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Physics World Discovery

Carbon Capture and Storage

Owain Tucker


1 IntroductionWhen I give talks on Carbon Capture and Storage (CCS), I often start with the latestCO2 concentration measurements from the Mauna Loa Observatory (figure 1). As aphysicist, I look at the data first, and listen to the rhetoric second. The data tell methat we, globally, are not doing enough to reduce CO2 emissions. Despite allsociety’s efforts to date, the atmospheric levels are still increasing. We need to dosomething different.

Simple physics links the increase in the concentration of CO2 and other green-house gasses (GHGs) to the increase in temperature.

Figure 1. Measured CO2 levels. Credit: NOAA ESRL Global Monitoring Division, Boulder, Colorado, US(http://esrl.noaa.gov/gmd/).

doi:10.1088/978-0-7503-1581-4ch1 1 ª IOP Publishing Ltd 2018

http://esrl.noaa.gov/gmd/

https://doi.org/10.1088/978-0-7503-1581-4ch1

In 1896 Svante Arrhenius introduced us to the effect of the atmosphericconcentration of CO2 on the Earth’s temperature. His work has been validatedmany times over and we can all peruse the Intergovernmental Panel on ClimateChange (IPCC) reports, which outline the experimentally verified evidence that theglobal temperatures are rising, that global CO2 concentrations have risen signifi-cantly since the start of the industrial revolution, and that global warming, andassociated climate change and climate disruption, is driven by the increase ingreenhouse gas concentration.

The largest contribution to the increase in GHGs is CO2. Around 36 billiontonnes a year of CO2 is emitted from fossil fuel combustion, cement production andchemical processes (figure 2). Climate science tells us that cumulative emissions,more than the annual rate of emission, are the key control on the eventual peakwarming. Humanity, therefore, has a fixed carbon budget of around 1 trillion tonnesof carbon, C, or 3.67 trillion tonnes of CO2, if it wants to limit warming to about2 °C, less if we are aiming at below 2 °C. To date, at least half of this budget has beenused up. In other words: every tonne emitted counts.

Every tonne counts, yet the global economy still emits around 100 million tonnes(yes, you read it correctly) of CO2 into the atmosphere every day! Most of theemissions come from the combustion of fossil fuel, while others come from industrialemissions. Some of the latter are even pure streams of CO2 released directly to theatmosphere.

Society enthusiastically talks about energy efficiency, and we see regulationslowly driving this forward. We actively try to substitute renewable energy sources

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Figure 2. Emissions of CO2, measured in gigatonnes per year, from 1959 to 2015 sourced from CDIAC andother references. See additional resources for more details.


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for fossil energy, and are making great strides in this direction. But then we stop. Forreasons discussed later, it is inconceivable that society will suddenly (within a decadeor two) stop making cement or fertilizer, give up using liquid transport fuels, or quitgenerating most of its power from fossil fuel. So, we need to decarbonise theseemissions while continuing to work on the alternatives.

What many scientists, and almost all of the public, do not know is that there is aproven, existing, technological solution that can all but eliminate CO2 emissions frommany sources, and that can also act as the engine for negative emission technologies.This technology can be added to our current energy and chemicals infrastructure withminimal change. The IPCChas recognised that this technology is key to the delivery ofmost 2 °C temperature equilibration pathways, and the International Energy Agency(IEA) notes that it is almost an absolute in any 1.5 °C pathway—as suggested in theParis accord. The technologyworks by removing the unwanted pollutant, CO2, beforeit reaches the environment and putting it back into geological strata similar to thosethat originally contained the hydrocarbons that are the source of the carbon. This isCarbon Capture and Storage.

CCS is an interesting topic. Technically it combines physics, chemistry, geologyand engineering, but any discussion that only looks at the technology misses thepoint.

In order to appreciate CCS, we need to look at the links between science andsociety; examining the integrated picture: What is CCS? What can it deliver? Whatare its strengths and weaknesses? And why isn’t it happening all around us today?

2 BackgroundCCS is a collective term for: capturing CO2, transporting it to a storage location,and storing or sequestering it in geological strata.

Capture generally involves creating a pure stream of CO2 by a gas-separationprocess. Sometimes, as in the case of post-combustion, this is achieved by separatingCO2 from nitrogen (N2) and oxygen (O2). In other cases, O2 is separated from airprior to combustion, and the pure O2 is reacted with fuel, leaving near pure CO2.Transport is simple and normally means compressing relatively pure CO2 till itcondenses, and then moving the liquid CO2 by pipeline or ship.

Storage is the reversal of natural gas or oil production. The dense phase CO2 ispumped into injection wells, normally over 1000 m deep, and injected into porespaces in rock. The rock pores are almost always filled with saline formation water.The CO2 displaces the water and fills the pores instead. The storage formation isselected for the presence of a permeable rock formation that will allow the injectionof CO2. The storage formation is overlain by an impermeable rock formation thatwill stop the CO2 from flowing up toward the surface.

Do we really need CCS?

We often hear that CCS is a distraction from the main goal of deploying alternativeenergies and moving away from a fossil fuel based society. We should ‘keep it in theground’. This view stems from the laudable aim of moving away from a reliance on


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fossil fuels as fast as possible, and a recognition that emissions of CO2 from fossilfuel combustion (coal, oil and gas) have to shoulder much of the blame for theincrease in global CO2 levels. I personally have added extra insulation to my house,installed solar hot water heating, and have an energy efficient condensing boiler—yet I still consume substantial quantities of energy, even the computer on which I amwriting this book consumes a few hundred watts.

I had to think long and hard about this question—why can’t we just be a littlecleverer? Only the other day I read an article stating that CCS was not needed assimply being more efficient with kettles would save the energy equivalent to onepower station. My thought was, very good, do it, but what about all the other powerstations? Look at the whole picture, do not get distracted by a small piece.

One reason we struggle as individuals is that it is difficult to picture the scale ofthe global, or even local, energy system. David McKay—a Fellow of the RoyalSociety and a former Chief Scientific Advisor to part of the UK government—put alot of effort into this question and published a book on the subject (see additionalresources). He noted that a human being can generate around 1 kW hour per day ofeffort (or 125 W solidly for eight hours). Next time you are in the gym turn thetreadmill, exercise bike, or (my favourite) the rowing machine, to watts and see howmany watts you can generate. This starts to make sense when you think about howmuch effort cleaning was before the invention of the vacuum cleaner, or washingbefore the washing machine. According to my energy monitoring, my house, whichhas electric cooking, peaks at around 6–8 kW electricity consumption but has thepotential to draw over 15 kW if the kettle, oven, microwave, hob, washing machine,and lights all draw power at the same time. By having such power at my fingertips, Ican easily do the work of many people. Because the power is cheap compared toemploying lots of people to do things that I do not have time to do, I am better off.Abundant low-cost power on demand effectively makes me, and the majority ofpeople in developed countries, better off.

Now picture the familiar wind turbine: onshore turbines come in at around3.6 MW per turbine installed capacity while offshore turbines are around 7 MW(some new models can be as large as 7 MW onshore and 10 MW offshore). Next addjet engines, combined cycle gas turbines, and then power stations to the picture andyou get figure 3.

The first thing to note about figure 3 is the fact that the vertical axis is logarithmic.A single combined cycle gas turbine (CCGT) in a normal power station can generate500 million watts—or in other words can produce the power equivalent to 2.5 millionpeople working constantly (here we are using a high power output of 200 W perhuman to be generous). One CCGT can have the same name plate capacity as over150 onshore wind turbines. The maximum UK electricity demand in the period10 October 2016 to 10 October 2017 was 52 GW in total—the maximum change indemand in one day in that period was 22 GW.

These numbers are just for electric power and do not include heating, whichrequires even more energy. While UK electricity demand peaks at around 52 GW(electrical), heat demand has been calculated to be up to 350 GW (thermal) during acold January morning. The numbers are so large that it is difficult to get your mind


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around the scale—but what they do show is the size of the energy system. Beforeapproaching topics like intermittency, energy storage, and demand management wecan see that intuition will not serve us well in this area.

When we look at the inertia in our global energy and industrial system (powerstations are expected to last twenty to thirty years), and at the over seven billion

Figure 3. Top: Log graph comparing power used and generated by different technologies. Humans can, whenworking very hard, generate about 200 W, while a standard ‘metric’ horse weighs in at 736 W. What isincredible is that even the domestic vacuum cleaner has the power of over two horses. Numbers arerepresentative. Bottom: infographic attempting to illustrate the scale of the system, where human = 1. Note theshrinking from each group.


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people who depend on it, we realise that the world is unlikely to be able to turn offthe fossil energy tap quickly. This is why most integrated assessment models (IAMs),such as those reviewed by the IPCC and the IEA, call for everything—rapid rolloutof renewable energy, energy efficiency, switching from more to less carbon intensivefuels, the use of bio fuels, and large-scale rollout of CCS on fossil and CCS on biofuels.

Microeconomics applied to CCS

Will an increase in CCS lead to the continuation of fossil fuel use? One reason thatCCS has not been embraced by governments is the fact that decarbonising increasesthe cost of using fossil fuel. Because it is applied to large industrial plants, such as a1 GW power station, in contrast to the more staged rollout of smaller renewableinstallations, the ticket price is very noticeable; even though the unit cost iscompetitive with renewables. Deploying CCS would therefore increase the cost offossil energy and would act as a carbon tax, potentially making alternative renewablesources more attractive. Simple microeconomics therefore tells us that CCS is goodfor alternative forms of energy, and simple logic tells us that harvesting energy fromfossil fuels, if the side effect of CO2 emissions has been responsibly removed, is not anissue for the global climate system. Basically, ‘clean’ fossil is OK. Deploying CCSforces fossil fuel users to, in economist speak, ‘internalise the cost of the externality’—in simple terms ‘pay for the CO2 emissions’.

So, CCS is logical, climate models tell us we need it, implementing it woulddramatically reduce emissions right now, and mandating it would increase the costof fossil fuel, act as selective taxation, and would incentivise renewables. MandatingCCS would also deliver fossil energy and industrial products without the CO2. Whatis not to like? But society, economics, and politics are immensely complicated. Iheard a very good quote on the radio a few days ago: ‘Politicians know what theyneed to do, they just do not know how to get re-elected after they do it’.

Where is CO2 emitted and from where can it be captured?

The Carbon Dioxide Information Analysis Center at Oak Ridge NationalLaboratory in the US collates CO2 emission data. Their latest dataset is for 2014.In 2014 they estimate that emissions from fossil fuel combustion were 9855 milliontonnes of Carbon, which equates to 36 168 million tonnes of CO2. This accounts forroughly 65% of the total greenhouse gas emissions, with other sources being: CO2

from forestry and other land use changes 11%, methane 16%, nitrous oxide 6%,fluorinated gasses 2%.

We will concentrate on the 36 Gt a year of emissions, or around 100 milliontonnes of CO2 every day.

CO2 can be captured from multiple sources with differing characteristics ofconcentration, pressure, volume, and abundance of sources. The main source typesare shown in figure 4.


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Direct air captureThe most widespread source is air, into which humanity has been releasing CO2

molecules for centuries, increasing the CO2 concentration to around 400 ppm, at thepressure of one atmosphere. If we want, we can round up these released moleculesand put them back underground. This is termed direct air capture, or DAC. The0.04% CO2 has to be separated from the 78% N2, 21% O2, and 0.9% Ar. Theadvantage of this source is that it is obviously available everywhere, so the capturecan take place in the location most suited to removal and storage. The disadvantageis that it requires a lot of energy and equipment, because the low concentrationmeans that a very large volume of air has to be processed to achieve meaningful flowrates of CO2. DAC is currently an active area of research.

BiomassPlants perform direct air capture all the time, but they convert the CO2 into anintermediate product, the sugar glucose. Glucose molecules are then joined up in theplants to form polysaccharides such as cellulose, the main component of plant cellwalls, and even further into complex organic polymers such as lignin, the key structural

Figure 4. Schematic showing different CO2 sources and capture systems (adapted from IPCC special reporton CCS).


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component of wood. The reactions are not particularly efficient: according to theNew York Times, a fifty-year-old oak forest would sequester about 13 tonnes per acreper year. Biomass can be directly used as a fuel in boilers, or it can be gasified beforeburning. If you simply let the CO2 from burning biomass return to the atmosphere thenthere is a net zero change, the fuels are termed carbon neutral (though not quite, ashumanity often uses fossil fuel to power harvest and transport machinery, and toprovide energy used to treat/dry/pelletise biomass).

We can, however, go further, and capture and store the CO2 emission streamsfrom biomass use, leading to negative emissions. It is generally termed BECCS—bioenergy with CCS. BECCS is one of a class of negative emission technologies orNETs. Other NETs include afforestation and reforestation, biochar, soil carbonsequestration, building with biomass, habitat restoration, enhanced ocean produc-tivity, enhanced weathering, and direct air capture (there are more).

While it is not widely appreciated, NETs are vital in most climate modellingscenarios because:

(i) NETs provide a way to offset hard to capture emissions, such as those frommarine transport, air travel and agricultural machinery.

(ii) Most integrated assessment climate models (IAMs) predict that CO2 concen-trations will exceed the level required to maintain a 2 °C warming; removal ofCO2 from the atmosphere is therefore vital in correcting this overshoot.

