Cementation and diagenetic fluid mixing in South Brae oil field, North Sea, U. K
- Glasgow Univ. (Scotland)
- SURRC, East Kilbride (England)
The reservoir rocks in the Brae oil field consist of small overlapping submarine fans that form a sediment apron along the western margin of the Viking graben. It is located in the United Kingdom sector of the North Sea and lies 240 km east of the Orkney Islands. Carbonate cementation was the first major diagenetic event, followed closely by compaction of the sediment and a minor development of authigenic chlorite and pyrite. This was ensued by a widespread long-term secondary quartz overgrowth phase. A dissolution event followed subjecting feldspar, the micaceous minerals, and the early calcite cement to varying amounts of alteration. Clay minerals, principally illite and kaolinite, and some late calcite and dolomite infilled these dissolution pores at a later stage. Progressive burial diagenesis has resulted in extensive reaction between the sediment and pore fluids, and the history of cementation is preserved in the isotopic composition of the authigenic calcite. Cemented horizons, veins, and concretions were analyzed. Concretions display the most depleted isotopic carbon values, with the carbon becoming progressively lighter towards the margin ({minus}9.53 to {minus}10.51% PDB). The veins have a similar depleted signature of {delta}{sup 13}C ({minus}8.4% PDB) but show the most positive {delta}{sup 18}O PDB and {delta}{sup 18}O SMOW, perhaps indicating their formation by a later pore fluid source enriched in {delta}{sup 18}O. These values are not indicative of an end-member CO{sub 2}, source but may suggest a mixture of bacterial fermentation and sulfate reaction. These calcites have formed in a marine environment, but the mean {sup 87}Sr/{sup 86}Sr calcite ratio (0.7119) is considerably more radiogenic than {sup 87}Sr/{sup 86}Sr of Upper Jurassic marine waters (0.707). The radiogenic strontium may have been contributed by the dissolution of silicates, such as feldspar supplying {sup 87}Sr//{sup 86}Sr (0.720).
- OSTI ID:
- 6688353
- Report Number(s):
- CONF-900605-; CODEN: AABUD
- Journal Information:
- AAPG Bulletin (American Association of Petroleum Geologists); (USA), Vol. 74:5; Conference: Annual convention and exposition of the American Association of Petroleum Geologists, San Francisco, CA (USA), 3-6 Jun 1990; ISSN 0149-1423
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
58 GEOSCIENCES
NORTH SEA
OIL FIELDS
RESERVOIR ROCK
DIAGENESIS
UNITED KINGDOM
CALCITE
CARBON DIOXIDE
CARBONATE ROCKS
DISSOLUTION
DOLOMITE
ILLITE
ISOTOPE RATIO
KAOLINITE
PERMEABILITY
POROSITY
STRONTIUM 86
STRONTIUM 87
ALKALINE EARTH ISOTOPES
ALKALINE EARTH METAL COMPOUNDS
ALUMINIUM COMPOUNDS
ALUMINIUM SILICATES
ATLANTIC OCEAN
BETA DECAY RADIOISOTOPES
CALCIUM CARBONATES
CALCIUM COMPOUNDS
CARBON COMPOUNDS
CARBON OXIDES
CARBONATE MINERALS
CARBONATES
CHALCOGENIDES
CLAYS
ELECTRON CAPTURE RADIOISOTOPES
EUROPE
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
GEOLOGIC DEPOSITS
HOURS LIVING RADIOISOTOPES
INTERMEDIATE MASS NUCLEI
ISOMERIC TRANSITION ISOTOPES
ISOTOPES
MAGNESIUM CARBONATES
MAGNESIUM COMPOUNDS
MINERAL RESOURCES
MINERALS
NUCLEI
OXIDES
OXYGEN COMPOUNDS
PETROLEUM DEPOSITS
RADIOISOTOPES
RESOURCES
ROCKS
SEAS
SEDIMENTARY ROCKS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
STABLE ISOTOPES
STRONTIUM ISOTOPES
SURFACE WATERS
WESTERN EUROPE
020200* - Petroleum- Reserves
Geology
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580000 - Geosciences