This content has been downloaded from IOPscience. Please scroll down to see the full text.

Download details:

IP Address: 143.167.24.57 This content was downloaded on 16/08/2018 at 10:19

Please note that terms and conditions apply.

You may also be interested in:

Integrated assessment models as learning tools Pieter Valkering

Improving the use of integrated assessment models: Reconciling model results with user needs Serge I P Stalpers

Exploring the media framing of carbon capture and storage and its influence on public perceptions Sarah Mander, R Wood and C Gough

UK co-ordinates research on carbon capture and storage Kulvinder Singh Chadha

Global economic consequences of deploying bioenergy with carbon capture and storage (BECCS) Matteo Muratori, Katherine Calvin, Marshall Wise et al.

Carbon Capture and Sequestration- A Review Akash Sood and Savita Vyas

Carbon Sequestration and Carbon Capture and Storage (CCS) in Southeast Asia Nik Hisyamudin Muhd Nor, Siti Norhana Selamat, Muhammad Hanif Abd Rashid et al.

Carbon capture and storage in the post-Kyoto climate change negotiations Karin Backstrand

Social acceptance of carbon capture and storage (CCS) in Germany Katja Pietzner, D Schumann, M Fischedick et al.

Carbon Capture and Storage

Carbon Capture and Storage

Owain Tucker Shell International Petroleum Company Limited, Aberdeen, UK

IOP Publishing, Bristol, UK ª IOP Publishing Ltd 2018

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of the publisher, or as expressly permitted by law or under terms agreed with the appropriate rights organization. Multiple copying is permitted in accordance with the terms of licences issued by the Copyright Licensing Agency, the Copyright Clearance Centre and other reproduction rights organisations.

Permission to make use of IOP Publishing content other than as set out above may be sought at [email protected].

Owain Tucker has asserted his right to be identified as the author of this work in accordance with sections 77 and 78 of the Copyright, Designs and Patents Act 1988.

ISBN 978-0-7503-1581-4 (ebook)

DOI 10.1088/978-0-7503-1581-4

Version: 20180701

Physics World Discovery ISSN 2399-2891 (online)

British Library Cataloguing-in-Publication Data: A catalogue record for this book is available from the British Library.

Published by IOP Publishing, wholly owned by The Institute of Physics, London

IOP Publishing, Temple Circus, Temple Way, Bristol, BS1 6HG, UK

US Office: IOP Publishing, Inc., 190 North Independence Mall West, Suite 601, Philadelphia, PA 19106, USA Although the author of this publication works for Shell, the views expressed in this publication represent the views of the author and should not be taken to be the views of Shell. Shell accepts no responsibility or liability for anything written in this publication.

Contents

Abstract viii Acknowledgements ix Author biography x

Carbon Capture and Storage 1 1 Introduction 1 2 Background 3 Do we really need CCS? 3 Microeconomics applied to CCS 6

Where is CO2 emitted and from where can it be captured? 6 Why does CCS reduce efficiency? 10 Separation technology 11

CO2 transport, compression and conditioning 14

CO2 storage 15 Containment and other challenges 22 Leakage pathways and Portland cement 25 Monitoring 26 Induced seismicity 27 Remediation plans 28 Ocean storage 28 3 Current directions 28 Scaling up CCS 28 Fundamental physics 34 New capture technologies 35 Making the political and economic case 35 4 Outlook 36 Additional resources 37

vii Abstract

Is carbon capture and storage (CCS) the technology that could be key to slowing climate change or an expensive diversion? Few people are aware that we already have the technology to remove most of the carbon dioxide emissions from fossil fuelled power and industry. This same technology is needed to deliver the negative emissions called for in almost all integrated assessment models. Collectively, this rather prosaic and unexciting technology is termed Carbon Capture and Storage, CCS—or Bio-energy with CCS, BECCS, when delivering negative emissions. This short book describes the technology, and takes a brief look at some of the reasons why society is not yet urgently reaching for it.

viii Acknowledgements

Many thanks to Carol Thompson who has tirelessly edited and improved the text, and to Den Gammer who kept me straight on the technical details of capture technology.

ix Author biography

Owain Tucker

Since the beginning of 2009 Owain has worked at the forefront of CCS, performing the subsurface modelling and later leading the team that aimed to redevelop the depleted Goldeneye gas field in the North Sea as a CO2 store. At the same time, he took on a role as the Global Deployment Lead for CO2 storage in Shell, and as such worked closely with the team in Canada who developed the Quest industrial CCS project that has been injecting over one million tonnes of CO2 each year since Owain’s birthday in 2015 (a complete coincidence, but a nice one). Owain works at the interface of academic research into CO2 storage and the development of new CO2 storage projects. He is involved with the UK CCS research council, the Scottish Centre of Carbon Capture and Storage, the Oil and Gas Climate Initiative, and the Carbon Capture and Utilisation technical section of the Society of Petroleum Engineers as well as many joint industry research projects. He has worked in Shell for over twenty years as a reservoir engineer, eBusiness consultant, economist and now CO2 storage lead. Though, he did jump ship for a brief spell at McKinsey & Company in strategy consulting. His early training is in physics and geophysics, from the University of Witwatersrand in South Africa; followed by a DPhil in experimental solid state physics at Oxford.

x Physics World Discovery Carbon Capture and Storage

Owain Tucker

Carbon Capture and Storage

1 Introduction When I give talks on Carbon Capture and Storage (CCS), I often start with the latest CO2 concentration measurements from the Mauna Loa Observatory (figure 1). As a physicist, I look at the data first, and listen to the rhetoric second. The data tell me that we, globally, are not doing enough to reduce CO2 emissions. Despite all society’s efforts to date, the atmospheric levels are still increasing. We need to do something 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 Carbon Capture and Storage

In 1896 Svante Arrhenius introduced us to the effect of the atmospheric concentration of CO2 on the Earth’s temperature. His work has been validated many times over and we can all peruse the Intergovernmental Panel on Climate Change (IPCC) reports, which outline the experimentally verified evidence that the global temperatures are rising, that global CO2 concentrations have risen signifi- cantly since the start of the industrial revolution, and that global warming, and associated climate change and climate disruption, is driven by the increase in greenhouse gas concentration. The largest contribution to the increase in GHGs is CO2. Around 36 billion tonnes a year of CO2 is emitted from fossil fuel combustion, cement production and chemical processes (figure 2). Climate science tells us that cumulative emissions, more than the annual rate of emission, are the key control on the eventual peak warming. Humanity, therefore, has a fixed carbon budget of around 1 trillion tonnes of carbon, C, or 3.67 trillion tonnes of CO2, if it wants to limit warming to about 2 °C, less if we are aiming at below 2 °C. To date, at least half of this budget has been used 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 the emissions come from the combustion of fossil fuel, while others come from industrial emissions. Some of the latter are even pure streams of CO2 released directly to the atmosphere. Society enthusiastically talks about energy efficiency, and we see regulation slowly driving this forward. We actively try to substitute renewable energy sources

45

40

35

30

25 emmitted per per year emmitted

2 20 Gt CO 15

10

5

0 1959 1961 1963 1965 1967 1969 1971 1973 1975 1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 2009 2011 2013 2015

land-use change emissions fossil fuel and cement emissions

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

2 Carbon Capture and Storage

for fossil energy, and are making great strides in this direction. But then we stop. For reasons discussed later, it is inconceivable that society will suddenly (within a decade or two) stop making cement or fertilizer, give up using liquid transport fuels, or quit generating most of its power from fossil fuel. So, we need to decarbonise these emissions while continuing to work on the alternatives. What many scientists, and almost all of the public, do not know is that there is a proven, existing, technological solution that can all but eliminate CO2 emissions from many 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 with minimal change. The IPCC has recognised that this technology is key to the delivery of most 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 the Paris accord. The technology works by removing the unwanted pollutant, CO2, before it reaches the environment and putting it back into geological strata similar to those that originally contained the hydrocarbons that are the source of the carbon. This is Carbon Capture and Storage. CCS is an interesting topic. Technically it combines physics, chemistry, geology and engineering, but any discussion that only looks at the technology misses the point. In order to appreciate CCS, we need to look at the links between science and society; examining the integrated picture: What is CCS? What can it deliver? What are its strengths and weaknesses? And why isn’t it happening all around us today?

