The World is entirely dependent on oil. The transportation sector in particular, so vital in our society for carrying people, goods, food and materials, relies on more than 95% of its gasoline, diesel and kerosene derived from petroleum, and consumes about 60% of the oil produced. We also depend on oil for the large variety of petrochemicals and derived products such as plastics, detergents and synthetic fabrics that today are so ubiquitous in our daily lives that we can hardly think about where they come from.
Oil is so important because it is the most versatile among our three primary fossil fuels. It has a high energy content, is easy to transport, and is relatively compact. Coal is heavier, more bulky and more polluting. Natural gas on the other hand is cleaner burning but bulky in volume and requires pipelines or expensive liquefaction for transportation, which raises safety concerns.
Unlike the case of coal and gas, daily publications of oil prices, reserves and production rates are highly publicized and have immediate effects on our economies and lives. The outcome of every OPEC meeting is covered by the World media like a national or presidential election.
In Chapter 4 the point was discussed that proven oil reserves are estimated at between 950 and 1100 billion barrels . Dividing that figure by the annual production rate of 27 to 30 billion barrels suggests an availability of some 40 to 50 years. This number is called a Reserve/Production or R/P ratio. It is commonly used, especially in industrial reports issued by major oil companies, and can give a useful warning sign of resource exhaustion when the number starts to decline. Today, the R/P ratio is still actually higher than it stood at any time in the past 50 years. At the same time, oil prices are fluctuating rapidly, but even with the cost of a barrel at $70 as in the recent past, it is still cheaper than at the heights of the oil crisis in the early 1980s, when a barrel sold for well over $80 (inflation adjusted) . This frequently leads to forecasts that anticipate a still long and comfortable era of relatively low-priced and abundant oil allowing a smooth transition to other energy sources. This optimistic vision of our oil future, supported by some economists, has been championed by those who believe in the crucial role of prices, continued improvements in exploration, drilling and production technologies to provide adequate oil production supplies for many years to come. Accordingly, it is assumed that whereas there is a finite amount of accessible petroleum oil on planet Earth, this is basically irrelevant because oil extraction will cease long before its actual physical exhaustion. The point that matters is the cost to find and exploit new reserves. When this cost of exploration and exploitation becomes too high, then oil will be replaced by some other source of energy, leaving part of the oil left in Earth's crust. The challenge is to find acceptable substitutes before oil becomes so expensive to produce that it would disrupt the economic and social fabric of our society. It is argued that similar transitions have taken place in the past when wood was replaced by coal, or coal by oil. Based on this argument, running low on oil will not have major direct relevance. This view, however, is not realistic. A more appropriate evaluation is the inevitable depletion and therefore ending of the era of relatively cheap accessible oil. We are probably already entering into an irreversible decline in oil production following its peak. This prediction is based on consumption data compared with oil field discoveries, reserves and extraction data. In fact, the R/P ratio gives little information about the long-term fate of a resource. Furthermore, it assumes that production will remain constant over the years, which is highly improbable. So is assumption that the last barrels of oil can be pumped from the ground as easily and quickly as the oil coming out of the wells today. Globally, the demand for oil is expected to grow by some 2% per year over the next decades . Three important parameters must be considered to project the future of oil production: (i) the cumulative production representing how much oil has been produced to date; (ii) the amount of recoverable reserves present in the known oil fields; and (iii) a reasonable estimate of the oil that still can be discovered and extracted. The sum of these represents the ultimate recovery which is the amount of oil that will have been extracted by the time that oil production ceases permanently. The current mean estimate by the United States Geological Survey (USGS) for the ultimate oil recovery is 3 trillion barrels (3000 Gbbl) . This estimate has, however, been questioned as unrealistically high by many geologists, who set the ultimate recovery at more in the region of 2000 Gbbl (Fig. 5.1). Naturally, the yet to discover - and therefore today unknown - new oil fields are the most speculative and controversial part of these estimates. However, the amount of oil is clearly finite and the question is not whether we will run out of readily available oil, but rather when.
In reality, the rate at which a well, an oil field or even a country can produce oil rises to a maximum and then, after more than half of the oil reserve has been produced, declines gradually to unproductive levels. This trend was realized by M. King Hubbert, a noted American geophysicist who worked as a research scientist for USGS and Shell. He found that in any large region, the extraction of a finite resource rises along a bell-shaped curve that peaks when about half of the resource has been exploited. This assumes that no outside regulatory, legislative or other major restraints have been placed on extraction and exploitation. Following this concept, Hubbert predicted in 1956 that oil production in the lower 48 states of United States would reach a maximum sometime between 1965 and 1972  (Fig. 5.2). U.S. oil production indeed peaked in 1970, and has declined ever since. Larger oil fields are generally found and exploited first,
giving a discovery peak which, in the lower 48 states of the U.S., occurred during the 1930s. The production peak then follows after a time lag (40 years in the case of the United States) depending on the amount of reserves in place and the rate of exploitation. A similar pattern of peak and decline was observed in many other countries, including the former Soviet Union. Countries such as the United Kingdom and Norway are close to the midpoint, whereas other countries particularly in the Middle-East - namely Saudi Arabia, the United Emirates, Iraq, Iran or Kuwait - are still only at earlier stages towards depletion .
