The re-evaluation of the source rock potential of Kolmani Field using outcrop data, ditch cutting data, and 2D seismic data for enhanced hydrocarbon prospectivity

The Kolmani Field, Gongola Basin, Upper Benue Trough, Northeast Nigeria has yielded positive results in regard to gas generation potential, but the source rock viability is questionable. To examine this issue, an in-depth geochemical analysis of the outcrop samples of the Bima, Yolde, and Pindiga Formations and ditch cuttings of 4230–6970 ft depth interval across Pindiga and Yolde Formation were conducted. The materials were analysed using total organic carbon (TOC) and Rock Eval Pyrolysis. The calculated TOC of the outcrop data includes shale samples from the Pindiga Formation with a TOC ranging from 0.03 to 0.54 wt%, Yolde Formation shale samples with a TOC ranging from 0.03 to 0.07 wt%, and Bima Sandstone shale samples with a TOC ranging from 0.04 to 0.09 wt% while the ditch cuttings TOC spans from 0.54 to 0.85 wt%. All outcrop samples indicated poor TOC while that of ditch cuttings indicated fair to moderate TOC. The Tmax displayed two different types of source rocks: immature (between 415 and 420 °C) and mature (435–473 °C). The kerogen type are Type III and Type IV kerogen, which are gas-prone and inert in nature, respectively. While the HI (S2/TOC) values revealed gas, the remaining hydrocarbon potential S1 (mgHC/g), suggested weak oil potentials. The normalised oil content (S1/TOC) indicates that hydrocarbons have been expelled.