ABSTRACT

The Judith River (Belly River) Formation of central Alberta (Twp. 41 to 50, Rge. 26 W4M to Rge. 7 W5M) is informally subdivided into the Foremost and overlying Oldman units. The Foremost contains eight recognizable sandstone-shale sequences, with sand deposition occurring in deltaic and nearshore bar environments.

Most Judith River oil pools in the area produce from sandstone reservoirs developed during one of these Foremost cycles. Oil production rates are highly variable, being directly related to reservoir quality. Factors critically affecting this quality are grain size, calcite cementation, shale volume, rock composition, and water saturation.

The Ferrybank (Twp. 43, Rge. 27 to 28 W4M) oil pool is an example of the effect that localized heterogeneities can have on reservoir performance. Deposited during Foremost cycle 5, the oil-bearing sandstone body at Ferrybank can be divided into an upper, reservoir unit and a lower, non-commercial unit based on sedimentological and petrophysical characteristics. The trapping mechanism is the result of reservoir deterioration and eventual pinchout, as the depositional edge of the sandstone is approached. Primary oil recovery from this field is expected to be 1,300,000 cubic metres.

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