Directional drilling apparatus incorporating indexing, fluid operated, spring biassed activation means

An indexing mechanism 134 allows distanced control of a drill bit in a submarine or subterranean drilling exercise. The drilling mud is feed to the drill bit under pressure. The indexing mechanism is arranged within the main housing so that a main restoring means 146 (spring) is dominating the force of the fluid pressure. A mandrel 120 is movable in a down stream direction and carries a cam sleeve 100 with it until a cam follower 143 reaches a first rest position A. The cam sleeve is equipped with ramps and associated steps restricting relative movement of the cam follower to one direction around a closed loop. When the fluid pressure is increased the force of this excedes the force of the restoring means and the mandrel is moved in the second direction again taking the cam sleeve with it, the cam follower moves to the second rest position B. When the fluid pressure is again, reduced, the mandrel moves in the first direction carrying the cam sleeve and the cam follower moves to a third rest position C. This movement results in allowing ports to be opened and closed allowing the drilling mud to by pass the drill bit. A further increase in the mud presure moves the follower to a forth position D. This downward movement of the indexing mechanisum is limited and the fluid presure can be significantly increased without causing any further downward movement to the mechanisum. In fact it takes a reduction in fluid pressure to allow the follower to be moved back to the inisial position A. Apparatus incorporating the same is also disclosed a stabilizer incorporated in the drill string. This is made up of a plurality of elements capable of being moved radially outwards, under suitable actuation, engaging the internal surface of the well bore. Further to this a three dimensional steering tool with a articulated joint is disclosed allowing a degree of eccentricity to the drill string immediately upstream to the joint - the effect is that the drill bit on the remote side of the articulated joint is forced out of a rectilinear relationship enabling the drill string to be steered.