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(11) | EP 0 461 819 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Ball-grab spear |
| (57) A ball-grab spear for undershot fishing. The spear comprises a mandrel (4), a cage
(1) disposed about said mandrel and movable relative thereto in two mutually orthogonal
directions, an array of wedging ramps (18) formed on the periphery of said mandrel,
a matching array of radial apertures (16) in said cage, and a plurality of balls (14)
disposed individually between a said ramp and a said aperture to be wedged radially
outwards of said mandrel through said apertures by relative movement of said mandrel
and said cage in either of said two mutually orthogonal directions. The spear can be locked to the bore of a downhole fish, e.g. a stuck anchor, by any selected combination of lift and/or torque. |
[0001] This invention relates to a ball-grab spear, and more particularly but not exclusively to a ball-grab spear for use downhole in hydrocarbon wells for undershot fishing of apparatus or articles having a bore.
[0002] In completed hydrocarbon wells (i.e. wells for the production of oil and/or gas), workover operations may be employed to do tubing replacements. In certain circumstances such as low pressure reservoirs it is not desirable to mill the packer. Accordingly the tailpipe is plugged to stop the workover fluid reaching the reservoir and the housing is released at the anchor. However a problem encountered with this technique is that the threads in the connector at the top of the anchor may strip out thus leaving the anchor in place. As the anchor is left flush to the top of the packer an overshot fishing tool is of no use to fish the stuck anchor.
[0003] Accordingly, it is an object of the present invention to provide a ball-grab spear which obviates or mitigates these disadvantages of known fishing tools.
[0004] According to the present invention there is provided a ball-grab spear comprising a mandrel, a cage disposed about said mandrel and movable relative thereto in two mutually orthogonal directions; an array of wedging ramps formed on the periphery of said mandrel, a matching array of radial apertures in said cage, and a plurality of balls disposed individually between a said ramp and a said aperture to be wedged radially outwards of said mandrel through said apertures by relative movement of said mandrel and said cage in either of said two mutually orthogonal directions.
[0005] Preferably, said mandrel is formed to have a periphery which is generally cylindrical about a longitudinal axis of said mandrel, and said cage is formed to be generally cylindrically tubular about a longitudinal axis, said mandrel and said cage being mutually disposed to have their respective longitudinal axes substantially coaxial, one of said two mutually orthogonal directions of relative movement being relative axial movement along said substantially coaxial longitudinal axes, and the other of said two mutually orthogonal directions of relative movement being relative angular movement about said substantially coaxial longitudinal axes. Each said wedging ramp of said array of wedging ramps is preferably formed as a surface which increases its radial separation from the longitudinal axis of said mandrel with increasing displacement in each of said two mutually orthogonal directions from a datum point on said surface. Each said ramp is preferably such that when said datum point is occupied by the respective ball, said ball is permitted to retract through the respective aperture of said cage to lie substantially flush with the outer surface of said cage. Each said surface may either be substantially planar or each said surface may be concave in a radial direction with respect to the longitudinal axis of said mandrel and conically tapered in a direction substantially parallel to the longitudinal axis of said mandrel.
[0006] Said spear preferably comprises ball radial movement limit means to limit the maximum extent of radially outward movement of said balls. Said ball radial movement limit means may comprise shaping of said cage apertures, said cage apertures preferably being conically convergent in a radially outward direction.
[0007] Said spear preferably comprises relative movement limit means to limit the maximum extent of relative movement of said mandrel and said cage in each of said two mutually orthogonal directions. Said relative movement limit means preferably comprises at least one radial projection on the periphery of said mandrel cooperatively associated with at least one L-shaped slot in said cage, said L-shaped slot having one arm thereof aligned substantially parallel to the longitudinal axis of said cage and having the other arm thereof aligned in a substantially circumferential direction with respect to the longitudinal axis of said cage. Said relative movement limit means preferably comprises a diametrally opposed pair of such projections on said mandrel and a diametrally opposed pair of such L-shaped slots in said cage.
