Papers by Agwom Yohanna madaki
Energy & Fuels, 2021
A petrophysical evaluation of caprock pore characteristics and seal capacity is critical for geol... more A petrophysical evaluation of caprock pore characteristics and seal capacity is critical for geologic storage of CO2. In this study, integration of X-ray diffraction, mercury injection capillary pressure (MICP), and spontaneous imbibition analyses is used to evaluate the pore characteristics and seal capacity of shale samples from the Ilaro formation, which could serve as a seal for CO2 injected into the reservoir units of the eastern Dahomey basin. X-ray diffraction reveals the samples as clay-rich and early diagenetic, while spontaneous imbibition reveals pore connectivity heterogeneity. MICP analysis shows the samples as being characterized by a low breakthrough pressure and reveals the mesopore dominance with majority of pore volumes dominated by 5 to 10 nmsized pore throats. Furthermore, high CO2 column heights are obtained from conversion of MICP data (at 20% saturation) for mesopore-dominated samples containing ankerite and kaolinite. The study reveals that should injected CO2 migrate upward from the reservoir units of the onshore eastern Dahomey basin, portions of the Ilaro formation may function as a good seal due to the mesopore mineralogical composition influence on the CO2−brine−rock interaction. This result should therefore serve as an important insight for future caprock sealing studies conducted on the onshore eastern Dahomey basin.
The Lower Congo basin’s Albian – Early Cenomanian Pinda group is the most productive carbonate re... more The Lower Congo basin’s Albian – Early Cenomanian Pinda group is the most productive carbonate reservoir within the West African margin basins. However, the understanding of its diagenetic features is very limited. Core samples obtained from the Democratic Republic of Congo offshore section of the formation were petrographically analysed to image the sedimentary facies along with diagenetic processes and links to reservoir quality. The sedimentary facies obtained indicate a dominant lagoon sedimentation within the oolitic – siliciclastic ramp. Diagenetic processes detected include micritization, dolomitization, dissolution, cementation, and compaction. Diagenetic links to reservoir quality within the facies is established in the dominant occurrence of moldic pores which have been occluded either by calcite or dolomite cement, leaving three facies with poor reservoir quality. The facie exempted from this class possesses a fair reservoir quality linked to microporosity within its sand...
Arabian Journal of Geosciences, 2021
Herein, we investigated the genesis of Toungo flake graphites in the basement complex of Adamawa ... more Herein, we investigated the genesis of Toungo flake graphites in the basement complex of Adamawa Massif, northeastern Nigeria, and evaluated their industrial quality. Field and laboratory evidences show that the foliated amphibolite and gneisses are the main rock unit hosting the graphite and are occasionally bordered by pegmatite. Petrographic data show that graphites in Mayo Butale (MB) and Walon Kole (WK) are associated with chlorite, suggesting a role of CO2-bearing aqueous fluids in the origin of the large and minor graphite flakes under regional greenschist facies conditions. The hydration processes related to the formation of chlorite drove the fluid composition toward CO2 saturation and graphite precipitation. The close association of the graphite with pegmatites shows that graphite precipitation occurs synchronously with melt crystallization during cooling, suggesting that C-bearing fluids exsolved from the parent melts of pegmatites. The flake sizes of Walon Kole (WK) and Mayo Butale (MB) graphites range between ~0.2 and 0.6 mm, reflective of high-quality flakes. Their light bulk densities (WK = 2.38 g/cm3; MB = 2.29 g/cm3) make them less susceptible to crushing and cracking, while their porosities (WK = 3.25–5.26%; MB = 1.4–6.88%) are suitable for use in refractory industries. Given their low moisture contents (WK = 0.27%; MB = 0.16%) and volatile matter (WK = 2.1%; MB = 4.90%), the graphites can be used to produce silicon carbides, fire-retardant additives, as well as refractory bricks, lubricants, automobile brakes, clutches, and pencil lead. Their ash contents (WK = 15%; MB = 18%) and compressive strengths (WK = 23 N/mm2; MB = 16.5 N/mm2) connote mechanical strength and good workability, thus suitable for producing crucibles, coatings of TV tube, and conductive concrete used in making cement. The graphite’s thermal shock resistance is satisfactory for use in refractory industries as it withstood severe cycles of heating. Taken together, the quality of Toungo graphites conform to the minimum industrial quality standards but can be beneficiated to meet the optimum industrial grades.
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Papers by Agwom Yohanna madaki