Large releases from CO2 storage reservoirs: analogs, scenarios,and modeling needs Page: 2 of 6
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Table 1. Summary of natural large releases of CO2.
Site CO2 Source Geologic model Event triggering Pathway Type of release
for accumulation leakage for leakage
Mammoth Magmatic + Accumulation at -2 Seismic activity and Faults and Fast, diffuse, vent, spring
Mountain, CA thermal km depth in reservoir pressurization fractures
USA decomposition of porous/fractured rock
carbonates under caprock
Solfatara, Magmatic + Relatively shallow No specific release event Faults and Diffuse and vent
Italy thermal zone of fractured rock captured fractures
decomposition of contains gas phase
carbonates and overlies aquifers,
then magma body at
several km depth
Matraderecsk Geothermal/copper CO2 accumulates in No specific release event Faults and Diffuse, vent, spring
e, Hungary -zinc mineralization karst water reservoir captured fractures
(~1 km depth)
Latera Thermal CO2 accumulates in No specific release event Faults and Diffuse, vent, spring
caldera, Italy decomposition of liquid-dominated, captured fractures
carbonates carbonate geothermal
reservoir capped by
Albani Hills, Magmatic + Deep pressurized Slow releases with several Faults and 1995 and 1999 events Fast,
Italy thermal reservoirs in structural sudden large releases also fractures diffuse, vent, spring/well
decomposition of highs of sedimentary occurring, possibly triggered
carbonates bedrock by seismic activity
Dieng, Magmatic Unknown Volcanic, possibly Fissure Eruptive
Indonesia "pneumatic", eruptions
Rabaul, Magmatic Unknown Unknown Fractures Fast, vent
Lakes Magmatic Accumulation in deep Rapid lake turnover NA Eruptive (limnic)
Monoun and lake and stable triggered at Monoun by
Nyos, stratification landslide; Nyos trigger
Laacher See, Magmatic NA Seasonal lake overturn and NA Diffusive and bubbling from
Germany mixing lake surface, diffuse from lake
Clear Lake, Thermal CO2 derived from No specific release event Faults and Gas vents, springs
CA, USA decomposition of liquid-dominated captured fractures
metasedimentary geothermal reservoir
rocks, minor hosted in marine
Paradox Thermal Reservoirs are No specific release event Faults and Diffuse, gas seeps, springs
Basin, UT, decomposition of vertically stacked, captured fractures
USA carbonates sandstone units, in
Florina Basin, Thermal Reservoirs are No specific release event Slow leakage Springs, gas seeps
Greece decomposition of vertically stacked, captured along rock
carbonates limestone and discontinui-
sandstone units ties
(upper unit at 300 m
depth)., capped by
silts and clays.
While detailed information on geologic models of natural CO2 accumulation or migration pathways
is often unavailable, a few general conclusions can be drawn from the analog summary in Table 1
with respect to the risk assessment of geologic storage of CO2.
1. Unsealed faults and fracture zones are the main pathways for gas migration in most natural
analogs with large CO2 discharge. It is thus mandatory to be able to predict qualitatively and
quantitatively the fast upward flow of CO2 in high-permeability zones that may extend from
depth to surface. During upward migration, CO2 is affected by transitions from super- to sub-
critical conditions, phase changes between liquid and gaseous CO2, phase partitioning between
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Birkholzer, Jens; Pruess, Karsten; Lewicki, Jennifer; Rutqvist,Jonny; Tsang, Chin-Fu & Karimjee, Anhar. Large releases from CO2 storage reservoirs: analogs, scenarios,and modeling needs, article, September 1, 2005; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc897395/m1/2/: accessed April 23, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.