Petroleum Geology of MC-3 Member, Mississippian Mission Canyon Formation, Pierson Area, Southwestern Manitoba

Muzaffar, Husain, S. P. Halabura

Mississippian beds in the Manitoba portion of the Williston basin produce oil from a series of stratigraphic units where porous cyclic carbonates are truncated by pre-Mesozoic erosion and sealed by Amaranth (Watrous/Spearfish) strata. In the Pierson area of southwest Manitoba, oil is trapped within the MC-3 member of the Mission Canyon Formation, correlative with the Alida beds of Saskatchewan. Production was first obtained in 1954 and subsequent exploration has led to the discovery of 11 pools of various sizes. As of December 31, 1987, 2.4 million bbl (375,510 m³) of 36° API gravity oil had been produced from the area, and currently eight pools are producing.

In Manitoba, the Mission Canyon is subdivided into three members: MC-1, MC-2, and MC-3, in ascending order. The MC-3 is further subdivided by the "MC-3 marker" into lower "MC-3a" and upper "MC-3b" units. Oil, in the Pierson area, occurs in these two units.

The MC-3 member consists of a cyclic sequence of lithofacies deposited in a shallow-water, moderate to high-energy, carbonate-dominated inner shelf environment that was present over much of southwest Manitoba. Five lithofacies have been recognized in core, but oil is found largely within the more porous shoal and backshoal facies (average porosity 14% and permeability 12 md). The cap rock, in most places, is a secondary, dense dolomite and anhydrite zone ("altered zone") directly below the pre-Mesozoic erosion surface. Where the "altered zone" is thin or absent, lower Amaranth shales (red beds) form the cap rock.

Entrapment is primarily stratigraphic, resulting from regional truncation of the MC-3 beds with accumulation localized and controlled by (1) local paleotopographic highs, (2) porosity and permeability pinch-out due to primary lithofacies variations, and (3) porosity closure resulting from variation in the thickness of the "altered zone."

AAPG Search and Discovery Article #91033©1988 AAPG Rocky Mountain Section, Bismarck, North Dakota, 21-24 August 1988