Solutions for future CO₂ storage

In the SWAP-project, Equinor has collected strategic subsurface data in order to explore the possibilities of storing large amounts of CO₂ in a saline aquifer east of the Troll field.

SWAP

SWAP IS PART OF EQUINOR’s Scale-up of CO₂ Storage project, and is closely connected to the company’s hydrogen strategy. In the production of hydrogen from natural gas, large amounts of CO₂ are formed, which Equinor is planning to store on the Norwegian Continental Shelf. The need for storage sites will increase as carbon capture becomes a widely used technology for reducing emissions from industry in Norway and Europe.

“Our intention was to explore the potential for large-scale CO₂ storage at the Horda platform, in the Troll area, and is closely connected to the potential future phases of the Northern Lights project,” says project leader Rune Thorsen in Equinor.

Better understanding of pressure

Northern Lights encompasses transport and permanent storage of CO₂ in a geological formation under the North Sea, and is a constituent part of the Norwegian full-scale CCS project. In an early phase, the Northern Lights project considered storing CO₂ at Smeaheia, an area east of the Troll oil and gas field. After the feasibility study, however, uncertainties arose regarding some of the assumptions undergirding the project.

Studies showed that there was a possibility that the reservoirs of the Smeaheia area could be linked with the reservoir sandstones at Troll. If there was a large degree of pressure communication between the areas, it could impact the storage capacity on Smeaheia. Since Troll will produce gas until 2054, the pressure at Smeaheia could also fall as the pressure falls at Troll in the years to come.

Usually, CO₂ is injected into a reservoir in a liquid state. If the pressure at Smeaheia falls significantly, the CO₂ could expand from liquid to gas, which occupies more space in the reservoir. Therefore, it might not be possible to store as much CO₂ at Smeaheia as the plans predicted. This was one reason that Northern Lights instead opted for a storage location in the Aurora area, south of Troll Vest.

“However, in the Scale-up of CO₂ Storage-project, we decided to continue working internally with the area that was abandoned in 2018,” says Thorsen. “We hadn’t lost faith in the Smeaheia area as a future storage location, but we needed more time to find answers to the uncertainties that had been identified. The time frame for the full-scale CCS project was so tight that we had to mature other alternatives in order to reach a positive investment decision in 2020.”

More well data

The first plans for the SWAP project appeared during the summer of 2018. Equinor had been awarded an exploration licence in the south of the Smeaheia area (PL921) during the spring of 2018. The goal was to explore for hydrocarbons in the Gladsheim structure. This structure is situated approx. 20 km south of the area that had been studied in the first phases of Northern Lights, and exploration drilling was scheduled to start during the fall of 2019.

The planned exploration drilling was identified as a rare opportunity for collecting additional strategic data, which could reduce the geological uncertainties identified by Northern Lights – so that the future road to CO₂ storage on Smeaheia might be both shorter and cheaper.

Towards the spring of 2019, the SWAP project assumed shape. SWAP – the Strategic Well Acquisition Project – became a project for gathering important subsurface data. Although these data would otherwise not have been acquired by the exploration licence, they are considered important pieces of information in order to create an understanding of the storage potential in the area around Troll.

A large part of the extra collection consisted of data from the cap rock. The data confirmed that the cap rock will remain impermeable if CO₂ should be injected into the reservoir. Core samples were taken and rock- mechanical tests executed in order to determine the quality and strength of the cap rock. The researchers also measured the porosity, permeability and fracture pressure of the rock in a thick slate, the Draupne formation. Usually, these types of samples of the cap rock are not taken in an exploration well.

Pressure measurement

Below the cap rock, Smeaheia consists of several geological formations that potentially can be used for storage. As a part of the SWAP project, a set of pressure measurements were conducted in the different reservoirs, in order to measure the degree of communication with the Troll field.

“The measurements showed that the pressure was reduced in the well area,” says Thorsen. “Then we knew that the sands we had hit, were connected with the Troll sands. This means that the reservoir is vast, and that it’s possible to inject large amounts of CO₂ without a significant increase of the pressure of the reservoir.”

“We have also taken small core samples of the different levels of the reservoirs, so-called sidewall cores (SWC), on which we will conduct different tests in the laboratory,” says Thorsen.

Now the researchers are working on updating models and increasing the understanding of the reservoir. Will it be possible to use this area for injection– for example in a future scale-up of the Northern Lights project?

“There is great reason for optimism,” says Thorsen. “The data suggest that the sealing is solid. The reservoir has thick rocks over a large extension. This means that the area probably can receive large amounts of CO₂.”

The results of the project can also have positive repercussions for Northern Lights.

“At a future scale-up of Northern Lights, the area we are exploring can probably be used as a storage site. This means that we can potentially use the infrastructure that will be built in the first phases of the project. This way, we can achieve large cost reductions,” says Thorsen.

About the project

Strategic Well Acquisition Project (SWAP)

Project owner: Equinor
Project period: 2019–2020
Total budget: 26.7 MNOK
CLIMIT-support: 17.3 MNOK
Partners: Petoro, DNO and Lundin