what does co2 geological storage really mean?

Climate change and the need for CO2 geological storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1. Where and how much CO2can we store underground? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2. How can we transport and inject large quantities of CO2? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

3. What happens to the CO2once in the storage reservoir? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

4. Could CO2 leak from the reservoir and, if so, what might be the consequences? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

5. How can we monitor the storage site at depth and at the surface? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

6. What safety criteria need to be imposed and respected? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

What CO2GeoNet can do for you . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Contents

Groundlevel

CO2 transitions from gas to

supercritical fluid

An approximate1000 m3 volume

of CO2 at ground level

20 m3

11 m3

Critical depth3.8 m3

3.2 m3

0

0.5

1

1.5 2.8 m3

epth

(km

)

itica

l flu

idCO

2 as

gas

This Brochure was produced thanks to the contributions of:Rob Arts, Stanley Beaubien, Tjirk Benedictus, Isabelle Czernichowski-Lauriol, Hubert Fabriol, MarieGastine, Ozgur Gundogan, Gary Kirby, Salvatore Lombardi, Franz May, Jonathan Pearce, Sergio Persoglia,Gijs Remmelts, Nick Riley, Mehran Sohrabi, Rowena Stead, Samuela Vercelli, Olga Vizika-Kavvadias.

2

No more smoking chimneysA pipeline brings CO2 and puts it in the ground

This is good for the Earth

For our childrenCO2 geological storage makes sense

Massimo, age 10, Rome - Italy

3 What does CO2 geological storage really mean?

© S

apie

nza

URS

A vision of the future

Mankind is releasing excess CO2into the atmosphere

It is now accepted that human activities are disturbingthe carbon cycle of our planet. Prior to the industrialrevolution and extending back some 10,000 years, thisfinely balanced cycle, involving the natural exchange ofcarbon between the geosphere, the biosphere, theoceans and the atmosphere, resulted in a low range ofCO2 concentrations in the atmosphere (around 280

ppm, i.e. 0.028%). However, over the past 250 years,our prolific burning of fossil fuels (coal, oil, gas) forpower production, heating, industry and transportation,has incessantly raised the amount of CO2 emitted intothe atmosphere (Fig. 1). About half of this human-induced excess has been reabsorbed by vegetation anddissolved in the oceans, the latter causing acidificationand its associated potentially negative impacts onmarine plants and animals. The remainder hasaccumulated in the atmosphere where it contributes toclimate change, because CO2 is a greenhouse gas thattraps part of the sun’s heat, causing the earth’ssurface to warm. Immediate radical action is needed tostop today's atmospheric CO2 concentration of 387ppm (already a +38% increase compared to pre-industrial levels) from rising beyond the critical level of450 ppm in the coming decades. Experts worldwideagree that above this level, it may no longer be possibleto avert the most drastic consequences.

Returning the carbon back into the ground

Our world has been heavily dependent on fossil fuelssince the start of the Industrial Age in the 1750s, so itis not surprising that the transformation of our societyinto one based on climate-friendly energy sources willtake both time and money. What we need is a short-term solution that will help reduce our dependence onfossil fuels by using them in a non-polluting way as afirst step, thus giving us the time needed to developtechnologies and infrastructure for a renewable-energyfuture. One such option is to create a closed loop in theenergy production system, whereby the carbonextracted from the ground originally in the form of gas,oil, and coal is returned back again in the form of CO2.Interestingly, underground storage of CO2 is not ahuman invention, but a totally natural, widespreadphenomenon manifested by CO2 reservoirs that haveexisted for thousands to millions of years. One suchexample is the series of eight natural CO2 reservoirs insouth-eastern France discovered during oil explorationin the 1960s (Fig. 2). These and many other naturalsites throughout the world prove that geologicalformations are able to store CO2 efficiently and safelyfor extremely long periods of time.

CO2 Capture and Storage: a promising mitigation pathway

Amongst the spectrum of measures that need to beurgently implemented to mitigate climate change andocean acidification, CO2 Capture and Storage (CCS*)

Climate change and the need for CO2 geological storage

4

Figure 2France's carbogaseousprovince.

Figure 1Global CO2 emissionslinked to man'sactivities amount to30 billion tons (Gt) peryear, corresponding to8.1 Gt of carbon: 6.5 Gt from burningfossil fuels and 1.6 Gtfrom deforestation andagricultural practices.

Natural CO2 fields

Exploited carbogaseous waters (drinking water, spa)

© B

RGM

im@

gé©

BRG

M im

@gé

* See glossary at the end.

can play a decisive role as it could contribute 33% ofthe CO2 reduction needed by 2050. CCS involvescapturing CO2 at coal- or gas-fired power stations andindustrial facilities (steel mills, cement plants,refineries, etc.), transporting it by pipeline or ship to astorage location, and injecting it via a well* into asuitable geological formation for long-term storage(Fig. 3). In view of the growing world population andrising energy demand in developing countries, as wellas the current lack of large-scale alternative 'clean'energy sources, the continued use of fossil fuels isinevitable in the short term. Hand in hand with CCS,however, humanity could progress in anenvironmentally friendly way while at the same timecreating a bridge to a worldwide economy based onsustainable energy production.

Worldwide development of CCS is flourishing

Major research programmes on CCS have beenconducted in Europe, the United States, Canada,Australia and Japan since the 1990’s. Muchknowledge has already been acquired at the world’sfirst large-scale demonstration projects, where CO2has been injected deep underground for several years:Sleipner in Norway (about 1Mt/year since 1996)(Fig. 4), Weyburn in Canada (about 1.8Mt/year since2000), and In Salah in Algeria (about 1Mt/year since2004). International collaboration on CO2 storageresearch, fostered by IEA-GHG* and CSLF*, at theseand other sites has been particularly important inextending our understanding and developing aworldwide scientific community that is addressing thisissue. An excellent example is the IPCC* specialreport on CO2 capture and storage (2005), whichdescribes the current state of knowledge and theobstacles that must be overcome to allow thewidespread implementation of this technology. Robusttechnical expertise already exists, and the world isnow confidently moving into the demonstration phase.In addition to technical developments, legislative,regulatory, economic and political frameworks arebeing drawn up, and social perception and supportare being assessed. In Europe, the goal is to have asmany as 12 large-scale demonstration projects up-and-running by 2015 to enable widespreadcommercial deployment by 2020. For this purpose, inJanuary 2008, the European Commission issued the“Climate action and renewable energy package”,which proposes a Directive on CO2 geological storageand other measures to promote the development andsafe use of CCS.

Key questions on CO2 geological storage

CO2GeoNet Network of Excellence was created underthe auspices of the European Commission as a groupof research institutions capable of maintaining Europe

Figure 4A vertical cross-section of the Sleipner site, Norway.The natural gas, extracted at a depth of 2500 m, containsseveral percent of CO2 that needs to be removed to complywith commercial standards. Instead of releasing it into theatmosphere, the captured CO2 is injected at approximately1000-m depth into the sandy Utsira aquifer*.


