Realizing CCS’s potential

Could the North Sea become a CO2 storage site? Elaine Maslin takes a look at two proposed projects and some of the challenges involved.

The CCS goal—how the Scottish Centre for Carbon Storage sees carbon capture and storage on and offshore. Image from the Scottish Centre for Carbon Storage.

For more than 50 years, the UK North Sea oil and gas industry has been pushing the boundaries of how to explore for and extract oil and gas from one of the harshest environments in the world.

Engineers and technology developers are now tasked with the reverse – to inject CO2 generated at power generation facilities back into the reservoirs from which they have been extracting hydrocarbons. The drive toward carbon capture and storage (CCS) is to enable the power generation industry to reduce the carbon emissions it creates while generating electricity from coal and gas.

Getting CCS right could have a significant impact on emissions. According to the Energy Technologies Institute, without CCS, decarbonizing the energy system would cost up to £40 billion (US$61 billion) extra per year more. According to the International Energy Agency, without CCS, the cost to halve emissions up to 2050 will be 40% higher.

With North Sea operators starting to assess decommissioning options for some of their facilities, now would seem an opportune time to consider existing facilities’ reuse. The UK government has seen this as an opportunity and two projects – White Rose and Peterhead – are currently vying for all or a share of some £1 billion ($1.5 billion) set aside to help fund a CCS demonstration project.

Cleaner power

David Few

“The objective is to produce a method of producing electricity that is carbon free,” says David Few, major projects director, Atkins Energy. Atkins has been involved in advising the UK government on the CCS demonstration project competition. “While a number of plants around the world are doing it, capturing and storing in some way, most are for enhanced oil recovery schemes. It is not yet being done so that it is pays for itself commercially.”

The one project that has been launched is SaskPower’s onshore Boundary Dam project in Canada, using Shell’s CANSOLV CO2 capture technology on a power plant. Shell is also involved in the onshore CCS Quest project, in Canada’s oilsands and in Chevron’s Gorgon project, Australia, which enable CO2 produced from offshore facilities to be sequestered and stored in sandstone beneath Barrow Island.

Offshore projects are even less common. In Norway, two projects, Sleipner and Snøhvit, inject CO2 that has been stripped from offshore natural gas production into reservoir formations. The Sleipner project was driven by Norwegian regulations that tax CO2, which encourages sequestration schemes. The drive for CCS at Snøhvit, which feeds an LNG project at Melkoya, onshore Norway, was to remove CO2 from the gas stream before it could solidify in the LNG production process. Neither involve sequestering CO2 from power generation plants.

Without the same pricing on CO2, or any LNG projects, CCS economics in the UK is less favorable. An earlier bid to help encourage a CCS demonstration project resulted in just one bidder, the Longannet Power Station project in Scotland, and it fell by the wayside. The plant is now earmarked for closure.

However, the latest CCS competition for all or a share of £1 billion ($1.5 billion) funding, has two potential candidates, both of which entered front-end engineering and design at the end of 2013 and early 2014, with the help of £100 million ($159 million) government funding.

Two projects in the running

Government support—then-Deputy Prime Minister Nick Clegg visited Peterhead Power Station in 2014 to announce early engineering funding for a CCS project there.Image from Cabinet Office.

The White Rose project is based on building a new, 436MW, oxy-fuel power plant burning coal next to the existing Drax Power Station in East Yorkshire, England. White Rose is run by a consortium of Drax, Alstom, BOC and National Grid. A 140km pipeline, half onshore and half offshore, would take about 1.7 million tonnes of CO2 per year out to a new platform and set of injection wells. There it would be pumped into a saline aquifer.

At the Peterhead Power Station project, SSE’s 400MW combined cycle gas power station would have one of its three existing turbines retrofitted with CANSOLV. The CO2 will be routed through existing pipelines to Shell’s St. Fergus Gas Terminal. From there, a new 20km pipeline will be constructed and tied in to an existing disused line out to the Goldeneye platform 100km offshore. There, the CO2 will be pumped 2km under the seabed.

Peterhead will be the world’s first commercial-scale, full-chain project to demonstrate the feasibility of CCS at a gas-fired power station, says Shell’s Tim Bertels, head of CCS Shell Global Solutions.

The next step for both projects is contract negotiation. “This is cutting edge technology,” Few says. “There is only one other plant in the world doing this for electricity generation – Boundary Dam. Others are progressing it, China and the US. The UK Department of Energy and Climate Change’s (DECC) idea is to seed-fund a new industry.”

The technology

Garth Raybould

One of the key technologies to enable CCS is sequestration technology, which is estimated to be about 33% of the cost of CCS projects, according to Professor Mercedes Maroto-Valer, director, Centre for Innovation in Carbon Capture and Storage, at Heriot Watt University’s Institute of Petroleum Engineering.

Shell co-owns the Bergen CO2 Technology Centre in Mongstadt, described by Bertels as the largest CCS test center. It was inaugurated in May 2012 to test two different capture technologies, including Shell’s CANSOLV.

When it comes to transporting the CO2 offshore and injecting it, CCS broadly involves a reversal of the gas extraction process, Few says. However, there are important differences. “Instead of extraction, you need injection technology. You are injecting very high-pressure CO2, at 175 bar, into the reservoir.”

