Natural Gas Formation and Exploration

 NATURAL GAS supplies more than 20 percent of the world’s total energy requirements. What is the source of natural gas? How clean is it? And how much is left?

Many scientists believe that aeons ago natural gas was formed from the decay of plant and animal remains, including plankton. According to this theory, over long periods of time, microbes, together with pressure from the accumulating sediment above and heat from deep in the earth below, converted the organic debris into fossil fuels—coal, gas, and petroleum. In time, much of the gas found its way into porous rocks, sometimes forming vast reservoirs, or gas fields, that were sealed beneath a layer of impermeable rock. Some gas fields are huge, containing trillions of cubic feet (cu m) of gas. How are gas deposits found?

Searching for Natural Gas

Remote sensing satellites, global positioning systems, reflection seismology, and computers have taken some of the guesswork out of gas exploration. Reflection seismology is based on the principle that sound reflects from layers of rock within the earth, thus giving scientists an acoustic picture of what lies below. The sound sources are man-made, usually involving small explosives or vibrators fitted to special trucks. The resulting shock waves travel into the earth’s crust and are reflected back to waiting instruments, which help scientists generate three-dimensional computer models of rock formations. These models, in turn, may indicate potential gas deposits.

In offshore exploration, sound waves are made by special guns that shoot compressed air, steam, or water into the sea. The resulting pressure waves penetrate the seabed and reflect back to hydrophones attached to a long cable towed behind the survey ship. Here, too, researchers use the signals to form computer models for analysis.

To justify the cost of extraction, a field must have sufficient gas. Hence, geologists have to ascertain both the pressure and the volume of a reservoir. The pressure can be measured quite accurately with gauges. The precise volume, however, is harder to determine. One method involves reading the initial pressure, releasing a measured amount of gas, and then taking another pressure reading. A small drop in pressure indicates a large reservoir; a large drop, a small reservoir.

Making the Gas Ready for Use

After being extracted, natural gas is piped to refineries for the removal of unwanted chemicals, such as carbon dioxide, hydrogen sulfide, and sulfur dioxide, as well as water vapor, which can corrode pipelines. Natural gas is then distilled at very low temperatures to remove incombustible nitrogen and to recover valuable helium, butane, ethane, and propane. The final product is essentially pure methane, which is colorless, odorless, and highly combustible. Because the methane is a natural product, it is also called natural gas.

To make natural gas safe for domestic use, manufacturers add tiny amounts of pungent sulfur-containing compounds so that leaks can be readily detected and safely stopped before an explosion occurs. Nevertheless, natural gas is a much cleaner fuel than other fossil fuels, such as coal and oil.

To facilitate transport, some natural gas is chilled to very low temperatures and converted into liquefied natural gas. Butane and propane often end up as liquefied petroleum gas (LPG), which is well-known to those who like to cook on gas barbecues with bottled gas. LPG is also commonly used as fuel for buses, tractors, trucks, and other vehicles. On the chemical front, butane and propane have found their way into plastics, solvents, synthetic fibers, and other organic products.

A Finite Energy Supply

As with all fossil fuels, natural gas is a finite resource. According to estimates, about 45 percent of the world’s recoverable gas remains to be found. If that figure is correct, at the present rate of usage, the supply may last about 60 years. But in many lands, energy consumption is increasing, so present predictions may be highly inaccurate.

To be sure, the almost frenetic rate of industrialization in some lands could lead one to think that earth’s resources are infinite. Granted, there is also nuclear power as well as renewable energy sources, such as solar and wind power.

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