Overshot tool having latch control means

Abstract

An overshot tool for releasable connection to a head assembly as part of a core barrel drilling apparatus. The overshot tool comprises a primary engaging portion and a secondary engaging portion and is configured for the automated coupling and de-coupling to a head assembly via selected engagement of the head assembly by the engaging portion. The overshot tool is configured to both deliver and retrieve a head assembly from a latched position at a cutting end the core barrel.

Claims

1. An overshot tool for releasable connection to a head assembly of a core barrel drilling apparatus, the tool comprising: a primary engaging portion arranged to engage a latch of the head assembly to provide an axial couple between the tool and the head assembly; a secondary engaging portion arranged to temporarily engage the latch in addition to the engagement of the latch by the primary engaging portion; a retainer including a shaft and a head, the retainer acting between the primary engaging portion and the secondary engaging portion; a housing having a region for engagement by the retainer, the primary engaging portion and the secondary engaging portion being axially movable relative to the housing, the retainer being configured i) to engage a first part of the region to releasably couple the primary and the secondary engaging portions for combined axial movement and ii) to engage a second part of the region to allow at least partial independent axial movement of the secondary engaging portion relative to the primary engaging portion, wherein by adjustment of a position of the retainer between the first part and the second part of the housing the tool is adjustable between a first mode to allow axial coupling between the tool and the head assembly and a second mode to provide a decoupling of the tool from the head assembly; and a bias member acting between the housing and the secondary engaging portion to bias the secondary engaging portion axially relative to the primary engaging portion, wherein the primary engaging portion includes an elongate shaft and the secondary engaging portion includes a sleeve positioned around the shaft, the sleeve being configured to slide axially over the shaft of the primary engaging portion.

2. The tool as claimed in claim 1, wherein the region of the housing includes a slot in which the first and the second parts of the housing include regions of the slot and the retainer is arranged to move within the slot between the first and the second parts.

3. The tool as claimed in claim 2, wherein the bias member is configured further to bias the secondary engaging portion rotatably relative to the primary engaging portion.

4. The tool as claimed in claim 3, wherein the bias member is a coil spring extending between the housing and the secondary engaging portion.

5. The tool as claimed in claim 1, further comprising a cover member to accommodate the primary and the secondary engaging portions and the housing, wherein the primary and the secondary engaging portions and the housing are arranged to slide axially within the cover member.

6. The tool as claimed in claim 5, further comprising a temporary rotational lock having at least two locking positions to temporarily lock the housing at the cover member at two rotational positions.

7. The tool as claimed in claim 5, wherein the cover member includes a cut-out positionable at the same axial and rotational position as the slot of the housing.

8. The tool as claimed in claim 2, wherein the retainer is fixed to and projects radially from the shaft and through the slot in the housing, wherein the bias member is configured to force rotational and axial movement of the retainer within the slot.

9. The tool as claimed in claim 8, wherein the first part at the slot extends in a circumferential direction to receive the retainer and the second part at the slot includes an axially extending length section being greater than a length section of the first part.

10. The tool as claimed in claim 1, wherein an engaging end of the primary engaging portion includes a bayonet configuration at a leading end of the tool engagable with the latch and an engaging end of the secondary engaging portion includes a bell portion arranged to engage the bayonet configuration in touching or near touching contact and to release the bayonet configuration from engagement with the latch.

11. The tool as claimed in claim 1, wherein the housing includes a coupling portion at a trailing end of the tool to mate with a valve housing or a free fall overshot attachment, the coupling portion capable of sliding axially within the housing and independently of an axial movement of the primary engaging portion.

12. The tool as claimed in claim 1, wherein the shaft includes a channel recessed into a radially outward facing surface of the shaft, the channel having a first part aligned axially with the shaft and a second part extending circumferentially around the shaft, a radially inner part of the retainer being configured for slidable engagement within the first and second parts of the channel.

