Work reported previously has shown that the application of a negative potential to a single point indenter or to a micro roller cone bit reduces the tendency of clays or shales to stick to the indenter or the bit, and thus reduces the tendency of a bit to "ball-up' while drilling. The effect is caused by electro-osmosis, the process by which, in the presence of an electric field, water migrates through the clay towards the cathode, and is liberated as a thin film at the metal-clay interface. This water film prevents adhesion of the clay to the metal of the cathode, and thereby reduces bit balling and increases ROP.

In this paper, we report results of further tests, using both roller cone and PDC drag bits in sizes up to four inches in diameter, drilling in both Pierre and Wellington shales. Making the bit the cathode again reduces the tendency of bit balling, and the rate of penetration is increased, in some cases by 100%. The greatest advantage is obtained at the highest rates of penetration. The power requirements to produce satisfactory results are modest, of the order of 10 Watts at 10 Volts for a four inch PDC bit.

This technique provides a novel method of preventing balling without the use of toxic chemicals, and should be of significant practical importance when applied to the field.

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