Hubbert, as well as several analysts including Campbell, Laherrere  and Def-feyes , also applied the method to the global world oil production, to determine when the peak for world oil production, the so-called "Hubbert's peak", will occur. For their calculations they estimated ultimate world oil recovery at between 1900 to 2100 Gbbl. Until now, about 900 billion barrels of oil have been produced. Accordingly, we are close to the midpoint of the oil era, corresponding to half of the ultimate recovery. The estimated peak for world oil production will occur between 2005 and 2015 [28,29]. Remarkably, these predictions do not shift significantly even if reserve and production estimates are off by some hundred billions of barrels . After the peak, world oil production will start to decline. What clearly matters, is not so much when our oil will be significantly depleted (not necessarily "gone"), but when the demand will begin to surpass production. Beyond that point, prices will inevitably rise sharply unless demand declines com-
1850 1875 1900 1925 1950 1975 2000 2025 2050
Figure 5.2 Hubbert's original 1956 graph superimposed line indicates actual oil pro-showing crude oil production in the 48 lower duction until 2004 following Hubbert's 200 U.S. States, based on assumed initial reserves billion barrels forecast. of 150 and 200 billion barrels. The bold,
1850 1875 1900 1925 1950 1975 2000 2025 2050
Figure 5.2 Hubbert's original 1956 graph superimposed line indicates actual oil pro-showing crude oil production in the 48 lower duction until 2004 following Hubbert's 200 U.S. States, based on assumed initial reserves billion barrels forecast. of 150 and 200 billion barrels. The bold, mensurably. This leads to the conclusion that a permanent oil crisis is rather close and inevitable.
In the forecasts, it was assumed that around 90% of the oil that can be recovered has already been discovered, putting the reserves at 900 billion barrels and the yet-to-find oil at only 150 billion barrels. This conclusion arises from the fact that today, about three-fourths of the world's oil reserves are located in about 370 giant fields (each containing more than 500 million barrels of oil) that are relatively well studied . As discoveries of these giant fields peaked in the 1960s, large additions to the known oil reserves are unlikely, unless new major oil fields in as-yet unexplored regions of the world are discovered . However, as mentioned, mankind has already increasingly gone to the "end of the world", even under the most hostile climatic conditions in search of oil, and only a few areas, such as Antarctica or the South China Sea, remain to be explored. This leaves little room for the discovery of a new Middle-East. Today, 80% of the produced oil flows from fields discovered before the early 1970s, and a large portion of those fields are already in declining production.
These rather pessimistic - though not unreasonable - forecasts however, usually do not take into account several elements, in particular economics and recovery factors. The oil recovery factor (which is the percentage of oil recoverable in a field) has increased roughly 10 to 35% over the past few decades due to the introduction of new technological advances such as three-dimensional seismic surveys and directional drilling that are now applied in most oil-producing fields. With continuing progress in so-called enhanced oil recovery (EOR) techniques, recovery factors from 40 to 50% are expected in the future, extending the global oil reserves. Oil prices can also play an important role. Higher prices trigger besides more economical use and savings, the exploration to find new oil fields, the exploitation of fields considered previously non-economical at lower prices, and the development of new extraction technologies. There is much more economically recoverable oil within the $50 to $100 per barrel price range than there was at $20, adding to our reserves.
