Mapping carbon storage potential and security in saline aquifers

Manchester researchers have created a first-of-its-kind tool to map and rank potential carbon storage areas in the North Sea for their capacity and ability to store CO2.

For the UK to meet its net zero targets, it will need to upscale its carbon capture and storage (CCS) activity and, critically, identify sites capable of retaining more than 99% of the CO2 for more than 100 years.

Currently, only 26 operational large-scale CCS facilities exist worldwide, with a combined capture of just 40 Mt CO₂per year – whereas the European CO₂ storage demand is expected to reach 300 Mt per year by 2050, including CO₂from cement production, heavy industries, hydrogen production and fossil fuel power generation

Many European countries have insufficient subsurface CO2 storage capacity to meet their decarbonisation targets, setting the scene for commercial cross-border carbon storage networks to be established. 2/3 of the potential storage areas are under the North Sea, which has extensive re-deployable workforce and infrastructure put in place by the oil and gas industry.

This huge opportunity comes with the challenge of storing a gas with complex behaviour during the pressure and temperature ranges between surface and storage conditions. CO₂ storage can only be considered at depths greater than 750-800 metres below sea-level, where the conditions mean the CO2 properties are more like cooking oil than a gas. 

Could the North Sea be the answer?

The complex subsurface behaviour of CO₂ means not all reservoirs are able to support CCS. The key to success is identifying reservoirs overlain by thick layers of mudstone that will trap the CO₂ and being able to distinguish thin sandstone layers and other overburden structures that could compromise the mud layer seals. 

For any subsurface storage site it is key to establish that CO₂ can be safely stored for hundreds of years, which requires a much better understanding of the overburden and in particular the immediate sealing rocks above any injection target reservoir.

Manchester scientists have developed a new approach to map and rank the containment confidence, capacity and storage potential of saline aquifers and disused oil and gas fields in the North Sea using ‘off the shelf’ data created by the petroleum industry. The approach looks at the ability of a given subsurface layer to store CO₂ and it quantifies the ability of its overburden mudstones to retain CO₂ using a ‘containment confidence’ matrix.

Developing a carbon storage mapping tool

Dr Christopher Lloyd and Professor Mads Huuse have developed a methodology to map and quantify the potential for carbon storage and assess containment confidence in the North Sea. The team analysed geophysical and geological data from the Norwegian and UK northern North Sea, focussing on the saline Utsira aquifer and overburden seal. Through detailed analysis of that seismic data, they developed a containment confidence matrix, a first-of-its-kind tool to rank the potential CO₂ storage areas in terms of their ability to retain CO₂.

Through this matrix, each element on a map of the aquifer-seal combination were assigned a Containment Confidence (CC) score identifying the areas with the lowest CC, and recommend sites to avoid for CO₂ storage, and the sites with the highest CC score, which can progress for further evaluation of storage capacity.

The matrix provided a methodology that subsurface geologists and industry could apply to any sedimentary basin. While the size and shape of the basins may vary, actual rock types are similar in many basins across the globe. As a result, the methodology could be used to map the CCS potential in most other basins across the world,  empowering a global acceleration of CCS projects.