Testing whether the caprock can withstand the pressure

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CO2 storage sites under the ocean floor in the North Sea consist of porous rock types with a harder and denser caprock type above it. THE PROTECT project is studying the ability of the caprock type to withstand pressurised CO2.
 

– THIS IS A typical interdisciplinary research project in which we attempt to find out what happens during the injection of large volumes of CO2 into a storage site,” says Sarah Gasda, project manager at Uni Research CIPR in Bergen.

“We have been joined by mathematicians, geochemists, geologists and other experts, and have conducted laboratory studies, modelling and simulations. Even if we have previous experience from CO2 storage in the North Sea, from Sleipner, for example, what we are talking about now is of a completely different magnitude,” says Gasda.

GREAT POTENTIAL

The storage potential in the North Sea is enormous. Probably several tens of billions of tonnes of CO2 – enough to meet the needs of all of Europe for many, many years to come.

“The challenge is the fact that the continuous injection of large volumes of CO2 will change the  pressure in the reservoir, and then we must know how the pressure will be distributed and what will happen with the cap rock,” says Gasda.

There is no other way of finding this out than by conducting research, collecting as much data as possible on all conceivable parameters, and then building simulation models based on that data. This is precisely what PROTECT is about. The project has received core samples of caprock from Equinor and studies the rock’s ability to withstand various types of stress.

Analyses of what happens on a small-scale basis– from a metre down to centimetres – are scaled up to create a model of what can occur in an entire reservoir.

SECURE STORAGE

“All types of rock are subject to natural movements, cracks and faults that may be affected by pressure. Chemical and thermal processes can also affect the caprock. The purpose of the project is to understand how pressure changes can affect the storage complex. This knowledge is important for good reservoir management and secure storage,” says Gasda.

Sarah Gasda stresses that any leaks from the CO2 storage sites will not be harmful to humans or  nature. “CO2 is neither toxic nor explosive, and there are already substantial natural ‘leaks’ of CO2 from the ocean floor.

Secure CO2 storage is primarily about efficiency and economics.  If we are paid to store a million tonnes of CO2 and 10 per cent leaks out again, it is not good for business,” she says.

FULL SCALE NEEDED

PROTECT has already conducted fullscale simulations of what will happen during 25 years of injection into the Utsira formation. The results show that the formation has a substantial capacity for the secure storage of CO2. However, models are just models.

“That is why the full-scale project is so important. We can not go all the way through simulations and models. In the final analysis, we need data from real projects order to determine with certainty how this will work in practice,” says Gasda.

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