13. A method of core drilling using an overshot tool forming part of a core barrel drilling apparatus, the method comprising: transporting the overshot tool in an axially forward direction through the core barrel apparatus; engaging a latch of a head assembly of the core barrel drilling apparatus via a primary engaging portion of the tool to decouple the head assembly from a fixed axial position at the core barrel apparatus and to axially couple the tool to the head assembly; transporting the coupled tool and the head assembly in an axially rearward direction through the core barrel drilling apparatus to retrieve the head assembly; and releasing the axial couple between the tool and the head assembly by moving axially a secondary engaging portion to contact the latch and releasing engagement between the primary engaging portion and the latch, wherein the tool comprises: the primary engaging portion, which is arranged to engage the latch of the head assembly to provide the axial couple between the tool and the head assembly; the secondary engaging portion, which is arranged to temporarily engage the latch in addition to the engagement of the latch by the primary engaging portion; a retainer including a shaft and a head, the retainer being arranged to act between the primary engaging portion and the secondary engaging portion; a housing having a region for engagement by the retainer, the primary engaging portion and the secondary engaging portion being axially movable relative to the housing and the retainer being configured to engage a first part of the region to releasably couple the primary and the secondary engaging portions for combined axial movement and the retainer being configured to engage a second part of the region to allow at least partial independent axial movement of the secondary engaging portion relative to the primary engaging portion, wherein by adjustment of a position of the retainer between the first part and the second part of the housing the tool is adjustable between a first mode to allow axial coupling between the tool and the head assembly and a second mode to provide a decoupling of the tool from the head assembly; and a bias member acting between the housing and the secondary engaging portion to bias the secondary engaging portion axially relative to the primary engaging portion, wherein the primary engaging portion includes an elongate shaft and the secondary engaging portion includes a sleeve positioned around the shaft, the sleeve being configured to slide axially over the shaft of the primary engaging portion.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) A specific implementation of the present invention will now be described, by way of example only, and with reference to the accompanying drawings in which:

(2) FIG. 1 shows a cross-section view of an overshot assembly comprising an overshot tool and a valve housing,

(3) FIG. 2 shows a longitudinal and cross-section view of an overshot tool,

(4) FIGS. 3a, 3b and 3c show cross-section views of a valve housing,

(5) FIGS. 4a, 4b, 5a, 5b and 5c show cross-section views of an overshot tool an valve housing engaging and retrieving an inner tube assembly,

(6) FIGS. 4c and 5d shows a part view of the overshot tool and the operation of the retainer mechanism,

(7) FIGS. 6a and 6b show cross-section views of an overshot tool and valve housing and show the overshot tool releasing from the latches of an inner tube assembly,

(8) FIG. 6c shows a part view of an overshot tool and the operation of the release mechanism,

(9) FIGS. 7a, 7b, 7c and 7d show a sequence of the overshot tool releasing from the latch in the core barrel head assembly,

(10) FIG. 8 shows a part cross-section perspective view of the overshot tool,

(11) FIG. 9 show a part perspective view of an overshot tool and in particular shows details of the retainer mechanism.

(12) FIGS. 10a and 10b show cross-section views of an overshot tool and valve housing assembly engaged with an inner tube assembly to locate the inner tube assembly in a drill string,

(13) FIG. 10c is a part view of the overshot tool showing the retainer mechanism,

(14) FIG. 11 shows a free fall assembly attached to an overshot tool with the overshot tool attached to a head assembly,

(15) FIGS. 12a and 12b show the overshot tool connected to an inner tube assembly in preparation for delivery of the inner tube assembly to the core barrel of a drill string,

(16) FIG. 12c shows a part view of the overshot tool and the position of the retainer mechanism for delivery of an inner tube assembly into a drill tube,

(17) FIG. 13c shows a part view of the release mechanism part way through the operation of the release mechanism, and FIGS. 13a and 13b show the overshot tool as it relates to the position of the release member shown in FIG. 13c, and

(18) FIG. 14c shows the release mechanism in the position where the overshot tool is released from the core barrel head and FIGS. 14a and 14b show the overshot tool as it relates to the position of the release member shown in FIG. 14c.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT OF THE INVENTION

(19) FIG. 1 shows an overshot assembly which is an assembly of an overshot tool 10 and valve housing 11. The overshot tool 10 is used to retrieve an inner tube assembly. It can also be used to deliver an inner tube assembly to the end of a drill string. The valve housing 11 can be used to pump the overshot tool 10 through a drill string. This will normally be to retrieve the inner tube assembly. The valve housing 11 is provided with seals 12 which provide flexible fluid seals between the valve housing 11 and the inner wall of the drill tube. An indicator valve 13 is provided within the valve housing 11 to provide an indication to the driller when movement of the valve housing 11 ceases. The indicator valve 13 is shown in FIG. 1 in its open position and comprises a ball 14 and fluid flow ports 15. In its open position, the indicator valve allows fluid that is pumped in behind the valve housing 11 to flow through opening 16 and the fluid flow ports 15. In its closed position and in order to pump the valve housing 11 along drill tubing, the ball 14 is set behind valve seat 17 which prevents fluid flow through the valve housing 11 and therefore enables fluid pressure to move the valve housing 11 along the drill tube (as shown in FIG. 3a).

