Stanford University

Global Climate & Energy Project

Geologic Storage of CO2

Lynn OrrStanford University

Energy /Capital Markets WorkshopNew York

October 23, 2007

The Need for Technology

Concentrations of CO2 will riseabove current values (380 ppm),even under the most optimisticscenarios.

Stabilization will require thatemissions peak and then decline.Peak timing depends on thestabilized concentration.

Improvements in efficiency,introduction of renewables,nuclear power, … all help.

New technology will be needed forthe really deep reductions.

Source: IPCC 2007

What resources can we use?Exergy flow of planet Earth (TW)

Geologic Storage of CO2?

• Can we capture the CO2? Efficiently? Cost?

• Do we have enough variety of geologic settings forstorage?

• Is there sufficient volume available in the subsurface tostore enough CO2 to have an impact?

• Do we know enough about the physical mechanisms thatwill trap the CO2 in the subsurface to design safe storageprojects that won’t leak?

• Do we have enough experience with actual operations toundertake storage at scale?

There are multiple routes for capturingCO2 (but it’s expensive!)

Source: IPCC Special Report Carbon Capture & Storage, 2006

• Gas separationprocesses areavailable forcommercial scale

• CO2 is routinelyseparated fromnatural gas

• Early storage fieldtests have usedCO2 that must beseparated anyway(Sleipner, InSalah, Weyburn)

Efficiency and Cost

• Typical efficiencies for the solvent/amine separations arelow: about 15% of the energy expended is required by thethermodynamics – the rest is lost to entropy creation andheat transfer losses.

• Est. costs (2002 $ per tonne CO2 avoided), efficiency (LHV)– New natural gas combined cycle: $37-74 47-50%

– New pulverized coal: $29-51 30-35%

– New IGCC $13-37 31-40%

– New H2 $ 2-56 52-68%

• Cost of CO2 capture is the largest component in cost ofstorage. A breakthrough in separations technology wouldmake a big difference.

Source: IPCC Special Report on CCS, 2005

Relative Carbon Emissions of AlternativeHydrocarbon Fuels

• Production of alternative liquid fuels from coal, tar sands, or oil shalesincreases GHG emissions significantly

• Volumes of CO2 storage required to mitigate the upstream emissions willbe very large if coal, tar sands and heavy oils are used to offset asignificant fraction of conventional hydrocarbon use.

Source: Farrell & Brandt, Env. Res. Let. 1, 2006

0 0.5 1 1.5 2 2.5 3

Conventional Oil

Enhanced Oil Recovery

Tar Sand & Heavy Oil

Gas to Liquids

Coal to Liquids

Oil Shale

Relative Carbon Emissions

Combustion Emissions

Min Mfg Emissions

Max Mfg Emissions

What Types of Rock Formationsare Suitable for Geological Storage?

Specific formation types

• Oil reservoirs

• Gas reservoirs

• Saline aquifers

• Deep unminable coal beds

Rocks in deep sedimentary basins with barriers to vertical flow

are suitable for CO2 storage.

Map showing world-wide sedimentary basins

http://www.glossary.oilfield.slb.com/

What about CO2 storage in basalt?

This is an unproven technology that is

the subject of ongoing research.

100 km

Northern California Sedimentary Basin

Location of Storage Sites inNorth America: Oil and Gas Fields

First North American Carbon

Sequestration Atlas, 2006

CO2 Storage Capacity(Billion Metric Tons)Big Sky 0.8MGSC 0.4MRCSP 2.5PCOR 19.6SECARB 32.4SOUTHWEST 21.4WESTCARB 5.3

TOTAL 82.4

Location of Storage Sites inNorth America: Saline Aquifers

First North American Carbon

Sequestration Atlas, 2006

CO2 Storage Capacity(Billion Metric Tons)Big Sky 271 1,085MGSC 29 115MRCSP 47 189PCOR 97 97SECARB 360 1,440SOUTHWEST 18 64WESTCARB 97 288

TOTAL 919 3,378

Location of Storage Sites inNorth America: Coal

First North American Carbon

Sequestration Atlas, 2006

CO2 Storage Capacity(Billion Metric Tons)Big Sky NA NAMGSC 2.3 3.3MRCSP 0.7 1.0PCOR 8.0 8.0SECARB 57 82SOUTHWEST 0.9 2.3WESTCARB 87 87

TOTAL 156 183

World Regional CO2 Storage

Opportunities

• Emission sources

Emission regions

(300 km buffer)Prospective basinsNon- Prospectiveprovinces

Source: John Bradshaw, Geoscience Australia

Key Questions

• How far does injected CO2 propagate (where will weneed to monitor)?

• How long does it take to immobilize the CO2 by somemechanism?

• What is the ultimate fate of the CO2?

• What fraction of the CO2 has the potential to escape (asa function of time)?

• Can we design injection processes that reduce thepotential for leakage?