Figure 3At power plants, theCO2 is captured byseparating it out fromthe other gases. It isthen compressed andtransported viapipeline or ship to itsgeological storagesite: deep salineaquifers, depleted oiland gas fields,unmineable coalseams.

at the forefront of large-scale international research.One of CO2GeoNet's goals is the communication ofclear scientific information on the technical aspects ofCO2 geological storage. To encourage dialogue on theessential aspects of this vitally important technology,CO2GeoNet researchers have prepared basic answersto several frequently asked questions. In the followingpages, you will find explanations as to how CO2geological storage can be carried out, under whatcircumstances it is possible, and what the criteria arefor its safe and efficient implementation.

© S

tato

ilHyd

ro©

BRG

M im

@gé

Three main storage options exist for CO2 (Fig. 1):1. Depleted natural gas and oil fields – well known

due to hydrocarbon exploration and exploitation,offer immediate opportunities for CO2 storage;

2. Saline aquifers – offer a larger storage potential,but are generally not as well known;

3. Unmineable coal seams – an option for the future,once the problem of how to inject large volumes ofCO2 into low-permeability* coal has been solved.

The reservoirs

Once injected underground into a suitable reservoirrock, the CO2 accumulates in the pores betweengrains and in fractures, thus displacing and replacingany existing fluid such as gas, water or oil. Suitablehost rocks for CO2 geological storage should thereforehave a high porosity* and permeability. Such rockformations, the result of the deposition of sedimentsin the geological past, are commonly located in so-called “sedimentary basins”. In places, thesepermeable formations alternate with impermeablerocks, which can act as an impervious seal.Sedimentary basins often host hydrocarbon

reservoirs and natural CO2 fields, which proves theirability to retain fluids for long periods of time, havingnaturally trapped oil, gas and even pure CO2 formillions of years. The subsurface is often depicted as an over-simplified, homogeneous, layer-cake structure inillustrations showing the possible storage options forCO2. In reality, however, it is composed of unevenlydistributed and locally faulted rock formations,reservoirs and cap rocks forming complex,heterogeneous structures. In-depth knowledge of thesite and geoscientific experience are required toassess the suitability of underground structures thatare proposed for long-term CO2 storage. Potential CO2 storage reservoirs must fulfil manycriteria, the essential ones being:• sufficient porosity, permeability and storage

capacity;• the presence of overlying impermeable rock – the

so-called “cap rock” (e.g. clay, clay stone, marl, saltrock), which prevents the CO2 from migratingupwards;

• the presence of “trapping structures” – in otherwords features, such as a dome-shaped cap rock,

Where and how much CO2can we store underground?

Figure 1CO2 is injected intodeep geological layersof porous andpermeable rocks (cf. sandstone inbottom inset), overlainby impermeable rocks(cf. claystone in topinset) that prevent theCO2 from escaping tothe surface. The mainstorage optionsinclude:1. Depleted oil/gasreservoirs withenhanced recoverywhere possible; 2. Aquifers bearingsalty water unfit forhuman consumption; 3. Deep unmineablecoal seams locallyassociated withenhanced methanerecovery.

6

CO2 cannot be injected just anywhere underground, suitable host rock formationsmust first be identified. Potential reservoirs for CO2 geological storage existthroughout the world and offer sufficient capacity to make a significantcontribution to mitigating human-induced climate change.

© B

RGM

im@

gé

that can control the extent of CO2 migration withinthe storage formation;

• location deeper than 800 m, where pressures andtemperatures are high enough to enable the storageof CO2 in a compressed fluid phase and thusmaximize the quantity stored;

• the absence of drinking water: CO2 will not beinjected into waters fit for human consumption andactivities.

Where to find storage sites in Europe

Sedimentary basins are widespread throughoutEurope, for example offshore in the North Sea oronshore surrounding the Alpine mountain chains (Fig. 2). Many formations in the European basins fulfilthe criteria for geological storage, and are currentlybeing mapped and characterized by researchers.Other European areas are composed of ancientconsolidated crust, such as much of Scandinavia, andthus do not host rocks suitable for CO2 storage.One example of an area with potential for storage isthe Southern Permian Basin, which extends fromEngland to Poland (represented on Figure 2 by thelargest ellipse). The sediments have been affected byrock-forming processes that left some of the porespace filled with saline water, oil or natural gas. Theclay layers that exist between the porous sandstoneshave been compacted to low-permeability strata,which prevent fluid ascent. Much of the sandstoneformations are located at depths between 1 and 4 km,where pressure is high enough to store CO2 as adense phase. The salt content in the formation watersincreases in this depth interval from about 100 g/l to400 g/l, in other words, much saltier than seawater(35 g/l). Movements in the basin have caused plasticdeformation of the rock salt, creating hundreds ofdome-shaped structures that subsequently trappednatural gas. It is these traps that are being studied foreventual CO2 storage sites and pilot projects.

Storage capacity

Knowledge of CO2 storage capacity is needed bypoliticians, regulatory authorities and storageoperators. Storage capacity estimates are usuallyhighly approximate and based on the spatial extent ofpotentially suitable formations. Capacity can beassessed on different scales, from national scale forrough estimates, through to basin and reservoir scalefor more precise calculations that take into account theheterogeneity and complexity of the real geologicalstructure.

Volumetric Capacity: Published national storagecapacities are generally based on calculations ofthe formations' pore volume. In theory, the storagecapacity of a given formation can be calculated bymultiplying its area by its thickness, its averageporosity and the average density of CO2 at reservoir

depth conditions. However, because the pore spaceis already occupied by water, only a small part canbe used for storage, generally assumed to be about1-3%. This storage capacity coefficient is thenapplied when assessing the volumetric capacity.

Realistic Capacity: More realistic capacity estimatescan be made on single storage sites throughdetailed investigations. Formation thickness is notconstant, and reservoir properties can vary overshort distances. Knowledge of the size, shape andgeological properties of structures allows us toreduce the uncertainties in the volume calculations.Based on this information, computer simulationscan then be used to predict CO2 injection andmovement within the reservoir in order to estimate arealistic storage capacity.

Viable Capacity: Capacity is not merely a question ofrock physics. Socio-economic factors also influencewhether or not a suitable site will be used. Forexample, moving CO2 from the source to thestorage site will be governed bytransportation costs. Capacity will alsodepend on the purity of the CO2, as thepresence of other gases will reducethe reservoir volume available forCO2. Finally, political choicesand public acceptance willhave the last say as towhether or not the available reservoircapacity will actually be exploited.

