| 摘要 |
A tool head is separably attached to the end of a hollow well drilling string for cutting operations within a well and for detachment of the cutting head from the string without removing the string from the well. The head is attached by a ball clutch structure having a pressure responsive release mechanism responsive to an actuating pressure on the release mechanism to release the cuttiong head and the release mechanism from the string, the release mechanism having an upwardly open passage and a downward flow permitting check valve for passing cutting fluid from the string through the passage to the cutting head. Release is effected by dropping a sealing member down the drill string to close the passage and by an increase in fluid pressure above the sealing member and the release mechanism. The release mechanism includes part of the check valve which retain balls of the clutch structure to prevent detachment of the head, that part of the check valve being anchored int its retaining position by shear pins which are fracturable by the increased fluid pressure to release that valve part from its retaining position. The invention relates to the tool structure and to its method of use in drilling or for milling off the inner ends of hollow plugs in well casings to provide gas passages in the casing wall.
|
