Methods Of Oil Drilling

Methods of oil drilling: how oil crews reach the hidden wealth of the world's oil reserves.

Oil has been the most heavily relied upon energy source in the world for decades. Petroleum products include the gasoline that powers cars and trucks, the asphalt that covers roads, and the lubricants used in engines and mass-production factory machinery. With such a great demand for petroleum products among the industrialized nations, it is vital that oil drillers be able to reach the reserves of crude oil hidden beneath the surface of the earth.

The first method oil drillers use is called Cable-Tool Drilling. It is the simplest way to drill and is used to create shallow wells in soft beds of rock. A bit held to a long steel cable by an iron rod called a stem is raised and dropped again and again. The force of the drop drives the bit deeper and deeper into the ground. The jagged bit crushes soil and rock and the drillers must occasionally pull it out to pour water in the opening to flush it out. The bailer, a long pipe, takes out the water and loose rocks and soil.

The second and most widely used method is Rotary Drilling. The equipment used is more complicated, but a rotary drill works more like a screwdriver, turning rapidly to force its way down. The rotary table rests on the floor of the oil derrick and is turned by an engine to turn the bit. The rotary table holds the kelly, the uppermost part of the hollow drill stem. The kelly attaches to the drill pipe, which connects to the drill collar that holds the bit. The draw works is what lowers and raises the drill stem out of the hole. A cable runs from the hoisting drum at the bottom of the derrick over two sets of pulleys farther up. A hook connects the lower pulley to the kelly to allow it to be raised and lowered.

As the bit drives into the ground, the kelly will begin to sink down level with the rotary table. The drilling crew must stop, pull up the kelly and disconnect it to add another section of drill pipe. This is done about every nine feet the bit drills. Also, mud is forced down the drill stem to carry pieces of rock out of the hole. The mud plasters the sides of the hole, helping to prevent cave-ins. Another way of preventing a cave in is to line it with steel pipe called casing. This also keeps the oil well from contaminating ground water.

The bit may become dull or encounter a different rock formation, requiring the drill crew to pull the pipe and change it. If the bit or drill pipe breaks off in the hole, the crew will try to pull it out with "fishing" tools. If that fails, they will pour cement into the hole over the obstruction and lower a tool called a whipstock down. They will try drilling again, passing the bit through the whipstock and around the obstruction. Once they have the drill down to where the oil reserve is, the drill crew can pull the drill pipe and focus on bring the oil to the surface.

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