© 2001,

AAPG/DEG

, 1075-9565/00/$15.00/0Environmental Geosciences, Volume 8, Number 3, 2001 149–151

E D I T O R I A L I N T R O D U C T I O N

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Geological Sequestration of Carbon Dioxide

JOHN BRADSHAW and PETER COOK

This special issue on geological sequestration of carbondioxide emerged from papers presented at the AAPG Inter-national conference in Bali in October 2000. The papersencompass a range of issues and approaches and serve to il-lustrate some of the various options that countries, compa-nies, and researchers are considering to deal with the issueof increased carbon dioxide in the atmosphere.

Geologists have been aware of the evidence of past cli-mate change since the science of geology was first estab-lished more than two centuries ago. Over the past 50 yearsthey have been able to collect direct geological evidence ofpast variations in the concentration of carbon dioxide in theatmosphere, and they were among the first scientists to sug-gest a correlation between levels of atmospheric carbon di-oxide and climate change. Despite this, earth scientists haveperhaps not been as active as they should have been in thecurrent “greenhouse” debate. But as this special volume of

Environmental Geosciences

makes clear, the earth sciencesmay well have a pivotal role to play, not only in understand-ing variability in atmospheric carbon dioxide but in helpingto resolve the problem of increasing levels of atmosphericcarbon dioxide.

Over the last three decades the degree of acceptance ofthe concept of global warming due to anthropogenic sourcesof carbon dioxide has evolved (Lewis and Shinn, this vol-ume). It began with statements that greenhouse gases “couldaffect the climate,” to being “cause for concern,” to “on the

balance of evidence there is a problem,” and finally theagreement among some governments to reduce carbon diox-ide emissions through the 1998 Kyoto Protocol. To addressconcerns regarding anthropogenic greenhouse gas emis-sions, calls have been made as a first step to improve the ef-ficiency of energy use and production and to reduce the car-bon intensity of fuels. This is entirely sensible. Ultimately,we must seek to move to zero emission renewable energysources such as solar energy, but that is some way off. Hy-drogen is seen by many as a nonpolluting fuel of the futureand so it probably is. But generating H

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from methane (cur-rently the most promising technology) still results in carbondioxide generation. Therefore, we must look at “transitionaltechnologies” that will facilitate the long-term move fromfossil fuels to new energy sources, and one of the most prom-ising of these is geological sequestration of carbon dioxide.

As the papers in this volume show, geological sequestra-tion can be implemented now, and is already being imple-mented in some locations. Consequently during the time lagassociated with the development of new energy technolo-gies, it has the potential to produce an immediate decreasein anthropogenic emissions. According to Beecy and Kuusk-raa (this volume) the cost benefit to the United States of se-questration could be from $2 to $5 trillion over the next 50years. Additionally, the enormous volumes of carbon diox-ide that can be geologically sequestered means that therewill be no shortage of opportunities or locations where thissequestration can be undertaken. Preliminary investigationsof a selected set of sites that represent only a proportion ofthe potential in Australia (Bradshaw and Rigg, this volume)

suggest that at least 450

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tonnes of carbon dioxidecan be geologically sequestered. This represents over 1000times the 1998 total Australian carbon dioxide emissions.When compared with other natural options such as forestry,the relative volumes of carbon dioxide that can be seques-tered geologically could exceed them by at least three ordersof magnitude. Negotiations at Kyoto failed to adequatelyrecognize the existence of other carbon sinks capable of se-questering carbon; some of them will be able to offer greatersequestration potential than “Kyoto forests” (forests plantedsince 1990). Forests will of course be an increasingly impor-tant carbon sink in the future. However, it is unlikely to bethe sole panacea for decreasing carbon dioxide emissions;there are problems with auditing the carbon sequestered inforests, and sequestration times are relatively short. Chad-wick et al. (2000) raise valid concerns regarding forestry as

a long-term sequestration option. Recently in the United States,18 million hectares of forests were destroyed during forest

fires, perhaps liberating up to 6.5

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tonnes of carbon diox-ide to the atmosphere. Similarly, storms across northwest Eu-rope in 1999 destroyed hundreds of millions of trees.

The papers in this special issue show the various proposalsearth scientists are making to minimize carbon dioxide emis-sions, and they discuss research in the United States, Austra-lia, Europe, and Japan. Geological sequestration involves theinjection of carbon dioxide at depth into stable geologicalstructures that have held (or have the potential to hold) fluidsand gases for many thousands or even millions of years. Theconcept of “putting it back where it came from” has receivedwidespread acknowledgment as an appropriate approach forcarbon dioxide emissions. It utilizes well-established tech-nology developed in the oil and gas industry around the world.

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For example, carbon dioxide has been reinjected into matureoil fields for the last two decades to enhance tertiary recoveryof oil. Stevens et al. (this volume) and Holtz et al. (this vol-ume) deal with this oil field technology as it is applied in theUnited States, principally Texas. There, carbon dioxide pro-duced from large naturally occurring gas fields in Coloradois piped a thousand kilometers or more to Texas and rein-jected. Replacing this “natural” carbon dioxide with cap-tured carbon dioxide from the flue gases of coal-fired powerplants will reduce carbon dioxide emissions and perhaps pro-vide economic benefits; this specific option is evaluated byHoltz et al. (this issue).

