A Comprehensive Outlook for CO2 Sequestration Feasibility Studies with Rock Physics

Over the past 50 years, the fossil fuel industry has been faced with many difficulties, but none are more pressing than the effects of the sector on the environment and its contribution to the acceleration of global warming through business-as-usual greenhouse gas emissions or the mitigation of global warming through CCUS. In either case, there is a need for the industry to improve its reputation by actively contributing to climate change solutions while meeting the increasing global demand for energy. With regard to CCUS, for large-scale injection and storage of CO2 in depleted reservoirs, feasibility studies of the reservoir properties should be carried out to determine the best storage conditions with the least environmental risk. In this paper, we carried out CO2 storage feasibility studies on two fields in the Niger Delta region of Nigeria. The fields had varying locations and limited available datasets, and different geological models were created for both fields as required. The NIA field is located in the onshore part of the Niger Delta, while the SEF field is located in a swampy marine environment. The methodology includes petrophysical and rock physics analyses, including geomechanics, fluid sensitivity, compressibility analysis, storage injectivity, fault seal, and volume analysis. Potential reservoirs were delineated and correlated, elastic parameters were generated from pseudo logs, cross plotted for comparison, and evaluated for physical strength. Fluid sensitivity was carried out using Gassmann's equation to understand dry rock sensitivity to fluid changes. Subsequently, a compressibility study was done to measure the drained and undrained properties of each reservoir and its resistance to compressive forces. Finally, storage injectivity, fault seal, and volume analysis were carried out to determine suitable reservoirs for CO2 storage. From the results, a total of 5 reservoirs were identified across both fields. Petrophysical analysis revealed reservoir thicknesses of 20-120m, moderate porosity (17-23%), and good injectivity (128-1900mD). Geomechanical analysis showed varied modulus values and a Poisson ratio of 0.25. Compressibility analysis indicated good drained and undrained compressibility. From the volumetric analysis, the results show substantial capacity for CO2 storage, while the fault seal analysis showed good sealing capacity.