What is a combustible fuel?

In the 20th century, coal was a resource that would not be exhausted in anyone's lifetime, and in the last decade of the 20th century, the resource base of coal was sufficient to meet the needs of the next 400 years, and at an annual growth rate in consumption of 26%, the estimated proven reserves published by the World Energy Council in 1980 would last for nearly 80 years (Note 5). If priority is given to the adequacy of energy supplies, coal as a resource cannot be ignored; if priority is given to environmental protection, coal must be exploited with caution. The latter is particularly relevant to this chapter, because converting a resource into reserves cannot be done without cost and technology, while using raw energy causes environmental pollution, and such decisions will inevitably hinder the expansion of coal reserves.

Coal Formation

One thing worth noting is that we can trace the entire evolution of coal without interruption. Coal formation requires many conditions, but it is generally formed from decaying plant remains at the bottom of swamps, where trees and other swamp plants die and fall into the water around them, and although some animals such as termites consume the dead plants, and the dead plants oxidize in the air, these processes are slowed down by the burial of the water, and so neither is able to consume all of the dead plants. Over thousands of years, large quantities of dead plants continue to accumulate, and the material below is compacted by the overlying material; these accumulations are called peat bogs, and it is evident that peat is a plant fuel formed from recently extinct material, and the process of peat-formation begins when peat bogs are buried by geologic movement below the rocky deposits.

The process of marsh evolution, sea level rise flooded the marsh, sea level fall dried up the marsh, geologists will be the rise and fall of the sea level are called "sea in" and "sea retreat". The marsh area is more like a stagnant water area, sometimes flooded, sometimes dried up, and the vegetation also undergoes this cyclical slow process. By observing the distribution of coal seams in a given area, paleoecologists can study the evolutionary patterns and consequences of this land- and water-guided vegetation follow-up.

The process of coal formation and evolution has a compaction phase, i.e., the extrusion of fluids, and most of the extruded fluid is water, so that more and more carbon-rich solids are left over from the compaction process for a given volume or mass. Carbon compounds are the source of chemical energy in coal, so it can be said that compaction increases the amount of energy contained in a given volume of coal.

Rank and quality

Coal that is early in age and highly compacted usually has a higher density of chemical energy (i.e., the amount of energy contained per unit mass) than coal that is later in age. Coal with a high energy density and a high degree of maturity requires less coal to be extracted for a given amount of energy and is therefore easier to transport. The maturity of a coal is its rank, and the different ranks and their characteristics are given in the appendix. Lignite is the shortest maturing coal, usually peat buried under sediments after the sea has receded; bituminous coals come next, and there are a number of different grades within this broad category, reflecting the fact that as the depth of burial deepens and the length of time of burial increases, it becomes less and less moist and less rich in volatiles (e.g., methane); anthracite is the earliest maturing coal, and is the most altered from its original vegetative state, with little or no moisture, and no volatiles. Anthracite is the earliest coal to be formed and has changed the most compared to its original plant state. The higher the rank of the coal, the higher the energy content and the harder it is, so there is no simpler way to categorize coal than to divide it into "hard coal," which has an energy content of 10,260 BTUs per pound or more, and soft coal, which has a lower calorific value. The energy content of coal is affected by the fact that during compaction, fluids are squeezed out and some volatiles, usually methane, are lost. Some people are initially surprised to see the increase in ash content with higher grades of coal; in fact, most of the material extruded during compaction is water, and the ash content (either by volume or by weight ratio) increases with the carbon content. If this is the case, doesn't higher ranked coal burn with more smoke? Not really. The question has to be viewed in relation to the energy content and the ash content, the rank can be determined by assay, and it is interesting to note that the results of rank tests show that the rank of a coal is not directly related to its calorific value or depth of burial, but more to its brightness. Geologists and geochemists have given the test an extremely catchy name: vitrinite reflectance. It simply means that the specular body component (mostly carbon) has a flashiness that increases with age and grade. Rock collectors should be able to notice that anthracite is as shiny in color as obsidian, while bituminous coal is dull black, lignite is called lignite because of its shapeless appearance, and peat is pretty much the same as the stuff you fish out of the bottom of a compost pile.

