Cable-tool drilling is a method of drilling in which a hole is made by the repeated blows generated by lifting and dropping a heavy chisel bit on rocks or underground formations. The heavy (usually blunt) chisel bit is the “tool” and the cable could be made of something as simple as a manila rope or multiple steel strands (wireline).
Cable-tool drilling is one of the earliest known methods used to drill for hydrocarbon fluids. This method of drilling did not have the luxury of a fluid circulating system common with modern rotary drilling which removes the crushed rock fragments. So after some time, drilling has to be paused to allow bailers to be used in removing rock fragments that have settled at the bottom of the hole before drilling can resume once again.
How Cable-tool Drilling Works
Creating holes with cable-tool is a slow process especially if deep holes must be drilled. The drilling process involves connecting the cable (rope or wireline) to a walking beam or a spring pole on the surface.
The hole is deepened by repeated strikes from the blunt chisel bit and the repeated impact (strike) is generated as the walking beam moves up and down. When the walking beam moves up, the cable with its tool gets lifted and when it moves downwards, the cable with its tool also accelerates downwards until it strikes the bottom of the hole.
This will go on repeatedly until the rock cracks. Drilling has to stop after a while to remove the cuttings. This method of drilling can take days to drill only a few feet plus it is difficult to control formation fluid pressures.
Modern-day Applications for Cable-tool Drilling
This is why these days it is no surprise to find the modern rotary rigs doing most oil and gas well drilling jobs. However, cable-tool drilling is still being applied when drilling really shallow wells, most especially water wells, or wells where dynamites are dropped for oil and gas exploration purposes.
Exploding dynamites generate waves used to obtain surface seismic data. Another name for cable-tool drilling is percussion drilling. “Percussion” because of the repeated blows on the rock by the chisel bit.