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Extreme Oil
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The Journey The History The Science
Exploration Production Transportation Refining
Early Prospecting - Modern Exploration Always a Messy Business - Modern Production Pipelines, Tankers, Trains, and Trucks Turning Crude Into Commodities

Excavation Feature
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Modern Exploration

By the 1920s, geology had firmly established its value in finding oil through a variety of useful geophysical methods, most of which persist in some form today. These methods assess specific properties -- such as density, magnetism, porosity, and so on -- associated with the sorts of rock formations that are more likely to have oil.

Gravitational methods, for example, rely on the physical principle that more mass -- and thus denser rocks -- pull with greater force. Geologists have devised a range of tests for small distortions in the earth's gravitational field that result from the presence of porous, sedimentary rocks that may contain oil. One early technique that applied these ideas used a WWI-era device called a torsion balance, which proved particularly useful for detecting oil trapped in salt domes. Another technique focused on changes in the period of a pendulum's oscillation over different areas. Both of these technologies have since been replaced with a gravimeter, which measures changes in the earth's pull on a mass balanced against a force exerted by the device itself.

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This photo of an oil gathering center on Alaska's North Slope revels the vast expanse of structures necessary for oil processing.
Another approach focuses on variations in the magnetic properties of rock formations, employing knowledge that igneous and metamorphic rock tend to be highly magnetized, but rarely contain oil. Still other methods detect hydrocarbons using sensitive chemical "sniffers"; measure electrical conductivity in rock layers; sample cores retrieved from hollow drills; or examine surface features using traditional surveys, aerial photography and satellite images.

The most common method used to find oil today is based upon the speed at which seismic waves propagate through the earth. Seismic surveys emit powerful shock waves that penetrate thousands of feet into the earth, measure reflected and refracted waves with arrays of microphones (geophones or hydrophones), then interpret the results to create rough images of the subsurface.

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Workers keep trucks like these running 24 hours a day in order to maximize productivity.
Though highly scientific, this is not all mild-mannered laboratory work. Seismic surveys on land may employ "thumper trucks" that pound the ground at low frequencies. Others use explosives drilled into the surface and detonated. At sea, survey ships send sharp, powerful pulses reverberating through the water from a compressed air gun, then specialists analyze the reflected signals received by a floating cable of hydrophones dragging more than a mile behind the ship. One of today's state-of-the-art oil exploration techniques, 3-D seismic, is an expansion of traditional seismic techniques that combines samples from multiple sources to allow analysts to view subsurface profiles in three dimensions.

Together, these methods form a powerful set of analytical tools that have led the way to oil in far-flung places, in more extreme geographies, and further and further below land and sea. Though wildcatting continues to this day, by now it is believed that the world's largest reservoirs -- those with more than a billion barrels, or "elephants" as they are sometimes called -- have already been found. While these sophisticated methods are costly and complex, they save millions of dollars by not drilling dry holes. Still, some of the greatest obstacles to oil exploration are not technical but rather political and economic. Large remaining resources are predicted to be in regions where priorities such as environmental protection, the risk of political instability, or the high cost of working in difficult environments all make oil development difficult, risky, and expensive.

-- Edwin Adkins

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