Many, though not all, NETs are all too easy to reverse, however, any NET thatincludes CO2 storage has an enviable degree of permanence. This makes BECCSand capture from sources such as fermentation (see below) particularly valuable. Asthe quantity of biomass is ultimately limited, and NETs are so important, we couldtake the view that it is a missed opportunity not to fit carbon capture and storage tobioenergy plants, turning them into CO2 sinks.

FermentationAt the other end of the spectrum lie pure streams of CO2—the most common comesfrom fermentation. The fermentation reaction can be defined as the breakdown ofglucose to form alcohol and CO2. From the smallest home brew kit, right up to giantindustrial ethanol plants, the yeast mediated fermentation reaction emits a watersaturated stream of all but pure CO2. In Decatur, Illinois, a bioethanol producernow captures over 1 million tonnes of CO2 a year, dehydrates it and stores itunderground. No purification other than dehydration is required, it just has to becompressed to a liquid and injected. They now make negative emission ethanol—you can drive an internal combustion engine car and have negative emissions!

The restAll the other emission sources come in between these two end points. It is generallytrue that economies of scale mean that it is more cost effective to start with capture,transport and storage on large, stationary emission sources. Imagine the cost toinstall CO2 pipes parallel to gas mains to every house with a gas central heatingboiler or gas cooking ring.


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Figure 5 schematically shows the concentration of CO2 emitted by differentprocesses used by society and gives an idea of the pressure at which the separationtakes place.

As the pressure increases, the size of the CO2 separation plant decreases for thesame capture rate in tonnes/year, simply because at a high pressure the gas is morecompressed. It is much more cost effective to build a small separation vessel thatworks at 30 bar than a large one that works at 1 bar. In addition, the energy requiredto compress the CO2 from the higher pressure to around 100 bar for transportreduces.

There are three main types of separation technology: separation with sorbents orsolvents; separation with membranes; and cryogenics. These will be discussed in thenext section.

Oxycombustion—a special caseCCS is all about separating the CO2 out from the other gasses. When we combust inair we have 78% N2 coming along for the ride, even though we are only interested inreacting with the 21% O2. If we combust in air we get a resultant mixture of N2 andCO2 and have to separate the CO2. However, we can make another choice andremove the O2 from the N2, and then burn the fuel in pure O2. The resulting wastegas stream is then nearly pure CO2. Air separation is termed oxycombustion. Theseparation process is performed in an air separation plant. Air separation is a maturetechnology as the first such plant was started up in 1902 and normally works using atype of countercurrent distillation (see additional resources for more detail).

Figure 5. Sources of CO2 ranked on CO2 concentration and pressure, numbers are indicative as specificindustrial processes can vary—for example while some ethylene processes may emit a high-pressure CO2

stream, much of the CO2 is emitted from furnaces at a low pressure. Credit: Original material from IPCCreport on CCS.


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In oxycombustion, the fuel is burned in pure O2 or an O2/CO2 mix leaving mainlyCO2 and H2O, so the resultant product simply needs to be dehydrated andcompressed. The challenge is that this technology is immature with only two pilotprojects to date—though a promising new technology is currently under develop-ment which will be discussed in the future directions chapter.

Over the past few centuries, all efforts have been focussed on improvingcombustion in air: burner and combustion optimisation, alloys, turbines, controlsystems and much more. A new technology like oxycombustion has to climb thisdevelopmental staircase before it can compete without support in a sector such aspower generation where power utilities expect to be able to buy the components fora, say 2 GW, power station, with performance guarantees for at least twenty years.

Why does CCS reduce efficiency?

People often cite the fact that a power plant or industrial process with CCS requiresmore energy than one without to make the same amount of electricity or product.Because there is a drop in ‘efficiency’, this is offered as a reason not to capture the CO2.

First we need to look at the metric. Efficiency is defined as, for example, theamount of electric energy output divided by the amount of fossil energy input.Nowhere in this definition is CO2 mentioned. If society is to start addressing climatechange—efficiency needs to be in terms of climate impacts, not energy input. Societyneeds to internalise the cost of emissions, a topic called ‘full cost accounting’.Researchers tell us that there is more fossil fuel in the ground than the carbon budgetcan support—therefore fossil fuel is not the scarce resource, rather, CO2 handlingcapacity in the atmosphere is the scarce resource. Efficiency should thereforepotentially be defined not with respect to the fossil fuel but to the CO2 emissions.

Next we need to look at how we extract energy from fossil fuels without CO2

emissions. As discussed above, air is a mixture of N2, O2, and a few other gassesincluding 400 ppm CO2. When we perform normal, ‘efficient’ combustion, we takeair at atmospheric pressure and add a carbon-based fuel—the fuel is oxidised andheat is emitted. In a gas turbine, we pressurise air, inject the hydrocarbon fuel into acombustor, and the now high-pressure hot gasses expand to atmospheric pressureand work is extracted. In a boiler, the combustion takes place at near atmosphericpressure and heat is extracted, which then heats water to steam. Work is extracted ina steam turbine, which expands the steam to sub-atmospheric pressure. The steamcondenser is operated as cold as possible to collapse the steam into vacuumconditions to maximise the steam-cycle efficiency.

The key points here are: the combustion processes start at atmospheric pressurewith an air mixture, and end at atmospheric pressure with a mixture of N2, whichhardly reacts, reduced O2 levels, and increased CO2. There is also a lot of watervapour, H2O.

In order to store the CO2, we need to separate out the CO2 from the N2, plus anyremaining O2 and contaminants like NOx, and compress the CO2 sufficiently totransport and inject it into the subsurface geological storage formations. Theseparation process required to disentangle the CO2 and N2 takes energy, as does


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the compression of the now separated CO2. Nothing comes for free. It takesadditional energy to capture the CO2 when oxidising hydrocarbons, compared tojust releasing the CO2 into the atmosphere: so, energy-based efficiency measureslook worse. It also requires more equipment than combustion with 100% release toatmosphere, so costs more in terms of capital too.

But we do not have a choice anymore. If we want the benefits of fossil fuel, and donot want to release the CO2, we need CCS. If we look at the history ofindustrialisation, societies generally started out by dumping waste products intothe environment, be it sewage, slag, industrial waste, sulphur dioxide and so on.Once the negative consequences of the release were understood society then movedto stop the practice, and became prepared to pay the price. This is the challenge thatsociety needs to face with CO2.

Separation technology

If the CO2 is not pure then it will generally make sense to concentrate it—to makethe best use of transport and storage infrastructure if nothing else.

A quick myth to debunkSome climate scientists are concerned that CCS can capture only 90% of the CO2

in an exhaust stream and is therefore not worth pursuing as we need ultimatelyto capture higher rates if we are to achieve the 1.5 °C global warming target asoutlined in the Paris accord. As you read through the technology descriptions belowyou will realise that this is not the case. The 90% number has been used as anengineering design parameter for the current first generation post-combustioncapture CCS plants. It turns out 90% CO2 capture from a flue gas stream withthe current technology sits at an economic sweet spot in terms of cost per tonne CO2

captured. It is possible to push up to 95% or even higher, but this requires moreenergy and a little more cost. The first-of-a-kind projects were happy with 90%as this is a very significant difference when compared to the normal practice of0% capture.

Pushing the capture percentage even further gets you nearer and nearer to aircapture and the last few percent get very costly, but if you introduce somebiologically sourced fuel into the input stream then you can get 100% abatementat a lower cost, even though some CO2 is still released.

Upsettingly, the 90% number has been hardwired into many climate modellingscenario models (Integrated Assessment Models) and this leads to commentslike—‘CCS is not deployable in the 1.5 °C Paris scenarios because it does notremove enough CO2’.

Chemical absorptionChemical absorption technology has been used at scale since the 1980s for CO2

capture. It relies on one or more reversible chemical reactions between CO2 and anaqueous solution of an absorbent—which is normally amine based or potassiumcarbonate based. Amines are organic derivatives of ammonia in which one or more


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hydrogen atoms in ammonia have been replaced by an alkyl group. The process worksby bringing the gas stream containing CO2 into contact with the solution in a large‘absorber vessel’ that has been filled with ‘packing’: generally corrugated andperforated plates that force the fluid to take a convoluted route through the absorberthereby maximising contact and hence CO2 absorption.When the gas stream exits, theCO2 remains behind, chemically bound to the amine which is in aqueous solution, andthe residual stream of N2 and O2 gasses is cleaned and released to the atmosphere.

The solvent—now termed ‘rich’—is then heated and transferred to a strippervessel where heat forces the reaction to reverse, with the CO2 being released andtransferred to the dehydration and compression equipment. The solvent is now ‘lean’and can be reused. The Quest plant (figure 6) uses this technique.

The improvement and development of the absorption process is an active area ofresearch. The process has been used in natural gas processing for many decades andhas been locally optimised. Use in post combustion capture brings new challenges,such as the presence of O2, lower pressures, and contamination from nitrogenoxides, sulphur oxides and particulate matter.

Scale-up to power station volumes has been done with post combustion CO2

capture: it is working at two coal fired power stations in North America: BoundaryDam Power Station near Estevan, Saskatchewan, Canada; and the WA ParishGenerating Station southwest of Houston, Texas, US. These are first-generationplants so do not benefit from the optimisation built on years of experience (thelearning curve) hence unit costs are still high.

Physical absorptionThis is also a proven technology, used at scale, where the CO2 is physically absorbedin a solvent—it is best used at high partial pressures because, according to Henry’s

Figure 6. The Quest CCS plant in Alberta Canada captures one mega-tonne of CO2 each year. The CO2 iscreated as part of the process that produces hydrogen from natural gas. The equipment pictured is just the CO2

capture plant which uses chemical absorption to strip the CO2 from the waste gas stream. Credit: Shell/Quest.


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law formulated in 1803, the amount of a gas that dissolves in a liquid is directlyproportional to the partial pressure of that gas in equilibrium with that liquid. Thetechnique has been used in gas processing since 1969.

An example of the physical absorption process is the Great Plains Synfuels Plantin North Dakota, US. This is a coal gasification plant with CCS which startedoperating in 1984. It captures more than three million tonnes of CO2 per year usingphysical absorption from a mixture of H2, CO and CO2 using chilled methanol—pre-combustion capture. Because of the link to partial pressure, and also the factthat it is best performed at low temperatures, the technique does not appear wellsuited to post-combustion capture.

Solid physical adsorptionSolid physical adsorption is a coupling of two processes—adsorption and thendesorption. Both need to work consistently, at scale without too large an energypenalty. The change from adsorption to desorption can be achieved by a change inpressure or temperature—pressure swing adsorption (PSA) or temperature swingadsorption (TSA). Various adsorbent materials are used, such as silica gel, activatedcarbon and zeolites. The technology is well suited to purifying streams of H2 and He,as the adsorbents hardly attract these low polarity molecules, whereas moleculessuch as CO2, CO, N2, H2O, and light hydrocarbons are strongly attracted.

PSA is a commercial technology used for H2 purification and has been deployedfor over fifty years, but it is not limited to H2. Different adsorbents can be used thatare tailored to the separation of O2 or CO2. PSA, or more specifically vacuum swingabsorption (VSA), for CO2 removal has been deployed on two commercial scalesteam methane reformers by Air Products at their hydrogen plant in Port Arthur,Texas, US. This went live in 2013, and in 2016 Air Products announced that thatthey had captured three million tonnes of CO2.

Cryogenic separationThis process, which is very similar to that used for O2 separation, is best suited toremoving CO2 from relatively high purity sources. CO2 liquifies at a much highertemperature than most other gasses so it does not take much cooling to turn it into aliquid, especially if the pressure is increased. Demonstration plants for technologyofferings from a number of different manufacturers exist, and the technology couldbe well suited to industrial capture and pre-combustion decarbonisation. Thistechnology is best suited to streams with very high CO2 concentrations and highpressures. It does not need solvents or adsorbents and vendors claim that it has oneof the lowest costs of CO2 capture. It can be used in conjunction with hydrogenmanufacture on steam methane reformers, and is also being used for gas purificationin CO2 enhanced oil recovery (EOR) applications. There is a plant that delivers100 kt CO2 per year at Port-Jerôme, in France, and an oil major tested a technologythey call Controlled Freeze Zone (CFZ) at the Shute Creek gas treatment plant atLaBarge in Wyoming, US.


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Membrane separationMembrane separation is a tried and tested solution for separating CO2 from naturalgas. The technology has been deployed off the coast of Brazil on very largeinstallations for gas treatment. The membranes are designed to selectively transmitCO2 but not CH4 when a pressure differential is placed across the membrane—theytherefore require compression and work well for high-pressure gas-separationapplications. Multiple stages of separation are normally required as the currentmembranes are not completely selective.

Membranes have, however, not yet been commercially deployed for CO2/N2

separation in post-combustion scenarios because it has proven difficult to developmembranes that can handle the heat.

Research into new membrane systems is continuing as the technology has manypotential advantages compared to other approaches—it is simple, does not involvechemical reactions, and is lightweight and compact. The challenge is to develop costeffective membranes with sufficient selectivity and longevity to deploy economically.

CO2 transport, compression and conditioning

Assuming that we have a concentrated stream of CO2 coming out of our capturesystem, the next question is how to transport it to somewhere where it can be stored.

Do we want to transport pure CO2 or contaminated CO2? Should it be leftsaturated with water vapour or should it be dehydrated? These questions cause a lotof confusion and debate, even though the answers are simple.

