Pipe joints or couplings – Convertible
Reexamination Certificate
1999-08-30
2001-08-28
Luu, Teri Pham (Department: 3627)
Pipe joints or couplings
Convertible
C285S018000, C285S039000, C285S307000, C285S316000, C285S330000, C285S922000, C175S320000
Reexamination Certificate
active
06279962
ABSTRACT:
This invention relates to a safety joint for use in a downhole assembly to permit separation of the assembly at the location of the joint.
Safety joints are well known in the oil and gas industries as a means of providing a point of separation of a downhole assembly. Typically, a safety joint may be used in a fishing string, a washover string or as part of a drill string to enable the majority of the string to be recovered should operative components at the bottom of the string become stuck.
In order to perform the required function a safety joint must be capable of transmitting axial loading both in the tension and compression directions of the joint, and must be capable of transmitting a high level of torque from the upper part of the joint to the lower part of the joint in the normal rotational direction of the string to which it is connected. Typically, in order to allow separation of the string at the safety joint the safety joint incorporates two major components which are connected together by a screw thread which can be released by reverse rotation of the string. The screw threaded connection is designed to unscrew at a torque significantly less than that required to unscrew the connections above it in the string with a result that reverse rotation of the string will cause separation of the string at the safety joint thereby allowing the portion of the string located above the safety joint to be recovered.
A known design of safety joint for use in a downhole assembly to permit separation of the assembly at the location of the joint comprises a body, means for securing the body to part of the assembly, a main shaft, means for securing the main shaft to the remainder of the assembly, and main interconnecting means for interconnecting the main shaft and the body to transfer axial loading therebetween and to transmit torque from the shaft to the body in one direction of rotation of the shaft, the interconnecting means being releasable in response to rotation of the shaft in the opposite direction of rotation to release the shaft from the body.
The present invention is characterized in that auxiliary interconnecting means are provided on the body for interconnecting the body to an auxiliary shaft, after removal of the main shaft from the body, to transfer axial loading between the auxiliary shaft and the body and to transfer torque from the auxiliary shaft to the body in the said opposite direction of rotation.
The present invention enables the safety joint to be operated in conventional manner to release the upper part of a downhole assembly which has become stuck below the safety joint. An auxiliary shaft can then be run into the hole on a suitable string for connection to the body to enable a torque to be applied to the body and thus to the stuck part of the assembly in a direction opposite to the direction of rotation to which the assembly was subject when it became stuck. The application of such reverse torque will, in certain instances, be effective to release the stuck portion of the assembly. Even if the reverse torque does not free the entire stuck assembly, it will result in separation of the stuck part of the assembly from the safety joint body, thereby allowing the safety joint body to be recovered. In fact, separation may occur at a pin joint some distance below the safety joint body with the result that not only the safety joint body, but also part of the stuck assembly may be recovered.
In a particularly preferred embodiment of the invention the auxiliary interconnecting means is releasable in response to rotation of the auxiliary shaft in the said one direction of rotation. Accordingly, if the application of a reverse torque does not free the stuck assembly nor separates the safety joint body from the stuck assembly, the auxiliary shaft and the components upon which it is mounted can be recovered from the hole.
In a particularly preferred embodiment of the invention the main interconnecting means comprises a first screw thread on the body for engagement by a corresponding screw thread on the main shaft and a main dog clutch for transmitting torque in the one direction of rotation from the main shaft to the body. Preferably, the auxiliary interconnecting means comprises a second screw thread on the body for engaging a corresponding screw thread on the auxiliary shaft, and an auxiliary dog clutch for transmitting torque from the auxiliary shaft to the body in the said opposite direction of rotation. Preferably, the main dog clutch is formed by dog teeth provided on the body and dog teeth provided on a collar secured to the main shaft. Preferably, the auxiliary dog clutch is formed by the dog teeth provided on the body and dog teeth provided on an auxiliary collar secured to the auxiliary shaft.
Preferably, the dog teeth provided on the collars have a negative flank angle on the leading (driving) faces thereof and the dog teeth provided on the body have a corresponding negative flank angle so that the application of torque in the driving direction from the respective collar to the body will result in the collar being pulled towards the body.
Preferably, the trailing (reverse) flanks of the dog teeth on the collars have a positive flank angle so that rotation of each collar in the direction opposite to its normal drive direction will result in a cam force being generated between the reverse face of dog teeth on the collar and the dog teeth provided on the body to cam the collar away from the body.
Preferably, the collars are slideably mounted on their respective shafts and spring biased in the downhole direction.
The outside diameter of the thread on the main shaft is preferably less than the inside diameter of the thread on the body which is adapted to mate with the thread on the auxiliary shaft. With such an arrangement, the thread on the body which is adapted to mate with the main shaft can be located axially below the thread of the body adapted to mount with the thread on the auxiliary shaft. Alternatively, the threads on the body adapted to mate with the threads on the main shaft and auxiliary shaft can be superimposed and occupy the same axial zone of the body.
REFERENCES:
patent: 2049289 (1936-07-01), Burns et al.
patent: 2049290 (1936-07-01), Burns et al.
patent: 2163212 (1939-06-01), Reddick
patent: 2307275 (1943-01-01), Johnson
patent: 2736384 (1956-02-01), Potts
patent: 3842914 (1974-10-01), Mott
patent: 4728124 (1988-03-01), Righi et al.
patent: 0238915 (1987-09-01), None
patent: 538666 (1941-08-01), None
patent: 2294068 (1996-04-01), None
McGarian Bruce
McGarian Valentine H.
Dykema Gossett PLLC
Luu Teri Pham
Smith International Inc.
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