Abstract

Oil resources at Valhalla field of west-central Alberta, Canada, are stratigraphically trapped within the Upper Cretaceous Doe Creek Member of the Kaskapau Formation. The reservoir is subdivided into four thin (1–10 m [3–33 ft]), cyclic alternations of offshore mudrock and shoreface sandstone that are designated the I − 1, I, I + 1, and I + 2 units. The thickest and most widespread I sandstone is the primary reservoir. Optimum reservoir quality corresponds to coarser grain shoreface sandstone; however, reservoir quality may be diminished by postdepositional calcite cement commonly observed near the top of shoreface sandstones. Open-hole well logs are used to predict depositional facies and calcite cement occurrence in wells that lack core control. Decreasing shale volume (Vsh) and increasing deep resistivity values correspond to progressively shallower water deposits. Zones of calcite-cemented shoreface sandstone greater than 0.5 m (1.6 ft) thick are interpreted when the neutron porosity exceeds the density porosity by more than 7%. Facies distributions predicted for the I sandstone closely match trends of the sandstone gross pore volume and daily total fluid production, and suggest that open-hole well logs may be used to anticipate reservoir quality and continuity.

Regional and local observations support previous interpretations that attribute the Doe Creek to forebulge erosion and southwestward sediment transport toward a foredeep where shoreface sandstones accumulated within a coastal embayment to the Western Interior seaway. Regionally, the Doe Creek interval thins northeast of Valhalla and is truncated beneath the K1 unconformity, and shoreface sandstone bodies are encased within offshore mudrocks and detached from their contemporaneous shoreline. Locally at Valhalla, the Doe Creek reservoir progrades toward the southwest and is extensively and commonly uniformly burrowed by a relatively diverse assemblage of trace makers.

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