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Integrated Basinal-Scale Study on Potential Shale Plays in Abakaliki Fold Belt and Calabar Flank, Nigeria

Abstract

Conventional crude oil resources are becoming depleted and difficult to find, dwindling price of crude oil and increasing demand for clean energy is of great concern globally. Sparse information are available on the occurrence of shale gas and shale oil in Nigeria, these challenges have triggered the search for them in the inland basins of Nigeria. This study is aimed at identifying shale plays in Abakaliki Fold Belt and Calabar Flank. Geologic and geochemical characterization of shale formations was conducted in order to define the shale oil/gas formations to be evaluated. Stratigraphic (well) data, vitrinite reflectance, downhole temperature dataset and 2D seismic lines were obtained for subsurface information and calibration of twenty-one (21) exploration wells. Integration of 2D seismic reflection profiles and simulated basin modelling was used to characterize the shale play types. Elemental analysis, mineralogical composition and pore space morphology of the samples were determined using Energy Dispersive X-ray Fluorescence analysis, Fourier Transform Infrared Spectroscopy and Scanning Electron Microscopy respectively. Preliminary studies identifies Eze-Aku Shale (Abakaliki Fold Belt) and Ekenkpon Shale (Calabar Flank) as a potential shale play. Simulated models for Abakaliki Fold Belt showed that the Eze-Aku Shale entered hydrocarbon generation window in the Late Cretaceous Era whereas main hydrocarbon generation from Ekenkpon Formation occurred in the Late Cretaceous Era-Paleocene Epoch. Three main play types involving the Eze-Aku Shale and Ekenkpon Shale as source are envisaged. The distribution of overpressures shows that the deeply buried Eze-Aku and Ekenkpon Shale are within overpressured zone. The mineralogy of Eze-Aku Shale and Ekenkpon Shale samples is dominated by more than 30wt.% silica content, thus suggesting favourable conditions for multiple fractures during hydraulic fracking. The results of Fourier Transform Infrared Spectroscopy show that quartz, calcite and kaolin mineral group are the major mineral components present in the samples. The pore space morphology of the samples indicates pore diameters within micropore and mesopore throat range and indicative of the retention capacity of the samples. This study identifies deeply buried Eze-Aku Shale (Abakaliki Fold Belt) and Ekenkpon Formation (Calabar Flank) as exploration targets that could hold huge amount of shale gas and shale oil in the inland basins of southeastern Nigeria.