Safety joint

A method of controllably disconnecting a drill string into two portions at a safety joint in the drill string where the safety joint incorporates upper and lower tubular bodies threaded together, the method comprising the steps of:

• (a) threading together upper and lower tubular bodies to complete the drill string which includes a mud flow path along the drill string through said upper and lower tubular bodies;
• (b) locking said threaded tubular bodies together with a lock means to prevent separation of said upper and lower tubular bodies;
• (c) securing said lock means energized by hydraulic oil in a locking position by filling a chamber means with hydraulic oil, which oil, when present, secures the lock means in a locking position;
• (d) transmitting from the surface along the drill string an ultrasonic signal having a specified frequency and amplitude;
• (e) receiving the particular transmitted signal at the safety joint with a receiver means which forms a unique output dependent on the received signal;
• (f) opening a valve means in response to operation of said receiver means;
• (g) removing oil from adjacent to the lock means through the valve means on operation thereof to enable the lock means to be retracted;
• (h) applying an axial pull to the drill string to separate the drill string at the safety joint;
• (i) continuing the pull to separate the upper and lower tubular bodies after movement of the lock means;
• and
• (j) selectively receiving only specified frequencies of vibration transmitted along the drill string.

Safety joint apparatus for use in a drill string comprising:

• (a) an upper tubular body having a threaded connection with a drill string portion thereabove and further having an axial passage therethrough communicated with the drill string to conduct drilling mud therethrough;
• (b) a lower tubular body having a threaded connection with a drill string portion therebelow and further having an axial passage therethrough communicated with the drill string to conduct drilling mud therethrough;
• (c) first threaded tubular surface means being defined within one of said upper or lower tubular bodies;
• (d) second threaded tubular surface means being defined by the other of said upper and lower tubular bodies, said first and second threaded tubular surface means having mating threaded relation and further including:
• (1) threads on one of said mating threaded surfaces formed of coacting helically arranged shoulders, one of said shoulders positioned at an angle to cooperatively receive in threaded engagement therewith the other of said mating threaded surfaces;
• (2) wherein said one shoulder is set at an angle to permit the other of said mating threaded surfaces to be pulled free of one of said mating threaded surfaces;
• (3) wherein the other of said mating threaded surfaces incorporates a plurality of lengthwise slots to define a set of individual concentrically arranged collet fingers permitting relative radial deflection of said fingers to enable the threads to threadedly engage the threads on the other of said mating threaded surfaces on rotation and to ride over the threads on axial pull to separate said first and second mating threaded surfaces;
• (4) a locking sleeve located internally of one of said upper and lower tubular bodies, said locking sleeve securing said fingers in a radially determined relationship which prevents inward radial deflection thereof to maintain said first and second mating threaded surfaces in a threaded position preventing axial movement therebetween, said locking sleeve being formed internally to define a locking receptacle having shoulders at each extremity thereof, said locking sleeve being linearly movable to a releasing position permitting radially inward deflection of said collet fingers;
• and
• (d) hydraulically energized release tool means capable of being hydraulically transported through said drill string to said safety joint apparatus and having radially movable retainer pad means pivotally attached to said tool means for said radial movement and defining shoulders at each extremity thereof and cam means for urging said pad means radially outwardly into interlocked relation within said locking receptacle with the shoulders thereof in driving relation with said shoulders defined by said locking receptacle, said release tool means being linearly movable within said one of said upper and lower tubular bodies when in said interlocked relation with said locking sleeve thus selectively moving said locking sleeve linearly to said releasing position and from said releasing position to said locking position.