渤中凹陷天然气烷烃碳同位素异常的成因探讨

RESEARCH ON THE ABNORMALITY OF CARBON ISOTOPE IN ALKANE GAS IN BOZHONG SAG

渤中凹陷天然气为有机成因气,但部分气藏烷烃碳同位素出现异常。通过对碳同位素异常的分析认为:QHD 30-1N-1井馆陶组天然气甲烷碳同位素偏负的原因可能是深部高成熟气运移至浅层与低熟气混合和/或天然气的运移、扩散效应造成;而CFD 18-1-1井、BZ26-2-1井及BZ22-2-1ST井天然气烷烃系列碳同位素局部倒转的原因则分别是由“既不同型又不同源”气、“同源不同型”气和“同型不同源”气的混合所造成。

Natural gas in the Bozhong sag is of organic origin. But there is an abnormal phenomenon in the carbon isotopes of the alkane gas in some gas reservoirs. Their origin is discussed in this paper. The carbon isotope of methane in the QHD30-1N-1well of the Guantao Formation is over-light obviously, which can possibly be attributed to the mixing of the high-mature gas in deep layer and low-mature gas in shallow layer or the migration and diffusion effect of natural gas. The partly reversion of alkane series carbon isotope of natural gas in the CFD18-1-1 well may be mainly caused by the mixing of gases with different types and different sources. That in BZ26-2-1 may be mainly caused by the mixing of gases from one source rock interval of varying types. While that in the BZ22-2-1ST well may be mainly caused by the mixing of same-type gases from different source rocks intervals.