And, it is not a gas phase when it is being exported and injected. It will have been dried and compressed into a dense phase, with similar viscosity to gas, but a density closer to a liquid. “You want it in that state because it is more efficient to transport and you want to keep it in that phase, otherwise pressure waves could be created in the pipeline,” Few says.

The composition of the CO2 is also important because it could have the potential to sour the well. “Part of the process of the flue gas treatment is to strip out moisture and certain trace gases. Otherwise it could create carbonic acid,” he says.

But, it will be a learning curve, Mareto-Valer says. “The more we do, the more we realize we need to do during transport, and that it is not as simple as reversing the flow,” she says. “There are a lot of things we will have to know, even in terms of using the right compressors, for the pressure, temperature and volumes involved, and particularly around large-scale pipeline deployment and pipeline sharing – putting different quality CO2 and volumes through.”

The team at Heriot Watt is looking at technologies to meter CO2, as it is transported offshore, for situations where pipelines are shared. “We know how to meter natural gas. However, we don’t have that much experience accurately metering CO2 in pipelines,” she says. “We will need to do this.”

The benefits of CCS, as laid out by the UK Government. Image from Cabinet Office.

Geology

Experts estimate that geological formations beneath the UK North Sea can store almost 80 billion tonnes of CO2 – more than enough to meet the needs of UK CCS projects for the next 100 years, according to the 2014 report “A UK Vision for Carbon Capture and Storage,” prepared by Orion Innovations (UK) for the TUC and the Carbon Capture and Storage Association.

The Carbon Capture and Storage Association maps where potential CCS sites are. Image from the Carbon Capture and Storage Association.

“The reservoir needs to be both porous and permeable,” says Garth Raybould, chartered geologist and consultant at Atkins. “Its size, shape and structure need to be known, and it normally needs to be surrounded by rocks of lower permeability. Coarse-grained sandstones are the best reservoirs, and are usually either depleted oil or gas fields or aquifers.

“The CO2 is usually intended to stay where it’s put, so the structure of the reservoir has to be known in enough detail to ensure that potential leakage points are identified,” Raybould continues. “Injection wells can then be located, and limits to CO2 quantities determined, to prevent the CO2 from reaching those points. Because the CO2 is lighter than the saline water already in the rock pores, its tendency is to rise, so it is especially important that the reservoir is overlain by low-permeability rocks to trap the CO2.”

Once in the ground, part of the CO2 is held in place by capillary trapping, i.e. it is held by the capillary forces in the rock, and partly dissolves in the pore water already in the rock (known as dissolution trapping). Over time, the CO2 could react with minerals in the rock to form new carbonate minerals (i.e. mineral trapping).

In Norway, DNV GL has developed recommended practices for CO2 capture, CO2 pipelines and CO2 geological storage. Still, little is known about the detectability and fate of CO2 at intermediate depths in the subsurface, according to the CMC Research Institute. It is looking into how the gas behaves once injected at its field research station, at which measurement, monitoring and verification technologies can be deployed to determine the detection threshold of CO2 at depths of 300m and 500m. At other locations, research is being conducted at depths of 2km or more.

Mareto-Valers says there is also work ongoing looking at CO2 behavior near the well space, as well as geomechanics, i.e. potential fracturing or rock deformation. “We need to make sure the CO2 will stay down there for a long period of time and that we have the right mechanism to monitor the CO2 and the integrity of the storage site,” she says.

Another area, which is being addressed, is how to accurately identify and track subsea CO2 leaks. Last year, DNV GL launched a joint-industry project to look at the potential risks around CO2 pipelines, named the CO2 Subsea Releases - Small Scale Experimental Programme. When it was formed, National Grid, Eni, and Petrobras were on board. This will look at how to monitor and discover small leaks.

Fugro GEOS, in partnership with Sonardyne, is also looking to develop a CO2 monitoring system using marine robotics under a project commissioned by the UK Energy Technologies Institute. Further initiatives are expected.

Conclusion

Shell’s Goldeneye platform, which could become a receiving and injecting platform for captured CO2. Image from Sembmarine SLP.

While the timing could be right to transition some fields from production to CO2 storage, the technologies’ complexities are yet to be fully understood.

Projects need to go ahead in order to prove and develop this technology, Maroto-Valer says. “In Europe, CCS is at a crossroads,” Shell’s Bertels told ONS in Stavanger last year. “In 2007, the European Commission committed to have 12 large-scale demonstration projects by 2015. Deployment has fallen far below this, with the risk that the lack of demonstration increases the long-term cost of deployment and decarburization.

“Worldwide, there are currently 12 projects in operation preventing some 25 million tonne CO2 per year entering the atmosphere, equivalent to taking five million cars off the road every year. This is a significant effort, perhaps, but in reality it is still insufficient because there are no projects under construction in Europe. There are still very few projects in the power sector. And the overall project flow has been shrinking.

“There must be a price on CO2 emissions and, in the long term, a strong price will be sufficient to drive CCS. But in the short term, we will need capital grants to support demonstration and operator support at plants.

“We will need to develop CCS infrastructure and clusters and, finally, developing and deploying CCS at the pace and scale required will be a significant global undertaking requiring broad and global collaboration between government, industry, academia and society at large.”