Page 8 - A Primer of Oilwell Drilling, 7th Edition

able-tool drilling and rotary drilling techniques have been avail-
Cable since people first began making holes in the ground. Rotary 3
Petroleum Extension-The University of Texas at Austin
rigs dominate the industry today, but cable-tool rigs drilled many
wells in the past. Over 1,600 years ago, the Chinese drilled wells with
various primitive yet efficient cable-tool rigs, which they continued
to use into the 1940s. To quarry rocks for the pyramids, the ancient
Egyptians drilled holes using hand-powered rotating bits. They drilled Cable-Tool and
several holes in a line and stuck dry wooden pegs in the holes. Then
they saturated the pegs with water. The swelling wood split the stone Rotary drilling
along the line made by the holes.
Most wells today are drilled with rotary rigs based on the Hamil
Brothers’ design at Spindletop.

CaBLE-TOOL dRILLINg
A steam-powered cable-tool rig was used by Drake and Smith to drill
the Oil Creek site in Pennsylvania. The early drillers in California
and elsewhere also used cable-tool rigs. The principle of cable-tool WALKING BULLWHEEL
BEAM
drilling is the same as that of a child’s seesaw. When a child is on
each end of a seesaw, it moves it up and down. The rocking motion
demonstrates the principle of cable-tool drilling.
To explore the concept further, one could tie a cable to the end
of the seesaw and let the cable dangle straight down to the ground.
Next, a heavy chisel with a sharp point could be attached to the dan-
gling end of the cable. By adjusting the cable’s length so the end of
the seesaw is all the way up, the chisel point hangs a short distance
above the ground. Releasing the seesaw lets the heavy chisel hit hard
enough to punch a hole in the ground. Repeating the process and CASING
rocking the seesaw causes the chisel to drill a hole. The process is
quite effective. A heavy, sharp-pointed chisel can slowly force its way
through rock, bit by bit, with every blow (fig. 15).
A cable-tool rig operates much like a seesaw with a powered
walking beam mounted on a derrick. The walking beam is a wooden
bar that rocks up and down on a central pivot. At Drake’s rig, a CABLE
6-horsepower (4.5-kilowatt) steamboat engine powered the walking
beam. As the beam rocks up, it raises the cable attached to a chisel,
or bit. Then, when the walking beam rocks down, heavy weights
above the bit, called sinker bars, provide weight to ram it into the
ground. The bit punches its way into the rock, and repeated lifting HEAVY
and dropping make the bit drill into the earth. The driller lets out WEIGHTS
the cable gradually as the hole deepens. The derrick provides space (SINKER BARS)
to raise the cable and pull the long drilling tools out of the hole us-
ing one of several winches called the bullwheel.

BIT

Figure 15. A cable-tool rig

15