2 Background

CCS 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-separation process. Sometimes, as in the case of post-combustion, this is achieved by separating CO2 from nitrogen (N2) and oxygen (O2). In other cases, O2 is separated from air prior 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 it condenses, and then moving the liquid CO2 by pipeline or ship. Storage is the reversal of natural gas or oil production. The dense phase CO2 is pumped into injection wells, normally over 1000 m deep, and injected into pore spaces 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 is selected for the presence of a permeable rock formation that will allow the injection of CO2. The storage formation is overlain by an impermeable rock formation that will 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 alternative energies and moving away from a fossil fuel based society. We should ‘keep it in the ground’. This view stems from the laudable aim of moving away from a reliance on

3 Carbon Capture and Storage

fossil fuels as fast as possible, and a recognition that emissions of CO2 from fossil fuel combustion (coal, oil and gas) have to shoulder much of the blame for the increase 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 am writing this book consumes a few hundred watts. I had to think long and hard about this question—why can’t we just be a little cleverer? Only the other day I read an article stating that CCS was not needed as simply being more efficient with kettles would save the energy equivalent to one power station. My thought was, very good, do it, but what about all the other power stations? 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 of the global, or even local, energy system. David McKay—a Fellow of the Royal Society and a former Chief Scientific Advisor to part of the UK government—put a lot of effort into this question and published a book on the subject (see additional resources). He noted that a human being can generate around 1 kW hour per day of effort (or 125 W solidly for eight hours). Next time you are in the gym turn the treadmill, exercise bike, or (my favourite) the rowing machine, to watts and see how many watts you can generate. This starts to make sense when you think about how much effort cleaning was before the invention of the vacuum cleaner, or washing before the washing machine. According to my energy monitoring, my house, which has electric cooking, peaks at around 6–8 kW electricity consumption but has the potential 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, I can easily do the work of many people. Because the power is cheap compared to employing 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 of people in developed countries, better off. Now picture the familiar wind turbine: onshore turbines come in at around 3.6 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 add jet engines, combined cycle gas turbines, and then power stations to the picture and you 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 generate 500 million watts—or in other words can produce the power equivalent to 2.5 million people working constantly (here we are using a high power output of 200 W per human to be generous). One CCGT can have the same name plate capacity as over 150 onshore wind turbines. The maximum UK electricity demand in the period 10 October 2016 to 10 October 2017 was 52 GW in total—the maximum change in demand in one day in that period was 22 GW. These numbers are just for electric power and do not include heating, which requires 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 a cold January morning. The numbers are so large that it is difficult to get your mind

4 Carbon Capture and Storage

Figure 3. Top: Log graph comparing power used and generated by different technologies. Humans can, when working very hard, generate about 200 W, while a standard ‘metric’ horse weighs in at 736 W. What is incredible is that even the domestic vacuum cleaner has the power of over two horses. Numbers are representative. Bottom: infographic attempting to illustrate the scale of the system, where human = 1. Note the shrinking from each group. around the scale—but what they do show is the size of the energy system. Before approaching topics like intermittency, energy storage, and demand management we can see that intuition will not serve us well in this area. When we look at the inertia in our global energy and industrial system (power stations are expected to last twenty to thirty years), and at the over seven billion

5 Carbon Capture and Storage

people who depend on it, we realise that the world is unlikely to be able to turn off the 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 rollout of renewable energy, energy efficiency, switching from more to less carbon intensive fuels, the use of bio fuels, and large-scale rollout of CCS on fossil and CCS on bio fuels.

Microeconomics applied to CCS Will an increase in CCS lead to the continuation of fossil fuel use? One reason that CCS has not been embraced by governments is the fact that decarbonising increases the cost of using fossil fuel. Because it is applied to large industrial plants, such as a 1 GW power station, in contrast to the more staged rollout of smaller renewable installations, the ticket price is very noticeable; even though the unit cost is competitive with renewables. Deploying CCS would therefore increase the cost of fossil energy and would act as a carbon tax, potentially making alternative renewable sources more attractive. Simple microeconomics therefore tells us that CCS is good for alternative forms of energy, and simple logic tells us that harvesting energy from fossil fuels, if the side effect of CO2 emissions has been responsibly removed, is not an issue for the global climate system. Basically, ‘clean’ fossil is OK. Deploying CCS forces 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 would dramatically reduce emissions right now, and mandating it would increase the cost of fossil fuel, act as selective taxation, and would incentivise renewables. Mandating CCS would also deliver fossil energy and industrial products without the CO2. What is not to like? But society, economics, and politics are immensely complicated. I heard a very good quote on the radio a few days ago: ‘Politicians know what they need 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 National Laboratory 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 million tonnes of Carbon, which equates to 36 168 million tonnes of CO2. This accounts for roughly 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 million tonnes of CO2 every day. CO2 can be captured from multiple sources with differing characteristics of concentration, pressure, volume, and abundance of sources. The main source types are shown in figure 4.

6 Carbon Capture and Storage

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

Direct air capture The most widespread source is air, into which humanity has been releasing CO2 molecules for centuries, increasing the CO2 concentration to around 400 ppm, at the pressure of one atmosphere. If we want, we can round up these released molecules and put them back underground. This is termed direct air capture, or DAC. The 0.04% CO2 has to be separated from the 78% N2, 21% O2, and 0.9% Ar. The advantage of this source is that it is obviously available everywhere, so the capture can take place in the location most suited to removal and storage. The disadvantage is that it requires a lot of energy and equipment, because the low concentration means that a very large volume of air has to be processed to achieve meaningful flow rates of CO2. DAC is currently an active area of research.

Biomass Plants perform direct air capture all the time, but they convert the CO2 into an intermediate product, the sugar glucose. Glucose molecules are then joined up in the plants to form polysaccharides such as cellulose, the main component of plant cell walls, and even further into complex organic polymers such as lignin, the key structural

7 Carbon Capture and Storage

component of wood. The reactions are not particularly efficient: according to the New York Times,afifty-year-old oak forest would sequester about 13 tonnes per acre per year. Biomass can be directly used as a fuel in boilers, or it can be gasified before burning. If you simply let the CO2 from burning biomass return to the atmosphere then there is a net zero change, the fuels are termed carbon neutral (though not quite, as humanity often uses fossil fuel to power harvest and transport machinery, and to provide energy used to treat/dry/pelletise biomass). We can, however, go further, and capture and store the CO2 emission streams from biomass use, leading to negative emissions. It is generally termed BECCS— bioenergy with CCS. BECCS is one of a class of negative emission technologies or NETs. Other NETs include afforestation and reforestation, biochar, soil carbon sequestration, 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 modelling scenarios because: (i) NETs provide a way to offset hard to capture emissions, such as those from marine 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 of CO2 from the atmosphere is therefore vital in correcting this overshoot.

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

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

The rest All the other emission sources come in between these two end points. It is generally true 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 to install CO2 pipes parallel to gas mains to every house with a gas central heating boiler or gas cooking ring.

8 Carbon Capture and Storage

Figure 5 schematically shows the concentration of CO2 emitted by different processes used by society and gives an idea of the pressure at which the separation takes place. As the pressure increases, the size of the CO2 separation plant decreases for the same capture rate in tonnes/year, simply because at a high pressure the gas is more compressed. It is much more cost effective to build a small separation vessel that works at 30 bar than a large one that works at 1 bar. In addition, the energy required to compress the CO2 from the higher pressure to around 100 bar for transport reduces. There are three main types of separation technology: separation with sorbents or solvents; separation with membranes; and cryogenics. These will be discussed in the next section.

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

Figure 5. Sources of CO2 ranked on CO2 concentration and pressure, numbers are indicative as specific industrial 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 IPCC report on CCS.

9 Carbon Capture and Storage

In oxycombustion, the fuel is burned in pure O2 or an O2/CO2 mix leaving mainly CO2 and H2O, so the resultant product simply needs to be dehydrated and compressed. The challenge is that this technology is immature with only two pilot projects 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 improving combustion in air: burner and combustion optimisation, alloys, turbines, control systems and much more. A new technology like oxycombustion has to climb this developmental staircase before it can compete without support in a sector such as power generation where power utilities expect to be able to buy the components for a, 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 requires more 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, the amount 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 climate change—efficiency needs to be in terms of climate impacts, not energy input. Society needs 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 budget can support—therefore fossil fuel is not the scarce resource, rather, CO2 handling capacity in the atmosphere is the scarce resource. Efficiency should therefore potentially 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 gasses including 400 ppm CO2. When we perform normal, ‘efficient’ combustion, we take air at atmospheric pressure and add a carbon-based fuel—the fuel is oxidised and heat is emitted. In a gas turbine, we pressurise air, inject the hydrocarbon fuel into a combustor, and the now high-pressure hot gasses expand to atmospheric pressure and work is extracted. In a boiler, the combustion takes place at near atmospheric pressure and heat is extracted, which then heats water to steam. Work is extracted in a steam turbine, which expands the steam to sub-atmospheric pressure. The steam condenser is operated as cold as possible to collapse the steam into vacuum conditions to maximise the steam-cycle efficiency. The key points here are: the combustion processes start at atmospheric pressure with an air mixture, and end at atmospheric pressure with a mixture of N2, which hardly reacts, reduced O2 levels, and increased CO2. There is also a lot of water vapour, H2O. In order to store the CO2, we need to separate out the CO2 from the N2, plus any remaining O2 and contaminants like NOx, and compress the CO2 sufficiently to transport and inject it into the subsurface geological storage formations. The separation process required to disentangle the CO2 and N2 takes energy, as does

10 Carbon Capture and Storage

the compression of the now separated CO2. Nothing comes for free. It takes additional energy to capture the CO2 when oxidising hydrocarbons, compared to just releasing the CO2 into the atmosphere: so, energy-based efficiency measures look worse. It also requires more equipment than combustion with 100% release to atmosphere, 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 do not want to release the CO2, we need CCS. If we look at the history of industrialisation, societies generally started out by dumping waste products into the environment, be it sewage, slag, industrial waste, sulphur dioxide and so on. Once the negative consequences of the release were understood society then moved to stop the practice, and became prepared to pay the price. This is the challenge that society needs to face with CO2.