When a concentrated CO2 stream is created it will normally be in the gas phase,saturated with water vapour, and might have small amounts of O2 and H2 alongwith other trace contaminants from the separation process.

Experience in North America, where there are already 4500 miles of CO2 pipelineused to transport naturally occurring CO2 from CO2 reservoirs to oil fields for CO2

EOR (enhanced oil recovery), confirms that dry, dense phase CO2, is not corrosive.CO2 condenses in the range of 20–70 bar and has a significant increase in density;for example, at 20 °C (figure 7), the density jumps from around 200 kg m−3 to770 kg m−3. If CO2 is to be injected into the subsurface, for CO2 storage or CO2

EOR storage, it will often need to be compressed to around 100 bar. In addition, itturns out that constructing a very large long pipeline for gas phase CO2 is normallymore expensive than building a compressor, so the industry generally works withdense phase CO2—just as it does with dense phase CO2 in fire extinguishers.

If water were allowed to condense in a pipeline, then the CO2 would dissolve inthe water to produce carbonic acid, which does corrode the most common pipelinematerial, carbon steel. The pipeline operator therefore has to choose either to changemetallurgy, to something more akin to stainless steel, or to dry the CO2. Again, it isgenerally found to be more cost effective to dry the CO2.

Oxygen is the next question—as long as the CO2 is dry, any O2 does not harmcarbon steel pipelines. However, when the CO2 is to be injected into the subsurface,the metallurgy of the tubing and casing in the injection wells become the limitingfactor (see section on well construction). It turns out that O2, when combined with


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CO2 and formation water can cause pitting corrosion in many of the alloys used inwell construction. Again, it is often more cost effective to reduce the level of O2,rather than repair wells or use special alloys. Interestingly, O2 reactivity is still anactive area of research. The oil industry produces oil and gas from the subsurface,and in the subsurface the O2 has all reacted with minerals so is not present in naturalgas or oil—hence there has been less need to study it so far.

Hydrogen can crack steel, so this too needs to be kept at extremely low levels. Thecommon practice is therefore to remove water, and reduce contaminants to levelswhere they do not affect the metallurgy.

Compression is normally a multi-stage affair as it is best to manage the movementof CO2 through the phase envelope to avoid the two-phase region. Compressors areimpressive machines and consume considerable energy to take CO2 from nearatmospheric pressure to generally around 100 bar. The Quest CCS compressor is an18 MWmachine and is shown in figure 8. The design of compressors is a whole topicin its own right, but a CO2 compressor does not differ from a natural gas compressorin its fundamental principles and will therefore not be discussed further.

CO2 storage

By CO2 storage we mean: isolate the CO2 from the atmosphere. This also meanskeeping it out of the oceans as the atmosphere is in contact with the ocean andtherefore exchanges gasses with it. In reality oceans are not completely mixed so deepocean releases might not reach the atmosphere for centuries. The level of mixingbetween deep ocean and shallow ocean is a topic of active climate research. To keep thesystem simple, however, we will state that CO2 should not be released into the ocean(where it can dissolve, reducing the ability of the ocean to take up atmospheric CO2 oreven releasing it back to the atmosphere) nor should it be released to the atmosphere.

0

100

200

300

400

500

600

700

800

900

0 20 40 60 80 100 120

Den

sity

(kg/

m3)

Pressure (bara)

Figure 7. CO2 density at 20 °C. Date from NIST Chemistry WebBook, SRD 69(Carbon Dioxide).


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In the IPCC special report on CCS there is a section specifically on ocean storage.This is discussed briefly in a later section.

How long is permanent?For how long should the isolation take place? Non-scientists say ‘permanent’, butpermanent needs to be defined. Permanent compared to a stellar evolution time line;definitely not. Permanent on a geological time scale; not possible because of platetectonic processes. So what we actually mean is permanent on human civilisationtime scale—perhaps a good definition would be ‘contained over such a period as toallow us to achieve stabilisation and ultimately a reduction of atmospheric CO2

concentrations in support of the Paris target of limiting warming to below 2 °C’.For geological storage (figure 9), we take the view that the CO2 will be injected

into rock formations with an expectation of permanence—i.e. there is no reason toexpect the CO2 to escape from the store. To assist with modelling we place thefollowing constraints onto the system: the evidence (and modelling) shows that it isexpected to remain contained for a thousand years, and after a thousand years thereis no reason to assume that the system will change and the CO2 will leak out.

There are other ways of separating CO2 from the atmosphere—it can betransformed into products, or even fuels. Trees can be planted, peat bogs can berestored. Every sequestration mechanism should face the same test: is it reallypermanent, however you define that? For example, consider what happens when asynthetic fuel is burned? What is the frequency of forest fires? Can we be sure that wecan maintain the peat bog? If the answer to this last question is yes, then it passes thetest. Similarly, for other mechanisms: some Roman cements still exist today andhave definitely shown that man made products can last a few thousand years.

Figure 8. Integrally geared centrifugal compressor at the Quest CCS project. This 18 MW eight stagecompressor can compress 1 Mtpa CO2 to over 100 bar. Credit: Shell/Quest.


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Types of geological storageGeological storage involves the injection of CO2 into rock strata which will retainthe CO2. In general, the CO2 will be injected at depths where the combination ofgeothermal gradient and hydrostatic gradient mean that below this depth CO2 is indense phase and significantly less pore space is required to store the same mass ofCO2. In the real example shown in figure 10 the transition from vapour to liquidhappens at around 2000 ft (610 m).

Some rock strata preclude the flow of fluids, while others allow it. We are allfamiliar with slate roof tiles—water does not penetrate. Slate is special as it is ametamorphic rock that is created by the alteration of mudstone—this cookingmeans that it retains its sealing properties when exposed at the surface. The originalnon-metamorphosed mudstone rock is much more common and also precludes theflow of water when in the subsurface (when exposed at the surface mudstoneweathers and breaks apart, which is why it is not used as a roofing material). Othersealing rock types include evaporites (salts), some carbonates, and some volcanics.Volcanic rocks like granite are often sealing but they are also often fractured, andthe fracture network can allow flow.

Rocks that allow flow either have a connected network of fractures, or aconnected network of pore spaces as shown schematically in figure 11 (right). Thesimplest to visualise is sandstone (figure 11 (left))—we are all familiar with the waywater flows though sand—and it can flow though sandstone in a similar manner.

Some carbonate rocks also have connected pore networks, though often flowmight be assisted by a fracture network. Basalts (solidified lava flows) can produceconnected networks, as the top of a lava flow tends to break apart. When the nextflow buries the breccia, it creates a seal on top of a permeable formation.

Plugged oil well

Caprock seal

Structural storage in depleted oil field

Caprock seal

Baffles within the store

Migration assisted storagein saline formation

Injection wells

Figure 9. Schematic illustration of geological storage. CO2 in green, see figure 14 for the colour/rock type key.


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For storage to take place, injected CO2 must not be able to flow vertically, i.e.back to the surface. This requires a caprock or seal. The seal will be made of a rockthat precludes flow. Geological seals are well understood and tested as they havebeen responsible for trapping buoyant oil and gas in the subsurface for millions ofyears. But it must be recognised that everything in geology is location specific hencesampling (coring) and testing of the rock may be required.

The CO2 itself needs to be injected into a permeable rock layer. The rock pores inthis layer will provide the space that will hold the CO2, while the connected porenetwork allows the CO2 to flow into more pore spaces. The pores are seldom empty.

Figure 10. CO2 density increases with pressure but decreases with temperature. At any depth we see acompetition between the hydrostatic gradient and the geothermal gradient. The figure above plots CO2 densityas a function of true vertical depth below the mean sea level (or sub-sea) for an offshore location in the NorthSea (hence the assumed constant temperature with depth from sea surface to sea bed in the left chart).

Figure 11. Sandstone at Arches National Park, US (left) and schematic of pore spaces in sandstone—filledwith formation brine (right).


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As a rule, they will be filled with formation water, or in some cases withhydrocarbons. The only time they are nearly empty is in the special case of reusingsome types of depleted gas field.

There are a few things that can happen to the CO2 once it is in the pore spaces:• It can just sit there, like natural gas, trapped by its buoyancy below the seal;• It can flow below the seal, if the topography is correct, and some will becometrapped by capillary forces (think of a cup of water spilled on the floor—butthe other way up);

• It can dissolve in the formation water;• Once dissolved it can mineralise.

All four things happen in differing ratios depending of the nature and mineralogyof the rocks and the structure of the geological store (figure 12). They also happen ondifferent time scales. Structural trapping is a function of the geometry of the storeand is therefore immediate; some dissolution occurs immediately as the CO2

contracts unsaturated water, and then more slowly as the rates become driven bydiffusion; capillary trapping only occurs at the tail end of a plume (think of a drop ofwater running down a window pane) so is more important when injection hasstopped; and mineralisation happens at many rates—the CO2 has to first bedissolved, and then a suite of reactions takes place, with rates ranging from minutesto millennia. There is more detail in the further reading section.

If the CO2 is injected into a depleted oil or gas field, there is, by definition, ageological trap. This can take a number of forms: like a bulge upward in thesubsurface, an anticline; a pinch out of the permeable rocks, stratigraphic trap; orsealing or juxtaposing faults. In this scenario, most of the CO2 will remain in

Figure 12. Different types of geological traps, showing structural trapping and migration assisted storage. Inthe former the dominant trapping mechanism is buoyant trapping under the caprock seal, with somedissolution and mineralisation trapping (indicated by the stippling below the contact). In the latter, the CO2

is still held under the seal by impermeable caprock, but is residually trapped by capillary forces, and there issignificant dissolution trapping, with related mineralisation, as the migrating plume can contact a large volumeof water.


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continuous phase for millennia. If there is a large and active aquifer, meaning thatwater sits in connected pore spaces underneath the store, then there will be a slowdissolution of CO2 in the water. The dissolution products make that water slightlyheavier than water without CO2 and over thousands of years this will set up a slowgravity driven circulation that will gradually consume the free CO2.

If CO2 is injected into a formation without a structural trap, but with a geologicalseal (figure 12 bottom), then it will migrate slowly up dip. As it migrates, it contactsnew unsaturated water and dissolves, it gets stuck behind small heterogeneities,it reacts with minerals, and at the trailing end once injection stops, capillary forcestrap significant quantities. This is termed migration assisted storage and all the CO2

will ultimately end up trapped in an immovable manner. The analogy here is spillinga cup of water on a table covered with a tablecloth. Naturally it is importantto make sure that the CO2 does not reach the edge of the store (or table)—hencemonitoring and modelling are key to ensure that containment will not becompromised.

Finally, if CO2 is injected into a very chemically reactive formation, such asbasalt, it can rapidly become mineralised. This form of storage is still in the researchphase, however, it could become important in the future as there are huge quantitiesof flood basalts in some areas of the world, such as the Deccan Traps in India.

Pressure dissipation and sustained injectivityIn the last section we noted that the subsurface is normally full of fluids—generallyformation brine. This brine is already at the hydrostatic pressure for its depth.Anybody who has learned to dive into a swimming pool will know how incompres-sible water can be! So when the CO2 is injected, it has to displace the formationwater. This is a standard diffusion equation problem: the pressure must diffuse awayinto the connected volume of water. The pressure change will relate to thecompressibility of the water and the effective compressibility of the rock system.

The management of pressure is at the core of CO2 storage. The increase inpressure could provide the energy to make water flow up old oil or water wells thathave not been plugged; if it gets large enough, it can create a tensile fracture in theseal formation; the high-pressure fluid also has the potential to interact with faults inthe subsurface changing the stress regime and triggering slippage of the fault.Finally, as the subsurface pressure increases, the injection pressure will need to goup, requiring stronger pipelines, a larger compressor, and more energy.

Two scenarios exist. Either the connected subsurface volume is large enough sothat the water and rock volume is so much larger than the volume of CO2 to beinjected that pressure is not an issue. This is the case in the Quest project in Alberta.Or, pressure can be managed by extracting water or another fluid. The Gorgonproject in Australia plans to extract water as it injects CO2. The other way tomanage pressure is to inject CO2 and remove hydrocarbons, along with water. Thisis called CO2 EOR and is discussed below.

It is vital that a storage project team understands and manages the subsurfacepressure increase, as this links to a key factor in successfully delivering CO2 storage,specifically sustained injectivity. We must not forget that the subsurface system is


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simply the disposal route for the CO2 coming from the capture plant. The captureplant, and linked industrial or power plant, needs to be able to safely sequester theCO2 to retain its climate friendly credentials and justify the increase in cost over itsCO2 emitting, non-sequestering counterparts. The storage system—be it a singlestore or a network of linked stores—needs to be able to take the CO2 it is given,when it is required and at the rates required.

CO2 EOR storage—an oxymoron?In the US it is common practice to inject CO2 into depleted oil fields, this section willnot try to explain all the details as it is possible to write books on it, but will give abrief outline.

Oil fields go through three phases in their life. The primary production phase,when the oil (with some gas) simply flows to the surface driven by the pressure in theaccumulation. As this pressure declines, the field enters the secondary productionphase when additional energy has to be supplied—this can be done by pumping theoil out of the wells, or by injecting water and pushing the oil out. This lattertechnique is termed a ‘water flood’. Initially the wells flow pure oil (with somenatural gas), but later the water breaks through and the wells then flow a mixture ofoil and water. As the saturation of water in the rock pores increases, and thesaturation of oil decreases some of the oil becomes trapped by capillary forces andcan no longer flow.

