Unveiling the Mysteries of Fractured Basement Oil Residues in the Upper Benue Trough, Nigeria

Abstract

This study offers additional evidence for the occurrence of oil residues within fractures of the basement rocks in the Upper Benue Trough, Nigeria. The data suggests that the observed oil residues were originally generated as light oils, which were later biodegraded into heavy oils. These Upper Benue Trough's oil stains are a valuable tool for hydrocarbon exploration in the region as they indicate the existence of a petroleum system in the basin. We find a strong similarity to the proportions of C27, C28, and C29 regular steranes of oils found in the sandstones and shales of the Bima Formation in the Upper Benue Trough when we plot the relative quantities of these steranes of the investigated basement rock oil types on a ternary graph. This shows a positive correlation between the oils from the Bima Formation and the fractures found in the Precambrian basement rocks. Additionally, the studied basement oils and the oils extracted from the Bima Formation had comparable sterane maturity criteria. Again, trisnorhopane thermal indicators are also identical in the studied oils. The C3222S/(22R+22S) homohopane isomerization ratio and Ts: Tm ratio of the examined basement rock oils are similar to those of the oils extracted from the Bima Formation's shales, suggesting that the Bima Formation's shale is the primary source rock for the examined basement rock oils. Oils have also been reported to develop similarly in the Precambrian basement rocks of the Bongar Basin in the Chad Republic, known as basement-buried hills. As members of the West African rift basins, the Nigerian Upper Benue Trough and the Bongar Basin share genetic ancestry. As a result, we should be looking for exploratory opportunities that mimic the Bongor Basin's basement buried hills, which are currently the location of commercial oil production.