渤海湾盆地二叠系碎屑岩储集层发育演化特征与勘探方向

Evolution characteristics and exploration targets of Permian clastic rock reservoirs in Bohai Bay Basin,East China

基于岩心观察、薄片鉴定、流体包裹体分析、碳氧同位素组成分析等技术方法,结合构造和埋藏演化史,系统分析渤海湾盆地上古生界二叠系碎屑岩储集层成岩演化过程、储集层成因及发育模式。研究表明:①渤海湾盆地上古生界整体经历3期埋藏和2期抬升过程,相应地发生3期干酪根热演化生酸溶蚀成孔和2期大气淡水淋滤成孔过程,深埋条件下近封闭成岩体系中溶蚀作用伴随自生黏土和石英沉淀,储集空间增加有限;②不同构造带差异性构造抬升—沉降过程造成二叠系碎屑岩储集层成岩-成储过程的差异性,并发育3类不同的储集层成因模式:Ⅰ类浅层成孔-中浅埋藏型储集层经历两期暴露—长期开放环境,于近地表经历两期大气水淋滤增孔作用,晚期浅埋,次生孔隙为主,物性最好;Ⅱ类浅层成孔-深埋调配保孔型储集层经历早期暴露开放—晚期埋藏封闭环境,溶蚀作用调配孔隙类型,以大量长石次生溶孔为主,物性次之;Ⅲ类多期埋藏溶蚀调配成孔型储集层经历近封闭—封闭环境下有机来源酸性流体溶蚀,以高岭石晶间微孔隙为主,物性最差。地质历史时期为大气水淋滤注水区,而现今位于斜坡带—洼陷带的Ⅱ类深埋储集层,为下步有利勘探目标。

Based on core observation,thin section examination,fluid inclusions analysis,carbon and oxygen isotopic composition analysis,and other approaches,the structural and burial evolution histories were investigated,and the diagenetic evolution process and genetic/development models were systematically discussed of the Upper Paleozoic Permian clastic rock reservoirs in the Bohai Bay Basin,East China.The Bohai Bay Basin underwent three stages of burial and two stages of uplifting in the Upper Paleozoic.Consequently,three stages of acid dissolution generated by the thermal evolution of kerogen,and two stages of meteoric freshwater leaching occurred.Dissolution in deeply buried,nearly closed diagenetic system was associated with the precipitation of authigenic clay and quartz,leading to a limited increase in storage space.Different structural uplifting-subsidence processes of tectonic zones resulted in varying diagenetic-reservoir-forming processes of the Permian clastic reservoirs.Three genetic models of reservoirs are recognized.The Model I reservoirs with pores formed in shallow strata and buried in shallow to medium strata underwent two stages of exposure to long-term open environment and two stages of meteoric freshwater leaching to enhance pores near the surface,and were shallowly buried in the late stage,exhibiting the dominance of secondary pores and the best physical properties.The Model II reservoirs with pores formed in shallow strata and preserved due to modification after deep burial experienced an early exposure-open to late burial-closed environment,where pore types were modified due to dissolution,exhibiting the dominance of numerous secondary solution pores in feldspar and the physical properties inferior to Model I.The Model III reservoirs with pores formed after being regulated after multiple periods of burial and dissolution experienced a dissolution of acidic fluids of organic origin under a near-closed to closed environment,exhibiting the dominance of intercrystalline micropores in kaolinite and the poorest physical properties.The target reservoirs lied in the waterflood area in the geological period of meteoric freshwater leaching,and are now the Model II deep reservoirs in the slope zone-depression zone.They are determined as favorable options for subsequent exploration.