济阳坳陷高青-平南断裂带CO_2气藏中稀有气体地球化学特征

济阳坳陷高青-平南发育多个CO_2气藏,对气藏组分、同位素以及组分同位索相关组合进行分析,认为气藏中CO_2主要是幔源-岩浆成因.气藏同时具有高~(40)Ar/~(36)Ar和高~3He/~4He值表明:气藏中稀有气体主要来自幔源,同时有部分壳源混入;气藏中~4He/~(40)Ar~*平均值为2.15,说明该地区气藏形成主要以岩浆缓慢脱气为主,大规模CO_2及稀有气体是岩浆冷却结晶阶段所释放.其形成机理为:在随岩浆上升的过程中,随着压力和温度不断下降以及岩浆成分的变化,岩浆中CO_2及稀有气体溶解度也随之降低并析出,产生的大量CO_2及稀有气体沿着深大断裂及一些二、三级断裂交汇处输送至地层的各类圈闭中,并在适当的位置聚集成藏.

Noble Gas Geochemistry of CO_2 Gas Pool in Gaoqing-Pingnan Fault Zone,Jiyang Depression

In the surroundings of the Gaoqing-Pingnan fault zone five CO_2 gas reservoirs are developed.Based on the data on compositions,isotope geochemistry and CO_2/~3He of the reservoirs,it is shown that CO_2 distributed in the Caoqing area was mostly originated from the mantle-sourced inorganic material associated with magmatic rocks.The 3He/4He ratios range in 2.02 × 10~(-6)～8.34 × 10~(-6) and ~(40)Ar/~(36)Ar ratios range in 628.9～3178.The higher ~3He/~4He and ~(40)Ar/~(36)Ar ratios in CO_2 gas pools prove a major mantle-magmatic origin of the noble gases,with a part of crustal source gas mixed.The average ~4He/~(40)Ar~* of 2.15 shows a slow degassing rate of magma.Its formation mechanism can be interpreted as follows: During the magma rising,the pressure and temperature would decrease,the magma composition would change,and the solubility of CO_2 and noble gases in magma would also decrease.Consequently,the CO_2 and noble gases could be separated from the magma,and large amount of CO_2 and rare gases could be transported to the various stratigraphic traps along the deep faults and some second-and third-order faults.