STUDY ON THE PRESERVATION CONDITION OF GAS RESERVOIR IN SUOTHWESTERN EDGE OF SICHUAN BASIN

In the southwestern edge area of Sichuan Basin there is an abnormal phenomenon,i.e.the lower strata (Upper Sinian and Lower Permian)produce the formation water with low salinity,but the upper stratum (the Jialingjiang formation of Lower Triassic)produces gas.On the basis of comprehensive studies for the properties of formation liquid and formation pressure of all wells in the area,the author has drawn out the influencing factors of the gas preservation.They are,faults,the reservoir character,and the subaerial meteoric water penetration from the outcrop of reservoir.Under the influence of structure movement,the thick and tight carbonate in the Upper Sinian and the Lower Permian is easy to create fissure zone,through which the subaerial meteoric water could penetrate into the deeper formations from the outcrop.The thin and low-porosity carbonate of the Jialingjiang formation was little influenced by the subaerial meteoric water.It has been advised that Jialingjiang Formation is the main prospecting formation in the southwestern edge area of Sichuan Basin.