Separation technology

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

A quick myth to debunk Some 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 ultimately to capture higher rates if we are to achieve the 1.5 °C global warming target as outlined in the Paris accord. As you read through the technology descriptions below you will realise that this is not the case. The 90% number has been used as an engineering design parameter for the current first generation post-combustion capture CCS plants. It turns out 90% CO2 capture from a flue gas stream with the 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 more energy 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 of 0% capture. Pushing the capture percentage even further gets you nearer and nearer to air capture and the last few percent get very costly, but if you introduce some biologically sourced fuel into the input stream then you can get 100% abatement at a lower cost, even though some CO2 is still released. Upsettingly, the 90% number has been hardwired into many climate modelling scenario models (Integrated Assessment Models) and this leads to comments like—‘CCS is not deployable in the 1.5 °C Paris scenarios because it does not remove enough CO2’.

Chemical absorption Chemical 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 an aqueous solution of an absorbent—which is normally amine based or potassium carbonate based. Amines are organic derivatives of ammonia in which one or more

11 Carbon Capture and Storage

Figure 6. The Quest CCS plant in Alberta Canada captures one mega-tonne of CO2 each year. The CO2 is created 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. hydrogen atoms in ammonia have been replaced by an alkyl group. The process works by bringing the gas stream containing CO2 into contact with the solution in a large ‘absorber vessel’ that has been filled with ‘packing’: generally corrugated and perforated plates that force the fluid to take a convoluted route through the absorber thereby maximising contact and hence CO2 absorption. When the gas stream exits, the CO2 remains behind, chemically bound to the amine which is in aqueous solution, and the 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 stripper vessel where heat forces the reaction to reverse, with the CO2 being released and transferred 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 of research. The process has been used in natural gas processing for many decades and has been locally optimised. Use in post combustion capture brings new challenges, such as the presence of O2, lower pressures, and contamination from nitrogen oxides, 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: Boundary Dam Power Station near Estevan, Saskatchewan, Canada; and the WA Parish Generating Station southwest of Houston, Texas, US. These are first-generation plants so do not benefit from the optimisation built on years of experience (the learning curve) hence unit costs are still high.

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

12 Carbon Capture and Storage

law formulated in 1803, the amount of a gas that dissolves in a liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid. The technique has been used in gas processing since 1969. An example of the physical absorption process is the Great Plains Synfuels Plant in North Dakota, US. This is a coal gasification plant with CCS which started operating in 1984. It captures more than three million tonnes of CO2 per year using physical 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 fact that it is best performed at low temperatures, the technique does not appear well suited to post-combustion capture.

Solid physical adsorption Solid physical adsorption is a coupling of two processes—adsorption and then desorption. Both need to work consistently, at scale without too large an energy penalty. The change from adsorption to desorption can be achieved by a change in pressure or temperature—pressure swing adsorption (PSA) or temperature swing adsorption (TSA). Various adsorbent materials are used, such as silica gel, activated carbon and zeolites. The technology is well suited to purifying streams of H2 and He, as the adsorbents hardly attract these low polarity molecules, whereas molecules such as CO2, CO, N2,H2O, and light hydrocarbons are strongly attracted. PSA is a commercial technology used for H2 purification and has been deployed for over fifty years, but it is not limited to H2. Different adsorbents can be used that are tailored to the separation of O2 or CO2. PSA, or more specifically vacuum swing absorption (VSA), for CO2 removal has been deployed on two commercial scale steam 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 that they had captured three million tonnes of CO2.

Cryogenic separation This process, which is very similar to that used for O2 separation, is best suited to removing CO2 from relatively high purity sources. CO2 liquifies at a much higher temperature than most other gasses so it does not take much cooling to turn it into a liquid, especially if the pressure is increased. Demonstration plants for technology offerings from a number of different manufacturers exist, and the technology could be well suited to industrial capture and pre-combustion decarbonisation. This technology is best suited to streams with very high CO2 concentrations and high pressures. It does not need solvents or adsorbents and vendors claim that it has one of the lowest costs of CO2 capture. It can be used in conjunction with hydrogen manufacture on steam methane reformers, and is also being used for gas purification in CO2 enhanced oil recovery (EOR) applications. There is a plant that delivers 100 kt CO2 per year at Port-Jerôme, in France, and an oil major tested a technology they call Controlled Freeze Zone (CFZ) at the Shute Creek gas treatment plant at LaBarge in Wyoming, US.

13 Carbon Capture and Storage

Membrane separation Membrane separation is a tried and tested solution for separating CO2 from natural gas. The technology has been deployed off the coast of Brazil on very large installations for gas treatment. The membranes are designed to selectively transmit CO2 but not CH4 when a pressure differential is placed across the membrane—they therefore require compression and work well for high-pressure gas-separation applications. Multiple stages of separation are normally required as the current membranes 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 develop membranes that can handle the heat. Research into new membrane systems is continuing as the technology has many potential advantages compared to other approaches—it is simple, does not involve chemical reactions, and is lightweight and compact. The challenge is to develop cost effective 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 capture system, 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 left saturated with water vapour or should it be dehydrated? These questions cause a lot of 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 along with other trace contaminants from the separation process. Experience in North America, where there are already 4500 miles of CO2 pipeline used 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 to −3 770 kg m .IfCO2 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, it turns out that constructing a very large long pipeline for gas phase CO2 is normally more expensive than building a compressor, so the industry generally works with dense 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 in the water to produce carbonic acid, which does corrode the most common pipeline material, carbon steel. The pipeline operator therefore has to choose either to change metallurgy, to something more akin to stainless steel, or to dry the CO2. Again, it is generally 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 harm carbon 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 limiting factor (see section on well construction). It turns out that O2, when combined with

14 Carbon Capture and Storage

900

800

700

600

500

400

Density (kg/m3) 300

200

100

0 0 20 40 60 80 100 120 Pressure (bara)

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

CO2 and formation water can cause pitting corrosion in many of the alloys used in well 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 an active 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 natural gas 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. The common practice is therefore to remove water, and reduce contaminants to levels where they do not affect the metallurgy. Compression is normally a multi-stage affair as it is best to manage the movement of CO2 through the phase envelope to avoid the two-phase region. Compressors are impressive machines and consume considerable energy to take CO2 from near atmospheric pressure to generally around 100 bar. The Quest CCS compressor is an 18 MW machine and is shown in figure 8. The design of compressors is a whole topic in its own right, but a CO2 compressor does not differ from a natural gas compressor in 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 means keeping it out of the oceans as the atmosphere is in contact with the ocean and therefore exchanges gasses with it. In reality oceans are not completely mixed so deep ocean releases might not reach the atmosphere for centuries. The level of mixing between deep ocean and shallow ocean is a topic of active climate research. To keep the system 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 or even releasing it back to the atmosphere) nor should it be released to the atmosphere.

15 Carbon Capture and Storage

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

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’, but permanent needs to be defined. Permanent compared to a stellar evolution time line; definitely not. Permanent on a geological time scale; not possible because of plate tectonic processes. So what we actually mean is permanent on human civilisation time scale—perhaps a good definition would be ‘contained over such a period as to allow 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 to expect the CO2 to escape from the store. To assist with modelling we place the following constraints onto the system: the evidence (and modelling) shows that it is expected to remain contained for a thousand years, and after a thousand years there is 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 be transformed into products, or even fuels. Trees can be planted, peat bogs can be restored. Every sequestration mechanism should face the same test: is it really permanent, however you define that? For example, consider what happens when a synthetic fuel is burned? What is the frequency of forest fires? Can we be sure that we can maintain the peat bog? If the answer to this last question is yes, then it passes the test. Similarly, for other mechanisms: some Roman cements still exist today and have definitely shown that man made products can last a few thousand years.

16 Carbon Capture and Storage

Injection wells Plugged oil well

Caprock seal

Migration assisted storage in saline formation

Caprock seal

Structural storage in depleted oil field

Baffles within the store

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

Types of geological storage Geological storage involves the injection of CO2 into rock strata which will retain the CO2. In general, the CO2 will be injected at depths where the combination of geothermal gradient and hydrostatic gradient mean that below this depth CO2 is in dense phase and significantly less pore space is required to store the same mass of CO2. In the real example shown in figure 10 the transition from vapour to liquid happens at around 2000 ft (610 m). Some rock strata preclude the flow of fluids, while others allow it. We are all familiar with slate roof tiles—water does not penetrate. Slate is special as it is a metamorphic rock that is created by the alteration of mudstone—this cooking means that it retains its sealing properties when exposed at the surface. The original non-metamorphosed mudstone rock is much more common and also precludes the flow of water when in the subsurface (when exposed at the surface mudstone weathers and breaks apart, which is why it is not used as a roofing material). Other sealing rock types include evaporites (salts), some carbonates, and some volcanics. Volcanic rocks like granite are often sealing but they are also often fractured, and the fracture network can allow flow. Rocks that allow flow either have a connected network of fractures, or a connected network of pore spaces as shown schematically in figure 11 (right). The simplest to visualise is sandstone (figure 11 (left))—we are all familiar with the way water flows though sand—and it can flow though sandstone in a similar manner. Some carbonate rocks also have connected pore networks, though often flow might be assisted by a fracture network. Basalts (solidified lava flows) can produce connected networks, as the top of a lava flow tends to break apart. When the next flow buries the breccia, it creates a seal on top of a permeable formation.

