Abstract：The carbonate reservoirs within the Ordovician in Dongpu area, Bohai Bay Basin are characterized by deep buried，complicated structural evolution history and variable diagenesis. Recent years, the study interval... [ view full abstract ]
Abstract：The carbonate reservoirs within the Ordovician in Dongpu area, Bohai Bay Basin are characterized by deep buried，complicated structural evolution history and variable diagenesis. Recent years, the study interval has become a target of hydrocarbon exploration. However, its diagenesis and diagenetic evolution are understudied. This study uses cores, thin sections, cathodoluminescence, SEM, fluid inclusions, associated with regional geology data to investigate the diagenesis and diagenetic evolution of carbonate reservoirs within the Ordovician in Dongpu area.
Our results reveal that micrite and dolomitic limestone，calcite dolomite and gypsiterous dolomite are the dominant rock types. The diagenesis types and heir evolution history are cementation, compaction, penecontemporaneous dolomitisation, penecontemporaneous dissolution, supergene dissolution, structural fracturing, hydrothermal dissolution, pressure solution, burial dolomitization, recrystallization. The homogenization temperature of fluid inclusions shows that temperature changes are mainly distributed in five interval range: 185 ~ 257°F, 257 ~ 329°F, 329 ~ 401°F, 401 ~ 473°F, 473 ~ 545°F. The five different fluid stage are correspond to the five types of diagenesis environment: syngenetic diagenesis stages, early atmospheric freshwater diagenesis stages, early shallow buried diagenesis stages, supergene freshwater dissolution stage, middle - deep buried diagenesis stages. Cementation, compaction and penecontemporaneous dolomitization mainly occurred in the syngenetic diagenesis stage, penecontemporaneous dissolution mainly developed in the early atmospheric freshwater diagenesis stage, supergene dissolution developed in supergene freshwater dissolution stage, structural fracturing, hydrothermal dissolution, pressure solution, burial dolomitization and recrystallization developed in middle - deep buried diagenesis stage.
Our study also suggests that the cementation, compaction and pressure solution are the dominated diagenesis, which significantly damaged pores within reservoir, whereas penecontemporaneous dolomitisation, penecontemporaneous dissolution, supergene dissolution, structural fracturing, hydrothermal dissolution are the main diagenesis which improved the porosity of reservoir. The development of the carbonate reservoir within the Ordovician in Dongpu area is the result of the superposition of these diagenesis.
