This paper presents the development of fluid-jet methods for the drilling of wells through unstable formations. The work demonstrates the technical capabilities of drilling through unstable formations including Methane hydrate and permafrost.

Abrasive fluid-jet systems are capable of drilling through rocks of all types, and with greater directional control that is not susceptible to the geologically induced deviations encountered with mechanical bits, since no mechanical contact is made with the rock while drilling. Abrasive fluid-jets drill rock through the erosion induced by very small particles which individually remove only small fragments but are in such numbers that the drilling rate is at or above that of conventional tools. The particles are powered by the velocity of the supporting fluid, generated in turn by pumps on the surface. The cutting occurs ahead of the nozzle body allowing a casing to be used which is of a larger diameter than the drilling assembly itself. Abrasive jets drill through the erosion of the rock under the specific impact point of the jet contact. They do not therefore exert significant force to the rock around the drilling point and erode the rock without inducing great disturbance to the surrounding material, thus enhancing borehole stability. Fluid-jet methods have the potential of improving drilling efficiency through unstable formations.

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