| 摘要 |
A device is disclosed which is to be incorporated into a drill string used for drilling in subterranean formations. The device includes a first member concentrically mounted with drill pipes disposed above the device and a second member concentrically mounted with drill collars or drill pipes disposed below the device. An intermediate member connects the first and second members and a retainer member maintains the device in its first operative position wherein the entire device is concentric with the longitudinal axis of the drill string. In the first operative position of the device rotation can be transmitted from the first member to the second member and the device acts as an ordinary member of the drill string. The first, second and intermediate members are configured to be capable of occupying a second operative position relative to one another wherein the first member is off-center relative to the second member and wherein the first member does not rotate the second member. The device is shifted into the second operative position by an axial force exceeding a predetermined level, which force breaks the retainer member or renders it incapable of holding the device in the first operative position. Rotation of the drill string from the surface causes a camming action and vibration in the second operative position of the device which helps to free stuck portions of the drill string.
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