If carbon dioxide buildup in the atmosphere needs to be dealt with, it is by no means an intractable problem. Carbon dioxide is not the sort of radioactive or chemical pollutant that concerns regulators when present at the partper- billion levels. It is a natural part of our environment. Without carbon dioxide, plants would not grow and our planet would be a more extreme and inhospitable place. Thus, we only need to guard against having too much of a good thing in our atmosphere.

Carbon dioxide released by the combustion of fossil fuel is most conveniently vented to the atmosphere. Unfortunately, the atmosphere is a relatively small reservoir of carbon and appears to be particularly sensitive to the addition of more. The biosphere is also a small carbon reservoir that releases carbon dioxide back to the atmosphere as readily as it absorbs it. In contrast, the ocean reservoir of dissolved carbon dioxide is 50 times larger than either the atmosphere or biosphere and can easily absorb much more. In addition, carbon dioxide dissolved in the oceans will precipitate to create carbonate formations and sub-sea sediments that sequester huge quantities of carbon for hundreds of million of years. However, the natural transfer of gas to the ocean is slow with respect to atmospheric ventilation due to the long deep-ocean circulation times of about 550 years. It would make a lot of sense, therefore, to bypass the atmosphere and store the carbon where it is destined to wind up anyway - in the oceans and inside the earth. The U.S. Department of Energy estimates that 200 years of carbon emissions from burning fossil fuels at current rates can be absorbed, or sequestered, by two sources alone - the oceans and depleted oil and gas fields.

Bypassing the atmosphere to accelerate the normal carbon dioxide sequestration cycle has been the subject of much debate. Research programs have been designed to make sure that all the consequences of this solution are properly understood. We need to make sure that we do not solve one environmental problem by creating others. Not only do we need to ensure that industrially sequestered carbon dioxide does not harm people, we also have to check that it has no important negative impacts on any part of our natural world.

Our operational solutions must be deliberately incremental so that no single action carries too great a risk. Sequestering carbon in the deep ocean and in deep geologic formations is just that kind of incremental solution. The target reservoirs are huge and already contain vast quantities of oxidised carbon. The injection of carbon dioxide can be continuously monitored to detect any deviations from our predictions, and operations can be stopped for evaluation at any time.

Probably the most straightforward proposal is to sequester carbon dioxide in depleted oil and gas reservoirs. In fact, the industry already does this when it uses carbon dioxide floods to enhance the tertiary oil recovery process. These reservoirs have a good track record for stability, having trapped hydrocarbons in the subsurface for millions of years. However, this is not a guarantee of future stability. Does the cap rock of the reservoir rock itself degrade as a result of pressure cycling or from being in contact with the slightly acidic solutions produced when carbon dioxide dissolves in water? These are questions that need answers.

Another attractive option is to bury carbon at sea. Shallow injection is futile, as the gas will quickly rise to the sea surface and reenter the atmosphere. However, carbon dioxide is considerably more compressible than water even in its liquid state. At pressures above 3,000 meters, liquid carbon dioxide is denser than seawater. Injected at this depth, the carbon dioxide will fall to the seafloor, dissolve rapidly to form bicarbonate ions and eventually precipitate as carbonate. Ocean sequestration involves the considerable cost of compressing gas to 4,500 psi and piping it miles offshore. But there are other possible ways to achieve the same effect that need to be investigated, such as taking advantage of the fact that carbon dioxide forms a dense, solid hydrate at modest depths within the ocean. While work proceeds on the feasibility of oceanic sequestration, it is important to address the environmental issues associated with the process.

First, can the oceans absorb the necessary amount of carbon dioxide, and how would oceanic acidity be affected? Even though it already contains 140 trillion tons of dissolved carbon, the ocean is grossly undersaturated in carbon dioxide. The oceans can easily absorb the 35 trillion tons that would result from burning all the world's remaining proven reserves of coal, oil and natural gas. The addition of 35 trillion tons of carbon would decrease the pH of the oceans by 0.3, which is well within the natural range of variability of seawater at various depths and in different parts of the world.

