But Finding Should Help Inform Future Project Siting, Researchers Argue
Tamar Hallerman
GHG Monitor
09/21/12
The discovery of a fracture near the world’s first CO2 injection site at Sleipner will likely not pose a threat to the safety of the emissions sequestered there but should help inform future site selection in the North Sea region, according to European researchers. Staff members from ECO2, a consortium funded by the European Commission tasked with establishing best practices for offshore CO2 injection and storage operations in the region, said that last year it found a “large fracture” almost two miles in length about 15 miles north of Statoil’s pioneering Sleipner injection site in the North Sea. The group said that two more testing trips to the site this summer using seismic and sonar data found that the fracture—which is up to 650 feet deep and 30 feet wide and is leaking naturally-occurring methane gas—is likely an old structure that is not related to any CO2 injection operations. ECO2 researchers underscored that despite the formation’s proximity to Sleipner, the CO2 sequestered there will likely “never reach” the fracture area and that the crack is vertically separated from the Utsira Sand reservoir used by Sleipner by several thick, low-permeability sedimentary seals.
In an interview this week, ECO2 project coordinator Klaus Wallmann said the fracture is undetectable by most typical seafloor mapping techniques because it has “almost no topography.” He added that researchers found the fracture because the geologic feature contained softer sediments near it than in the surrounding area. While Wallmann underscored that the fracture will likely not put the safety of Sleipner’s nine million tons of stored CO2 at stake, he said the discovery should inform future site selection and monitoring efforts in the region. “Future storage sites need to be monitored for these natural seepage sites,” he said. “More detailed seafloor monitoring needs to be done using the advanced technologies we have applied here. It’s not really enough to choose storage sites only according to seismic data—you also need very good surveys of seabed structures to identify and locate these natural seeps and to see whether any deep gases are being released.” Wallmann underscored that if injection did occur closer to the fracture—he said that years ago an injection site was being planned closer to the fault—results could have been “horrific” if a leak did occur.
Companies Likely to Invest in Mapping Technology
Wallmann said that companies in the region appear willing to invest in the technology, “The costs are not very high—a few million euros,” he said. “Since the demonstration projects cost billion of euros, a few million isn’t really so relevant as to be a gamechanger.” In the meantime, Wallmann said that ECO2 will continue to monitor the fracture and the area surrounding the Sleipner site, which is the world’s oldest CO2 storage operation. Wallmann said that ECO2 is also talking with Statoil, which is part of the group consortium, about using the seafloor mapping technology utilized by the group for future siting and monitoring efforts. Statoil has been injecting roughly one million tons per year of captured CO2 from its offshore gas processing unit off the west coast of Norway since 1996. Injection operations are expected to continue through 2025. Statoil said it is following the progress of ECO2’s work “with deep interest.” “Sleipner follows a detailed and extensive monitoring plan, and simulations and models are continuously improved as we accumulate knowledge of the seafloor and subsurface,” Statoil spokesman Ola Anders Skauby told GHG Monitor.
