Reserve recoverable

For an offshore field, recoverable volumes of less than 0.5 trillion scf (Tcf) are typically uneconomic to develop. This would equate to an oil field with recoverable reserves of approximately 80 MMstb. 

So far, the economics of developing discovered fields has been discussed, and the sensitivity analysis introduced was concerned with variations in parameters such as reserves, capex, opex, oil price, and project timing. In these cases the risk of there being no hydrocarbon reserves was not mentioned, since it was assumed that a discovery had been made, and that there was at least some minimum amount of recoverable reserves (called proven reserves). This section will briefly consider how exploration prospects are economically evaluated. 

Table 2. World Estimated Recoverable Reserves of Coal in Billions of Metric Tons...

The importance of a coal deposit depends on the amount that is economically recoverable by conventional mining techniques. The world total recoverable reserves of lignitic coals were 3.28 x 10 metric tons at the end of 1990 (3), of which ca 47% was economically recoverable as of 1994 (Table 4). These estimates of reserves change as geological survey data improve and as the resources are developed. 

Country Proved in place Resources, 10 tce Proved recoverable reserves Added recoverable b reserves 1980 Production, 10 tee 1987 1989 1990 ... 

A comparison of available resources and production shows that Germany, ranked second in resources, was ranked first in production in 1990. Indeed a number of central and eastern European countries are producing proved recoverable reserves at a rate that should lead to exhaustion of local deposits before the end of the twenty-first century. On the other hand, the massive Russian reserves could allow production for a much longer time. 

Resources. World resources of silver are estimated to be about half a million tons. However, only about 250,000 metric tons are considered economically recoverable reserves. These are associated with ores of copper, gold, lead, and 2inc, and extraction depends on the economic recovery of those metals. Canada and the CIS vie for the greatest reserves of silver in the ground. 

The part of the resource that is economically recoverable varies by country. The estimates made in the survey show that the proven recoverable reserves would last about 1200 years at the 1988 annual rate of production and that the estimated additional amount in place represent almost 1700 years at 1988 annual consumption. 

On a uniform calorific value basis, coal constitutes 69% of the total estimated recoverable resources of fossil fuel in the United States. Petroleum and natural gas are about 7% and oil in oil shale, which is not as of this writing used as a fuel, is about 23%. The 1989 total recoverable reserves of coal are about 500 times the 1989 aimual production (2), whereas the reserves of oil and gas are smaller, the production and consumption rate of oil and gas in the United States is three times that of coal. 

The demand for energy is continually increasing and the highest energy consumption in the world occurs in the United States. In 1989 consumption totaled 8.6 x 10 MJ (81.3 x 10 Btu) or 11.7 metric tons of coal-equivalent per capita (85). World recoverable reserves were about 120 times the annual coal production in 1988 and about 10 times that for the additional reserves beheved to be in place (1). Estimated coal consumption reduces the known recoverable reserves at about 1%/yr. Whereas the use of bituminous coal is expected to continue to increase in terms of tonnage, the percentage of coal used in the United States has stabilized as shown in Table 11. 

A primary concern in coal-fired power generation is the release of air pollutants. Limits on SO2 output, 0.52 g/MJ equivalent of coal input to a new plant, have been estabflshed. Eor a bituminous coal of 27.9 MJ/kg there is thus an upper limit of 0.72% sulfur content. Relatively few coals can meet this requirement. The U.S. Department of Energy indicated recoverable reserves of 420 x 10 t in 1987 (2) that were categorized by sulfur content 33.5% had 0.6% S or less, 15.4% had between 0.61% and 0.83% S, 16.1% had between 0.84 and 1.67% S, 12.4% had between 1.68 and 2.50% S, and 22.6% had more than 2.5% S. The lowest sulfur coal, 86%, is found west of the Mississippi River, mainly in Montana and Wyoming, quite distant from the electric power demand centers in the East. A trend to utilization of the western coals has developed. 

Fuel Proven reserves Estimated undiscovered recoverable reserves Estimated identified and undiscovered resources... 

Coal is the most abundant and most economical fossil fuel resource in the world. Proven coal reseiwes exceed 1 trillion tons, and indicated reserves are estimated at 24 trillion tons. Coal is found in eveiy continent of the world, including Antarctica, although the largest quantities of coal are in the Northern Hemisphere. Coal is mined in some sixty countries in nineteen coal basins around the world, but more than 57 percent of the world s total recoverable reserves are estimated to be in the United States, and China, which together account for more than two-thirds of the world s coal production. 

