Importance

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Abstract

A down-hole decelerator for decelerating a device dropped down a borehole in a drilling mud column has an elongate casing immersible in the mud flow with its longitudinal axis along the axis of the borehole. A plunger is slidable axially within the casing to vary the volume of two chambers within the casing and terminates outside the casing in a nose for impacting on a landing plate within the borehole when the decelerator reaches the end of its travel on being dropped down the borehole. Apertures extend through the wall of the casing between the chambers and the outside of the casing so that, when the casing is initially immersed in the mud column on being dropped down the borehole, mud flows into the chambers through an apertures, and, when the nose impacts on the landing plate within the borehole, the plunger is forced inwardly of the casing to decrease the volume of the chambers and deceleration of the device takes place by virtue of the resulting controlled flow of mud out of the chambers through the apertures. The device is thereby efficiently safeguarded against damage by impact with the landing plate.

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First Claim