Cementation and diagenetic fluid mixing in South Brae oil field, North Sea, U. K

Conference · Tue May 01 04:00:00 EDT 1990 · AAPG Bulletin (American Association of Petroleum Geologists); (USA)

OSTI ID:6688353

McLaughlin, O M; Haszeldeine, R S ^[1]; Fallick, A E; Rogers, G ^[2]

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1. Glasgow Univ. (Scotland)
2. 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--
• Conference Information: Journal Name: AAPG Bulletin (American Association of Petroleum Geologists); (USA) Journal Volume: 74:5
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
020200* -- Petroleum-- Reserves
Geology
& Exploration
58 GEOSCIENCES
580000 -- Geosciences
ALKALINE EARTH ISOTOPES
ALKALINE EARTH METAL COMPOUNDS
ALUMINIUM COMPOUNDS
ALUMINIUM SILICATES
ATLANTIC OCEAN
BETA DECAY RADIOISOTOPES
CALCITE
CALCIUM CARBONATES
CALCIUM COMPOUNDS
CARBON COMPOUNDS
CARBON DIOXIDE
CARBON OXIDES
CARBONATE MINERALS
CARBONATE ROCKS
CARBONATES
CHALCOGENIDES
CLAYS
DIAGENESIS
DISSOLUTION
DOLOMITE
ELECTRON CAPTURE RADIOISOTOPES
EUROPE
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
GEOLOGIC DEPOSITS
HOURS LIVING RADIOISOTOPES
ILLITE
INTERMEDIATE MASS NUCLEI
ISOMERIC TRANSITION ISOTOPES
ISOTOPE RATIO
ISOTOPES
KAOLINITE
MAGNESIUM CARBONATES
MAGNESIUM COMPOUNDS
MINERAL RESOURCES
MINERALS
NORTH SEA
NUCLEI
OIL FIELDS
OXIDES
OXYGEN COMPOUNDS
PERMEABILITY
PETROLEUM DEPOSITS
POROSITY
RADIOISOTOPES
RESERVOIR ROCK
RESOURCES
ROCKS
SEAS
SEDIMENTARY ROCKS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
STABLE ISOTOPES
STRONTIUM 86
STRONTIUM 87
STRONTIUM ISOTOPES
SURFACE WATERS
UNITED KINGDOM
WESTERN EUROPE