[0008] Said mandrel preferably has a respective pocket formed adjacent to and communicating with each said wedging ramp, each said pocket preferably being formed adjacent the respective said datum point, each said pocket being dimensioned to permit the respective ball to retract within that pocket to lie substantially wholly radially within the inner surface of said cage, whereby relative movement of said mandrel and said cage is uninhibited by said balls when so retracted. These pockets thereby facilitate assembly of said spear from the components thereof prior to operational use and in the absence of said relative movement limit means, and also facilitate subsequent disassembly.
[0009] Said cage is preferably provided with bore-engaging frictional engagement means for frictional engagement with the bore of a fish in use of said spear, whereby frictionally to inhibit rotation and longitudinal movement of said cage with respect to a said bore such that movement of said mandrel around and/or along the longitudinal axis thereof tends to produce relative movement of said mandrel and said cage with consequent movement of said balls relative to the respective wedging ramps. Said bore-engaging frictional engagement means preferably comprises a plurality of radially extending resilient fingers secured to or integral with said cage.
[0010] Said mandrel preferably has a drillstring connector, for example a box, at one end thereof for attachment of the spear to a drillstring whereby torque and/or lift can be applied to said spear in use thereof. The other end of said mandrel is preferably fitted with a bullnose to facilitate insertion of the spear into the bore of a fish in use of said spear.
[0011] Embodiments of the invention will now be described by way of example, with reference to the accompanying drawings wherein:-
Fig. 1 is a perspective view of a first embodiment of ball-grab spear in accordance with the present invention;
Fig. 2 is a half-sectioned longitudinal elevation, to an enlarged scale, of the central length of the first embodiment;
Fig. 3 is detail taken from Fig. 2;
Fig. 4 is a diametral section of part of the detail shown in Fig. 3, to an enlarged scale;
Fig. 5 is a development of another detail of the first embodiment, to an enlarged scale;
Fig. 6 is a half-sectioned longitudinal elevation of the mandrel of a second embodiment of ball-grab spear in accordance with the present invention;
Fig. 7 is a half-sectioned longitudinal elevation of the cage of the second embodiment;
Fig. 8 is a transverse cross-section of the mandrel of the second embodiment, taken on the line VIII-VIII in Fig. 6;
Fig. 9 is a transverse cross-section of the mandrel of the second embodiment, taken on the line IX-IX in Fig. 6;
Fig. 10 is a transverse cross-section of the mandrel of the second embodiment, taken on the line X-X in Fig. 6;
Fig. 11 is a longitudinally sectioned detail of a wedging ramp forming part of the mandrel of the second embodiment, to an enlarged scale;
Fig. 12 is a plan view of the wedging ramp of Fig. 11;
Fig. 13 is a sectional view of the wedging ramp of Figs. 11 and 12, taken on the line XIII-XIII in Fig. 12;
Fig. 14 is a transverse cross-section of the mandrel of the second embodiment, taken on the line XIV-XIV in Fig. 6;
Fig. 15 is a development of part of the cage of the second embodiment, to an enlarged scale;
Fig. 16 is a transverse cross-section of the part of the cage developed in Fig. 15, taken on the live XVI-XVI in Fig. 7;
Fig. 17 is another transverse cross-section of the part of the cage developed in Fig. 15, taken on the line XVII-XVII in Fig. 7;
Fig. 18 is a lower end view of the cage of the second embodiment;
Fig. 19 is an elevation of a detail of the cage of the second embodiment; and
Fig. 20 is a half-sectioned longitudinal elevation of a bullnose normally fitted on the lower end of the mandrel of the second embodiment.
[0012] Referring to Figs. 1-5 of the drawings a first embodiment of ball-grab spear 1 in accordance with the present invention comprises an assembly consisting of an outer member in the form of tubular cage or housing 2 coaxially surrounding a mandrel or inner member 4. The housing 2 has a flange 6 at the upper end of the spear and a series of friction springs 8 arranged towards the lower end of the spear 1. The inner member 4 has a threaded drillstring connector box 10 at the top end and a nose piece 12 at the bottom end.
