Impact of the drilling fluid system on the effectiveness of a high pressure jetting assisted rotary drilling system.

An enhanced drill bit combining high pressure fluid jetting with a conventional rotary drilling system incorporating a tailored drilling fluid was designed to improve drilling performance in hard crystalline rock. Full scale drilling experiments (8 ½ inch bit size) were performed utilizing a specially designed sepiolite fluid and comparing its performance with water and xanthan gum as a standard geothermal drilling fluid. The novel drilling system improved the rate of penetration by over 70% compared to the conventional drill bit without jetting assistance. In addition, the sepiolite drilling fluid retained its fluid properties even after high pressure jetting.