FLUVIAL RESERVOIR ARCHITECTURE INTERPRETATION BELOW THE SEISMIC RESOLUTION IN AN OFFSHORE OILFIELD

Reservoir discontinuity is a practical representation of reservoir heterogeneity, which leads to the non-uniformed flow of hydrocarbons during production and to the increase in the difficulties of producing the remaining oil in clastic reservoirs. A feasible solution is to detect the internal bounding surfaces of the reservoir based on infill drilling data. However, for offshore oilfields, reservoir discontinuity analysis will have to rely on seismic data due to their sparse well spacings. Moreover, from the interpretation of a fluvial reservoir system in Chinaapos;s Bohai Bay, it turns out that the thickness of the sandstone is usually smaller than the seismic tuning thickness. In order to interpret a fluvial reservoir architecture which is below the seismic resolution, we elaborated a hierarchy of the fluvial reservoir architectures and classified the compound sandstones as different architectural elements according to their sedimentary periods. Forward models were designed to analyze the seismic responses of the architectures. The results demonstrate that amplitude-related seismic attributes could be sensitive to different reservoir architectures below the seismic resolution. The amplitude-related seismic attributes can be extracted through a time window guided by the horizons. The horizon-based attributes can be treated as digital images which may contain the information of compound sandstones with hidden discontinuity boundaries. We propose a direction-adaptive mathematical morphology gradient algorithm that can detect the boundaries of reservoir architectures in different directions on horizon-based seismic attributes. The application to field data demonstrates that the boundaries detected by the proposed algorithm have a good consistency with well logs. This method could enhance our capability to visualize and understand the complexity of reservoir heterogeneity.