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discovery well, the area of the field can be determined. Wells drilled in the known extent of the
field are called developmental wells. Wells drilled between producing wells in an established
field to increase the production rate are called infill wells.
Text 3
Cable Tool Rigs
When the first commercial oil well in the United States was drilled at Titusville,
Pennsylvania, in 1859, a cable tool rig was used. Cable tool rigs had been in use for hundreds of
years before that to drill for freshwater or for brines that were evaporated for salt.
A cable tool rig is relatively simple. The hoisting system consists of a tower with four
legs called a derrick, 21.9 to 26.5 m high. An engine, originally a steam engine, causes a wooden
walking beam to pivot up and down on the Sampson post. The bit, a solid steel rod about 1.2 m
long with a chisel point on it, is suspended down the well from the opposite end of the Sampson
post by a rope or cable. As the walking beam pivots up and down, it causes the rope and bit to
rise and fall. The bit pounds the well down by pulverizing the rock. The rope or cable is wound
around a reel called a bull wheel. The rope or cable goes from the bull wheel, up over a single
wheel (crown block) at the top of the derrick, then down to a temper screw on end of the walking
beam, and finally down the well to the bit. As the well is pounded deeper, more rope or cable is
let out by turning the temper screw.
After drilling 0.9 to 2.4 m, the bottom of the well becomes clogged with rock chips. The
bit is then raised, and a bailer is lowered into the well on a sand line to remove the rock chips
and water. After the bailer is raised and emptied, the bit is run back into the well to pound
deeper. Heavy casing is run down the well from wire rope wound around the calf wheel. The
wire rope runs through a multiple sheave crown block at the top of the derrick. The casing
(large-diameter pipe) is used in the well to keep water from filling the well and to prevent the
sides from caving in. Lighter equipment, such as the bailer, is run in the well on a sand line from
the sand reel.
Cable tool drilling is very slow with 7.6 m per day being an average and 18.3 m being
very good. It does not effectively control subsurface pressures, and blowouts were common
during cable tool operations. However, all fields discovered during the 1800s were drilled by
cable tool rigs. A cable tool rig in New York drilled a well to a depth of 3,397 m in 1953.
The rotary drilling rig that replaced the cable tool drilling rig was introduced in various
areas throughout the world from 1895 to 1930. The greatest advantage of the rotary drilling rig is
that it could drill the well considerably faster. There were, however, some major problems to be
worked out with the early rotary drilling rigs, and they were not immediately accepted. In 1950,
there was an equal number of active cable tool and rotary drilling rigs in the United States.
Today, almost all wells are drilled with rotary drilling rigs.

Task 3. Answer the following questions, using the vocabulary from Task 1.
1. If a surveyor wants to stake a well what does he accurately determine?
2. What are the functions of a bulldozer in site preparation?
3. How is the start of drilling a well called?
4. What does usually spudding in a medium or deep well begin with?
5. What types of wells can you name? Say a few words about each of them.
6. Where was the first commercial oil well in the United States drilled?
7. What does a cable tool rig consist of? How does it work?
8. When was the rotary drilling rig that replaced the cable tool drilling rig
introduced?

Task 4. Look at Figure 1. It shows a cable tool drilling rig. Look at the figure and
using the information from the text try to describe the way it works.