Gas reservoirs in northeastern Sichuan basin are distributed in three overpressured systems

i.e.Lower Cambrian-Silurian(∈

1

-S)

Lower Permian-Lower Triassic(P

1

-T

1

)and Upper Triassic-Middle Jurassic(T

3

-J

2

)

and are characterized by multilayer superimposition.The scale of gas accumulations depends on degasification of water-soluble gas under overpressured condition.A burial depth of 4500m can be taken as boundary

under which water is produced

while above which gas is produced

and gas output increases along with the increase of uplifting.Formation and preservation of gas accumulations in northeastern Sichuan basin are determined by burial depth in Yanshan period

elevation in Himalayan period and preservation of abnormal pressure system.Pressure sealing is the key factor to gas accumulation.Therefore

gas exploration in this area should be based on prospecting the superimposed multilayers

and aiming at the overall abnormal pressure system.