Abstract

Over 50% of the established oil reserves (1.325 million cubic meters) of the Little Bow field in southern Alberta are stratigraphically trapped within upper Mannville G, U and W pools. These pools are hosted by three parallel, elongate sandstone bodies within an estuarine valley-fill which lies at the base of the Lower Cretaceous Glauconitic member. The paleovalley is 2.0–2.5 km wide, 4–30 m thick, and has been mapped over a length of 55 km. The three reservoir sandstone bodies are 3–4 km long, 300–500 m wide, and up to 22 m thick. Reservoir pressure histories and original fluid contacts indicate hydrodynamic isolation of the three pools. Examination of well logs and seismic sections indicates the three sandstone bodies are separated by 100–200 m wide shale units. These shale units are interpreted as the fills of mud-prone, estuarine channels. The sandstone bodies of G, U and W pools are interpreted as deposits of longitudinal sand bars that lay between the muddy channels in a configuration similar to that found within the modern Gironde estuary.