The first oil well was drilled in Titusville, Pennsylvania (USA), in August 1859 by Colonel Edwin L. Drake, who found crude oil at a depth of 21 m. Thus began what is now the largest industrial activity. By 1975 there were 600,000 oil wells worldwide, producing more than 55 million barrels of oil per day (1 barrel equals 159 litres).
Composition, origins and location
Oil is a complex mixture of hydrocarbons (carbon and hydrogen compounds). Its range of densities is very wide: from light gases, such as methane, to heavy solids, such as asphalt. And their colors range from yellow to black, passing through green, red and brown. A typical crude oil contains 85% carbon and 15% hydrogen. Natural gas is the least dense fraction of crude oil, although it is often found in its natural state.
Oil is the product of the decomposition, under special conditions, of microscopic plants and animals that lived hundreds of millions of years ago and deposited as sediments. Natural gas has a simpler origin: thus, methane can be formed by bacterial decomposition of plant matter, and is found in marshy areas.
Once formed, the oil deposits moved, until they were trapped in porous rocks at depths between 30 m and more than 7,500 m. Therefore, oil deposits are not large cavities filled with a sea of oil and gas, but are more dispersed.
The first prospectors drilled in places where it sprouted naturally to the surface. Today prospecting is more scientific, although surface methods may still be useful. The appearance of the soil and the presence of appropriate types of sedimentary rocks may indicate good drilling sites. The technicians use seismic tests (measurements of the effects of mechanical waves in the ground): they explode explosives in shallow holes and, with microphones, detect the origin of the echoes produced by the underground structures. Gravimetric tests can also be carried out: sensitive instruments, sometimes carried in aircraft, detect variations in the gravitational field that may indicate the presence of geological structures containing oil.
These techniques make the chances of finding oil rise from 1 in 30 to 1 in 5.
Drilling methods.
the first drills operated by percussion through a dry hole. If they found oil, they couldn't stop him and he'd go off like a geyser. Modern techniques solve this by using rotary drills immersed in a special "mud", with which they fill the well as it is drilled, in order to create a pressure that prevents leakage.
The drill bit goes at the end of a column of steel pipes, through which the mud is pumped. As the bit passes through the ground, the material pulled out is brought to the surface by the mud. There, the mud is examined by geologists, who inspect the nature of the stratum through which the drill bit has passed. The mud is screened to separate the debris and then reintroduced into the well.
Two typical dangers are oil or gas eruptions and blockage of the drill. To prevent eruptions, drilling rigs are equipped with a safety device that can quickly seal off the hole. Clogged drills can sometimes be released with special equipment. If this fails, they are left in the hole, the largest possible piece of the drill string is recovered and a new hole is drilled next to it.
Once the hole is drilled, a 22.9 cm pipe is inserted and cement is injected between the hole and the walls of the hole to seal it. A production column of 7.6 cm is placed at a suitable depth and an explosive charge is lowered to the bottom: when it is detonated, holes are produced through the lining and the cement to allow the oil to pass through.
Transport and storage.
pipelines are the cheapest way to transport oil and gas from wells to refineries. They are made of welded steel, are 1.20 m in diameter and are covered with asphalt felt for protection (often buried). Along the pipeline, pumping stations maintain flow and pressure.
pipelines are the cheapest way to transport oil and gas from wells to refineries. They are made of welded steel, are 1.20 m in diameter and are covered with asphalt felt for protection (often buried). Along the pipeline, pumping stations maintain flow and pressure.
Transport by sea is more expensive. The supertankers are the largest ships built to date: they carry hundreds of thousands of tons of oil. liquefied natural gas can also be transported by sea in even more expensive tankers.
The oil is usually stored in tanks of more than 30 m in diameter and 9 m high. Liquefied natural gas can be stored both in refrigerated tanks and in storage cavities that are made impeccable by pre-freezing the surrounding soil: holes of 40 m in diameter are dug and then the liquefied gas is pumped into them; once filled and covered with an insulating surface, the same content keeps the tank at a low temperature.
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