济阳坳陷天然气氦同位素特征及二氧化碳成因与第三纪岩浆活动的关系  

HELIUMISOTOPIC CHARACTERISTICS, GENESIS OF CO_2 IN NATURAL GASES AND DISTRIBUTION OF TERTIARY MAGAMATITE IN THE JIYANG DEPRESSION

作　　者：孙明良[1] 陈践发 廖永胜[1] 

机构地区：[1]中国科学院兰州地质研究所,胜利油田地质科学研究院

出　　处：《地球化学》1996年第5期475-480,共6页Geochimica

摘　　要：济阳坳陷是渤海湾盆地的一部分，位于我国东部超壳断裂、郯庐断裂带内，主要为中、新生代形成的沉积坳陷。在第三纪的喜山期岩浆活动较强烈，因此，坳陷内第三纪火成岩分布广泛。对该坳陷内的天然气氦同位素研究表明，济阳坳陷天然气中氦同位素组成，Ｒ／Ｒａ（Ｒ和Ｒａ分别表示天然气样品和大气中的３Ｈｅ／４Ｈｅ值）值分布范围０．１１－３．０６。说明一些天然气中具有明显的幔源氦加入，将天然气中氦同位素组成与其地质背景结合可知，天然气中氦同位素组成与坳陷内第三纪火成岩分布有十分密切的相关关系，凡在天然气藏下伏地层或气藏附近，有第三纪火成岩分布时，则天然气具有较高的氦同位素比值、其Ｒ／Ｒａ值为１．０２－３．０６，说明具有明显的幔源氦的加入，而在无第三纪火成岩发育地区天然气中Ｒ／Ｒａ值为０．１１－０．４７，表明仅少量的幔源氦的混入。这可能说明天然气中幔源氦主要是通过断裂和岩浆活动到达浅层地壳而聚集到天然气藏中。济阳坳陷天然气组分分析表明，该坳陷的天然气中二氧化碳含量变化较大，其分布范围为＜１％－９９％。二氧化碳的碳同位素组成研究表明该坳陷的二氧化碳存在有机和无机成因两种类型，其中有第三纪火成岩发育地区，二氧化碳含量一般大于６０％，其δ（?The Jiyang Depression, one part of the Beihai gulf basin, is loccated in the Tanlu fault belt which is deep-seated fault in east China. It is a sedimentary depression that was formed during Mesozoic to Cenozoic Era. The Tertiary igneous rocks broadly distribute in this depression,since of magmatic activity was very frequent during the Xishan Epoch.The R/Ra ratios of helium isotopes in natural gases in the Jiyang Depression is from 0.11 to 3.06, which implies that mantle-derived helium has obviously been entered in the matural gas reservoirs. The helium isotopic composition in the natural gases shows intimate relation with the Tertiary igneous rocks in this depression. The R/Ra ratios range from 1.02 to 3.06 in the natural gas reservoirs around or below the Tertiary igneous rocks. The relative high R/Ra ration implies that significant mantle-derived helium has been entered in the natural gas reservoirs. The R/Ra ratios are from 0.11 to 0.47 in the gas reservoirs around the places wsthow the Tertiary magmatite distribution. The lower R/Ra ratio indicates that in this gas reservoirs there is a little of mantle-derived helium. The content of carbon dioxide in natural gases from the Jiyang Depression varies greatly. It ranges from < 1 % to 99% . The characteristic of carban isotopes indicated that there were organic and inorganic genetic carbon dioxide in this depression. The content of carbon dioxide in natural gases is generally more than 60% and their δ13C are more than-8‰ in the region where there are distribution of Tertiary ignous rocks, which implies that carbon dioxide is inorganic genetic. Contrarily in the region Without distribution of the Tertiary magmite, the carban dioxide content in natural gases is generally lower than 10% and their δ13C are less than-8‰, which expiain that the carbon dioxid is organic genetic. In addition, the δ13C of CO_2 in natural gases show positive relation with the R/Ra ratios of helium, which may illustrate that the natural gas reservoirs which have high R/Ra ratios be

关 键 词：天然气 氦同位素 二氧化碳 第三纪 岩浆活动 

分 类 号：P618.130.4[天文地球—矿床学] P588.11[天文地球—地质学]