Overshot tool having latch control means

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.

RELATED APPLICATION DATA

This application is a § 371 National Stage Application of PCT International Application No. PCT/EP2014/052636 filed Feb. 11, 2014 claiming priority of AU Application No. 2013900702, filed Mar. 1, 2013.

FIELD OF INVENTION

The present invention relates to an overshot tool having means for engaging and disengaging a latch in a core barrel head assembly used in core drilling operations and in particular although not exclusively to an overshot tool having an automated latching control mechanism to allow automated coupling and retrieval of the head assembly from within a bore hole.

BACKGROUND ART

Diamond core drilling utilises an annular drill bit connected to a core barrel assembly. The core barrel is attached to the end of a number of tubular drill rods connected to form a drill string. The drilling progressively removes cylindrical cores of rock or material through which the drill and drill tube advance using a sequence of runs. This type of drilling utilises an inner tube assembly which has an inner tube connected to a head assembly to receive the core sample. The head assembly comprises a latch body connected to a valve housing which in turn is connected to a bearing housing which in turn is connected to an inner tube connector. The inner tube assembly connects to the inner tube connector and may comprise an inner tube, core lifter and core lift case. The inner tube assembly locates within a core barrel which comprises a combination of drill bit, reamer, outer tube, landing ring and locking coupling. The inner tube assembly can be retrieved from the surface when the inner tube is full. Empty inner tube assemblies can be delivered from the surface to the bottom of the drill string in order to recommence drilling.

The drill bit is advanced by rotating the drill string while applying downward pressure. In addition, drilling fluid such as water or drilling muds are pumped through the centre of the drill string, past the inner tube assembly and through the end of the drill bit in order to carry cuttings and other drilling debris to the surface via the annulus between the wall of the hole and the external surface of the drill string.

The hole being drilled may range from vertical, angled downwardly, horizontal, inclined upwardly or directly upwardly. The holes being drilled may be either normal or dry. In dry holes, the drilling fluid drains away or partially drains away naturally through crevasses or other openings in the rock strata through which the drill passes. In normal holes, the drilling fluid does not drain away.

Hereafter, normal holes, which retain water or partially retain water will be referred to as wet holes.

Of course, in the case of horizontal or near horizontal holes, it is likely that drilling fluid would naturally drain away particularly when the inner tube assembly is being retrieved or after the inner tube assembly is pumped back into the end of the drill string.

With either locating an inner tube assembly within a drill string or retrieving an inner tube assembly, when the inner tube is full, it is most often the case that an overshot tool is used to either lower the inner tube assembly into place, be used to pump the inner tube assembly into place or be lowered by itself to retrieve the inner tube assembly. In the case of a dry hole, the overshot tool will hold the inner tube assembly and their combined weight will allow the inner tube assembly to be lowered into position. In the case of a wet hole, or where the hole is partially wet or where the hole is horizontal, inclined upwardly or upwardly vertical, then the overshot tool has a sealing section which is fluid tight and enables fluid pressure to push the overshot tool and the attached inner tube assembly along the drill tubing.

The overshot tool, when used to retrieve an inner tube assembly when the inner tube assembly is full, can either fall under gravity to latch with the core barrel assembly or again be pumped into place to latch with the core barrel assembly.

A conventional latch in an inner tube assembly of a smaller diameter comprises a pair of pivoted and opposed arms. The lower portions below the pivot point of the arms have a resilient or biasing means which draw the lower ends together. This in turn causes the upper ends of the latch members to project outwardly from the inner tube assembly. In this position they can engage with a locking coupling included in the core barrel to latch the inner tube assembly with respect to the core barrel.

The overshot tool needs to cooperate with this latch so that the inner tube assembly can be held with respect to the overshot tool when it is being placed into position within the drill string and core barrel or alternatively must cooperate with the latch when the overshot tool is being used to retrieve the inner tube assembly.

In the case of retrieval, the overshot tool needs to engage the latch so that it releases the inner core assembly from the core barrel while at the same time the latch also needs to engage the overshot tool so that the overshot tool is held by the core barrel latch which allows for withdrawal of the inner tube assembly from the drill tube.

Once the retrieved inner tube assembly is at the surface, the latch needs to be easily disengaged from the overshot tool.

