Abstract

In the Lloydminster heavy oil area in Alberta and Saskatchewan, the Mannville sandstone-shale sequence (Lower Cretaceous) contains in excess of 3 billion bbl (500 million cu m) of oil in place. Only 8.1% of this oil is recoverable by conventional methods so that the scope for thermal or other exotic recovery methods is large. Most of the oil is in the Sparky and General Petroleums (GP) sandstones (middle Mannville) which are widespread tabular bodies relatively easy to correlate from well to well. The Sparky and GP are probably marine prodeltaic sedimentary deposits with their source on the northeastern side of the depositional basin.

Detailed log examination and mapping show that the Sparky and GP oil is trapped downdip (south or west) from gullies or channels filled with shaly rocks. These gullies, locally as much as 235 ft (72 m) deep, were formed by subaerial erosion on an intra-Mannville disconformity. Uplift, erosion, and reinitiation of deposition encompassed only a part of Albian (Early Cretaceous) time, possibly less than a million years. Gully fill and higher Mannville beds above the disconformity are mainly fluviatile with a Cordilleran provenance.

The disconformity has not been widely recognized. It is important in development of the heavy oil resources near Lloydminster and its recognition may be important in the search for oil, natural gas, and coal elsewhere in western Canada.

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