ABSTRACT

An integrated petrographic, sedimentological and petrophysical analysis of Upper Mannville sandstones in the Countess-Makepeace area (Twp. 21-24, Rge. 16-19 W4M) was conducted to determine the geological controls on reservoir quality and production performance.

Low permeability, gas productive, Upper Mannville sandstones occur in a 40 m thick interval immediately overlying the Ostracode zone and underlying an areally extensive coal marker.

The Upper Mannville sandstone sequence consists of three sandstone units. In descending order, they are the Upper Mannville A, B, and C units. The Upper Mannville sandstone sequence was deposited in a complex estuarine/coastal-plain setting. It represents a stacking of prograding, shallow water, upward-coarsening sandstone bodies with associated tidal channel deposits.

The reservoir quality sandstones are very fine to medium grained, poor to moderately well sorted feldspathic litharenites and lithic arkoses. Grain size and mineralogy are variable and have a major effect on reservoir and quality and production performance.

Average in situ effective porosity and permeability are 15 per cent and 1 millidarcy, respectively. As a result of the low permeability, all wells require fracture stimulation in order to be economic producers. This case history demonstrates the value of an integrated approach to reservoir characterization. A complete understanding was obtained by combining depositional-diagenetic environment interpretation, facies interpretation, mineralogy and pore system evaluation with recognition of reservoir quality rock types on wireline logs.

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