THE EVOLUTION MODLE OF THE PUGUANG GAS FIELD IN NORTHEAST OF SICHUAN

The composition of gas in the Puguang gas field shows that methane is high and hexane,propane and heavier hydrocarbon are low,and coefficient of gas desiccation(C₁/C₁-C₅) is 0.989 6～0.999 6,clearly,the gas is the type of split gas.The oil was from the sources rocks of Lower Silurian and Permian,and formed the oil field during Late Triassic to Jurassic,The gas in the field is from the split gas of the oil field and the kerogen in the sources rock.The bitumen in the reservoirs little contributes to the gas.The reservoirs in gas field developed in the first to third secters of the Feixianguang Formation,upper Chang-xing Formation,which are the Lower Triassic and Upper Permian respectively,and the rocks are dissolved pore dolomite,doloarenite,oolite dolomite,oolite dolorudite and saccharoidal dolomite.The seal covers are mainly gyps and salt rocks,which developed in the second and fourth secter of the Jialingjiang Formation in Lower Triassic and the Leikoupo Formation in Middle Triassic,it is impotent factor to prevent the gas leak in the field.The gas field is a structure-lithology reservoir.There were three times of oil and gas migration and accumulation.The modle would be "multi-accumulation,oil spilted to gas,located in later stage".