In certain cases the field operator can choose to try tertiary production byinjecting CO2. The CO2 acts as a solvent, and mobilises trapped oil that remainsafter a water flood. During the process some of the CO2 is permanently andimmovably trapped in the subsurface, in other words it is ‘stored’. The productionwells bring a mixture of oil, water, natural gas, and CO2 to the surface. The gassesare separated from the oil and water and reinjected. Sometimes the natural gas isseparated from the CO2 and sent to market, and only the CO2 reinjected.

The recirculated CO2 works to liberate more oil, and additional CO2 (termedmake-up gas) is bought to compensate for the CO2 that is trapped (stored) in theformation.

When CO2 EOR is talked about in terms of CO2 storage, people tend to bepolarised. Some see it is an economical way to store CO2—the oil production meansthat the storage is for free, and the fact that the operator pays for the CO2 meansthat there is income to offset against the cost of capture. Others see it as undesirablebecause it produces hydrocarbons—hydrocarbons that, if burned, can emit CO2 ifnot fitted with CCS.

Setting the question of ‘should society produce and use oil’ to one side, we cancompare CO2 EOR storage to storage in saline formations or depleted oil and gasfields. Both store CO2. The process of producing and reinjecting CO2 in CO2 EORtakes energy (large compressors) which will generally come with CO2 emissions, sothe avoided CO2 (stored less emitted during the process of storage in this case) is abit lower. On the plus side, CO2 EOR storage produces oil and hence adds valueback into the system—something termed Carbon Capture Utilisation and Storage or


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CCUS—it creates jobs, and can help to pay for the storage and capture. It istherefore more economically efficient than pure storage.

There is not enough CO2 EOR storage potential to sequester all the CO2 emitted,nor are there suitable oil fields near all emitters, however, it can be used as a ‘pumpprimer’ paying for infrastructure, both capture and transport, which will first be usedfor CO2 EOR storage, and then later for pure storage. So, acknowledging theinescapable fact that our industrialised society continues to need oil, we might aswell store some CO2 while producing oil.

Containment and other challenges

One of the first questions I am asked about CO2 storage is: ‘How do you know it willnot all leak out again?’. People are rightly concerned over this. Pictures of oil wellsblowing out, Hollywood disaster movies, reports of volcanic emission events likeCameroon’s Lake Nyos, and concerns around fracking, are in their minds.

The first thing to do is to turn the question around and consider how difficult itwould be to get water or liquid CO2 through a quarter of an inch of ordinary roofingslate. Now picture trying to get it through thousands of feet of subsurface rock,much of it impermeable to gas and water. Add to this the proven fact that oil and gashave been naturally trapped in the subsurface for millions of years—and subsurfacecontainment can look exceptionally secure.

So where are the weak points? We know that natural CO2 seeps, like those infigure 13, exist. By studying these we can identify the geological features necessaryfor CO2 percolation from the deep (in the cases above, volcanic) sources to thesurface. Once we know this we can make every effort to ensure that a CO2 store doesnot have these features. We do this in two ways, through:

(i) site selection: do not choose a storage site that is already leaking or is likelyto leak; and

(ii) engineering: do the engineering properly, inject into the correct layers, donot let fluids migrate behind casing, do not push the system past its capacity.

Figure 13. (Left) natural CO2 seep in Italy (Credit: Jen Roberts and Mark Naylor). (Right) gas vent nearFlorina in northern Greece. There is a CO2 tolerant species flowering around the margin, then stressedvegetation outside (Credit: CERTH/RISCS project).


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Effective site selection is vital. We think about CO2 containment in terms ofbarriers—using something called the Bow-tie risk assessment methodology. Forexample: does the store have a caprock? How can I be sure that it is effective? Isthere evidence that containment has been compromised? Is there evidence tosupport that it has not been compromised? Are there likely to be faults that willmove—i.e. risking containment and potentially causing induced seismicity thatcould result in damage at the surface? Have humans made holes in the seal—i.e.are there legacy well bores penetrating it and what is the status of isolation barriersin those wells?

The process of selecting a storage site is rigorous, and time consuming. Incountries where CO2 storage is taking place there are strong regulatory regimes, andinjection is only permitted when the regulators are convinced as to the security of asite. Over the past few years the global community has come together under the

CO

Injection tubing

Slotted liner

Packers, make seals between casing, tubingand liner

Soil or seabed sediment

Cement

Sandstone

Storage formation,Sandstone

Mudstone

Unconsolidated

Shale

Caprock seal, Shale

Mudstone

Carbonate

Carbonate

Marl

Permeable rock layer, might hold drinking waterSurface casing

Intermediate casing

A-annulus filled with completion fluids

Production or “long string” casing

Conductor (hammered into loose soil/sediment)

Figure 14. Schematic of well construction, not to scale.


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auspices of the International Standards Organisation (ISO) to draft a set ofstandards relating to CCS that include how to select a storage site (see furtherreading).

Engineering and construction are key. The oil and gas industry operates manyinjection wells and experience has shown that problems occur when key engineeringprinciples are overlooked. A recent case in point was the release of methane from anunderground gas storage facility in California. In this region, underground gasstorage (used to help utilities smooth out seasonal variations in supply and demand)had not been subject to the same well engineering and construction regulations as oiland gas extraction, and the well design had only a single barrier to prevent therelease of gas. The oil and gas industry normally designs wells with a double barrierphilosophy, with monitoring of the integrity of the barriers, so that there shouldalways be a backup barrier to prevent leakage. CO2 storage regulations mandate thistype of engineering with multiple barriers.

Well constructionA typical well is shown in figure 14. The operator starts by hammering in a surfacecasing, perhaps 36 inches (the oil industry works in strange units and uses inches forcasing and borehole sizes) in diameter, made of thick steel. The conductor ishammered to the point of no return. Its purpose is to stop the loose soil or sedimentsfalling into the well. Next the ‘top hole’ is drilled and a surface casing is run. This isoften about 28 inches in diameter. This casing will normally be cemented to surfaceand its purpose is to isolate the groundwater formations. A blow out preventer isattached to the surface casing. This then forms a pressure vessel for the next step ofdrilling.

The drilling of the next sections of well depend on the nature of the formations.Well drilling is a complex balance between drilling as deep as you can with one holesize, and ensuring that the pressures from fluids in the rocks do not overcome theweight of the drilling mud. Drilling mud is a carefully engineered fluid made of oil orwater, clays, and other minerals and thickening agents. Its purpose is to cool thedrilling bit, carry drill cuttings to the surface, and hold back the pressure of the fluidsin the rocks. The density has to be carefully controlled.

The interplay between mud weight, formation strength, and the fluids held in theformation dictates the maximum depth to which a drilling rig can drill before settinganother casing. In the example here, we have used one intermediate casing, and thenthe final production casing which extends to just above the storage formation.

Each casing is cemented in at the base, and sometimes all the way to the surface.The cement, plus some remaining drilling mud that coats the sides of the well—termed filter cake—gives structural support and also provides pressure isolation.

When ready, the drilling team drills into the storage formation and then runs steelliner tubing. This is sometimes a solid wall pipe which is cemented in place, and thenholes are shot into it using perforating explosives, or it is a slotted or pre-drilled linerwhich acts like a sieve to hold any loose sand from the rocks in place while stillletting the CO2 flow in.


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The CO2 is injected via the injection tubing into the storage formation. Thistubing holds the CO2 pressure. If a leak forms in the injection tubing the CO2 willflow into the A-annulus which is filled with fluid. This is the next barrier and isdesigned to hold the complete pressure of the CO2. Pressure gauges are attached tothe A-annulus so any leak from the injection tubing will immediately be detected, theCO2 turned off and isolation plugs run into the tail pipe below the packer allowingthe tubing to be replaced or repaired.

Leakage pathways and Portland cement

It is always possible to play the game of ‘what if’ with a containment system. In fact,it is one of the standard ways in which we all work. What if the casing fails, what ifthe caprock leaks…and so on. In the enthusiasm to test the what-if scenarios, fluidmodellers often introduce short cuts into their system—imagine a direct pathwayfrom the storage formation to the surface, or let’s inject into a shallower zone. This isan excellent way of stress testing the system, but the next step must not be neglected.What physics and geology are required for this pathway to actually exist and atwhat rate would escaped CO2 flow? An example of a leak from an exploration wellthat was drilled into a formation that naturally contains CO2 and that was neversealed is shown in figure 15—this one is a bit of a tourist attraction, albeit mainly forgeologists! When this question is answered, it is often found that the pathwayphysically or geologically cannot exist, or that flow would be so slow as to takethousands of years to even seep.

Cement is a good example of how even ‘rational’ people forget the scientificthought process. Cement is made when a mixture of tri and di-calcium silicate andtricalcium aluminate, tetracalcium aluminoferrite, and gypsum (as well as other,minor components and additives) is mixed with water. This allows for the hydration

Figure 15. Natural CO2 seeping to the surface at Crystal Geyser, Green River, Utah, US. The CO2 is naturalhowever, the seep was caused by the drilling of an oil exploration well many decades ago.


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of the components to make calcium silicate hydrate and calcium hydroxide andreleases heat.

If you take a plug of standard oil-industry cement, namely Class G Portlandcement, and flow carbonic acid past it, the cement is leached. The calcium hydroxidecan react with the carbonic acid, and decalcification of the calcium silicate hydratealso takes place. If the carbonic acid is replaced and the dissolution products arecontinuously removed, the ultimate result is a porous amorphous silica gel. This istaken as evidence that Portland cement will not work as an effective impermeablebarrier in acidic environments. But when we look at the actual downhole situationwe see something very different: this is a stagnant scenario. There is no Maxwelliandaemon with a hosepipe generating a flow of carbonic acid. The bottom of a 30 m orlonger plug of cement sits in a stagnant pond of liquid CO2. There is no reaction hereas there is no water. Assume then that the plug is just below the water contact in aCO2 store, so it is exposed to carbonic acid. The reaction with the plug rapidlybecomes diffusion dominated as reaction products have to diffuse out and freshreagents must diffuse in. The experiments and modelling tell us that the cementbecomes more sealing in the absence of leaching. These facts have been backed up bylab tests and cores taken from the walls of wells in US CO2 EOR projects where CO2

and then water are sequentially pumped into wells.If the cement plug, or casing sheath, already has an existing leakage pathway,

then leaching can occur and the system either gets worse or self-heals. This is anengineering or an emplacement issue and there is much debate about cementshrinkage, microannuli which have the potential to cause leak paths, and shalecreep and mud plugging which seal leak paths. This has nothing to do with thereactivity of Portland cement, rather it is all about the emplacement of a plug withrespect to the storage formation. This is not to say that there may not be bettercements than Portland cement, or even Portland cement with additives that reduceshrinkage or which encourage healing of cracks (an active research field). It does saythat if a legacy well has been correctly installed and later plugged so that it does nothave leak paths, then it is unlikely to form new leak paths. We must also rememberthat CO2 has been injected in CO2 EOR fields for decades, fields with natural gascontaminated with CO2 have been produced for just as long, and even pure CO2

fields have been produced since the 1980s to supply the CO2 EOR projects.If the well already has a leak path or starts to leak then we get CO2 to surface. An

example is shown in figure 15. This well was drilled decades ago and encounterednatural CO2 instead of hydrocarbons. In the past the CO2 used to create an artificialgeyser and it became a tourist attraction, however when I visited in 2017 it hadreduced to bubbles only. If a well in a CO2 store does start to leak then the operatoris obliged to repair it, using the same techniques as oil and gas operators use to repairblow outs.

Monitoring

It is often said that were the motor car invented today, it would never be permittedto operate! Perhaps it is better to say that were the car invented today, regulations


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would be created from the start to ensure that the cars were safe and well suited tothe job. The authorities would demand evidence that the cars were not endangeringlife and were performing as the manufacturers stated. This is the case for CO2

storage. Regulators are not simply content that a site has been correctly selected, andconstruction has been carried out to a high standard. They further require that thestorage operator shows that the site is containing CO2 and that it is operatingaccording to prediction—termed ‘conformably’. Is the pressure dissipation takingplace in the way you said it would when you obtained a storage permit for the site? Ifnot, what is this observation telling you? Is there any evidence of out of zonemigration of CO2? Is the surface pipework leaking?

In the subsurface, predicting the behaviour of the CO2 involves the developmentof numerical models, very similar to those in atmospheric physics. Some are finitedifference models that combine the physics of the fluid dynamics and of pressuredissipation: reservoir engineering models. Others are finite element models of thestresses of the rocks and their behaviour as a pressure perturbation is introduced:geomechanical models. In special cases, it might be required to build geochemicalmodels as well. Although the three types of models can be linked, it is seldom doneon a full field basis, because they are extremely computer resource hungry andsimply take too long to run!

Induced seismicity

Certain events over the past few years in Oklahoma, US, have focused a spotlight onthe subject of induced seismicity. In Oklahoma, the hydrocarbon gas industrydisposes extracted saline pore water via injection wells. In recent decades, the rate ofwater injection has increased because the shale gas revolution has led to theproduction of significantly more waste water. Suddenly, the incidence of earth-quakes that were large enough for people to feel increased, as did the magnitude ofthese earthquakes. It must be noted that this was an area that was not subject tosignificant natural seismicity. Building construction codes were not set up for activeseismicity nor were the local population used to felt events.