17 Carbon Capture and Storage

Figure 10. CO2 density increases with pressure but decreases with temperature. At any depth we see a competition between the hydrostatic gradient and the geothermal gradient. The figure above plots CO2 density as a function of true vertical depth below the mean sea level (or sub-sea) for an offshore location in the North Sea (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—filled with formation brine (right).

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 rock that precludes flow. Geological seals are well understood and tested as they have been responsible for trapping buoyant oil and gas in the subsurface for millions of years. But it must be recognised that everything in geology is location specific hence sampling (coring) and testing of the rock may be required. The CO2 itself needs to be injected into a permeable rock layer. The rock pores in this layer will provide the space that will hold the CO2, while the connected pore network allows the CO2 to flow into more pore spaces. The pores are seldom empty.

18 Carbon Capture and Storage

As a rule, they will be filled with formation water, or in some cases with hydrocarbons. The only time they are nearly empty is in the special case of reusing some 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 become trapped by capillary forces (think of a cup of water spilled on the floor—but the 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 mineralogy of the rocks and the structure of the geological store (figure 12). They also happen on different time scales. Structural trapping is a function of the geometry of the store and is therefore immediate; some dissolution occurs immediately as the CO2 contracts unsaturated water, and then more slowly as the rates become driven by diffusion; capillary trapping only occurs at the tail end of a plume (think of a drop of water running down a window pane) so is more important when injection has stopped; and mineralisation happens at many rates—the CO2 has to first be dissolved, and then a suite of reactions takes place, with rates ranging from minutes to 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, a geological trap. This can take a number of forms: like a bulge upward in the subsurface, an anticline; a pinch out of the permeable rocks, stratigraphic trap; or sealing 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. In the former the dominant trapping mechanism is buoyant trapping under the caprock seal, with some dissolution 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 is significant dissolution trapping, with related mineralisation, as the migrating plume can contact a large volume of water.

19 Carbon Capture and Storage

continuous phase for millennia. If there is a large and active aquifer, meaning that water sits in connected pore spaces underneath the store, then there will be a slow dissolution of CO2 in the water. The dissolution products make that water slightly heavier than water without CO2 and over thousands of years this will set up a slow gravity driven circulation that will gradually consume the free CO2. If CO2 is injected into a formation without a structural trap, but with a geological seal (figure 12 bottom), then it will migrate slowly up dip. As it migrates, it contacts new unsaturated water and dissolves, it gets stuck behind small heterogeneities, it reacts with minerals, and at the trailing end once injection stops, capillary forces trap 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 spilling a cup of water on a table covered with a tablecloth. Naturally it is important to make sure that the CO2 does not reach the edge of the store (or table)—hence monitoring and modelling are key to ensure that containment will not be compromised. Finally, if CO2 is injected into a very chemically reactive formation, such as basalt, it can rapidly become mineralised. This form of storage is still in the research phase, however, it could become important in the future as there are huge quantities of flood basalts in some areas of the world, such as the Deccan Traps in India.

Pressure dissipation and sustained injectivity In the last section we noted that the subsurface is normally full of fluids—generally formation 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 formation water. This is a standard diffusion equation problem: the pressure must diffuse away into the connected volume of water. The pressure change will relate to the compressibility of the water and the effective compressibility of the rock system. The management of pressure is at the core of CO2 storage. The increase in pressure could provide the energy to make water flow up old oil or water wells that have not been plugged; if it gets large enough, it can create a tensile fracture in the seal formation; the high-pressure fluid also has the potential to interact with faults in the subsurface changing the stress regime and triggering slippage of the fault. Finally, as the subsurface pressure increases, the injection pressure will need to go up, requiring stronger pipelines, a larger compressor, and more energy. Two scenarios exist. Either the connected subsurface volume is large enough so that the water and rock volume is so much larger than the volume of CO2 to be injected 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 Gorgon project in Australia plans to extract water as it injects CO2. The other way to manage pressure is to inject CO2 and remove hydrocarbons, along with water. This is called CO2 EOR and is discussed below. It is vital that a storage project team understands and manages the subsurface pressure 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

20 Carbon Capture and Storage

simply the disposal route for the CO2 coming from the capture plant. The capture plant, and linked industrial or power plant, needs to be able to safely sequester the CO2 to retain its climate friendly credentials and justify the increase in cost over its CO2 emitting, non-sequestering counterparts. The storage system—be it a single store 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 will not try to explain all the details as it is possible to write books on it, but will give a brief 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 the accumulation. As this pressure declines, the field enters the secondary production phase when additional energy has to be supplied—this can be done by pumping the oil out of the wells, or by injecting water and pushing the oil out. This latter technique is termed a ‘water flood’. Initially the wells flow pure oil (with some natural gas), but later the water breaks through and the wells then flow a mixture of oil and water. As the saturation of water in the rock pores increases, and the saturation of oil decreases some of the oil becomes trapped by capillary forces and can no longer flow. In certain cases the field operator can choose to try tertiary production by injecting CO2. The CO2 acts as a solvent, and mobilises trapped oil that remains after a water flood. During the process some of the CO2 is permanently and immovably trapped in the subsurface, in other words it is ‘stored’. The production wells bring a mixture of oil, water, natural gas, and CO2 to the surface. The gasses are separated from the oil and water and reinjected. Sometimes the natural gas is separated from the CO2 and sent to market, and only the CO2 reinjected. The recirculated CO2 works to liberate more oil, and additional CO2 (termed make-up gas) is bought to compensate for the CO2 that is trapped (stored) in the formation. When CO2 EOR is talked about in terms of CO2 storage, people tend to be polarised. Some see it is an economical way to store CO2—the oil production means that the storage is for free, and the fact that the operator pays for the CO2 means that there is income to offset against the cost of capture. Others see it as undesirable because it produces hydrocarbons—hydrocarbons that, if burned, can emit CO2 if not fitted with CCS. Setting the question of ‘should society produce and use oil’ to one side, we can compare CO2 EOR storage to storage in saline formations or depleted oil and gas fields. Both store CO2. The process of producing and reinjecting CO2 in CO2 EOR takes energy (large compressors) which will generally come with CO2 emissions, so the avoided CO2 (stored less emitted during the process of storage in this case) is a bit lower. On the plus side, CO2 EOR storage produces oil and hence adds value back into the system—something termed Carbon Capture Utilisation and Storage or

21 Carbon Capture and Storage

CCUS—it creates jobs, and can help to pay for the storage and capture. It is therefore 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 ‘pump primer’ paying for infrastructure, both capture and transport, which will first be used for CO2 EOR storage, and then later for pure storage. So, acknowledging the inescapable fact that our industrialised society continues to need oil, we might as well 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 will not all leak out again?’. People are rightly concerned over this. Pictures of oil wells blowing out, Hollywood disaster movies, reports of volcanic emission events like Cameroon’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 it would be to get water or liquid CO2 through a quarter of an inch of ordinary roofing slate. 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 gas have been naturally trapped in the subsurface for millions of years—and subsurface containment can look exceptionally secure. So where are the weak points? We know that natural CO2 seeps, like those in figure 13, exist. By studying these we can identify the geological features necessary for CO2 percolation from the deep (in the cases above, volcanic) sources to the surface. Once we know this we can make every effort to ensure that a CO2 store does not 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 likely to leak; and (ii) engineering: do the engineering properly, inject into the correct layers, do not 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 near

Florina in northern Greece. There is a CO2 tolerant species flowering around the margin, then stressed vegetation outside (Credit: CERTH/RISCS project).

22 Carbon Capture and Storage

Effective site selection is vital. We think about CO2 containment in terms of barriers—using something called the Bow-tie risk assessment methodology. For example: does the store have a caprock? How can I be sure that it is effective? Is there evidence that containment has been compromised? Is there evidence to support that it has not been compromised? Are there likely to be faults that will move—i.e. risking containment and potentially causing induced seismicity that could 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 barriers in those wells? The process of selecting a storage site is rigorous, and time consuming. In countries where CO2 storage is taking place there are strong regulatory regimes, and injection is only permitted when the regulators are convinced as to the security of a site. Over the past few years the global community has come together under the

Soil or seabed sediment Unconsolidated Injection tubing Conductor (hammered into loose soil/sediment) Mudstone Cement Permeable rock layer, might hold drinking water Sandstone Surface casing

Mudstone

Carbonate Intermediate casing

Marl CO

Shale A-annulus filled with completion fluids

Carbonate Production or “long string” casing

Caprock seal, Packers, make seals between casing, tubing Shale and liner

Storage formation, Sandstone

Slotted liner

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

23 Carbon Capture and Storage

auspices of the International Standards Organisation (ISO) to draft a set of standards relating to CCS that include how to select a storage site (see further reading). Engineering and construction are key. The oil and gas industry operates many injection wells and experience has shown that problems occur when key engineering principles are overlooked. A recent case in point was the release of methane from an underground gas storage facility in California. In this region, underground gas storage (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 oil and gas extraction, and the well design had only a single barrier to prevent the release of gas. The oil and gas industry normally designs wells with a double barrier philosophy, with monitoring of the integrity of the barriers, so that there should always be a backup barrier to prevent leakage. CO2 storage regulations mandate this type of engineering with multiple barriers.

