塔里木盆地哈得逊油田东河砂岩油藏原油伴生气二氧化碳的碳同位素组成特征及成因初探

哈得逊油田东河砂岩油藏由哈得1号和哈得4号两个圈闭组成。16口油井原油伴生气中CO2的含量在0.46%～4.97%,δ13CCO2值分布在-12.3‰～-7.0‰,这两组数值在油田不同地区呈有规律的分布,由北往南,均逐渐增加,至哈得4号圈闭内δ13CCO2达到峰值。依据现有的CO2成因鉴别标准,它们既有有机成因,也有无机成因。与其伴生的氦气的3He/4He值为n×10-8,具有典型的壳源沉积特征。综合分析认为,东河砂岩油藏中的CO2主要来源于无机成因的海相碳酸盐岩和东河砂岩储层中钙质胶结物的热分解。δ13CCO2值和CO2含量分布的不均匀性可能与油藏正在充注调整有关。

Carbon Isotopic Composition and Origin of Carbon Dioxide within the Associated Gas from Lower Carboniferous Donghe Sandstone Reservoirs in Hadexun Oilfield,Tarim Basin

Analysis of associated CO2 and Helium isotope composition in oil from 16 oil wells drilled in Carboniferous Donghe Sandstone reservoir in Hadexun Oilfield shows that CO2 content in the associated gas reaches to 0.46%～4.97% and δ13CCO2 distributes between-12.3‰ and-7.0‰.The values of CO2 content and δ13CCO2 differ in different areas,in which the values of both shows a regular increase from the north to south and the δ13CCO2 reaches to climax(-7.0‰) in HD4 trap.Integrated study shows that the associated CO2 mainly originates in anorganogene marine carbonate rock and thermal decomposition product of calcite cement in Donghe Sandstone reservoir.As the local structural high forming during the late stage of Himalayan movement,HD4 trap is the major target zone of hydrocarbon migration and charge.In addition,the strong diffusibility of CO2,possible concentration increasing owing to pressure drop and consequent CO2 exsolution,also makes CO2 accumulates in HD4 trap.