--> --> Characteristics and Genesis of Deeply Buried Reservoir Sandstone (Shahejie Formation), in Nanpu Sag, East China

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Characteristics and Genesis of Deeply Buried Reservoir Sandstone (Shahejie Formation), in Nanpu Sag, East China


The Shahejie formation is very important rock unit for hydrocarbon exploration and production in Nanpu Sag of Bohai Bay Basin. In present study, methodology includes thin section study, core observation, Fluorescence, scanning electron microscope (SEM), Cathodoluminescence (CL), fluid inclusion, laser scanning confocal microscope, and geochemical analysis (C & O isotope) to evaluate the reservoir characteristics and origin of deeply buried Es1 sandstone member of Shahejie Formation. An experimental study indicates that the reservoir rock consisting of feldspathic litharenite and lithic arkose. The studied sandstone has good porosity and permeability. The reservoir pore space is dominated by intergranular pores, fractures pores, dissolution pores, and intergranular dissolve cement pores. The research indicates that the effective reservoir pore space consists of structural fractures, micropores, and nanopore throats. The main radius of matrix pores is 4-120 µm, matrix throat radius is 10-600 nm and main range of fracture opening degree is 100-400µm in general. The reservoir is classified as a fractured porous reservoir, primary porous reservoir, and dissolution porous reservoir rocks. The reservoir was formed by the common action of deposition, diagenesis, and tectogenesis. Sedimentation is the foundation and assumption for reservoir development but the effective reservoir is mainly controlled by primary pores, fractures, microfacies-lithofacies, tectonic elements and dissolution pores. Moreover, compaction, cementation, filling fractures are the main causes of reservoir density. Replacement is also a factor for the formation of the porous reservoir. Excessive dissolution is the key to reservoir formation and buried dissolution also promotes the formation of the high-quality reservoir. Similarly fractured formed by tectogenesis, significantly improve the permeability of the reservoir and also play role in porosity. The reservoir gradually evolved and formed under the control of various geological and diagenetic activities. The present study provides the important information and reference for oil and gas exploration and development in Nanpu Sag.