稠油降解气的特征与识别及其勘探潜力

Characteristics and Recognition of Biodegradation Gas of Heavy Oil and Its Exploration Potential

稠油降解气是指原油在厌氧微生物降解过程中形成的天然气,属于次生型生物气,分布在浅层,能大规模聚集成藏。稠油降解气与稠油有密切的伴生关系,即大多分布在稠油油田的附近或周围。稠油降解气以干气为主,乙烷以上的重烃类含量甚微,非烃中N2含量较高。甲烷的碳同位素值呈高负值特征(-100‰～-55‰),而CO2却显示出异常重的碳同位素值,因此较易识别。稠油在厌氧细菌作用下降解成气的过程是通过多个环节完成的,是微生物参与的水—烃反应。目前全球已发现的浅层重油大多是厌氧细菌降解的结果,在稠油油藏的附近分布着大量可供勘探的稠油降解气藏。我国东部的含油气盆地和准噶尔盆地西北缘已发现了不少这类具有较大勘探潜力的次生生物气藏。

Biodegradation gas of heavy oil, belongs to secondary biogenic gas, is originated from the anaerobes biodegradation of crude oil. Generally, degradation gas of heavy oil occurs in shallow reservoirs and may be accumulated in large scale, so it has good resources potential. Biodegradation gas of heavy oil has closely associated with heavy oil, in other word, the majority of biodegradation gas of heavy oil distribute around the oilfield. Biodegradation gas of heavy oil is mainly composed of methane, and just a little of heavy hydrocarbon, also the content of N2 is high in nonhydrocarbon. The carbon isotope value of methane shows the features of high minus value with being around -100 to-55 While the CO2 shows unusual heavy carbon isotope value, so it is easy to be recognized. Methane would be generated from heavy oil anaerobic biodegradation, the process of biodegradation run through multi-tache, which was regarded ‰ ‰as sort of water-hydrocarbon reactions involving anaerobe . At present, most of shallow heavy oil is resulted from anaerobic bacteria biodegradation, and several biodegradation gas pools distribute around the heavy oil accumulation that can be explored. Much attention would be paid to secondary biogenetic gas pools with high exploration potential in eastern petroliferous basins and in northeastern margin of Junggar Basin.