R. J. Pottorf1
(1) Exxon Production Research Company, Houston, TX
Abstract: Hydrocarbon migration analysis using fluid inclusions from the Tampen Spur, northern North Sea
The Tampen Spur study area, situated east of the East Shetland Basin in the northern North Sea, includes Middle Jurassic Brent reservoirs of the Ellon, Grant, Alwyn, North Alwyn, Strathspey, and South Brent Fields. The Brent reservoir at fields nearest the adjacent trough of the Oseberg kitchen contains oil with a free gas cap (Ellon, Grant), whereas the reservoir at other studies fields contains only undersaturated oil. The principal hydrocarbon source rock is the Upper Jurassic Kimmeridge shale, which ranges from immature at structural highs to gas-generation maturities in the deepest parts of the kitchen. ‘Drainage analysis on the top of the Brent Group structure suggests a potential hydrocarbon charge coming from the kitchen to the Ellon, Grant and Alwyn Fields, and a fill-and-spill scenario progressing northwards form these three fields (deep) to the others (shallow).
To reconstruct the hydrocarbon migration history of the Tampen Spur, fluid inclusions in the Brent sandstones were analyzed using fluid inclusion volatiles and standard petrographic/microthermometric techniques. Core samples from 14 wells were chosen to include the variation in fluid types (gas, oil, water) encountered within the fields. The key results are:
- Most of the water-leg samples show evidence of hydrocarbon migration or paleo-oil accumulations.
- Changes in hydrocarbon compositions and fluid inclusion occurrences observed along the migration pathway probably result from the gradual displacement of earlier reservoired oil by later generated and migrated gas. Fields closest to the kitchen have been more severely impacted by gas migration.
- Integrating fluid inclusion results with the thermal/burial histories suggests that hydrocarbon migration began approximately 55-65 Ma in the area.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana