The gas reservoirs of deep beds in Dongpu Depression are considered to be sublacus-trine fan which underwent diagenetic changes under abnormal high pressure condition.Because of the shielding of the overlying sealed beds

the separated materials includingS

4+

Fe

2+

Ca

2+

and Mg

2+

etc.ions contained in mudstone clay minerals were not easyto move out

thus causing intensely ferrian carbonate-precipitation

replacement

quartzsecondary enlargement nearby.The permeability of sandstone dropped rapidly

so inter-granular pores

intragranular pores and micropores became the main preserving spaces ofthe reservoirs

and hence the reservoirs characterized by 1.high capillary-pressure;2.highaquifer-satuation;3.high pressure-sensitivity and 4.high heterogeneity.It is suggestedthat a systematic study including geological and geophysical researches

the techniques ofwell-drilling and well-completion should be carried out to improve the success of gas exploration.