Repsol YPF

In the face of the increasing warnings about climatic change with consequences that are difficult to predict, the need to look for effective and economically viable solutions is essential. One of the most ingenious and surprising solutions is that of capturing CO2 and storing it deep below the earth, where it is harmless and can be stored indefinitely without any danger. Although it may seem like science fiction, the truth is that this technique has been used on a small scale for decades and there are currently several prototypes in operation, as well as more ambitious projects which will be launched in the coming years. 

For example, a programme called Sacs, which is backed by the European Commission, is already injecting this gas at a depth of a thousand metres at a North Sea oil rig. This not only prevents it being pumped into the atmosphere but due to increasing the pressure of the oilfield also facilitates oil extraction. Meanwhile, in the United States, the Energy Department has launched a project for a prototype coal plant for producing electricity and hydrogen. To begin with, it will retain 90% of this gas in deep geological formations, although it is hoped that all of it will be captured in the long term. 

Where can it be stored once it is captured?

According to the calculations performed, the depth at which the gas must be stored is between 800 and 2500 metres below ground. The oil and gas fields, whether they are active or exhausted, as well as deep aquifers and coal beds which are not being used are ideal candidates for storing CO2. Due to their geological characteristics, they guarantee long term isolation and furthermore, at these depths, CO2 acquires such a density due to the temperature and pressure that the volume it occupies reduces several hundred times, making it possible to store enormous amounts easily. The International Energy Agency (IEA) estimates that, in exhausted oilfields alone, 920,000 tonnes of CO2 can be stored, which represents around 45% of the world’s emissions up to 2050. 
 
Faced by a fear that the gas could gradually leak into the atmosphere, the IPCC Report on the Capture and Storage of CO2 states that when it is injected in a geological formation it can be stored for a period of between 10,000 and 10,000,000 years. Such a long period of time that this system is considered to be one of the safest options for the future. 

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