Geophysical and Petrophysical Analysis of the Asu River Group Potential Source Rocks in the Southern Benue Trough

The Asu River Group, deposited during the Albian transgression in the Southern Benue Trough, is widely cited as a potential hydrocarbon source rock, yet its burial history, thermal maturity, and geophysical expression in the subsurface remain poorly characterised, hindering petroleum system evaluation in Cross River and Ebonyi states. This study integrates geophysical log analysis from five exploration wells with two-dimensional basin modelling to evaluate the source rock potential and thermal maturity of the Asu River Group. Gamma-ray and resistivity logs were used to identify and correlate the Asu River Group across the well locations. Geochemical data from available sidewall core samples, including total organic carbon content, Rock-Eval pyrolysis parameters, and organic petrography observations, were compiled to characterise source rock richness and type. TOC values in the Asu River Group range from 0.8 to 3.2 weight percent, classifying intervals as fair to very good source rocks. Basin modelling using PetroMod software incorporated published vitrinite reflectance data as maturity calibration points to constrain heat flow history. Results indicate that the Asu River Group reached peak oil generation at approximately 70 million years ago in the deepest parts of the Calabar Flank sub-basin. A residual present-day maturity window of 0.6 to 1.1 percent Ro in the deepest wells confirms that the source rock remains in the oil-generative window. Geophysical identification of the source rock interval is proposed using a combination of high gamma-ray and low resistivity log signatures for basin-wide mapping. Keywords: Asu River Group, source rock, petroleum system, Southern Benue Trough, basin modelling