Frequently asked questions
Can the injection of carbon dioxide into geological formations (for CCS) lead to earthquakes and if so, can this risk be managed?
In principle, the injection of carbon dioxide into geological formations can lead to earthquakes, but these would be very small, similar in size to those experienced when a large water reservoir is filled or emptied. They would probably be undetectable by human beings, particularly in the case of the UK where the injection would take place under the North Sea.
The earth’s tectonic plates move constantly. When this causes rocks to slip on a fracture, vibrations or sound waves are created – these are earthquakes (also called seismic events or seismicity).
The high-pressure injection or withdrawal of a fluid underground generally does not in itself cause a significant earthquake, but can cause the rocks to slip on a fracture, which therefore causes an earthquake. This is because the injection or withdrawal of a fluid underground has an impact on the pressure balance – where injection or withdrawal of a fluid causes an increase in pressure above the natural pressure, the likelihood of causing a slip (and therefore an earthquake) is greater.
Many activities involve injection and withdrawal of fluids underground – including oil and gas production, water injection, geothermal energy production and injection of carbon dioxide. These activities therefore all have the potential to induce earthquakes - either by breaking the rock (fracturing) or by allowing slip on existing faults (large natural fractures). However, a big earthquake that is felt by humans to a significant level (above magnitude 4) requires a very large slip and that is generally only possible through the earth’s natural forces acting on a fault. Such earthquakes would be extremely difficult to achieve by breaking rocks through injection or withdrawal of fluids underground.
When choosing an underground site in which to store carbon dioxide, very extensive and specific site characterisation is carried out – which can identify those sites where injection of carbon dioxide might cause a slip (and therefore an earthquake). These sites can therefore be avoided.
In addition, extensive modelling and monitoring is carried out before, during and after injection of carbon dioxide into an underground storage site, which can predict the impacts of carbon dioxide injection and any potential risks. If a risk of an earthquake is found, various actions can be taken to reduce this risk – in particular reducing the pressure by reducing the amount of carbon dioxide injected, or altering the location or orientation of an injection well to avoid any potential slip.
In the UK, all carbon dioxide storage sites will be located offshore (under the seabed) and therefore any minor seismic event/earthquake would not be felt by the public. If any major event was to occur offshore, this would be detected by onshore seismic measurement technologies.
There are currently 20-30 large scale carbon dioxide injection tests globally. A recent report by the US Department of Energy’s National Energy Technology Laboratory found that no earthquakes have been associated with any of the global carbon dioxide injection tests, or any of the many projects using carbon dioxide for Enhanced Oil Recovery. Managing carbon dioxide injection is an ongoing process and in a very small number of cases where a risk of induced seismicity may be found, action will be taken to reduce this risk (such as shut down of injection wells).
As a result of an earthquake near/in a carbon dioxide storage site, it can be questioned whether this may cause any of the stored carbon dioxide to escape. It is known that oil and gas reservoirs in the North Sea frequently experience minor earthquakes, with no detected escape of oil and gas. In addition, a magnitude 6 earthquake (100 times stronger than a magnitude 4) - completely unrelated to carbon dioxide injection - recently took place near a pilot carbon dioxide injection test in Japan, with no carbon dioxide escape detected.
As the CCS industry develops, it is important that continued research is carried out on the potential for induced seismicity from the injection of carbon dioxide into underground storage sites.