| 摘要 |
<p>Overshot fishing tools for removing stuck thin-wall tubing from well boreholes. The tool comprises at least one slip formed to apply a radially inwardly directed grip on the thin-wall tubing. The grip is concentrated in a longitudinally limited region of the tubing, preferably in a single circumferential line thereon. The grip concentration induces necking of the thin-wall tubing, which ultimately parts (unless previously pulled free). The slip is formed to maintain its grip even when the tubing diameter is reduced below the size at which prior art fishing tools could lose grip. A preferred form of the overshot fishing tool has two such slips, each operatively associated with an internally tapered slip-actuating slip bowl. The upper slip bowl is preferably arranged for limited longitudinal movement inside the tool casing such that the upper slip applies a primary grip to the thin-wall tubing and moves its slip bowl down to actuate the lower slip to apply a secondary grip to the tubing. The overshot fishing tool is particularly applicable to fishing coil tubing as used for workovers in hydrocarbon wells.</p> |