Well construction A typical well is shown in figure 14. The operator starts by hammering in a surface casing, perhaps 36 inches (the oil industry works in strange units and uses inches for casing and borehole sizes) in diameter, made of thick steel. The conductor is hammered to the point of no return. Its purpose is to stop the loose soil or sediments falling into the well. Next the ‘top hole’ is drilled and a surface casing is run. This is often about 28 inches in diameter. This casing will normally be cemented to surface and its purpose is to isolate the groundwater formations. A blow out preventer is attached to the surface casing. This then forms a pressure vessel for the next step of drilling. 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 hole size, and ensuring that the pressures from fluids in the rocks do not overcome the weight of the drilling mud. Drilling mud is a carefully engineered fluid made of oil or water, clays, and other minerals and thickening agents. Its purpose is to cool the drilling bit, carry drill cuttings to the surface, and hold back the pressure of the fluids in the rocks. The density has to be carefully controlled. The interplay between mud weight, formation strength, and the fluids held in the formation dictates the maximum depth to which a drilling rig can drill before setting another casing. In the example here, we have used one intermediate casing, and then the 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 steel liner tubing. This is sometimes a solid wall pipe which is cemented in place, and then holes are shot into it using perforating explosives, or it is a slotted or pre-drilled liner which acts like a sieve to hold any loose sand from the rocks in place while still letting the CO2 flow in.

24 Carbon Capture and Storage

The CO2 is injected via the injection tubing into the storage formation. This tubing holds the CO2 pressure. If a leak forms in the injection tubing the CO2 will flow into the A-annulus which is filled with fluid. This is the next barrier and is designed to hold the complete pressure of the CO2. Pressure gauges are attached to the A-annulus so any leak from the injection tubing will immediately be detected, the CO2 turned off and isolation plugs run into the tail pipe below the packer allowing the 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 if the caprock leaks…and so on. In the enthusiasm to test the what-if scenarios, fluid modellers often introduce short cuts into their system—imagine a direct pathway from the storage formation to the surface, or let’s inject into a shallower zone. This is an 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 at what rate would escaped CO2 flow? An example of a leak from an exploration well that was drilled into a formation that naturally contains CO2 and that was never sealed is shown in figure 15—this one is a bit of a tourist attraction, albeit mainly for geologists! When this question is answered, it is often found that the pathway physically or geologically cannot exist, or that flow would be so slow as to take thousands of years to even seep. Cement is a good example of how even ‘rational’ people forget the scientific thought process. Cement is made when a mixture of tri and di-calcium silicate and tricalcium 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 natural however, the seep was caused by the drilling of an oil exploration well many decades ago.

25 Carbon Capture and Storage

of the components to make calcium silicate hydrate and calcium hydroxide and releases heat. If you take a plug of standard oil-industry cement, namely Class G Portland cement, and flow carbonic acid past it, the cement is leached. The calcium hydroxide can react with the carbonic acid, and decalcification of the calcium silicate hydrate also takes place. If the carbonic acid is replaced and the dissolution products are continuously removed, the ultimate result is a porous amorphous silica gel. This is taken as evidence that Portland cement will not work as an effective impermeable barrier in acidic environments. But when we look at the actual downhole situation we see something very different: this is a stagnant scenario. There is no Maxwellian daemon with a hosepipe generating a flow of carbonic acid. The bottom of a 30 m or longer plug of cement sits in a stagnant pond of liquid CO2. There is no reaction here as there is no water. Assume then that the plug is just below the water contact in a CO2 store, so it is exposed to carbonic acid. The reaction with the plug rapidly becomes diffusion dominated as reaction products have to diffuse out and fresh reagents must diffuse in. The experiments and modelling tell us that the cement becomes more sealing in the absence of leaching. These facts have been backed up by lab 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 an engineering or an emplacement issue and there is much debate about cement shrinkage, microannuli which have the potential to cause leak paths, and shale creep and mud plugging which seal leak paths. This has nothing to do with the reactivity of Portland cement, rather it is all about the emplacement of a plug with respect to the storage formation. This is not to say that there may not be better cements than Portland cement, or even Portland cement with additives that reduce shrinkage or which encourage healing of cracks (an active research field). It does say that if a legacy well has been correctly installed and later plugged so that it does not have leak paths, then it is unlikely to form new leak paths. We must also remember that CO2 has been injected in CO2 EOR fields for decades, fields with natural gas contaminated 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 encountered natural CO2 instead of hydrocarbons. In the past the CO2 used to create an artificial geyser and it became a tourist attraction, however when I visited in 2017 it had reduced to bubbles only. If a well in a CO2 store does start to leak then the operator is obliged to repair it, using the same techniques as oil and gas operators use to repair blow outs.

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

26 Carbon Capture and Storage

would be created from the start to ensure that the cars were safe and well suited to the job. The authorities would demand evidence that the cars were not endangering life 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, and construction has been carried out to a high standard. They further require that the storage operator shows that the site is containing CO2 and that it is operating according to prediction—termed ‘conformably’. Is the pressure dissipation taking place in the way you said it would when you obtained a storage permit for the site? If not, what is this observation telling you? Is there any evidence of out of zone migration of CO2? Is the surface pipework leaking? In the subsurface, predicting the behaviour of the CO2 involves the development of numerical models, very similar to those in atmospheric physics. Some are finite difference models that combine the physics of the fluid dynamics and of pressure dissipation: reservoir engineering models. Others are finite element models of the stresses of the rocks and their behaviour as a pressure perturbation is introduced: geomechanical models. In special cases, it might be required to build geochemical models as well. Although the three types of models can be linked, it is seldom done on a full field basis, because they are extremely computer resource hungry and simply take too long to run!

Induced seismicity Certain events over the past few years in Oklahoma, US, have focused a spotlight on the subject of induced seismicity. In Oklahoma, the hydrocarbon gas industry disposes extracted saline pore water via injection wells. In recent decades, the rate of water injection has increased because the shale gas revolution has led to the production of significantly more waste water. Suddenly, the incidence of earth- quakes that were large enough for people to feel increased, as did the magnitude of these earthquakes. It must be noted that this was an area that was not subject to significant natural seismicity. Building construction codes were not set up for active seismicity 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 before the start of injection, and there were no monitoring plans. In many aspects, the operators at the Oklahoma sites were unlucky, there are thousands of water disposal wells across the US, and the vast majority show no induced seismicity. It is now thought that, in this case, critically stressed faults (faults that are holding against an applied stress, i.e. they contain pent up energy), possibly in the granitic basement rocks that lie at the bottom of the sedimentary sequence, are moving in response to the changes in pressure. When CO2 was injected into a different region of the US, in Decatur Illinois, the site was extensively studied prior to permitting, and there was a comprehensive monitoring 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

27 Carbon Capture and Storage

events are normally above 5 or 6, while global calamity events are normally around 8 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 level can be expected, and the author suspects that if we installed such sensitive equipment in 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 a monitoring plan to identify issues, but also a plan for reacting to the monitoring results—this is logical. Suitable monitoring plus a reaction, can equate to a barrier, termed a reactive barrier. This approach has the advantage of demonstrating that the operator is able to respond to leakage or migration scenarios that might threaten the integrity of the storage site.

Ocean storage Much thought has been given to the idea of ocean storage. Indeed, it receives a whole chapter in the IPCC special report on CCS. The logic is simple—inject the CO2 into the deep ocean where the pressure and temperature are such that CO2 is denser than water. Mixing happens very slowly at these depths and the CO2 will remain isolated from the shallow waters for hundreds to thousands of years. The challenge here is the possible impact of the CO2 lake on the marine life. As we learn more about the deep oceans we find more and more life. The question, however, is moot as the Convention on the Prevention of Marine Pollution by Dumping of Wastes and Other Matter 1972, the London Convention, forbids this practice in any case. In a related area, the creation of hydrates is a topic being actively explored. Here the proposal is to inject the CO2 into sediments below the deep ocean floor. This can create hydrates within those sediments immobilising the CO2. This idea will not be explored further here as this short book concentrates on technology that currently exists and can be deployed at scale today, but references are given in the further resources.

3 Current Directions Scaling up CCS If CCS is going to realise its potential and make a significant contribution to reducing global CO2 emissions then it needs to scale up from a few tens of millions of tonnes per year, to billions of tonnes of CO2 captured, transported and stored each year. 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 will reduce through learning and innovation. On the storage area the challenge is larger and relates to finding and accessing sufficient underground storage capacity. This will be expanded upon below.

