中国生物成因气的类型划分与研究方向

生物成因气直接来源于微生物对有机质的改造,是经微生物作用所形成的富含甲烷的气体,其可以大规模和大范围地生成。依据生物气的形成途径和成因机理,可将广义生物成因气划分为早期生物成因气、低熟气、晚期生物成因气、原油降解次生生物气和浅层油气次生蚀变改造型天然气等5类,其分别属于原生型生物气和次生型生物气。运用天然气组分特征和碳同位素组成等地球化学指标,可以对生物气进行类型识别。由于生物成因气主要分布在浅层,易于开采,而且天然气性质好,勘探成本较低,认为应加大生物气的勘探力度。指出虽然目前在我国已经发现了约30个生物气藏,但除柴达木盆地外,大多以小型气田为主,且对生物气形成机理和富集规律还没有完全掌握;而对生物气的准确评价,不仅可以为浅层气来源提供依据,丰富有机地球化学理论,还可以以此追索油气运移的路径轨迹、发现新的隐蔽油藏和烃源岩等,因此生物气地质地球化学研究工作的深入开展,将会大大拓宽油气勘探的领域。

TYPES AND RESEARCH DIRECTION OF BIOGENIC GAS IN CHINA

Biogenic gas, originated from the organic matter's alteration by microorganism, is natural gas with high contents of CH4, which may be cosmically large-scale occur. Base on the pathway and mechanism of formation, biogenic gas was divided into five different sorts, as follow :early biogenic gas, low mature gas, late biogenic gas,secondary biogenic gas from degradation of crude oil and upgrading gas from secondary alteration of shallow oil and gas, which belonging to pristine and secondary biogenic gas respectively. Different sorts of biogenic gas may be identified according as the carbon isotope and the character of gas constituents. Because biogenic gas is in the shallow stratum, and easy to do exploitation; furthermore, because of the good quality and the lower exploration cost, biogenic gas should be given a great deal exploration prospecting. Although, there have been found about 30 biogenic gas reservoirs, a lot of them are small gas reservoirs except that in Qaidam basin. The mechanisms of formation and concentrate regulation about biogenic gas don't still understand absolutely. The evaluation of biogenic gas may not only provide the source of shallow gas and make theory of organic geochemistry fuller, but also help to tracing the pathway of oil and gas migration and discover new subtale oil reservoir and source rock. Consequently, along with the farther research of biogenic gas in geology and geochemistry, the scopes of oil and gas exploration prospecting will extend enormously.