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

4

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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 a

ccumulations 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.