Abstract

The Nottingham North Alida Beds Unit is located on the northern margin of the Williston Basin in southeast Saskatchewan. The reservoir comprises Lower Mississippian shallow shelf carbonates of the Mission Canyon Formation which display several transgressive cycles in an overall shallowing upwards sequence.

There are two transgressive cycles preserved at the Nottingham Unit, each containing two separate reservoirs. Reservoir quality is dependent upon the original depositional environment and subsequent diagenetic history. Cycles average 32 metres in thickness and are laterally continuous across the Unit.

The cycles start with the oncolite boundstones and deepen upwards into a thick succession of shallow marine carbonates with crinoid ossicles, brachiopods, foraminifera, ostracods, calcispheres, solitary and colonial corals, and bryozoa. Cycles are completed by a subaerial caliche soil profile facies.

Regional mapping suggests the oncolites were deposited in a tidal flat setting. The oncolites are capped by an intertidal laminated algal mudstone, which is dolomitized in most cases.

The oncolite boundstone has good primary porosity and corresponding high permeability in contrast with the secondary leached porosity and low permeability of the rest of the reservoir.

The core on display comes from the 16-30-5-32 WPM Mississippian oilwell and shows only a portion of the lower cycle of the Mission Canyon MC-2 and MC-3.

In addition to the 16-30 core, photographs of thin sections from a selection of sixteen cores available in the thirty well Unit are described to show the best preserved sedimentary and diagenetic features.