松辽盆地CO_2气藏的形成与分布特征

Formation and distribution characteristics of CO_2 gas pools in Songliao Basin

对松辽盆地已发现的10个CO2气藏气体组分、碳及氦同位素等地球化学特征进行了分析,认为松辽盆地CO2气藏主要为幔源成因,表现的特征主要为δ^13 CCO2〉-8‰,氦的同位素也比较重,R/Ra=1.9-7.2.盆地地质背景及包裹体分析显示,长岭、德惠及古龙等断陷CO2气藏主要为晚期成藏,CO2包裹体主要为晚期气包裹体,主要赋存于沿切穿石英颗粒及其加大边的微裂隙中,呈带状分布,包裹体均一温度主要分布在120-140℃之间,推测二氧碳气的成藏时期主要在48-72 Ma间;CO2的形成和分布与多级次断裂相关,包括岩石圈断裂、壳断裂、基底断裂和盖层断裂等,分析认为CO2的分布尤其与NE-NNE深大晚期走滑断裂相关,这类断裂在断陷期表现为基底控陷断裂,晚期发生NE-NNE向左行走滑作用,沟通了晚期火山作用上涌的CO2而使CO2成藏.

It is held that the CO2 gas pools in Songliao Basin are mainly of mantle origin by the analysis of the components,the carbon isotope composition and the helium isotope composition of the gas in ten CO2 gas pools found.The main characters of the CO2 gas pools are δ13CCO2>-8‰ and R/Ra=1.9~7.2.The analysis of geological background and fluid inclusion indicates that the CO2 pools in Changling,Dehui and Gulong fault depressions are mainly formed lately.The reasons are as follows:Firstly,the CO2 inclusions are late period fluid inclusions,which distributes in the cracks of transecting quartz grain or transecting widen quartz.Their homogenization temperature is 120~140 ℃.So,the forming stage of CO2 may be mainly between 72 Ma and 48 Ma.Secondly,the formation and distribution of CO2 is related to many kinds of faults,including lithosphere faults,crust fractures,basement rifts and overburden faults,especially related to NE-NNE deep faults which have strike slip motion in late stage.These kinds of faults mainly control depression formation in early stage and have NE-NNE left-lateral strike slip motion in late stage.Also,volcano erupted with amazing amount of CO2 in this stage and the faults became the migration channel of the CO2 ,which prompted the formation of the CO2 pools.