Submarine fans and related depositional systems ii: variability in reservoir architecture and wireline log character

Abstract

The architecture and heterogeneity of deep-marine clastic reservoir systems can be assessed at three scales. At the macroscale, lateral and vertical variations in the stacking patterns of submarine fans or fan complexes fundamentally affects the shape and scale of a reservoir and its trapping geometry. At the mesoscale, the distribution and type of architectural elements, (e.g., channel-levees, lobes, sheet sands) within the fan system have a major impact upon reservoir compartmentalisation and the distribution, continuity and connectivity of sand/shale bodies. Finally, at the microscale, the vertical and horizontal arrangement of reservoir and non-reservoir facies and lithotypes defines flow units which fundamentally control fluid flow and production performance. Each type of submarine fan and related deep-marine clastic reservoir system (sand-rich fans, mixed sand–mud ramps etc.) exhibits a predictable arrangement of architectural elements which form the basic building blocks of the system. These features control reservoir architecture, seismic expression and the geometry of sandbodies and non-reservoir section. A suite of reservoir architectural models is proposed for different deep-marine clastic systems using unpublished and cited data from outcrop and subsurface studies. These conceptual models are idealised simplifications which provide a preliminary framework for understanding broad scale reservoir archsitecture and wireline-log character within contrasting types of fan and related systems. The models are of value in the exploration for turbidite reservoirs by highlighting the risk on reservoir presence and distribution from an appreciation of the architectural style. Within appraisal and production they provide a basic framework from which an objective reservoir description can be made. Use of such conceptual analogue models for reservoir description will not adequately reflect the reality and individuality of a specific reservoir. Their use in understanding detailed reservoir complexity should therefore be approached with caution.