Abstract: Triassic Gas Resources of Western Canada Sediment Basin: Geological Play Definition and Resource Assessment

T. D. Bird, J.E. Barclay, R. I Campbell, P. J. Lee

Natural gas resource potential of Triassic strata in the Western Canada Sedimentary basin (excluding the Foothills Belt) was evaluated using a combination of geological play analysis and statistical estimation.

Geological analysis was undertaken to characterize exploration plays with respect to type and geological distribution. Triassic strata belong to a platformal succession of mixed siliciclastic, carbonate, and evaporite deposits situated mainly along the western portions of the Western Canada basin. The thickest deposits and most of the discovered oil and gas occur in the westward thickening and deepening depocentre called the Peace River Embayment. Exploration plays consist of stratigraphic and stratigraphic-structural combination traps. Reservoirs occur in shoreline, tidal channel, shallow marine sandstones and coquinas, aeolian sandstones, tidal flat algal mat carbonates and marine shelf carbonates. All pools formed under similar geologic conditions (depositional style, facies, struc ure, reservoir, source, trap, seal, and migration) are assigned to a specific play and make up a natural population. Once the play is defined, statistical estimation is done using the Discovery Process Model. The size or volume of each pool, together with its order in the sequence of discovery, are used to estimate the play potential and size range of undiscovered pools.

Ten established (mature) plays were defined in this assessment. Several of these plays still have significant gas potential, particularly the Halfway/Doig Formation shelf sandstones play, influenced by Peace River Arch/Embayment structures (e.g., Monias field), and the subcropping Baldonnel Formation carbonate play, involved in Laramide-aged gentle folds (e.g., Laprise field). Conceptual and immature play potential was estimated using the total resource (reserves plus potential) for each mature play, with the 10 mature plays serving as the sample population. Statistical analysis indicates that at least 13 plays are likely to exist and since this number includes 2 immature plays (1 conceptual play is postulated). This is reasonable considering the basin is mature with respect to explor tion, and established play definitions are sufficiently broad to include variations in trapping mechanism. Conceptual and immature plays contain only 12% of the estimated total undiscovered potential. Expected volumes of conceptual, immature and mature plays, when summed, indicate that 48% of the total resource remains to be discovered.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994