There are also many tests, including determining the coagulation properties and free expansion index of coals, related to how they behave during either slow or fast oxidation. These parameters can indicate which coal is best suited for the purpose.

By liquefaction or gasification, coal can be converted into a liquid fuel - a synthetic fuel. This potential was discovered by accident. Synthetic fuels overcome the disadvantages of coal's inconvenience and, to some extent, its environmental hurdles, such as pollutants like sulfur compounds that can be removed in the synthesis process. However, the synthesis process consumes energy, so there is an efficiency cost, which makes the cost of coal products too high, and at present, synthetic fuels from coal still cannot compete with oil and gas products.

Table 1.1 gives the proven reserves and calorific equivalent values of known coal resources around the world. It should be noted that some of the areas in the table have very small resources, but these areas have also been poorly explored; for example, the U.S. Geological Census Bureau is currently surveying sub-Saharan central Africa, where it is expected that there may be large, but so far unknown, resources of low-grade coal.

Table 1.1 Proven reserves of hard coal in different regions Source: Hedley, Don 1986, World Energy: The Facts and The Future, Euroraonitor Publicatitms, London, p. 186.

If these figures are compared with the world's annual energy consumption of about 300 quarts, the reserves are undoubtedly huge. The fact that most of the proven reserves are concentrated in the developed countries, and the fact that one third of the total proven reserves in sub-Saharan central Africa are in and controlled by South Africa, also illustrates this point. Is industrialization possible only in regions with coal resources, or can coal reserves be found only in industrialized countries?

Oil and gas

The projected resource base for global oil is 2.2 trillion barrels (5.8 million BTU/barrel), equivalent to 12,700 quarts. Of this, 610 billion barrels are recoverable reserves (note 6), and in the 1960s M. King. M. King Hubbard noted in his book that undiscovered resources have the potential to add another 600 billion barrels to the reserves, essentially doubling the current controlled reserves predicted by experts (Note 7).

Oil and Gas Generation

It is generally believed that oil and gas, like coal, are formed from the remains of large quantities of dead plants and animals, and that the conditions in which these materials are buried save them from consumption or oxidation by other organisms. Though offensive to the advertising department, scientific theory does suggest that dinosaur remains do not make up a major portion of oil deposits, and that certain dinosaurs, as large as they were, would have required millions of such big guys to die in the same place for even a moderately sized oil deposit. Oil and gas deposits are more likely to consist of numerous small aquatic organisms that feed on the rich nutrients that overflow into the sea (and sometimes lakes). As a result, many oil deposits are located in ancient deltas, from which rivers can carry large quantities of nutrients and detritus to the sea.

Things change, and rocky sediments (mud, silt, and sand) gradually leave the rivers and begin to pile up, forming huge layers of sand, silt, mud, or layers of chemical deposits, such as calcium carbonate. Just like coal formation, more and more rock material is deposited over layers rich in decaying organic matter. Normally, as the rock is deposited, the fluid in the rock voids forms a continuous phase so that the fluid at any depth can support the weight of the overlying fluid (hydrostatic head), and similarly the rock particles remain in continuous contact, supporting the weight of the overlying rock particles. This situation is the result of a process of deposition and compaction, a process in which the added sediment pushes out fluid from the compacted sediment below. However, as the depth of burial increases, it is more likely that the impermeable layer interrupts the continuity of the expelled fluid, and the confined fluid must carry some of the load of the rock, which results in a rapid increase in pressure, a condition known as overpressure, which is typical at depths below 10,000 ft. This is called "overpressure" and is typical at depths below 10,000 feet.