In conclusion, we know that the capacity for CO2 storagein Europe is high, even if uncertainties exist related toreservoir complexity, heterogeneity and socioeconomicfactors. The EU project GESTCO* estimated the CO2storage capacity in hydrocarbon fields in and around theNorth Sea at 37 Gt, which would enable largeinstallations in this region to inject CO2 for severaldecades. Updating and further mapping of storagecapacities in Europe is a matter of ongoing research, inindividual member states and through the EUGeocapacity* project for Europe at large.

Figure 2Geological Map ofEurope showing thelocation of the mainsedimentary basins (redellipses) where suitablereservoirs for CO2storage can be found(based on theGeological Map ofEurope at 1:5,000,000scale).


© B

GR

Compression

CO2 is compressed into a dense fluid form thatoccupies significantly less space than a gas.Once the CO2 has been separated from the flue gasin the power plant or industrial facility, the resultinghighly concentrated CO2 stream is dehydrated andcompressed, making transport and storage moreefficient (Fig. 1). Dehydration is necessary to avoidcorrosion of equipment and infrastructure and,under high pressure, the formation of hydrates (solidice-like crystals that can plug equipment and pipes). Compression is carried out together with dehydrationby a multistage process: repeated cycles ofcompression, cooling and water separation.Pressure, temperature and water content all need tobe adapted to the mode of transport and to thepressure requirements at the storage site. Keyfactors for the design of the compressor installationare gas flow rate, suction and discharge pressures,heat capacity of the gas, and efficiency of thecompressor. The technology for compression isavailable and already widely used in many industrialfields.

Transportation

CO2 can be transported by either ship or pipeline.Ship transportation of CO2 is currently only operatedat very small scales (10,000-15,000 m3) forindustrial uses, but this could become an attractive

option in the future for CCS projects where a near-coast source is very far from a suitable reservoir. Thevessels used for transporting liquefied petroleum gas(LPG) are suitable for CO2 transportation. Inparticular, the semi-refrigerated systems are bothpressurized and cooled, and thus the CO2 can betransported in the liquid phase. The newest LPGships have volumes of up to 200,000 m3 and arecapable of transporting 230,000 t of CO2. However,ship transport does not provide continuous flowlogistics, and intermediate storage facilities arerequired at the port to handle the reloading of CO2.Pipeline transportation is currently employed forlarge quantities of CO2 used by oil companies inEnhanced Oil Recovery* (approximately 3000 km ofCO2 pipelines in the world, most in the UnitedStates). This is more cost-effective than shiptransportation and also offers the advantage ofproviding a continuous flow from the capture plant tothe storage site. Existing CO2 pipelines all operate athigh pressures under supercritical conditions for CO2under which it behaves like a gas but has a liquiddensity. Three important factors determine thequantity that a pipeline can handle: its diameter, thepressure along its length and, consequently, its wallthickness.

Injection

When the CO2 arrives at the storage site, it is injectedunder pressure into the reservoir (Fig. 2).Injection pressure must be sufficiently greater thanreservoir pressure to move the reservoir fluid awayfrom the injection point. The number of injection wellsdepends on the quantity of CO2 to be stored, theinjection rate (volume of CO2 injected per hour), thepermeability and thickness of the reservoir, themaximum safe injection pressure, and the type ofwell. As the main objective is the long-termcontainment of CO2, we must be certain of thehydraulic integrity of the formation. High injection ratescan cause pressure increases at the point of injection,particularly in low-permeability formations. Injectionpressure usually should not exceed the fracturepressure of the rock as this may damage the reservoiror the overlying seal. Geomechanical analysis andmodels are used to identify the maximum injectionpressure that will avoid fracturing the formation.

How can we transport and injectlarge quantities of CO2?

Figure 1Stages of geologicalstorage of CO2. Inorder to bring CO2from its emission pointtowards its safe anddurable storage, it hasto go through a wholechain of operationsincluding capture,compression,transportation andinjection.

8

After its capture at the industrial facility, the CO2 is compressed, transported, and theninjected into the reservoir formation through one or several wells. The whole chain has to be optimized to enable the storage of several millions of tons of CO2 per year.

© B

RGM

im@

gé

Chemical processes might affect the rate at whichCO2 can be injected into the formation. Dependingon the reservoir rock type, the composition of thefluids, and the reservoir conditions (such astemperature, pressure, volume, concentration,etc.), mineral dissolution and precipitationprocesses can occur near the well. This can lead toincreased or decreased injection rates. As soon asCO2 is injected, part of it dissolves in the saltyreservoir water and the pH* slightly decreases,buffered by the dissolution of carbonate mineralspresent in the host rock. Carbonates are the firstminerals to dissolve as their reaction rate is veryhigh and dissolution starts as soon as injectionbegins. This dissolution process can increase theporosity of the rock and the injectivity*. However,following dissolution, carbonate minerals can re-precipitate and cement the formation around thewell. High flow rates can be used to limitpermeability reduction near the well, thusdisplacing the geochemical equilibrium area ofprecipitation farther away. Drying is another phenomenon induced byinjection. After the acidification phase, the residualwater that has remained around the injection welldissolves in the injected dry gas, which in turnconcentrates chemical species in the brine*.Minerals (such as salts) can then precipitate when

the brine is sufficiently concentrated, thus reducingpermeability around the well.These injectivity issues depend on complexinteracting processes that occur locally around theinjection well, but that are also highly dependent ontime and distance to the injection well. Numericalsimulations are used to assess such effects.Injection flow rates need to be carefully handled toovercome processes that might limit the injectionof the desired quantities of CO2.

CO2 stream composition

The composition and purity of the CO2 stream,which are a result of the capture process, have asignificant influence on all subsequent aspects ofa CO2 storage project. The presence of a fewpercent of other substances, such as water,hydrogen sulphide (H2S), sulphur and nitrogenoxides (SOx, NOx), nitrogen (N2) and oxygen (O2),will affect the physical and chemical properties ofthe CO2 and its associated behaviour and impacts.The presence of such substances must thereforebe carefully considered when designing thecompression, transportation and injection phasesand also when adjusting the operating conditionsand equipment.

In conclusion, the transportation and injection oflarge quantities of CO2 is already feasible.However, if the geological storage of CO2 is to bewidely deployed, all the stages involved need to betailored to each storage project. The keyparameters are the thermodynamic properties ofthe CO2 stream (Fig.3), flow rates, and upstreamand reservoir conditions.

Figure 3 Density of pure CO2(in kg/m3) as afunction oftemperature andpressure. The yellowline corresponds to atypical pressure andtemperature gradientin a sedimentarybasin. At depthsgreater than 800 m(~8 MPa), reservoirconditions facilitatehigh densities (blueshading). The greencurve is the phaseboundary betweengaseous and liquidCO2. Typical pressureand temperatureconditions for capture,transport and storageare indicatedrespectively by A, B and C.

