南海北部二氧化碳对天然气水合物形成与分布的影响

Impact of CO_2 on formation and distribution of gas hydrate in northern South China Sea

南海北部天然气富含CO2等非烃气体,非烃气体对于水合物既有建设性,也有破坏性。含CO2的天然气向上运移渗漏到浅层,条件适当时,CO2可作为碳源,被还原成CH4,在浅层形成水合物成藏。选取南海北部的几组不同CO2、N2含量的气体组分进行的实验表明,含CO2的天然气形成水合物的温度比纯甲烷水合物要高,致使水合物的赋存深度增加,从而拓展了水合物稳定带的厚度。高含CO2的天然气藏发生强渗漏并运移至上覆甲烷水合物层时,CO2可能会置换甲烷水合物中的甲烷,使原有的水合物矿藏遭受破坏或甲烷饱和度下降。

In the northern South China Sea, non-hydrocarbon gases such as CO2 are abundant, which are both constructive and destructive for gas hydrates. When the natural gases containing CO2 leak upward to shallow for- mations, CO2 could be reduced to CH4 as carbon source under appropriate conditions, forming gas hydrates within shallow sediments. The experiments of gas samples with different CO2 and N2 contents have indicated that the temperature for gas hydrate formation of CO2-bearing gases is higher than that of CH4-bearing gases, resulting in deeper occurrence of hydrates and bigger thickness of hydrate stale zones. If strong seepage happened, natural gases with higher CO2 content would migrate upward to CH4 hydrate zone through deep faults. The replacement process of CH4 by CO2 will start. The previous gas hydrates will be damaged or the saturation of CH4 will decline.