There are three conditions under which oil and gas reservoirs exist: pore-permeable rock, confinement, and oil-bearing rock. Pore-permeable rocks make up the reservoir itself, with oil and gas stored in a large number of tiny pores between rock particles and between crystals in rock formations such as sandstone or chert. Increasing rock loads during burial force fluids out of the shale material that is being compacted, and the oil and gas move up through the water in the pore and permeable reservoirs to occupy the tiny pores between the grains or crystals of the reservoir rock, while a portion of the water is always left behind in the rock deposits. There is generally a layer of water at the periphery of the rock particles, with oil and gas occupying the intervening pore spaces, and the lighter oil and gas moving up to the surface and spilling out to the atmosphere, unless a trap, i.e., a nonpermeable layer, is encountered. Figure 1.1 shows the pore morphology of the reservoir as observed under a microscope.

Figure 1.1 Reservoir pore space Note: The light-colored area represents sand grains, the light-shaded portion is water at the periphery, and the dark-shaded portion represents oil or gas in the center of the pore space. The reservoir rock shown in this figure has good physical properties. Image courtesy of Mr. Loyd Brown

Almost all oil reservoirs contain some amount of gas. Some of the gas can be dissolved in the oil, like carbonic acid in a drink, but if the amount of gas exceeds the amount that can be dissolved, a free gas top forms, and because gas is light and mobile, a small amount escapes to the surface through microfractures or pore paths, which is mostly methane.

Fluid hydrocarbons are essentially produced in aqueous phase (oceans, rivers, lakes) depositional environments. Water initially fills all the pores of the reservoir rock, and even if a large amount of hydrocarbons were transported into the reservoir rock, it would not be able to displace all of the primary water. If large amounts of hydrocarbons are not transported to the reservoir rock, there is more water remaining, and the more water in the pore space, the worse the reservoir performance.

Oil Markets

Oil began to attract attention from time to time in the mid-19th century (oil was found seeping to the surface in Oil Creek, Pennsylvania). While oil could be burned, the amount found on the surface was not large enough to be commercial in scale, and it burned with pungent smoke. Some pioneering entrepreneurs fished the oil out of the streams, bottled it, and sold it as a rare medicine. About 1850 Samuel Kier put into operation the first petroleum still to process oil from salt wells, and the distilled product became an excellent oil for lighting, whereupon demand instantly soared, and over the next few years its price increased dramatically from 75 cents to $2 per gallon (note 8).

In 1859 Edwin Drake hired a salt-well driller to drill a well near Titusville, Pennsylvania, and encountered a fissure at a depth of from 62 to 67 feet, which was capable of gushing out about 10 barrels of oil a day, which was certainly an extremely high yield when compared with the former production of oil which had only been fetched from a surface fissure or from the surface of a creek. that was undoubtedly an extremely high yield. The new abundance of oil quickly proved its great potential as a fuel, triggering the first round of drilling, and by the turn of the 19th and 20th centuries, hundreds of wells had been drilled in western Pennsylvania and northwestern Virginia. The drilling frenzy sent oil prices plummeting, and demand, though rising quickly, lagged behind the growth in production. Production at the time fluctuated wildly, and when production came up, new discoveries brought prices down, and sustained demand growth would send them up again.

Liquid fuels have distinct advantages over solid fuels. Liquids can flow from the point of storage to the point of use, just as kerosene moves up a wick or gasoline flows into an engine, and the point of fuel is always assured of a small amount of fuel, which burns more evenly and is easier to control. Fluid fuels can also be treated with a simple distillation process to meet different combustion standards, including cleaner burning standards. These advantages have made petroleum increasingly popular with consumers, and its market share is quickly surpassing that of coal.

The early years of the petroleum industry, though "crude" (crude), were characterized by rapid growth. Petroleum geologists quickly discarded the notion that oil flowed in underground rivers. Improvements in drilling and extraction techniques followed. By the early 20th century, oil was being produced in the shallow waters of the Gulf of Mexico and in various other parts of the world.