Groundlevel

CO2 transitions from gas to

supercritical fluid

An approximate1000 m3 volume

of CO2 at ground level

20 m3

11 m3

Critical depth3.8 m3

3.2 m3

0

0.5

1

1.5

2

2.5

2.8 m3

2.7 m3

2.7 m3

Little further compression

below this depth

Dep

th (k

m)

CO2 a

s su

perc

ritic

al fl

uid

CO2 a

s ga

s

00 50 100 150 200

Temperature [°C]

10

20

30

40

50Pressure [MPa]

Figure 2When injected underground, CO2 becomes a densesupercritical* fluid at around 0.8 km depth. Its volume isdramatically reduced from 1000 m3 at the surface to 2.7 m3 at 2-km depth. This is one of the factors thatmakes the geological storage of large quantities of CO2so attractive.

9

© IP

CC

© B

GR

What does CO2 geological storage really mean?

What happens to the CO2once in the storage reservoir?

Figure 1The injected CO2,which is lighter thanwater, tends to riseand is stopped byoverlying impermeablerocks.

Microscopic view.

10

Trapping mechanisms

When injected in a reservoir, the CO2 fills the rock’spore spaces, which in most cases are already filledwith brine i.e. salty water.As the CO2 is injected, the following mechanismsbegin to come into play. The first is considered themost important and prevents the CO2 from rising tothe surface. The other three tend to increase theefficiency and security of storage with time.

1. Accumulation below the cap rock (Structuraltrapping)As dense CO2 is ‘lighter’ than water, it begins torise upwards. This movement is stopped whenthe CO2 encounters a rock layer that isimpermeable, the so-called ‘cap rock’. Commonlycomposed of clay or salt, this cap rock acts as atrap, preventing the CO2 from rising any farther,and leading to its accumulation directly beneath.Figure 1 illustrates the upward movement of theCO2 through the pore spaces of the rock (in blue)until it reaches the cap rock.

2. Immobilization in small pores (Residual trapping)Residual immobilization occurs when the porespaces in the reservoir rock are so narrow thatthe CO2 can no longer move upwards, despite thedifference in density with the surrounding water.This process occurs mainly during the migrationof CO2 and can typically immobilize a few percentof the injected CO2, depending on the propertiesof the reservoir rock.

3. Dissolution (Dissolution trapping)A small proportion of the injected CO2 isdissolved, or brought into solution, by the brinealready present in the reservoir pore spaces. Aconsequence of dissolution is that the water withdissolved CO2 is heavier than the water without,and it tends to move downwards to the bottom ofthe reservoir. The dissolution rate depends on thecontact between the CO2 and the brine. Theamount of CO2 that can dissolve is limited by amaximum concentration. However, due to themovement of injected CO2 upwards and the waterwith dissolved CO2 downwards, there is acontinuous renewal of the contact between brineand CO2, thus increasing the quantity that can bedissolved. These processes are relatively slowbecause they take place within narrow porespaces. Rough estimates at the Sleipner projectindicate that about 15% of the injected CO2 isdissolved after 10 years of injection.

4. Mineralization (Mineral trapping)The CO2, especially in combination with the brinein the reservoir, can react with the minerals

Once injected in the reservoir, the CO2 will rise buoyantly filling the pore spacesbelow the cap rock. Over time, part of the CO2 will dissolve and eventually betransformed into minerals. These processes take place at different time scales andcontribute to permanent trapping.

© B

RGM

im@

gé

Figure 43D modelling of CO2migration in an aquifer,after the injection of150,000 tons over 4 years in the Doggeraquifer in France.Depicted here is thesupercritical CO2 (left)and the dissolved CO2in brine (right) 4, 100and 2000 years afterinjection began. Thesimulation is based onfield data andexperiments.


actually forming the rock. Certain minerals candissolve, whereas others can precipitate,depending on the pH and the mineralsconstituting the reservoir rock (Fig. 2).Estimations at Sleipner indicate that only arelatively small fraction of the CO2 will beimmobilized through mineralization after a verylong period of time. After 10,000 years, only 5%of the injected CO2 should be mineralized while95% would be dissolved, with no CO2 remainingas a separate dense phase.

The relative importance of these trappingmechanisms is site specific, i.e. it depends onthe characteristics of each individual site. Forinstance, in dome-shaped reservoirs, CO2 shouldremain mostly in a dense phase even over verylong timescales, while in flat reservoirs such asSleipner, most of the injected CO2 will bedissolved or mineralized. The evolution of the proportion of CO2 in thedifferent trapping mechanisms for the Sleipnercase is illustrated in Figure 3.

How do we know all this?

The knowledge of these processes comes from fourmain sources of information:• Laboratory measurements: small-scale experiments

for mineralization, flow and dissolution can beconducted on rock samples, giving insight into short-term and small-scale processes.

• Numerical simulations: computing codes havebeen developed that can be used to predict CO2behaviour over much longer timescales (Fig. 4).Laboratory experiments are used to calibratenumerical simulations.

• The study of natural CO2 reservoirs, where theCO2 (generally of volcanic origin) has been trappedunderground for long periods of time, oftenmillions of years. Such a setting is referred to asa ‘natural analogue’*. These sites provide us withinformation on gas behaviour and the very longterm consequences of the presence of CO2 in theunderground.

• Monitoring of existing CO2 geological storagedemonstration projects, such as Sleipner (offshoreNorway), Weyburn (Canada), In Salah (Algeria) andK12-B (offshore The Netherlands). The results ofthe simulations in the short term can be comparedwith real field data and help refine the models.

Figure 2Dense CO2 migrating upwards (light blue bubbles),dissolving and reacting with the grains of the rock,leading to precipitation of carbonate minerals on thegrain boundaries (white).

Mineral

10

5

10

15

20

25

10 100Time (years)

Million tons of CO2 trapped

1000 10000

Supercritical

Dissolved

Injection time

Figure 3Evolution of the CO2 in its different forms in the Sleipner reservoir according to flow simulations.CO2 is trapped in supercritical form by mechanisms 1 and 2, in dissolved form by mechanism 3, and in mineral form by mechanism 4.

Only by constantly cross-referencing and cross-checking these four sources of information is itpossible to acquire reliable knowledge on all theprocesses occurring some 1000 m below our feet.

In conclusion, we know that the safety of a CO2storage site tends to increase with time. The mostcritical point is to find a reservoir with a suitable caprock above it that can withhold the CO2 (structuraltrapping). The processes related to dissolution,mineralization and residual trapping all work in favourof preventing CO2 from migrating to the surface.

