72 PETROLEUM TECHNOLOGY, ECONOMICS, AND POLITICS
Although there are many variations in design, all modern
rotary drilling rigs have essentially the same components
(Figure 3.1). The hoisting, or draw works, raises and lowers
the drill pipe and casing, which can weigh as much as 200 tons
(200,000 kg). The height of the derrick depends on the number
of joints of drill pipe to be withdrawn as a unit before being
unscrewed. The rotary table located in the middle of the rig
floor rotates the drill column. The table also gaps the drill stem
when the hoist is disconnected and pipe sections are inserted or
removed. It imparts rotary motion to the drill stem through the
kelly attached to the upper end of the column. The kelly fits into
a shaped hole in the center of the rotary table. The couplings
between pipe sections are called tool joints.
The drilling bit is connected to drill collars at the bottom of the
stem. These are thick steel cylinders, 20 to 29 feet (6 to 9 meters)
long; as many as 10 may be screwed together. They concentrate
weight at the bottom of the column and exert tension on the more
flexible pipe above, reducing the tendency of the hole to go offline and the drill pipe to fracture. Drill bits have many designs and
the variations include the number of blades, type of metal, and
shape of cutting or brading components. To alleviate the problem
of dull wear-out or jamming, a mud-circulating system is one of
the most important parts of a rig (Ranney, 1979). This system maintains the drilling mud in proper condition, free of rock cuttings or
other abrasive materials that might cause problems with the drilling operation, as well as retains the proper physical and chemical
characteristics of the mud.
3.2.3 Drilling
Drilling an oil well is tedious and is often accompanied by difficulties. Some problems result from formation penetration and
the occurrence of high-pressure gas, fissures, or unexpected high
pressures in permeable rock. Others result from metallurgical or
mechanical failures in the bit, the drill stem, the draw works, or the
mud system. Many tools and techniques have been developed to
solve most problems; probably the best known is the fish used to
recover broken bits. Another technique involves intentional deviation of the borehole to avoid difficult formations, to go around an
unrecoverable fish, or sometimes to restore the direction of the hole
after an accidental deviation.
Although there are many variations in design, all modern
rotary drilling rigs have essentially the same components
(Figure 3.1). The hoisting, or draw works, raises and lowers
the drill pipe and casing, which can weigh as much as 200 tons
(200,000 kg). The height of the derrick depends on the number
of joints of drill pipe to be withdrawn as a unit before being
unscrewed. The rotary table located in the middle of the rig
floor rotates the drill column. The table also gaps the drill stem
when the hoist is disconnected and pipe sections are inserted or
removed. It imparts rotary motion to the drill stem through the
kelly attached to the upper end of the column. The kelly fits into
a shaped hole in the center of the rotary table. The couplings
between pipe sections are called tool joints.
The drilling bit is connected to drill collars at the bottom of the
stem. These are thick steel cylinders, 20 to 29 feet (6 to 9 meters)
long; as many as 10 may be screwed together. They concentrate
weight at the bottom of the column and exert tension on the more
flexible pipe above, reducing the tendency of the hole to go offline and the drill pipe to fracture. Drill bits have many designs and
the variations include the number of blades, type of metal, and
shape of cutting or brading components. To alleviate the problem
of dull wear-out or jamming, a mud-circulating system is one of
the most important parts of a rig (Ranney, 1979). This system maintains the drilling mud in proper condition, free of rock cuttings or
other abrasive materials that might cause problems with the drilling operation, as well as retains the proper physical and chemical
characteristics of the mud.
3.2.3 Drilling
Drilling an oil well is tedious and is often accompanied by difficulties. Some problems result from formation penetration and
the occurrence of high-pressure gas, fissures, or unexpected high
pressures in permeable rock. Others result from metallurgical or
mechanical failures in the bit, the drill stem, the draw works, or the
mud system. Many tools and techniques have been developed to
solve most problems; probably the best known is the fish used to
recover broken bits. Another technique involves intentional deviation of the borehole to avoid difficult formations, to go around an
unrecoverable fish, or sometimes to restore the direction of the hole
after an accidental deviation.