Patent ID: 6244363
Filing Date: 2001-06-12
Classification: E21B

Abstract:
A retrieval head for coupling to a down hole tool for retrieving a drill bit composed of a plurality of bit segments, the down hole tool adapted to travel through a drill string and a drive sub attached to the drill string, the tool further adapted to release bit segments clamped between the drive sub and a bit locking sleeve held within the drive sub so that the bit segments can collapse onto the retrieval head, the retrieval head including:a body having a first length and a contiguous second length, the first length being of a first constant diameter and the second length having a portion of reduced diameter relative to the first diameter; the first diameter being dimensioned so that the bit segments can initially collapse radially inwardly wholly onto an outer circumferential surface of the first length; and, the reduced diameter portion being dimensioned so that when the bit segments are arranged about the reduced diameter portion, the bit segments can pass through the drive sub, bit locking sleeve and drill string; whereby, in use, when bit segments clamped to the drive sub are collapsed onto the first length and the down hole tool, to which the retrieval head is coupled, is pulled upwardly, the bit segments slide relative to and along the retrieval head from the first length, by abutment of the bit segments with the drive sub and/or bit locking sleeve, to the reduced diameter portion where the bit segments together with the retrieval head can pass through the bit locking sleeve and drill string to be retrieved by said down hole tool.