| 摘要 |
<p>A retrieving mechanism for subsurface releasing and retrieving of a downhole tool. The apparatus includes an overshot defining a central opening therethrough and an annular cavity therein and a mandrel positionable in the overshot central opening. A slotted C-ring with an internally threaded surface is annularly positioned in the cavity in the overshot. The mandrel includes an externally threaded portion. Longitudinal insertion of the mandrel in the overshot results in ratcheting expansion and contraction of the ring for threaded engagement with the mandrel. The threaded surfaces define a thread profile having a first surface, angled with respect to a central axis of the apparatus, which facilitates the longitudinal insertion of the mandrel in the ring, and a second surfacer extending normally to the apparatus central axis, which prevents longitudinal disengagement. A seal is located above the ring for sealing engagement with a mandrel sealing surface. In a lower portion of the overshot, a rotation plug extends radially inwardly, and on a lower portion of the mandrel a corresponding lug extends radially outwardly. The lugs may be positioned adjacent one another for selectively preventing rotation of the overshot relative to the mandrel.</p> |