© B

RGM

im@

gé

© B

RGM

Leakage pathways

In general, potential leakage pathways are eitherman-made (such as deep wells) or natural (such asfracture systems and faults). Both active and abandoned wells could constitutemigration pathways because firstly, they form adirect connection between the surface and thereservoir, and secondly, they are composed of man-made materials that may corrode over long periodsof time (Fig. 1). An added complication is that not allwells are created using the same techniques, andthus newer wells are generally more secure thanolder ones. In any case, the risk due to leakagethrough wells is expected to be low because bothnew and old wells can be monitored very effectivelyusing sensitive geochemical and geophysicalmethods, and because technology already exists inthe petroleum industry for any remedial action thatmay be needed. Flow along natural faults and fractures that couldexist in the cap rock or the overburden* is morecomplex because we are dealing with irregular,planar features with variable permeability. A goodscientific and technical understanding of bothleaking and non-leaking natural systems will allow usto design CO2 storage projects that have the same

characteristics of naturally occurring reservoirs thathave trapped CO2 and methane for thousands tomillions of years.

Natural analogues: lessons learned

Natural systems (so-called “analogues”) areinvaluable sources of information for improving ourunderstanding of deep gas migration and the naturalexchange of gases between the earth and theatmosphere. The main findings derived from the studyof numerous leaking and non-leaking natural gasreservoirs are:• under favourable geological conditions, naturally

produced gas can be trapped for hundreds ofthousands to millions of years;

• isolated gas reservoirs and pockets even exist inthe least-favourable geological settings (volcanicareas);

• the migration of any significant amount of gasrequires advection (i.e. pressure-driven flow)because diffusion is a very slow process;

• for advection to occur, the fluid conditions in thereservoir need to be close to lithostatic pressure*to keep faults and fractures open or tomechanically create new pathways;

• areas where naturally produced gas leaks to thesurface are situated almost exclusively in highlyfractured volcanic and seismic regions, with gasvents lying along active or recently activated faults;

• significant gas leaks exist only rarely and tend tobe restricted to highly faulted volcanic andgeothermal areas where CO2 is continuouslyproduced by natural processes;

• gas anomalies at the surface usually occur aslocalized spots that have a limited spatial impacton the near-surface environment.

Therefore, the combination of a number of specificconditions are needed before leakage can occur.Consequently, it is highly unlikely that a well-chosenand carefully engineered CO2 geological storage sitewill leak. Although the potential for leakage is small,the associated processes and potential effectsmust be fully understood in order to choose, designand operate the safest possible CO2 geologicalstorage sites.

Could CO2 leak from the reservoir and, if so, what might be the consequences?

Figure 1Possible pathways forCO2 in a well. Escape via alteredmaterial (c, d, e) oralong interfaces (a, b, f).

12

Based on the study of natural systems, carefully chosen storage sites are not expectedto show any significant leakage. Natural reservoirs containing gas help us understandthe conditions under which gas is trapped or released. In addition, leaking sites help usunderstand what the possible impacts of CO2 leakage could be.

afte

r Nor

dbot

ten

et a

l. 20

05

Impact on humans

We breathe CO2 all the time. CO2 is only dangerousfor human health at very high concentrations, withvalues up to 50,000 ppm (5%) causing headaches,dizziness, and nausea. Values above this level cancause death if exposure is too long, especially byasphyxia when the concentration of oxygen in the airfalls below the 16% level required to sustain humanlife. However, if CO2 leaks in an open or flat-lyingarea, it quickly becomes dispersed into the air, evenwith low winds. The potential risk to populations isthus restricted to leakage in enclosed environmentsor topographical depressions, where concentrationsmay rise because CO2 is denser than air and tendsto accumulate close to the ground. The knowledge ofthe characteristics of degassing areas is useful inrisk prevention and management. In reality, manypeople live in areas characterized by daily naturalgas emanations. For example, in Italy at Ciampino,near Rome, houses are located only 30 metres fromgas vents, where CO2 concentrations in the soilreach 90% and about 7 tons of CO2 are releaseddaily into the atmosphere. The local inhabitantsavoid any danger by following simple precautions,such as not sleeping in the basement and keepingthe houses well ventilated.

Impact on the environment

Potential impacts on the ecosystems would varydepending on whether the storage site is locatedoffshore or onshore.In marine ecosystems, the main effect of CO2leakage is local lowering of the pH and itsassociated impact, primarily on animals that live onthe seafloor and can not move away. However, theconsequences are spatially limited and theecosystem soon shows signs of recovery after theleakage subsides.

In terrestrial ecosystems, impact can be broadlysummarized as follows: • vegetation – Although soil gas CO2 concentrations

of up to about 20-30% can actually favour plantfertilization and increase the growth rate forcertain species, values above this threshold canbe lethal to some, but not all plants. This effect isextremely localized around the gas vent, however,and the vegetation remains robust and healthyonly a few metres away (Fig. 2).

• groundwater quality – The chemical compositionof groundwater could be altered by the additionof CO2, as the water becomes more acidic andelements may be released from the aquifer’srocks and minerals. Even if CO2 should leak intoa drinking-water aquifer, the effects would remainlocalized and quantification of the impacts iscurrently being investigated by researchers.Interestingly, many aquifers throughout Europeare enriched in natural CO2, and this water isactually bottled and sold as “sparkling mineralwater”.

• rock integrity – The acidification of groundwatercan result in rock dissolution, decreasedstructural integrity, and the formation of sinkholes.However, this type of impact only occurs undervery specific geological and hydrogeologicalconditions (tectonically active, high flow rateaquifers, carbonate-rich mineralogy), which are notlikely to occur above a man-made geologicalstorage site.

In conclusion, as the impacts of any hypotheticalCO2 leakage will depend on the specific site, athorough knowledge of the underlying geological andstructural setting will allow us to identify anypotential gas migration pathways, choose sites withthe lowest potential of CO2 leakage, predict gasbehaviour and thus evaluate, and prevent, anysignificant impact on humans and the ecosystem.

Figure 2Impact of CO2 leakageon vegetation with ahigh (left) and reduced(right) flux.Impact is limited tothe area where CO2escapes.


© S

apie

nza

URS

All CO2 storage sites will need to be monitored for operational, safety,environmental, societal and economic reasons. A strategy has to be drawn up todefine what exactly will be monitored and how.

• Plume imaging – tracking of the CO2 as it migratesfrom the injection point. This provides key data forcalibrating models that predict the futuredistribution of CO2 at the site. Many maturetechniques are available, most notably repeatseismic surveys, which have been successfullyapplied at several demonstration and pilot-scaleprojects (Fig. 1).

• Cap-rock integrity – necessary to evaluate if theCO2 is isolated within the storage reservoir andto enable early warning of any unexpectedupward CO2 migration. This can be especiallyimportant during the injection phase of a project,when reservoir pressures are significantly, buttemporarily, increased.

