Wireline jar

Claim 2

An upstroke mechanically operated wireline jar for downhole operations in oil wells and similar installations comprising a casing having an internal downwardly facing shoulder defining an anvil, a rod which is slidable axially in said casing the upper end of said rod projecting from the casing and having means for connecting the jar to a wireline, said rod bearing hammer means, in said casing, which is adapted to strike the said anvil means on an upward stroke of the rod, resilient biasing means acting between said rod and said casing so as to resist initial upward displacement of said rod from a rest position defined by the resilient biasing means, said displacement being caused as a consequence of tension in said wireline, and tripping means comprising an intermediate coupling member between said rod and said biasing means for abruptly disconnecting said biasing means from said rod upon a predetermined upward displacement of the rod whereby upon said disconnection said force on said rod accelerates its upward movement, causing the hammer means to impact the anvil means, resetting of the jar being carried out by means of a downward force applied by the rod on said intermediate coupling member against an upwardly biasing member, characterised in that said resilient biasing means comprises spring means 5 situated in said casing 2 below the rod 3, said spring means abutting a fixed abutment 6 at its upper end and being coupled at its lower end to said intermediate coupling member 4 so as to exert a downward bias force on said coupling member when the latter is upwardly displaced by displacing the rod: from said rest position.

Claim 3

A wireline jar according to Claim 1 wherein said intermediate member comprises a sleeve 4 in said casing, said sleeve defining an internal shoulder at its lower end and having a bush 15 depending therefrom, said jar further comprising a second rod 7 on which said bush is slidably mounted, said second rod having a first end within said sleeve defining a shoulder 6 adjacent to said first rod 3 and a second end fixedly mounted on said casing, said spring means 5 being supported coaxially on said second rod 7 between the bush 15 depending from the sleeve and the shoulder on said second rod, a second spring 16 mounted on said second rod between the sleeve and the casing, said second spring acting so as to arrest downward movement of the sleeve, coupling means 9 contained in through-apertures in the walls of said sleeve, said coupling means simultaneously physically engaging the internal walls of the casing and a respective bevelled groove 10 in the first rod 3, said casing furthermore having two axially spaced apart circumferential bevelled slots 11 and 17 in its internal wall alongside the path of displacement of the sleeve, so that on upward displacement of the first rod 3 in the preset condition of the jar through said predetermined displacement, the sleeve 4 is likewise displaced until the coupling means enters the uppermost slot 11 in the casing and releases the first rod 3 from the said sleeve 4, the latter being then returned by said spring means 5 to its initial location, corresponding to the unstressed condition of the wireline, and when the first rod 3 is displaced downwards, after tripping, by means of a downward movement of the wire- . line, the first rod 3 enters the sleeve 4, engages the coupling means 9, and drives the sleeve 4 downwards against the bias of the second spring 16 until said coupling means enters the lower said slot 16 in the internal wa11 of the casing, so as to temporarily secure the sleeve to the casing whilst further downward movement of the first rod 3 occurs, thereby permitting re-entry of the coupling means 9 in the groove 10 of the first rod and re-engagement of the latter with the said sleeve.

Claim 4

A wireline jar according to Claim 2 wherein the coupling means comprise a plurality of arcuate segments 9,each of said segments having bevelled concave and convex edges.

Claim 5

A wireline jar according to Claim 2 or Claim 3 wherein said bush 15 abuts the bottom end of the casing when the jar is in its preset, rest condition.

Claim 6

A wireline jar according to Claim 2 or any claim appendant thereto wherein said bush 15 has a threaded stop ring fitted at its bottom end which limits the downward displacement of the sleeve.

Claim 7

A wireline jar according to Claim 2 or any claim appendant thereto wherein said second rod 8 is screw-threadedly mounted in the bottom of the said casing 2 such that the bottom end of the second rod is accessible from outside the jar, and wherein the said end of the second rod is adapted to receive a key 18 by means of rotation of which the rod may be raised or lowered in said casing.