Dolomitization and late secondary porosity development in Nisku reefs (late Devonian) of Alberta

Conference · Tue Mar 01 04:00:00 EST 1983 · Am. Assoc. Pet. Geol., Bull.; (United States)

OSTI ID:6375352

Anderson, J H

Dolomitization and associated calcite dissolution are important controls on reservoir quality in coral reefs on the Nisku Formation. Average porosities of 13 to 15% and permeabilities of 3 darcys are recorded in the fully dolomitized reefs, while lower average porosities of 3 to 5% and permeabilities of 350 millidarcys are recorded in partly dolomitized reefs. Dolomitization occurred over a long period of burial and resulted in the formation of two major types of dolomites that are volumetrically significant. The first is characterized by matrix-selective, gray, cloudy, 20 to 150-..mu.. crystals that grade from scattered subhedral and euhedral rhombs to interlocking crystalline mosaics. The second major type of dolomite is characterized by pervasive, brown, cloudy, 60 to 300-..mu.. crystals that occur in the flanks of structurally updip reefs and throughout the downdip reefs. Concentration of dolomite crystals and dissolution of individual rhombs along stylolites indicate that the matrix dolomite initially formed at shallow depths. As dolomitization progressed, dolomite recrystallization and cementation along with extensive calcite dissolution resulted in dramatic increases in porosity and permeability. Calcite dissolution continued after dolomitization ceased, but much of the dissolution is coeval with dolomitization. Late dolomites and secondary porosity in the Nisku reef trend increase in abundance down structural dip, toward the southwest. Thus, much of the dolomite and late Paleozoic and early Mesozoic when the regional structure tilted to the southwest. Although all Nisku reefs form stratigraphic traps, late diagenetic overprints in some significantly enhanced their reservoir quality.

• Research Organization: Univ. of Texas, Austin
• OSTI ID: 6375352
• Report Number(s): CONF-8304200-
• Conference Information: Journal Name: Am. Assoc. Pet. Geol., Bull.; (United States) Journal Volume: 67:3
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
020200* -- Petroleum-- Reserves
Geology
& Exploration
03 NATURAL GAS
030200 -- Natural Gas-- Reserves
Geology
& Exploration
ALBERTA
ALKALINE EARTH METAL COMPOUNDS
CALCIUM CARBONATES
CALCIUM COMPOUNDS
CANADA
CARBON COMPOUNDS
CARBONATE MINERALS
CARBONATES
DEVONIAN PERIOD
DISSOLUTION
DOLOMITE
GEOLOGIC AGES
GEOLOGIC STRUCTURES
GEOLOGIC TRAPS
MAGNESIUM CARBONATES
MAGNESIUM COMPOUNDS
MINERALS
NORTH AMERICA
ORIGIN
OXYGEN COMPOUNDS
PALEOZOIC ERA
POROSITY
REEFS
RESERVOIR ROCK