The Norwegian-based oil company Statoil is producinggas from the Sleipner field in the North Sea, which com-prises 9% carbon dioxide. Over the last 3 years Statoil haveinjected more than three million tonnes of carbon dioxideinto the Utsira Formation. The paper by Gale et al. (this vol-ume) on Sleipner provides technical proof of the concept forgeological sequestration though other issues, such as costs,have yet to be clarified. Other papers by Gale and Freund(this volume) and Stevens et al. (this volume) discuss addi-tional options to geologically sequester carbon dioxide intomethane-saturated coal beds, thereby displacing the meth-ane (which can then potentially be used as a fuel). In a morechallenging concept, Koide et al. (this volume) proposedeep crustal sequestration, with the possibility of methanegeneration over geological time scales.

Can geological sequestration of carbon dioxide be doneeconomically across a broad range of circumstances andsettings? This is a difficult question to answer because thetotal cost is very much dependent on the cost of first sepa-rating carbon dioxide from other gases. In the case of sepa-ration of carbon dioxide from natural gas, the cost is mod-est, but with current technology, the cost of separation ofcarbon dioxide from flue gases derived from coal-fired powerstations is very high. However, it appears that the cost of geo-logical sequestration alone could be of the order of US$10–20 a tonne of carbon dioxide, which is of the same order asthe projected value of a tradable tonne of carbon dioxide.But until the rules of the Kyoto Protocol are modified totake into account not only “Kyoto Forests” but also geologi-cal sequestration, then this option will probably not be fullyconsidered or effectively exploited.

For this to happen we must have a firm basis for under-standing the processes involved in geological sequestrationof carbon dioxide. Evidence so far from Sleipner suggeststhat it can be done effectively and safely. The informationthat we have on the use of carbon dioxide in enhanced oilrecovery (mainly in the United States) similarly provides uswith additional understanding of the processes that takeplace when carbon dioxide is injected into the subsurface.This in turn raises the issue of whether in the right circum-stances we can combine geological sequestration of carbondioxide with enhanced oil recovery (EOR) or enhancedcoal-bed methane recovery (ECBMR), thus obtaining notonly the benefit of sequestering carbon dioxide but theadded financial benefit derived from EOR and ECBMR.

The issue of carbon dioxide emissions is a vexed one; theprocess of global warming, its links with carbon dioxideemissions, and the best way to respond to it raises manyquestions. We do not have the answers to all these ques-tions, and many of them are on the cutting edge of researchcurrently under way in various countries. But as is evidentfrom the papers brought together in this volume, we arestarting to define what questions to ask. For example, howeffectively and for how long can carbon dioxide be seques-tered in the subsurface? How does carbon dioxide react inthe rocks? How does supercritical carbon dioxide behave inreservoirs and how can it be monitored? What is the truecost of geological sequestration?

Answering such questions is vital not only to establish-ing whether or not geological sequestration of carbon diox-ide is technically, economically, and environmentally feasi-ble, but also in ensuring its acceptability by scientists, bygovernments, and by the community at large. The appear-ance of this volume is important to this process of accept-ability. Geological sequestration of carbon dioxide is alsoan exciting area of science and we hope that some of thatexcitement is apparent as you read this series of outstandingpapers.

REFERENCES

Chadwick, A., Holloway, S., and Riley, N. (2000). Deep CO

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se-

questration offshore provable greenhouse strategy.

Offshore

Magazine,

November

, 134–135.

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ABOUT THE AUTHORS•

John Bradshaw

John Bradshaw is Project Manager of

Project 1 (Regional Analysis) in the GEO-

DISC research project at the Australian Pe-

troleum Cooperative Research Centre. He

has a B.Sc. (Honours) and Ph.D. in Applied

Geology from the University of New South

Wales. John is an exploration technologist,

with a regional knowledge of Australian

sedimentary basins, and is employed as a Principal Research Scientist

at the Australian Geological Survey Organisation. He has also

worked for Esso (Australia) and on staff exchange for a year with

WMC Petroleum and Ampolex/Mobil. He has extensive fieldwork

experience throughout central Australia and Papua New Guinea,

where he consulted for several years. John has previously run major

industry-funded research projects examining the petroleum systems

of Australia. He is a member of GSA, PESA, and AAPG.

Peter J. Cook

Peter Cook is currently Executive Direc-

tor of the Australian Petroleum Coopera-

tive Research Centre (APCRC) and a direc-

tor of various companies. Previous positions

include Senior Research Fellow (Australian

National University), Division Chief-Asso-

ciate Director (Australian Geological Sur-

vey), and Director of the British Geological

Survey (1990–1998). It was during his time as Director of BGS that

he became interested in the issue of geological sequestration of CO

2

,

and on his return to Australia he established the GEODISC program

of the APCRC. He has acted as an adviser to government organiza-

tions and companies in Europe, Asia, Australia, and North America,

and he has held academic positions in Australia, the United States,

France, and the United Kingdom. Peter Cook holds degrees in geol-

ogy from the United Kingdom, Australia, and the United States. His

research career has included studies of the sedimentology, geochem-

istry, and economic geology of ancient and modern environments in

both inland and coastal parts of Australia and the evolution of Austra-

lia over the past 500 million years. He was leader of a major

UNESCO program on phosphate deposits, was involved in various

international marine programs, and for a number of years has been

chairman of a major program of the Intergovernmental Oceano-

graphic Commission. In recent years he has been involved in examin-

ing the role of the earth sciences in global environmental and ocean

issues, including CO

2

sequestration, in sustaining the global resource

base and in energy issues. He is the author or coauthor of many books

and research papers. He is a Fellow of the Australian Academy of

Technological Sciences and Engineering and a member of the

AAPG, the Geological Society of London, and the Geological Soci-

ety of Australia.