Various means exist for performing all of the above functions. However, it is the case that there are a number of different pieces of equipment that are used depending on the type of hole being drilled. The hole may be wet or dry and it may be vertically down or vertically up or any inclination in between. This means that the set of equipment, being the inner tube assembly and overshot tools differ in their configuration and operation depending on the type of hole being drilled.

It is against this background and the properties and difficulties associated therewith that the present invention has been developed.

Certain objects and advantages of the present invention will become apparent from the following description taking in connection with the accompanying drawings, wherein, by way of illustration and example, and embodiment of the present invention it is disclosed.

SUMMARY OF THE INVENTION

It is an objective of the present invention to provide an overshot tool configured to cooperate with a latch mechanism of a head assembly via an automatic coupling/decoupling engagement such that the tool may be coupled to the head assembly and both components retrieved from the borehole quickly, conveniently and reliably. It is a further specific objective to provide an arrangement that provides both automated and manual decoupling of the tool from the head assembly to allow detachment by personnel at the surface and decoupling down the hole when the overshot tool is used to deliver the head assembly into the final latched position at the cutting end of the core barrel apparatus.

It is a further specific objective to provide an overshot tool that is sensitive to the method of delivery down the borehole so as to provide a feedback signal to an operator that the tool has reached its desired destination at the head assembly. It is a further specific objective to provide an overshot tool that is resistant to decoupling from the head assembly when used to deliver the head assembly into position should the assembly encounter obstructions during delivery.

The automated coupling and decoupling function of the present overshot tool is provided by primary and secondary engaging portions where at least one of the engaging portions is controlled by a latch control that is responsive to the environment in which the tool is placed and additionally the forces acting on the tool. Accordingly, the latch control is configured to control an axial and optionally a rotational movement of the primary and secondary engaging portions. The coupling and decoupling is achieved specifically via engagement by the primary engaging portion (to provide coupling) and the secondary engaging portion (to provide decoupling). The specific activation of the secondary engaging portion is controlled by the latch control and is responsive to forces acting on the tool at the cutting end of the borehole where the head assembly is maintained or released at its latched position against the inner surface of the core barrel. Additionally, the specific objectives are achieved by providing a latch control that is conveniently implemented as a pin and slot arrangement acted on by a bias member that is configured to provide from either an axially forward or rearward end.

According to a first aspect of the present invention there is provided an overshot tool for releasable connection to a head assembly of a core barrel drilling apparatus, the tool comprising: a primary engaging portion to engage a latch of a head assembly to provide an axial couple between the tool and the head assembly; a secondary engaging portion to temporarily engage the latch in addition to the engagement of the latch by the primary engaging portion; a 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 axially movable relative to the housing, the retainer configured i) to engage a first part of the region to releasably couple the primary and 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; 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 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.

Preferably, the primary engaging portion comprises an elongate shaft and the secondary engaging portion comprises a sleeve positioned around the shaft, the sleeve configured to slide axially over the shaft. The elongate shaft comprises an axially forwardmost end that represents an axially forwardmost part of the tool and is configured specifically to engage the latch of the head assembly.

Preferably, the housing comprises a slot in which the first and second parts of the housing comprise regions of the slot and the retainer is capable of movement within the slot between the first and second parts. Preferably, the bias member is configured to bias the secondary engaging portion rotatably relative to the primary engaging portion. Preferably, the bias member is a coil spring extending between the housing and the secondary engaging portion. Such an arrangement is advantageous to provide a reliable and robust configuration for the latch control mechanism that provides the automated or semi-automated latching of the secondary engaging portion and hence a coupling and decoupling action of the tool.

Preferably, the tool further comprises a cover member to accommodate the primary and the secondary engaging portions and the housing wherein the primary and secondary engaging portions and the housing are capable of sliding axially within the cover member. The cover member acts to protect the inner components of the tool and to allow the various components to slide axially and rotate circumferentially around the axis in use.

Optionally, the tool further comprises a temporary rotational lock having at least two locking positions to temporarily lock the housing at the cover member at two rotational positions. The rotational lock is configured to provide quantised default positions of the secondary engaging portion relative to the housing and the primary engaging portion. Accordingly, a degree of force is required to adjust the releasable lock between the two positions so as to change the state of the tool to be configured for latching or unlatching of the head assembly. Such force may be provided by the pressure of a supply fluid or the weight of a free fall delivery assembly acting on the overshot tool.

