Xujiahe Formation can be divided into a lower and an upper reservoir assemblages Pooling modes for the former are thought to be high-pressure drive and low-pressure suction and pull and that for the later are regarded as water-soluble gas migration and release and buoyancy transmitting gas through dominant pathway.For the high pressure drive mode

the controlling factor of gas enrichment is the existence of 'faulted but unbroken'fracture system superimposed on the early palaeostructure

and for the low-pressure suction and pull mode

the key factors of gas pooling include sufficient gas source

open faults

compressional structure suction

and decompression by stratum denudation.For the water-soluble gas migration and release mode

the determining elements of gas reservoiring are the continuous migration of structural high

late uplift

and low relief structural and lithologic combination trap with good physical properties;for the mode of buoyancy transmitting gas through dominant pathway

the crucial condition for gas reservoiring is the existence of effective traps on dominant pathway.