Deep geological CO2 storage: principles, and prospecting for bio- energy disposal sites

The principles of hydrocarbon exploration and production provide well established and tested principles and technologies to investigate storage of fluids in the subsurface. CO2 can be stored in the subsurface using settings of: A) thick permeable coal seams; B) depleted oil and gas fields; C) saline aquifers of regional extent, with an overlying seal. The North Sea Sleipner project shows that CO2 can be injected into the pore space of deep geological aquifers deeper than 800m at 1Mt/yr, using established technology. Suitable sediment sequences of saline aquifers exist in all hydrocarbon-producing areas, are volumetrically much larger than exploited oil and gas fields, and hold the potential to easily store all worldwide CO2 emissions until 2050. Geological principles are established to assess the entire continents for candidate sites of CO2 storage. This shows that opportunity is may be widespread, but need more specific local investigations. Onshore sub-Saharan Africa is considered the most problematic region – but even here there are sediment sequences. No demonstration projects currently exist for CO2 storage using small-scale onshore facilities. A simple estimate, assuming CO2 value of $20 per ton, suggests that single boreholes onshore may be viable over 20 years with supply rates of 100,000 ton CO2 per year. In principle, atmospheric CO2 could be captured by cultivated biomass, and stored deep below ground, in a country distant from the original fossil-fuel CO2 emission site.