渤海湾盆地渤中凹陷混积岩优质储层特征及成因机理

High Quality Reservoirs Characteristics and Forming Mechanisms of Mixed Siliciclastic-Carbonate Sediments in the Bozhong Sag,Bohai Bay Basin

陆相断陷湖盆中混积岩储层勘探不断突破,使之成为一类新的优质储层而备受沉积学家关注.以渤海湾盆地渤中凹陷沙河街组一段、二段混积岩为研究对象,通过已钻遇混积岩岩心的储层沉积学及元素地球化学分析,揭示了混积岩储层特征及其成因机理.研究表明以陆源碎屑为主和以生物碎屑为主的混积岩往往具有较好的储集物性.这类储层除保存较好的原生孔隙,还保存一定的与生物组构有关孔隙以及次生孔隙.混积岩储层主要经历了泥晶化、胶结作用、溶蚀作用及压实作用等成岩作用.准同生期泥晶化作用、早成岩期大气淡水淋滤作用和准同生期白云岩化作用是导致混积岩中优质储层形成的主控因素.包壳结构抑制了早期压实作用,有利于原生孔隙的保存;早期大气淡水淋滤产生大量的次生溶蚀孔隙.混积岩优质储层形成条件及其控制因素分析为混积岩优质储层的预测提供了有效的技术方法,并对陆相断陷湖盆中深层油气勘探具有重要的指导意义.

Mixed siliciclastic-carbonate reservoir is considered as one of new important high-quality reservoirs because giant hydrocarbon accumulations have continually been discovered in the continental rifting basin,which have attracted great interest of sedimentologist. This study investigates the mixed siliciclastic-carbonate sediments in the first and second Member of the Shahejie Formation in the Bozhong Sag,Bohai Bay Basin. A combination of reservoir geological and geochemical research was used to reveal the characteristics and formation mechanisms of mixed siliciclastic-carbonate reservoirs. The results show that and bioclastic-dominated mixed rocks represent the high-quality property of reservoirs since they do not only preserve a great amount of primary pores,but also preserved an amount of primary pores with organic matter fabrics or associated secondary pores. The main diagenesis recognized in the mixed sediment reservoirs are micritization,cementation,dissolution and compaction. The micritization and precipitation of ctenoid dolomite during penecontemporaneous stage,together with meteoric dissolution during the early diagenetic period are the two key elements to form highquality reservoirs. The micritic crusts effectively resisted the compaction,preserving high amount of primary porosity. Moreover,secondary pores were well generated by meteoric dissolution. This study on the formation conditions and controlling factors of excellent reservoirs of mixed sediment would not only provide an effective technique for the prediction of high-quality reservoirs,but also facilitate the hydrocarbon exploration at the medium-deep depth in the continental rifting basin.