Application of electrochemical technology to the improvement of rock-drilling systems

Studies of rock drilling with water-based mud have indicated the existence of a current of electrons from the rock to the drill. If this so-called “normal current” is reduced to zero or is reversed by an applied potential, there is a significant reduction in drill wear. The wear rate is enhanced if oxygen is bubbled through the drilling mud and reduced if nitrogen is used, but in any case the electrical effects can still be observed. Observation of the normal drilling current with an oscilloscope has suggested that, when the drill is “sharp”, the normal current is a time-varying d.c. signal with most of the signal levels at frequencies below 25 Hz. As the drill becomes dull, the number of higher frequency signals and the overall signal amplitude increase. We suggest that this change in signal frequency with wear can be used to monitor the condition of an operational drill.