Once discovered, oil, an energy source, flowed dutifully to consumers under pressure from the strata themselves, something that had never happened before. The vast majority of the investment in the acquisition of this energy source is in the drilling of wells, and once the wells are drilled, subsequent production requires neither a large amount of labor nor is otherwise very costly. The fact that it costs so little and produces so much makes oil a source of wealth, hence the name "black gold". Nevertheless, its value per unit of volume or weight was not prohibitively high, and even in the 1970s, when prices skyrocketed, the price of oil (or its refined product, gasoline) did not exceed the price of any liquid product, such as milk. But at a time when a single well could have an initial production rate of 20,000 barrels per day, or even 30,000 barrels per day, and such a well could earn nearly $250,000 per day even at the low oil prices of the 1980s, the profitability of such wells was unquestionable. Of course, such high-producing fields were extremely rare, and the success rate of exploratory wells at the time was only 5% (based on the geological information available). If you compare it to milk, no cow can produce 30,000 barrels of milk a day, so the farmer doesn't have to go to the trouble of buying 19 cows for nothing to find another such high-producing cow, and he's not likely to spend $1.2 million dollars on a cow that doesn't produce milk.

Liquid fuels are more convenient and energy-dense than any other kind of fuel. The fuel led to the development of self-powered "horseless carriages," and the automobile industry grew so rapidly that adults in the U.S. soon owned one. Ghawar) mega-field in Saudi Arabia.

The abundance of oil resources has contributed greatly to the growth of the U.S. economy, and increased demand has fueled the growth of the oil industry. Oil profits came mainly from sales, and international production met much of the market demand, but governments in exporting countries began to nationalize oil production after they realized that a huge source of their wealth was being produced by foreign companies and that the fruits of that production were being enjoyed by foreigners. In some places, nationalization has been gentle, such as Saudi Arabia's sharing of ARAMCO (the Arabian American Co.), which was restructured so that the original oil-producing company retained an operating interest; in others, however, it has not been so gentle, such as Libya. But nationalization in other places was not so quiet, such as Libya's nationalization of its interest in British Petroleum, and the nationalization process in Iraq and Iran (Note 9). 1960 saw the formation of the Organization of the Petroleum Exporting Countries (OPEC) by Venezuela, Saudi Arabia, Kuwait, Iran, Iraq, and Indonesia, but it wasn't until 1973 that the organization was strong enough to compete with the Western oil companies in terms of oil prices, and the member countries even came together for consultations. came together for consultations, while the Arab countries also used the fledgling power as a political weapon. At this time, the U.S. relied on imports for 36 percent of its oil supply, and the oil embargo hit the U.S. hard.

Americans thus experienced a prolonged period of oil shortages and rising gasoline prices.OPEC members were acutely aware that if they kept production low and prices high, then in the long run their oil would be worth more. We can take the comparison with agriculture again: farmers don't have the option of delaying production, and crops not harvested today will be lost after farm time; but OPEC had no oil production in 1973 and could save it for the future. Some have denounced this market manipulation as "illegal," while others have accused Americans of "breaking the rules" with their buyer's monopoly (a buyer's monopoly, as opposed to a seller's monopoly, is a situation in which a single consumer, or a group of consumers, acts in concert to control demand by controlling a large portion of a market's prices). The question of who is to blame, and the different conclusions reached by each person's view of nationalism, market freedom and fairness, are questions that cannot be answered simply, but the key is to understand that it is the "irregularities" and "foul play" described above that lead to The key point is to understand that it is these "violations" and "fouls" that have led to the supply shortage.

