Hydrocarbon prospectivity of Chad (Bornu) Basin, northeastern Nigeria: From the viewpoint of organic geochemistry and organic petrology

Posted on 2020-01-13 in Events
Jan 17, 2020

Please join us for a seminar this Friday January 17 at 3:30 pm in rm 155 Geology presented by guest speaker Adebanji Adegoke:

Hydrocarbon prospectivity of Chad (Bornu) Basin, northeastern Nigeria: From the viewpoint of organic geochemistry and organic petrology

The Chad (Bornu) Basin is a Cretaceous–Tertiary rift basin in northeastern Nigeria that is genetically related and has the same structural settings with the prolific Termit Basin in the Niger Republic. The Upper Cretaceous sediments in the Chad (Bornu) Basin were characterised using an integration of organic geochemical analyses and organic petrography. This is to provide a detailed overview of the characteristics of the sediments as potential source rocks. The Gongila and Fika sediments in the basin have TOC contents up to 2.37 wt.% and Hydrogen Index (HI) values largely below 200 mg HC/g TOC, suggesting that the sediments generally have only fair generative potential and contain Type III and Type IV kerogens. This is evidenced by palynofacies observations whereby the kerogen is characterised by large amounts of non-fluorescent AOM and phytoclasts. However, pyrolysis GC data indicate that some of the investigated samples, especially from the Fika shale contain mixed Type III/II kerogen, suggestive of mixed oil and gas potential, although gas being more dominant. The Gongila and Fika sediments have vitrinite reflectance and Tmax values in the range of 0.57–1.79 % and 433–498 ˚C, respectively, indicating early-mature oil window to late stage of gas window. Detailed geochemical analyses and organic petrography provide evidence for a mixed aquatic algae and terrigenous organic matter input deposited under environmental conditions that were mostly suboxic. Biostratigraphy and isotopic compositions revealed that the Fika sediments were essentially deposited in environments that ranged from coastal deltaic through fluvio-marine to shallow inner neritic. The sediments are also suggested to be deposited in palaeogeographic settings close to land. Some of the likely reasons for failure of hydrocarbon exploration activities in the Chad (Bornu) Basin, Nigeria, unlike in the Termit Basin in Niger Republic, despite their genetic similarities, include low primary bioproductivity and non-deposition or erosion of the more organically-rich Eocene to Oligocene sediments in the Chad (Bornu) Basin. Also, the igneous intrusions in the basin, which followed the Maastrichtian deformation episode, could have been responsible for the cessation of hydrocarbon generation, as the organic matter might have been “overcooked”.