(20) Upon the valve housing 11 becoming stationary as would be the case when the overshot tool 10 engages an inner tube assembly, an increase in fluid pressure will cause the ball 14 to move through the valve seat 17 from the position of FIG. 3a to its position of FIG. 1 so that the fluid ports 15 are now open and allow fluid to freely flow forward of the valve housing 11 and around the overshot tool 10. This change in pressure provides an indication at the surface to the drill operator that the overshot tool 10 has landed. The valve housing 11 has a wire rope connector 18 to which a retrieval wire rope is secured. This enables the overshot tool 10 and valve housing 11 combination to withdraw an inner tube assembly from the drill hole. The valve housing 11 is secured to the overshot tool 10 either threadably or by a pin or both. The overshot tool 10 comprises a spike 20 and a latch control means 21. The latch control means 21 has an axial bore through which a portion of the shaft of the spike 20 locates. The spike 20 and latch control means 21 are located within a housing 22 and the housing 22 is in turn located within a cover member 23.

(21) The latch control means 21 comprises a sleeve within which a portion of the shaft of spike 20 is slidably journalled. As will be explained below, the latch control means 21 moves to various positions along the spike 20 to control operation of a latch, and that movement is controlled by a retainer 24 which is threadably mounted with respect to the latch control means 21. An end 25 of the retainer 24 projects from the inner bore of the latch control mean 21 and is selectively locatable within either a longitudinal slot 26 or circumferential slot 27 which are both located on the spike 20 as shown in FIG. 8. The shaft of the retainer 24 locates within a control slot 29 which is located within the wall of the housing 22. The head 30 of the retainer 24 projects above the outer surface of the housing 22 and locates generally within a cut out 31 within the cover member 23. As will be explained below, the head 30 will in certain circumstances abut against an edge of the cut out 31.

(22) A spring 32 is connected to both the housing 22 and the latch control means 21. It provides both a compressive and torsional force to the latch control means 21. The spring 32 is compressed and normally provides a force that pushes the latch control means 21 away from the housing 22. The spike 20 has a tip 35 that comprises a conical portion 36 and a circumferential ledge 37. The conical portion 36 and ledge 37 are designed to engage with the latch in the inner tube assembly.

(23) The spike 20 is journalled for sliding movement within a bearing 39 in the housing 22. The spike 20 is retained within the housing 22 via a pair of bolts 40 that threadably engage the end of the spike 20. The heads of the bolts 40 are located within slots 41 which in turn allows a small amount of longitudinal movement of the spike 20 with respect to the housing 22. When the end 25 of the retainer 24 is located within the circumferential slot 27 on the shaft of the spike 20 then the spring 32 acting on the latch control means 21 will in turn bias the spike 20 into its forward position shown in FIG. 2. When the end 25 of the retainer 24 is located within the longitudinal slot 26 on the spike 20, the spring 32 will push the latch control means 21 forward so that the bell portion 43 locates over the head portion 44 of the spike 20. The latch control means 21 has an abutment collar 45 which cooperates with the latch in the head assembly and its operation is described below.

(24) The cover member 23 is journalled for rotation on the housing 22. Detent balls 58 locate within detent apertures 57 to hold the cover member 23 in one of two positions. This is to position the cut out 31 in relation to the head 30 of the retainer 24 to either arrest movement of the retainer 24 or to allow movement to a predetermined extent.

(25) Figure groups 4 to 7 show the engagement of the overshot tool 10 with an inner tube assembly. The Figures show a head assembly 47 and do not include the inner tube in which the sample is collected. The inner tube is threadably connected to an end of the head assembly 47. The head assembly 47 combined with the inner tube is referred to as the inner tube assembly.

