The assessment of potential source rocks of Maastrichtian Araromi formation in Araromi and Gbekebo wells Dahomey Basin, southwestern Nigeria
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Date
2019
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Heliyon
Abstract
Drilled core samples of the Araromi Formation in the eastern Dahomey basin penetrated by Araromi and Gbekebo
exploratory wells were investigated to establish the source rocks potentials in the onshore area of the basin. The
sediments are of Maastrichtian age deposited in the shallow marine environment with varying thicknesses.
Rock-Eval data of forty seven (40) shales give Total Organic Carbon (TOC) range of 0.50ā4.78 wt%, Hydrogen
Index (HI) value range of 1 - 327mgHC/gTOC, Tmax values from 398 Cā437 C and Source Potential (SP) values
range from 0.01 - 14.56kgHC/ton of rock. The maceral compositions of the shales are liptinite (av. 26.0%),
abundance vitrinite (av. 38.1%) and inertinite (av. 35.9 %) with vitrinite reflectance (VRo) ranging from 0.51 -
0.68 %Ro. Hydrocarbons and biomarkers results reveal a bimodal n-alkane envelope between (nC16 and nC18) and
(nC27 and nC29) suggesting organic matter of mixed origin of algae and higher plant generally in the two well. The
Significant contribution of marine algae in the deeper part of Gbekebo well was observed by the presence of C30
24-n-propyl cholestane (%C30 sterane range from 0.45 to as high as 5.23%).
Integration of the Rock-Eval, organic petrology and biomarkers data reveal that the kerogen constituents of the
source rocks in Araromi well are mainly Type II/III, III and IV with a high amount of inertinite constituents
suggesting they have been reworked. Type II and II/III kerogen derived from marine algae are better preserved in
the deeper part of Gbekebo well located more southerly in the basin than in the Araromi well. The source rocks
are generally immature to marginally mature and hydrocarbon exploration effort should be targeted towards
Gbekebo well area where we have more promising potential source rocks capable of generating more hydrocarbons essentially at a deeper depth.
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Geochemistry Geology