Late Quaternary gas source rocks in Hangzhou Bay are mainly of flood-plain and shallow marine fa-cies.The total amount of gas generated from the source rocks in flood-plain facies is estimated to be 103.252 BCM

with the total adsorbed gas 27.466 BCM

total dissolved gas 69.31 BCM

total diffused gas 429 MCM

and total free gas 6.047 BCM.While those from the source rocks in shallow marine facies are 141.275BCM

55.668 BCM

74.983 BCM

1.028 BCMand 9.596 BCM

respectively.These estimations show that the biogas generated in shallow layers in the study area would have first been dissolved in formation water and adsorbed by clays

and most of the gas dissolved in water in clay layers would migrate in the form of dissolved gas.Free methane can appear only when it has been saturated in the formation water.Free gas mainly occurs in the inter-granular spaces of sediments.The amount of free gas migration in shallow layers is much smaller than that of dissolved gas.The amount of free gas in flood-plain facies is less than that in shallow marine facies.The total amount of adsorbed gas in shallow marine facies sediments is over twice as large as that in flood-plain facies sediments

while the amount of adsorbed gas in mudstone is over 18 times of that in sandstone.All these indicate that preservation of methane is related to the grain sizes of sediments in shallow layers

and small grain size and large specific surface area are favorable for adsorption of methane. These estimates also indicate that Hangzhou Bay has large potentials for exploration and development of shallow biogas.