莺歌海盆地浅层CO_2可能的岩石化学成因

A POSSIBLE CO_(2 ) GENESIS BY PETROCHEMICAL REACTION INSHALLOW FORMATION OF YINGGEHAI BASIN

莺歌海盆地东方和乐东等地区部分天然气中富含CO2。热力学分析表明,盆地7000～8000m深度段的地层远远没有达到纯钙质碳酸盐岩热分解所需的温度,碳同位素和伴生稀有气体氦同位素组成指示CO2主要为壳源岩石化学成因。研究发现上覆层段的储集砂岩中含有丰富的菱铁矿(该矿具有低的热分解温度),其能够与(铝)硅酸盐岩发生化学反应生成CO2,后者有可能成为气藏中CO2来源的一部分。认为泥底辟发育演化的断裂活动及热流体上侵为岩石之间这种化学反应提供了能量和促进了硅酸盐的水解,也为CO2的运移和聚集提供了通道。

Some natural gases in Yinggehai basin are rich in CO_(2). Carbon and associated rare element gas isotopic compositions indicate that the genesis of the CO_(2 )is mainly by petrosal chemical reaction. Thermodynamics parameters show that the temperature in formation within 7 000~8 000 m of the basin is not so higher as decomposed temperature of pure calcic carbonate. Whereas there is abundant siderite in shallow reservoir rock with low decomposed temperature(280℃).It can react with silicate to produce CO_(2) which may be the part of the CO_(2 ) in gas reservoir. Diapiric development and hot fluid upwards provides the petrosal chemical reaction with sufficient energy and promotes the hydrolysis of silicate. The geologic activities offer CO_(2 ) the path for migration and aggregation.