Wells – Processes – Freeing stuck object – grappling or fishing in well
Patent
1990-06-22
1991-06-04
Neuder, William P.
Wells
Processes
Freeing stuck object, grappling or fishing in well
166 98, 294 8622, E21B 3120
Patent
active
050205994
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a drilling tool, but more particularly relates to a tool intended for use in connection with the drilling of an oil or gas well.
In a typical oil or gas well, when the well has been drilled, the interior of the well is lined with a tubular casing. Typically the casing is formed from pipe sections which are of decreasing sizes at increased depth The casing is used to support the sides of the bore.
Running through the center of the well will be a drilling string or a production string, again consisting of numerous tubular elements which are connected together. The tubular pieces of the drilling string or the production string are screwed together, each tubular member having a right-handed threaded projection or "pin" at its lower end, and a box, at its upper end, provided with a threaded bore adapted to receive the right-handed threaded pin at the lower end of the next adjacent tubular element.
During the life of the well, or during the drilling procedure, there may be a need to remove, to the surface, the drilling string or the production string. This is normally accomplished by lifting the drilling or production string and successively unscrewing the tubular members that form the string as they reach the surface. However, it can happen that the drilling string or the production string becomes stuck or lodged in some way within the well, and this prevents the string from being pulled to the surface. For example, due to subterranean pressures, it is possible that the outer casing which supports the sides of the well may fail, and if the casing or formation does collapse in this way, pressure will be applied directly to the drilling or production string, thus preventing any movement of the string.
In such a case it is necessary to clear the obstruction, but firstly all the pipe in the drilling or production string above the obstruction must be removed and taken to the surface. It is not possible to accomplish this merely by pulling upwardly on the production or drilling string, but instead the top of the string above the obstruction must be moved counter-clockwise in order to unscrew one of the couplings between the interconnected lengths of pipe forming the drilling or production string. It will be understood that the "loosest" screw-threaded connection will unscrew, and whilst this may be the connection located immediately above the obstruction, this is unlikely. Thus, in a typical case, only part of the drilling string or production string above the obstruction will be removed from the well, leaving another part of the string within the well.
In order to recover this part of the drilling or production string that remains in the well it is not possible to lower a fresh string and re-establish contact by screwing a right-handed pin at the lower end of the fresh string into the box at the top of the remaining length of string, since again the complete string cannot be lifted, and it will again be necessary to perform an unscrewing operation before lifting the string, and such an unscrewing operation is unpredictable in that the "loosest" connection in the complete string will unscrew.
It has been proposed to remove the remaining part of the drilling or production string, in such a situation, using a special recovery string formed of tubular parts all inter-connected with left-hand threads. Thus the string can be rotated in a counter-clockwise direction without any fear of the connections in the recovery string from becoming undone. The lower end of the recovery string engages the box at the top of the remaining length of string, and thus the top of this remaining length of string is rotated in a counter-clockwise direction, thus again unscrewing the "loosest" connection between the top of the string and the obstruction. This procedure can be repeated several times until the entire length of the remaining string has been removed from the well. However, this proposal does have the disadvantage that a separate recovery string has to be maintained, having left-hand threads.
A furt
REFERENCES:
patent: 3618177 (1971-11-01), Wood
patent: 4706745 (1987-11-01), Bishop et al.
Neuder William P.
The Red Baron (Oil Tools Rental) Limited
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