Drilling

Geologists and other scientists have developed techniques that indicate the possibility of oil or gas being found deep in the ground. These techniques include taking aerial photographs of special surface features, sending shock waves through the earth and reflecting them back into instruments, and measuring the earth’s gravity and magnetic field with sensitive meters.

Nevertheless, the only method by which oil or gas can be found is by drilling a hole into the reservoir. In some cases oil companies spend many millions of dollars drilling in promising areas, only to find dry holes. For a long time, most wells were drilled on land, but after World War II drilling commenced in shallow water from platforms supported by legs that rested on the sea bottom.

Later, floating platforms were developed that could drill at water depths of 1,000 m (3,300 ft) or more. Large oil and gas fields have been found offshore: in the United States, mainly off the Gulf Coast; in Europe, primarily in the North Sea; in Russia, in the Barents Sea and the Kara Sea; and off Newfoundland and Labrador, and Brazil.

Most major finds in the future may be offshore.A semisubmersible oil-production rig sits in the waters off Pascagoula, Mississippi. Anchored in place, a semisubmersible rig has legs that fill with air, allowing the production platform to float above the surface of the water. Offshore wells produce about 25 percent of the world’s annual output of oil.