[0013] A series of balls 14 are arranged to extend through radially tapered slots 16 in the housing 2 under the control of radiused tapered grooves 18 in the inner member 4. As is most clearly shown in Figs. 3 and 4, the grooves 18 are conically tapered in the longitudinal direction (and rounded off at longitudinally opposite ends), while being concave in a radial direction (and thus effectively being tapered in both circumferential directions). The grooves 18 thus form wedging ramps which are tapered in two mutually orthogonal directions (longitudinal, and circumferential or angular).
[0014] A stop member 20 secured to the inner member 4, extends radially outwards from the inner member 4 through an L-shaped slot 22 in the outer housing 2. The mutual cooperation of the stop member 20 and the L-shaped slot 22 ensures that relative movement of the mandrel 4 and the cage 2 is limited to a predetermined axial extent (set by the longitudinal arm of the slot 22) and to a predetermined angular extent (set by the circumferential arm of the slot 22) as shown in Figs. 1 and 5.
[0015] In use, the ball-grab spear 1 is inserted downhole and the housing 2 enters the bore of the downhole article or equipment to be lifted (e.g. a stuck anchor). Once the cage or housing 2 has entered the bore sufficiently (the flange 6 preventing excessive insertion), the mandrel or inner member 4 can be lifted which has the effect of causing the balls 14 to move to the lower ends of the grooves 18 where they are constrained to extend through the radially tapered slots 16 in the housing 2 as can be seen in Fig. 2. The balls 14 thus grip the bore of the equipment to be lifted and this grip is maintained provided that lift continues to be applied to the inner member 4. The grip obtained by the balls 14 is sufficient to allow a relatively high lifting force to be applied. As the balls 14 sit in radiused tapered grooves 18 they can also be locked in torque with little or no overpull since the circumferential taper of the grooves 18 ensures that torque applied to the mandrel 4 wedges the balls 14 radially outwards against the bore of the fish.
[0016] If it is desired to release the balls 14 and lift the ball grab spear, the inner member 4 is pushed downwards thus moving the balls 14 towards the larger end of the grooves 18 to release their gripping action. At the same time the stop member 20 moves in the direction of arrow A in Fig. 5 and by applying a rotational force to the inner member 4 the stop member 20 will take up the position shown dotted in Fig. 5, i.e. at the closed end of the circumferential arm of the L-shaped slot 22. An upward force can then once again be applied to the ball-grab spear 1 to lift the whole tool without the balls 14 being forced radially outwardly since the inner member 4 and housing 2 are constrained against relative longitudinal movement by the stop member 20. The bottom face of the stop member 20 may be knurled to aid in spear release. The radially extending resilient fingers 8 on the cage 2 frictionally restrain movement of the cage 2 both longitudinally and angularly with respect to the fish, thus ensuring that lift and/or torque applied to the mandrel 4 wedges the grooves 18 under the cage-restrained balls 14.
[0017] For reliable operation the balls 14 should be harder than the equipment being fished e.g. 40-55 RC (Rockwell C scale) and the inner member 4 should have the grooves 18 locally hardened to be harder than the balls, e.g. 50-55 RC, to avoid damage.
[0018] The arrangement is such that at no time does the housing 2 see contact stress from the ball and taper thrust. The balls 14 should bottom out in the grooves 18 before this happens.
[0019] Referring now to Figs. 6-20, these illustrate a second embodiment of ball-grab spear 100 in accordance with the present invention. (Note that in Figs. 6, 7 and 20, major components of the spear 100 are shown mutually separate, and the cross-sectional views of Figs. 8, 9, 10 and 14 are superimposed on Fig. 6 at respective positions not corresponding to their respective section lines).
[0020] Fig. 6 is a half-sectioned longitudinal elevation of a mandrel 102 forming the core of the spear 100. The mandrel 102 has a generally cylindrical periphery 104 along a major part of its length intermediate the top and bottom ends thereof. A regular array of wedging ramps 106 is formed on the mandrel periphery 104, regularly angularly spaced by 90 degrees around the periphery 104 and regularly longitudinally spaced along the periphery 104 in two rows of five alternating with two rows of four staggered at half longitudinal pitch. (Details of the ramps 106 will be given below).
