商都坳陷浅层CO_2气藏成因与典型气藏分析

商都地区CO2气藏的气体组分主要为CO2,体积分数为87.0%～99.9%,碳同位素δ13C值分布在-5.2‰～-6.5‰之间,氦同位素3He/4He体积比分布在(1.69～3.35)×10-6之间,为典型幔源CO2气.乌兰哈达-高勿素断裂是一条长期活动的超深断裂,不仅控制着盆地沉积和演化,而且输导了多期次岩浆活动,提供了幔源CO2运移通道.商都坳陷新生代沉积演化有利于储盖组合的发育,具有良好的CO2气藏形成条件.通过对典型CO2气藏解剖,其具有气藏浅、产量高的特点.SZ5井累计产气量是容积法计算储量的2.23倍,认为存在幔源CO2的不断补充.

Origin of shallow carbon dioxide gas reservoir in Shangdu Depression and the analysis of typical gas reservoir

The main gas component of gas reservoir is carbon dioxide,the content of carbon dioxide is 87.0%~99.9%,the value of δ13C is-6.5‰~-5.2‰,the volume ratio of 3He to 4He is(1.69~3.35)×10-6,which shows that the gas is typical carbon dioxide gas of mantle origin.The Wulanhada-Gaowusu fault is a long-term active super-deep fault,which not only controls the sedimentation and the evolution of the basin,but also conducts magma activities several times and provides the migration channel of carbon dioxide.The Cenozoic sedimentary evolution is favorable to the development of the reservoir-seal assemblage,and there are good carbon dioxide gas reservoir formation conditions in Shangdu Depression.Through the analysis of typical carbon dioxide gas reservoir,it is held that the gas reservoir has the characteristics of shallow burial depth and high yield,and there is the endless supplement of carbon dioxide gas according to the gas production yield of SZ5 well which is 2.23 times of the geological reserves calculated by volumetric method.