As discussed, besides conventional oil there are also many non-conventional oil sources, including heavy oils, tar sands and oil shales. These add significantly to petroleum oil sources as their exploitation is becoming profitable with increasing oil prices. These reserves, as discussed, are many. The Orinoco belt in Venezuela has been assessed to contain a whopping 1.2 trillion barrels heavy oil, of which 270 billion barrels are thought to be economically recoverable . The Athabaska and Cold lake tar sands deposits in Canada may contain the equivalent of 300 billion barrels of economically recoverable oil . Non-conventional oil, because of its nature, is more difficult to extract than conventional oil. However, with technological innovations and massive investments, sources that were considered before as too expensive to exploit, are becoming economically viable. In Canada, the operating costs to produce a barrel of oil from tar sands (by in-situ recovery) fell from $22 to less than $10 between 1980 and 2003, making this non-conventional oil supply presently competitive with conventional oil . The requirement, however, for very large quantities of natural gas needed for the thermal recovery process may limit this favorable picture. The amount of oil extracted from the Atha-baska region is expected to grow from 1 millions barrels a day in 2004 to 2 million barrels a day within a decade. While proponents of "Hubberts peak" theory acknowledge the very large amounts of non-conventional oil resources, they also think that industry would be hard-pressed for the energy, capital and time needed to extract non-conventional oil at a level to make up for the declining conventional oil production. In their view, the exploitation of non-conventional oil would have only a limited effect on the timing of the world oil production peak. Production of these substitutes is, as also mentioned earlier, highly energy-intensive. For example, tar sands must be treated thermally, whether in situ or in treatment plants, to extract oil, using non-renewable, limited and valuable natural gas, and generating overall more CO2 than the production of conventional oil. These factors must be seriously considered. Eventually, atomic energy and all other sources of alternative, non-fossil energies could be used to allow the exploitation of these heavy hydrocarbon sources [30-32].
Numerous predictions have been made in the past concerning the peak point of global oil production. Mankind has been said to be running out of oil repeatedly since the beginning of its use on an industrial scale. As early as 1874, the state geologist of Pennsylvania, which was the largest oil producer at the time, estimated that there was only enough oil to keep the kerosene lamps of the nation burning for four more years. In 1919, the U.S. Geological Survey, using data based on R/P ratios, predicted that the "end of oil" would come within 10 years. In fact, the 1920s and 1930s saw the discoveries of the largest oil fields known at that time. Since then, many have prophesized the soon to come (generally within a few years or decades) end of oil. Among others, BP predicted in 1979 that the world production peak would occur in 1985 , while others forecast that the peak would occur between 1996 and 2000. A long history of too-often wrong predictions has led to general skepticism for new and generally pessimistic forecasts for oil's future .
Using an estimated "ultimate" recovery for conventional oil of 3 trillion barrels, similar to the USGS estimate, Odell, for example, predicted in 1984 that global oil production from conventional oil would peak only around 2025 . The steadily increasing exploitation of non-conventional oil sources could push the peak further as far as 2060, but at a cost clearly much beyond the period of "cheap oil" that we currently enjoy.
As we can see, predicting the future is not easy, as quoted by many renowned personalities. What is certain however is that there is only a finite amount of petroleum oil (and natural gas) on the planet Earth. Combined oil production from conventional and unconventional sources will soon - and certainly not later then the middle of the 21st century - reach a maximum and then decline (Fig. 5.3). It is thus imperative to start switching progressively away from oil-based fuels to alternatives. This switch cannot be delayed for too long, so as not to get caught in a real crisis with very high oil prices and all their economic and geopolitical consequences. In that sense, moderately high oil prices are not necessarily detrimental, as they flatten out or decrease excessive demand, encouraging at the same time savings and the development and transition to alternative fuel sources. Oil is
needed for the essential services, fuels and materials it provides us with, including heating, transportation and mobility. If other sources providing the same are found to be competitive or even better, we will switch to them. In the past in England and in most industrialized nations, coal replaced wood when the latter became increasingly scarce and therefore expensive, as well as being inferior to coal in its caloric value and convenience of use. During the 20th century, oil took the place of coal in many uses, not only due to its lower cost but also because it was easier to transport, cleaner, more flexible, and had a higher energy density. Oil was convenient as a transportation fuel, in household use, industrial production, and in electricity generation. Following the oil crises of the 1970s, the utilization of oil in many areas decreased dramatically in favor of natural gas, together with nuclear power for electricity generation as well as a renewed interest for coal. Currently, the largest oil-consuming sector in most industrialized countries is that of transportation, with more than 95% reliance on oil. Therefore, a major reduction in oil consumption will have to come from this sector through more efficient internal combustion engines, the introduction of new technologies such as hybrid propulsion and fuel cells, or the use of alternative fuels. The production of liquid fuels (called syn-fuels) from coal was shown to be technically feasible during the 1930s, and has already been used in some special situations as during World War II by Germany and South Africa during the Apartheid boycott era. Considering its large available coal reserves, similar operations were studied by the United States as a response to the decreasing domestic oil production and increasing oil prices, particularly following the oil crises of the 1970s. These plans, however, were rapidly given up when oil prices stabilized in the mid-1980s. It was generally thought that only when the price of a barrel of oil rose above $35-40 and remain at that level for a long period of time, would it become economically feasible to consider producing synthetic fuels. Nevertheless, even if the production of liquid fuels from coal or natural gas were to be economically viable on a large scale, it would necessitate vastly increased production of these non-renewable fossil fuels and still be very wasteful from an energy point of view. It would also generate increasing amounts of CO2, greenhouse gas, SO2 and other gases, as well as solid waste. Natural gas liquefaction, as discussed earlier, is gaining increasing significance as a means of easier transportation from remote areas, and also as a source for the production of liquid hydrocarbon fuels and products. The Fischer-Tropsch chemistry used first converts natural gas into syn-gas, and then to hydrocarbon fuels. The direct conversion of natural gas (methane) into liquid fuels, primarily through methanol without first producing syn-gas, is therefore of great interest and promise (see Chapter 12). Such processes, which are still under development, could result in the direct commercial production of methanol from methane. Methanol, as a liquid, has the advantage of being much more easily transported than methane. It is also a convenient fuel for internal combustion engines or fuel cells, and can be converted catalytically into ethylene and propylene, and through these into synthetic hydrocarbons and their products.