[0021] The top end of the mandrel 104 is formed with an integral box 108 to serve as a drillstring connector such that torque and/or lift can be applied to the mandrel 102 and hence to the spear 100 as a whole, during use thereof. The bottom end of the mandrel 104 has a reduced diameter and a screw thread 110 for attachment of a bullnose 112 (shown in outline only in its fitted position in Fig. 6, and detailed below with reference to Fig. 20).
[0022] Fig. 7 is a half-sectioned longitudinal elevation of a cage 114 which forms another major component of the spear 100. The cage 114 is generally cylindrically tubular, and in the fully assembled and operational spear 100, the cage 114 encompasses the mandrel 102 (Fig. 6) with the respective longitudinal axes of the cage 114 and the mandrel 102 being substantially coaxial.
[0023] The cage 114 is provided with a regular array of apertures 116 whose angular and longitudinal positions on the cage 114 match those of the wedging ramps 106 on the mandrel periphery 104 such that in a particular relative alignment of the cage 114 around the mandrel 102, the cage apertures 116 each overlie a respective one of the wedging ramps 106. (In fact, symmetry of the spear 100 gives two such relative alignments, separated by 180 degrees around the longitudinal axis, but relative movement limit means detailed below restrict relative angular movement to a much narrower range precluding more than one such alignment in normal use of the spear 100).
[0024] Each cage aperture 116 extends radially through the cage 114 between the inner and outer surfaces thereof, and is conically convergent in a radially outward direction. (The technical significance of this radial tapering of the apertures 116 will be detailed below).
[0025] The upper end of the cage 114 is formed with an integral flange 118 to inhibit over-insertion of the spear 100 into the bore of a fish.
[0026] Turning now to details of the wedging ramps 106, these are essentially planar surfaces (one of which is shown in the enlarged-scale plan view of Fig. 12) formed in the mandrel periphery 104 such that each ramp 106 has an increasing radial separation from the longitudinal axis of the mandrel 102 in both circumferential (anti-clockwise as viewed from above) and longitudinal (downward) directions from a respective datum point (denoted 120 for the ramp 106 traversed by the section line VIII-VIII, which passes exactly through that datum point). Thus the cross-section of Fig. 8 shows the near-minimum radial extent of the respective ramp 106 at the respective datum point 120, while the cross-section at Fig. 9 shows the increased radial extent of the respective ramp 106 longitudinally further down the respective ramp 106 (actually not the same ramp as that sectioned in Fig. 8, but nevertheless mechanically identical per se).
[0027] From the datum point 120 at the upper end of the ramp 106, there is a lateral (circumferential) extension 122 of the ramp 106 which extends anti-clockwise as viewed from beneath in Fig. 8 and leftwards as viewed in Fig. 12. This ramp extension 122 maintains the minimum-radius extent of the ramp 106 under the datum point 120, as is most clearly seen in Fig. 8, and serves as a latched-retracted 'parking' area for associated fish-grappling balls, as will be detailed below.
[0028] Immediately above each of the wedging ramps 106 is a relatively deep ball pocket 124 which opens at its lower edge onto the respective ramp 106. The ball pockets 124 can be seen in longitudinal mid-section in the right half of Fig. 6 (and also to an enlarged scale in Fig. 11), in diametral cross-section (viewed from beneath) in Fig. 10, and in plan in Fig. 12. The function of the ball pockets 124 will be explained below.
[0029] Near the upper end of the cage 114, above the array of apertures 116 and below the top flange 118, the cage 114 is apertured by a diametrally-opposed pair of L-shaped slots 126. Portions of both slots 126 are visible in Fig. 6, whereas both slots 126 are shown in a fully opened-out circumferential development in Fig. 15, in a lower transverse cross-section (viewed from below) in Fig. 16, and in a higher transverse , cross-section (viewed from above) in Fig. 17. The mutually identical L-shaped slots 126 each have one horizontal (circumferential) arm 128 extending from the corner of the respective slot in a direction which is anticlockwise (as viewed from above) and rightwards as viewed from outside the upright cage 114 (i.e. as shown in the left half of Fig. 6, and also as shown in Fig. 15), each slot 126 further having one vertical (longitudinal) arm 130 extending upwards from the corner of the respective slot 126.
