Storage
site analogues and experimental investigations provide
quantification of processes occurring during the life of subsurface
CO2 capture, and possible escape mechanisms. Analogue investigation
provides information at the scale of the storage sites under unique
geological conditions and time frames. Experimental investigations
under controlled conditions provide detailed data on specific processes
observed in analogue sites. St Johns, NM, USA, is a natural laboratory
which presents an opportunity to observe measure and model the
migration of CO2 through a primary cap-rock and subsequent overburden
at geological conditions analogous to the above-seal portions of
planned CO2 storage sites. The Fizzy gas reservoir, North Sea,
and other reservoirs in the North German Basin (Behrmann et al.
1981) are excellent examples of secure natural CO2 storage sites.
By comparing in detail how the cap-rock at St. Johns was breached
and the CO2 subsequently migrated to the surface and contrasting
how the CO2 has been retained at Fizzy will provide insights on
how to avoid for cap-rock failure and how to monitor engineered
storage sites. The thermo-tectonic development of the St. Johns
and Fizzy analogue sites, i.e. the fluid mobility and compositional
variability with time, can be reconstructed on the basis of petrological
and fluid inclusion studies, combined with cathodoluminescence
(CL) techniques and microstructural analysis (healed microfractures).
The changing stress conditions with time are important parameters
for the conditions of crack-healing processes and the mechanical
stability of the cap rock. Detailed petrological studies allow
distinguish carbonate and quartz cement generations, and microstructures
related with fluid-rock interaction, like fluid pathways, paleo-porosity,
diffusional textures, and healed micro-fractures (Van den Kerkhof
and Hein, 2001). Fluid inclusions reflect fluid migration, notably
of CO2-H2O-bearing fluids through the cap rock. Fluid inclusions
inform about temperatures and pressures during trapping. By comparing
past and present gradients, conclusions can be drawn about uplift
or subsidence of the area since the time of fluid entrapment. Furthermore,
fluid inclusions allow the comparison of paleo-fluids with present
pore and circulating fluids, to establish the deformational evolution
of the rock (Vollbrecht et al., 1994; Schild et al. 1998). Chronology
of paleo-stress directions can be derived from the compiled structural
data (Schmidt net).
PANACEA has established a number of valuable connections with organizations that are actually involved in the process of CO2 storage for various purposes (disposal, EOR/EGR and scientific prototyping). It has also created a link with one NER300 project.