松辽盆地梨树断陷负碳同位素系列天然气成因探讨

On the Generation of Gas with Reverse δ^(13)C Order in Lishu Depression of Songliao Basin

松辽盆地梨树断陷孤家子气田和新立油气田所产天然气单体烃碳同位素组成为负碳同位素系列,为探讨其成因,从其地质背景、天然气的化学组成、碳同位素组成和轻烃组成等多方面进行综合分析。认为研究区无深大断裂带发育,化学组成中以烃类气体为主,干燥系数>0.95,但其重烃含量反而高于有机来源的后五家户油气田的天然气,CO2含量甚微且与重烃组成正相关,轻烃组成中的庚烷值和异庚烷值落在脂族曲线的高熟延长线上,表征了负碳同位素系列天然气中具有不可忽视的油型裂解气的贡献。

Gas samples collected from Gujiazi Gas-field and Xinli Oilfield had reverse carbon isotopic order.Geological settings,molecular,carbon isotopic and light hydrocarbon composition were used to discuss the generation of gases with reverseδ 13 C order.It can be concluded that there is significant distribution of oil-type cracked gas according to its geological and geochemical characteristics,there are no deep giant faults developed in the studied area,hydrocarbon is the most component with C1/C1-5 >0.95,trace CO 2 abundance,as well as same variance trend of C + 2 hydrocarbons and CO 2 content in Lishu Depression.Moreover,the C + 2 hydrocarbons contents of gas samples in the studied area are larger than those in Houwujiahu Area,which has obvious biogenetic gas contribution.The heptane and isohepatan ratios are obvious in the high mature region of aliphatic curves,it indicates the contribution of high temperature thermal cracking gas of sapropelic organic matter.