The Oklahoma seismicity is now the subject of much research and monitoring,and what has become clear is that there was little or no site characterisation beforethe start of injection, and there were no monitoring plans. In many aspects, theoperators at the Oklahoma sites were unlucky, there are thousands of water disposalwells across the US, and the vast majority show no induced seismicity. It is nowthought that, in this case, critically stressed faults (faults that are holding against anapplied stress, i.e. they contain pent up energy), possibly in the granitic basementrocks that lie at the bottom of the sedimentary sequence, are moving in response tothe changes in pressure.

When CO2 was injected into a different region of the US, in Decatur Illinois, thesite was extensively studied prior to permitting, and there was a comprehensivemonitoring programme. Seismic events are measured on a logarithmic energy scale.In order to be ‘felt’ an event has to, in general, be above magnitude 3. Significant


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events are normally above 5 or 6, while global calamity events are normally around8 or 9. The Decatur project in Illinois did detect seismic events, ranging from M-2(negative magnitudes), to M1 (see additional resources for more details). This levelcan be expected, and the author suspects that if we installed such sensitive equipmentin any area of the world with subsurface activity then such events would be heard.

Remediation plans

Many CO2 storage permitting authorities require the operator not only to have amonitoring plan to identify issues, but also a plan for reacting to the monitoringresults—this is logical. Suitable monitoring plus a reaction, can equate to a barrier,termed a reactive barrier. This approach has the advantage of demonstrating thatthe operator is able to respond to leakage or migration scenarios that might threatenthe integrity of the storage site.

Ocean storage

Much thought has been given to the idea of ocean storage. Indeed, it receives awhole chapter in the IPCC special report on CCS. The logic is simple—inject theCO2 into the deep ocean where the pressure and temperature are such that CO2 isdenser than water. Mixing happens very slowly at these depths and the CO2 willremain isolated from the shallow waters for hundreds to thousands of years. Thechallenge here is the possible impact of the CO2 lake on the marine life. As we learnmore about the deep oceans we find more and more life. The question, however, ismoot as the Convention on the Prevention of Marine Pollution by Dumping ofWastes and Other Matter 1972, the London Convention, forbids this practice in anycase.

In a related area, the creation of hydrates is a topic being actively explored. Herethe proposal is to inject the CO2 into sediments below the deep ocean floor. This cancreate hydrates within those sediments immobilising the CO2. This idea will not beexplored further here as this short book concentrates on technology that currentlyexists and can be deployed at scale today, but references are given in the furtherresources.

3 Current DirectionsScaling up CCS

If CCS is going to realise its potential and make a significant contribution toreducing global CO2 emissions then it needs to scale up from a few tens of millions oftonnes per year, to billions of tonnes of CO2 captured, transported and stored eachyear. In the capture area, the challenge is just that of building new industrial plant—it will be costly initially and as the technology matures the unit cost per tonne willreduce through learning and innovation. On the storage area the challenge is largerand relates to finding and accessing sufficient underground storage capacity. Thiswill be expanded upon below.


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The size of the challengeCCS has been proven at what is termed small industrial scale—by this we mean thescale that is equivalent to removing about quarter of a million cars a year from theroads: capturing and storing around 1 million tonnes of CO2 a year. Interestingly,even this small industrial scale capture is large when compared to renewable sources:the really impressive Desert sunlight solar farm in California has an installedcapacity of 550 MW and its owners estimate that it displaces approximately 300 000tonnes of CO2 each year.

Statoil (recently renamed Equinor) has been storing CO2 in the North Sea forover twenty years. Shell has added CO2 capture to hydrogen manufacturing units attheir bitumen upgrader in Alberta Canada. Here they capture over one milliontonnes of CO2 each year, pipe it sixty miles, and inject it into a deep salineformation. Also in Canada, in Saskatchewan, SaskPower has fitted one unit of acoal power station with CCS—this CO2 is piped to the Weyburn EOR field. Moreexamples are referenced in the additional resources section.

The size of the current plants are nothing compared to what is required todecarbonise the entire planet—100 million tonnes of CO2 a day, plus othergreenhouse gasses (figure 16). The International Energy Agency, the IEA, dividesthe decarbonisation challenge between technologies and suggests that CCS cancontribute 12% of the reductions required in 2050 to achieve a 2 °C global rise intemperature: equating to around 6.1 Gt CO2 each year. CCS, along with renewables(32%) and other technology options, has to ramp up to massive scale.

Recent work, done in partnership with the IEA Greenhouse Gas R&DProgramme (IEAGHG), has shown that this should be possible, although the scaleof the system needed would be similar to that of the world’s present gas-productioninfrastructure (see additional resources). This sounds large, but it is logical—if weneed to decarbonise any gas, oil, coal and industrial emissions that cannot yet (or

Figure 16. Total CO2 emissions from fossil fuel and cement each year based on data from the Global CarbonBudget team (see additional resources).


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over the next forty years) be replaced by alternatives, plus all the biologicallysourced CO2 that needs to be captured to create the negative emissions required toremove CO2 from the atmosphere, then this must be a lot.

While capture is simply a matter of building industrial plants and pipelines,storage is different. We will need to identify good locations for storage, thoroughlycharacterise the sites, and then inject large volumes of CO2. Current subsurfaceaccommodation processes—simply the compressibility of water and rock—lead toonly between 0.5% and 1% of the pore space being filled before reaching the naturalpressure constraints of the containing system—assuming that there is no naturalpressure relief via a wider natural fluid flow system. Further, increasing subsurfacepressures could also lead to an increased chance of pushing formation brine intooverlying layers, potentially via legacy well bores, and also increasing the risk ofinduced seismicity. Pressure management will therefore be a fact of life for futurestores—and, unless the storage is via CO2 EOR where pressure is managed as part ofthe entire hydrocarbon production process, this will require water extraction. Theincreased subsurface pressures should drive the water out of extraction wells—justlike artesian wells—but this brackish, or sometimes very salty, water will have to betreated and disposed of, or used in agriculture, industry and even for drinking.

Water extraction and pressure managementExtracting water can dramatically increase the storage efficiency—instead of 0.5% ofthe pore volume, in theory the system could reach numbers like 80% pore utilisation.In practice, this will not be the case as (i) it takes substantial time to drain water outof a porous medium; (ii) the pressure induced by the buoyancy of too large a columnof CO2 would fracture the caprock; (iii) but the main constraint would be CO2

breaking through to the water extraction wells.The CO2 will flow towards the area of lowest pressure, the CO2 being more

mobile than water. This effect is compounded by the fact that rocks are nothomogenous, so CO2 will preferentially flow in some layers, so the injected CO2 willnot move in a straight flood front. Some of it will tend to run ahead and ‘breakthrough’ to the water extraction wells. i.e., CO2 could arrive at a water extractionwell sooner than expected, in the worst case before the well has been closed in,therefore being released to the atmosphere. This means that the floods will need tobe actively managed, changing injection patterns (sweep) to maximise subsurfaceutilisation.

The whole topic of maximising the storage efficiency while still constraining thecost to society is a new and exciting area of research and is only just beginning to beinvestigated.

Legacy wellsHigh-level estimates show that there should be plenty of rock formations that aresuited to storage. However, when you start to explore for an injection location youhit an anthropogenic problem: the holes left in the subsurface by other humans. Manhas been drilling into the Earth for over a century: for mineral exploration, waterextraction, waste disposal (there is a surprising amount of this), and oil and gas


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exploration and extraction. Not all wells are mapped, not all wells have effectiveisolation barriers (long cement plugs). While many types of rocks actually move andsqueeze old wellbores closed, not all do. The existing storage projects working todayhave been carefully sited to avoid such legacy wells. Giga tonne scale storage cannotafford to be as discriminating and will inevitably encounter potentially leaking wells.

Well seeps and leaks can be repaired with existing technology—by bringing adrilling rig onto the site and either removing the old plugs and setting new ones, ordrilling a new well that intersects the old one to allow pumping of cement and othersealants into the subsurface to halt flow toward the well. This is extremely costly andideally needs to be avoided wherever possible!

The cost of repairing a legacy well leads to an interesting challenge, mainly drivenby a lack of information. We cannot be certain that a well, especially one thatappears to have a poor set of isolation barriers, will leak. Nature likes to close uptunnels and holes, but we cannot be absolutely sure that a tortuous leak path doesnot still exist. Pre-emptively trying to drill out and re-plug an old well might takemonths, and could actually reopen a perfectly sealed wellbore. What is required hereis research: research into sealing mechanisms, like salt and shale creep; research intothe effect of well drilling mud (made of clay, water and other substances) at sealingany microannuli in the well cement sheaths; and research into methods of assessingthe up to 3000 m deep wells for potential leak points.

If a leak is identified we need to develop clever, low cost ways of sealing the well.Research at the University of Montana into microbes that secrete calcium carbonateis one such angle. These could be delivered by targeted injection or slim holemethods, perhaps using coiled tubing, and would then seal up any flow paths in theold wells. Other researchers are looking at novel ways of removing old steel casing,and then stimulating the rocks to squeeze in.

Cost-effective monitoring—instrumenting the EarthWe would all agree that we want to be sure that stored CO2 is not leaking back intothe atmosphere. CO2 storage permits almost always require that the operator has amonitoring and verification plan to show just this.

Current monitoring plans rely on oil and gas technologies—such as large-scaleseismic surveys, down-hole monitoring with surface readout electric or fibre opticgauges, and ship borne seabed and seawater surveys. This technology has workedwellfor the oil and gas industry, as large area surveys are only required once to discover thefield, then smaller targeted surveys are used occasionally during the relatively short,perhaps twenty year, life of most fields. Down-hole, subsurface, monitoring is onlyrequired during the production of the field, so once again everything ties up.

CO2 storage is different. First, we want to be sure that the storage is effectivelypermanent. In Europe the regulation expects a default monitoring duration of twentyyears after the end of injection, in addition to extensive monitoring during injection.In the US, the post-closure period defaults to fifty years unless there is strong evidenceto shorten it, and the area to be monitored is the area of the pressure plume—whichcan be tens to hundreds of miles round the injection site.


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Something therefore needs to change. Onshore, local people do not want seismictrucks driving across their fields every few years, nor do we want to disturb marinemammals with offshore seismic surveys. Surface read-out gauges require open wellbores, but an open well is a potential leak path, so these need to be sealed as soon aspossible after injection ceases. In addition, maintaining wells offshore, on a platformor subsea, is both dangerous to the people who service the wells, and costly. Shipborne marine survey techniques require large (currently) CO2 emitting boats andcrews—again risk and cost increases.

A final challenge is also present. Drinking water aquifers extend over hundreds ofmiles—collecting rain from distant mountain ranges and transporting it to pop-ulations. Deep salt water aquifers are no different, stretching hundreds of miles andcrossing county and country boundaries. If used to combat climate change, CO2

storage needs to take place for at least the next fifty years, and not all projects will beoperating at the same time. This temporal dislocation could lead to projects startingand finishing, and then others starting up decades later in the same hydraulicallyconnected saline formation. How do we ensure that we know that the pressuresinduced by any new project will not cause issues in the old, now closed, project? Weneed some way to monitor the subsurface for at least a century—in other words weneed to instrument the Earth.

The subsurface environment is hostile: high temperatures of around 100 °C, highpressures of over 100 atmospheres, and corrosive salty and CO2 rich fluids. But thereis a geothermal gradient from which work can be extracted, and wells have steelcasings which are already used for data transmission—albeit from short livedbattery powered gauges. What is required is to develop a gauge carrier that canscavenge energy and transmit data to the surface occasionally or upon interrogation.This carrier can then be coupled to a huge array of potential gauges, temperature,pressure, salinity, dissolved CO2, even strain and radiation. The gauges can beplaced below well abandonment plugs and left for centuries. I term these gaugescentury gauges or even infinity gauges. The applications for such gauges are not justlimited to CCS, but extend into any area where increasing our knowledge of thesubsurface is useful—a concept termed instrumenting the Earth.

Significant research is takingplace in the seismic acquisitionworld. Insteadof layingout largearraysofgeophonesand then lettingoff apatternof explosive chargesorusingvibroseis trucks, researchers at Lawrence Berkeley National Laboratory and also inJapan are developing continuous seismic sources which remain fixed in place, and arecoupling these with buried fibre optic cables. In this way, they hope to achieve regularmonitoring of the subsurface with no impact on the neighbourhood.

Many of you will have heard of the UK population’s attempt to name a researchvessel Boaty McBoatface. The vessel is now called the Sir David Attenborough, butan autonomous underwater vehicle (AUV) was christened Boaty McBoatfaceinstead. A research partnership in the UK has developed sensors and softwarethat will allow the AUV to map the seabed, look for bubble streams that couldindicate a leak, and test the water quality—removing the need for a ship, deliveringmore data with significantly lower risks to sailors and lower cost.


