Petroleum is not found in underground pools. Rather, like aquifers of water, it is located within the pores and cracks of rock, called reservoir rock. Oil is naturally buoyant and over time it tends to rise through microscopic pores and cracks in the rock. The pressure pushing the petroleum out of the rock is what makes the oil come to surface as a liquid.

Oil is usually found in ancient depressions or basins. This is where ancient trees and plants washed down from ancient rivers and microorganisms dropped from ancient seas tended to accumulate in large quantities. Over millions of years enough rock amassed on top of the organic material to generate the heat and pressure necessary to cause the plant material and dead organisms to chemically change into oil. This geological formations are called source rock.

Just as important as the source rock are cap stone, layers of impermeable rock that entrap the oil by keeping it from rising. Capstones must be curved like an upside down "U" or "V" to concentrate the oil. If they aren’t the oil disperses over too large of an area to be sucked out of the ground. These deposits sometimes form oil shale.

Capstones are usually made of shale or salt. The upside down "U" shape geological formations the geologists are looking for include anticlines (an underground hill formed by upholding or rock strata), folds, faults and salt domes.

Hyperthermophilic (extreme-heat-loving) microbes have been found in heated oil reservoirs 10,000 feet below Alaska’ss North Slope and the bed of the North Sea.

Websites and Resources: American Petroleum Institute ; Investopedia Oil Handbook ; Petrostratgies Learning Institute ; U.S. Energy Information Administration ; New York Times article New York Times ; Wikipedia article Wikipedia ; Oil. com ; Petroleum Online ; Natural

Book: “The Prize” by Daniel Yergin.

Petroleum Exploration

The world's first oil explorers did not use science of geology to find petroleum deposits. Some used divining rods and invoked spirits. Others claimed to have "oil bones" which shook whenever they passed near a deposit. By the end of the 19th century the science of petroleum geology began to take shape. And what geologist were looking for back then is not all that different from what they are looking for today. [Source: Investopedia, The Industry Handbook: The Oil Services Industry]

To find oil the geologist must first find the source rock, or basin, that produces the petroleum. The second thing they look for is a cap stone. To look for clues to the locations of these underground formations on the surface, geologists use aerial photography, satellite imagery and the analysis of exposed rock. Boats with devices that measure hydrocarbons leaking out of the ocean floor and planes with sensor that detect magnetic and electrical fields are also used to look for promising sites.

To analysis the rock underground explosions are set off with dynamite or low intensity vibrations are generated with trucks. The seismic waves produced by the trucks and explosives bounce off of layers of rocks and are recorded with very sensitive seismographs. Seismic waves bounce off different kinds of rocks in different ways and through this method geologist get a picture of the underground rock formations, sometimes several miles deep.

In some places explosive charges are laid over 100 meters or so in a straight line and detonated to send seismic waves deep into the earth. The rebounding waves are picked up with sensitive geophones and sent to a truck full of electronic gear, where they are processed as waves on computer screens and analyzed for signs of oil-bearing rock formations. In the oceans, seismic ships search for oil and gas by trawling with long seismic cables and using sound waves to create three-dimensional images that look like hospital CT scans.

The oil and gas industries have been asked to reduce the use of seismic air guns — which are used to locate oil deposits under the sea bed using noise that can be heard across entire oceans — because of the threat to whales and other marine creatures.

Geologist are always looking for new "elephant" fields like those in Saudi Arabia and Iraq but they say all the easy deposits have been found. Sometimes geologist get lost on the desert and have to be rescued by helicopters.

Drilling for Oil

Once a promising formation has been found workers are called in to drill a well. Petroleum in the earth can not be located with certainty or extracted until drilling into the earth is done. Drilling is very expensive and financially risky. It cost millions of dollars to produce the equipment and get it to the exploration site. Often the work is done in an inhospitable environments, such as the Arctic, the ocean, rain forests or the middle of a desert, which adds millions more in costs. And even after all that, nine out of ten wells come up dry.[Source: Investopedia, The Industry Handbook: The Oil Services Industry]

Oil drilling and services is broken into two major areas: drilling and oilfield services. Drilling companies physically drill and pump oil out of the ground. The drilling industry has always been classified as highly skilled. The people with the skills and expertise to operate drilling equipment are in high demand, which means that for an oil company to have these people on staff all the time can cost a lot. For this reason, most drilling companies are simply contractors who are hired by oil and gas producers for a specified period of time.

