南海早中新世东沙台地流花生物礁-滩组合的白垩状结构化及白垩状孔隙储集层

Chalky texture formation and chalky porous reservoir of Liuhua reef-bank complex on the Early Miocene Dongsha platform,South China Sea

南海早中新世珠江期东沙台地流花生物礁-滩组合中,具白垩状结构的灰岩属于广义的白垩状结构灰岩。白垩状结构灰岩的主要鉴定特征是:在宏观上,岩石为白色或淡色松软、酥脆、多微孔的灰岩,其比重较轻;在微观上,岩石组构具有低镁方解石微晶及微亮晶格架和晶间孔喉网络,其中含亮晶胶结物甚少。流花生物礁-滩组合的白垩状结构化主要形成于成岩早期大气淡水成岩环境,在成岩中—晚期中埋—深埋环境中,通过进一步溶蚀、淋滤,产生大量溶蚀孔洞,从而形成白垩状孔隙储集层。论述了流花生物礁-滩组合广泛发育白垩状结构灰岩的证据、白垩状结构化产生于大气淡水成岩环境的证据及白垩状孔隙储集层的形成机理。

Chalky texture limestones in Liuhua reef-bank complex of the Dongsha platform of the Early Miocene Zhujiang Stage in South China Sea belong to the chalky texture limestones in a broad sense.The diagnostic characteristics of chalky texture limestone lie in that macroscopicly,the rock is white or light colored,loose,soft,friable and microporous limestone with lighter specific gravity;that microscopicly,the rock has a framework of micrite and microspar of low magnesium calcite with intercrystalline pore and throat networks,containing very little sparry cement.The chalky texture formation of the Liuhua reef-bank complex was formed in meteoric fresh water diagenetic environment of early diagenetic stage.A large amount of solution pore and vug spaces were successively formed in mediate-deep to deep buried environments of middle-late diagenetic stage,thus chalky porous reservoirs were generated.The article discusses evidences why the chalky texture limestone was widely developed in Liuhua reef-bank complex and the formation of chalky texture occurred in meteoric freshwater diagenetic environment,and what the formation mechanism of chalky porous reservoirs is.