Conway, M.W. McMechan, D.E. McGowen, J.M. Brown, D. Chisholm, P.T. Venditto, J.J. "Expanding Recoverable Reserves Through Refracturing" SPE paper 14376, 1985 SPE Annual Technical Conference and Exhibition, Las Vegas, September 22-25. 

Figure 2. Canadas potential recoverable reserves of fossil fuels (in barrels-of-oil equivalent). Total 1000 billion source Federal Government Publication An Energy Policy for Canada. ...

The Canadian tar sands deposits in Alberta are the second largest oil reserves in the world after those of Saudi Arabia. It is estimated that the total recoverable reserves are approximately equivalent to 200 billion barrels of oil, an order of magnitude larger than the oil reserves of the United States. Tar sands are mixtures of bitumen (a heavy, viscous oil), sand, water and clay. The bitumen is a solid at room temperature. With surface mining operations, the mixture is heated in large tanks until the sand and clay settle and the oil floats on the hot water to the top of the tank. There are also in situ oil... 

The uranium reserves are estimated as a function of the market value. This 5 million ton figure is based on a market value of 130/pound. If the market value is 60/pound, the profitably recoverable reserve is only 2 million tons. The absolute total uranium reserves are about 15 million tons. 

Since the recoverable reserve figure is not the most important number, the above reserve tonnages have to be divided by two based on 50% recovery in order to show recoverable reserves. 

After taking into account the deductions from reserves due to losses in mining, the total amount of recoverable reserves amounts to 148.5 billion tons of underground coal and 68.5 billion tons of surface coal reserves or a total of 217 billion tons. 

As we can see from the recoverable reserve figures, we have many years supply of coal if we are allowed to mine it. But unless a commitment is made to coal by our Government which will remove the restrictions already in place, this coal will not be mined regardless of how many years of reserves there are. 

The United States contains about one-third of the world s coal reserves, and coal represents over 90 percent of U.S. proven reserves of fossil fuels. Recoverable reserves of U.S. coal are estimated to be 250 billion tons. Bituminous coals (with a heating value of 10,GOO-15,000 BTU/lb) comprise nearly one-half of total U.S. coal reserves. Eastern U.S. coals are generally bituminous. Western and southwestern U.S. coals are mainly sub-bituminous... 

Not included in reserves data are undiscovered but probably recoverable reserves in unexplored or unproven provinces. Currently, these probable reserves are estimated by the U.S. Department of Energy at 307-500 tcf, much of which almost certainly will become proven reserves when they become economically feasible. 

Whatever the ultimate recoverable reserves may be, current estimates of proven reserves of natural gas comprise about 50 percent of U.S. proven reserves of total petroleum energy. 

The amount of carbon stored in recoverable reserves of coal, oil, and gas is estimated to be 5,000-10,000 PgC, larger than any other reservoir except the deep sea, and —10 times the carbon content of the atmosphere. Until —1850s this reservoir of carbon was not a significant part of the short-term cycle of carbon. The industrial revolution changed that. 

A few examples of the use of this formula are cited here. In their base-case projection, the Energy Information Administration projects the annual growth rate in consumption of petroleum products to be 1.2% from 1992 to 2010. The world s proved and currently recoverable reserves of crude oil as of January 1, 1993, was estimated to be 6448 EJ, or 1092.4 billion barrels of oil [World Oil 214(8), August 1993], and the world s consumption of crude oil was 144 EJ in 1992 (Energy Information Administration). Presuming the growth rate in consumption does not change, the depletion time is then calculated by... 

If the total estimated remaining recoverable reserves are five times the proved and currently recoverable reserves as of January 1, 1993, the depletion time is calculated by... 

The fundamental problem in increasing the supply of low sulfur domestic fossil fuels to meet demand is indicated in Table III. The cumulative consumption of fossil fuels, both in direct use (e.g., transportation and space heating) and for the generation of electricity during the period 1960-2000, is compared with known recoverable and total estimated domestic reserves. Only for coal are we safely within our known recoverable reserves. On the other hand, for natural gas essentially the total estimated reserves in the ground, irrespective of the economics of recovery, will be depleted. 

Figure 1. Lignite (Brown Coal) proved and recoverable reserves in Europe.

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