(26) FIGS. 4a and 4b show the overshot tool 10 that has been pumped into a hole and has just engaged with the latches 48 of the head assembly. The latches 48 comprise a pair of arms 49 that are pivotally connected to the head assembly 47 via pivots 50. The inner ends 51 of the latch arms 49 locate behind the ledge 37 on the spike 20. An elastomeric o-ring 52 locates around the inner ends 51 and bias the inner ends 51 so that they engage against the head portion 44 of the spike 20. This holds the inner ends against the ledge 37 to thereby hold the latch 48 in a closed position with respect to the spike 20. The arms 49 have upper ends 53 which abut with the locking coupling of a drill string (not drawn) to hold the head assembly 47, in its drilling position where it is positioned to receive core sample as drilling progresses. In order for the upper ends 53 of the latch 48 to engage with locking coupling in the core barrel, the upper ends 53 need to project radially outward to a greater extent than what is shown in FIG. 4b. The diameter of the head portion 44 of the spike 20 is sized so that the inner end 51 are pushed outwardly against the O ring 52 to thereby retract the upper ends 53 to the position shown in FIG. 4b. This retracted position of the upper ends 53 provides clearance both with respect to the locking coupling and the inner wall of the drill tubing.

(27) The example shown in FIGS. 4a, 4b, 4c, 5a, 5b, 5c and 5d are where the overshot tool 10 is required to be pumped into position which may be the case in respect of a wet hole where a column of water is maintained within the drill tube. It may also be the case in respect of a horizontal or upwardly inclined hole. Generally, it is required in a hole that is not sufficiently vertical (in the downward direction) to allow free fall of the inner tube assembly and associated overshot assembly.

(28) FIG. 4c illustrates the setting of the cover member 23 for retrieval. FIGS. 4a and 4b show the overshot tool 10 just as it connects to the head assembly 47 that is to be retrieved. The tip 35 of the spike 20 pushes through the inner ends 51 of the arms 49 to thereby unlatch the head assembly 47 from the locking coupling of the core barrel. The latch 48 is now engaged with the spike 20 with the inner ends 51 of the arms 49 located behind the ledge 37.

(29) Prior to sending the overshot tool 10 into the drill tube to retrieve the head assembly 47 the latch control means 21 is positioned with respect to the housing 22 so that the retainer 24 is in the position shown in FIG. 4c. In addition, the cover member 23 is rotated so that a slot 61 in the cover member 23 is not aligned with the slot 60 of the control slot 29. This is a pre-loaded position so that the spring 32 holds the retainer 24 in this position. When the spike 20 engages with the latch 48 the fluid pressure continues to act on the valve housing 11 and there is simultaneous operation of both the indicator valve 13 and the retainer 24 associated with the latch control means 21. Both of these things occur substantially simultaneously.

(30) In the case of the indicator valve 13, the pressure will be sufficient to force the ball 14 through the valve seat 17 to the position shown in 4a, 3b and 3c. The valve seat 17 is a polymer and is sufficiently resilient to enable movement of the ball 14 at a predetermined pressure. This release of the ball 14 opens the fluid ports 15 which will enable fluid to flow through the valve housing 11. The valve arrangements within the head assembly 47 will be closed which will prevent fluid flow and allow the overshot tool 10 and valve housing 11 to be pumped through the drill string. Upon reaching a halt, the ball 14 moves through the valve seat 17 and causes a momentary pressure spike which provides an indication to the operator at the surface that the overshot tool 10 has landed.

(31) At the same time, the spike in fluid pressure results in the valve housing 11 pushing the housing 22 and cover member 23 forward towards the head assembly 47 so that the housing 22 is caused to move in relation to both the latch control means 21 and spike 20. Engagement of the end 25 of the retainer 24 within the circumferential slot 27 results in the spike 20 and latch control means 21 moving rearwardly as is shown in FIG. 5d. This in turn causes the spring 32 to be compressed and for the retainer 24 to be moved rearwardly in relation to the control slot 29. It reaches the end of edge end 55 of the control slot 29 and the torsional force exerted by spring 32 causes the latch control means 21 to rotate so that retainer 24 moves into slot portion 60. This is illustrated in FIG. 5d where the latch control means 21 is now able to move longitudinally with respect of spike 20 as a result of the end 25 now engaging the longitudinal slot 26. This moves the latch control means 21 to the positions shown in FIG. 5b where the abutment collar 45 blocks any further inward movement of the upper ends 53 of the latch arms 49. This is the intermediate position of the latch control means 21 and physically prevents any movement of the outer ends of the latch 53 inwardly and thereby prevents any disengagement of the inner ends 51 of the latch arms 49 from the tip 35 of the spike 20.

