Why is this research needed?
In order to meet its climate change commitments, the UK needs to capture carbon dioxide (CO2) from power stations and industrial facilities and store it safely underground. CO2 can be injected through a drilled hole or ‘well’ into rocks located deep beneath the surface of the earth. Rocks suitable for CO2 storage resemble a sponge or swiss cheese, with a solid rock ‘frame’ enclosing microscopic voids called pores. The injected CO2 forms a mobile plume, which collects in the pores and can move through the rocks driven by buoyancy forces until it becomes trapped permanently within the rocks. This process can be visualised by thinking of a plume of smoke rising from a chimney: think of the chimney as the injection well, the atmosphere as the storage rock and the smoke represents the CO2 plume.
It is important that scientists are able to predict where and how quickly CO2 will move, and where it will be trapped. This can be done in two ways. First, it is possible for scientists to build computer models of a CO2 plume. These computer models can then be used to predict the long-term fate of the CO2 in a similar manner to a long-term weather forecast. The UK Meteorological Office routinely uses computer models of the global climate to predict weather patterns in the UK: we expect our models to be much more accurate! Second, it is possible to directly image the CO2 plume in the sub-surface using something called a seismic survey. Seismic surveys are routinely used in oil and gas exploration. They use sound waves to record changes in the physical properties of rocks in the ground. The presence of CO2 in the rock causes a specific acoustic response, or seismic signature, which shows scientists the location of the CO2. Seismic imaging is similar in concept to an ultrasound scan, routinely used in hospitals to take pictures of babies in the womb and diagnose various pathologies, or radar and sonar, used to locate planes in the air and ships at sea.
Scientists and engineers require a lot of information in order to accurately predict the behaviour of a CO2 plume in the ground. They require information about changes in the physical properties of rocks; about chemical reactions that might occur between the CO2, the rock and existing fluids in the rock pores; and finally, they must develop a detailed understanding of specific physical processes which determine the fate of the CO2 over thousands of years. It is clear that a significant amount of multi-disciplinary research is needed to obtain this important information!
What is this research investigating?
This research project has been carefully designed to answer some fundamental questions about the behaviour of a CO2 plume.
- How do CO2 plumes move through the rock?
- How is the CO2 stored in the rock?
- How much CO2 dissolves into water already present in the rock pores?
- How do changes in the type of rock impact the distribution and seismic response of the CO2 plume?
In an attempt to answer these questions, our scientists are combining laboratory experiments conducted on rock samples obtained from wells drilled during oil and gas exploration with experimental data measured at CO2 injection test sites from around the world. Our state-of-the-art laboratory facilities will use 3D micro-scanning of rock samples representing the range of CO2 storage rocks present in the UK. These measurements will then be used to develop digital computer models of the interaction between the rock and a CO2 plume, which will be tested against field measurements made at actual CO2 injection sites.
What does the research hope to achieve
This research project will provide vital information about the impact of geology on the distribution and properties of CO2 stored deep underground. It is hoped that new computer models developed by research scientists will take us one step closer to the first industrial-scale CO2 storage project in the UK!