Rising gas prices have hit Americans hard. The once cheap and abundant energy supply shrunk dramatically, prices soared, and from 1973 to 1983, Americans saved nearly 20% on oil and reduced total energy consumption by 11% (in fact, energy consumption fell from a peak in 1979 to a trough in 1983, a situation that in turn demanded an increase in energy use) (note 10), and during the same time, the U.S. domestic oil production boom, which had been lagging for many years, was set off. boom. Shallow, large oil fields had been discovered decades earlier, production had long since diminished, and imports of foreign crude oil discouraged incentives to drill deeper wells, to find new fields, or to target old fields with expensive new technologies to increase recovery (it should be noted that wells do not increase proportionately in cost when they reach their production limits, and that this so-called production limit is still a very high production rate in international terms, while most American wells have been producing at their production limits for years). The U.S. domestic oil shortage manifested itself in two ways: the domestic production and reserve base was declining; and the growth in demand was being met by increased imports of crude oil. U.S. petroleum engineers and chemists were well aware that fields with diminishing production still had two-thirds or three-quarters of their original geologic reserves remaining in the ground (the technical reasons for this will be explored in the next chapter), reserves being that portion of the known resources that could be produced under existing technological and economic conditions. As a result, oilmen have assiduously pursued enhanced recovery technology, using it to double the reserves of the United States and to increase production from old fields by a large percentage.

The first oil crisis, followed by the first energy crisis did not occur in the 1970s.Energy crises lead to the transition from one energy source to another, and even affect the rise and fall of nations.Oil shortages in the United States and Europe caused energy crises in both world wars.In 1943, the U.S. Secretary of the Interior (and oil magnate) Harold Ickes ( In 1943, Harold Ickes, the U.S. Secretary of the Interior (and oil magnate), published an article titled "We Are Running Out of Oil," and in 1948, the U.S. proposed an "energy crisis." The Suez Crisis of 1956 caused a major disruption in the market for energy, and at that time, an oil embargo was placed on the U.K. and France, not on the U.S. The Six-Day War of 1967 was followed by the Arab Crude Oil Crisis. Six-Day War was followed by an embargo by Arab crude producers, and the 1973 embargo was more successful and far more far-reaching, with both embargoes causing oil prices to rise sharply (note 11).

The rise in oil prices was followed by a sudden rush by Western consortia to increase their investments in Third World crude oil producing countries. The main thrust of traditional development theory is that development requires the injection of large amounts of capital [the lack of infrastructure in underdeveloped countries that can absorb capital is a phenomenon that demonstrates the fatal flaw in traditional theory. Ahmad Abubakar explains why] (note 12), many poor oil-producing countries have been given huge loans, while their oil wealth has been divided equally.

Exploration is heating up globally, new technologies are increasing reserves, demand is saturated, and the supply of oil has been roughly equal to the demand. But under pressure, the burden of huge loans to the oil-producing countries still have to maintain a high level of production, production capacity continues to increase at the same time, the world market price of crude oil has been declining. Too many oil-producing countries have abandoned crude oil production limits in order to maintain their financial credibility internationally. OPEC has tried to set an output limit for each member country, but at this time several non-OPEC member crude oil exporters have appeared, and what's more, there are still several heavily indebted member countries that have lied about their production in order to fulfill their loan repayment tasks.

The combination of all aspects of market pressure caused oil prices to plummet within a couple of years, to a low of less than a third of the highest oil prices. In the U.S., buying imported crude oil again began to be cheaper than producing its own marginal wells, and by 1990 the U.S. was importing more than half of its crude oil, more than it had before the 1973 oil embargo, and if it did not rely on imports, there would be a shortage of crude oil, and the shortage would continue, but if it chose a purely free-market mechanism (which would include the foreign market) there would not be a global shortage of supply.

Americans have always had contradictory views on energy supply. On the one hand, Americans believe that there should not be any restrictions on the market and that the cheapest oil should be purchased; on the other hand, when there is a disruption in supply and a shortage at home, Americans want politicians to step in to get the oil companies to stabilize the price of oil. Americans want to make sure that there is enough supply so that they can drive wherever they want, and Americans want to force other crude oil exporting countries to supply "us Americans" with crude oil from their fields. 1990, when demand was curbed by the U.S. sanctions against Iraq and Iraqi-controlled Kuwait, politicians and consumers alike spoke out against oil. Consumers spoke out against the rising prices of petroleum products, partly supplied by oil extracted during the previous low oil prices. This situation is a wonderful irony: when oil prices fell in the 1980s, the producing wells of the time, all of which had come on stream in the late 1970s when oil prices were high, were costly to invest in but had no mechanism to keep oil prices up. Does it make sense to pin price reductions on production from high-cost wells when there is a buyer's market, and to demand that oil prices not rise when a seller's market emerges?