In a way, natural gas is often seen as a successor to oil because it burns more cleanly, releases less CO2 per energy unit than any other fossil fuel, and there are still large reserves available. It is, however, more expensive to transport and store than oil, necessitating huge pipeline networks on land and liquefaction to LNG for overseas shipping. Furthermore, due to its lower energy density its use as a transportation fuel has been generally limited to vehicles able to accommodate large pressurized tanks, such as buses. Natural gas is consequently employed mainly in stationary applications such as heating, cooking and electricity generation. Despite the dramatic increase in consumption, having more than doubled since 1970, our proven natural gas reserves are now three times larger than 30 years ago, with a R/P ratio close to 70 years. Regarding the ultimate recoverable amount and the future of natural gas as a fuel, similarly to petroleum oil, there are two major opposing points of view. One side claims that the amounts of natural gas to be ultimately recovered are only equal to or even less than those of petroleum oil. The other side, asserts that there is still enough natural gas left to fill our growing needs for a long time. By adapting Hubberts concept to predict the future of world gas production, Campbell and Laherrere - the most prominent proponents of this method - forecast that gas field discoveries and production would follow the same pattern as that of oil, and that global supplies of natural gas will decline not long after that of oil. Laherrere estimates the world ultimate natural gas reserves at 350 Tm3, and conventional sources as representing 280 Tm3. Unconventional sources such as coalbed methane, tight sand or shale gas are estimated around 70 Tm3. Based on these estimates, if the consumption rate continues to increase at the current pace, world gas production would peak around the year 2030 . Hubbertians, therefore dismiss gas as a viable long-term alternative to oil to fulfill our future energy needs. However, economic conditions and increasingly higher natural gas prices may also cause the demand to decrease and thus extend its availability. As in the case of oil, there are other estimates that are more optimistic. The USGS assessed the global conventional natural gas resources as over 430 Tm3, the energetic equivalent of almost 2600 billion barrels or 345 Gt of oil . Other recent estimates for ultimately recoverable conventional natural gas range between 380 and 490 Gt oil equivalent . Consequently, Odell forecasts a conventional natural gas production peak at around 2050 [38, 39]. Taking also into account unconventional natural gas sources, he predicts the extraction peak for combined conventional and unconventional natural gas by 2090. As the recoverable resources for unconventional natural gas are known to an even lesser extent than those for conventional natural gas, this prediction is at best speculative. Some unconventional gas sources such as coalbed methane and tight gas are already exploited on a large scale, principally in the United States. There is a very large potential for the utilization of methane hydrates, which are considered to be present in staggering quantities under the sea floor and arctic permafrost. First, however, these must be assessed more accurately. Further, their practical exploitation must be demonstrated by the development of new and effective technologies. Until then, methane hydrates remain a promising, but as-yet uncertain, energy source.
When considering unconventional sources of natural gas, an interesting but as-yet unproven theory which was developed and vigorously defended by late Tho mas Gold (a noted astrophysicist) should also be considered. This involves the possible availability of large natural gas resources of abiological or abiotic origin at greater depths in the Earth's crust (abiological deep methane) . According to this suggestion, extraterrestrial carbon of asteroids could have combined under high temperature and pressure deep under the Earth's surface with hydrogen to form hydrocarbons. The most stable of them, methane, would then migrate to the outer crust and accumulate in geological formations. Following this concept, at least part of natural gas could be of non-biological origin. For the time being however, this suggestion of abiological natural gas remains controversial. Observations that vents deep on the bottom of the oceans discharge methane were later recognized to be due to the discharge of hydrogen sulfide which then converts the CO2 of sea water to methane under the influence of microorganisms.
Based on our present knowledge, natural gas must also be considered as a finite resource, the production of which will - not unlike that of oil - reach a peak, most probably during the latter part of the 21st century. As in the case of petroleum oil, new solutions must therefore be found to replace progressively declining natural gas reserves.
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