• Well integrity. This is an important issue as deepwells could potentially provide a direct pathway forCO2 migration to the surface. CO2 injection wellsplus any observation wells or pre-existingabandoned wells must be carefully monitoredduring the injection phase and beyond to preventsudden escape of CO2. Monitoring is also used toverify that all wells have been efficiently sealedonce they are no longer required. Existinggeophysical and geochemical monitoring systems,which are standard practice in the oil and gasindustry, can be installed within or above wells toprovide early warning and ensure safety.

• Migration in the overburden. At storage sites whereadditional, shallower rock units have properties thatare similar to those of the cap rock, the overburdenmay form a key component in reducing the risk ofCO2 escape into the sea or the atmosphere. Ifmonitoring in the reservoir or around the cap rockindicates an unexpected migration through the caprock, monitoring of the overburden will benecessary. Many of the techniques used in plumeimaging or monitoring cap-rock integrity can be usedwithin the overburden.

• Surface leakage and atmospheric detection andmeasurement. To ensure that the injected CO2 hasnot migrated to the surface, a range ofgeochemical, biochemical and remote sensingtechniques is available to locate leaks, assess andmonitor CO2 distribution in the soil and itsdispersion in the atmosphere or the marineenvironment (Fig. 2).

• Quantity of stored CO2 for regulatory and fiscal

How can we monitor the storagesite at depth and at the surface?

14

Why do we need monitoring?

Monitoring site performance will be critical to ensurethat the principal goal of CO2 geological storage isattained, namely the long-term isolation from theatmosphere of anthropic CO2. The reasons formonitoring storage sites are numerous, including:• Operational: to control and optimize the injection

process.• Safety and environmental: to minimize or

prevent any impact on people, wildlife andecosystems in the vicinity of a storage site, andto ensure the mitigation of global climate change.

• Societal: to provide the public with theinformation needed to understand the safety ofthe storage site and to help gain publicconfidence.

• Financial: to build market confidence in CCStechnology and to verify the stored volumes ofCO2 so that they are credited as 'avoidedemissions' in future phases of the EuropeanUnion’s Emission Trading Scheme (ETS).

Monitoring of both the initial state of the environment(so-called “baseline”) and the subsequent siteperformance is an important regulatory requirementin the EC Directive on CCS, published in draft form on23rd January 2008. Operators need to be able todemonstrate that the storage performance conformsto regulations and will continue to do so over the longterm. Monitoring is an important component that willreduce uncertainties in site performance, and thus itshould be strongly linked to safety managementactivities.

What are the monitoring targets?

Monitoring can be focused on various targets andprocesses in different parts of the site, such as:

Figure 1 Seismic imaging tomonitor the CO2 plume*at the Sleipner pilotbefore injection (whichbegan in 1996) andafter injection(respectively 3 and 5years later).

Pre-injection (1994) 2.35 Mt CO2 (1999) 4.36 Mt CO2 (2001)

© S

tato

ilHyd

ro

purposes. Although the amount of CO2 injected canbe readily measured at the wellhead, quantificationin the reservoir is technically very challenging. Ifleakage to the near-surface occurs, then theamounts being released will have to be quantifiedfor accounting purposes within national greenhousegas inventories and future ETS schemes.

• Ground movements and microseismicity*. Theincreased reservoir pressure due to CO2 injectioncould, in specific cases, increase the potential formicroseismicity and small-scale groundmovements. Microseismic monitoring techniquesand remote methods (surveys from aircraft orsatellites) able to measure even tiny grounddistortion are available.

How is monitoring done?

A wide range of monitoring techniques has alreadybeen applied at existing demonstration and researchprojects. These include methods that directly monitorthe CO2, and those that indirectly measure its effectson rocks, fluids and the environment. Directmeasurements include the analysis of fluids fromdeep wells or the measurement of gasconcentrations in the soil or atmosphere. Indirectmethods include geophysical surveys, and monitoringpressure changes in wells or pH changes ingroundwater. Monitoring will be required for storage sites whetherthey are offshore or onshore. The selection ofappropriate monitoring techniques will depend on thetechnical and geological characteristics of the siteand the monitoring aims. A wide range of monitoringtechniques is already available (Fig. 3), many ofwhich are well established in the oil and gasindustries; these techniques are being adapted to aCO2 context. Research into optimization of existingmethods or the development of innovative techniquesis also underway with the goal of improving resolution

Figure 2 Monitoring buoy withsolar panels for energysupply, floats anddevice to sample gasat the bottom of thesea.

Figure 3A small selectionillustrating the range oftechniques available tomonitor differentcomponents of a CO2storage system.


and reliability, reducingcosts, automating opera-tion, and demonstratingeffectiveness.

Monitoring strategy

When designing amonitoring strategy, manydecisions must be madethat depend on thegeological and engineer-ing conditions specific toeach individual site, suchas reservoir geometryand depth, expectedspread of the CO2 plume, potential leakagepathways, overburden geology, injection time andflow rate, and surface characteristics, such astopography, population density, infrastructure andecosystems. Once decisions have been maderegarding the most appropriate measurementtechniques and locations, baseline surveys must beconducted prior to injection operations to serve as areference for all future measurements. Finally, eachmonitoring programme must be flexible so that it canevolve as the storage project itself evolves. Amonitoring strategy capable of integrating all theseissues, while at the same time improving costeffectiveness, will form a critical component in riskanalysis and the verification of site safety andefficiency.

In conclusion, we know that the monitoring of a CO2storage site is already feasible with the manytechniques that are available on the market or underdevelopment. Research is currently underway, notonly to develop new tools (particularly for sea-flooruse), but also to optimize monitoring performanceand reduce the costs.

© C

O 2Ge

oNet

© C

O 2Ge

oNet

Although CO2 geological storage is now broadlyaccepted as one of the credible options for mitigatingclimate change, the safety criteria with respect tohuman health and the local environment remain to beestablished before industrial-scale operations can bewidely deployed. Such criteria can be defined as therequirements imposed upon the operators by theregulating authorities to ensure that impacts on localhealth, safety and the environment (includinggroundwater resources) are negligible in the short,medium and long term. One key issue of CO2 geological storage is that itshould be permanent, and consequently, storagesites are not expected to leak. However, the 'what if?'scenario means that the risks must be assessed andthe operators required to respect measures thatprevent any leakage or anomalous behaviour of thesites. According to the IPCC, the injected CO2 needsto remain underground for at least 1000 years, whichwould allow atmospheric CO2 concentrations tostabilize or decline by natural exchange with oceanwaters, thereby minimizing surface temperature risedue to global warming. However, local impacts need tobe assessed on a time scale ranging from days tomany thousands of years. Several main steps can be identified during thelifetime of a CO2 storage project (Fig. 1). Safety will beensured throughout by:• careful site selection and characterization;• safety assessment;

• correct operation; • an appropriate monitor-

ing plan; • an adequate remedia-

tion plan.

