PETROLEUM GEOLOGY OF THE DEVONIAN THREE FORKS FORMATION,

The Sinclair Field (Townships 7 to 8, Ranges 28 to 29W1) is the newest oil field discovery in Manitoba and has greatly expanded in size and production since its discovery in 2004. The oil field had been previously explored in the 1960’s, but the pay was missed by early exploration efforts. Proven and probable reserves are estimated at 3.8 million m3. The Devonian Three Forks Formation is a cyclical transgressive-regressive sequence of shaley, silty dolarenite, interbedded with shale and brecciated in many places. Deposition of the Three Forks was influenced by several weathering events due to transgressive and regressive cycles and basin tectonics. It is subdivided into four units. Unit 1 is the lowermost unit and the most widespread, and is the most oxidized and weathered of the units. Unit 2 is an interbedded siltstone and shale, massive shale and occasionally brecciated, and is productive as a secondary reservoir at the Sinclair Field and Daly Field (Townships 9 to 10, Ranges 27 to 29W1). Unit 3 is a red-brown highly oxidized silty shale. Unit 4, the uppermost unit represented in Manitoba, is an interbedded siltstone and silty shale with thick subunits of highly distorted and brecciated siltstone beds. Unit 4 is the primary and most productive reservoir at Sinclair Field. Thinning o