This opposition to higher gas prices reached a crescendo during the Year of Planet Earth, when Americans and much of the world became committed to the environment out of fear of a worldwide return of temperatures, acid rain, and so on. Newspapers and magazines blamed fossil fuels for the environmental crisis, but when it came to limiting energy use through price increases, the increases were not accepted.

Environmentalists themselves are full of oil consumers, and their changing attitudes are not to say that the environmental movement is not important, indicating that this phenomenon is not to sing the praises of the oil industry, only to note that: the operation of each company may reflect some of the personality traits of its leaders, but after all, the company is not a human being, and the energy company, like any other company, has to respond to the market and try to maximize its profits. maximize their profits. So accusations that these companies are short-sighted, don't pay enough attention to the environment, or fail to protect marginal markets (consumers who can't afford it) carry a lot of weight, but they must be borne by all, and accusations of intentional offense or malice are meaningless.

Future production potential

The market forces that control the behavior of a company are twofold: on the one hand, consumers buy the product; on the other hand, consumers buy shares in the company and thus own it. In the latter case, it is the individual who makes the strategic plans for the company, while in the former case it is the individual who plans for the company's production. As long as consumers still need large amounts of energy, this need provides the driving force for increased production, which has always been closely linked to the state of the economy, and as long as the shareholders establish priorities for the return on their investment, prices in the short term are set accordingly.

All this is to say that oil and gas should be seen as a finite but not ultimately depleted resource. At the time this book was written, supply was still changing with demand, and this will continue into the 21st century. At current levels of consumption, the world's existing reserves could last until the 21st century 30s, but there are still many undiscovered reserves, and geologists and engineers are convinced of this, otherwise there would be no more exploration drilling. Because supply is lower than demand, reserves can be increased substantially by producing from old declining wells using enhanced recovery techniques within the known resource envelope.

There is still a large portion of the world that has not been explored. Just for comparison, there are 600,000 producing wells in the U.S. compared to only 6,000 on the African continent, which has more sedimentary basins than the U.S.; and further, even in fully developed fields, the recoverable reserves of oil have never exceeded one-third of the total known resources in the reservoir. There is still a great deal of oil waiting to be discovered, and much more that could be produced from older fields if necessary (see Table 1.2). So it is fair to say that people alive at the time this book was written will hardly be alive to see the day when oil and gas reserves are depleted.

Table 1.2 Oil and Gas Reserves in Different Regions of the World Quart Source: Derived from data in the Oil Gas Journal, Dec. 25, 1989, pp. 44-45. Unconventional Oil and Gas Resources

Many authors view tar sands, tight gas-bearing sandstones, and geopressurized aquifers (gas-bearing) as separate resources, and their assignment to a large category in this book represents only the extremes of conventional oil and gas. Tar sands are also oil reservoirs, with the difference that they do not contain lighter hydrocarbon molecules, so the oil cannot flow, and at one time in geologic time such reservoirs may have been conventional oil reservoirs, but they were gradually exposed to the surface by erosion, and over an unknown number of generations almost all of the lighter molecules evaporated. Canada is well known for its tar sands, especially famous for the vast expanse of the Athabasca.

Dense gas-bearing sandstones, which are very shale-rich gas reservoirs, are essentially impermeable, making it difficult for fluids to pass through. The gas has little viscosity because of its very small molecules, so some production from such reservoirs is possible, and the reservoir production enhancement techniques to be discussed in the next chapter can be used for such reservoirs. The resource and reserve figures given in this book include the unconventional resources described here, but the resources of tight gas-bearing sandstones are likely to be underestimated because the shale reservoirs in which tight gas-bearing sandstones are found are often ignored in conventional exploration.