Oilfield Services - Oilfield service companies assist the drilling companies in setting up oil and gas wells. In general these companies manufacture, repair and maintain equipment used in oil extraction and transport. More specifically, these services can include: 1) Seismic Testing - This involves mapping the geological structure beneath the surface. 2) Transport Services - Both land and water rigs need to be moved around at some point in time. 3) Directional Services - Believe it or not, all oil wells are not drilled straight down, some oil services companies specialize in drilling angled or horizontal holes.

Types of Drilling

In the drilling industry, there are several different types of rigs, each with a specialized purpose. Some of these include: 1) Land Rigs - Drilling depths ranges from 5,000 to 30,000 feet. 2) Submersible Rigs - Used for ocean, lake and swamp drilling. The bottom part of these rigs are submerged to the sea's floor and the platform is on top of the water. ) Jack-ups - this type of rig has three legs and a triangular platform which is jacked-up above the highest anticipated waves. 4) Drill Ships - These look like tankers/ships, but they travel the oceans in search of oil in extremely deep water. [Source: Investopedia, The Industry Handbook: The Oil Services Industry]

Rotary drilling from a steel tower called a derrick is the most common drilling method. A drill bit bores into the earth much the same way a carpenter drill drills through wood. The drill bit is attached to the end of strong hollow steel drill pipe sections, which are usually 60, 90 or 120 feet in length and fit inside a lining that is places in the drilled hole. In deep wells the pipes near the surface may be 36 inches wide while those thousands of feet below the surface where the drilling is taking place may be only few inches wide. This is because the hole gets progressively narrower the deeper into the earth it goes and each successive lining must be narrower than the one above it.

The top of the drill pipes fits into a square shaft called a kelly. The kelly fits loosely through bushings in a hole in the rotary table on the derrick floor. The bushing allow the kelly and drill string to descend as drilling progresses. An electric- or steam-powered engines turns the rotating table, which turns the kelly, drill, and bit.

A rock bit has wheels with sharp diamond-covered teeth. As it chews through the rock a mixture of clay, chemicals and oil or water is pumped down through the hollow pipes to cool and lubricate the pipes and bit and hold back the pressure of oil, gas or water which can cause a blow out, or a gusher.

For wells reaching the end, sound waves are shot through the rock to make three-dimensional maps and the deposits is worked by driller deeper, sideways and repositioning wells, water and carbon dioxide are pumped into the ground to repressurize fields and recover more.

Carbon dioxide injection is used in very deep wells. The carbon dioxide decreases the viscosity of the oil and puts pressure on it making it easier to pump out. On the surface the wells are covered by domed shelters. Oil companies that have used the method on declining wells have seen their out their output triple.

In the mid 1960s, the Soviet Union conducted experiments using a half dozen nuclear explosions to stimulate conventional oil production. The technique did increase production but unfortunately the oil was radioactive.

Drilling Process

The towering derricks can be moved from site to site. Drilling can be straight down and at angles of 50 degrees to get around obstacles and reach hard-to-reach deposits. It is not pretty. A typical 182-foot drilling tower is surrounded by dried pills of muck pumped out of the drill hole and piles of gritty drilling equipment.

Workers on drilling platforms are called roughnecks. They use giant wrenches to join sections of pipe and are often so skilled they can tell the kind of rock they are going through just by the way the drill behaves. Describing one team at work, Brad Lemley wrote in Discover magazine: “The four-man hard-hatted crew works in perfect synchrony, joining 90-foot sections of drilling pipe with massive orange wrenches . The pipe snakes through the installed lining and drills the hole deeper. Then pressurized fluid forces the bored earth to the surface making space for another batch of ever-narrower steel sleeves.”

It is dangerous work. Striking a gas deposit can send the d rills shooting upward like a missile and anyone who gets in the way has a string likelihood of getting seriously injured or killed. Its also tough work. One roughneck told Discover, “It kind of rips you up. We’ve all been smashed, cut, and beat up. I tore my biceps last week.”

During the drilling process, rock is analyzed for signs of oil. A well-loggers is a device that contain a powerful capsule of radioactive metal — usually americium, iridium or strontium — that is lowered into a well shaft to probe for oil deposits, using beams of neutron and gamma radiation that penetrate dense rock. When not in use the devise kept in a canister about the size of a small beer keg. The type of radiation that is emitted — neutron radiation — is very dangerous to humans.

In the old days a gusher, a huge spout of oil shooting up in the air, was the sign of major find. These days a gusher is called a blowout and it is regarded as a major disaster because the pressure that is released is useful in pumping out the oil and the oil spills out everywhere has to be cleaned up at a considerable expense.

