Well Number

Sample depth

    Oil sample characteristics

Tectono-strat unit (see Richards and Hillier, 2000)

14/5-1A

1728 m

Biodegraded, but of mature character. Corresponding Type II source rock contained predominantly structureless organic matter; similar to that in a side-wall core sample analysed from 2677m below rig floor (within the uppermost parts of  the late syn-rift sequence).

Middle post-rift

14/5-1A

1948 m

Biomarkers exhibit a high degree of maturity, and show the oil is derived from the early post-rift, Type I source rock

Early post-rift

14/5-1A

1950 m

The sample is immature as indicated by presence of the thermally unstable compound C27-22,29,30-trisnor-17b(H)-hopane, the concentration of which reaches zero at the earliest oil window. The differences between this and the sample from 1948 m may be due to the fact that part of the organic matter in this interval represents indigenous, immature material, whereas another part is derived from migration of low mature material.

Early post-rift

14/10-1

?3000 m

Oil (API 27.1) was collected at surface during terminal logging. The complete sterane isomerisation observed indicates that this oil has been expelled from a mature source rock. This source rock contained structureless organic matter with a significant algal component, and is equivalent to the Type I lacustrine claystones found in the the early post-rift source rock interval in Well 14/5-1A. However, the source rock interval from which this recovered oil was derived was apparently more mature than the early post-rift source rocks analysed from well 14/5-1A.

Late syn-rift

14/9-1

1830 m

Oil was centrifugally spun from a core sample. This oil has an early mature, highly paraffinic composition, and has been derived from a Type I lacustrine source rock. The oil is carbon isotope depleted, and is similar in nature to the Valanginian to Barremian source rocks comprising the lowermost part of the early post-rift succession recorded in Well 14/5-1A. The oil is also isotopically similar to the oil recovered at surface in Well 14/10-1.

Middle post-rift

14/24-1

1790 m

Post-well geochemical analyses indicate that a sandstone from near the base of the middle post-rift sequence contained traces of hydrocarbons that were not detected during drilling, presumably due to their very low concentration (although dull gold to yellow fluorescence was noted while drilling through the underlying source rocks). These hydrocarbons are characterised by normal alkanes with a mature configuration, and do not resemble the indigenous hydrocarbons detected in the immediately underlying claystones. They probably represent migrated hydrocarbons originating from a deeper, mature zone of the underlying Type I claystones.