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C/sup 13/-rich diagenetic carbonates associated with heavy-oil deposits

Conference · · Am. Assoc. Pet. Geol., Bull.; (United States)
OSTI ID:5922002
;
The isotopic composition of secondary calcites in 120 samples from biodegraded heavy-oil deposits of the Lower Cretaceous Mannville Group of Alberta ranged in sigma/sup 13/C from - 1.3 to + 14.1 per thousand PDB. The calcites postdate oil emplacement and are anomalously enriched in C/sup 13/ in comparison with common sedimentary and diagenetic carbonates associated with conventional oil pools and authigenic carbonates of other shallow Cretaceous sediments of Alberta. In contrast to previously reported occurrences of heavy carbonates (Moneray Formation, Kimeridge Clay of Dorset, Caspian syncline), the heavy-oil calcites are not related to organic-rich clayey sediments and no coexisting low /sup 13/C-carbonates were found. The API gravities of the biodegraded oil correlate with the sigma/sup 13/C values of the carbonate, suggesting a relationship between the biodegradation process and C/sup 13/-enriched cements. Different isotopic systematics were observed in 25 samples from other heavy-oil deposits (Indonesia, Malagasy, Brazil, Sicily, Zaire, California, Kentucky, Utah) whose sigma/sup 13/C ratios ranged from -21.6 per thousand to + 1.1 per thousand PDB. An explanation may involve oxidation of the paraffinic oil components by microorganisms producing alcohols, organic acids, and ketones. A change to anoxic conditions causes fermentation of these biodegradation products, leading to the formation of /sup 13/C-rich CO/sub 2/, which precipitates as heavy carbonate. If anoxic conditions are not achieved, oxidation will persist and lead to the formation of light carbonate cements. The detection and understanding of the formation mechanism of anomalously heavy carbonates can be useful in both future exploration strategy and exploitation of heavy oil deposits, particularly to enhanced recovery schemes based on CO/sub 2/ flooding.
Research Organization:
Univ. of Alberta, Edmonton
OSTI ID:
5922002
Report Number(s):
CONF-8506201-
Conference Information:
Journal Name: Am. Assoc. Pet. Geol., Bull.; (United States) Journal Volume: 69:5
Country of Publication:
United States
Language:
English

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Related Subjects

02 PETROLEUM
020200 -- Petroleum-- Reserves
Geology
& Exploration
04 OIL SHALES AND TAR SANDS
040201* -- Oil Shales & Tar Sands-- Site Geology-- (-1989)
ALBERTA
ALKALINE EARTH METAL COMPOUNDS
CALCITE
CALCIUM CARBONATES
CALCIUM COMPOUNDS
CANADA
CARBON 13
CARBON COMPOUNDS
CARBON DIOXIDE INJECTION
CARBON ISOTOPES
CARBONATE MINERALS
CARBONATES
CRETACEOUS PERIOD
DIAGENESIS
ENERGY SOURCES
ENHANCED RECOVERY
EVEN-ODD NUCLEI
FLUID INJECTION
FOSSIL FUELS
FUELS
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC FORMATIONS
ISOTOPE RATIO
ISOTOPES
LIGHT NUCLEI
MESOZOIC ERA
MINERALS
MISCIBLE-PHASE DISPLACEMENT
NORTH AMERICA
NUCLEI
OIL SAND DEPOSITS
OXYGEN COMPOUNDS
PETROLEUM
RECOVERY
STABLE ISOTOPES