The associated criticalaims are to:• ensure that the CO2

remains in the reser-voir;

• maintain well integrity;• preserve the physical

properties of the reser-voir (including porosity,permeability, injectivity),and the impermeablenature of the cap rock;

• take into considerationthe composition of the

CO2 stream, paying particular attention to anyimpurities not eliminated during the captureprocess. This is important to avoid any adverseinteraction with the well, reservoir, cap rock and,in case of leakage, any overlying groundwater.

Safety criteria for project design

Safety must be demonstrated before operationsbegin.With respect to site selection, the main componentsthat must be examined include: • the reservoir and cap rock;• the overburden and particularly the impermeable

layers that could act as secondary seals;• the presence of permeable faults or wells that

could act as pathways to the surface;• the drinking-water aquifers;• the population and environmental constraints at

the surface.

Oil and gas exploration techniques are used toassess the geology and geometry of the storage site.Fluid flow, chemical and geomechanical modelling ofthe CO2 within the reservoir allows predictions of CO2behaviour and long-term outcome, and definition ofthe parameters for efficient injection. As a result,careful site characterization should enable thedefinition of a ‘normal’ storage behaviour scenario,corresponding to a site suitable for storage where weare confident that the CO2 will remain in the reservoir.Risk assessment then needs to consider lessplausible scenarios for future states of the storage,including occurrences of unexpected events. Inparticular, it is important to envisage any potentialleakage pathways, exposure and effects (Fig. 2).Each leakage scenario should be analysed by expertsand, where possible, numerical modelling applied, inorder to evaluate the probability of occurrence andpotential severity. As an example, the evolution of theCO2 plume extent should be mapped carefully todetect any connection with a faulted zone. Sensitivityto variations in the input parameters anduncertainties should be evaluated carefully in riskassessment. Estimating potential effects of CO2 onhuman beings and the environment should beaddressed through impact assessment studies,which is usual practice in any licensing process of anindustrial facility. In this process, both normal andleaking scenarios will be examined to assess any

What safety criteria need to be imposed and respected?

16

Figure 1The different steps of a storage project.

~ t0 + 1 yeart0

Knowledge of the siteConfidence in the long-term evolution

Main steps of a storage project

Tim

e

~ t0 + 3 years

~ t0 + 5 years

~ t0 + 40 years

~ t0 + 45 years

…

Site selection

Site characterisation

Storage design& construction

Injectionoperations

Site closure

Post-closure

In order to ensure storage security and efficiency, conditions for project design andoperation must be imposed by the regulating authorities and respected by the operators.


Figure 2Example of potentialleakage scenarios.

defined by modelling; • composition of the injected CO2 stream; • integrity of the injection well(s) and any well located

within or nearby the extension of the CO2 plume; • extension of the CO2 plume and detection of any

leakage;• ground stability.

During injection, the actual behaviour of the injectedCO2 will need to be repeatedly compared againstpredictions. This constantly improves our knowledgeof the site. If any anomalous behaviour is detected,the monitoring programme should be updated andcorrective actions taken if necessary. In the case ofsuspected leakage, appropriate monitoring tools couldbe focused on a specific area of the storage site, fromthe reservoir up to the surface. This would detect theascent of CO2 and, moreover, any adverse impact thatcould be harmful to drinking-water aquifers, theenvironment and, ultimately, human beings. When injection is completed, the closure phasestarts: wells should be properly closed andabandoned, the modelling and the monitoringprogramme updated, and, if necessary, correctivemeasures taken to reduce risks. Once the level of riskis considered to be sufficiently low, the liability ofstorage will be transferred to national authorities andthe monitoring plan can be stopped or minimized.

The proposed European Directive establishes a legalframework to ensure that CO2 capture and storage isan available mitigation option, and that it can be donesafely and responsibly.

In conclusion, safety criteria are essential for thesuccessful industrial deployment of CO2 storage.They have to be adapted to each specific storagesite. These criteria will be particularly important forpublic acceptance, and essential in the licensingprocess for which regulatory bodies must decide thelevel of detail for safety requirements.

© BRGM

- 900 m

- 1 700 m

- 2 200 m

Freshwater aquifer

to be protected

Deep aquifer(reservoir)

Plant producing and capturing CO2

Geological fault

Observation well

CO2 injection well

Potable water catchment

CO2 migration scenarios

a

b

Leakage due to sealing deficiency of the cap rock

Leakage via existing faults

c Leakage via an abandoned well

CO2 plume in the reservoir

Seal

Former oil production well

ba

c

potential risk linked to the facility.The monitoring programme, from short to long term,should be established according to the risk-assessment analysis and should control the criticalparameters defined within the different scenarios. Itsmain objectives are to image CO2 plume migration,check well and cap-rock integrity, detect any leakage ofCO2, assess groundwater quality and ensure that noCO2 has reached the surface. The remediation andmitigation plan is the last component of safetyassessment and aims at detailing the list of correctiveactions to be deployed in the event of leakage oranomalous behaviour. It covers cap-rock integrity andwell failure, during injection and post-injection periodsand considers extreme remediation solutions, such asstorage reversibility. Existing know-how encompassesstandard oil and gas techniques, such as workovercompletion, decreasing injection pressure, partial orcomplete gas withdrawal, water extraction to relievepressure, shallow gas extraction, etc.

Safety criteria during operation and post-closure

The main safety concern is associated with theoperational phase: after injection stops, the decreasein pressure will make the site safer. Confidence in the ability to inject and store CO2 in asafe way relies on experience of industrial companies.CO2 is a fairly common product used in variousindustries, so the handling of this substance does notraise any new problems. The design and control ofoperations will be based mainly on oil and gasindustry know-how, in particular seasonal natural gasstorage or enhanced oil recovery (EOR). The mainparameters to be controlled are:• injection pressure and flow rate – the former should

be maintained below fracturing pressure, i.e. thepressure above which fractures are induced withinthe cap rock;

• injected volume, in order to meet predictions

Aquifer: permeable body of rock containing water. Themost superficial aquifers contain fresh water used forhuman consumption. The ones at greater depth arefilled with salty water that is unsuitable for any humanneeds. These are called saline aquifers.Brine: very salty water, i.e. containing highconcentration of dissolved salts.Caprock: impermeable layer of rocks that acts as abarrier to the movement of liquids and gases andwhich forms a trap when overlying a reservoir.CCS: CO2 Capture and Storage.CO2 plume: spatial distribution of the supercriticalCO2 within the rock units.CSLF: Carbon Sequestration Leadership Forum. Aninternational climate change initiative that is focusedon the development of improved, cost-effectivetechnologies for the separation and capture of carbondioxide and its transport and long-term safe storage.Enhanced Oil Recovery (EOR): a technique thatimproves oil production by injecting fluids (like steam orCO2) that help mobilize the oil in the reservoir. EU Geocapacity: an on-going European researchproject that is assessing the total geological storagecapacity that exists in Europe for anthropic CO2emissions. GESTCO: a completed European research project thatassessed the geological storage possibilities of CO2in 8 countries (Norway, Denmark, UK, Belgium,Netherlands, Germany, France and Greece).IEA-GHG: International Energy Agency – GreenhouseGas R&D programme. An international collaborationwhich aims to: evaluate technologies for reducingemissions of greenhouse gases, disseminate theresults of these studies, and identify targets forresearch, development and demonstration andpromote the appropriate work.Injectivity: characterizes the ease with which a fluid(like CO2) can be injected into a geological formation. Itis defined as the injection rate divided by the pressuredifference between the injection point inside at the wellbase and the formation.

