渤海湾盆地南堡凹陷中—下寒武统白云岩成因及储层形成机理

Genesis of dolomite reservoir of Middle-Lower Cambrian in Nanpu sag,Bohai Bay Basin

结合露头以及岩心观察、薄片鉴定、电测井解释、地球化学分析研究渤海湾盆地南堡凹陷寒武系白云岩岩石学和地球化学特征,综合分析白云岩成因及白云石化模式,揭示白云岩储层演化特征及有利储集层发育机制。认为中—下寒武统白云岩是渤海湾盆地南堡凹陷下古生界主要的内幕型储层,发育于府君山组上部与下部、馒头组顶部、毛庄组顶部。低能开阔缓坡到半局限—局限混积陆棚的独特沉积环境,形成了纵向稳定分布于不同级别层序界面附近的4套有利白云岩储层,其不同层位的泥粉晶、粉细晶、细中晶白云岩地球化学特征差异明显,暗示了3种主要的白云石化环境:蒸发、埋藏以及高温热液环境;经历了蒸发泵吸、渗透回流、埋藏以及热液4种白云石化作用,形成以晶间孔、晶间溶孔、粒间溶孔为主的储集空间类型,是同生沉积环境主控与后期成岩作用辅助的综合产物,成为南堡油田油气增储上产的重要接替层位。

The petrologic and geochemical characteristics of Cambrian dolomite in Nanpu Depression,Bohai Bay Basin are studied through outcrop and core observation,thin section analysis,electric log interpretation and geochemical analysis.Meanwhile,the dolomite genesis and dolomitization model are comprehensively analyzed to reveal the evolution characteristics of dolomite reservoir and the development mechanism of favorable reserving horizons.It is considered that the Mid-Lower Cambrian dolomite is the main interior reservoir of Lower Paleozoic in Bohai Bay Basin,developed in the upper and lower part of Fujunshan Formation and the tops of Mantou Formation and Maozhuang Formation.In the unique sedimentary environment from a low-energy open gentle slope to semi-confined-confined hybrid shelf,four sets of favorable dolomite reservoir has been formed adjacent to the sequence boundary at different levels with vertical and stable distribution,where the micritic-silty,silty-fine grained and fine-meso grained dolomite at different horizons have significant geochemical characteristics.It is suggested that three major kinds of dolomitization environment,i.e.,evaporation,burial and high-temperature hydrothermal environment,experiencing four kinds of dolomitization effect,i.e.,evaporative pump suction,seepage reflux,burial and hydrothermal fluid,and thus forming the reserving space types dominated by intercrystalline pore,intercrystalline dissolution pore and intergranular dissolution pore.The reservoir is the integration of the dominant syndepositional environment and the auxiliary later-diagenesis to become a replacing area for increasing hydrocarbon reserve and production in Nanpu Oilfield.