Evaluation of Geothermal Gradient Variations and Their Implications for Hydrocarbon Maturation in the Chad Basin, Borno State, North East Nigeria

The Chad Basin in Borno State, North East Nigeria, is a frontier intracratonic sedimentary basin where limited exploration drilling has constrained understanding of the geothermal regime and its control on source rock maturation. This study evaluates geothermal gradient variations across the Nigerian sector of the Chad Basin and assesses their implications for hydrocarbon generation and preservation. Bottom hole temperatures from eleven petroleum exploration wells drilled in the Bornu sub-basin between 1974 and 2018 were corrected for drilling disturbance using the Horner correction method. Equilibrium temperature profiles were constructed for each well, and geothermal gradients were calculated for basement-to-surface intervals. Basin-wide heat flow values were computed using corrected temperatures combined with formation thermal conductivity measurements from drill cuttings. Results indicate geothermal gradients ranging from 22 to 38 degrees Celsius per kilometre across the basin, with the highest values associated with zones of thinned crystalline basement in the Yobe sub-basin. Burial history and maturation modelling using a calibrated BasinMod 2D workflow indicate that Late Cretaceous lacustrine shales enter the oil window between 2,200 and 2,800 metres burial depth, generating a broad maturation window across the basin centre. The study concludes that geothermal conditions in the Chad Basin are broadly favourable for oil generation and recommends focused thermal modelling in deep sub-basin depocentres as priority exploration targets. Keywords: geothermal gradient, hydrocarbon maturation, Chad Basin, Borno State, source rock.