Herbert Hofsttter

CCS Carbon Capture & Storage

In order to stabilize the greenhouse gases in

the atmosphere, many countries have

committed themselves to reduce their

greenhouse gas emissions. These emissions

are dominated by CO2.

CO2 capture and storage (CCS) in geological

reservoirs may be part of the strategy to

reduce global anthropogenic CO2 emissions.

General

Ice core evaluation

TLV (Threshold Limit Value) 5,000 ppm

Lethal concentration 150,000

ppm

Density relative to air

density 1.53

Density 1.977

kg/nm3

Colour colourless

Odour slightly

acetous

Triple Point T: -56.6C

p: 5.18 bar

Critical Point T: 31.06C

p: 73.8 bar

Supercritical

Region (1)

Supercritical

Region (2)

CO2 Properties

The volume decreases rapidly at

~700m depth, when

CO2 reaches

supercritical state.

At depths below 1.5km the density and

specific volume

become nearly

constant.

IPCC Special Report on Carbon dioxide Capture and Storage, 2005.

CO2 Properties

capturing of CO2 at power plants

(through Absorption,

Adsorption or

Membranes)

bring CO2 in supercritical phase

transport to storage area

injection of CO2 into selected formations

Capture Processes

Absorption: Physical:

Rectisol Selexol

Chemical: Monoethanolamine (MEA) Diethanolamine (DEA)

Adsorption: Pressure Swing Adsorption (PSA) Temperature Swing Adsorption (TSA) Electrical Swing Adsorption (ESA)

Membranes: Gas separation membranes Gas absorption membranes

CO2 Storage

Terrestrial Storage:

Depleted oil and gas reservoirs

Saline formations/Aquifer

Minerals

Unminable coal seams

Marine Storage:

American Petroleum Institute, 1986

Hydrocarbon traps

Porous rock

Porous rock

Sandstone core

UV Light

Impermeable shale

(seal)

Permeable sandstone

(storage reservoir)

Impermeable shale

Depleted Oil and Gas Reservoirs

have proved their tightness over periods of time

lot of data available (porosity, permeability, thickness of seal rock and reservoir rock)

lot of boreholes (wells) available

probable CO2 storage capacity can be calculated (simulated) out of production

data (pressure, volumes etc.)

initial pressure to be considered

Saline Formations/Aquifer

geographically wide distribution

huge potential for CO2 storage capacity

only little information and experience available compared to depleted

reservoirs

unsecure sealing characteristics, no drilled wells

volume expansion

initial pressure

Unminable Coal Seams

onto pore surface of coals altering quantity of methane is adsorbed

CO2 injection can replaces methane, which can be recovered (2 to 3 molecules of CO2 are absorbed for one molecule CH4)

swelling can occur drop in permeability (fracturing can probably overome this neg. impact of underground swelling)

like aquifers also coalbeds are not well understood at the moment

(CO2 related)

Storage Potential, worldwide

Gt CO2 (min) Gt CO2 (max)

Depleted Oil and

Gas Reservoirs 675(1) 900(1)

Unmineable Coal

Seams 3-15 200

Aquifer 1,000 possible 10,000

(1) + 25% possible from future exploration wells

Ocean Storage

theoretical potential would be enormous

two models: dissolution and lake (hydrates)

Risk: environmental damages

- suffocation of ocean organisms - acidity of ocean increases due to generation of carbonic acid [H2CO3]

main uncertainty: will dissolved CO2 or the hydrates move to the sea level and equilibrate with the atmosphere?

IPCC Special Report on Carbon dioxide Capture and Storage, 2005.

Risks Well

Oil/gaswells were designed for a different purpose and

for different media (CO2

ocurrence not considered if

not originally in the reservoir)

Abandoned wells with questionable data about

completion.

Leaking casing, cementation and completion.

Leaking faults and seals

fresh water

injection wellabandoned well

CO2CO2

CO2

CO2

CO2

CO2

CO2

CO2

CO2

caprock

fault

fracture

spill point

CO2 Corrosion

CO2 dissolves in water and form carbonic acid [H2CO3]

decreasing pH

general corrosion or pitting corrosion

of carbon steel

corrosion occure in presence of a liquid phase and at

locations where CO2 condenses from the vapor

phase

O2

CO2

H2S

Dissolved gas concentration in water phase [ppm]O

2

CO2

H2S

10 ppm

500 ppm

1000 ppm

0

Overa

ll corr

osio

nra

te c

arb

on

ste

el

Surface

cementation

Partial

cementation

Liner

cementation

Liner

cementation

Challenge for the material

For safe storage mandatory:

CO2 resistant cement

CO2 resistant equipment

- wellhead & X-mas tree

- tubings (fiberglass), gas tight

connections

- packer

- side door

- differential pressure valve (WL

retrievable)

- alkaline packer fluid (e.g. K2CO3)

- slickline and tools (gauges etc.)

Risk assessment

Requirements on CO2 injector wells:

right material selection for casing and cementation

cementation job has to be proved by tests and logs

completion has to withstand mechanical, chemical and thermal demands

Emergency Shutdown (ESD) on the well head

Subsurface Safety Valve (SSSV)

sensors (sensible to CO2, H2S) linked to ESD and SSSV

monitoring

Conclusion Open Questions

Is CO2 a waste material - legal aspects?

Is CCS a storage, a production technique (EOR/EGR) or sequestration?

Environmental impact if CO2 migrates to the surface?

Who is the owner of the stored carbon dioxide? (The state is owner of

hydrocarbon bearing formations.)

Impact on rock matrix?

General well integrity?