CHARACTERISTICS OF TYPICAL SEDIMENTARY FACIES AND THEIRS PETROPHYSICS OF CHANGXING FORMATION IN YUANBA DISTRICT

Beside Puguang gas field,Yuanba gas field is another new large marine gas field discovered by Sinopic in Sichuan basin.In Yuanba gas field,Changxing Formation of Late Permian is the main production layer.Based on the representative drilling wells located in different kind of sedimentary facies,the core observation,datum of well interpretation and testing data of sample,the characteristics of each sedimentary facies and their reservoir petro-physics are researched and summarized.The result shows that:(1) in Yuanba district,open platform facies,platform edge shallow facies,platform edge reef facies,platform edge slope facies and shelf facies have all developed in Changhsingian;(2) in the northwest of Yuanba district,the closer to platform margin,the more obvious of reef buildups;(3) Changxing Formation can be divided into two reef cycles,and both of them developed in the second Member;(4) in southeast of Yuanba district,the platform edge slope facies is narrow and steep,but it is on the contrary in northwest of this district;(5) the petro-physics of the platform edge exposed shallow facies is the best,and it usually formed a good porous reservoirs,and followed by the petro-physics of platform edge reef facies,platform edge shallow facies and open platform facies.They usually formed porous and fractured composite reservoirs,and slope and shelf only formed fractured reservoirs.