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What are the consequences of a leak, what are the rates and what does a leaklook like?Most human activity takes place on the surface of the planet. As a result, we areprogrammed to think in terms of spills, leaks from factory tanks, run off from fieldsand the like. CO2 storage injects CO2 under kilometres of rock. It is incrediblydifficult to get things to flow through many rock types. As a result, even were CO2 tostart to leak from the store, it would have a challenging task to get to the surface.Add to this the fact that CO2 dissolves in water and the challenge becomes thatmuch larger. If CO2 were to manage to percolate upward, it might take hundreds ofyears to get there, unless it shortcuts through a wellbore. Even wells do notnecessarily provide an easy path—subsurface leaks often flow along a well for awhile then out into other rocks. The cement plugs used to abandon wells sometimeshave microannuli between the cement and the casing, and CO2 can potentiallypercolate here; but even if it does, at what rates?

Ab initio modelling struggles to answer questions related to leak rate—roughlyyou get out what you put in, although carefully framed questions and scenarios canhelp to constrain the system. I often see people suggesting leak paths that areprecluded by physics or by other evidence. What is needed is actual physicalexperiments. Some researchers are studying natural, normally volcanic in origin,seeps. Others like those at the Field Research Centre in Alberta, Canada, are drillingwells and injecting CO2 to make a synthetic leak. Similar work was done offScotland by the QICS project. These let us see what a new leak looks like—onewhere the flow of CO2 is not in equilibrium with the surrounding rock and water.What does it look like on seismic, what happens when it stops, how fast does it flow?

Other researchers are looking at the effect of isolated CO2 leaks on naturalsystems—onshore and offshore. This research is finding that the effects are verylocalised—one way that people identify natural seeps is to look for differentvegetation like that pictured in figure 13.

New storage frontiersMost of the world has not been systematically assessed for storage capacity, butwhere assessments do exist they are difficult to compare. Research consortia haveassessed the US, Australia, and most of Europe—and this needs to be extended tocover areas with huge populations and growth potential, such as India, and Asia.

A key component to this research is to develop a classification system for CO2

storage resources. This has just been completed by a combined industry andacademic team under the auspices of the Society of Petroleum Engineers, whoalso maintain the most used Petroleum Resource Classification system. This is titledthe Storage Resources Maturation System, and is linked closely to a generalisedUnited Nations classification system. The SRMS was built to parallel the petroleumsystem because of the similarities between subsurface storage and subsurfaceextraction of naturally stored petroleum. The parallel will allow financial backersto deploy their petroleum expertise when assessing the viability of storage projects.The next task is to deploy the SRMS and develop how-to guides to help ensureuniformity of classification.


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An exciting new area of storage research is basalt storage. The oceanic crust ismade of basalt. Large areas of many continents are covered by flood basalts.Researchers at the Lawrence Livermore lab performed an injection test into floodbasalts at Wallula in Washington State, US, and there are currently proposals toexplore pillow basalts off the Pacific coast of the US. Basalts also have permeablezones—for example breccia zones at the tops of flows—covered by impermeablelayers of fresh basalt. In Iceland the CarbFix project has been injecting carbonatedwater and storing the CO2 in oceanic basalts as part of a geothermal energy project.An interesting additional point is that the reactivity with CO2 is much greater inbasalt than in sedimentary rock, leading to a large quantity of mineralisation—bothan advantage from the long term storage perspective and a challenge from the shortterm injectivity point of view.

Fundamental physics

The physics of pure CO2 phase behaviour is well understood, however, CO2 hasmany interesting properties. Perhaps the most unusual is that the phase change fromliquid to gas takes place in the working range of a normal project. If we think aboutpiping natural gas, it stays as a gas from the field all the way to our gas ring in thekitchen—even though high pressure gas mains can run at pressures over 100 bar.Water is the same, unless you heat it significantly it remains a liquid. Look atfigure 17, CO2 changes from gas to liquid between 10 and 70 bar at normalenvironmental temperatures. If CO2 is released from high pressure to atmosphericpressure, it rapidly cools and solids can form—this is why CO2 fire extinguishersmake a white fog of condensed water.

1000

100

supercritical fluid

fluid phase

triple point-56.6°C at 5.2 bara

critical point31.3°C & 73.8 bara

solid phase

vapour phase

Temperature, °C

Pres

sure

, bar

a

atmospheric sublimation point-78.5°C at 1 bara

liquid phase

10

1

-120 -100 -80 -60 -40 -20 0 20 40 60 80

0.1

0.01

0.001

10,000

Figure 17. Pure CO2 phase diagram.


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If we are to estimate the effects of CO2 releases, in order to design facilities, wellsand pipelines, we need to be able to simulate the full phase envelope of CO2. What ismore, we need to be able to do this not just for CO2, but for mixtures of CO2 withCH4, and other contaminants. If a well backflows, the mixture will also includewater that will make ice and hydrates when the system cools. At the moment westruggle to simulate the behaviour of CO2 mixtures, and have challenges when solidsco-exist with liquid and vapour—this is quite a challenging computational physicsproblem.

New capture technologies

Most capture plants in operation today deploy amine absorption, a tried and testedtechnology. Some use second-generation amines, which are more efficient. Capturelinked to power generation, simply takes a normal power train, say a gas turbine,then adds a capture unit to it, and finally adds a compressor.

One team of researchers and engineers at 8 Rivers Capital, based in NorthCarolina, US, guided by Rodney Allam, has gone back to basics and has looked atthe whole power chain. What you need for zero carbon power is to convert gas toelectricity and to deliver high pressure CO2 for storage. The team invented the Allamcycle which uses air separation to make O2 and get rid of the N2, followed byoxycombustion. All normal so far, but then they use CO2 as the working fluid for aturbine rather than steam. The CO2 is also used to moderate the combustion,managing the temperature. The cycle takes place at a pressure greater thanatmospheric reducing the level of CO2 compression required compared to postcombustion capture. All this leads to, it is hoped, a lower capital outlay, similar tothat of an unabated plant, while having a similar efficiency to a conventional gaswith CCS power plant. An industrial scale pilot is currently under construction inTexas.

While capture has been shown to work on coal fired power, it has not yet beendeployed at even the few hundred megawatt scale on gas, nor have the crucialnegative emission BECCS plants been constructed. There are many industrialapplications where CCS is needed, many have been piloted but again few havebeen deployed at a true commercial scale.

Making the political and economic case

The lack of deployment of CCS, despite the call for it in integrated assessmentmodels, leads us to the interaction between economics, science, public policy andscience communication.

Despite lots of research showing that deploying CCS is needed to deliveremissions targets, and that CCS makes economic sense, governments have failedto create the conditions that will encourage industry to deploy CCS. The exceptionsare CO2 EOR storage in the US where industrial emissions have been captured foryears, along with CO2 from natural CO2 gas fields; and Norway where a CO2 taxincentivised the deployment twenty years ago.


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A common question from political decision makers is: ‘How long can we delaybefore deploying it?’ This summarizes the conundrum with CCS. Although deepdecarbonisation of electricity, heat, and industry plus negative emissions arerequired to head off the massive and costly effects of climate change, these effectsare not weighing hard on the economies of today. How do today’s decision makersbalance the need to invest today in for example, hospitals, roads, and police, with theneed to invest in deep rapid decarbonisation such as that delivered by CCS that willonly pay off in a generation or two?

Companies recognise the challenge of climate change, and compile reports fortheir shareholders showing their resilience under difference scenarios. What thecompany executives cannot work out is how to finance investment in CCS.Investment in many renewable technologies is paid for by subsidies and feed-intariffs, electric cars are incentivised by tax breaks. But these mechanisms are seldompresent for CCS—can a cement or fertilizer manufacturer sell low CO2 products at apremium? Is a government willing to spend more on building a new high-speed railline with low CO2 steel?

This is where some incredible thinking is needed—thinking at the interface ofscience, economics, policy and sociology—thinking that harks back to the dayswhen leading political figures were also leading natural philosophers. Whoeversolves this challenge, and many such as teams at Imperial College and CambridgeUniversity, are working on it, might well be credited with solving the CO2 problem.

4 OutlookTake a look at the Mauna Loa CO2 curve again (figure 1). Is the concentration ofCO2 in the atmosphere increasing or decreasing? How rapidly do we need to make alarge difference in CO2 emissions rates to stand a 50% chance of hitting 2 °C, letalone a 50% chance of 1.5 °C?

Even a cursory inspection of the data and climate model predictions leads us toask the question—can we afford not to implement CCS along with every energysaving technology, every alternative energy, and make every effort to reduce ourpersonal carbon footprint?

Take a careful look at the global economy—look at society as it is, rather than aswe would like it to be. How quickly can the energy, industrial, and transport systemtransform without massive social upheaval? Where can we recommend interventionsthat will make a difference?

The status quo is 100% leakage of CO2 into the atmosphere—that is released fromsmoke stacks and exhausts the world over. Industrialised, urbanised, society isalarmingly fragile and dependent upon energy and energy intensive manufacturing.

CCS, in all its guises, with its strengths and failings, offers global society a way torapidly remove a significant proportion of the CO2 now released to the atmosphere,without dramatically disturbing fragile economies, and without rationing energy. Ifscaled up it can buy time and significantly increase the chance of hitting 2 °C ormaybe even 1.5 °C.


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Additional resourcesGlobal warming

The definitive source for information on global warming, the effects on peopleand the planet is the IPCC—the Intergovernmental Panel on ClimateChange. www.ipcc.ch

The most recent report at the time of writing was the Fifth Assessment Report,chapters of which were published in 2013 and 2014. All the reports arefound here: https://www.ipcc.ch/publications_and_data/publications_and_data_reports.shtml#2

The IPCC is now working on two new reports, a special report on 1.5 °C whichis in review, and also on the main sixth assessment report.

The formal reference to the IPCC fifth assessment report is:Stocker T 2014 Climate change 2013: the physical science basis: WorkingGroup contribution to the Fifth assessment report of the IntergovernmentalPanel on Climate Change (New York: Cambridge University Press) pp. xi,1535 pages.

No discussion on global warming would be complete without the originalreference from 1896:Arrhenius S 1896 On the influence of carbonic acid in the sir upon thetemperature of the ground Phil. Mag. J. Sci. 41 237–76.

A very useful summary of the state of CO2 reductions was given in theNovember 2017 issue of The Economist, ‘What they don’t tell you aboutclimate change: Negative-emissions technology’:https://www.economist.com/news/leaders/21731397-stopping-flow-carbon-dioxide-atmosphere-not-enough-it-has-be-sucked-out

How to fight climate change

The online magazine Quartz has some very accessible articles describing theneeds for CCS as part of the decarbonisation mix:https://qz.com/1144298/humanitys-fight-against-climate-change-is-failing-one-technology-can-change-that/https://qz.com/1145525/climate-change-is-a-surprisingly-straightforward-problem-to-solve/https://qz.com/re/the-race-to-zero-emissions/

CO2 concentrations in the atmosphere

When I first started looking at global warming and CO2 levels I wanted to seethe data for myself, and where better to get it than from one of the earliestCO2 laboratories in the world, set up by Charles David Keeling on top of theMona Loa volcano in Hawaii. Data have been collected at this location sincethe 1950s.


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http://www.ipcc.ch

https://www.ipcc.ch/publications_and_data/publications_and_data_reports.shtml#2

https://www.ipcc.ch/publications_and_data/publications_and_data_reports.shtml#2

https://www.economist.com/news/leaders/21731397-stopping-flow-carbon-dioxide-atmosphere-not-enough-it-has-be-sucked-out



https://qz.com/1144298/humanitys-fight-against-climate-change-is-failing-one-technology-can-change-that/



https://qz.com/1145525/climate-change-is-a-surprisingly-straightforward-problem-to-solve/



https://qz.com/re/the-race-to-zero-emissions/

Keeling C D, Bacastow R B, Bainbridge A E, Ekdahl C A, Guenther P Rand Waterman L S 1976 Atmospheric carbon dioxide variations at MaunaLoa Observatory, Hawaii Tellus 28 538–51

All the information on how the measurements are made, on CO2 in theatmosphere and the latest data can be found at this web locationhttps://www.esrl.noaa.gov/gmd/ccgg/trends/

and a lot more information can be found at the Scripps Institution ofOceanography in a site dedicated to the Keeling curve.https://scripps.ucsd.edu/programs/keelingcurve/

Emission sources and quantities of emissions over time

More information on emission sources and levels over the decades can be foundat CDIAC, however the archive is moving.http://cdiac.ess-dive.lbl.gov/GCP/carbonbudget/2016/

Discussions on the global carbon budget, emissions, and sinks, can be found atthe Global Carbon Project. When the papers talk about the remainingcarbon budget, how much was emitted in any year, they are often referring toreports generated by this group of academic institutes.http://www.globalcarbonproject.org/carbonbudget/

The project publishes a paper each year, which has in incredible author list. Thereference for the 2016 paper is given below:Le Quéré C et al 2016 Global carbon budget 2016 Earth Syst. Sci. Data8 605–649

Also take a look at the CarbonBrief article that discusses the results:https://www.carbonbrief.org/what-global-CO2-emissions-2016-mean-climate-change

For historical emissions, like in figure 16, seeFossil fuel combustion and cement production emissions: Boden T A,Marland G and Andres R J 2016 Global, regional, and national fossil-fuel CO2 emissions Oak Ridge, TN: Carbon Dioxide Information AnalysisCenter, Oak Ridge National Laboratory, US Department of Energy) doi10.3334/CDIAC/00001_V2016

The European Union Joint Research Centre maintains the Emissions Databasefor Global Atmospheric Research (EDGAR) and publishes annual reports.http://edgar.jrc.ec.europa.eu/http://edgar.jrc.ec.europa.eu/news_docs/jrc-2015-trends-in-global-CO2-emissions-2015-report-98184.pdf

The fact that CO2 emissions are effectively cumulative over a human time scaleis described by Myles Allen from the University of Oxford:Allen M R et al 2009 Warming caused by cumulative carbon emissionstowards the trillionth tonne Nature 458 1163

When discussing carbon budgets, it is important to identify if it is a Carbonbudget or a CO2 budget. Some authors only count the Carbon atoms in the


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https://www.esrl.noaa.gov/gmd/ccgg/trends/

https://scripps.ucsd.edu/programs/keelingcurve/

http://cdiac.ess-dive.lbl.gov/GCP/carbonbudget/2016/

http://www.globalcarbonproject.org/carbonbudget/

https://doi.org/10.5194/essd-8-605-2016

https://doi.org/10.5194/essd-8-605-2016

https://www.carbonbrief.org/what-global-CO2-emissions-2016-mean-climate-change

https://www.carbonbrief.org/what-global-CO2-emissions-2016-mean-climate-change

https://doi.org/10.3334/CDIAC/00001_V2016

https://doi.org/10.3334/CDIAC/00001_V2016

http://edgar.jrc.ec.europa.eu/

http://edgar.jrc.ec.europa.eu/news_docs/jrc-2015-trends-in-global-CO2-emissions-2015-report-98184.pdf

http://edgar.jrc.ec.europa.eu/news_docs/jrc-2015-trends-in-global-CO2-emissions-2015-report-98184.pdf

https://doi.org/10.1038/nature08019

CO2 molecule, meaning that to convert from a Carbon budget to a CO2

budget requires multiplying the tonnes of Carbon by 3.67 (the atomic mass ofC is 12 u, while CO2 is 44 u).