Second, as carbon dioxide slowly dissolves, it creates local plumes of acidity. Are these plumes detrimental to fish or other life at the sea floor? Scientists at Monterey Bay Aquarium Research Institute in California have undertaken small-scale tests by discharging liquid carbon dioxide onto the seafloor and then watching the behavior of the marine fish. Fish swim up to the liquid blob, investigate it, and then calmly swim away, apparently with no ill effects. Current research is now focused on immobile and microscopic invertebrates found at, and under, the sea floor.

If one theme runs through the thinking about carbon dioxide sequestration, whether in the ocean or in geological formations, it is that more research is needed. However, bypassing the atmosphere by sequestering carbon dioxide directly in the oceans has the makings of a very elegant solution to controlling "man-made" carbon dioxide emissions to the atmosphere.

ADDRESSING THE CARBON ISSUE

I have covered this particular approach to carbon dioxide sequestration in some detail not because it is necessarily the best or the only possible solution, but because it is typical of the highly responsible and rigorous research work that is being undertaken by universities, institutes and oil companies to find cost-effective ways to mitigate the environmental cost of using fossil fuels. There is a growing understanding in our industry that a carbon-sensitive world offers us opportunities as well as threats. If the accumulation of "man-made" carbon dioxide in the atmosphere is a global problem, the separation, compression, transport and storage of it elsewhere will become huge businesses. Who else has the technical expertise, financial strength and global management skills to help stabilise the composition of the earth's atmosphere? The petroleum industry has the unique capabilities and the motivation to solve the carbon problem. Let me mention some of the initiatives that have been started recently to address the carbon issue.

BP, ChevronTexaco, Shell, ENI and several other oil companies are collaborating on a project to reduce the cost of carbon dioxide separation from stack gas.

Offshore Norway, Statoil responded to the concerns about hydrocarbon emissions by developing a system capable of separating one million tons of carbon dioxide per year from natural gas coming from the Sleipner reservoir and reinjecting it into the shallower Utsira formation. The process is being monitored using time-lapse 3D seismic surveys - an interesting adaptation of technology that was designed to monitor producing reservoirs.

Princeton University, BP and the Ford Motor Company have joined to find "credible methods of capturing and sequestering a large fraction of carbon emissions from fossil fuels." Together, the two companies will spend $2 million a year for the next 10 years to support this project.

Stanford University has formed a consortium of leading technology companies including Schlumberger, ExxonMobil and General Electric to address world energy and environmental concerns through the development of a portfolio of practical energy technologies that address the potential long-term risks of climate change. The 10-year Stanford University Global Climate & Energy Project (G-CEP) is designed specifically to accelerate the development and use of low greenhouse gas emission technologies. The involvement of Schlumberger will focus on the hydrocarbon reservoir addressing carbon dioxide sequestration issues.

During the 1970s, the future of our industry was threatened by concern over the supply of oil. Our response was to harness the creativity of our people and invest heavily in new exploration and development technologies. The results are impressive. Today, the remaining proven oil reserves are estimated to be 2,450 billion barrels, almost five times higher that the estimate of 550 billion barrels made by the Club of Rome in 1972. The price of oil has been stabilised at a low level, and consumer confidence in supply restored so that oil demand has grown robustly for the last 17 years.

Consumer concerns about the environmental costs of burning fossil fuels present a similar threat to the future of the oil and gas industry. Our challenge is to develop environmentally acceptable energy solutions that will allow the world to continue to benefit for as long as possible from the convenience and cost effectiveness of oil and gas and prevent any premature move to more expensive energy sources. These solutions will come through ongoing partnerships between the best academic institutions and industry to accelerate the development of commercially viable technology.

Given this growing industry commitment to confront the environmental costs associated with the use of our products, I am convinced that once again we will surprise our customers, critics and perhaps even ourselves by our ability to adapt to ever-changing customer needs. I am equally certain that oil and gas will continue to be the best source of energy solutions for most of this century.

An extract from the Dewhurst Lecture at the 17th World Petroleum Conference, Rio de Janeiro, September 3, 2002

This is one of almost 50 chapters and articles in the 336-page large format book, Before the Wells Run Dry. Copies of the book are available for £9.95 from Green Books.

Continue to Section D of Part One: Renewable Energy and Nuclear Power

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