Hard rock cutting with high pressure jets in various ambient pressure regimes.

An alternative drilling technology has been developed, in which ultra-high pressure jetting with in excess of 2500 bar jet pressure is combined with mechanical drilling techniques. In order to investigate the cutting performance of the fluid jets in hard rock formations, experiments under various ambient conditions were performed. Core samples from several drilling sites were tested under atmospheric conditions and enabled a solid basis for the comparison of the jettability of different hard rock formations. To simulate deep downhole conditions as realistically as possible, a pressure vessel capable of up to 450 bar internal pressure was designed and built. The experiments, performed under different ambient pressure regimes, show a completely different cutting performance than under atmospheric conditions. The main influencing parameters were determined and adapted to enable a sufficient performance for all tested conditions. Furthermore the usage of drilling fluids in place of water was investigated. The study shows that high pressure jetting is feasible in the challenging simulated downhole environment, including high ambient pressure, several jets with different pressures acting simultaneously, drilling mud as jetting resp. surrounding fluid and high traverse velocities. [ABSTRACT FROM AUTHOR]