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