Norway bets on CO2 capture, storage despite risks

SLEIPNER PLATFORM, North Sea (Reuters) - Norway sees carbon capture and storage (CCS) as a leading weapon to combat climate change and says the Sleipner field where it has buried carbon for 13 years demonstrates the technology is safe.

Green groups are skeptical about storing millions of tons of carbon dioxide underground without risking leaks, even though the United Nations believes a fourth of the cuts in emissions needed to keep climate change under control can come from CCS.

"There are quite big areas in the North Sea that are likely to be suitable for safe CO2 storage," said Olav Kaarstad, senior adviser on CCS for Norway's oil and gas producer StatoilHydro.

"We are learning as we go along but we are very optimistic," he said during a visit to the Sleipner T platform, which houses a treatment plant that takes carbon dioxide (CO2) out of the natural gas stream.

StatoilHydro calls Sleipner "the mother of all CCS projects" but its green status came partly out of necessity as gas found there naturally has a higher CO2 content than clients wanted.

So StatoilHydro and partners Exxon Mobil and Total built the sequestering plant several hundred meters from Sleipner's main A platform, a football stadium-sized rig resting 30 meters above an often raging North Sea on four cylindrical concrete columns. The platforms are linked by a bridge which doubles as a pipeline for the removed CO2.

Instead of emitting the CO2 to the atmosphere and paying Norway's carbon tax of around $30 per metric ton, it is pressurized and injected into a sandstone layer some 1 km under the seabed.

StatoilHydro monitors the injected CO2 by regular seismic scans to gain a picture of how it moves within the reservoir. It also tests miniscule changes in gravity on the seafloor, which indicate CO2 density in the reservoir underneath.

"We have done a lot of research on the reservoir and how the CO2 is behaving, and we feel confident that this is a secure and safe storage," StatoilHydro CEO Helge Lund told Reuters on a sunny but windy day at Sleipner, located nearly 200 km (120 miles) or about an one hour helicopter flight from the coast.

SAFE STORAGE?

Sleipner's CO2 is absorbed by a porous sandstone layer, a giant reservoir some 700 km long and 70-80 km wide called Utsira, which is capped by hundreds of meters of tiny mudstones impermeable for carbon dioxide, StatoilHydro says.

Environmental group Greenpeace said that data showed the reinjected CO2 moving higher and higher toward the seafloor, which they believe may ultimately cause it to leak out.

Carbon dioxide increases the acidity of its environment, which could help it eat its way out of apparently secure barriers well before the gas becomes neutralized over 10,000 years.

When StatoilHydro injected oily water into another part of the Utsira reservoir at the Tordis field some 300 km north of Sleipner, up to 175 cubic meters of the oil escaped in 2008, according to the company, through an undetected crater.

"This case proves how difficult it is to inject and store anything in underground reservoirs, even in the Utsira formation, which is considered to be one of the best studied geological formations on earth," Greenpeace said in a report published this week called "Reality check on carbon storage."

Tectonic activity is another cause for worry. Carbon dioxide in pure form can asphyxiate because it is heavier than air.

In the worst recent case, 1,700 people died after a 1986 earthquake released 1.2 million metric tons of CO2 from the depths of Lake Nyos in Cameroon, the International Energy Agency said.

Norway's government has called CCS its "moon landing" mission and has set up pilot projects to remove carbon from onshore power plant emissions and bury them under the North Sea floor, with Sleipner providing know-how and experience.

StatoilHydro reinjects a million tons of CO2 at Sleipner each year and says it can safely pump in three times more -- giving it potential to store emissions not only from Norway but also elsewhere in Europe once CCS projects come on stream.