Strachan – Ferrier – Edson

Exploration Assessment of Pekisko and Banff Reservoirs, Strachan-Ferrier-Edson Region, West-Central Alberta

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Summary:
Location: T36-54, R7-20W5
Strata: Mississippian
Year of Study: 2000

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Introduction

Mississippian strata in the west-central Alberta Plains have been important oil and gas producers since the 1950’s, when intensive exploration began along their updip subcrop edges. As we enter the new century, the subcrop edges are well-known, and hold little potential for major new discoveries. Downdip, however, new and prolific discoveries have been made, which occur in stratigraphic/diagenetic traps unrelated to the subcrop. Until now, these reservoirs have not been well documented or mapped, and explorers have had little guidance in generating new prospects along these fairways.

Petrel Robertson Consulting Ltd. has completed a regional exploration and development assessment of the Mississippian Banff and Pekisko section in the Plains and outer Foothills of the Strachan-Ferrier-Edson area, which addresses exploration for downdip reservoirs. Our work builds on concepts developed in Petrel’s recent studies of the Mississippian in northeastern British Columbia, northwestern Alberta and southwestern Alberta and adjacent Montana. The database includes logs from every well that penetrates the Mississippian, descriptions of 51 cores west of the subcrop edge, petrographic analysis, and a complete hydrogeological review of drillstem test and production data.

The Banff and Pekisko formations were deposited on a westward-deepening ramp as a complete transgressive-regressive cycle, prograding westwardly toward the Prophet Trough. On the basis of lithology, depositional textures and biotic assemblages, we recognize six shoreline to marine environments, from evaporitic sabkha to basinal shales. We are thus able to map stacked high-frequency aggradational parasequences within the Banff-Pekisko cycle – five within the Banff, and four within the Pekisko. Parasequences boundaries are marine flodding surfaces, separating shallow water (often dolomitized) facies below from deeper water facies above.

Banff and Pekisko downdip reservoir development is controlled by original depositional facies and by subsequent diagenetic events. The best downdip Banff reservoirs are within thick crinoidal shoals, formed at the outer margin of the mid bank facies belt. To the east, similar facies are degraded by late calcite cements. Downdip Pekisko reservoirs occur primarily in the inner ramp depositional belt, but are best developed in discontinuous, slightly shallower, dolomitized facies packages. Despite their stratigraphic separation, most of these reservoirs appear to be hooked to one common regional aquifer for the Banff and one for the Pekisko.

In the northern part of the study area, additionally porosity development and trapping opportunities occur along a southwest-northeast trend, roughly coincident with the Snowbird Tectonic Zone of the Precambrian basement, and the Nisku shelf/basin margin. Porosity anomalies are best developed within two specific Banff and Pekisko parasequences, but the entire regional Pekisko aquifer appears to be broken by this trend.

The Strachan-Ferrier-Edson report includes:

• 14 regional stratigraphic cross-sections
• AppleCore logs of all cores examined
• A suite of regional structure
• gross isopach and net porosity maps
• a suite of regional hydrogeological maps and plots
• a digital tops database
• and three exploration template studies.

A comprehensive text summarizes this information, and uses it to synthesize an exploration summary, and recommended exploration and development methods.