Abstract
Deposits of natural gas in the earth's crust are commonly tapped for heating homes, generating electricity, moving vehicles, and other uses in the chemicals industry. But when natural gas is produced as a byproduct of oil production, it is sometimes wasted— simply burned off at the wellhead instead of being transported to consumers. The process is called “flaring.”
Enormous amounts of gas are flared. Although the price of oil and energy—as well as concern about global warming—is high, natural gas (especially its methane component, which is highest in hydrogen) is expensive to transport from wellheads to consumers. Transporting its heavier components, such as propane and butane, is relatively easy because they can be liquefied easily, but the proportion of methane in natural gas is typically 85-95 percent, depending on the location of the wellhead.
Since 1870, at least 230 trillion cubic feet of natural gas have been flared worldwide— the equivalent of 10 years of natural gas consumption in the United States at 2000 rates. The value of this gas is more than $880 billion, based on the energy it contains and the current price of oil. Gas flares may also contribute to acid rain, deposits of soot, and respiratory diseases, according to some claims. Throughout the 1990s, the United States flared approximately 220 billion cubic feet per year. South and Central America's combined rates have typically been about three times higher.
Transportation
There are several ways to transport natural gas or chemicals derived from natural gas, from the practical to the outlandish. The most attractive method is to build an overland pipeline between the wellhead and gas consumers, but only if distances are not too great and the terrain is suitable for pipeline construction. Where demand allows, using a large pipe, up to 3 meters in diameter, drives transport costs down considerably. The pipelines connecting Alaska or Canada with the continental United States, and Siberia with Europe, are examples of large pipelines.
On a global basis, however, many oil and gas fields are too far removed from consumers, or the oceans too deep to be crossed. The maximum depth in which submarine pipelines have been laid so far is 1,000 meters.
A gas flare in the North Dakota Badlands.
When a pipeline isn't feasible, cooling the gas to minus 161.5 degrees Celsius turns it to a liquid, which can then be transported in tankers. Converting the gas into liquefied natural gas and transporting it, however, is costly—and 25 percent of its potential energy is lost during the liquefaction process. Methane can also be converted to methanol, an alcohol, for use as a gasoline substitute, but this causes even more energy to be lost.
Another transportation scheme was proposed for Shell Oil Company for use in Africa in the early 1970s: using giant airships with 97 million cubic feet of capacity (of which 87 million cubic feet is natural gas). The original cost estimate for such an airship was $48 million, which would result in a more than 100-to-l ratio of capital cost to the value of fuel transported. Such airships would be the size of the largest buildings—14 times larger than the Hindenburg, the largest airship ever built—and would cruise at a speed between 106 and 118 miles per hour and at an altitude of 2,000 feet. Careful attention would have to be paid to safety in this unlikely scenario. The methane payload could be surrounded by helium gas to minimize the risk of fire, and flying over less populated areas or over the sea could also increase safety.
Uses
Another possibility in some areas is to increase the use of compressed natural gas, a clean-burning substitute for gasoline. Although it has seen limited use for point-to-point transportation, it is not widely used worldwide. Diesel vehicles, however, can be run with a fuel mixture of natural gas and a small amount of diesel fuel. In areas near wellheads that flare gas—like West Africa, where large towns are within a few hundred miles of wellheads— converting buses, utility vehicles, and public service vehicles to run on this mixture would be an economical alternative to using diesel fuel.
Flaring could be reduced further by locating energy intensive industries, such as aluminum smelters or desalination plants, close to wellheads, or by using gas to pump oil through pipelines. Methane can also be used for producing ammonia, petrochemicals, proteins, and other chemical processes. One of the main economic problems with using gas as a chemical feedstock is the global overproduction of petrochemicals, but in two or three decades the supply-and-demand scenario for petrochemicals might be very different. Also, many parts of the world are likely to face water shortages in the future which could result in an increased demand for irrigation and water-handling equipment derived from petrochemicals.
One use for methane that receives little attention—and that could increase demand for the gas—is to use it for launching large payloads into space. NASA and certain research centers—notably Princeton and Stanford universities—have studied space colonization, retrieval of materials from asteroids, exploration of Mars, and other projects involving large payloads. And there are other more fanciful and controversial ideas: satellite power stations, reflectors that intercept solar energy and beam it down to Earth, power relay satellites for moving energy from one terrestrial site to another by using a microwave beam, and the disposal of nuclear waste in space.
All these projects would require heavy launch vehicles. Based on current space shuttle technology, it is possible to modify a shuttle so that it has a lift-off mass of 2,000 to 2,400 tons for low Earth orbit construction projects, including the transport of 75 passengers and 90 days of supplies. But transporting the construction materials themselves with current shuttles would cost too much. From the ongoing debate on this issue in the U.S. astronautics community, it is clear that a heavier launch vehicle is needed. Several designs have been proposed, and important candidates are the designs developed by Boeing and the Johnson Space Center. Detailed scientific studies have assumed the use of one or two American designs. These are both two-stage reusable launch vehicles, similar in concept to the space shuttle, but able to deliver 230 and 424 tons, respectively, to low Earth orbit. The larger launch vehicle would have a lift-off mass of 11,000 tons, 9,200 of which would be propellant (liquid methane and liquid oxygen would be used in the first stage, and liquid hydrogen and liquid oxygen in the second). For all these propellants, methane would be an ideal feedstock because it has the highest hydrogen content of all hydrocarbons. Methane could also fuel the necessary gas liquefaction processes at the launch base.
An alternative to these heavy lift launch vehicle designs is the Russian Energía, the most powerful launch vehicle currently available—capable of carrying more than 100 tons into orbit.
Practical matters
The best local approaches for transporting and using natural gas vary based on geography, regional oil and gas prices, distance to markets, the political and technical practicality of installing pipelines, availability of alternative energy supplies, and other factors such as material and labor costs. For example, launching large payloads into space could only be viewed in normal commercial terms if and when heavy lift launches are available on a free market basis. And for giant airships, there would be a maximum range beyond which they would not be economical to operate.
A strategy of capturing natural gas that might otherwise be flared must deliver enough energy to consumers to be commercially viable. There are also a number of safety issues that need to be addressed, including the inherent safety of giant airships and the use of compressed gas cylinders. Some alcohols used as transport fuels are also poisonous. However, based on the number of fatalities, natural gas is the safest of all energy sources to extract and transport when compared to coal mining, oil rig operation, and oil transportation on the seas.
Looking ahead, it will be difficult to persuade oil and gas companies to recover natural gas if the rate of return on investment is lower than that of their existing operations. For example, it is difficult to make an economic case for a submarine pipeline for gas that is flared far from shore. Liquefying the gas for transport may be possible, but perhaps not commercially viable, depending on an oilfield's location.
It is also difficult to predict the amount of gas that can be collected instead of flared in the future because gas extraction is directly linked to the oil industry—and the rate of developing oilfields depends on many factors, including oil price, politics, technical hurdles, and trade agreements.
Natural gas clearly has benefits in terms of its safety and cleanliness, and it produces lower amounts of greenhouse gases than oil or coal. In view of these factors and the Earth's limited hydrocarbon reserves, it is in the interests of the international community to minimize gas flaring and maximize opportunities to capture and use natural gas. Governments of countries that flare gas should remove the political and bureaucratic obstacles for companies or organizations willing to put the gas to good use. •