(32) Once the latch control means 21 rotates so that the retainer 24 is within slot 60 of the control slot 29, the spring 32 acts to push the latch control means 21 forward and the retainer 24 slides within slot 60 until it abuts against edge 62 of the cut out 31 in the cover member 23. This is illustrated in FIG. 5d. In this position, the spring 32 continues to apply force to the latch control means 21 so as to hold the retainer 24 against the edge 62.

(33) The release of the indicator valve 13 provides an indication to the driller at the surface that the overshot tool 10 has engaged the head assembly 47. As the latch control means 21 will have operated automatically, then the combination of the overshot tool 10, valve housing 11 and inner tube assembly will be ready for removal. In order to release the overshot tool 10 from the head assembly 47 upon arrival of the combination of the overshot tool 10, valve housing 11 and inner tube assembly to the surface, the cover member 23 is rotated so that the slot 61 and the cover member 23 aligns with slot 60 in the housing 22. This results in spring 32 pushing the latch control means 21 fully forward to its second position where it disengages the spike 20 from the latch as previously described above. The rotation of the cover member 23 is illustrated in FIG. 6c and the release position is shown in FIGS. 6a and 6b.

(34) This allows a very convenient and safe release of the overshot tool 10 from the head assembly 47. This release is illustrated progressively in FIGS. 7a, 7b, 7c and 7d where the bell portion 43 of the latch control means 21 locates over the head portion 44 of the spike 20 such that the end of the bell portion 43 abuts against the ledge 37. In this position, the outer surface of the bell portion 43 abuts against the inner surfaces of the latch arms 49 adjacent the inner ends 51 of the latch arms 49 so that the inner ends 51 move away from the head portion 44 and out of engagement with the ledge 37. Once the inner ends 51 of the arms 49 no longer engage the ledge 37 then as seen in FIGS. 7a, 7b, 7c and 7d, the overshot tool 10 can be withdrawn from the latch 48 and the end of the head assembly 47.

(35) FIGS. 8 and 9 show more clearly the relationship of the longitudinal slot 26, circumferential slot 27 and retainer 24. As can been seen in, for example, FIG. 12c, when the retainer 24 is located in the three shorter lengths of the control slot 29, that are parallel and proceed slot 60 that cause back and forth movement of the retainer 24 portion of the control slot 29, the end 25 of the retainer 24 will be in the circumferential slot 27 and thereby lock movement of the latch control means 21 with respect to the spike 20. However, when the retainer moves into slot 60 out of the three shorter lengths of the control slot 29 (as shown in FIG. 9), then the end 25 aligns with the longitudinal slot 26 which then frees the latch control means 21 to move longitudinally with respect of the spike 20. This enables the latch control means 21 to move between its first and second position and also an intermediate position as will be described below.

(36) It may also be possible to use the overshot tool 10 and valve housing 11 to connect to an inner tube assembly at the surface and then pump this combination through the drill string. This is not necessary in general practice, but is possible with the overshot tool 10 connected to the head assembly 47 as shown in FIGS. 10a and 10b it would be possible to deliver an inner tube assembly to the end of the drill rods if required. The part conical portion 36 bears against a surface 54 within the head assembly 47. This enables the overshot tool 10 to push against the head assembly 47 while the latch 48 prevents release of the overshot tool 10. In this position, the overshot tool 10 combined with the valve housing 11 could be used to pump the inner tube assembly into the end of the drill string. This is generally not required, as the inner tube assembly itself would normally, in certain types of holes, be pumped into the drilling position. But as explained below, this invention is capable of being used in this way.

(37) In order to achieve this, the retainer 24 is placed within the control slot 29 in the position shown in FIG. 10c. The retainer 24 is held in this position by the compressive action of spring 32 pushing the latch control means 21 with respect to the housing 22 to thereby hold the retainer 24 in the position shown in FIG. 10c. In addition, the end 25 of the retainer 24 is located within the circumferential slot 27 on the spike 20. This in turn forces the spike 20 forward so that the bolts 40 are in the forward portion of their slots 41. Further, the spring 32 provides a torsional load to the latch control means 21 which in turn means that the retainer 24 is pushed against the edge end 55 of the control slot 29.