28 Carbon Capture and Storage

The size of the challenge CCS has been proven at what is termed small industrial scale—by this we mean the scale that is equivalent to removing about quarter of a million cars a year from the roads: 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 installed capacity of 550 MW and its owners estimate that it displaces approximately 300 000 tonnes of CO2 each year. Statoil (recently renamed Equinor) has been storing CO2 in the North Sea for over twenty years. Shell has added CO2 capture to hydrogen manufacturing units at their bitumen upgrader in Alberta Canada. Here they capture over one million tonnes of CO2 each year, pipe it sixty miles, and inject it into a deep saline formation. Also in Canada, in Saskatchewan, SaskPower has fitted one unit of a coal power station with CCS—this CO2 is piped to the Weyburn EOR field. More examples are referenced in the additional resources section. The size of the current plants are nothing compared to what is required to decarbonise the entire planet—100 million tonnes of CO2 a day, plus other greenhouse gasses (figure 16). The International Energy Agency, the IEA, divides the decarbonisation challenge between technologies and suggests that CCS can contribute 12% of the reductions required in 2050 to achieve a 2 °C global rise in temperature: 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&D Programme (IEAGHG), has shown that this should be possible, although the scale of the system needed would be similar to that of the world’s present gas-production infrastructure (see additional resources). This sounds large, but it is logical—if we need 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 Carbon Budget team (see additional resources).

29 Carbon Capture and Storage

over the next forty years) be replaced by alternatives, plus all the biologically sourced CO2 that needs to be captured to create the negative emissions required to remove 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, thoroughly characterise the sites, and then inject large volumes of CO2. Current subsurface accommodation processes—simply the compressibility of water and rock—lead to only between 0.5% and 1% of the pore space being filled before reaching the natural pressure constraints of the containing system—assuming that there is no natural pressure relief via a wider natural fluid flow system. Further, increasing subsurface pressures could also lead to an increased chance of pushing formation brine into overlying layers, potentially via legacy well bores, and also increasing the risk of induced seismicity. Pressure management will therefore be a fact of life for future stores—and, unless the storage is via CO2 EOR where pressure is managed as part of the entire hydrocarbon production process, this will require water extraction. The increased subsurface pressures should drive the water out of extraction wells—just like artesian wells—but this brackish, or sometimes very salty, water will have to be treated and disposed of, or used in agriculture, industry and even for drinking.

Water extraction and pressure management Extracting water can dramatically increase the storage efficiency—instead of 0.5% of the 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 out of a porous medium; (ii) the pressure induced by the buoyancy of too large a column of 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 not homogenous, so CO2 will preferentially flow in some layers, so the injected CO2 will not move in a straight flood front. Some of it will tend to run ahead and ‘break through’ to the water extraction wells. i.e., CO2 could arrive at a water extraction well 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 to be actively managed, changing injection patterns (sweep) to maximise subsurface utilisation. The whole topic of maximising the storage efficiency while still constraining the cost to society is a new and exciting area of research and is only just beginning to be investigated.

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

30 Carbon Capture and Storage

exploration and extraction. Not all wells are mapped, not all wells have effective isolation barriers (long cement plugs). While many types of rocks actually move and squeeze old wellbores closed, not all do. The existing storage projects working today have been carefully sited to avoid such legacy wells. Giga tonne scale storage cannot afford to be as discriminating and will inevitably encounter potentially leaking wells. Well seeps and leaks can be repaired with existing technology—by bringing a drilling rig onto the site and either removing the old plugs and setting new ones, or drilling a new well that intersects the old one to allow pumping of cement and other sealants into the subsurface to halt flow toward the well. This is extremely costly and ideally needs to be avoided wherever possible! The cost of repairing a legacy well leads to an interesting challenge, mainly driven by a lack of information. We cannot be certain that a well, especially one that appears to have a poor set of isolation barriers, will leak. Nature likes to close up tunnels and holes, but we cannot be absolutely sure that a tortuous leak path does not still exist. Pre-emptively trying to drill out and re-plug an old well might take months, and could actually reopen a perfectly sealed wellbore. What is required here is research: research into sealing mechanisms, like salt and shale creep; research into the effect of well drilling mud (made of clay, water and other substances) at sealing any microannuli in the well cement sheaths; and research into methods of assessing the 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 carbonate is one such angle. These could be delivered by targeted injection or slim hole methods, perhaps using coiled tubing, and would then seal up any flow paths in the old 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 Earth We would all agree that we want to be sure that stored CO2 is not leaking back into the atmosphere. CO2 storage permits almost always require that the operator has a monitoring and verification plan to show just this. Current monitoring plans rely on oil and gas technologies—such as large-scale seismic surveys, down-hole monitoring with surface readout electric or fibre optic gauges, and ship borne seabed and seawater surveys. This technology has worked well for the oil and gas industry, as large area surveys are only required once to discover the field, then smaller targeted surveys are used occasionally during the relatively short, perhaps twenty year, life of most fields. Down-hole, subsurface, monitoring is only required 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 effectively permanent. In Europe the regulation expects a default monitoring duration of twenty years 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 evidence to shorten it, and the area to be monitored is the area of the pressure plume—which can be tens to hundreds of miles round the injection site.

31 Carbon Capture and Storage

Something therefore needs to change. Onshore, local people do not want seismic trucks driving across their fields every few years, nor do we want to disturb marine mammals with offshore seismic surveys. Surface read-out gauges require open well bores, but an open well is a potential leak path, so these need to be sealed as soon as possible after injection ceases. In addition, maintaining wells offshore, on a platform or subsea, is both dangerous to the people who service the wells, and costly. Ship borne marine survey techniques require large (currently) CO2 emitting boats and crews—again risk and cost increases. A final challenge is also present. Drinking water aquifers extend over hundreds of miles—collecting rain from distant mountain ranges and transporting it to pop- ulations. Deep salt water aquifers are no different, stretching hundreds of miles and crossing 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 be operating at the same time. This temporal dislocation could lead to projects starting and finishing, and then others starting up decades later in the same hydraulically connected saline formation. How do we ensure that we know that the pressures induced by any new project will not cause issues in the old, now closed, project? We need some way to monitor the subsurface for at least a century—in other words we need to instrument the Earth. The subsurface environment is hostile: high temperatures of around 100 °C, high pressures of over 100 atmospheres, and corrosive salty and CO2 rich fluids. But there is a geothermal gradient from which work can be extracted, and wells have steel casings which are already used for data transmission—albeit from short lived battery powered gauges. What is required is to develop a gauge carrier that can scavenge 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 be placed below well abandonment plugs and left for centuries. I term these gauges century gauges or even infinity gauges. The applications for such gauges are not just limited to CCS, but extend into any area where increasing our knowledge of the subsurface is useful—a concept termed instrumenting the Earth. Significant research is taking place in the seismic acquisition world. Instead of laying outlargearraysofgeophones and then lettingoff apattern ofexplosive chargesor using vibroseis trucks, researchers at Lawrence Berkeley National Laboratory and also in Japan are developing continuous seismic sources which remain fixed in place, and are coupling these with buried fibre optic cables. In this way, they hope to achieve regular monitoring of the subsurface with no impact on the neighbourhood. Many of you will have heard of the UK population’s attempt to name a research vessel Boaty McBoatface. The vessel is now called the Sir David Attenborough, but an autonomous underwater vehicle (AUV) was christened Boaty McBoatface instead. A research partnership in the UK has developed sensors and software that will allow the AUV to map the seabed, look for bubble streams that could indicate a leak, and test the water quality—removing the need for a ship, delivering more data with significantly lower risks to sailors and lower cost.

32 Carbon Capture and Storage

What are the consequences of a leak, what are the rates and what does a leak look like? Most human activity takes place on the surface of the planet. As a result, we are programmed to think in terms of spills, leaks from factory tanks, run off from fields and the like. CO2 storage injects CO2 under kilometres of rock. It is incredibly difficult to get things to flow through many rock types. As a result, even were CO2 to start 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 that much larger. If CO2 were to manage to percolate upward, it might take hundreds of years to get there, unless it shortcuts through a wellbore. Even wells do not necessarily provide an easy path—subsurface leaks often flow along a well for a while then out into other rocks. The cement plugs used to abandon wells sometimes have microannuli between the cement and the casing, and CO2 can potentially percolate here; but even if it does, at what rates? Ab initio modelling struggles to answer questions related to leak rate—roughly you get out what you put in, although carefully framed questions and scenarios can help to constrain the system. I often see people suggesting leak paths that are precluded by physics or by other evidence. What is needed is actual physical experiments. Some researchers are studying natural, normally volcanic in origin, seeps. Others like those at the Field Research Centre in Alberta, Canada, are drilling wells and injecting CO2 to make a synthetic leak. Similar work was done off Scotland by the QICS project. These let us see what a new leak looks like—one where 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 natural systems—onshore and offshore. This research is finding that the effects are very localised—one way that people identify natural seeps is to look for different vegetation like that pictured in figure 13.