The International Energy Agency (IEA) publishes on CO2 emissions from fuelcombustion, reporting emissions by region and by sector:https://www.iea.org/publications/freepublications/publication/CO2EmissionsfromFuelCombustion_Highlights_2016.pdf

The US EPA reports material on emissions, though much is this is vanishing asa result of changes in the priorities of the current administration.https://www.epa.gov/ghgemissions/global-greenhouse-gas-emissions-data#Sector

Bio energy with CCS—or BECCS is one of a suite of negative emissiontechnologies. These are becoming more and more important as it looksincreasingly likely that we will overshoot the CO2 levels required to maintainthe global average temperature increase to 2 °C. The article below gives auseful introductionhttps://www.carbonbrief.org/beccs-the-story-of-climate-changes-saviour-technology

How much CO2 does a woodland capture?http://www.nytimes.com/2012/12/04/science/how-many-pounds-of-carbon-dioxide-does-our-forest-absorb.html

The energy system and how to decarbonise

This is a huge and contentious area, where opinion is often used to skewstatistics. One example I repeatedly notice is when papers report that ‘todaythe country/state/region used more renewable energy than ever before’. Thestatement is generally true, but they neglect to point out that demand wasparticularly low because it was a holiday or a weekend or hot/cold and thatthe wind was particularly strong…and so on.

One author who noticed this was physicist Sir David MacKay, a professor ofengineering at Cambridge, Fellow of the Royal Society, and one time chiefscientific advisor to the UK government’s Department of Energy andClimate Change. David looked at the system as a scientist, and exploredwhat it would take to run everything from renewable sources, and wrote abook ‘Sustainable energy—without the hot air’. This book can be down-loaded from the website below, and was even praised by Bill Gates.MacKay D J C 2009 Sustainable Energy—Without the Hot Air (Cambridge:UIT).https://www.withouthotair.com/

The book is well worth a read before making any judgements on the energysystem. Once you have read the book, if you want to start exploring theelectricity system further then an invaluable resource is the UK Gridwatchwebste.http://www.gridwatch.templar.co.uk/


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https://www.iea.org/publications/freepublications/publication/CO2EmissionsfromFuelCombustion_Highlights_2016.pdf



https://www.epa.gov/ghgemissions/global-greenhouse-gas-emissions-data#Sector



https://www.carbonbrief.org/beccs-the-story-of-climate-changes-saviour-technology



http://www.nytimes.com/2012/12/04/science/how-many-pounds-of-carbon-dioxide-does-our-forest-absorb.html

http://www.nytimes.com/2012/12/04/science/how-many-pounds-of-carbon-dioxide-does-our-forest-absorb.html

https://www.withouthotair.com/

http://www.gridwatch.templar.co.uk/

Here you can download minute by minute data for electricity generation and seewhat is actually happening. I get childishly excited when it is stormy and amalways looking to see what the new high in wind generation will be.

Robert Sansom examines the challenge of heat in his doctoral thesis:Decarbonising low grade heat for a low carbon future, Imperial College 2014.https://spiral.imperial.ac.uk/handle/10044/1/25503

The International Energy Agency, the IEA, have published a lot of material onCCS and on its importance in contributing to deep decarbonisation. Theirwork is summarized on the IEA websitehttps://www.iea.org/topics/ccs/

Digging further into the field takes a lot of effort and aspects like capacityprovision and grid strengthening for intermittent renewable energy, theenergy demand from space heating, the embodied carbon in battery manu-facture, emissions from biofuel manufacture, and the effect on heathermoorland of clearing roads for wind turbines all have to be taken intoaccount. It becomes very complicated very quickly and it is no wonder thatpeople try to simplify it in order to get the message across. For those whowant to take the plunge then the UK’s Energy Technology Institute (ETI) is agood jumping in point. They have spent a decade looking at the UK Energysystem, funding research, and pilot projects into areas ranging from hydrogencombustion to tidal technology to smart homes to cleaner heavy-duty goodsvehicles.

There is so much material available from the ETI that it is challenging to knowwhere to start, however, perhaps start off by reading about energy systemmodellinghttp://www.eti.co.uk/programmes/strategy/esme

then look at the technology programmeshttp://www.eti.co.uk/programmes

The value of CCS to society

Many have looked at the value of CCS, a recent prominent report was writtenby the Parliamentary Advisory Group on Carbon Capture and Storage, titledLowest Cost Decarbonisation for the UK: The Critical Role of CCS. Thiscan be found here:http://www.ccsassociation.org/news-and-events/reports-and-publications/parliamentary-advisory-group-on-ccs-report/

The UK government convened a taskforce in 2013 to look at the cost of CCS,the team reported out in Many 2013 and the report can be found here:https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/201021/CCS_Cost_Reduction_Taskforce_-_Final_Report_-_May_2013.pdf

Technical overview of CCS

A very useful place to start on CCS is with the Global CCS Institute websitehttps://www.globalccsinstitute.com/understanding-ccs


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https://spiral.imperial.ac.uk/handle/10044/1/25503

https://www.iea.org/topics/ccs/

http://www.eti.co.uk/programmes/strategy/esme

http://www.eti.co.uk/programmes

http://www.ccsassociation.org/news-and-events/reports-and-publications/parliamentary-advisory-group-on-ccs-report/



https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/201021/CCS_Cost_Reduction_Taskforce_-_Final_Report_-_May_2013.pdf



https://www.globalccsinstitute.com/understanding-ccs

This is complemented by the IEA Greenhouse Gas R&D Programme, theIEAGHGhttp://ieaghg.org/ccs-resources

Next come two resources that need to be read together, the first is the IPCCspecial report on CCShttps://www.ipcc.ch/pdf/special-reports/srccs/srccs_wholereport.pdf

but as this is dated it needs to be read in conjunction with a special issue of theInternational Journal of Greenhouse Gas Control,Special Issue commemorating the 10th year anniversary of the publication ofthe Intergovernmental Panel on Climate Change Special Report on CO2Capture and Storage Edited by J Gale et al Volume 40, Pages 1–458(September 2015), http://www.sciencedirect.com/science/journal/17505836/40

A question that is often asked is ‘can we build CCS plants and stores fast enough’.The IEAGHG looked at this in 2017, and wrote a report where they determined

that the answer is, yes as long as you develop an industry as large at that thatexists for natural gas extraction. This makes intuitive sense, we need to put alarge fraction of the CO2 from the combustion of oil, gas, coal and bio-capture back into the Earth, so the infrastructure will need to be pretty large:CCS Industry Build-Out Rates—Comparison with Industry Analogueshttp://ieaghg.org/publications/technical-reports/129-publications/new-reports-list/803-2017-tr6

CO2 capture technologies and oxygen separation technology

There is a lot of technical material on capture and separation technologies. Thissection will only point to a few reports and web resources for further reading.

The UK Carbon Capture and Storage Association has accessible summaries ondifferent types of capturehttp://www.ccsassociation.org/what-is-ccs/capture/pre-combustion-capture/http://www.ccsassociation.org/what-is-ccs/capture/post-combustion-capture/

as do the Zero Emission Platform, a European Technology Innovation Platform.http://www.zeroemissionsplatform.eu/ccs-technology/capture.html

Linde, a major industrial gas company, has written a very accessible report onoxygen separation.http://www.linde-engineering.com/internet.global.lindeengineering.global/en/images/AS.B1EN%201113%20-%20%26AA_History_.layout19_4353.pdf

Industrial CCS is explained by the GCCSI

https://www.globalccsinstitute.com/understanding-ccs/industrial-ccshttp://hub.globalccsinstitute.com/sites/default/files/publications/199858/Introduction%20to%20Industrial%20CCS.pdf

A slightly dated but still very useful review report from the IPCC on CCS stillcontains some of the best information on industrial and power related pointsources of CO2 and the concentrations of CO2 in various emission streamshttp://www.ipcc.ch/pdf/special-reports/srccs/srccs_summaryforpolicymakers.pdfhttps://www.ipcc.ch/report/srccs/


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http://ieaghg.org/ccs-resources

https://www.ipcc.ch/pdf/special-reports/srccs/srccs_wholereport.pdf

http://www.sciencedirect.com/science/journal/17505836/40

http://ieaghg.org/publications/technical-reports/129-publications/new-reports-list/803-2017-tr6

http://ieaghg.org/publications/technical-reports/129-publications/new-reports-list/803-2017-tr6

http://www.ccsassociation.org/what-is-ccs/capture/pre-combustion-capture/

http://www.ccsassociation.org/what-is-ccs/capture/post-combustion-capture/

http://www.zeroemissionsplatform.eu/ccs-technology/capture.html

http://www.linde-engineering.com/internet.global.lindeengineering.global/en/images/AS.B1EN%201113%20-%20%26AA_History_.layout19_4353.pdf

http://www.linde-engineering.com/internet.global.lindeengineering.global/en/images/AS.B1EN%201113%20-%20%26AA_History_.layout19_4353.pdf

https://www.globalccsinstitute.com/understanding-ccs/industrial-ccs

http://hub.globalccsinstitute.com/sites/default/files/publications/199858/Introduction%20to%20Industrial%20CCS.pdf

http://hub.globalccsinstitute.com/sites/default/files/publications/199858/Introduction%20to%20Industrial%20CCS.pdf

http://www.ipcc.ch/pdf/special-reports/srccs/srccs_summaryforpolicymakers.pdf

https://www.ipcc.ch/report/srccs/

CO2 capture technologies are reviewed by the GCCSI (9 page summary)https://hub.globalccsinstitute.com/sites/default/files/publications/29701/co2-capture-technologies.pdf

and explained by the US National Energy Technology Laboratoryhttps://www.netl.doe.gov/research/coal/carbon-capture/pre-combustion

The Plains CO2 Reduction Partnership provides an extensive 189 page report onthe current status of CO2 capture technology development and application(in 2011)https://www.undeerc.org/pcor/newsandpubs/pdf/CarbonSeparationCapture.pdf

The IEAGHG gives a useful summary of CO2 capture at gas fired power plants:http://www.ieaghg.org/docs/General_Docs/Reports/2012-08.pdf

Post combustion flue gas separation is described in a very accessible manner bythe GCCSI:https://hub.globalccsinstitute.com/publications/building-capacity-co2-capture-and-storage-apec-region-training-manual-policy-makers-and-practitioners/module-2-co2-capture-post-combustion-flue-gas-separation

Some recent work on membrane separation was reported by Mukhtar et al.Mukhtar H et al 2016 IOP Conf. Ser.: Earth Environ. Sci. 36 012016

More on pressure swing absorption can be read about in this 2016 articlehttp://www.chemengonline.com/psa-technology-beyond-hydrogen-purification/?printmode=1

The GCCSI has recent (July 2017) information on the costs of CCShttps://www.globalccsinstitute.com/publications/global-costs-carbon-capture-and-storage

Deep ocean storage

This has been discussed in detail by the IPCC in chapter six of the special reporton CCShttps://www.ipcc.ch/pdf/special-reports/srccs/srccs_chapter6.pdf

while the use of CO2 hydrates for storage was explored by the IEAGHGhttp://ieaghg.org/docs/General_Docs/Reports/PH4-26%20CO2%20hydrates.pdf

and the London Convention and Protocol’s rules on CCS are discussed on theInternational Maritime Organisation’s own websitehttp://www.imo.org/en/OurWork/Environment/LCLP/EmergingIssues/CCS/Pages/default.aspx

Geological storage—capacity

The availability of storage capacity is often questioned; does the world haveenough? The first thing to do is to have a frame of reference and the Societyof Petroleum Engineers have tried to work on this problem, by extending