Ground-pressure aquifers are sandstone formations that are 100% water-saturated, but with dissolved gas in the water, just as a beverage is saturated with carbonic acid. Technically, all formations are under ground pressure, i.e., each is under pressure from its overlying formation, and ground-pressure aquifers are special in that the water contains a lot of dissolved gas under very high ground pressure. It is possible that these water-bearing formations could be exploited for the gas in them if the price is guaranteed.

Casein

Casein, like coal, is a primitive source of energy with a large resource base that has not yet been proven to be economically viable, so there are no reserve estimates, and some projects, such as in northwestern Colorado, where UNOCAL (United California Oil Company) at the Parachute Creek Some projects, such as UNOCAL's Parachute Creek site in northwestern Colorado, have produced a certain amount of shale oil, but there are project subsidies, such as price guarantees, for this production. The production of synthetic crude oil from cheese root has a number of technical hurdles and, in the long run, a less than optimal cost/efficiency ratio. If oil and gas resources are depleted and energy prices rise back to the levels seen during the energy crisis, large-scale exploitation of such resources is possible. But energy prices really need to be that high to trigger commercial production of other resources as well.

Biofuels

Biofuels are the latest demise of biochemical energy, a primitive source of energy that is more complicated to evaluate. Some authors insist on overstating the resource base of biofuels without considering the application of "agricultural waste products," while others ignore the past and current contributions of biofuels to humanity. In fact, biofuels have been the primary fuel for mankind since before the advent of coal in 1880 (Note 13), and about half of the population still relies on biofuels to meet their energy needs, but these are mostly poor people with such low energy needs that many energy analysts have ignored the contribution of biofuels. Whereas other experts believe that the total energy from all biofuels is 15 to 20 times the amount of energy currently produced industrially by mankind, "they also point out that only a small fraction of biofuels has the potential to provide energy" and that if sustainability is to be assured the annual consumption of biofuels must be less than the annual growth (which is a necessity that This is because these organisms have many other uses besides fuel, including providing food for humans, livestock and wildlife). The energy content of the total plant growth on Earth is estimated to be about 3,000 x 1015 BTUs, of which 23% is in swamps, meadows, and tundra zones; 29% is in forests, 10% is in crop fields, and 38% comes from aquatic plant systems.

There are several logical assumptions that can account for bioenergy production, and thus determine whether biofuels are truly sustainable. A study by the International Institute for Applied Systems Analysis (IIASA) showed that up to 40 percent of plants grown on land can be "carefully planted," resulting in 750 quarts of energy; but crops and wood account for 56 percent of that. This leaves 330 quarts of energy, and another 60 quarts can be obtained from the waste products of agriculture and the timber industry. Considering that the efficiency of energy conversion is generally less than 50 percent, only 180 quarts of energy can be obtained from this if the management and production processes are in place (Note 14). Since the amount of base resources can be used without regard to recoverability or efficiency, the total annual resource base should be 390 quarts.

Some may counter that improvements in cultivation methods will increase annual output, but some of the practices that make agriculture highly productive are themselves very energy intensive, and losses during harvesting and transportation should be taken into account in calculating the total reserves of plant fuel. Furthermore, even in forests, a large portion of this biomass is not wood fuel, including wildlife, small plants, microorganisms, and so on. A complete harvest would mean stripping the land bare, which would be extremely bad for the environment.

If the large resource base of biofuels is converted to reserves and the issue is revisited, the best use of land (best use) and biological resources must be considered. Society has become increasingly aware of environmental issues, and IIASA studies have shown that 60% of terrestrial plants are not suitable for energy production, which may also be based on geographic reasons (Arctic tundra plants are scattered and difficult to collect efficiently) or environmental considerations (preserving a portion of the original forest), but whatever the reason, various data suggest that more than half of the available biofuels have already been utilized. It should also be noted that harvesting all agricultural waste and forest growth organisms is extremely detrimental to the environment, and that residues and stubble from fields and forest surfaces are essential to prevent soil erosion and support small life forms that digest organic matter, which is extremely beneficial to the soil.