of Middle Sichuan, South Sichuan and North-west Sichuan gas area, in the Xujiahe Formation, Leikoupo Formation and Jialinjiang Formation (in age of Triassic) and Maokou Formation (Permian) for the purpose of comparing the difference of carbon isotope between free gas and water-soluble gas. It had been found that the alkane gas detached from water had more 13C component. It seems that the water can make obvious fractionation on carbon isotope of natural gas. During the gas accumulation, if much gas released from water and mixed to free gas, the isotope of free gases maybe is affected. So, the study of carbon isotope of water-soluble gases can help to judge the gas origin and gas accumulation mechanism from a new perspective. Mixing of water-soluble gas may be the reason that caused the gases from Kuqa Depression of Tarim Basin, Jiulongshan region and Weiyuan gasfield of Sichuan Basin, volcanic gas reservoirs of the Songliao Basin to have carbon isotope anomalies.