Oil characteristics and the onset of biodegradation on the eastern flank of the Malay Basin, offshore Peninsular Malaysia

There is a great variety of oil types in the eastern Malay Basin flank area. We observe heavier, hence lower quality, oil at shallow reservoir levels, but mostly light oil in deeper petroleum reservoirs. The oils are characterized by varying amounts of wax, a fairly low sulphur content and, occasionally, significant levels of CO2. Many of the shallow reservoir oils appear to have been derived from originally light oils that suffered from biodegradation, and are slightly enriched in sulphur, compared to the native oils. Oils in reservoirs with a temperature of less than 75 °C appear to have been biodegraded, whereas hotter reservoirs with temperatures above 90 °C appear to have been unaffected.