石油および環境バイオテクノロジージャーナル

概要

Source Rock Evaluation in The Lake Chad Area of the Bornu Basin, Nigeria

Ola Peter Sunday, Adekoya John Adeyinka and Olabode Solomon Ojo

Source rock evaluation of the Lake Chad area of the Bornu Basin which contains a comparatively thicker sedimentary succession based on interpreted seismic and gravity data was undertaken in this study. A total of twenty-nine shale samples from three wells (Kutchali-1, Faltu-1 and Herwa-1) were analysed to arrive at the bulk geochemical properties, organic matter particles and vitrinite reflectance (VR) data of the strata penetrated by the wells. The Lake Chad area appears to contain the main ingredients required to make a rich source rock with over 96% of the total organic carbon (TOC) values being in the range of 0.63-2.88 wt% and over 95% having Tmax greater than 435°C in most of the sampled intervals. The variation of Tmax and VR with depth in the wells reveals irregular decreases or subtle decreasing trends that are suggestive of cooling in the basin’s thermal history probably as a result of uplift and erosion. The uplift could have been caused by epeirogenic movement or by folding related to the Santonian inversion witnessed by the West African Rift Subsystem. In terms of hydrocarbon generation potential, most of the samples have HI values greater than 50 mgHC/g TOC, but generally less than 200 mgHC/g TOC. These HI values suggest dominance of Type III with less Type II Kerogen; thus, a predominantly predominantly gas prone area. A study of some bulk geochemical parameters (TOC, Tmax and HI) of the three study wells has revealed that the succession penetrated by one of them (Faltu-1 well) contains several potential gas source intervals and two potential oil source intervals with the latter probably lying between 2500 m and 3000 m depth.