3D modeling and carbon dioxide storage capacity estimation of the non-hydrocarbon Santa reservoir, onshore Zululand Basin, South Africa

Carbon dioxide (CO2) storage in geologic formations is a highly effective and promising strategy for significantly reducing CO2 emissions into the atmosphere. This study focuses on assessing the volume of CO2 that can be stored in a non-hydrocarbon reservoir located in the onshore Zululand Basin, South Africa. We utilised well logs and seismic data employing geostatistical methods to develop three-dimensional(3D) models. The petrophysical modeling has demonstrated favourable reservoir properties, indicating adequate porosity and permeability essential for effective CO2 storage. By applying the compressibility method, we estimated the CO2 storage capacity of the reservoir. The reservoir is predominantly composed of sandstone, exhibiting a mean effective porosity of 20% and a permeability value of 100 to 1000 mD. Three distinct facies were identified within the reservoir: sandstone, siltstone, and shale. In the northwestern, central, and southern areas of the reservoir, porosity and permeability are lower due to the presence of shale and siltstone. Our analysis of the shale volume model demonstrates a strong dominance in sandstone, with water saturation values of 10% and 20%. This makes the reservoir an ideal candidate for CO2 storage, due to its favourable petrophysical characteristics. The static storage capacity assessment indicates that the reservoir can store up to 0.54 million tons (Mt) and 0.1 Mt of CO2. Sensitivity analyses revealed that as water saturation increases, storage capacity decreases and declines with an increase in storage capability.