四川盆地蓬莱气区灯二段储集层特征及主控因素

Reservoir characteristics and main controlling factors in the second member of the Dengying Formation in the Penglai Gas Field,Sichuan Basin

四川盆地蓬莱气区灯二段油气勘探的突破揭示该层在川中古隆起北斜坡区域勘探潜力巨大。基于岩心薄片、物性测试、碳氧同位素测试和碳酸盐岩U-Pb定年等综合分析,明确蓬莱气区灯二段优质微生物白云岩储层成因机制。结果表明,灯二段主要岩石类型为微生物白云岩,垂向上底部以微生物丘间微相泥—粉晶白云岩为主,中部以微生物丘核微相凝块石白云岩、泡沫绵层石白云岩为主,上部以微生物丘坪微相纹层—叠层石白云岩、砂屑白云岩为主。其中,丘核建造为主的层段孔、渗特征和孔隙结构最好,以丘坪建造为主的层段次之,而丘间的泥—粉晶白云岩储层物性较差。蓬莱气区微生物丘沉积微相展布是控制灯二段优质白云岩储层发育分布的基础,同沉积断层活动使得准同生期角砾白云岩优质储层连片发育,准同生期与表生期溶蚀作用的叠加最终决定了灯二段微生物岩优质储层形成。

The enormous exploration potential within the second member of the Dengying Formation in the northern slope area of the paleo-uplift at the central Sichuan Basin was revealed by the exploratory break-throughs in the Penglai area,Sichuan Basin.Methods in this study include core and thin section observations,petrophysical tests,carbon and oxygen analyses,and carbonate U-Pb dating.It aims to illustrate the mechanism of formation for high-quality microbial dolomite reservoir in the second member of the Dengying Formation in the Penglai Gas Field.The dominant rock type in the second member of the Dengying Formation in the Penglai Gas Field was microbial dolomite.Vertically,the intermound microfacies dominated by dolo-mudstone was at the base.The mound core microfacies dominated by dolo-thrombolite and dolo-spongiomicrobialite was at the central part.The mound flat microfacies dominated by laminated dolo-stromatolite and intraclastic dolograinstone was at the top.Amongst these,the porosity,permeability,and pore structure of mound core build-ups were the best.The quality of reservoirs for the mound flat build-ups were the second-best.In contrast,dolo-mudstone of the intermound microfacies had the poorest reservoir ability.The distribution of microfacies in microbial mounds was the basis for controlling the development of high-quality dolomite reservoirs in the second member of the Dengying Formation in the Penglai Gas Field.The activity of syn-sedimentary faults allowed the widespread development of superior reservoirs of syngenetic brecciated dolostone.The combination of penecon-temporaneous and telogenetic dissolution eventually controlled the formation of microbial reservoirs in the second member of the Dengying Formation.