WESTERN CANADA MANNVILLE GAS POTENTIAL SEEN AS HIGH

Nov. 6, 1995
Wendy J. Warters, Doug J. Cant, Ping H. Tzeng, Pei J. Lee Geological Survey of Canada Calgary The Geological Survey of Canada estimates that the expected potential or undiscovered gas resource of the Mannville group and its stratigraphic equivalents in the Western Canada sedimentary basin is 33.8 tcf (Fig. 1)(90756 bytes) . This estimate is based on the recently completed natural gas resource assessment study of the Mannville group. This study is the sixth part to be completed of a Western

Wendy J. Warters, Doug J. Cant, Ping H. Tzeng, Pei J. Lee
Geological Survey of Canada Calgary

The Geological Survey of Canada estimates that the expected potential or undiscovered gas resource of the Mannville group and its stratigraphic equivalents in the Western Canada sedimentary basin is 33.8 tcf (Fig. 1)(90756 bytes).

This estimate is based on the recently completed natural gas resource assessment study of the Mannville group. This study is the sixth part to be completed of a Western Canada Sedimentary Basin Gas Assessment project that is being conducted by GSC.

The basin encompasses all of Alberta, northeast British Columbia, southern Saskatchewan, and southwestern Manitoba. It was necessary for assessment purposes to divide the basin into play groups using geological criteria, primarily major stratigraphic time/ rock units, and structural/tectonic provinces.

These major play groups are: the Devonian, Permo-Carboniferous, Triassic, Jurassic, Mannville, Colorado, Upper Cretaceous-Tertiary, and Foothills. The Colorado and Upper Cretaceous-Tertiary are the final play groups that remain to be assessed.

MANNVILLE GEOLOGY

The Mannville group was deposited as a foreland clastic wedge to the east of the Cordillera which was uplifted as a result of the Columbia orogeny. The Mannville group is zero to more than 700 m thick and rests on the Pre-Cretaceous unconformity, which progressively cuts down through strata of Jurassic age in the west to Devonian age in the east.

The Lower Mannville group is characterized by continental deposits, with the lowermost units being the alluvial plain to braided river deposits of the Cadomin formation. These are overlain by fluvial and lacustrine deposits of the Basal Quartz/Ellerslie, Gething, Cutbank/Sunburst, Dina, and McMurray formations that grade upward into marginal marine deposits. With continued southward transgression of the Boreal sea, a series of transgressive shorelines was deposited, the Bluesky, Wabiskaw, and Cummings formations.

A major change in the depositional style occurred within the Mannville group at this point from the regionally transgressive Lower Mannville group to the regionally regressive Upper Mannville group. The progradational shoreline deposits of the Glauconite and Clearwater formations mark this change. These, in turn, were followed by further northward progradation represented by the Spirit River formation, Grand Rapids formation, and the Upper Mannville group (Fig. 2)(35319 bytes).

ASSESSMENT PROCEDURE

For the Mannville assessment the Western Canada sedimentary basin was divided into six geographic areas: 1. northwest Alberta and British Columbia 2. Athabasca 3. Lloydminster 4. central Alberta 5. southern Alberta, and 6. Saskatchewan.

Each of these areas was further subdivided based on the stratigraphy of the Mannville group resulting in a total of 17 plays (Fig. 3)(73552 bytes).

Stratigraphic and production data from over 170,000 wells and over 13,000 gas pools were integrated into this study.

The natural gas resource potential of each play was estimated by the Petrimes data base, which utilizes the pool volume and date of discovery to estimate the total play potential and size range of the undiscovered pools.

Discovered in-place gas volumes for pools in the Mannville group were obtained from both provincial and federal data bases and were incorporated into GSC's Petrimes database system.

SUMMARY OF RESULTS

The Mannville group contains 53.1 tcf discovered gas resource, which accounts for 23.6% of the total discovered gas resource in the Western Canada basin (Fig. 1)(90756 bytes).

The expected potential (undiscovered) gas resource for the Mannville group is estimated to be 33.8 tcf. Based on this estimate, 39% of the total gas resource of the Mannville group remains to be discovered.

Based on geographic area, the plays in the central Alberta area have the highest discovered gas resource and the plays in Northwest Alberta and British Columbia have the highest expected potential (undiscovered) gas resource (Table 1)(15502 bytes). These statistics correspond to drilling depths and therefore drilling costs. Future discoveries are more likely to be found in the deeper and less densely explored regions of the basin such as Northwest Alberta and British Columbia.

Table 2 (39728 bytes) lists the discovered and expected potential gas resource for each of the 17 plays. The Northwest Alberta and British Columbia-Cadomin play has the highest expected potential gas resource.

More detailed studies of the stratigraphy of the Cadomin formation and the overlying Gething formation may lead to future exploration targets.

The Central Alberta-Upper Mannville play has the second highest expected potential gas resource, and the Lloydminster-Upper Mannville play has the third.

Future discoveries in the Lloydminster-Upper Mannville play will probably result from the extrapolation of discovered productive trends in Alberta into Saskatchewan where there is a marked decrease in the number of discovered gas pools as you cross the provincial boundary.

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