In wire line drilling it is known to lower a core barrel coupled to a grappling means provided with a wire or cable into a drill rod string formed by a plurality of hollow rods. This method is preferably used in drilling dry holes.

Before drilling commences the grappling means must be disengaged from the core barrel at the bottom of the string in its working position and pulled up out of the string.

Prior art devices for disengaging the grappling means from the core barrel are burdened with several disadvantages. Most of them are released, when the core barrel is in its working position and axially latched by latching dogs, by pulling heavily on the wire. The drawback there is that the core barrel catches on some projection in the string while the wire is still being fed into the string, and when the core barrel is released from it temporary obstruction in the string to fall freely once again, the retardation force occurring when the wire is once again tensioned releases the latching mechanism and the grappling means is disengaged from the core barrel, which then falls down to the working level, resulting in bit destruction in many cases.

A device is also known which disengages the grappling means from the core barrel with the aid of a sleeve which is movable axially on the grappling means (see US-A-3 701 389). The primary drawback with this device is that it may release the means coupling the grappling means and core barrel before the barrel has arrived at its working position in the bottom drill rod if the barrel comes against something projecting into the drill rod bore during lowering of the barrel.

The object of the present invention is to provide a device of the kind mentioned in the first part of claim 1, by means of which the drawbacks of previously known devices have been circumvented.

This object is fulfilled by the device in accordance with the invention having the characterizing features set forth in the characterizing portion of claim 1. Preferred embodiments of the invention are defined in dependent claims 2-4.

The foremost advantages of the invented device is that it can release the means connecting the grappling means and core barrel only when the barrel is at a predetermined distance from, or assumes a working position in the bottom drill rod, and that it is actuated by a recess in the wall of the bottom drill rod.

The upper portion of a rotatable drill rod string denoted by the numeral 1 is illustrated in Figure 1. In Figures 1-3 there is illustrated the upper portion of a conventional core barrel 2, e.g. of the kind illustrated in US-A-3 701 389, and intended for lowering in the string to assume a working position in the bottom section thereof, which is provided with a drill bit. A grappling means provided with a long wire or cable is used to lower the core barrel 2 to its working position, this wire also being used to pull up the barrel from the string when drilling is stopped. Only a lower portion of this grappling means, denoted bythe numeral 3, is illustrated in Figures 1-3, this portion being removably connected by means of a screw thread to the remaining portion 4 of the grappling means, which is of a conventional configuration.

As will be seen from Figure 1, the lower portion of the grappling means 3 is coupled to the upper portion of the core barrel 2 by means of spring-biased locking jaws 5, swivelably mounted on the core barrel, engaging with an inwardly directed flange 6 on the lower, sleeve-shaped portion 3a of the grappling means. This connection is made before the barrel is inserted in the string. Before connection, an axially movable disengaging sleeve 8 concentric to, and inside the portion 3a, has been displaced upwards against the bias of a compression spring 7 to the position illustrated in Figure 1, and an annular projection 8a on the sleeve 8 is caused to engage with a plurality of, and preferably three, latching dogs 9, of which one is shown in the Figures, the dogs being distributed round the periphery of the grappling means and pivotally mounted thereon. The dogs 9, the upper ends of which are mounted in the grappling means and kept in place by the projection 3b and an elastic O-ring 12, are kept in engagement with the projection 8a, thereby retaining the sleeve 8 bythe lower portion of a sleeve 10 threaded onto the cylindrical surface of the grappling means being taken into a lower position to urge the dogs 9 radially inward.

When the core barrel 2 with the grappling means 3 connected to it has been lowered down the top rod 1 to the position illustrated in Fig. 1 the sleeve 10 is turned manually so that it is displaced upwards on the grappling means from the position shown in Fig. 1 to an upper position, in which the upper edge of the sleeve engages against an abutment 11 on the grappling means. The lower portion of the sleeve 10 thus relinquishes engagement with the latching dogs 9, the bottom portions of which are pressed outwards by the bottom surfaces of the projection 8a incorporated in the spring-biased sleeve 8 press against a sloping surface 9a in a recess in each dog 9. The outwardly directed movement of the dogs 9 continues until they engage against the inner surface of the rod 1, but is not sufficiently long for the dogs to relinquish their grip on the projection 8a so that the sleeve 8 can move downwards.

The barrel 2 and grappling means 3 can now be lowered into the drill rod string 1. During this procedure the dogs 9 glide along and press against the bore of the string and can therefore not release the disengagement sleeve 8, not even if the grappling means 3 assumes a decentralised position in the string, since at least one of the three dogs always retains its grip on the projection 8a. First when the barrel 2 is in, or is immediately above its working position in the lower portion of the string can the dogs 9 leave their retaining position around the sleeve 8, and be moved into an annular recess 13 in the bore of the bottom drill rod. The outwardly directed movement of the dogs 9 is achieved by the pressure of the projection 8a against the surfaces 9a provided by the spring 7. When the projection 8a leaves the dogs 9, the sleeve 8 is displaced downwardly inside the grappling means 3 and is inserted between the locking jaws 5 and the sleeve portion 3a so that the jaws are displaced radially inwards against spring bias. Immediately after the sleeve 8 has left the dogs 9, these are displaced radially inwards by the action of the force in the elastic 0 ring 12. The downward movement of the sleeve 8 continues until its bottom edge rests against the upper side of the flange 6. This condition is illustrated in Fig. 2.

The grappling means 3 can now be pulled up with the aid of the wire attached to its upper portion, since the sleeve 8 has inhibited the coupling grip between the grappling means and the core barrel. During the first phase of withdrawal, the locking jaws 5 glide against the inner surface of the sleeve 8 and cannot engage with the flange 6, since the inner diameter of the sleeve is somewhat less than the inner diameter of the flange.

In Fig. 3, the grappling means 3 is shown disengaged and in a position at a distance from the core barrel 2. The locking jaws 5 of the barrel are also shown in the figure, after they have left the grappling means and have swung radially outwards, and the latching means 5b thereon have been inserted under a shoulder 14 in the bottom drill rod to prevent the axial displacement of the barrel upwards from its working position during drilling.

When the grappling means 3 has been taken up out of the string, the sleeve 8 is pressed upwards against the bias of the spring 7 by some suitable tool, e.g. a screwdriver 15, in the manner shown in Fig. 4, until the projection 8a is accommodated in the recesses of the dogs 9, the sleeve 10 then being screwed downwards onto the grappling means until the sleeve has assumed the position shown by full lines in Fig. 4, where it prevents the dogs 9 from swinging radially outwards. The screwdriver 15 can then be removed and the grappling means lowered into the string 1 for connection to the core barrel 2, when it is desired to pull up the latter from the string. As the grappling means is sunk in the string, the sleeve 10 assumes the attitude shown by full lines in Fig. 4, signifying that the sleeve 8 can never be displaced axially downwards relative the rest of the grappling means, not even when the dogs 9 are opposite the recess 13. When the lower portion of the grappling means (the flange 6) strokes against the locking jaws 5 of the core barrel, the jaws are swung radially inwards from the position shown in Fig. 3 and taken into engagement with the flange 6 simultaneously as the latching portions 5b of said jaws are swung inwards and leave the shoulder 14. The grappling means is now connected to the barrel in the manner shown in Fig. 1 and can be pulled up from the drill rod string.