New storage frontiers Most of the world has not been systematically assessed for storage capacity, but where assessments do exist they are difficult to compare. Research consortia have assessed the US, Australia, and most of Europe—and this needs to be extended to cover 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 and academic team under the auspices of the Society of Petroleum Engineers, who also maintain the most used Petroleum Resource Classification system. This is titled the Storage Resources Maturation System, and is linked closely to a generalised United Nations classification system. The SRMS was built to parallel the petroleum system because of the similarities between subsurface storage and subsurface extraction of naturally stored petroleum. The parallel will allow financial backers to 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 ensure uniformity of classification.

33 Carbon Capture and Storage

An exciting new area of storage research is basalt storage. The oceanic crust is made of basalt. Large areas of many continents are covered by flood basalts. Researchers at the Lawrence Livermore lab performed an injection test into flood basalts at Wallula in Washington State, US, and there are currently proposals to explore pillow basalts off the Pacific coast of the US. Basalts also have permeable zones—for example breccia zones at the tops of flows—covered by impermeable layers of fresh basalt. In Iceland the CarbFix project has been injecting carbonated water 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 in basalt than in sedimentary rock, leading to a large quantity of mineralisation—both an advantage from the long term storage perspective and a challenge from the short term injectivity point of view.

Fundamental physics

The physics of pure CO2 phase behaviour is well understood, however, CO2 has many interesting properties. Perhaps the most unusual is that the phase change from liquid to gas takes place in the working range of a normal project. If we think about piping natural gas, it stays as a gas from the field all the way to our gas ring in the kitchen—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 at figure 17,CO2 changes from gas to liquid between 10 and 70 bar at normal environmental temperatures. If CO2 is released from high pressure to atmospheric pressure, it rapidly cools and solids can form—this is why CO2 fire extinguishers make a white fog of condensed water.

10,000

solid phase 1000 liquid phase supercritical fluid

100

atmospheric 10 sublimation point -78.5°C at 1 bara critical point 31.3°C & 73.8 bara triple point Pressure, bara 1 -56.6°C at 5.2 bara

0.1 fluid phase

vapour phase 0.01

0.001 -120 -100 -80 -60 -40 -20 0 20 40 60 80

Temperature, °C

Figure 17. Pure CO2 phase diagram.

34 Carbon Capture and Storage

If we are to estimate the effects of CO2 releases, in order to design facilities, wells and pipelines, we need to be able to simulate the full phase envelope of CO2. What is more, we need to be able to do this not just for CO2, but for mixtures of CO2 with CH4, and other contaminants. If a well backflows, the mixture will also include water that will make ice and hydrates when the system cools. At the moment we struggle to simulate the behaviour of CO2 mixtures, and have challenges when solids co-exist with liquid and vapour—this is quite a challenging computational physics problem.

New capture technologies Most capture plants in operation today deploy amine absorption, a tried and tested technology. Some use second-generation amines, which are more efficient. Capture linked 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 North Carolina, US, guided by Rodney Allam, has gone back to basics and has looked at the whole power chain. What you need for zero carbon power is to convert gas to electricity and to deliver high pressure CO2 for storage. The team invented the Allam cycle which uses air separation to make O2 and get rid of the N2, followed by oxycombustion. All normal so far, but then they use CO2 as the working fluid for a turbine rather than steam. The CO2 is also used to moderate the combustion, managing the temperature. The cycle takes place at a pressure greater than atmospheric reducing the level of CO2 compression required compared to post combustion capture. All this leads to, it is hoped, a lower capital outlay, similar to that of an unabated plant, while having a similar efficiency to a conventional gas with CCS power plant. An industrial scale pilot is currently under construction in Texas. While capture has been shown to work on coal fired power, it has not yet been deployed at even the few hundred megawatt scale on gas, nor have the crucial negative emission BECCS plants been constructed. There are many industrial applications where CCS is needed, many have been piloted but again few have been 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 assessment models, leads us to the interaction between economics, science, public policy and science communication. Despite lots of research showing that deploying CCS is needed to deliver emissions targets, and that CCS makes economic sense, governments have failed to create the conditions that will encourage industry to deploy CCS. The exceptions are CO2 EOR storage in the US where industrial emissions have been captured for years, along with CO2 from natural CO2 gas fields; and Norway where a CO2 tax incentivised the deployment twenty years ago.

35 Carbon Capture and Storage

A common question from political decision makers is: ‘How long can we delay before deploying it?’ This summarizes the conundrum with CCS. Although deep decarbonisation of electricity, heat, and industry plus negative emissions are required to head off the massive and costly effects of climate change, these effects are not weighing hard on the economies of today. How do today’s decision makers balance the need to invest today in for example, hospitals, roads, and police, with the need to invest in deep rapid decarbonisation such as that delivered by CCS that will only pay off in a generation or two? Companies recognise the challenge of climate change, and compile reports for their shareholders showing their resilience under difference scenarios. What the company executives cannot work out is how to finance investment in CCS. Investment in many renewable technologies is paid for by subsidies and feed-in tariffs, electric cars are incentivised by tax breaks. But these mechanisms are seldom present for CCS—can a cement or fertilizer manufacturer sell low CO2 products at a premium? Is a government willing to spend more on building a new high-speed rail line with low CO2 steel? This is where some incredible thinking is needed—thinking at the interface of science, economics, policy and sociology—thinking that harks back to the days when leading political figures were also leading natural philosophers. Whoever solves this challenge, and many such as teams at Imperial College and Cambridge University, are working on it, might well be credited with solving the CO2 problem.

4 Outlook

Take a look at the Mauna Loa CO2 curve again (figure 1). Is the concentration of CO2 in the atmosphere increasing or decreasing? How rapidly do we need to make a large difference in CO2 emissions rates to stand a 50% chance of hitting 2 °C, let alone a 50% chance of 1.5 °C? Even a cursory inspection of the data and climate model predictions leads us to ask the question—can we afford not to implement CCS along with every energy saving technology, every alternative energy, and make every effort to reduce our personal carbon footprint? Take a careful look at the global economy—look at society as it is, rather than as we would like it to be. How quickly can the energy, industrial, and transport system transform without massive social upheaval? Where can we recommend interventions that will make a difference? The status quo is 100% leakage of CO2 into the atmosphere—that is released from smoke stacks and exhausts the world over. Industrialised, urbanised, society is alarmingly fragile and dependent upon energy and energy intensive manufacturing. CCS, in all its guises, with its strengths and failings, offers global society a way to rapidly remove a significant proportion of the CO2 now released to the atmosphere, without dramatically disturbing fragile economies, and without rationing energy. If scaled up it can buy time and significantly increase the chance of hitting 2 °Cor maybe even 1.5 °C.

36 Carbon Capture and Storage

Additional resources Global warming The definitive source for information on global warming, the effects on people and the planet is the IPCC—the Intergovernmental Panel on Climate Change. 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 are found 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 which is 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: Working Group contribution to the Fifth assessment report of the Intergovernmental Panel on Climate Change (New York: Cambridge University Press) pp. xi, 1535 pages. No discussion on global warming would be complete without the original reference from 1896: Arrhenius S 1896 On the influence of carbonic acid in the sir upon the temperature of the ground Phil. Mag. J. Sci. 41 237–76. A very useful summary of the state of CO2 reductions was given in the November 2017 issue of The Economist, ‘What they don’t tell you about climate 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 the needs 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-prob lem-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 see the data for myself, and where better to get it than from one of the earliest CO2 laboratories in the world, set up by Charles David Keeling on top of the Mona Loa volcano in Hawaii. Data have been collected at this location since the 1950s.

37 Carbon Capture and Storage

Keeling C D, Bacastow R B, Bainbridge A E, Ekdahl C A, Guenther P R and Waterman L S 1976 Atmospheric carbon dioxide variations at Mauna Loa Observatory, Hawaii Tellus 28 538–51 All the information on how the measurements are made, on CO2 in the atmosphere and the latest data can be found at this web location https://www.esrl.noaa.gov/gmd/ccgg/trends/ and a lot more information can be found at the Scripps Institution of Oceanography 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 found at 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 at the Global Carbon Project. When the papers talk about the remaining carbon budget, how much was emitted in any year, they are often referring to reports 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. The reference for the 2016 paper is given below: Le Quéré C et al 2016 Global carbon budget 2016 Earth Syst. Sci. Data 8 605–649 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, see Fossil 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 Analysis Center, Oak Ridge National Laboratory, US Department of Energy) doi 10.3334/CDIAC/00001_V2016 The European Union Joint Research Centre maintains the Emissions Database for 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-emis sions-2015-report-98184.pdf The fact that CO2 emissions are effectively cumulative over a human time scale is described by Myles Allen from the University of Oxford: Allen M R et al 2009 Warming caused by cumulative carbon emissions towards the trillionth tonne Nature 458 1163 When discussing carbon budgets, it is important to identify if it is a Carbon budget or a CO2 budget. Some authors only count the Carbon atoms in the