[0030] In the fully assembled spear 100 (i.e. wherein the cage 114 is fitted around the mandrel 102), each of the L-shaped slots 126 cooperate with a respective one of a diametrally opposed pair of dogs 132 (Figs. 6 and 14) secured to the mandrel 102 and projecting radially outwards from the mandrel periphery 104 to an extent that each dog 132 reaches at least the outer surface of the cage 114. In plan, each dog 132 is square, i.e. its longitudinal and circumferential dimensions are substantially equal and dimensioned to fit within either one of the arms 128 and 130 of the respective L-shaped slot 126, as shown in Fig. 15. The combination of the dogs 132 and the slots 126 constitutes a relative movement limit means which limits relative movement of the cage 114 with respect to the mandrel 102 in both longitudinal and circumferential directions, as will be more fully detailed below.
[0031] The lower end of the cage 114 is longitudinally slotted to form a plurality of resilient fingers 134 (Figs. 6, 18, 19) which are cranked outwards to form re-entrant shoulders for frictional engagement with the bore of a fish in use of the fully assembled spear 100. The free ends of the fingers 134 are retained, with limited radial freedom, at the bottom end of the cage 114 in the fully assembled spear 100 by means of an internally enlarged rim 136 at the upper end of the bullnose 112 (as shown in outline in Fig. 7).
[0032] In the fully assembled spear 100, the bullnose 112 is secured to the screw-thread 110 on the bottom end of the mandrel 102 (as shown in outline in Fig. 6) by means of a matching internal screw-thread 138 (Fig. 20).
[0033] To assemble the above-described components of the spear 100, a hard metal ball 140 (Figs. 6, 8, 11, 13) is located in each of the ball pockets 124 where it is temporarily retained, e.g. by a small quantity of viscous grease, or by a patch of soluble adhesive, or by a tubular assembly jig (denoted '148' and shown in outline in Figs. 6 and 7) in conjunction with a locknut (not shown) screwed on a thread 150, such that each ball 140 lies fully below the mandrel periphery 104, as shown in Fig. 6 (where only one such ball 140 is illustrated, the remainder of the balls 140, one for each pocket 124 associated with a respective wedging ramp 106 in the array thereof, being omitted for clarity).
[0034] Next, the cage 114 is slid along the mandrel 102 until each of the apertures 116 is aligned over one of the ball-containing pockets 124 on the mandrel periphery 104. The temporary retention of the balls 140 in their respective pockets 124 is terminated, the balls 140 are urged out of their pockets 124 and into contact with the respective overlying cage aperture 116 (e.g. by agitation or centrifugation of the partially assembled spear 100), and the cage 114 is then moved marginally down the mandrel 102 to bring each ball 140 (now cage-guided) down onto the respective wedging ramp 106 as particularly depicted in Fig. 13. The cage 114 is further adjusted (if necessary) relative to the mandrel 102 to bring each of the slots 126 over one of the positions on the mandrel 102 at which the dogs 132 are to be secured. The dogs 132 are now inserted through the slots 126 and secured to the mandrel 102 (Figs. 6 and 14) so as to be in cooperative relationship with the slots 126 (Fig. 15).
[0035] The bullnose 112 is now screwed onto the bottom end of the mandrel 102 such that the respective screw threads 138 and 110 full engage, and the internally enlarged bullnose rim 136 overlies the free ends of the fingers 134 to allow them limited radial freedom.