The state of knowledge differs for the three main types ofpotential storage sites.

Mechanisms: immobilize CO2 bycapillary trapping

• Pushing CO2 with water,causes CO2 bubbles to beisolated in the tiny pores inthe rock.

• These trapped bubbles arevery difficult to move.

• Can we make use of trappingto design injection schemesthat trap the CO2 effectively?

Capillary trapping can immobilize CO2 relatively quickly. If theCO2 is trapped, it can’t leak during the time required for it todissolve. Once dissolved, it does not move upward in the rocks.

Trapped bubbles (after removal of the rock)(Image: N. R. Morrow)

Gravity-Dominated DisplacementsNgv= 55, Pc= 0

a) Homogeneous

b) Short Correlation Length

c) Long Correlation Length

d) Layered Aquifer

(i) (ii) (iii)

0 Sg 0.8 0 Sg 0.8 0 Sgt 0.36

Strong gravity forces move less dense CO2 to the top of the aquifer.Capillary trapping occurs at the base of the gravity tongue as brine invadesbehind gas during gravity relaxation after injection ceases.

Water injection to trap CO2

Injecting water after the CO2 can trap part of it relatively quickly.

Mechanisms: dissolution of CO2 inbrine

• Diffusion of CO2 into brine createsmore dense brine at the upperinterface.

• That configuration is unstable, andgravity-driven fingers develop (butthe fingers move slowly).

24 years 52 years 108 years

Source: Riaz, Hesse, Tchelepi & Orr, J Fluid Mech 2006

The combination of capillarytrapping and dissolutionimmobilizes much of theinjected CO2, but not instantly.

Storage security increaseswith time.

Storage in Coal Beds

• Storage mechanism isadsorption of CO2 on coal

• CO2 adsorbs more stronglythan does CH4 or N2

• Complex flow in fractured coals

• Adsorbed gas reducespermeability – managingpermeability reduction will beessential

• Very limited field experience todate – not yet ready for primetime

Potential for leakage?

Source: IPCC Special Report Carbon Capture & Storage, 2006

Careful site selection, good injection design, careful operationwill be required.

Experience: Oil and Gas Reservoirs

• Known geologic seal(otherwise the oil or gaswould not be there.

• Data needed for flowprediction available fromgeology, producinghistory.

• 30+ years of experiencewith injection of CO2 forenhanced oil recoveryprovides significantpractical experience.

Image: DOE Basin Oriented Studies for EOR, Permian Basin, 2006

Experience: aquifer injection in theNorth Sea

• Sleipner West: 1 milliontonnes/yr injection.

• CO2 separated fromproduced gas.

• About 10 million tonnesinjected so far.

• CO2 has been retained wellin the target formation.

Estimated Costs for GeologicStorage (2002 $/tonne)

• Onshore saline aquifers:– Australia $0.2 – 5.0

– Europe $1.9 – 6.2

– USA $0.4 – 4.5

• Offshore saline aquifers

– Australia $0.5 – 30.2

– North Sea $4.7 – 12

• Depleted Oil Fields

– USA $0.5 – 4

• Depleted Gas Fields– USA $0.5 – 12.2

• Enhanced Oil Recovery– USA $-92 – 66.7

(depends strongly on oil price)Source: IPCC Special Report on CCS, 2005

• Enhanced Coalbed CH4:– Australia $-20 – 150

(depends strongly on gas price)

There is considerableuncertainty in the costestimates – but storage atcosts well below the cost ofCO2 separation appearspossible at significant scale

Note: Operators currentlybuy CO2 at ~$15/tonne forEOR.

Reality check: the volumesare very large!

• At a CO2 density of 500 kg/m3 (1000 m depth at 50˚C),injection of 1 billion tonnes/yr of CO2 is equivalent to ~35 million barrels/day.

• At a CO2 density of 700 kg/m3, 1 Gt CO2 is equivalent to~ 25 million barrels/day.

• Current worldwide emissions of CO2, ~ 25 Gt/yr:~ 625 – 825 million barrels/day!

• World oil production is currently ~85 million barrels/day.

• These volumes are large enough that it is clear that CO2storage in geologic formations will be but one of avariety of ways to reduce CO2 emissions to theatmosphere.

Do we know enough to undertakelarge-scale geologic storage?

• Can we capture the CO2? Yes, though cost is an issue.

• Do we have enough variety of potential geologic settingsfor storage? Yes, in the US, at least.

• Do we know enough about the physical mechanisms thatwill trap the CO2 in the subsurface to design safe storageprojects that won’t leak? Yes for oil and gas, betterquantification needed for aquifers, no for coal storage.

• Is there sufficient volume available in the subsurface tostore enough CO2 to have an impact? Yes.

• Do we have enough experience with actual operations toundertake storage at scale? Yes for oil and gas, not yetbut beginning for aquifers, no for coal beds.