ABSTRACT

The Bigoray Nisku "C" pool and the Pembina Nisku "L" pool are two examples that illustrate the sedimentology, diagenesis and reservoir geology of the important West Pembina reef fairway. The Bigoray Nisku "C" pool is a partially dolomitized reef, measures 1.1 by 0.85 km and contains a productive area of 89 hectares. The ERCB recognizes an OOIP of 1209 10³m³ for the Nisku "C" pool. Ultimate recovery is estimated to be in the order of 523 10³m³ or approximately 43 per cent of the OOIP. This hydrocarbon recovery will be accomplished using a displacement type waterflood scheme. In contrast the Nisku "L" pool is a completely dolomitized reef and is being exploited by means of a crestal vertical displacement miscible slug EOR scheme. This pool measures approximately 2.0 by 1.5 km, and contains a productive area of about 219 hectares. With an estimated 5,000 10³m³ of OOIP, the Nisku "L" pool constitutes one of the largest pinnacle reefs discovered in the Nisku reef trend. Ultimate recovery is estimated to be in the order of 3,860 10³m³ or approximately 77 per cent of the OOIP. This high projected ultimate recovery is due to the miscible displacement enhanced oil recovery scheme and to the overall suitability of the reservoir to this type of scheme. These two pools illustrate the interplay between sedimentary and diagenetic processes, which have to be considered when evaluating proposed or ongoing EOR schemes. By understanding the geology of the partially dolomitized "C" pool, the morphology, internal geometry, diagenesis and control on reef development has been deduced for the dolomitized "L" pool. Consequently, these geological studies, in effect, help ensure a good "fit" between the engineers' simulation model and the actual reservoir. In turn, a realistic simulation will most likely determine the optimum design and operational parameters for the EOR scheme being evaluated.

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