Diagenesis and porosity development of Mission Canyon reservoir interval in 07 43B pool, Pierson Field, Manitoba
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The 07 43B pool is in the northeastern part of the Pierson field located in southwestern Manitoba. This pool is situated within the subcrop of Mississippian MC-3a beds which constitute the producing zone. The MC-3a beds can be correlated with beds in the adjacent Waskada area of southwestern Manitoba. In the study area, the MC-3a beds represent a carbonate tidal flat complex. Four lithofacies have been identified. These are: algal, vadolite, bioclastic grainstone and peloidal grainstone facies. Except for the vadolite facies, all other facies refer to depositional environments. The vadolite is likely to have formed from subaerial exposure in a strandline environment during early diagenesis. Diagenetic alteration has been broadly divided into early and late. The early diagenesis is characterized principally by biological diagenesis, formation of vadolite, and calcite cementation. The late stage of diagenesis includes dolomitization, anhydritization, the formation of other authigenic minerals, compaction, pressure solution, fracturing, and leaching. A relative chronology of these events has been reconstructed which, in general, shows considerable overlap of the diagenetic processes. The development of porosity is not true facies selective. Late diagenetic processes have been inferred to control the preservation of primary porosity as well as the development of leached porosity and minor intercrystalline porosity. However, facies with higher primary porosity (e.g. vadolite) are more likely to show higher porosity development, and consequently represent the principal reservoir facies. Oil has been found in the traps of primarily structural origin; this is true with the limitation of updip and/or lateral facies change involving porosity development.