Method and apparatus for cutting metal casings with an

Abstract

A method and apparatus for cutting metal casings with an ultrahigh-pressure abrasive fluid jet is shown and described. Examples of such casings include piles and conductors of offshore oil production platforms. In accordance with a preferred embodiment of the present invention illustrated herein, the apparatus is lowered inside the casing to be cut to a desired depth where it is secured to an inner surface of the casing. An ultrahigh-pressure stream of fluid is forced through a nozzle provided in a jet manifold of the apparatus to produce an ultrahigh-pressure fluid jet, into which a volume of abrasives is entrained, thereby generating an abrasive fluid jet. A drive mechanism is provided to rotate the abrasive fluid jet in a substantially horizontal plane to produce a circumferential cut in the casing. The abrasive fluid jet may also be moved in a vertical plane if necessary to complete the cut, for example if the initial cut is in the form of a helix. The performance of the jet is monitored by listening to the sound intensity of the jet with hydrophones. In accordance with the present invention, the cut in the casing may be made by the abrasive fluid jet in either a water or air environment, an air environment being created in a vicinity of the abrasive fluid jet by displacing a volume of water. The volume of abrasives may be entrained in the ultrahigh-pressure fluid jet by a vacuum created by the jet passing through the nozzle or, in an alternative embodiment, the abrasives may be entrained in a pressurized stream of a low density medium such that the pressurized abrasives are injected into the ultrahigh-pressure fluid jet.