Geophysical Characterisation of CO2 Sequestration Potential in the Cretaceous Sandstone Reservoirs of the Anambra Basin: An Original Assessment Framework

Carbon capture and geological storage in deep saline aquifer sandstone reservoirs represents a potential mitigation strategy for industrial CO2 emissions from Nigerian cement and power generation facilities, yet the geological suitability of Nigerian sedimentary basins for CO2 sequestration has never been assessed through an integrated geophysical characterisation framework. This research develops an original geophysical assessment framework for CO2 geological sequestration potential and applies it to the Cretaceous sandstone reservoirs of the Anambra Basin. The framework combines seismic reflection interpretation, well log petrophysics, geomechanical modelling, and CO2 flow simulation to evaluate trap integrity, reservoir capacity, and injectivity at three candidate sites. Seismic reflection data interpretation provides structural maps of the Ajali Sandstone Formation at depths of 1,200 to 2,400 metres, identifying anticlinal closures with estimated storage volumes of 180 to 420 million tonnes of CO2 equivalent based on Bachu-Adams type capacity equations. Petrophysical analysis of sonic and density logs from four wells provides input parameters for the CO2 injection flow simulation, including permeability (8 to 180 milliDarcy) and porosity (16 to 28 percent) distributions. Geomechanical modelling using the poro-elastic analytic solution confirms that injection pressures below 60 percent of minimum principal stress can be maintained within safe limits for reservoir caprock integrity at two of the three candidate sites. Capillary sealing capacity of the Mamu Formation shale cap rock is assessed using mercury injection capillary pressure analogues from published data for equivalent lithologies. The research contributes a nationally applicable geophysical assessment framework for CO2 sequestration potential evaluation. Keywords: CO2 sequestration, Anambra Basin, seismic interpretation, reservoir capacity, caprock integrity