SUMMARY OF THE ABIOGENIC ORIGIN THEORY AND THE ABIOGENIC GAS POOLS(FIELDS)

The research on the abiogenic origin theory in China is in the forward position in the world.Extensive scientific research and practi ce have proven that a relatively large percentage of hydrocarbons,especially oil ,are generated organically.However,this does not rule out the possibility that a nother large proportion of hydrocarbons,gas in particular,may be of abiogenic or igin.The identifications of organic and abiogenic gases are as the follows:1) Th e abiogenic origin CH_4 has a δ~13 C_1 value greater than -30‰; 2) The abiogenic alkane gases have negative carbon isotope sequences; 3) CH_4/ ~3He values are n×10~5～7; 4) Abiogenic δ~13 Cco_ 2 values are greater than -8‰.The Changde Gas Field is possible the first abiog enic hydrocarbon gas field in the world.Favorable locations for abiogenic gas fi elds can be selected by following criteria:1) Existance of Moho up-pouring or m antle plume; 2) High thermal or thermal structural area with a heat flow value g reater than 1.3 HFU and a geothermal gradient higher than 3.5℃/100m; 3) Anomalo us R/Ra1,especially R/Ra2 zones;4) Presence basalt rock zone along the faults near the gas resource.