The Sebei-1 field consists of seven vertically superimposed gas reservoirs with various biogas enrichments.These reservoirs are divided into high-enrichment reservoirs(HER) and low-enrichment reservoirs(LER) based on such data as reserves per unit volume

abundance of gas reserves

and flow rate tested.The pooling conditions for these two types of reservoirs are compared and analyzed.The results are used to define the controlling factors for the biogas enrichment in the field.The lower four deeper reservoirs with burial depth greater than 950 meters are the HER type

while the upper three shallow ones belong to the LER type.The former ones are favorable for gas pooling and enrichment as they are located in the central of a gas-generation zone with biogas charging both from the local area and central depression

and apart from that

they also have favorable re-servoir-seal assemblage

trapping and preservation conditions.In contrast

the later ones are unfavorable for gas pooling and enrichment as the source rocks have not reached peak gas generation

the biogas are mainly sourced from the lower gas reservoirs through diffusion

and the preservation conditions are relatively poor.Based on the analysis of pooling conditions

the paper suggests that the pooling patterns for the HER and LER reservoirs be described as source-charged and dispersion-charged respectively.