Devonian hydrocarbon source rocks and their derived oils in the Western Canada Sedimentary Basin

Devonian strata within the Western Canada Sedimentary Basin contain large r eserves of oil and gas. These vast hydrocarbon reserves can be largely attr ibuted to the occurrence of abundant mature, excellent to good quality Devo nian source rocks. The Middle Devonian Elk Point Group contains several uni ts with hydrocarbon potential including the Evie Formation in British Colum bia, the Keg River Formation in northern Alberta, and the Winnipegosis Form ation in east-central Alberta and southern Saskatchewan. Many of these are proven source rocks of oils occurring in Middle Devonian reservoirs. Elk Po int Group potential source rocks contain a wide variety of organic matter t ypes reflecting the diversity of their depositional environments. No hydroc arbons have been definitively linked to a Beaverhill Lake Group source rock but it is possible that such a unit is the source of Slave Point Formation reservoired oils in northwest Alberta. The Late Devonian Woodbend Group co ntains the Duvemay Formation, the most prolific Devonian source rock in the Alberta Basin. It is characterized by marine Type II/I organic matter with TOC contents up to 15% in immature samples and is the source of most oils in the Bashaw Reef Complex, the Rimbey-Meadowbrook Reef Trend, and in the S wan Hills Formation in Alberta. The stratigraphically equivalent Muskwa For mation in northern Alberta has a much lower hydrocarbon potential than the Duvernay Formation. Oils have been correlated to Winterburn Group source ro cks within the Nisku Formation of east-central Alberta, Camrose Member/Nisk u Formation of southern Alberta, and the time-equivalent Birdbear Formation of southeast Saskatchewan. Winterburn Group potential source rocks in cent ral to southern Alberta can have high TOC contents (up to 15%) and contain Type I and Type II organic matter deposited in open marine to lagoonal pala coenvironments. The Cynthia Member shale of the Nisku Formation in west-cen tral Alberta, previously thought by some workers to be a source rock, is ac tually organic-lean. The underlying Bigoray Member is more organic-rich and may be a minor contributor to hydrocarbons in the West Pembina area. The W abamun Group contains no regionally extensive potential source rocks. Almos t all the oil generated from Devonian source rocks appears to have remained within Devonian-aged reservoirs and very little is biodegraded. In contras t, where Exshaw Formation sourced oil is found in Devonian reservoirs, such as in the Grosmont and Nisku formations in the vicinity of the Athabasca M annville Group bitumen deposit (i.e. "Carbonate Trend"), it tends to be bio degraded.