External pulling tool and method of operation

Abstract

An external pulling tool for retrieving a fish from a wellbore comprises a mandrel fixedly secured to an upper sub, an outer cover fixedly secured to and depending from the upper sub, a collet assembly telescopically surrounding the bottom portion of the mandrel and a support sleeve telescopically surrounding the collet assembly and positioned between the collet assembly and the outer cover. An expandable fluid cavity is formed between a portion of the facing surfaces of the support sleeve and the mandrel. A coil spring, which is disposed between the support sleeve and the upper sub, downwardly biases the support sleeve so that it rests against a lower shoulder on the outer cover when fluid pressure is not applied to the expandable cavil. The collet assembly includes a plurality of collet fingers, each having a collet head at the end thereof. The collet fingers are naturally outwardly radially biased in the direction of the outer cover. When the support sleeve rests on the lower shoulder, the collet heads are radially inwardly displaced or wedged. Before lowering or raising the outer cover to surround the fish, the support sleeve is raised by introducing fluid pressure into the expandable catty, which causes the collet heads to assume their inactive position. When lowering the external pulling tool onto the fish in this manner, collet fingers, which have low bucking resistance, do not collide with nor are axially displaced by the fish.