[0036] The spear 100 is now fully assembled and ready for operational use. In particular, the position of each of the balls 140 on its respective wedging ramp 106 is now controlled (subject to a certain extent of lost motion) by the respective ball-encircling cage aperture 116. In turn, the position of the cage 114 relative to the mandrel periphery 104 is limited in each of two mutually orthogonal directions relative to the longitudinal axis of the mandrel 102 (respectively circumferential (or angular), and longitudinal) by the engagement of the dogs 132 with the respective L-shaped slots 126. Specifically, circumferential (or angular) movement of the cage 114 relative to the mandrel periphery 104 is controlled by engagement of the dogs 132 with the horizontal (or circumferential) slot arms 128, and longitudinal movement of the cage 114 relative to the mandrel periphery 104 is controlled by engagement of the dogs 132 with the vertical (or longitudinal) slot arms 130. The slight underdimensioning of the widths and heights of the dogs 132 relative to widths of the slot arms 128 and 130 results a minimal play or lost motion in the relative position limit means constituted thereby, but without affecting the principle of limitation of relative movement of the cage 114 and the mandrel 102 in each of the two mutually orthogonal directions. Subject to the above-mentioned lost motions, the positions of the balls 140 on the respective wedging ramps 106 are correspondingly controlled and limited. Radial outward movement of the balls 140 relative to the longitudinal axis of the mandrel 102 (now coincident with the longitudinal axis of the spear 100 as a full assembly) is limited by the radially outwardly convergent conical tapering of the cage apertures 116, such that the balls 140 cannot fall out of the spear 100 but otherwise have freedom of radial movement inwardly limited only by the local radial extent of the immediately underlying portion of the respective wedging ramp 106.
[0037] In use of the assembled spear 100, it is secured to the bottom end of a drillstring (not shown) by means of the box connector 108 at the upper end of the mandrel 102. Initially, the cage 114 is lifted and then rotated clockwise (as viewed from above) relative to the mandrel periphery 104, such that the balls 140 are each dragged upwards to the datum point 120 of the respective wedging ramp 106 where the balls 140 are allowed to retract radially to lie within the outer surface of the cage 114 and thence leftwards (as viewed from the outside of the upright spear 100, or clockwise around the mandrel periphery 104 as viewed from above) to come into the 'parking' extension 122 of the respective ramp 106 where each ball 140 is allowed to remain rapidly retracted within the outer surface of the cage 114 and is also cage-retained away from radially greater parts of the respective wedging ramp 106 to inhibit premature fish-grappling ball wedging; in this relative position the dogs 132 are fully engaged within the horizontal (circumferential) arms 128 of the slots 126 to prevent any substantial longitudinal movement of the cage 114 relative to the mandrel 102. The spear 100 is lowered down a well on the end of the drillstring until the bullnose 112 penetrates the bore of a fish (e.g. a stuck anchor, not shown), aided by the frusto-conical leading end 142 of the bullnose 112 (Fig. 20). The spear 100 is further lowered fully into the bore of the fish, to an extent limited by the flange 118 (Fig. 7). The shoulders of the radially extending resilient fingers 134 (Fig. 7) frictionally engage the bore of the fish so as to retard longitudinal and/or angular movement of the cage 114 relative to longitudinal and/or angular movement of the mandrel 102 as applied through the drillstring.
[0038] Once the spear 100 is fully inserted into the bore of the fish, a clockwise torque is applied to the drillstring (as viewed from above) which turns the mandrel 102 clockwise relative to the frictionally retarded cage 114. Since the positions of the balls 140 on their respective wedging ramps 106 are largely determined by engagement of the balls 140 with the array of cage apertures 116, such anti-clockwise movement of the cage 114 relative to the mandrel periphery 104 (as viewed from above) urges the balls 140 out of their respective 'parking' extensions 122 toward the respective datum points 120 to lie on the respective wedging ramps 106 at respective positions in which the radial extent of longitudinally lower portions of the wedging ramps 106 is greater than at the datum points(such movement is to the right as viewed in Fig. 12 and upwards (equivalent to anti-clockwise) as viewed in Fig. 13). Such relative angular movement is permitted by and results in movement of the dogs 132 along the respective horizontal (circumferential) arms 128 of the L-shaped slots 126 leftwards (as viewed in Fig. 15; anti-clockwise as viewed from beneath Fig. 16; clockwise as viewed from above in Fig. 17) away from the closed ends of the arms 128 towards the respective junctions of the respective horizontal and vertical arms 128 and 130. A lift is now applied to the drillstring and hence to the mandrel 102 to drive the balls 140 longitudinally down the respective ramps 106 and hence radially outwards through the cage apertures 116 to grapple the bore of the fish.
