OUTER SELF-RELEASABLE FISHING TOOL Russian patent published in 2006 - IPC E21B31/18 

FIELD: borehole drilling and repair, particularly fishing tools.

SUBSTANCE: fishing tool comprises body with inner spiral conical surface and screw ledge, spiral strip-like engaging member installed inside the body and displaceable in axial direction. The engaging member is provided with driving flag arranged in lower part thereof and with outer spiral surface. Screw fishing thread, guiding ring and guiding means are formed on inner engaging member surface. Inner annular surface is made on conical spiral surface in lower body part and eccentrically to body axis. Annular seat is created below inner annular surface eccentrically to body axis. The annular seat is above body thread arranged in lower part thereof. Longitudinal ledge cooperating with lower end of engaging member and with side flag surface is formed in inner annular surface and in inner seat surface and extending for the full depth of screw ledge of the body. Annular seat neck is created on outer surface of guiding ring eccentrically to axis thereof. The neck is fixed inside eccentric annular seat on inner flag surface so that flag may be displaced in axial and radial directions.

EFFECT: increased reliability of fishing tool self-releasing.

3 dwg