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https://hub.globalccsinstitute.com/sites/default/files/publications/29701/co2-capture-technologies.pdf

https://hub.globalccsinstitute.com/sites/default/files/publications/29701/co2-capture-technologies.pdf

https://www.netl.doe.gov/research/coal/carbon-capture/pre-combustion

https://www.undeerc.org/pcor/newsandpubs/pdf/CarbonSeparationCapture.pdf

https://www.undeerc.org/pcor/newsandpubs/pdf/CarbonSeparationCapture.pdf

http://www.ieaghg.org/docs/General_Docs/Reports/2012-08.pdf

https://hub.globalccsinstitute.com/publications/building-capacity-co2-capture-and-storage-apec-region-training-manual-policy-makers-and-practitioners/module-2-co2-capture-post-combustion-flue-gas-separation



https://doi.org/10.1088/1755-1315/36/1/012016

http://www.chemengonline.com/psa-technology-beyond-hydrogen-purification/?printmode=1

http://www.chemengonline.com/psa-technology-beyond-hydrogen-purification/?printmode=1

https://www.globalccsinstitute.com/publications/global-costs-carbon-capture-and-storage

https://www.globalccsinstitute.com/publications/global-costs-carbon-capture-and-storage

https://www.ipcc.ch/pdf/special-reports/srccs/srccs_chapter6.pdf

http://ieaghg.org/docs/General_Docs/Reports/PH4-26%20CO2%20hydrates.pdf

http://ieaghg.org/docs/General_Docs/Reports/PH4-26%20CO2%20hydrates.pdf

http://www.imo.org/en/OurWork/Environment/LCLP/EmergingIssues/CCS/Pages/default.aspx

http://www.imo.org/en/OurWork/Environment/LCLP/EmergingIssues/CCS/Pages/default.aspx

their globally adopted Petroleum Resources Classification system into CO2

Storage, creating the CO2 Storage Resources Maturation System (SRMS):http://www.spe.org/industry/CO2-storage-resources-management-system.php

The most recent attempt to estimate the global storage capacity at the time ofwriting has been made by a team at MIT and Exxon Mobil. The teamestimates that there is between 8000 gigatonnes (Gt) and 55 000 Gt ofpractically accessible geological storage capacity for carbon dioxide:Developing a Consistent Database for Regional Geologic CO2 StorageCapacity Worldwide, https://doi.org/10.1016/j.egypro.2017.03.1603

This was a top down approach to assessing storage capacity. Some countrieshave attempted a more bottom up approach.

Naturally the US has done it twice with the USGS and the US DOE bothissuing assessmentsU.S. Geological Survey. National assessment of geologic carbon dioxidestorage resources—Results. ver. 1.1; 2013: https://pubs.usgs.gov/circ/1386/U.S. Department of Energy Office of Fossil Energy. Carbon Storage Atlas5th edn 2015: https://www.netl.doe.gov/research/coal/carbon-storage/atlasv

While Europe ran the GeoCapacity project looking at sources and sinks. Thisproject finished in 2009 and the final report can be found on the webhttp://www.geology.cz/geocapacity/publications/D42%20GeoCapacity%20Final%20Report-red.pdf

The UK created an online database of the storage potential on the UKContinental Shelf (offshore). This database can be accessed athttp://www.co2stored.co.uk/home/index

The Norwegian Petroleum Directorate has created a CO2 storage atlas for theNorwegian Continental Shelfhttp://www.npd.no/en/Publications/Reports/Compiled-CO2-atlas/

South Africa has done the same assessing onshore and offshore CO2 storagepotentialhttp://www.sacccs.org.za/wp-content/uploads/2010/11/Atlas.pdf

There are others as the list is growing, the GCCSI often reports them in theirannual status update.

Geological storage—containment risks

Being able to demonstrate that CO2 storage will contain CO2 on a millennialscale is important. An example of how to perform containment risk assess-ment (using the bow-tie methodology) is given in the paperContainment Risk Management for CO2 Storage in a Depleted Gas Field,UK North Sea: https://doi.org/10.1016/j.egypro.2013.06.390

And an overview of risk assessment and risk management in geological storageis given in the following paper:Recent advances in risk assessment and risk management of geologic CO2

storage: https://doi.org/10.1016/j.ijggc.2015.06.014


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http://www.spe.org/industry/CO2-storage-resources-management-system.php

https://doi.org/10.1016/j.egypro.2017.03.1603

https://pubs.usgs.gov/circ/1386/

https://www.netl.doe.gov/research/coal/carbon-storage/atlasv

http://www.geology.cz/geocapacity/publications/D42%20GeoCapacity%20Final%20Report-red.pdf

http://www.geology.cz/geocapacity/publications/D42%20GeoCapacity%20Final%20Report-red.pdf

http://www.co2stored.co.uk/home/index

http://www.npd.no/en/Publications/Reports/Compiled-CO2-atlas/

http://www.sacccs.org.za/wp-content/uploads/2010/11/Atlas.pdf


https://doi.org/10.1016/j.ijggc.2015.06.014

CO2 is trapped in the subsurface in a number of ways. The authors explored therelative contributions of different trapping mechanisms using coupled geo-chemical and fluid dynamic software. The results are reported in the paperCO2 Fate Comparison for Depleted Gas Field and Dipping Saline Aquifer:https://doi.org/10.1016/j.egypro.2014.11.592

On page 21 Leakage pathways and Portland cement are discussed. Portlandcement is described by Schlumberger, who provide cement and cementingservices to the oil industry, on their website in this useful articlehttp://www.slb.com/~/media/Files/resources/oilfield_review/ors89/apr89/2_cement.pdf

and degradation mechanisms are discussed by the IEAGHGhttps://hub.globalccsinstitute.com/publications/integrity-wellbore-cement-co2-storage-wells-state-art-review/2-cement-degradation-mechanisms

Storage capacity can be increased while at the same time reducing the risk ofinduced seismicity, and pressure interference by removing brine from thestore at the same time as injecting the CO2. A new report will soon bereleased by the ETI on this topic as part of a study effort described at thislocation:http://www.eti.co.uk/programmes/carbon-capture-storage/impact-of-brine-production-on-aquifer-storage

Induced seismicity is an important topic. An introduction is given by the team atLawrence Berkeley National Laboratoryhttp://esd1.lbl.gov/research/projects/induced_seismicity/primer.html#defined

while the Oklahoma quakes are discussed in this article by Walsh and ZobackOklahoma’s recent earthquakes and saltwater disposal, http://advances.sciencemag.org/content/1/5/e1500195.full

The Office of The Secretary Of Energy & Environment in Oklahoma has awhole website devoted to the subject:https://earthquakes.ok.gov/

Joshua White, Lawrence Livermore National Laboratory, and William Foxall,at Lawrence Berkeley National Laboratory, have published a useful paperlisting experience with induced seismicity in CO2 injection.White J A and Foxall W 2016 Assessing induced seismicity risk at CO2

storage projects: Recent progress and remaining challenges Int. J.Greenhouse Gas Control 49 413–24

Natural CO2 seeps have been looked at by Jennifer Roberts, who allowed me touse one of her pictures. She looked at the health risk from seeps in ItalyPhysical Sciences—Geology—Social Sciences—Environmental Sciences:Roberts J J, Wood R A, and Haszeldine R S 2011 Assessing the healthrisks of natural CO2 seeps in ItalyPNAS 108 16545–8; published ahead of print September 12, 2011,


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http://www.slb.com/~/media/Files/resources/oilfield_review/ors89/apr89/2_cement.pdf

http://www.slb.com/~/media/Files/resources/oilfield_review/ors89/apr89/2_cement.pdf

https://hub.globalccsinstitute.com/publications/integrity-wellbore-cement-co2-storage-wells-state-art-review/2-cement-degradation-mechanisms

https://hub.globalccsinstitute.com/publications/integrity-wellbore-cement-co2-storage-wells-state-art-review/2-cement-degradation-mechanisms

http://www.eti.co.uk/programmes/carbon-capture-storage/impact-of-brine-production-on-aquifer-storage

http://www.eti.co.uk/programmes/carbon-capture-storage/impact-of-brine-production-on-aquifer-storage

http://esd1.lbl.gov/research/projects/induced_seismicity/primer.html#defined

http://advances.sciencemag.org/content/1/5/e1500195.full

http://advances.sciencemag.org/content/1/5/e1500195.full

https://earthquakes.ok.gov/

https://doi.org/10.1016/j.ijggc.2016.03.021

https://doi.org/10.1073/pnas.1018590108

Brine extraction to increase storage capacity and reduce risks

Amulti-disciplinary project, funded by the Energy Technologies Institute (ETI),has studied how brine production can enhance the storage potential of salineaquifers already identified as ideal CO2 stores.http://www.sccs.org.uk/news/394-brine-production-can-greatly-enhance-co-storage-potential-of-north-sea-aquifers-new-study-finds

Actual CCS projects around the world

The Global CCS Institute maintains a database of CCS facilities which can beaccessed at the following linkhttps://www.globalccsinstitute.com/projects/large-scale-ccs-projects

each year they also prepare a report on the global status of CCShttp://www.globalccsinstitute.com/status

Significant quantities of technical material from some active and cancelled CCSprojects is available on the web.

The Quest CCS project in Alberta Canada, in partnership with the Albertagovernment, has published the majority of its technical study work incapture, transport and storage, as well as permits and annual performanceupdates, on the web.http://www.energy.alberta.ca/CCS/3822.asp

Knowledge sharing reports:http://www.energy.alberta.ca/CCS/3848.asp

In the UK the government have published technical reports for the Peterheadpost combustion gas CCS project (where I personally led the storage team)and the White Rose oxycombustion coal CCS project. When these projectswere cancelled they had progressed to the end of Front End Engineering andDesign (FEED) which means that they were designed and costed and readyfor a final investment decision.https://www.gov.uk/government/collections/carbon-capture-and-storage-knowledge-sharing

Buried very deeply in the UK Government archives is the study work from twoearlier CCS projects, the Longannet and Kingsnorth post combustion coalCCS projects. Again there is a wealth of material available on the website.http://webarchive.nationalarchives.gov.uk/20111205105811/https://www.decc.gov.uk/en/content/cms/emissions/ccs/demo_prog/feed/feed.aspx

The Walulla basalt pilot project, assessed the feasibility of injecting CO2 intoflood basalts, a geological formation that covers large areas of the US, India,and Siberia.http://www.bigskyco2.org/research/geologic/basaltprojectMcGrail B P 2014 et al Injection and monitoring at the Wallula Basalt PilotProject Energy Proc. 63 2939–48.http://www.sciencedirect.com/science/article/pii/S1876610214021316

Another project that is often in the news is CarbFix in Iceland. Matter J M,Broecker W S, Stute M, Gislason S R, Oelkers E H, Stefánsson A, Wolff-


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http://www.sccs.org.uk/news/394-brine-production-can-greatly-enhance-co-storage-potential-of-north-sea-aquifers-new-study-finds

http://www.sccs.org.uk/news/394-brine-production-can-greatly-enhance-co-storage-potential-of-north-sea-aquifers-new-study-finds

https://www.globalccsinstitute.com/projects/large-scale-ccs-projects

http://www.globalccsinstitute.com/status

http://www.energy.alberta.ca/CCS/3822.asp

http://www.energy.alberta.ca/CCS/3848.asp

https://www.gov.uk/government/collections/carbon-capture-and-storage-knowledge-sharing

https://www.gov.uk/government/collections/carbon-capture-and-storage-knowledge-sharing

http://webarchive.nationalarchives.gov.uk/20111205105811/https://www.decc.gov.uk/en/content/cms/emissions/ccs/demo_prog/feed/feed.aspx

http://webarchive.nationalarchives.gov.uk/20111205105811/https://www.decc.gov.uk/en/content/cms/emissions/ccs/demo_prog/feed/feed.aspx

http://www.bigskyco2.org/research/geologic/basaltproject


http://www.sciencedirect.com/science/article/pii/S1876610214021316

Boenisch D, Gunnlaugsson E, Axelsson G, Björnsson G 2009 Permanentcarbon dioxide storage into basalt: the CarbFix Pilot Project, Iceland EnergyProc. 1 3641–6https://www.or.is/carbfix

A very exciting project is the Archer Daniel Midlands project in Decatur,Illinois. This project is storing CO2 from bio ethanol manufacture, thereforeit creates negative emissions—effectively removing CO2 from the atmos-phere. Delivery of negative emissions is critical for most of the IPCC models.https://energy.gov/fe/archer-daniels-midland-company

CCS standards

Recent work by a large community of specialists volunteering their time has ledto the development of International Standards on CCS. Key are the stand-ards on how to determine if a CO2 storage location is fit for purpose.https://www.iso.org/committee/648607.html

Many countries have regulations on CO2 storage. This includes Canada, theUS, Europe and Australia. This list is ever growing so it is best to look to anumbrella body such as the Global CCS Institute. They have a list ofregulations on their website: https://hub.globalccsinstitute.com/publications/international-ccs-policies-and-regulations-wp51awp54-report/2-current-status-ccs-regulation


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https://www.or.is/carbfix

https://energy.gov/fe/archer-daniels-midland-company

https://www.iso.org/committee/648607.html

https://hub.globalccsinstitute.com/publications/international-ccs-policies-and-regulations-wp51awp54-report/2-current-status-ccs-regulation



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