38 Carbon Capture and Storage

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 of C is 12 u, while CO2 is 44 u). The International Energy Agency (IEA) publishes on CO2 emissions from fuel combustion, reporting emissions by region and by sector: https://www.iea.org/publications/freepublications/publication/CO2Emissions fromFuelCombustion_Highlights_2016.pdf The US EPA reports material on emissions, though much is this is vanishing as a 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 emission technologies. These are becoming more and more important as it looks increasingly likely that we will overshoot the CO2 levels required to maintain the global average temperature increase to 2 °C. The article below gives a useful introduction https://www.carbonbrief.org/beccs-the-story-of-climate-changes-saviour-tech nology 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 skew statistics. One example I repeatedly notice is when papers report that ‘today the country/state/region used more renewable energy than ever before’. The statement is generally true, but they neglect to point out that demand was particularly low because it was a holiday or a weekend or hot/cold and that the wind was particularly strong…and so on. One author who noticed this was physicist Sir David MacKay, a professor of engineering at Cambridge, Fellow of the Royal Society, and one time chief scientific advisor to the UK government’s Department of Energy and Climate Change. David looked at the system as a scientist, and explored what it would take to run everything from renewable sources, and wrote a book ‘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 energy system. Once you have read the book, if you want to start exploring the electricity system further then an invaluable resource is the UK Gridwatch webste. http://www.gridwatch.templar.co.uk/

39 Carbon Capture and Storage

Here you can download minute by minute data for electricity generation and see what is actually happening. I get childishly excited when it is stormy and am always 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 on CCS and on its importance in contributing to deep decarbonisation. Their work is summarized on the IEA website https://www.iea.org/topics/ccs/ Digging further into the field takes a lot of effort and aspects like capacity provision and grid strengthening for intermittent renewable energy, the energy demand from space heating, the embodied carbon in battery manu- facture, emissions from biofuel manufacture, and the effect on heather moorland of clearing roads for wind turbines all have to be taken into account. It becomes very complicated very quickly and it is no wonder that people try to simplify it in order to get the message across. For those who want to take the plunge then the UK’s Energy Technology Institute (ETI) is a good jumping in point. They have spent a decade looking at the UK Energy system, funding research, and pilot projects into areas ranging from hydrogen combustion to tidal technology to smart homes to cleaner heavy-duty goods vehicles. There is so much material available from the ETI that it is challenging to know where to start, however, perhaps start off by reading about energy system modelling http://www.eti.co.uk/programmes/strategy/esme then look at the technology programmes http://www.eti.co.uk/programmes

The value of CCS to society Many have looked at the value of CCS, a recent prominent report was written by the Parliamentary Advisory Group on Carbon Capture and Storage, titled Lowest Cost Decarbonisation for the UK: The Critical Role of CCS. This can 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 website https://www.globalccsinstitute.com/understanding-ccs

40 Carbon Capture and Storage

This is complemented by the IEA Greenhouse Gas R&D Programme, the IEAGHG http://ieaghg.org/ccs-resources Next come two resources that need to be read together, the first is the IPCC special report on CCS https://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 the International Journal of Greenhouse Gas Control, Special Issue commemorating the 10th year anniversary of the publication of the Intergovernmental Panel on Climate Change Special Report on CO2 Capture 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 that exists for natural gas extraction. This makes intuitive sense, we need to put a large 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 Analogues http://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. This section will only point to a few reports and web resources for further reading. The UK Carbon Capture and Storage Association has accessible summaries on different types of capture http://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 on oxygen 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-ccs http://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 still contains some of the best information on industrial and power related point sources of CO2 and the concentrations of CO2 in various emission streams http://www.ipcc.ch/pdf/special-reports/srccs/srccs_summaryforpolicymakers.pdf https://www.ipcc.ch/report/srccs/

41 Carbon Capture and Storage

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 Laboratory https://www.netl.doe.gov/research/coal/carbon-capture/pre-combustion The Plains CO2 Reduction Partnership provides an extensive 189 page report on the 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 by the 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 article http://www.chemengonline.com/psa-technology-beyond-hydrogen-purification/ ?printmode=1 The GCCSI has recent (July 2017) information on the costs of CCS https://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 report on CCS https://www.ipcc.ch/pdf/special-reports/srccs/srccs_chapter6.pdf while the use of CO2 hydrates for storage was explored by the IEAGHG http://ieaghg.org/docs/General_Docs/Reports/PH4-26%20CO2%20hydrates. pdf and the London Convention and Protocol’s rules on CCS are discussed on the International Maritime Organisation’s own website http://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 have enough? The first thing to do is to have a frame of reference and the Society of Petroleum Engineers have tried to work on this problem, by extending

42 Carbon Capture and Storage

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 of writing has been made by a team at MIT and Exxon Mobil. The team estimates that there is between 8000 gigatonnes (Gt) and 55 000 Gt of practically accessible geological storage capacity for carbon dioxide: Developing a Consistent Database for Regional Geologic CO2 Storage Capacity Worldwide, https://doi.org/10.1016/j.egypro.2017.03.1603 This was a top down approach to assessing storage capacity. Some countries have attempted a more bottom up approach. Naturally the US has done it twice with the USGS and the US DOE both issuing assessments U.S. Geological Survey. National assessment of geologic carbon dioxide storage resources—Results. ver. 1.1; 2013: https://pubs.usgs.gov/circ/1386/ U.S. Department of Energy Office of Fossil Energy. Carbon Storage Atlas 5th edn 2015: https://www.netl.doe.gov/research/coal/carbon-storage/atlasv While Europe ran the GeoCapacity project looking at sources and sinks. This project finished in 2009 and the final report can be found on the web http://www.geology.cz/geocapacity/publications/D42%20GeoCapacity%20 Final%20Report-red.pdf The UK created an online database of the storage potential on the UK Continental Shelf (offshore). This database can be accessed at http://www.co2stored.co.uk/home/index The Norwegian Petroleum Directorate has created a CO2 storage atlas for the Norwegian Continental Shelf http://www.npd.no/en/Publications/Reports/Compiled-CO2-atlas/ South Africa has done the same assessing onshore and offshore CO2 storage potential http://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 their annual status update.

Geological storage—containment risks

Being able to demonstrate that CO2 storage will contain CO2 on a millennial scale is important. An example of how to perform containment risk assess- ment (using the bow-tie methodology) is given in the paper Containment 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 storage is 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

43 Carbon Capture and Storage

CO2 is trapped in the subsurface in a number of ways. The authors explored the relative contributions of different trapping mechanisms using coupled geo- chemical and fluid dynamic software. The results are reported in the paper CO2 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. Portland cement is described by Schlumberger, who provide cement and cementing services to the oil industry, on their website in this useful article http://www.slb.com/~/media/Files/resources/oilfield_review/ors89/apr89/2_ cement.pdf and degradation mechanisms are discussed by the IEAGHG https://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 of induced seismicity, and pressure interference by removing brine from the store at the same time as injecting the CO2. A new report will soon be released by the ETI on this topic as part of a study effort described at this location: 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 at Lawrence Berkeley National Laboratory http://esd1.lbl.gov/research/projects/induced_seismicity/primer.html#defined while the Oklahoma quakes are discussed in this article by Walsh and Zoback Oklahoma’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 a whole 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 paper listing 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 to use one of her pictures. She looked at the health risk from seeps in Italy Physical Sciences—Geology—Social Sciences—Environmental Sciences: Roberts J J, Wood R A, and Haszeldine R S 2011 Assessing the health risks of natural CO2 seeps in Italy PNAS 108 16545–8; published ahead of print September 12, 2011,

44 Carbon Capture and Storage

Brine extraction to increase storage capacity and reduce risks A multi-disciplinary project, funded by the Energy Technologies Institute (ETI), has studied how brine production can enhance the storage potential of saline aquifers 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 be accessed at the following link https://www.globalccsinstitute.com/projects/large-scale-ccs-projects each year they also prepare a report on the global status of CCS http://www.globalccsinstitute.com/status Significant quantities of technical material from some active and cancelled CCS projects is available on the web. The Quest CCS project in Alberta Canada, in partnership with the Alberta government, has published the majority of its technical study work in capture, transport and storage, as well as permits and annual performance updates, 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 Peterhead post combustion gas CCS project (where I personally led the storage team) and the White Rose oxycombustion coal CCS project. When these projects were cancelled they had progressed to the end of Front End Engineering and Design (FEED) which means that they were designed and costed and ready for 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 two earlier CCS projects, the Longannet and Kingsnorth post combustion coal CCS 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 into flood basalts, a geological formation that covers large areas of the US, India, and Siberia. http://www.bigskyco2.org/research/geologic/basaltproject McGrail B P 2014 et al Injection and monitoring at the Wallula Basalt Pilot Project 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-

45 Carbon Capture and Storage

Boenisch D, Gunnlaugsson E, Axelsson G, Björnsson G 2009 Permanent carbon dioxide storage into basalt: the CarbFix Pilot Project, Iceland Energy Proc. 1 3641–6 https://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, therefore it 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 led to 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, the US, Europe and Australia. This list is ever growing so it is best to look to an umbrella body such as the Global CCS Institute. They have a list of regulations on their website: https://hub.globalccsinstitute.com/publications/ international-ccs-policies-and-regulations-wp51awp54-report/2-current-status- ccs-regulation

46