元坝地区长兴组典型沉积相及各相带物性特征

元坝气田是四川盆地继普光气田之后所发现的又一大型海相气田,其中,晚二叠世长兴组是元坝气田的主力产层。研究以不同相带钻井为代表,经过岩芯观察、地震资料、测井解释及样品的孔渗数据分析,对元坝地区长兴组所发育的各种沉积相带特征及各沉积相带的物性特征进行对比研究,结果表明:(1)开阔台地、台地边缘浅滩、台地边缘生物礁、台地边缘斜坡及陆棚相在元坝地区长兴期均有发育;(2)在元坝西北部,越靠近台地边缘,其生物礁建隆越明显;(3)长兴组主要可划分出两期成礁旋回,则均发育于长二段;(4)东南部台地边缘斜坡相带窄,坡度陡,西北部则相反;(5)台地边缘暴露浅滩相物性最好,通常形成良好的孔隙型储层;台地边缘生物礁相、台地边缘浅滩相及开阔台地相物性次之,通常形成孔隙-裂缝复合型储层;而斜坡-陆棚相只形成裂缝型储层。

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.