Petrophysical Characterization and TOUGH2 Modeling of Potential CO₂ Storage Formations in Nigeria

Abstract

This paper evaluates petrophysical characteristics and long-term storage of CO2 of the chosen Nigerian formations, such as the saline aquifers and depleted oil reservoirs, in a systematic manner to guide the application of Carbon Capture and Storage (CCS). Porosity was determined as n=20 core samples using the method of helium pycnometry, and the results had a range of 5.5 to 16.7% with Saline Aquifer C having the maximum porosity. Permeability was tested with constant head (up to 130 mD) and falling head (as low as 7 mD), and measurement uncertainties were estimated at 2%. Laboratory analyses were supplemented by well log data, geophysical surveys, and remote sensing techniques to characterize structural features, faults, and fractures. Numerical modeling used TOUGH2 with boundary conditions reflecting regional pressure and temperature regimes, with mineralogy held constant and no chemical reactions during a 100-year run; parameters in the model characterized by petrophysical data, with uncertainty of about ±10% in permeability and ±2% porosity. Sensitivity analyses revealed that CO2-retention capacity would be approximately 95% with a range of 85-98% depending on site-specific parameters. It was estimated that pressure could rise to safe levels (3.112 Mpa), but these were made on assumptions that mineralogy is homogeneous and that there are no important geochemical interactions. These findings suggest that Saline Aquifer C is a promising CO2 storage option with good petrophysical properties and capacity forecasts. Nevertheless, the ambiguities of the measurements and the model assumptions point to the necessity of additional site-specific research, particularly of mineralogical heterogeneity and chemical stability, prior to large-scale CCS deployment. This study provides an empirical basis for informing CCS policy, site selection, and risk mitigation strategies in Nigeria.