Potential Leakage of CO2ffrom
Sub-seafloor Storage SitesSub seafloor Storage Sites
Rachel M Dunk Rachel M Dunk
Q1: Where might sub-seafloor storage occur?
Offshore or Onshore?
SaG
asaline A
Oil
& A
quifO fers
Hendricks et al. (2004) Dooley et al. (2005)
Q1: Where might sub-seafloor storage occur?
Offshore or Onshore?
Q2: How do possible leakage fluxes compare to other sources of CO2 to the ocean?to other sources of CO2 to the ocean?
Relative Riskimportant for communication
• SURFACE OCEAN: Invasion of atmospheric (fossil fuel) CO2 – ‘Non Purposeful Storage’
• SEAFLOOR: Injection of volcanic CO2 –Natural Process
Surface Ocean Invasion of CO2
0 40
μmol/kg(m
)
500
403530
Dep
th ( 500
1000
2520
D 1000 15105
Latitude60°N40°N20°N0°60°S 40°S 20°S
15005
LatitudeJGOFS/WOCE, Pacific Meridional Section.
Surface Ocean Invasion of CO2
Cumulative Uptake for Period 1800-1994
Ocean uptake of CO2: 432 GtCO2 emissions: 894 Gt2
Oceanic CO Invasion Rate1980s
Oceanic CO2 Invasion Rate1990s 2000-2005
Gt/yr 6.6±2.9 8.1±1.5 8.1±1.8
SOURCES: Sabine et al. (2004) & IPCC AR4 (2007)
Mt/day 18.1±8.0 22.1±4.0 22.0±5.0
Injection of Volcanic CO2
Injection of Volcanic CO2
Injection of Volcanic CO2
HOTARCBABMORTOTAL COFCOFCOFCOFCOF )()()()()( 22222 +++=
F(3He) CO2/3He F(CO2)
(%)
MORs 489 ± 217 2.1 ± 0.9 1.0 ± 0.6 45 ± 28 (27.8)
Back Arc Basins 109 ± 48 12 8 ± 10 7 1 4 ± 1 3 61 ± 58 (37 8)
2 ( 2)
1012 mol/yr Mt CO2/yrmol/yr 109 mol/mol
Back-Arc Basins 109 ± 48 12.8 ± 10.7 1.4 ± 1.3 61 ± 58 (37.8)
Volcanic Arcs 53 ± 28 23.5 ± 10.0 1.3 ± 0.8 55 ± 37 (34.1)
Hotspots 2 ± 1 4.5 ± 2.6 0.01 ± 0.01 0.5 ± 0.4 (0.3)
TOTAL 3 7 ± 1 7 162 ± 74TOTAL 3.7 ± 1.7 162 ± 74
The Comparison…
• SURFACE OCEAN = 8.1±1.8 GtCO2/yr~600-1000 times > amount of CO2 stored to datef 2
• SEAFLOOR = 162±74 MtCO2/yr~8-23 times > amount of CO2 stored to date f 2
If CCS makes a significant contribution to GHG emission abatement…
2050 2100
15-120 new sites/yr, each injecting 1-4 MtCO2/yr:
Number of Projects
Storage Rate (GtCO /yr)
600-5,000
2 5 5 0
1,400-11,000
5 5 11
2050 2100
Storage Rate (GtCO2/yr) 2.5-5.0 5.5-11
Cumulative Storage (GtCO2) 50-100 250-500
The Comparison…IF sites meet a ‘Gold Standard’… retain 99% of CO2 for 1000 years
…THEN leakage rate << natural fluxin 2100 ~2.5-5.0 MtCO2/yr20-100 times lower than volcanic flux
IF sites are inherently leaky… nominal leakage rate of 200tCO2/site/yr
…THEN leakage rate > natural fluxin 2100 could be greater than 2 GtCO2/yr10 times greater than volcanic flux¼ of current atmospheric invasion rate
Q3: Do we have good analogues for leakage to the marine environment?to the marine environment?
Two sources of in-situ information:
Natural Vent SitesNatural Vent Sites
Purposeful Release ExperimentsPurposeful Release Experiments
P id l t i f tiProvide complementary information –NOT (at present) comprehensive…( p ) p
Known Sites of CO2 Venting…
Inferred Sites of CO2 Venting…
Mesocosm Experiments…PeECE
Release Experiments…
FOCE Concept
A good analogue?THE WHOLE ENVIRONMENT: •Habitat/Ecosystem/Biotopey p
Vent Sites:
Regional scale mis-match between natural vent sites (tectonicallyRegional scale mis-match between natural vent sites (tectonically active) and potential storage targets (tectonically stable). Possible exceptions = Japan & The Mediterranean Sea.
Habitat mapping may contribute to identification of best analogues on a case by case basis.
Experiments:
Can be sited in location of interest (subject to regulations, permitting, and public/NGO opinion)
A good analogue?THE SCALE OF CO2 RELEASE:•Area, Rate, Duration
Vent Sites:
High heat flow presence of faults & fractures providing fluidHigh heat flow, presence of faults & fractures providing fluid migration pathways upper limit on expected flow rates…
However, deeper sites may provide indication of flow rates through oweve , deepe s tes ay p ov de d cat o o ow ates t ougimpeding hydrate caps…
System in equilibrium? (Rather than initial perturbation)y
Experiments:
Currently limited by ability to transport CO2 to depthCurrently limited by ability to transport CO2 to depth
Allows investigation of initial perturbation
A good analogue?THE NATURE OF CO2 RELEASE:•Chemical & Physical Conditionsy
Vent Sites:
Influence of thermal regimeInfluence of thermal regime……CO2 vents may be at ambient or near ambient temperatures.
