Boring or penetrating the earth – Tool removable or insertable through or around driving or... – Laterally shiftable cutter element movable through shaft
Reexamination Certificate
1999-12-06
2001-06-12
Bagnell, David (Department: 3672)
Boring or penetrating the earth
Tool removable or insertable through or around driving or...
Laterally shiftable cutter element movable through shaft
C166S066500, C166S099000, C294S086250
Reexamination Certificate
active
06244363
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a retrieval head for use in conjunction with a down hole tool for in situ retrieval of a drill bit composed of a plurality of bit segments.
BACKGROUND TO THE INVENTION
A system for in situ replacement of a drill bit for a ground drill is described in Applicant's International Application No PCT/AU94/00322 (WO 94/29567), the contents of which is incorporated herein by way of reference. The system in WO 94/129567 comprises a drive sub which is adapted for connection to a lower end of a core barrel attached to a drill pipe; a core drill bit composed of a plurality of separate bit segments; a bit locking sleeve for selectively locking the bit segments onto seats provided about an inner surface of the drive sub and subsequently releasing the bit segments from those seats; and, a down hole tool for operating the bit locking sleeve and installing and retrieving the drill bit segments.
A slidable cradle extends from a lower end of the down hole tool for carrying the bit segments to and from the drive sub. When installing the bit segments, the cradle is extended from a lower end of the tool against the bias of a spring. Bit segments are then held by elastic bands about the cradle with one end abutting a stop provided at a distant end of the cradle and an opposite end of each segment bearing against a head of the down hole tool. When the down hole tool is lowered into the ground drill and reaches a predetermined position within the drive sub, the cradle is retracted into the main body of the tool by the spring. This causes an upper end of the bit segments to slide along the head of the tool so as to extend laterally of the periphery of the tool. The bit locking sleeve is simultaneously pushed by the tool so as to catch the ends of, and move inside, the bit segments thereby expanding the bit segments to the inner diameter of the drive sub and locking the bit segments into a cutting position.
When it is necessary to change the core bit and thus retrieve the bit segments, the tool is again lowered into the drill pipe and drive sub with the cradle locked into the extended position. At a predetermined position, the down hole tool engages the bit locking sleeve at which time the cradle extends from the lower end of the drive sub. The down hole tool is then pulled upwards a short distance. This pulls the bit locking sleeve upwards thereby releasing the bit segments from the seats on the drive sub. The bit segments collapse onto the cradle by action of the elastic band. Upon further upward pulling of the down hole tool, the tool releases itself from the bit locking sleeve and can thus be pulled to the surface with the bit segments.
Field trials of the above system have proved very successful. However, it is believed that one possible source of failure of the system is that when the bit segments are released so as to collapse onto the cradle there is a remote but nevertheless existent possibility that they can jam in the drive sub and in particular with the bit locking sleeve. This can arise because when the bit segments are released and commence to collapse onto the cradle, they pivot or tilt radially inwardly from the lower end of the bit segments with increasing angle until the bit locking sleeve is pulled completely away from the bit segment. If the tool is withdrawn very quickly so that the uppermost end of the bit segments have not had sufficient time to fully collapse onto the cradle, perhaps due to the viscous nature of the fluid within which the drill is operating, the upper end of the bit segments can jam with the lower end of the bit locking sleeve.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a retrieval head adapted for use with a down hole tool which will substantially eliminate any possibility of jamming of the bit fingers during the retrieval process.
According to the present invention there is provided 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 slide 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.
Preferably the reduced diameter portion includes a first part of progressively decreasing diameter contiguous with the fist length.
Preferably the first part comprises a first part frustum contiguous with the first length.
Preferably the reduced diameter portion includes a second part contiguous with the first part.
Preferably the second part includes a second frustum contiguous with the first frustum and having a diameter which reduces at a greater rate than that of the first frustum.
Preferably said retrieval head further includes a stop coupled to an end of said second length distant said first length against which said bit segments can abut to prevent said segments from failing off said retrieval head.
Preferably said retrieval head further includes centering means provided on the outer circumferential surface of the first length for substantially centering the retrieval head within the drill string, drive sub and bit locking sleeve.
Preferably said centering means comprises a plurality of raised ridges running longitudinally of said first length and spaced about the circumference of said first length.
Preferably said ridges are spaced by a distance to receive a single bit segment.
Preferably opposite ends of said ridges progressively taper in height to the level of said outer circumferential surface of said first length.
Preferably said retrieval head filter includes magnetic means disposed along a portion of said first and second lengths for attracting bit segments upon release from said drive sub and holding said bit segments to said retrieval head.
Preferably said retrieval head comprises a central core extending along said first and second lengths for housing said magnetic means, and sleeve means of non-magnetic material for covering said core.
Preferably said sleeve means comprises a first sleeve part for covering said first length and a separate second sleeve part for covering said second length.
Preferably said retrieval head is further provided with means for releasably coupling said retrieval head to a down hole tool.
REFERENCES:
patent: 4059155 (1977-11-01), Greer
patent: 4760888 (1988-08-01), Saito
patent: 5662182 (1997-09-01), McLeod et al.
patent: 5785134 (1998-07-01), McLeod et al.
patent: 5954146 (1999-09-01), McLeod et al.
patent: 88401/82 (1983-03-01), None
patent: 0 208 532 A2 (1986-07-01), None
patent: WO 94/29567 A1 (1994-12-01), None
Bagnell David
DHT Technologies LTD
Hawkins Jennifer M.
LandOfFree
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