Drill string shock absorber

Claim 1

In a shock absorber for use in a well drilling string in a well bore having a drilling jar formed by inner and outer members with up and down jar impact faces engageable to engage and deliver an up or down jar impact to the well string when it is stuck and wherein the shock absorber includes an elongated telescopic structure having an inner tubular body and an outer housing with means for connecting the structure in a well drilling string for conducting drilling fluid therethrough, the structure further having rotary drive means between the body and the housing and resilient means engageable between the body and housing to cushion telescopic contraction and extension of the inner body and outer housing forming the structure, the invention including: means to substantially neutralize the effect of well drilling fluid on the body; seal means in longitudinally spaced relation between the body and housing to provide a liquid receiving chamber in which the resilient means is recieved; extension and contraction stop shoulder means on the body and housing to limit longitudinal extension and contraction therebetween, said shoulder means being formed on the body and housing outside the liquid receiving chamber; said extension stop shoulder means being longitudinally spaced on the body and housing to engage and prevent further extension of the body and housing before the up drilling jar impact faces engage to deliver an up jar by a pull on the well string, and said contraction stop shoulder means being spaced to engage and prevent further contraction of the body and housing before the down drilling jar impact faces engage to deliver a down jar by pushing on the well string so as to inhibit damage to the structure of the shock absorber during jarring blows to the stuck well string by the drilling jar.