--> Abstract: Multiscale Characterization of a Marine Shelf Sandstone, the Cardium Formation in the Wapiti Field, Alberta Basin, Canada, by M. Socas-Bassons and C. P. North; #90937 (1998).

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Abstract: Multiscale Characterization of a Marine Shelf Sandstone, the Cardium Formation in the Wapiti Field, Alberta Basin, Canada

SOCAS-BASSONS, MERCEDES, and COLIN P. NORTH, University of Aberdeen; Mark Savage, Petro-Canada Oil and Gas

The Wapiti Field in the Alberta Basin, Canada, has produced oil and gas from the Upper Cretaceous (Turonian) Cardium formation since 1984. This reservoir unit is a NW-SE striking progradational sand body, 30 km by 10 km in area, and between 9 and 13 m in thickness, deposited during a period of slow sea-level rise. The sand body comprises essentially a single shallowing-upwards and coarsening-upwards package. But the production performance across this field is much more variable than traditionally expected for marine shelf sandstones of this type, and many wells are showing an unexpected decline in flow.

In an attempt to explain the production characteristics in this field, detailed study of the reservoir has been carried out in a variety of ways, and from pore scale up to entire reservoir scale. This study was based on the analysis of petrological, sedimentological, petrophysical (including core probe-permeametry and capillary pressure data), wireline log, and 3D seismic data. The outcome has been the identification of a combination of depositional and diagenetic controls, with no single factor alone being dominant and the relative influence of each varying across the field both vertically and laterally.

The main depositional control is relative proximity to nearby fluvial sources of sediment, which in turn determines gram size, sorting and mineralogy. Further from a fluvial input of sediment, grain size decreases, sorting improves, sedimentary structures change, and the proportions of feldspar and chert decrease. Acting along with the depositional effects there is a range in diagenetic effects because of the variation in primary porosity and permeability, and detrital mineralogy. The result is that growth of pore-filling cements and the development of secondary porosity are not uniform. The resulting reservoir heterogeneities are further compounded because early subaerial siderite diagenesis, which occurred during exposure at a tune of still-stand, has across the field penetrated to different levels in what would otherwise have been the best-quality reservoir sand.

Several fluid-flow simulations have been carried out to test the sensitivity of the entire field to specific geologic controls, in order to predict the regions of the field where the greatest improvements to recovery are likely to be made. The input to the simulations, representing particular geological scenarios, was created by a combination of deterministic and stochastic modelling techniques. These studies also help to explain the very existence of the field, since no obvious trapping mechanism has been proved.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah