Petroleum Exploration and Recovery

Petroleum, also called crude oil, is a thick, yellowish black substance that contains a mixture of solid, liquid, and gaseous chemicals called hydrocarbons. Since its discovery as an energy source in the mid-1800s, petroleum has become one of humans' most valuable natural resources. Petroleum is arguably the single-most important product in the modern global economy.

Hydrocarbons separated (refined) from crude oil provide fuels and products that affect every facet of life in industrialized nations like the United States. Natural gas and propane are gaseous hydrocarbons that are used to heat homes and fuel stoves. Natural gas actually exists as a gas in underground reservoirs (underground rock formations containing oil or natural gas) and is not refined from crude oil, but it is still considered a petroleum product. The liquid portion of petroleum becomes such essential products as home heating oil, automobile gasoline, lubricating oil for engines and machinery, and fuel for electrical power plants. Asphalt road surfaces, lubricating oils for machinery, and furniture wax are all composed of semi-solid hydrocarbons. Petroleum products are the building blocks of plastics. The hydrocarbon gas ethylene is even used to help ripen fruits and vegetables!

Oil and water don't mix, but these two essential natural resources do have a lot in common. Naturally occurring petroleum forms from the chemical remains of organisms that lived and died in ancient seas. Petroleum collects in deeply buried rock layers called sedimentary rock that are, more often than not, the geologic remains of water-laid deposits like beds of sand or coral reefs on the sea floor. (Sediment is particles of rock sand or silt.) Petroleum reservoirs are similar to groundwater reservoirs, the water below Earth's surface. Petroleum scientists use many of the same skills and methods to find and extract oil that groundwater scientists use to prospect for underground water. Finally, many untapped petroleum deposits are buried beneath the seafloor, and much of our present and future petroleum supply lies offshore.

Formation of petroleum deposits

Hydrocarbons are organic (part of or from living organisms) chemicals; they form by the breakdown of microscopic organisms that were once living. (Biological organisms combine the chemical elements hydrogen and carbon during their lives, thus the term hydrocarbon.) Microscopic plants and animals that collect on the seafloor provide the organic material that eventually becomes petroleum. Dark, smelly, organic-rich mud collects where a heavy rain of dead plants and animals accumulates in an oxygen-poor seafloor environment. (Oxygen-rich waters support animals and bacteria that eat or decompose the organic material.)

Oil and Gas in the North Sea

Today, energy companies explore and drill for oil and natural gas in extreme offshore environments like the North Sea, a frigid, wind-blown expanse of ocean between Great Britain and Scandinavia. (Most relatively straightforward oil and gas deposits on land have long since been located and exploited. Earth's largest remaining petroleum reserves lie beneath regions that are rife with poverty, corruption, and hostility for petroleum-hungry developed nations like the United States.) Prospecting for oil and gas in the North Sea is an extreme challenge for geologists and engineers, but our ever-growing need for petroleum makes it economically worthwhile.

Geologists from companies like British Petroleum (BP) and Norsk Hydro (a Norwegian petroleum company) seek petroleum deposits in complex rock layers beneath the seafloor. The waters of the North Sea fill an ocean basin that was created by rifting (separation of continental blocks) between the British Isles and Scandinavia that began about 200 million years ago. Oil and gas deposits are the organic remains of microscopic plants and animals that lived and died in the ancient North Sea. Extractable petroleum now lies in sandstone reservoir rocks that have been folded and broken since their formation.

Weather conditions in the North Sea are severe; workers and equipment must withstand harsh cold and violent storms. Petroleum engineers have designed and built strong platforms (large buildings, attached to the sea floor or floating, that house workers and machinery needed to drill for oil or gas) and powerful drills that can extract crude oil and natural gas from hard rock deep beneath the North Sea's notorious towering waves and roaring wind. In spite of extreme weather, difficult geology, and technological challenges, the oil and gas fields of the North Sea are productive, economical sources of petroleum.

Unfortunately for petroleum users, oil doesn't simply collect in underground puddles. Organic material must undergo a series of complex changes over many thousands of years before it becomes petroleum that can be extracted for human use. First, organic-rich mud layers become source rocks like shale and mudstone when they are buried beneath thick stacks of newer sediment. Heat, pressure, and bacteria within source rocks chemically transform plant and animal parts into hydrocarbons. Next, pressure squeezes the petroleum out of the source rocks and it migrates (moves) to reservoir rocks where it fills tiny openings, fractures, and cavities.

Productive petroleum reservoir rocks, such as sandstone and some types of limestone, are like swiss cheese. They have lots of empty space between mineral grains (high porosity) and the space is interconnected so petroleum can flow easily through the rock (high permeability). Finally, exploitable petroleum reservoirs are typically contained beneath layers of relatively impermeable rock called cap rock that keeps oil from escaping onto the land surface. Geologic structures like faults (fracture or break along which rocks slip) and folds (bends in rock layers due to the stress imposed by the movement of Earth's tectonic plates) trap petroleum from the sides. Petroleum geologists use maps and rock samples from the land surface as well as images of the subsurface to search for deeply-buried oil and natural gas deposits.

History of the modern petroleum industry

Petroleum has been known to mankind for thousands of years. Ancient Mesopotamians, Egyptians, Greeks, and Romans collected the sticky black substance called bitumen from tar pits and seeps (an area where groundwater or oil slowly rises to the surface) and used it to pave roads, heal wounds, waterproof buildings and, to a limited extent, for lighting. The modern quest for petroleum began in the mid-1800s when rapid industrialization and population growth prompted a search for a new type fuel that could replace coal in furnaces and whale oil in lamps. (Coal, like petroleum, is an organic fossil fuel that must be mined from underground. Coal beds are the fossilized remains of land plants that grew in ancient swamps.)

North American prospectors seeking inexpensive lamp oil first struck oil in Ontario, Canada in 1858. They made the first major petroleum discovery one year later in Titusville, Pennsylvania in 1859. John D. Rockefeller (1839–1937), a businessman who saw economic potential in Pennsylvania oil, founded the Standard Oil Company in 1865, the same year the American Civil War (1861–65) ended. (Rockefeller went on to become the world's first billionaire. Most major U.S. energy companies, including Exxon-Mobil, Chevron-Texaco, Conoco-Phillips, and the American portion of British Petroleum-AMOCO were originally part of Standard Oil.) By 1901, when a gusher (fountain of pressurized petroleum) shot up into the air above the famous Spindletop well near Beaumont Texas, the American oil industry was positioned to capitalize on an invention that has changed the face of modern civilization, the internal combustion engine. An internal combustion engine takes the energy in fuel and combusts (burns) it inside the engine to produce motion.

Petroleum releases heat energy and gaseous carbon dioxide when combusted. Like wood, coal and other organic fuels, petroleum can be used to heat homes, cook food, and power steam engines in trains, ships, and factories. However, petroleum fuels are more efficient than coal and wood, meaning that they produce more energy and less pollution per unit volume. Smoke-belching nineteenth century steam trains required a carload of coal and a full-time laborer to feed the coal into the just to leave the station. Today, automobiles powered by internal combustion engines drive hundreds of miles (kilometers) using only a few gallons of gasoline. Petroleum-fueled engines and furnaces generate electricity, heat homes, propel ships, and run industrial machinery.

Problems of petroleum use

Petroleum is presently industrial nations' most affordable, efficient, and accessible source of energy. Its use, however, presents a number of grave environmental, economic, and social problems. Petroleum that spills and leaks from oil and natural gas wells, tankers, pipelines, refineries, and storage tanks into ocean, surface, and ground water causes serious water pollution that threatens the health of plants and animals, including humans. (Hydrocarbons are carcinogenic; they cause cancer.) Explosions and fires threaten petroleum workers and people who live near petroleum facilities. Smokestacks and automobile exhaust pipes emit poisonous gases and ash particles that block sunlight, cause acid rain, and negatively affect biological health.

Strict regulations and new technologies have made petroleum extraction, processing, and use cleaner and safer in recent years. However, two more-difficult problems remain as the reliance on petroleum continues to grow. First, only a few regions, including many politically unstable countries in the Middle East, South America, and Africa produce significant amounts of petroleum. Counties that use more oil than they produce, like the United States, are at the mercy of oil producers like Saudi Arabia and Venezuela. Economic and social conflicts often arise over oil, and sometimes these oil-related disagreements escalate to armed conflict. Second, the carbon dioxide gas emitted during petroleum combustion is a greenhouse gas. Scientists have observed rising levels of carbon dioxide in Earth's atmosphere (mass of air surrounding Earth), and worry that it may lead to global climate change. Scientists, energy companies, governments, environmentalists and other groups share a common concern for meeting the needs of Earth's ever more energy-dependent human population while reducing the negative effects of petroleum use.

Laurie Duncan, Ph.D., andTodd Minehardt, Ph.D.

For More Information

Books

Pipkin, Bernard W., and D. D. Trent. "Energy Resources." In Geology and the Environment. Pacific Grove, CA: Brooks/Cole, 2001.

Press, Frank, and Raymond Siever. "Energy and Mineral Resources from the Earth." In Understanding Earth. New York: W. H. Freeman and Company, 2003.

Yergin, Daniel. The Prize: The Epic Quest for Oil, Money and Power. New York: Simon and Schuster, 1992.

Websites

The Energy Institute. "Fossils into Fuels." Schoolscience.http://www.schoolscience.co.uk/content/4/chemistry/fossils/p1.html (accessed on August 24, 2004).

"Looking for Oil and Gas?" San Joaquin Geological Society.http://www.sjgs.com/exploration.html (accessed on August 24, 2004).