Depositional facies and reservoir-enhancing dolomitization surrounding monadnocks in the Slave Point Formation, Dawson Field, Alberta, Canada.

摘要

The Dawson field is a prolific dolomitized oil reservoir located in northwestern Alberta, Canada, in the Devonian Slave Point Formation. These Devonian shallow marine carbonates backstepped onto antecedent topography of the block-faulted Precambrian Peace River Arch. Monadnocks formed as the result of faulting augmented by fluvial (Granite Wash) erosion, which created a series of relatively small, isolated land masses of the Precambrian arch. These land masses acted as nuclei for localized reef and patch reef growth surrounding monadnocks. Six major environmental facies can be recognized within the Slave Point: the shallow shelf, back reef, reef, forereef, off reef, and basinal facies. Oil production is commonly associated with upper forereef, reef, and back reef facies. Geochemical and petrographic evidence, and facies associations suggest that the dolomitizing fluid(s) responsible for the formation of matrix and saddle dolomites, was seawater that had traveled through the porous sands and gravels of the underlying Granite Wash.