Glossary

18

Going further:The Intergovernmental Panel on Climate Change (IPCC) Special Report on CCS:http://www.ipcc.ch/pdf/special-reports/srccs/srccs_wholereport.pdf

The European Commission’s webpage on CCS:http://ec.europa.eu/environment/climat/ccs/The EC Directive: http://ec.europa.eu/environment/climat/ccs/eccp1_en.htmThe ETS system:http://ec.europa.eu/environment/climat/emission.htm

IEA GHG monitoring tools webpage:http://www.co2captureandstorage.info/co2tool_v2.1beta/introduction.html

IPCC: International Panel on Climate Change. Thisorganization was established in 1988 by WMO (WorldMeteorological Organization) and UNEP (United NationsEnvironment Programme) to assess the scientific,technical and socio-economic information relevant for theunderstanding of climate change, its potential impactsand options for adaptation and mitigation. IPCC and AlGore were awarded the Nobel Peace Prize for 2007.Lithostatic pressure: the force exerted on a rockbelow ground surface by the overlying rocks.Lithostatic pressure increases with depth.Microseismicity: slight tremor or vibration in theearth's crust, unrelated to earthquakes, which can becaused by a variety of natural and artificial agents.Natural analogue: naturally occurring CO2 reservoir.Both leaking and non-leaking sites exist, and their studycan improve our understanding of the long-term fate ofCO2 in deep geological systems. Overburden: the geological strata lying between thereservoir cap rock and the land surface (or seabed).Permeability: property or capacity of a porous rock totransmit a fluid; it is a measure of the relative ease offluid flow under a pressure gradient.pH: measure of the acidity of a solution, where pH 7corresponds to neutral. Porosity: percentage of the bulk volume of a rock thatis not occupied by minerals. These gaps are calledpores and they can be filled by various fluids; typicallyin deep rocks this fluid is salty water but it can also beoil or gas like methane or also naturally formed CO2.Reservoir: body of rock or sediment that is sufficientlyporous and permeable to host and store CO2.Sandstone and limestone are the most commonreservoir rocks.Supercritical: the state of a fluid at pressures andtemperatures above critical values (31.03 °C and 7.38MPa for CO2). Properties of such fluids arecontinuously variable, from more gas-like at lowpressure to more liquid-like at high pressure.Well (or borehole): a circular hole made by drilling, espe-cially a deep hole of small diameter, such as an oil well.

CO2GeoNet is a European Network of Excellencethat is engaged in providing unbiased andscientifically sound information about the safety andefficiency of CO2 geological storage. The partnershipconsists of more than 150 scientists at 13 publicresearch institutes, with each partner having a highinternational profile in all aspects of CO2 geologicalstorage research. The Network is sponsored by theEuropean Commission under the 6th FrameworkProgramme.

The institutes involved in the network are:BGR , BGS , BRGM , GEUS , HeriotWatt University , IFP , Imperial College ,NIVA , OGS , IRIS , SINTEF , TNO ,Sapienza University of Rome .

Activities of the Network

The Network researchers work together to constantlyimprove our knowledge about geological storage ofCO2 and the tools needed for its safe deployment.They are involved in several high-priority researchprojects that address every level of the issue: thereservoir, the cap rock, potential passageways forCO2 migration up to the ground surface, potentialimpacts on humans and local ecosystems in theevent of leakage, and public outreach andcommunication. CO2GeoNet’s strength lies in its ability to createmulti-disciplinary teams of highly experiencedspecialists, thereby allowing it to better understandthe individual facets of geological storage and howthey are linked together within a larger and morecomplex system. In addition to its research activities, CO2GeoNet canalso:• offer training & capacity building for the scientists

and engineers who will be needed to enable CO2storage;

• provide scientific advice and project proposal audits(geotechnical quality, environmental protection, riskmanagement, planning and regulatory issues, etc.);

• disseminate independent, unbiased informationbased on its research results;

• engage with stakeholders and help address theirconcerns and needs.

In order to raise public awareness about thegeological storage of CO2 as a viable option formitigating climate change, CO2GeoNet has tackledthe basic question “What does CO2 geological storagereally mean?”. A panel of eminent scientists fromCO2GeoNet has prepared state-of-the art answers tosix pertinent questions, based on more than a decadeof European research and the experience ofdemonstration projects worldwide. The goal of thisendeavour is to deliver clear and unbiased scientificinformation to a broad audience, and to encouragedialogue on essential questions concerning thetechnical aspects of CO2 geological storage. This work, summarized in this booklet, was presentedduring the Network’s first Training and Dialogueworkshop held in Paris on 3rd October 2007. The wideaudience included stakeholders, industrialists,engineers and scientists, policymakers, journalists,NGOs, sociologists, teachers, and students. In total,170 people from 21 different countries attended,during which they had the opportunity to share theirviews and gain a more complete understanding of CO2geological storage.

For further information, or enquiries regarding thepossibility of a similar tailored training course ongeological storage, please contact the CO2GeoNetSecretariat at [email protected] or visit ourwebsite at www.co2geonet.eu.

What CO2GeoNet can do for you


www.co2geonet.euSecretariat: [email protected]

BGS Natural Environment Research Council-British Geological Survey, BGR Bundesanstalt für Geowissenschaften und Rohstoffe,BRGM Bureau de Recherches Géologiques et Minières, GEUS Geological Survey of Denmark and Greenland, HWU Heriot-WattUniversity, IFP, IMPERIAL Imperial College of Science, Technology and Medicine, NIVA Norwegian Institute for Water Research,OGS Istituto Nazionale di Oceanografia e di Geofisica Sperimentale, IRIS International Research Institute of Stavanger, SPR SINTEFPetroleumsforskning AS, TNO Netherlands Organisation for Applied Scientific Research, URS Sapienza University of Rome Dip.Scienze della Terra.

Prin

ted

in S

epte

mbe

r 200

8 - G

raph

ic d

esig

n: B

L Co

mm

unic

atio

n

ISBN: 978-2-7159-2453-6

what does co2 geological storage really mean?

Documents

co2 leak

co2 emitted intothe

large quantities of

storage reservoir

childrenco2 geological

storage site

industrial age

critical level of450