(38) In this configuration, the combination of the inner tube assembly, overshot tool and valve housing 11 can be inserted within the upper end of the drill tube and then pumped into place. In this case a stuffing box is located on the end of the drill tube which enables fluid to be pumped into the drill tube behind the valve housing 11. The stuffing box is designed to allow a wire rope connected to the wire rope connector 18 to be fed into the drill tube as the combination advances to the end of the drill tube.

(39) The combination will eventually reach the position where the inner tube assembly will latch into its drilling position. Once the inner tube assembly stops moving, the fluid pressure behind the valve housing 11 will increase and exert pressure which will result in both operation of the indicator valve 13 in the valve housing 11 and forward movement of the housing 22 with respect to the spike 20. Both of these operations occur substantially simultaneously.

(40) In relation to the indicator valve 13, the fluid pressure is sufficient to push the ball 14 through the valve seat 17 to thereby open the fluid flow ports 15 this is as previously described and illustrated in FIGS. 3a, 3b and 3c. At the same time, the housing 22 moves with respect of the spike 20. The spike 20 is in the position shown in FIG. 6b. In this position, the bolts 40 are at the upper ends of the slots 41. As the end 25 of the retainer 24 is located within the circumferential slot 27, then movement of the spike 20 also results in movement of the latch control means 21 which is effectively locked with respect to the spike 20. This causes movement of the retainer 24 so that the head abuts against the end 55 of the control slot 29. Once the retainer 24 reaches the end 55 of the control slot 29 the torsional force applied to the latch control means 21 by the spring 32 causes the latch control means 21 to rotate so that the retainer 24 locates within slot portion 60. In this position, the end 25 of the retainer 24 aligns with the longitudinal slot 26 in the spike 20 and allows the latch control means to slide forwardly with respect to the spike 20.

(41) Once in the slot portion 60, the compressive force applied by spring 32 pushes the latch control means 21 forward and as the end 25 of the retainer 24 is in the longitudinal slot 26 and the head 30 locates within slot 61 of the cover member 23, then the latch control means 21 moves from its first position as shown in FIGS. 10a and 10b to a second position where the latch control means 21 acts to open the latch 48 to thereby release the spike 20 as previously described and with reference to FIGS. 7a, 7b, 7c and 7d. The overshot tool 10 and valve housing 11 are then free to be returned to the surface by winching in the wire which is connected to the wire rope connector 18. The core barrel assembly is now latched in position where the upper ends 53 of the arms 49 are now engaged with the locking coupling and thereby latch the inner tube assembly into place. With the overshot tool 10 released from the latch 48, then it is free to be returned to the surface.

(42) The overshot tool 10 may also be used for lowering an inner tube assembly into a dry hole where there is no fluid within the length of the drill tube or where the drill tube may only be partially filled. In this case, instead of using a valve housing 11 a free fall attachment 65 is connected to the overshot tool 10. This is illustrated in FIG. 11. The free fall attachment 65 has a series of guide rollers 66 that assist movement of the combination through the drill tube. Importantly, the weight of the free fall attachment 65 is sufficient to compress the spring 32. Accordingly, when the inner tube assembly latches in place, the weight of the free fall attachment 65 will cause movement of the housing 22 and cover member 23 with respect to the latch control means 21 and spike 20. However, while the combination of the free fall attachment 65, overshot tool 10 and inner tube assembly is suspended from the winch wire (attached to wire rope connector 18) there will be no relative movement between the housing 22 and the latch control means 21.

