Oil - The Quest For Oil
drill drilling rock petroleum
On August 27, 1859, Edwin Drake struck oil sixty-nine feet below the surface of the earth near Titusville, Pennsylvania. This was the first successful modern oil well, which ushered in the "Age of Petroleum." Not only did petroleum help meet the growing demand for new and better fuels for heating and lighting, but it also proved to be an excellent fuel for the internal combustion engine, which was developed in the late 1800s.
Sources of Oil
Almost all oil comes from underground reservoirs. The most widely accepted explanation of how oil and gas are formed within the earth is that these fuels are the products of intense heat and pressure applied over millions of years to organic (formerly alive) sediments buried in geological formations. For this reason they are called fossil fuels. They are limited (nonrenewable) resources, which means that they are formed much more slowly than they are used, so they are finite in supply.
At one time it was believed that crude oil flowed in underground streams and accumulated in lakes or caverns in the earth. Today, scientists know that a petroleum reservoir is usually a solid sandstone or limestone formation overlaid with a layer of impermeable rock or shale, which creates a shield. The petroleum accumulates within the pores and fractures of the rock and is trapped beneath the seal. Anticlines (archlike folds in a bed of rock), faults, and salt domes are common trapping formations. (See Figure 2.1.) Oil and natural gas deposits can be found at varying depths. Wells are drilled to reach the reservoirs and extract the oil. Deep wells are more expensive to drill and are usually attempted only to reach large reservoirs or when the price of oil is high.
How Oil Is Drilled and Recovered
Oil is crucial to the economies of industrialized nations, and oil production is strongly influenced by market prices.
Scouting for new deposits and drilling exploratory wells is expensive. It is also costly to drill, maintain, and operate production wells. If the price of oil falls too low, operators will shut off expensive wells because they cannot recover their higher operating costs. In general, when oil prices are high, oil companies drill; when prices are low, drilling drops off.
Figure 2.2 shows a diagram of a rotary drilling system, or rotary rig. The rotating bit at the end of lengths
of pipe drills a hole into the ground. Drilling mud is pushed through the pipe and the drill bit, which forces the mud and bits of rock from the drilling process back to the surface, as shown by the "up" arrows in the diagram. As the well gets deeper, more pipe is added. The oil derrick supports equipment that can lift the pipe and drill bit from the well when drill bits need to be changed or replaced.
Oil deposits are not distributed evenly over the world, and some that have been tapped for decades are being exhausted. As an oil reservoir is depleted, various techniques can be used to recover additional petroleum. These include the injection of water, chemicals, or steam to force more oil from the rock. These recovery techniques can be expensive and are used only when the price of oil is relatively high.