The Triassic Xujiahe Formation(T

3

χ) in central Sichuan Basin features in interbeded sandstone and mudstone and extensive distribution.Many gas fields(e.g.

Guang'an

Hechuan and Bajiaochang) and gas-bearing structures(e.g.

Chongxi) have been found in this formation.Horizontally

this gas-bearing combination is distributed in different structural zones;vertically

it has many alternating intervals of reservoirs.These reservoirs have similar pooling settings

but they are separated from each other with no communication.According to the analyses of geological features for gas accumulation in T

3

χ

the main factors controlling massive gas accumulation are considered as the followings:1)development of alternating coal bed and sandstone combinations in a large open shallow-water lacustrine basin under gentle structural settings;2)the wide distribution of quality re-servoirs under the joint control of paleotectonics

sedimentary micro-facies and fractures in the Indo-Chinese epoch;3)overall uplifting of the Sichuan Basin at the end of the Cretaceous

gas expulsion through expansion

and reservoir compartmentalization.