Empirical Analysis of Thermal Maturation and Petroleum Generation Kinetics in Cretaceous Source Rocks of the Mid-Benue Trough, Nasarawa State, North Central Nigeria

The Mid-Benue Trough in Nasarawa State contains Cretaceous lacustrine and marine source rock intervals whose petroleum generation kinetics and maturation history have not been empirically characterised, limiting quantitative petroleum system modelling in this frontier basin. This study provides an empirical analysis of thermal maturation and petroleum generation kinetics for Cretaceous source rocks of the Mid-Benue Trough. Outcrop and shallow borehole samples of Eze-Aku Shale and Awgu Shale were characterised by Rock-Eval pyrolysis to determine total organic carbon, hydrogen index, oxygen index, and production index. Vitrinite reflectance measurements on polished whole rock sections provided absolute maturity calibration. Kinetic parameters for primary cracking of kerogen to oil and gas were determined from open-system pyrolysis experiments at four heating rates (0.5, 2, 5, and 20 degrees per minute) using an automated pyrolysis-gas chromatograph. First-order Arrhenius activation energy distributions were fitted to the experimental data using the Ungerer and Pelet distributed activation energy model. Results indicate a mean activation energy of 214 kilojoules per mole with a standard deviation of 16.4 kilojoules per mole for the Eze-Aku Shale kerogen, consistent with Type II marine kerogen composition confirmed by elemental analysis. Basin modelling incorporating the calibrated kinetic parameters and a heat flow history constrained by vitrinite reflectance depth profiles predicts oil generation onset at 2,100 to 2,400 metres burial depth, depending on local geothermal gradient. Keywords: thermal maturation, petroleum generation kinetics, Cretaceous source rock, Mid-Benue Trough, Nasarawa State.