摘要
前言 生物气(biogenic gas)是一种重要的能源,其探明储量占世界天然气探明储量的20%以上。大型生物气田主要位于白垩系至第四系中。泥盆系也有生物气的显示。气田埋深一般为数百米至一千多米,个别可达三千米。生物气的特征是"轻",碳同位素比值ÒC<-55%甲烷与乙烷以上重烃的比值大于100,甚至大于1000。
Abstract
To help to search biogenic gas out,the rule of its spatial and temporal distribution are depicted here on the basis of recent developments of microbiology and geochemistry. Methane is produced and dissipated at high rates in top sediments. The key point for its accumulation lies on the presence of the factors which inhibit the metabolism of methanogenic bacteria near the surface and leave it to flourish at greater burial depths. The essential controlling factors are as follows:nutrient supply,mainly carbohydrate supply,high SO content of bottom water,post-oxic sedimentary environment transgression and regression,low temperature,high pH value,high depositional rate and pressure.In the geological history,when and where there were frequent transgressions/regressions due to either tectonic or ice age,a broad coastal plain with a vast river network to supply terrigenous carbohydrates and a relatively cold weather,there was biogenic gas. Its accumulations can be grouped under three major types,i. e. West Siberia type (coastal marine facies),Black Sea type (transitional marine-lacustrine facies of restricted basin) and Qaidam type (inland brackish lacustrine facies). Some case histories of China and additional information on West Siberia are presented. It seems a great deal of biogenic gas fields remains undiscovered,and the prospects are bright.
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