Getting to grips with geology is critical to win UK’s rush for carbon storage

By Gudmund Olsen, AGR

AGR operates and maintains CCS projects over the long-term – from subsurface through to full drilling project management and third-party verification, to ensure CO₂ remains safely underground
AGR operates and maintains CCS projects over the long-term – from subsurface through to full drilling project management and third-party verification, to ensure CO₂ remains safely underground (photo: AGR)

The UK’s first ever carbon storage licensing round has opened with the regulator expecting tough competition for the much sought-after sites.

The process, which closes in mid-September, is anticipated to pave the way for decarbonising large parts of the UK economy. It will also showcase the country’s ambition and commitment to reducing industrial emissions and extending the life of sedimentary basins around the country.

Alongside six storage licenses, which have already been awarded, 13 new areas – made up of a mixture of saline aquifers and depleted oil and gas field storage – have the potential to lock away the targeted 20 to 30 million tonnes of CO2 per year by 2030.

The areas under offer are located off the coast of Aberdeen, Teesside, Liverpool and Lincolnshire in the southern North Sea, central North Sea, northern North Sea, and East Irish Sea.

De-risking carbon storage
With technical criteria being a main factor in evaluating bids, those looking to secure licences will understandably be focused on getting the technology right, but it is imperative that the geological risks are taken into consideration. The right sites must be selected for the right reasons. This demands a critical geological evaluation as part of the due diligence process.

For more than two decades, AGR has been engaged by authorities, energy companies and certification agencies to develop and implement CO2 storage (carbon storage) strategies onshore and offshore. This work has been an interesting journey, generating optimism that a huge amount of CO2 can be stored in the North Sea.

AGR helps its clients reach their ambitious low carbon goals
AGR helps its clients reach their ambitious low carbon goals (photo: AGR)

There are many valid concepts for CO2 storage that meet environmental requirements and instil long-term confidence in containment in the short and long-term.

Seismic screening of storage sites
When dense phase CO2 is pumped into a porous saline aquifer below sufficient depth (800m+) it remains away from the atmosphere. Over time, the CO2, which has not been dissolved in the aquifer water or trapped in pores, will move upwards (since the dense CO2 phase is more buoyant than water) along permeable conduits/reservoirs until it is capped by a geological seal. It is therefore hugely beneficial if the movement of the CO2 plume can be monitored by seismic. The concern being that over time, CO2 will be dissolved and may react with minerals in the host rock to reach a solid state.

When screening for CO2 storage, cost benefit plays an important role. The location of the CO2 source and means of transporting to the storage site are also crucial.

AGR has worked on a range of CCS projects from feasibility studies to assessing potential reservoirs, through to drilling, completing and injection tests of CO₂ wells
AGR has worked on a range of CCS projects from feasibility studies to assessing potential reservoirs, through to drilling, completing and injection tests of CO₂ wells (photo: AGR)

While it may be tempting to store CO2 in a drilled location, where geology is well understood, legacy wells pose a threat of overburden integrity and containment.

Screening of suitable CO2 storage sites typically requires the use of seismic to create a 3D model of the potential reservoir. Depending on the geology, 2D or most likely 3D seismic will be necessary before any qualified reservoir can be determined. Well control and good well data will is vital before a reservoir can be qualified.

Failure is not an option
Failure of CO2 containment will not only be harmful to the environment but also signal economic failure.

The invasion of CO2 into hydrocarbon bearing intervals is also an issue of concern. In some cases, CO2 is stored in reservoirs next to oil and gas fields, by virtue of existing infrastructure and geological well and seismic data. In addition, CO2 may be used for displacing oil to achieve better field recovery. In several projects we have worked on, there is a risk of CO2 migrating into oil and gas reservoirs. Monitoring CO2 plume migration will control such event.

It is a strategic choice whether to store CO2 in a trap, similar to an oil and gas accumulation, or to allow the CO2 to percolate a saline aquifer. In the latter case, the risk of top seal failure is less, compared to the accumulation of a CO2column that builds overpressure by buoyancy.

Also, the risk of CO2 invasion in water resources being used for irrigation, industrial and humans, is a potentially detrimental concern.

Fault leakage is somewhat ill predicted. To fully characterise the risk of fault leakage, fault history and tectonic stress need to be taken into consideration. Seismic will give a history of fault movements, whereas geomechanical modelling will enable characterisation of seal capacity.

Tectonic events may cause massive leaks particularly if CO2 is stored as an accumulation in an untested structure. While storage in a depleted field would be less risky as the containment has been tested, legacy wells will still pose a risk.

Letter of the law
Finally, there are judicial considerations. Most countries have regulations and targets to meet the Paris Agreement to reduce CO2 emissions. However, the transport of CO2 across borders may not be simple and straightforward.

Judicial questions on how to treat CO2 as “garbage” need to be understood and agreed before the carbon bins are packed and loaded ready for international travel. Bi-lateral agreements are needed with the current framework: a standard would be desirable. Most notably, the lack of a legislative framework poses an economic risk as most carbon capture and storage (CCS) emissions are driven by authorities to meet emission reduction targets. Therefore, when CO2is shipped across borders, who takes the credit and the responsibility of meeting a country’s governmental CO2emission goals? It is also unclear how operators of bioenergy plants can get credit for capturing CO2 leading to a negative carbon emission. In all cases, the CCS project must make commercial sense.

There is an international standard (ISO 27914), which describes the procedures for screening, qualification and certification of CO2 storage. This is a comprehensive set of criteria to be followed as a prerequisite for issuing a certificate of operations. Each phase of CO2 storage site: screening, selection and characterisation/qualification is subject to a certificate being issued.

With over two decades of studying these risks AGR is well-placed to advise companies on each site location.

These risks, if well understood and managed, can be overcome and carbon storage will undoubtedly become a game-changing business for the energy sector as well as making a dramatic impact on decarbonising our industry.

Gudmund Olsen, Manager Reservoir Engineering at AGR
Gudmund Olsen, Manager Reservoir Engineering at AGR

With almost 40 years of industry experience, Gudmund Olsen has a deep knowledge of the North Sea. His track record in reservoir management and reservoir engineering covers advising some of the most historical discoveries and field development projects in the basin. The projects have delivered high value to their owners.
During the last two decades, Olsen has been heavily involved in carbon storage projects globally, advising regulators, operators and investors on screening carbon storage sites and modelling CO2 injection strategies for increased oil recovery. He is currently managing the Reservoir Engineering group at multi-disciplinary engineering consultancy, AGR.