Polarity symbols

Breakdown voltage

Electrical engineering

Physics

Engineering

Composite material

Voltage

Drill

Electrode

Metallurgy

Materials science

Drilling

Rate of penetration

Drill bit

Drill string

Polarity reversal

Quantum mechanics

Transformer

Petroleum engineering

International Journal of Rock Mechanics and Mining Sciences

Electrical discharge drilling is a promising method that allows for the reduction of the costs of well drilling in hard rocks including the energy costs. This paper describes experimental drilling of a well in granite. The well has the diameter of 340 mm and the depth of 15 m, and transformer oil was used as the drilling fluid. In order to study the characteristics of the drilling process and drill string stability we used two drill bits with the interelectrode gaps of 40 mm and 70 mm and applied pulse voltage of positive and negative polarity to the drill bit electrodes. The results are as follows. Increasing the inter-electrode gap has allowed us to reduce the energy costs while increasing the drilling rate, but it has slightly reduced the lifetime of the drill string insulation. The polarity of the voltage pulse has no effect on the penetration rate. At the same time, in the case of negative pulse polarity, the electrical stability of the drill string insulation is higher than that for the positive one. For the 70 mm inter-electrode drill gap, the specific energy consumption and energy input per unit length of the inter-electrode gap are lower while the performance of a single pulse is greater. In this paper we are also discussing the peculiarities and prospects of industrial implementation of electrical discharge drilling. In addition to increasing the overall reliability of the drill string and pulse power source, it is necessary to find suitable insulation material with high flashover resistance in water-based mud.

Electrical discharge drilling of granite with positive and negative polarity of voltage pulses