Abstract
Upper Cretaceous shales partially exposed in the northern fringes of the Dahomey Basin are well developed in the subsurface in Southwestern part of the basin where Agbau-1 well is sited. These shales were evaluated in respect to their paleoenvironments and potentials for hydrocarbon using foraminiferal assemblages, biomarkers and Rock Eval pyrolysis studies. The dominance of benthonic foraminifera species suggests a shallow marine environment and high percentage of calcareous to arenaceous benthic www.eujournal.org 195 foraminifera indicate high water salinity and hypersline environment. Dysoxic oxygen condition is also prevalent probably because most of the benthic foraminifera recovered are epifauna that live in a reduced oxygen condition. 1.90 wt%, 244 mgHC/gTOC and 429℃ average values of total organic carbon, hydrogen index and Tmax reveal that the Upper Cretaceous shales have relatively fair to good organic matter, predominantly Type II-III kerogen and currently immature. Though three is a trend of an increase in maturity down the hole. All the steranes have uniform distributions (C27>C28>C29), suggesting a relatively higher input from the marine red algae and a low level of land plant contribution to the source organic matter. Pristane/phytane ratios and C29/C27 steranes confirmed the organic matter type to be a Type II/III and anoxic source rock depositional condition as well as a reducing diagenetic system in the sediment water column. The Upper Cretaceous shales in Dahomey Basin can be targeted for exploration as an unconventional petroleum resource.
Highlights
Introduction Hydrocarbon production from the prolificNiger Delta basin has been the most valuable source of income and energy in Nigeria
ISSN: 1857-7881 (Print) e - ISSN 1857-7431 foraminifera recovered are epifauna that live in a reduced oxygen condition. 1.90 wt%, 244 mgHC/gTOC and 429°C average values of total organic carbon, hydrogen index and Tmax reveal that the Upper Cretaceous shales have relatively fair to good organic matter, predominantly Type II-III kerogen and currently immature
Results from individual foraminifera counts are eight (8) planktic, thirty-one (31) calcareous and eighteen (18) Arenaceous (Fig. 4). These results showed that the calcareous foraminifera species were abundant and diverse at the deeper part of the well while the arenaceous foraminifera species dominates the shallow portion of the well (Fig. 4)
Summary
Introduction Hydrocarbon production from the prolificNiger Delta basin has been the most valuable source of income and energy in Nigeria. Rigorous exploration activities in the adjacent frontier basins and deeper Cretaceous plays are among the few options of supplementing the depleting Niger Delta resources. The discovery of oil in offshore Cretaceous sediments of the Ise Formation in the Gulf of Guinea has increased the study and search for oil in the eastern Dahomey Basin. Further studies on two Cenomanian shales samples in the underlying Abeokuta Formation (presents day Afowo formation) by (BeicipFranlab, 1994 and Adeoye et al, 2020) showed a TOC range of 4.2 and 7.1 wt.% with HI values of 324 and 531 mg HC/gTOC as potential resources for more discovery of oil and gas to increase the national reserve. The eastern section of the Dahomey basin contains more hydrocarbon resources in term of extensive tar sand deposits within the Abeokuta Group (Ise, Afowo and Araromi Formations), which extends over a belt of 120 km long (Enu, 1987). The eastern section of the Dahomey basin contains more hydrocarbon resources in term of extensive tar sand deposits within the Abeokuta Group (Ise, Afowo and Araromi Formations), which extends over a belt of 120 km long (Enu, 1987). Ekweozor and Nwachukwu (1989) and Ekweozor and Telnaes (1990) examined the origin and composition of the tar sand from the Abeokuta Group
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