(43) Prior to inserting the inner tube assembly into the drill tube, the position of the latch control means 21 is pre-set to the extreme end of the control slot 29 as shown in FIG. 12c. This position provides a degree of safety as it will require two separate operations to release the overshot tool 10 from the head assembly 47. This prevents accidental release of the overshot tool 10 in the case where the progress of the inner tube assembly through the drill tube is interrupted. Clearance between the landing seal 56 and the inner surface of the drill tube is not great and all that may be required to jam the progress of the inner tube assembly would be some deposits on the inner surface of the drill tube or some damage to the inner surface of the drill tube. If this occurs, then the full weight of the free fall attachment 65 will be applied to the overshot tool 10 which will result in the latch control means 21 indexing through the first section of the control slot 29. The first application of the weight of the free fall attachment 65 will result in the housing 22 moving downwardly which in turn results in the retainer 24 moving to end 67 of the control slot 29 as seen in FIG. 12c. Once in this position, the torsional force applied by spring 32 will result in the latch control means 21 rotating and bearing against end 67 of the control slot 29 as seen in FIG. 12c. Once the cessation of movement of the inner core assembly is sensed at the surface, the cable is winched in and the weight of the free fall attachment 65 is removed from the overshot tool 10. However, the retainer 24 goes to the position shown in FIG. 4c and the overshot tool 10 is not released from the head assembly 47. This then allows the driller to again lower the core barrel assembly in attempt to bypass the obstruction. If it does bypass the obstruction, then it can continue to its landing position at the end of the drill rods. However, if it again jams, then the weight of the free fall attachment 65 will act to release the overshot tool 10 from connection to the head assembly 47. In this case at least the overshot tool 10 and free fall attachment 65 can be recovered and then an attempt can be made to retrieve the inner tube assembly.

(44) It is also possible that the inner tube assembly may be released from the overshot tool upon reaching water in a partially water filled hole. As the inner tube assembly with the attached overshot tool and free fall attachment 65 are lowered into the water, the movement of all of these components will be impeded. This will be sensed at the surface by the winch cable becoming slack.

(45) At the same time, the weight of the free fall attachment 65 and overshot tool will operate the latch control by indexing it through the first section of the control slot 29. The inner tube assembly could now be released by a further tensioning of the cable and a subsequent release of the cable which in turn will result in the weight of the overshot tool 10 and free fall attachment 65 which will then result in release of the overshot tool from the inner tube assembly. The inner tube assembly will then be free to float to its latched position within the core barrel and while this is occurring, which will take some time, the operator can retrieve the overshot tool 10 by winching it out of the hole. This will obviously save some time as the overshot tool 10 may be out of the drill tube by the time the inner tube assembly latches into the core barrel.

(46) In a fully dry hole, the inner tube assembly will latch into drilling position with the latch control means 21 and retainer 24 in the position shown in FIG. 12c. Once in this position, then it will be necessary for the driller to lift the free fall attachment 65 and overshot tool 10 twice in order to release the overshot tool 10 from the latch 48 as the process of attachment will have resulted in the weight of the overshot tool 10 and free fall attachment 65 already indexing the retainer once as shown in FIG. 13c. This release is illustrated progressively in FIGS. 13a, 13b and 13c where FIG. 13c shows the retainer 24 located at the end of both slot 60 and 61 which results in the latch control means 21 moving to its second position as shown in FIG. 13b where it releases the overshot tool from the head assembly 47. This then allows the overshot tool 10 and free fall attachment 65 to be retrieved to the surface.

(47) The free fall attachment 65 combined with the overshot tool 10 can also be used to lower an inner core assembly fully into a hole which is partially wet. In this case, the combination of the overshot tool 10, free fall attachment 65 and inner tube assembly will be lowered via the winch cable until the combination contacts the water within the drill tube. At this point, movement of the combination may be retarded by the water however it will still continue to fall under its own weight with the overshot tool 10 and free fall attachment 65 connected. Similarly, the weight of the free fall attachment 65 will be sufficient to operate the latch control means 21 and retainer 24 in the matter described above when the inner tube assembly reaches the core barrel.

(48) As will be appreciated from the above description, the invention provides useful means of controlling the operation of an overshot tool 10 to both retrieve and deliver an inner tube assembly into and out of a core barrel. Further, the set of tools described above can be used both in relation to wet and dry holes and can also be used either in relation to pumping in or lowering under gravity.

(49) This will be a significant advantage to drillers who prior to this invention were required to carry multiple sets of tools for either circumstance. This invention provides a unified set of tools which can be used in both applications.

(50) It will be appreciated by those skilled in the art that the invention is not restricted in is use to the particular invention described. Neither is the present invention restricted in its preferred embodiment with regard to the particular elements and/or features described or depicted herein. It will be appreciated that the invention is not limited to the embodiment or embodiments disclosed, but is capable of numerous rearrangements, modification and substituents without departing from the scope of the invention.