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.

Petroleum potential of campano-maastrichtian shales of Anambra Basin, south astern Nigeria

“…Most of these works were carried out by oil companies operating in the area, but with only very few publication on source rock which have proved to be great geological interest and controversial Akaegbobi (1995). It was also observed that some sediment sample in the Anambra Basin show very low vitrinity reflectance, Ekweozor & Gormly (1983). This allows the assumption that the formation of the petroleum hydrocarbon took place under low temperature condition.…”

“…Anambra basin is a cretaceous depocenter containing thick sequences of elastic sediment ranging from bituminous shales lignites through sandstone and marl and it's Paleo-geographical strategic positioning as the proto-Niger Delta provides and ideal ground for geochemical evaluation of shales as oil/gas prone source rock. Various published work e.g Ekweozor and Gormly [1983) Petters and Ekweozor (1982) have revealed that the Campano-Maastrichtian Nkporo shale exhibit characteristics of potential hydrocarbon source system for a series of oil/gas and condensate shows found within Ajali sandstone…”

“…Olade (1975), Akaegbobi et al [2000]. The basin summary has been given by various workers, Agagu (1986), Agagu andEweozor (1980), Agagu etal (1986) Ekweozor and Gormly (1983); Avbovbo (1978a). The sediment infill of the southern Nigeria Basin has been controlled by three main tectonic phases.…”

Organic geochemical evaluation of the oil/gas-generative potential of organic matter in Cretaceous strata from the Lower Benue Trough, Nigeria

“…1), which were formed as a result of the Santonian tectonic inversion. The western part of the lower Benue Trough consisting of the Anambra Basin has been studied in terms of geology, stratigraphy and petroleum system (Reyment, 1965;Short and Stauble, 1967;Murat, 1972;Agagu;Agagu and Ekweozor, 1982;Petters and Ekweozor, 1982;Whiteman, 1982;Ekweozor and Gormly, 1983;Ojoh, 1990;Nwajide and Reijers, 1996).…”

Composition of Smectite from Maastrichtian Sediment of the Afikpo Basin, southeast Nigeria

“…According to Kulke (1995), petroleum exploration in this basin was provoked as a result of existence of surface seeps dating back to the early 1930s. Nevertheless, due to the Santonian inversion and prevalence of continental sediments, including discoveries in the prolific Niger-Delta, the exploration and exploitation for petroleum has been ongoing in this area (Doust and Omatsola, 1990;Ekweozor and Gormly, 1983;Haack et al, 2000;Ugwueze, 2015). The first marine transgression in Nigeria occurred during the middle Albian.…”