[0039] Because of the above-described clockwise rotation and subsequent lift of the drillstring and hence of the mandrel 102 results in the balls 140 being forcibly transferred to portions of their respective wedging ramps 106 which are of greater radial extent than at their respective datum points 120, the balls 140 are driven radially outwards with respect to the longitudinal axis of the spear 100 and hence the balls 140 are typically wedged into contact with the bore of the fish.
[0040] At this stage in operation of the spear 100 (readily determinable at the wellhead by noting resistance to further turning and/or lifting of the drillstring) a lift force and/or clockwise torque may be applied to the mandrel 102 through the intermediary of the drillstring. Such a lift and/or torque will tend to drive the balls 140 longitudinally further down and/or circumferentially across their respective wedging ramps 106 to tighten the grip of the balls 140 on the bore of the fish. Such relative longitudinal movement is permitted by and results in movement of the dogs 132 vertically along the respective vertical (longitudinal) arms 130 of the L-shaped slots 126 upwards (as viewed in Figs. 7 and 15) away from the respective junctions of the respective horizontal and vertical arms 128 and 130 towards the respective closed upper ends of the vertical arms 130.
[0041] The spear 100 is now fully tightened in its grip in the bore of the fish against movement in each of the two mutually orthogonal directions (angular and longitudinal) such that fishing torque and/or lift can be applied by the spear 100 to the fish.
[0042] It is to be particularly noted that the spear 100 is now locked against being positively disengaged from the fish by application of anti-clockwise torque alone (as viewed from above) since the location of the dogs 132 in the vertical arms 130 of the L-shaped slots 126 precludes clockwise rotation of the mandrel 102 relative to the cage 114 (which in turn controls the positions of the array of balls 140 through their engagement with the cage apertures 116), such that release of the spear 100 from the bore of the fish requires the mandrel 102 first to be lowered to bring the dogs 132 to the bottom of the vertical slot arms 130 before anti-clockwise rotation of the mandrel 102 to bring the dogs 132 back along the horizontal slot arms 128, thus to drive the balls 140 across the respective wedging ramps 106 substantially to their respective datum points 120 where the underlying minimum radial extent of the respective wedging ramp 106 permits the balls 140 to retract fully radially inwardly of the cage apertures 116 and thus entirely out of fish-bore-engaging contact.
[0043] Correspondingly, when the balls 140 are fully disengaged as described immediately above, they are locked against re-engagement with the fish by reason of the location of the dogs 132 with the closed ends of the respective horizontal slot arms 126 such that lift alone then applied to the spear 100 will lift the entire spear 100 and force the cage 114 to lift therewith.
[0044] Thus the relative movement limit means comprising the L-shaped slots 126 and the dogs 132 to limit relative movement of the cage 114 and the mandrel 102 in each of the two mutually orthogonal directions provides the advantageous feature that the spear 100 can be selectively locked in each of its fish-bore-engaging and disengaged configuration.
[0045] Reliable operation of the spear 100 is preferably enhanced by selective hardening of the balls 140 and of the wedging ramps 106, preferably by forming these components of suitable grades of steel surface-hardened by a suitable nitriding process. With non-limiting effect, the mandrel 102 is preferably formed of AISI 4145 steel of hardness 30-36 RC (Rockwell "C" scale) and nitrided on the regions of the wedging ramps 106 to a hardness of 58-62 RC in a depth of 0.025 inches (0.635 millimetres); the balls 140 preferably being formed of stainless steel with a somewhat lesser hardness than the surface of the wedging ramps 106 but harder than the bore of a typical fish; the cage 114 preferably being formed of AISI 4140/45 steel with a hardness of 30-36 RC; the bullnose 112 preferably being formed of AISI 4140 steel of hardness 30-36 RC; and the dogs 132 preferably being formed of 4130.50D steel.
[0046] The mandrel 102 may be provided with a hollow through bore 144, continued through a corresponding bore 146 through the bullnose 112, by which the spear 100 can have mud or other fluids pumped therethrough while downhole, e.g. for flushing, venting, measurement, or other purposes.
