Abstract:

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 includingS⁴⁺,Fe²⁺,Ca²⁺ and Mg²⁺ 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.