Cable Tool Drill

The technology first used in the petroleum fields of Alberta descended from the drills used by the Chinese as long as 2,000 years ago. The salt drillers of Sichuan Province had figured out how to suspend a sharpened iron bit from a wooden tripod and, by raising and lowering it repeatedly, smash through earth and rock in order to reach the desired brine. They poured in water to flush out the drillings and inserted bamboo tubes to keep the bore hole open. They even brought up natural gas, which they originally feared as an evil spirit from the underworld but eventually used to fuel the heating process

employed to evaporate the water from the salt.

A variant of the Chinese salt drill was the spring pole rig used in the United States beginning in the early nineteenth century and then brought to Canada. This device was constructed of a bit attached either to wooden rods or to a cable suspended from a flexible sapling propped up on a fulcrum. Using a kick board or foot loops, the bit was lowered repeatedly against the ground, thereby pulverizing the earth into which the bit was driven. One Canadian feature was the addition of runners so that the rig could be moved as a sled from well to well.

Not that much had changed by the beginning of the twentieth century when the standard device was a cable tool drill. Like the earlier models, it relied upon the power of percussion to break through earth and rock. Made of tempered steel, the chisel-nosed bit would be widest to “spud in” a well or begin drilling; as it descended it was replaced with narrower bits, becoming as small as 15 cm (6 in.). At each strike, the bit would be turned slightly so that the hole pounded into the ground would reflect the diameter of the bit itself.

Modern advances over the Chinese technology included the substitution of steam power for foot power to raise the bit as well as the replacement of the wooden tripod or sapling with a constructed derrick. Derricks were square open towers ranging in height from 20 to 30 m (66 to 96 ft.) and raised over rig cellars dug into the ground about 6 m (20 ft.) deep. Until the 1920s, these derricks were built of wood which was then phased out in favor of steel.

Cable tool drilling was difficult work and often quite dangerous. The bits had to be pulled out and sharpened regularly. As the drill bit descended, it produced chips that would fill the hole, requiring drilling periods to alternate with baling periods when the bore hole would be

flooded and the resulting mud would be lifted out with a baler. Thus, progress was painstakingly slow, and when a bit did finally pierce a reservoir, it was possible for the pressure of the gas to send it shooting up through the rig as a screaming projectile.