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Integrated Natural Fracture Characterization in a Metamorphic Buried Hill Reservoir: A Case Study From South JinZhou25–1 Field, Bohai Bay Basin, Eastern China


With an estimated total reserve of more than 650 million barrels, South JinZhou25–1 Field is the first and largest offshore fractured metamorphic granite buried hill reservoir that has been brought into production in the Bohai Bay Basin, Eastern China. The reservoir quality and production mainly rely on the complex fracture network. Thus, a deep understanding of fracture distribution and connectivity is crucial to the efficient development of the field. The aim of this paper is to predict the fracture distribution and its compartmentalization with core, well logging and 3D seismic data. Core observation and FMI interpretation show that the buried hill reservoir mainly developed tectonic fractures with apertures between 0.5mm-1mm and tilt angles between 65°-85°. The dominant fracture orientations can be grouped into two directions, that is, NE-SW and NW-SE. Most favorable zones for fracture development, within 100 meters from the top of the buried hill, are determined with conventional logs calibrated by core and FMI. Anomalies on seismic attributes and S-wave impedance have been successfully used to predict horizontal fracture distribution within the buried hill reservoir, which indicates that fractures mainly occurred at paleo-topographic highs and in areas where the fault density is above 2 km/km2. Thus, fracture formation is believed to be affected by faults and paleo-topography. The insight of fracture characterization of the buried hill reservoir makes it possible to optimize the well locations, reduce the risk of well drilling and improve the efficiency of the development in the field.