Microseismic Monitoring and Geomechanical Modelling of CO2 - bris

APPENDIX B. IN SUPPORT OF CARBON CAPTURE AND STORAGE
leakage 8 . At a second site in North America, CO 2 removed from the waste stream of a gasification
plant in North Dakota is piped to Weyburn, Canada, and stored in a mature oil field. CO 2 has been
injected since 2000, and now over 3 million tonnes are being stored every year. It is anticipated that
the field will store over 50 million tonnes of CO 2 - this is equivalent to the emissions of half a million
(gas-guzzling American) cars per year. Again the comprehensive monitoring program, using both the
latest geophysical techniques as well as geochemical tracers, gives no indication of any leakage 9 . BP
have been storing CO 2 at their In Salah gas field since 2004 at a rate of ∼1 million tonnes per year,
while smaller scale projects that demonstrate the entire chain of CCS operations - from capture at a
power plant to storage underground - are now operational at Schwarze Pumpe in Germany, and at
Lacq in France.
The majority of the public are barely aware of the existence of these successful CCS operations.
Environmental groups are more trusted than politicians and power companies, and some of these
groups (especially Greenpeace, the largest) prefer to highlight scare stories that have only the smallest
relation to CCS operations. Perhaps the most widely circulated centres on the release of CO 2 from
a volcanic lake in Cameroon, Lake Nyos 10 . The lower layers of the lake became saturated with CO 2
emitted from volcanic vents on its bottom, and when the lake overturned approximately 2 million
tonnes were released during the night of 21st August, 1986.
villages, and 2000 people were suffocated.
dangers of large scale leakage near to urbanised areas.
The cloud of CO 2 enveloped nearby
This story is used to highlight in the public mind the
However, could a Lake Nyos style event ever occur above a CCS operation The CO 2 at Nyos was
volcanic in origin, but it was the overturning of the lake that allowed the CO 2 to escape so rapidly.
A common public misconception is that oil is found underground in vast caverns or ‘lakes’, and that
CO 2 would be stored in a similar manner.
In fact oil, and CO 2 , are trapped in the microscopic
pores between the grains that make up a sedimentary rock. The low permeability of such systems
prevents the rapid movement of fluids. Simple physical calculations show that the pressure gradients
needed to move CO 2 trapped in sedimentary rock at rates comparable to the release at Lake Nyos are
unfeasibly large. In short, not possible. Furthermore, the instruments deployed to detect CO 2 leaks
above storage sites are so sensitive that they pick up seasonal variations in plant growth rate! 11
so are capable of detecting the tiniest CO 2 leak. A Lake Nyos style CO 2 release from a CCS operation
is not a possibility.
A second issue raised recently relates to a water leak from the Utsira formation above the Tordis
Field in the North Sea 12 . Statoil are currently storing polluted water from the Tordis Field in the
Utsira formation, and in 2008 it was found that injection had created fractures allowing leakage to
the sea-floor. As discussed above, the Utsira formation is also being used for CCS at Sleipner. The
problem, according to Greenpeace, is that as the Utsira has fractured at Tordis, it must therefore be
unstable at Sleipner as well. In fact, Tordis and Sleipner are over 300km apart from each other. The
8 Torp and Gale, 2004
9 Wilson et al., 2004
10 Rochon et al., 2008, p7 & p30
11 Wilson et al., 2004, p88
12 Bjureby et al. 2009 and Greenpeace Briefing, 2009
and
192