PETROLEUM GEOCHEMISTRY OF LATE CRETACEOUS AND EARLY TERTIARY SHALES PENETRATED BY THE AKUKWA‐2 WELL IN THE ANAMBRA BASIN, SOUTHERN NIGERIA†

Abstract

The concentration, type and thermal maturity of organic matter from the Imo Shale, Nkporo Shale and the upper parts of the Nkalagu Formation which were penetrated by the Akukwa‐2 well are presented. The organic carbon content ranged from 0.4–3.5%. The kerogens from the various formations were of the humic and mixed varieties. Evidence from independent thermal maturity parameters (namely, average vitrinite reflectance (R0%), Tmax and transformation ratio from Rock‐Eval, n‐alkanes distribution pattern, and hopane “fingerprint”) combined to locate the top of the ‘oil window’ within the Nkporo Shale at a depth of approximately 2,000 m from the surface. This corresponds to a threshold temperature of circa 65°C.Sedimentary organic matter which is favourable for both gas and oil generation is therefore probably abundant in the Anambra basin. Hydrocarbon reservoirs are possibly located at relatively shallow depths where accumulations of heavy oils may also be expected.