When you think about drilling for oil, you may imagine a tall steel structure with black oil gushing out of it. But gushers are a thing of the past. Modern drilling methods have practically eliminated them.
Many kinds of oil derricks are used. Some are as tall as a twenty-story office building, others are attached to trucks, and still, others are located on platforms and barges for offshore drilling.
Rotary drilling accounts for about 85 percent of the wells in the United States. Rotary drilling uses a rapidly-turning bit that bores into the earth. Different kinds of bits are used for different kinds of rock. Attached to the bit is a drilling pipe in ten-meter sections called joints, each weighing about two hundred kilos.
A flat steel turntable grips and turns the pipe, which extends through it into the earth. As the pipe turns, the bit attached to it cuts into the earth. Section after section of pipe is added as the drill chews its way downward.
During the drilling, "drilling mud" is pumped down inside the pipe, which cools and lubricates the bit. As the hole deepens, a long steel pipe, called casing, is added from time to time.
Cutting through rock dulls the bit, so it must be replaced often.
This means all the drill pipes must be pulled out of the hole. There is a lot of work involved in this, and it may take four to six hours to replace the bit and put the pipe down again. When a well has reached a certain depth, the bit and drill are pulled up, and the casing is run all the way down and filled with chemical mud. A small gun is lowered to make holes in the casing and start the oil flowing. Later, water is pumped in to get rid of the mud.
Pressure begins to rise from the well, and finally, oil begins to bubble out of valves into an open tank.
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