Influence of other chemicals – in particular building blocks for ue ce o ot e c e ca s pa t cu a bu d g b oc s ochemosynthesis & toxic compounds (CH4, H2S, heavy metals)……leaked CO2 may also contain these species – particularly following transport through the reservoir & overburdenfollowing transport through the reservoir & overburden.
Experiments:
Can be made to measure…
Q4: How might primary leakage occur?
Initial retention of CO2 is almost entirely dependent on physical trapping beneath the caprock Primary characteristic of a secure pp g p yCO2 storage reservoir is a good reservoir/seal pair
Best case scenario
incorporatesincorporates multiple confining
layerslayers
Q4: How might primary leakage occur?
CO2-Seal InteractionsPotential Negative Consequences
Dehydration of the cap rock by reaction with dry injected CO2y p y y j 2 shrinkage & creation of new flow pathways.
Corrosion of the reservoir rock matrix by CO2/water mixtures compaction/collapse of the formation & development of cracks and new migration paths.
Dissolution of components of the cap rock by CO2/water mixtures collapse or failure as a seal.
P t ti l P iti CPotential Positive Consequences
Infilling of faults and fractures in the seal due to precipitation of secondary mineralssecondary minerals
HIGHLY SITE SPECIFIC – ARE MODELS GOOD ENOUGH?
Q5: Will leaked CO2 reach the ocean?
Secondary Trapping Mechanisms
(1) Buoyancy Trapping
(2) Hydrate Formation
(3) Dissolution(3) Dissolution
(4) Residual Trapping
(5) Reactions (carbonate dissolution)
Q5: Will leaked CO2 reach the ocean?Ascent characteristics & efficiency of secondary trapping mechanisms
are strongly dependent on physical properties of leaked CO2
(1) Buoyancy Trapping
Q5: Will leaked CO2 reach the ocean?Ascent characteristics & efficiency of secondary trapping mechanisms
are strongly dependent on physical properties of leaked CO2
(2) Hydrate Formation
Image coourtesy of Shitashimm
a-san Sakai et al., Science 1990
CO2 Hydrates – A self sealing system?
Physical Properties - Case StudiesAscent characteristics & efficiency of secondary trapping mechanisms
are strongly dependent on physical properties of leaked CO2
Case Study 1: Sea of Japan (Cold, Deep)
Case Study 2: Gorgon (Warm, Shallow)
Case Study 3: Barents Sea (Cold, Shallow)
Outstanding Questions/Issues…
(1) Composition of the CO2
Outstanding Questions/Issues…
(2) Modelling hydrate formation processes in di t ( ill ff t lt j ti )sediments (capillary effects, salt rejection)
Outstanding Questions/Issues…
(3) Reaction with sedimentary carbonates ( t f ti hi h d t i t t f(rate of reaction – which determines extent of neutralisation achieved)
(4) Convincing models combining all processes(4) Convincing models combining all processes that can be used to predict CO2 migration in overburdenoverburden
Q7: What is the fate & impact of CO2 in the ocean?the ocean?
Nature Duration & Location of leakageNature, Duration & Location of leakage
Dissolution Characteristics (presence/absence of hydrate, current(presence/absence of hydrate, current regime, enclosed versus restricted)
Hydrate Formation = Ubiquitous
Hydrate Formation = Ubiquitous
Dissolution Plumes…
Enstad et al. (2006)
ocean disposalocean disposal
500m x 500m lake
current = 10 cm/s
dissolution flux
~700 ktCO2/yr
Dissolution Plumes…A: Alendal & Drange (2001) B: Chen & Akai (2004)
1 kgCO2/s1 kgCO2/s
10 cm/s 0.6 kgCO2/s
2.3 cm/s
1 kgCO2/s
5 cm/s
0.1 kgCO2/s0.1 kgCO2/s
2.3 cm/s 5 cm/s
Impacts on Biota…
Impacts on Biota…
Impacts on Biota…
Disturb food webs & ecosystem services? –
e.g. organic matter g grecycling rates & therefore marine
cycles of C &cycles of C & nutrients – potential impacts extending to
surface ocean…
Q8: What are the high risk scenarios?
High probability of 1° leakageHigh probability of 1 leakage
+
Preferential flow paths (well bores, gas p ( , gchimneys) through overburden
+
Vulnerable object in leakage path
Methane Gas Hydrates - Geohazard
Methane Gas Hydrates - Geohazard
Presence indicates potential flow paths
Ri k h i b CO d CHRisk = exchange reaction between CO2 and CH4
Vulnerable Ecosystems: Coral Reefs
Q9: Thoughts on detection/monitoring
• Increase understanding of CO2 behaviour in subsurface - model testing and refinementsubsurface model testing and refinement.
• Verify storage. • Early detection of any leakage. • Develop & test monitoring techniques/methods. p g q• Safeguard the environment.
Define desirable detection thresholds (leakage rate to be detected & timescale of detection)
Monitoring Approaches
• Pragmatic approach
• Tracking movement of CO2 in the subsurface + mass balance checks prior warning of penetration or b i f h k l id ifi i fbypassing of the cap-rock seal + identification of unexpected CO2 migration pathways/leakage points.
• Identify ‘watch points’ (e.g. wellbores, faults) detailed baseline surveys + continuous monitoring
• Detailed monitoring of identified ‘watch points’ should be combined with periodic surveys across the
i f i f h ientire footprint of the storage reservoir.
Visual Tracking
pH Mapping
Acoustic Detection
New Techniques
Thank-you
• Funded by IEA-GHG• Report to be published toward end of year