稠油区浅层天然气成因探讨

Discussion on the shallow natural gas genesis of heavy oil area

中国含油气盆地稠油分布广泛,在这些稠油分布区与稠油伴生一些浅层天然气,这些天然气大多数甲烷碳同位素较常规天然气碳同位素轻,干燥系数大,非烃中氮气含量高,研究认为这些与稠油伴生的浅层天然气为原油在厌氧细菌(主要是产甲烷菌)作用下形成的原油降解气,同时混有少量热成因天然气。通过对稠油分布区的地质环境、地层水组成和储层特征等方面研究,提出微生物降解原油具备形成天然气所需的地质条件,认为原油降解气具有较大勘探潜力。

Heavy oil is widely distributed in the northwest edge of Junggar Basin, associated with which there is also any shallow natural gas. Compared with conventional natural gas, the carbon isotope of methane in shallow natural gas is lighter, larger in dry coefficient, and higher N2 contend of non-hydrocarbon. Based on analysis ,the shallow natural gas associated with heavy oil is crude oil biodegraded gas derived from microbial degradation of crude oil because of anaerobic bacteria （mainly methanogens ）, at the same time there is any thermogenic gas associated. By comprehensive study, the shallow natural gas in northwest Junggar Basin is mainly bacterial decompositional gas from crude oil mixed with any thermogenic gas. Beside,geology environment and reservoir characteristics in northwest Junggar Basin are favorable to bacterial decompositional gas from crude oil ,and this type natural gas is great in exploration potential.