Importance

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Abstract

Low-cost, medium-curvature, deviated drainholes are drilled from a vertical cased well in soft formations, using the jet-drilling technique with a coiled-tubing. The high-velocity liquid jet is oriented at a small angle from the axis of the coiled tubing in the selected direction. The jet nozzle assembly is held by a pin in a reference groove in the tubing wall, parallel to its axis. A similar pin in a conventional sonde containing orientation sensors is also inserted in the same groove, so that the jet's spatial orientation is fully determined, with respect to the vertical and North. The jet angle with respect to the tubing axis is pre-set by mechanical or hydraulic locking devices and periodically re-adjusted, based on the sonde's spatial orientation data. The jet nozzle angle may be re-adjusted at the surface after wireline retrieval of the nozzle assembly, or the adjustment may be done downhole by running-in suitable wireline tools, whose pins replace that of the sonde in the reference groove, and whose actuators connect with the mechanical or hydraulic devices. The jet nozzle may also be automatically adjusted downhole by a servo-system utilizing as input the sonde sensors data. The nozzle head surface is a portion of a sphere, pivoting in a hemi-spherical dome cavity at the tubing end. The high velocity jet, when loaded with abrasive particles, may also be used to cut windows into the vertical casing. The combined use of this orientable jet-drilling nozzle with a coiled tubing and with multiple whipstocks described in application Ser. No. 07/814,585, results in additional savings.

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First Claim