盐城凹陷天然气藏成因研究

The origin of natural gas in Yancheng sag.

盐城凹陷天然气藏的发现是苏北盆地油气勘探的重大突破 ,但对天然气成因还有不同认识。利用天然气的化学组成、稳定碳同位素、苯及甲苯碳同位素、在线同位素质谱和流体包裹体技术 ,比较系统研究了盐城凹陷天然气的成因。其天然气的甲烷含量高、重烃含量低、干燥系数高 ,属高成熟裂解气 ,稀有气体同位素特征表明未受幔源气侵入影响 ;天然气碳同位素呈正碳分布 ,乙烷碳同位素值为 -2 8.3 1‰～ -2 6.91‰ ,ln(C1/C2 )稳定 ,ln(C2 /C3 )分布范围大 ,结合地质背景判断为混源气 ,主体为原油裂解气 ,气源可能与苏北盆地的海相古生界有关 ;流体包裹体均一化温度主频范围为 95～ 10 5℃ ,表明气藏形成时间为晚第三纪 ,以水溶相和气相方式运移为主。图 3表 3参

The discovery of natural gas from Yancheng sag in northern Jiangsu basin is a b reakthrough in the history of oil and gas explo ration, but its origin is still in dispute. Using chemical composition of the ga s, carbon isotope of alkane gas, carbon isotope of benzene and toluene, on line carbon isotope composition and fluid inclusion methods, a detail study on the o rigin of natural gas has been carried out. The natural gas has a high methane co ntent, low heavy hydrocarbon content, high dry coefficient, positive carbon isot ope distribution and varying δ 13 C 2 ranging between -26.91‰ and - 28.31‰, stable value of ln(C 1/C 2) and varying value of ln(C 2/C 3). This shows the gas may have multiple source origin. The further research indicates th e main gas is the result of crude oil cracking. The gas source rocks may be mari ne Paleozoic strata. The homogenization temperature of fluid inclusions indicate s the gas reservoir formed in the late Tertiary and the gas migrates mainly in t he form of water phase and gas phase.