Fugro’s Geo-data supports development of offshore carbon storage

Carbon capture, usage and storage (CCUS) is now viewed as a key part of the world’s future low-carbon energy portfolio and plays a crucial role in realising emission reduction targets. To accelerate the energy transition in the UK, the North Sea Transition Authority has recently launched a licensing round for offshore CO2 storage on the UK Continental Shelf.

The new carbon storage areas, alongside the six licences which have been issued previously, could have the ability to make a significant contribution towards the aim of storing 20-30 million tonnes of CO2 by 2030. Whilst legislation and standards of CO2 storage are evolving, winning bidders will require extensive site characterisation to help plan, develop and operate carbon storage sites safely and efficiently.

Traditional CO2 leakage detection methods are inadequate

The principal uncertainty in relation to offshore CO2 storage is modelling and detecting the volume of CO2 that has the potential to leak from the reservoir, migrate up to the seabed and ultimately be released back into the environment.

The traditional methods to model fluid migration based on oil and gas 3D seismic data do not have sufficient resolution to detect the likely future CO2 leakage pathways. The maximum resolution of exploration and production scale 3D seismic data simply aren’t high enough, being constrained to 5 – 10 m bed resolution.

The starting point

Operators bidding for offshore CO2 storage licences will rely heavily on site characterisation to provide a framework for managing the containment risks associated with the project. To establish a baseline, they need to be able to understand the overburden model (the multiple layers of rock above the reservoir) from a containment-risk perspective and identify all potential CO2 leakage pathways.

Fugro’s innovative approach for this initial stage involves:

• Cost-effective, high-resolution 2D geophysical surveys – we combine seismic high-resolution (HR) and ultra-high-resolution (UHR) bandwidths to achieve a resolution of >0.5 m at a penetration depth of 500 m; and between 3 m and 10 m at 1200 m. Essentially shooting deep and shallow simultaneously. Improved definition in the overburden enables us to identify potential CO2 leakage pathways with far greater precision to optimise location of CO2 monitoring equipment at seabed.
• Oceanographic and environmental sensors – the dissolution of CO2 occurs within the first 4 m above the seabed, increasing the acidity of the water. We use seabed landers, observational tools that are lowered into position on the seafloor and equipped with oceanographic and environmental sensors, to continuously measure, monitor and verify any changes in the marine environment within the vicinity of potential leakage pathways identified in our geophysical surveys.

Always on the look-out for leakage

Monitoring for potential leakage of CO2 must be carried out at regular intervals throughout the injection phase (which could last for up to 40 years, depending on the capacity of the reservoir) to detect any new fractures or changes in the characteristics of the leakage pathways.

The monitoring responsibilities will of course continue long after the CO2 has been permanently sealed in its storage location, deep below the seabed.

Conducting a traditional seismic survey is a very expensive operation requiring large technical vessels with a high day rate. In contrast, our cost-optimised solution:

- Relies on smaller vessels (which have a lower day rate, use less fuel and require fewer offshore personnel, thereby also reducing cost and safety risks);
- Is more focused, because the baseline and subsequent data can be used to target identified potential CO2 leakage pathways with a high degree of accuracy;
- Combines HR and UHR resolution to provide a much better definition of the overburden;
- Enables subtle changes to be identified quickly by comparing current and previous datasets.

Seabed landers continuously monitor the water column to detect any changes that indicate a potential leakage of CO2.

The data is relayed in near real time to our network of remote operation centres, meaning that any anomalies are identified without delay, with precise information about their location and rate of leakage.

Looking to the future

The UK has a large capacity for offshore CO2 storage, along with the skills and experience to be able to develop it quickly in the North Sea.

The offshore CO2 storage industry is in its infancy.  Government legislation, standards and insurance requirements are evolving quickly, leaving investors and operators with questions that have yet to be answered. What should the sensors on the seabed landers be monitoring? What are the detection limits for CO2 leakage? What is the recommended frequency for the geophysical surveys? And how frequently should surveys be repeated?

Much has yet to be decided, but we’re poised and ready to help the industry take on this exciting new challenge.

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