Fluid remobilization from deep sedimentary basins and its implications for hydrocarbon generation in the Benue Trough, Nigeria: Preliminary insights into associated natural hydrogen potential

Hydrothermal fluid migration from sedimentary basins records basin evolution and guides exploration. These fluids enhance thermal maturation of organic matter and contribute to natural hydrogen generation. Passive oil seeps in the outcropping fractured basement of Gombe Inlier strongly suggests the existence of mature source rocks at depth, hence the need for basin modeling. A regional 2D cross section of the Gongola Sub-basin was constructed using field observations, a 2D seismic profile calibrated with data from the Kolmani River-1 well (2787 m), and gravity data. The main source rocks include lacustrine shales of the pre-Bima, Bima, and marine black shales of the Pindiga Formations. Modeling results show that pre-Bima and Bima source rocks are overmature and reached peak oil generation during the Maastrichtian. The Pindiga Formation remains immature to marginally mature, except in deeper zones with sufficient burial. Local thermal anomalies associated with igneous intrusions may have further enhanced source rocks maturity. Field observations of pyrite-filled fractures and heavy oil accumulations suggest that hydrocarbon and hydrothermal fluids migrated along shared pathways, controlled by deep-seated faults and regional unconformities. Furthermore, samples from the basement show high radioactive concentration with radiolytic natural hydrogen generation of up to 9.03mg/g/Ma. Fracture porosity measurements from basement outcrops in the Gombe and Kaltungo inliers indicate values of up to 6%, decreasing to ∼2% at depths greater than 5km. These findings highlight basement reservoirs as an additional exploration target. These results highlight the potential for both conventional and unconventional (buried hill-type) reservoirs.