Offshore Drilling

There are three kinds of offshore drilling platforms: 1) one kind that is self contained at supported by piles embedded in the ocean floor; 2) a second kind is that is attached to a floating tethers; and 3) a third kind that is a mobile platform attached to submersible barge. The latter is considered the most economical type because it capable of drilling a lot of wells over a large area. People that work on offshore rigs generally get paid very well and work one week at sea and have one paid week off.

In some places large floating platform collects crude from several wells and pipe it to the shore. The cost of such a system — with platform half the size of a football field floating on pontoons and tethered to the ocean floor, harvesting 50,000 barrels a day from two miles below the sea floor — can be over $4 billion. After the oil reaches the platform is often stripped of its water, sand and gas in separator tanks before being pumped to the shore in a submerged pipeline. Small offshore platforms consists of just a few girders and pipes about 20 to 30 feet above the water.

At first oil companies drilled for oil in the continental shelf in waters a few hundred feet deep at most. Now they are drilling in the open ocean in seas that over a mile deep, using sophisticated drilling ships that are guided to their positions by satellites and drill using equipment guided by $6 million underwater remotely-controlled vehicles operated by a joystick on the ship. Exxon Mobile says that it has the capability of drilling in waters 3,000 meters deep. The cost of drilling a wells this way is about $330,000 a day.

Describing a drilling from a ship in the Gulf of Mexico Tim Appenzeller wrote in National Geographic: “The drill, suspended from the “Enterprise’s “ derrick through a swimming-pool-size gap in the hull, has penetrated 17,000 feet below the sea floor. Instead of boring straight down, it has swerved more than a mile sideways, around a massive plume of rock salt. But now with 2,000 feet to go, progress is stalled. Water has begun seeping into the well from the surrounding rock, and engineers are determined to stem its spread before drilling farther. Otherwise, the trickle of water could turn into an uncontrolled surge of crude.”

Pumping Petroleum and Deep-Well Injection

Oil is brought to the surface from a well is sunk into the porous rock. Pressure for the oil pushes it up the well. When the pressure drops pumps are installed to bring it up.

When oil is discovered through drilling, steel pipe casing is lowered into the well hole. Cement is lowered in the casing to isolate the oil from other formations and keep sand, mud, clay, rock and water from contaminating the petroleum. A perforating gun is then used to make holes on the cement. Tubing about two inches in diameter is inserted in the hole.

After the above system is installed the oil generally seeps naturally towards the surface. A system of valves and pressure gauges are set up to keep it flowing in a controlled matter and to prevent blow outs. The oil is collected in storage tanks. If natural gas is present in the oil, there is a system of separators, which remove the gas from the petroleum and places it in separate storage tanks. Sometimes the gas is burned off. The petroleum is then transported by pipeline or tankers to refiners.

When natural pressure forcing the oil upwards gives out, the oil must be pumped. This is often does by forcing water or oil into the reservoir to produce enough pressure to force the oil to come to the surface. An oil field may have more than 10,000 wells pumping oil from it. Oil pump jacks are what you see bobbing up and down in old oil fields like the ones in California and Texas. When the oil slows to trickle the well is closed down and plugged so oil, water and other contaminants do not seep into aquifers.

When a well is on its last legs water or carbon dioxide can be pumped into the well. Deep-well injection is being used to get rid of carbon dioxide and boost oil and gas production by forcing residual deposit to the surface. In old fields deep-well injection has boosted production by as much as 50 percent. Deep-well injection can also bring briny water to the surface can pollute streams and aquifers. Carbon dioxide can convert to acid in ground water. In some places where deep-well injection has taken place earthquakes have been reported.

Image Sources: 1) 2) 3) 4) 5) 6) 7) 8)

Text Sources: World Almanac, United States Geological Survey (USGS) Minerals Resources Program, Investopedia Industry Handbooks, U.S. Energy Information Administration, Department of Energy and National Geographic articles. Also the New York Times, Washington Post, Los Angeles Times, Smithsonian magazine, Natural History magazine, Discover magazine, Times of London, The New Yorker, Time, Newsweek, Reuters, AP, AFP, Lonely Planet Guides, Compton’s Encyclopedia and various books and other publications.

Last updated March 2011

This site contains copyrighted material the use of which has not always been authorized by the copyright owner. Such material is made available in an effort to advance understanding of country or topic discussed in the article. This constitutes 'fair use' of any such copyrighted material as provided for in section 107 of the US Copyright Law. In accordance with Title 17 U.S.C. Section 107, the material on this site is distributed without profit. If you wish to use copyrighted material from this site for purposes of your own that go beyond 'fair use', you must obtain permission from the copyright owner. If you are the copyright owner and would like this content removed from, please contact me.