Sedimentary Architecture of Field Analogues for Reservoir Information ( SAFARI ): A Case Study of the Fluvial Escanilla Formation, Spanish Pyrenees

Quantified information on the geometries of sandbodies and their internal heterogeneities is a necessary prerequisite for the realistic modelling of reservoirs and their behaviour during production. A database for sedimentary architectures of field analogues for reservoir information (SAFARI) is being set up, based on the analysis of critical problems within reservoirs of the Norwegian continental shelf. The Upper Eocene Escanilla Formation of the Ainsa Basin in the Spanish Pyrenees was selected as one of several analogue fluvial study objects. Excellent outcrop conditions allowed continuous tracing of sedimentary units over large areas, and sandbody geometries could be studied in three dimensions. Data documenting the large-scale sedimentary architecture and smaller scale sandbody heterogeneity patterns were collected, along with various point-related measurements and general characteristics of the formation. Principles of bounding surface hierarchies and classification of architectural elements were adopted to ensure systematic data handling. The Escanilla Formation has a maximum preserved thickness of 750 m in the study area, and contains sediments formed in medial/distal alluvial fan to axial fluvial system settings. The coarse member deposits, which constitute 30–55% of the formation, consist of a number of different channel/channel-belt types, the most common ones being channel- and sheet-braided bodies, coarsg-erained point bar bodies and deeply incised trunk stream sandbodies. The fine member deposits are characterized by crevasse splays and immature palaeosols. Deposition occurred in response to thrust activity and was influenced by differential subsidence in a foreland basin. The outcrop data are stored in the SAFARI database system, where they may be analysed in order to quantify critical parameters such as sandbody geometries and interconnectedness, channel-body orientation and flow-unit distribution.