[0047] When the wedging ramps 106 have the configuration particularly shown in Figs. 12 and 13, the spear 100 can be locked to a fish with clockwise torque (as viewed from above). However, if the ramps 106 are oppositely 'handed' (i.e. reversed right-to-left from the Fig. 12 layout) and the slots 126 correspondingly reversed, the spear 100 will be modified for locking to a fish with anti-clockwise torque.
1. A ball-grab spear comprising a mandrel, a cage disposed about said mandrel and movable
relative thereto in two mutually orthogonal directions, an array of wedging ramps
formed on the periphery of said mandrel, a matching array of radial apertures in said
cage, and a plurality of balls disposed individually between a said ramp and a said
aperture to be wedged radially outwards of said mandrel through said apertures by
relative movement of said mandrel and said cage in either of said two mutually orthogonal
directions.
2. A spear as claimed in Claim 1, wherein said mandrel is formed to have a periphery
which is generally cylindrical about a longitudinal axis of said mandrel, and said
cage is formed to be generally cylindrically tubular about a longitudinal axis, said
mandrel and said cage being mutually disposed to have their respective longitudinal
axes substantially coaxial, one of said two mutually orthogonal directions of relative
movement being relative axial movement along said substantially coaxial longitudinal
axes, and the other of said two mutually orthogonal directions of relative movement
being relative angular movement about said substantially coaxial longitudinal axes.
3. A spear as claimed in Claim 2, wherein each said wedging ramp of said array of wedging
ramps is formed as a surface which increases its radial separation from the longitudinal
axis of said mandrel with increasing displacement in each of said two mutually orthogonal
directions from a datum point on said surface.
4. A spear as claimed in Claim 3, wherein each said ramp is such that when said datum
point is occupied by the respective ball, said ball is permitted to retract through
the respective aperture of said cage to lie substantially flush with the outer surface
of said cage.
5. A spear as claimed in Claim 3 or Claim 4, wherein each said surface is substantially
planar.
6. A spear as claimed in Claim 3 or Claim 4, wherein each said surface is concave in
a radial direction with respect to the longitudinal axis of said mandrel and conically
tapered in a direction substantially parallel to the longitudinal axis of said mandrel.
7. A spear as claimed in any preceding Claim, wherein said spear comprises ball radial
movement limit means to limit the maximum extent of radially outward movement of said
balls.
8. A spear as claimed in Claim 7, wherein said ball radial movement limit means comprises
shaping of said cage apertures to be conically convergent in a radially outward direction.
9. A spear as claimed in any preceding Claim, wherein said spear comprises relative movement
limit means to limit the maximum extent of relative movement of said mandrel and said
cage in each of said two mutually orthogonal directions.
10. A spear as claimed in Claim 9, wherein said relative movement limit means comprises
at least one radial projection on the periphery of said mandrel cooperatively associated
with at least one L-shaped slot in said cage, said L-shaped slot having one arm thereof
aligned substantially parallel to the longitudinal axis of said cage and having the
other arm thereof aligned in a substantially circumferential direction with respect
to the longitudinal axis of said cage.
11. A spear as claimed in Claim 10, wherein said relative movement limit means comprises
a diametrally opposed pair of such projections on said mandrel and a diametrally opposed
pair of such L-shaped slots in said cage.
12. A spear as claimed in any preceding Claim, wherein said mandrel has a respective pocket
formed adjacent to and communicating with each said wedging ramp, each said pocket
being dimensioned to permit the respective ball to retract within that pocket to lie
substantially wholly radially within the inner surface of said cage, whereby relative
movement of said mandrel and said cage is uninhibited by said balls when so retracted.
13. A spear as claimed in Claim 12, wherein each said pocket is formed adjacent to the
respective said datum point.
14. A spear as claimed in any preceding Claim, wherein said cage is provided with bore-engaging
frictional engagement means for frictional engagement with the bore of a fish in use
of said spear, whereby frictionally to inhibit movement of said cage with respect
to a said bore such that movement of said mandrel relative to the longitudinal axis
thereof tends to produce relative movement of said mandrel and said cage with consequent
movement of said balls relative to the respective wedging ramps.
15. A spear as claimed in Claim 14, wherein said bore-engaging frictional engagement means
comprises a plurality of radially extending resilient fingers secured to or integral
with said cage.