Characterisation of Geothermal Gradient Variations in the Bornu Basin and Implications for Hydrocarbon Maturation

The thermal regime of the Bornu Basin, which underlies portions of Borno, Yobe, and Jigawa states in North East Nigeria, exerts fundamental control on the maturation level of organic-rich source rock intervals and the prospectivity of identified hydrocarbon leads within this underexplored Cretaceous basin. This study characterises geothermal gradient variations in the Bornu Basin using bottom-hole temperature data corrected for drilling disturbance, vitrinite reflectance measurements on ditch cuttings and core, and published heat flow estimates. Bottom-hole temperatures from twenty wells distributed across the basin were corrected using the Horner plot method, and geothermal gradients were calculated for each well. Vitrinite reflectance profiles with depth were constructed from measured values on cuttings samples spanning the Fika Shale and underlying units. One-dimensional burial and thermal history models were constructed at five representative well locations using BasinMod software, calibrated to match measured vitrinite reflectance and temperature profiles. Transformation ratio modelling of Type II kerogen was conducted to assess whether identified source intervals have entered the oil generation window. The study identifies a zone of elevated heat flow in the northeastern portion of the basin possibly associated with crustal thinning, which if confirmed by additional data substantially improves source rock maturation levels in this area. Findings are submitted to the Nigerian National Petroleum Corporation Upstream Investment Management Services. Keywords: geothermal gradient, vitrinite reflectance, basin modelling, Bornu Basin, hydrocarbon maturation.