Depositional and diagenetic models for Devonian Birdbear (Nisku) reservoirs, northeastern Montana
Carbonates comprising the approximately correlative Upper Devonian Birdbear ad Nisku Formations were deposited over an immensely broad, shallow shelf that extended from eastern North Dakota over an immensely broad, shallow shelf that extended from eastern North Dakota to central Alberta. Major oil production is concentrated in Nisku pinnacle reefs bordering the central Alberta basin and Birdbear stromatoporoid banks and biostromes bordering the Williston basin in northeastern Montana. Birdbear fields are located on structures coincident with favorable reservoir facies. Birdbear porosity, formed upon dolomitization, is dominated by interconnected intercrystalline and microvugular voids, skeletal molds, and leaching-enhanced intraskeletal voids. Depositional models over the region are varied, but all have in common early marine inundation of a nearly featureless shelf and coastal plain, followed by universal gradual shoaling by vertical sediment accretion culminating in an extremely restricted depositional setting. Mud-rich depositional textures and contained fossil assemblages demonstrate the predominance of low-energy, shallow subtidal to supratidal waters of more or less elevated salinites. Depositional models are constructed as vertical facies sequences, each subject to local and regional facies changes. Principal events of a generalized Birdbear diagenetic model include desiccation, brecciation, and caliche development in mudstone; displacive growth of nodular and nodular-mosaic gypsum; and lithification by pervasive dolomitization. Any specific diagenetic model and resultant reservoir characteristics, however, are valid only for that particular set of rock fabrics and burial settings embodied in any given depositional model.
- Research Organization:
- ERCO Petroleum Services, Inc., Houston, TX
- OSTI ID:
- 6386145
- Report Number(s):
- CONF-8309274-
- Journal Information:
- Am. Assoc. Pet. Geol., Bull.; (United States), Journal Name: Am. Assoc. Pet. Geol., Bull.; (United States) Vol. 67:8; ISSN AAPGB
- Country of Publication:
- United States
- Language:
- English
Similar Records
Lagoon and tidal flat sedimentation of the Upper Devonian Nisku Formation in southern Alberta
Stratigraphic and diagenetic controls on the distribution of reservoir properties in the Devonian Nisku Formation at Joffre Field, Alberta
Related Subjects
020200* -- Petroleum-- Reserves
Geology
& Exploration
03 NATURAL GAS
030200 -- Natural Gas-- Reserves
Geology
& Exploration
CARBONATE ROCKS
DEVONIAN PERIOD
DIAGENESIS
FEDERAL REGION VIII
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC MODELS
MINERAL RESOURCES
MONTANA
NORTH AMERICA
PALEOZOIC ERA
PETROLEUM DEPOSITS
RESERVOIR ROCK
RESOURCES
ROCKS
SEDIMENTARY ROCKS
SEDIMENTATION
USA