生物气成因机制与勘探前景

Formation Mechanism and Exploration Potential of Biogenic Gases

生物气即生物成因气,指的是在厌氧条件下,沉积有机质被厌氧细菌进行生物化学降解产生的气体。生物成因气生成主要有两种途径,乙酸盐发酵和CO_2还原,以后者为主要途径。生物气生成的主要控制因素是甲烷菌的存在以及碳水化合物的供应,另外还受盐度、温度以及pH值的影响。生物成因气的特征为甲烷的含量在90%以上,重烃、氮气和二氧化碳含量较低,δ^(13)C_1值较低,并常富含轻碳同位素^(12)C。世界上所有的生物成因气藏都分布在具有一定规模未成熟源岩的盆地中,尤其是较新盆地,生物气的勘探范围已由陆地向海域扩展,勘探领域也不再局限于狭义的传统生物气。我国生物气资源量丰富,在东部各中、新生代盆地以及许多西部盆地都钻遇了生物气藏,具有良好的勘探前景。

Biogenic gas is a kind of gas produced by microorganisms in anaerobic environment, and it is the final product of the degradation of organic matter. There are two ways of the biogenic gases production, including acetate fermentation and carbon dioxide reduction, and the latter is the main production method. The formation process of biogenic gas is controlled by the existence of methane bacteria and the supply of carbohydrates, and influenced by temperature, salinity, and pH. The biogenic gas comprises high methane content（over 90%）, low content of heavy hydrocarbon, nitrogen, carbon dioxide, as well as δ^（13） C_1, and the biogenic gas is often rich in light carbon isotopes ^（12） C. Almost all the biogenic gas reservoirs are situated in the basins with immature source rock, especially new basins. The exploration areas have been extended from land to sea, and the exploration fields are no longer limited to narrow sense of traditional biological gas. The biogenic gas resources are abundant in China, gas reservoirs have been discovered in Cenozoic and Mesozoic basin in Eastern China as well as some Western, and their exploration potential is encouraging.