CHARACTERIZATION AND ARCHITECTURE OF CRETACEOUS INCISED VALLEY DEPOSITS: AN EXAMPLE OF FLUVIO-MARINE RESERVOIRS OF CENTRAL ALBERTA, CANADA

Fluvial and marine-influenced sandstones usually filling incised valleys are known to comprise the best reservoir bodies in coastal environments. Over the last decades, multiple studies of ancient and modern analogues have shown that these bodies are subject to highly variable spatial geometries and complex internal heterogeneities that can significantly affect production and enhanced recovery techniques. Besides analogue studies, detailed sedimentological and stratigraphic characterizations of onsite reservoir bodies are critical to (1) ascertain geological models of complex incised valley deposits and (2) unravel the dominant controlling parameters that drive the erosion and subsequent infilling.

The Grand Rapids Formation, Late Albian of western Canada, consists of regional marine shoreface parasequences incised by multiple valleys filled with fluvial to estuarine sediments. Deposition occurred at the southern end of the Boreal Sea, where large-scale fluvial systems drained large amounts of sediments from the Canadian Rocky Mountains to the west. The Grand Rapids Formation is host to significant reserves of heavy oil and has been intensely explored over the last 60 years. Its relatively shallow burial depth at 300-400m favours its exploitation and preservation. The study area expanding over 600km² comprises up to 5,000 m of cores and wireline logs from over 1,900 wells drilled since the 1950s. This extremely dense dataset offers a high resolution record of subsurface geology and allows the construction of a detailed sequence stratigraphic framework able to (1) define the facies and (2) depositional environments, (3) delineate the lateral and vertical extent of incised valleys, and (4) discuss their architecture and forcing parameters to better constrain the shape of reservoir bodies.