Bivouac

Exploration Study of Mississippian and Cretaceous Strata, Bivouac Area


Summary:
Location: Blocks S.E. (Alberta) T94-116, R5-13W6, NW : (BC) 94-I, P
Strata: Mississippian / Cretaceous
Year of Study: 2000


Introduction

Mississippian and Cretaceous strata in northeastern British Columbia and northwestern Alberta are proven gas producers and intriguing exploration targets. Reservoirs occur at shallow depths (300 to 1500 metres), and feature reserve potentials of up to 100 BCF or greater from individual pools. Expansion of pipeline systems and growing natural gas demand through the late 1990's have made exploration for these widespread targets economically feasible.

Petrel Robertson Consulting Ltd. has completed a regional exploration and development assessment of the Mississippian and Cretaceous (Banff through Bluesky) section in the Bivouac area, which straddles the Alberta - B.C. border. This work builds on concepts and mapping developed in recent studies of the Cretaceous at Buick Creek/Laprise and Silver/Dahl, and in a study of the Mississippian to the southwest in B.C. The study database includes logs from every well in the study area, examination and logging of 169 selected cores, petrographic and sample cuttings analysis, and a complete hydrogeological review of drillstem test and production data.

Seven Mississippian and Cretaceous stratigraphic units are prospective across the Bivouac area. The oldest unit, the upper Banff clastics, includes reservoir-quality aeolian siltstones which produce gas along the subcrop edge, and also demonstrate productive potential downdip. Above the Banff, the Pekisko, Shunda, Elkton and Debolt were deposited on broad carbonate ramps, dipping northwestward toward the Prophet Trough. Although each unit is distinct, they exhibit common depositional elements, and similar controls on reservoir development. Reservoir quality is best developed along each subcrop edge, where diagenesis has (in general) enhanced primary porosity through solution and dolomitization processes. Subcrop edge gas pools occur in the Debolt, Elkton, and Pekisko in the Bivouac area, and in the Shunda to the southeast. Undrilled areas along each edge are highly prospective for new discoveries.

Structure also plays a key role in Mississippian reservoir development. Basement structural trends define fairways across which numerous block faults exist. Reactivation of block faults occurred during Antler (Late Devonian - Early Mississippian), Columbian (Late Jurassic - Early Cretaceous), and Laramide (Late Cretaceous - Tertiary) orogenies. Antler-related movements influenced the development of Mississippian reservoir facies, particularly in the Shunda Formation. Linear trends of reservoir development, perpendicular to the subcrop edge of each carbonate unit, appear to be related to fault trends. These may result from selective reservoir enhancement within particular fault blocks, or along particular fluid migration pathways. A large oil accumulation within the Shunda at Desan is the best example of a structurally-controlled reservoir. Numerous exploration leads indicate the existence of other substantial oil and gas pools of this type.

Cretaceous reservoir units lie above the regional pre-Gething unconformity, which bevelled the Mississippian succession eastward. The Gething Formation fills valleys with fine-grained fluvial sands, fining upward to heterolithic alluvial plain to marginal marine strata. Gas and some oil production occur where valleys define a stratigraphic trapping configuration, and underlying Triassic or Mississippian strata provide an adequate seat seal. Bluesky sandstones were deposited as transgressive shoreface units, as the Fort St. John/Clearwater Sea swept across the Western Canada Sedimentary Basin. The Bluesky contains an important medium-gravity oil field at Hay River, and is highly prospective for oil and gas throughout a broad arc in northeastern B.C.

The Bivouac report includes: 24 regional stratigraphic cross-sections, a complete suite of gross isopach and net reservoir maps, two regional structure maps, selected seismic models, a suite of regional drillstem test and production maps, pressure-elevation plots illustrating all valid tests, a hydrodynamic report, and seven individual pool studies. A comprehensive text summarizes all this information, and uses it to synthesize an exploration summary and recommended exploration and development methods for each prospective unit.

For more information contact:

Leslie Sears
Petrel Robertson Consulting Ltd.
500, 736- 8th Avenue S.W.
Calgary, Alberta
T2P 1H4

Phone: (403) 218-1618
Fax: (403) 262-9135
lsears@petrelrob.com
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