莺歌海盆地乐东区片钠铝石特征及其对浅层CO2充注的指示

作为天然CO₂的示踪矿物，片钠铝石的形成与CO₂充注密切相关.莺歌海盆地乐东区乐东X构造莺歌海组-黄流组CO₂气藏内发育含片钠铝石砂岩，在开展的岩石学和地球化学研究基础上，确定了研究区片钠铝石的产状和纵向分布特征，分析了形成片钠铝石的“碳来源”和气水条件，进而探讨了与片钠铝石具有成因联系的CO₂的成因.乐东X构造含片钠铝石砂岩为细—极细粒长石石英砂岩和岩屑石英砂岩，片钠铝石主要以充填孔隙及交代颗粒的形式产出，是成岩共生序列中形成较晚的自生矿物之一.在纵向上，片钠铝石仅集中发育于高含CO₂气层的底部以及其下的水层中，这一分布特征以地质实例的形式证实了片钠铝石的形成需要水的参与.研究区浅层CO₂充注后形成的碳酸盐矿物为片钠铝石和铁白云石.片钠铝石的碳氧同位素特征表明形成片钠铝石的“碳”与LDX构造气层中CO₂具有相同的碳来源，以无机幔源成因CO₂为主.红河断裂以及莺歌海盆地中央坳陷内一系列底辟构造及伴生的垂向裂隙可能为CO₂的运移通道. 

Dawsonite Characteristics and Its Implications on the CO2 in Yinggehai-Huangliu Formation of Ledong Area,Yinggehai Basin

It has been proved that there is a great relationship between the genesis of dawsonite and the injection of CO₂, while dawsonite, the trace mineral of CO₂, is developed in the Yinggehai-Huangliu Formation, Ledong Area, Yinggehai Basin. Petrologic and isotopic geochemical characteristics were investigated by polarizing microscope, scanning electron microscope (SEM) and carbon-oxygen isotopic analysis. The diagenesis sequence indicates that dawsonite and ankerite formed after CO₂ flooding, meanwhile, the carbon-oxygen isotopic analyses show that the mantle-magmatic CO₂ provided the carbon sources for the deposite of dawsonite. Thereby, it can be deduced that, CO₂ in gas reservoir and CO₂ which for dawsonite genesis had the same carbon source, both of which had got the contribution from the mantle-magmatic CO₂. The migration pathway for the mantle CO₂ might be the Red River fault zone and the central diaper structures in Ledong Area, Yinggehai Basin. The longitudinal distribution characteristics of dawsonite, which mainly developed in the interface between gas (with high CO₂ content) and water layer, provide the geological evidence showing that water is essential for the interaction between CO₂ and the minerals.