Investigating the role of natural tracers in subsurface CO2 storage and monitoring

Since the Industrial Revolution, burning of fossil fuels (coal, oil and gas) has greatly increased the carbon dioxide (CO2) content of the atmosphere. The higher level of CO2 is widely accepted to be a major contributor to greenhouse warming of the Earth and acidification of the oceans. The effects of this warming on the world are still controversial. However, many scientists now believe that the Earth’s atmosphere will heat up by at least 2 to 3 centigrade over the next 100 years. The effects of this warming include rising sea levels, melting of the polar icecaps and increasing risks of severe weather events such as hurricanes. To try to limit this warming to 2 centigrade, governments from the EU and around the world are looking at ways of reducing CO2 emissions. One of the major sources of CO2 is the generation of electricity. Worldwide fossil fuel burning produces 85% of the world’s electricity. In the next 10-20 years, it will be difficult to reduce the use of fossil fuel for electricity generation. Renewable energies need time to be introduced and developed, and the world also needs extra methods of generating electricity to safeguard against shortages of intermittent renewable energy – for example, when the wind does not blow enough to turn windmills. It is now possible to burn fossil fuels, and capture the CO2 at power stations, or other concentrated emission sites such as cement works and oil refineries. This CO2 can then be pressurised to liquefy it, and pumped through pipelines to places where the liquid CO2 can be injected underground to be stored. This particular proposal examines some of the controls which affect how CO2 is stored underground and how any leakage out of a reservoir, or to the surface could be detected. To store CO2 a porous reservoir is needed, overlain by an impermeable seal, such as mudstone which stops the CO2 from escaping and rising to the surface. The CO2 must be stored for a long time (thousands of years) to ensure it does not cause further warming. Unfortunately, the first engineered CO2 storage project has only been operating for 10 years. So to find out more about storing CO2 over a long time we need to look at natural CO2 gas fields. Natural CO2 fields are similar to oil or methane gas fields except they contain CO2. Within these gas fields there is also a small amount of unreactive noble gases. These noble gases have different sources and can be used to work out where the natural CO2 has come from. Recent research has shown that natural CO2 fields from around the world have trapped CO2 for millions of years. This research has also shown that a lot of CO2 is trapped as a result of it dissolving into the porewater within the gas field. This proposal will firstly develop detailed computer models to independently predict how much chemical dissolution into the porewater could realistically occur within the CO2 fields. Several scientists also believe that once CO2 is pumped underground it will crystallise new mineral. This would ‘lock’ the CO2 into the reservoir and is the most secure form of storage. This work would analyze recent minerals formed within a CO2 field to test if the amount of light carbon (carbon 12) to heavy carbon (carbon 13) was the same as would be expected if the minerals were crystallised from the CO2 stored in the field. The project will also investigate if noble gases can be used to record if CO2 has moved through the mudrock seal from different natural CO2 fields. As CO2 moves through the mudrock it is believed that some noble gases contained in it will be left behind, stuck onto organic debris. In a similar fashion noble gases can also be stuck onto natural coals. This project will test if the noble gases derived from coal burnt in a power station and its produced CO2 exist in large enough quantities to be used to trace the CO2 once it is injected underground.