Global sea level and temperature rise (climate change) have been constantly perceived to be caused by the untoward concentration of greenhouse gases (GHGs) in the earth’s atmosphere, and carbon dioxide (CO2) the major constituent of GHGs 1–5. Other energy sources especially renewables have received significant investments, but due to the ever-increasing demand for energy globally, fossil fuels will still be in the mix for the foreseeable future 1,6,7. With man’s continued reliance on fossil fuels, and CO2 being a byproduct of fossil fuels combustion, drives and initiatives to mitigate the adverse effects of climate change must constantly be on the front burner. Goal 13 (climate action), one of the goals within the Sustainable Development Goals (SDGs) as adopted in 2015 by the United Nations (UN) speaks to the necessity of taking “urgent actions to combat climate change and its impact” and targets the integration of climate change strategies into national planning and policies 8,9. Geological carbon storage is presently the most efficient technology for large-scale reduction of atmospheric carbon and stemming the upward tide of associated climate challenges, as the International Energy Agency asserts it can bring about around 19% reduction in emissions of CO2 worldwide by 2050 10. Yearly CO2 emissions on a global scale from cement manufacture and burning of fossil fuels was 36.58 Giga tonnes per annum (Gtpa) in 2018, with 10.06 Gt (28% of the world’s entirety) contributed by China, USA emitted 5.42 Gt (15% of the world’s total sum), and India accounted for 2.65 Gt, representing 7% of total CO2 emission of the world 11,12. With 28 carbon capture and storage (CCS) projects operational worldwide as of 2020 and sequestering 41 Mtpa 13, this represents a meagre 0.12% of the CO2 emissions attributable to hydrocarbon and cement industries worldwide. About 37% of these are principally geological carbon storage projects, while 73% are for enhanced oil recovery (EOR) drives, with the USA, Brazil and, Australia being the nations that sequestered the most 12.
Within the South African context, studies have shown that South Africa has the potential of storing ~ 150 Gt of CO2, with the offshore basins showing greater prospects 14–19, but it is unlikely that commercially available CCS will be in place in the country before 2030 due to the present challenges of doubts in policies around climate action, delayed pilot/test underground carbon injection projects, low-priced carbon rates, dearth of commercial or profitable case studies, and the acceptability of the public to carbon storage projects in regions hosting potential storage sites 20–26. South Africa fulfils its energy needs principally from fossil fuels, with 77% of the nation’s total electricity generation from coal-fired power plants and its power sector the 9th biggest emitter among power sectors in the world (~ 218 Mt of CO2) (Fig. 1), though these are low emissions in comparison to developed nations, cumulative emissions from the next nine African nations are below it 27.
In the bid to attain climate neutrality, Denmark, currently the largest oil producer in the European Union (EU), is set to completely phase out the production of hydrocarbon, new oil and gas extraction permits have been cancelled and when the calendar reads 2050, the hydrocarbon valves will be shut off for good. Presently, subsidies are being provided to stimulate large-scale CCS projects 28,29. This means more searchlights will be beamed on oil reservoirs (without oil recovery) to make them viable CO2 sinks. Oil reservoirs present many advantages for CO2 storage, such as the presence of below-surface and on-the-ground installations and equipment that can be tailored to CO2 injection and storage (usually with some modifications), the presence of quality seal and establishment of caprock integrity which have held oil in place through geologic time, and availability of geological, hydrogeological, geophysical and engineering data for characterization of the reservoir and other petroleum system elements, among others 5, 30–36.
The objective of this research is therefore to consider an oil reservoir in the offshore Bredasdorp basin, South Africa, for CO2 storage, with no enhanced oil recovery (EOR). The knowledge gained from the study will also be useful for reservoirs with pockets of unrecoverable oil due to economic, technical, commercial, or logistics reasons, and bypassed oil/unswept zones.