摘要
四川盆地东北部下三叠统飞仙关组鲕滩气藏天然气烃类气体以甲烷为主,含量主要分布在75%～90%之间,C2+含量很少,为0%～0.15%,干燥系数为0.9970～0.9998,是典型的干气;非烃气体以H2S和CO2为主,含量分别为4.21%～16.24%和0.97%～10.41%。天然气δ13C1值为-29.0‰～-31.5‰,δ13C2值为-29.4‰～-32.4‰。多参数表明鲕滩气藏天然气是以腐泥型为主的高过成熟天然气。高含H2S的天然气分布区域与含石膏地层分布基本一致,这些H2S为飞仙关组气藏附近的石膏经热化学硫酸盐还原作用(TSR)而生成,CO2是其主要的副产物。在TSR过程中,C2+重烃气体比甲烷更容易与硫酸盐发生反应,也就是C2+重烃气体的消耗速率大于甲烷,从而导致发生TSR反应的天然气C2+含量低、H2S和CO2含量高。天然气δ13C1值与甲烷含量之间具有很好的负相关关系,而与天然气酸性系数H2S/(H2S+CnH2n+2)具有正相关关系。根据同位素动力学的分馏效应,随着TSR的进行,烃类分子中的12C损耗速率大于13C,残留下来的烃类分子中则更加富集13C,也就是TSR反应使天然气碳同位素变重。
Hydrocarbons in oolitic reservoir g ases of Feixianguan Formation in northeastern Sichuan basin mainly consist of methane with 75%-90%of CH 4 ,0%-0.15%ofC 2 + ,and the ratio of C 1 /(C 1 -C 5 )is 0.9970-0.9998.It is a typical dry gas.Nonhydrocarbon mainly consists of H 2 S and CO 2 ,and their relative contents are5%-20%and 1%-10%,respectively.The isotope composition of C 1 ranges from -29.0‰to -31.5‰,while that of C 2 from -29.4‰to -32.4‰.The oolitic re servoir gases are associated with th e sapropelic organic matter.The high sulfur-bearing gas distribution area is identical to th e gypseous distribution area.The H 2 S in natural gases is formed by thermochemical sulfate reduction(TSR),and the CO 2 is the main by-product of TSR.During TSR,the C 2 -C 5 hydrocarbon gases take priority of r eaction with sulfates over methane.Therefore,the natural gases that undergo TSR lack C 2 -C 5 hydrocarbons but contain methane,H 2 S,and other nonhydrocarbon gases,such as carbon dioxide.There is an inverse correlation betweenδ 13 C 1 and the absolute concentration of methane,which shows that a methane i s replaced by other gases(mainly H 2 S and CO 2 ),and the remaining methane becomes isotopically heavier.There is also a fairly well correlation between gas sourness犤H 2 S /(H 2 S +C n H 2n+2 )犦andδ 13 C 1 ,suggesting that TSR has directly ca used an alteration of the carbon isotope compositions of the remaining methane.The positive relationship between methaneδ 13 C 1 values and gas sourness leads to the i nference that as sulfate reduction of methane procee ded,12 C in methane was more rapidly deplete d than 13 C as a result of kinetic isotope fractionation with the residual methane becoming more enriched in 13 C.
出处
《地球化学》
CAS
CSCD
北大核心
2004年第6期567-573,共7页
Geochimica
基金
"十五"国家重点科技攻关项目(2001BA605A-04)
中国石油天然气集团公司天然气成藏与开发重点实验室资助项目