Preferably, the cover member comprises a cut-out positionable at the same axial and rotational position as the slot of the housing. The cut-out is configured to allow the pin of the latching mechanism to project through the wall of the cover member such that the cover member does not obstruct the latching mechanism and in particular the pin that extends radially outward from the primary engaging portion.

Preferably, 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. Accordingly, the retainer forms a radially extending region of the shaft such that rotational and axial adjustment of the retainer provides a corresponding movement of the shaft relative to the other components of the tool. The relative position of the shaft is therefore determined by the relative position of the retainer within the various slots and channels of the present overshot tool.

Preferably, the first part at the slot extends in a circumferential direction to receive the retainer and the second part at the slot comprises an axially extending length section being greater than a length section of the first part. Accordingly, the retainer is configured to travel circumferentially and axially within the slot.

Optionally, an engaging end of the primary engaging portion comprises a bayonet configuration at a leading end of the tool being engagable with the latch; and an engaging end of the secondary engaging portion comprises a bell portion to engage the bayonet configuration in touching or near touching contact and release the bayonet configuration from engagement with the latch. Such an arrangement is advantageous to engage a particular configuration of latch at the head assembly that may comprise resiliently biases latching arms having engaging ends movable radially inward and outward.

Preferably, the housing of the tool comprises 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. The present tool therefore is configured to mate with an overshot attachment or a valve housing to allow the tool to be both delivered and extracted from the borehole when coupled or decoupled from the head assembly. The latch control of the tool is configured to be sensitive to the coupling state of the valve housing or overshot attachment at the tool to both provide a feedback signal to an operator at surface level and to change the coupling state of the tool to either couple or decouple at the head assembly.

Preferably, the shaft comprises 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 configured for slidable engagement within the first and second parts of the channel. The channel in cooperative engagement with the retainer acts to restrict relative movement of the shaft both in an axial and rotational direction. Accordingly, the second engaging portion and the primary engaging portion are configured to move relative to one another by a limited range of movement both in the axial and circumferential or rotational directions via various slots and channels as described herein.

According to a second aspect of the present invention there is provided a method of core drilling using a tool forming part of a core barrel drilling apparatus, the method comprising: transporting an overshot tool in an axially forward direction through a core barrel apparatus; engaging a latch of a head assembly via a primary engaging portion of the tool to decouple the head assembly from 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 apparatus to retrieve the head assembly, wherein the tool comprises: a primary engaging portion to engage the latch of the head assembly to provide the axial couple between the tool and the head assembly; a second engaging portion to temporarily engage the latch in addition to the engagement of the latch by the primary engaging portion; a 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 axially movable relative to the housing and the retainer configured to engage a first part of the region to releasably couple the primary and secondary engaging portions for combined axial movement and the retainer 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; 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 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.

Optionally, the method may further comprise a release of the axial couple between the tool and the head assembly by moving axially the secondary engaging portion to contact the latch and releasing engagement between the primary engaging portion and the latch.

In one embodiment, the overshot tool has a first means for engaging a latch in a head assembly, the latch locking to the first means when engaged, and latch control means associated with the first means which is movable with respect of the first means wherein, in a first position, the latch control means allows the first means to engage the latch, and in a second position, the latch control means opens the latch to release the first means from the latch.

The first means on the overshot tool may comprise a number of different arrangements for connecting to the latch in the head assembly. Preferably the first means may comprise a spike which locates into and engages with the latch in the head assembly. Other arrangements may be suited to the first means and will depend on the type of latch used in the head assembly. For the sake of clarity, the first means will be described in the remainder of the specification as comprising a spike, however it will be realised that the invention is not to be restricted to this particular feature.

The latch may comprise a conventional dual arm latch where each arm is diametrically opposed to the other and pivotally secured with respect to the head assembly. However, other latch arrangements such as three of more latch arms or an alternative style of latch would be equally suited to this invention. For example, 4 or 6 arms may be used with larger diameter drilling systems.

In preference, the latch comprises at least two opposed and pivoted latch arms having inner ends that are biased towards one another to push the upper ends outwardly to abut with a locking coupling in a core barrel. The biasing means may comprise an elastomeric member located around the inner ends of the latch arms which acts to draw them together. This in turn causes the outer ends to pivot outwardly with respect to the head assembly.

The spike preferably has a tip that is shaped to that it will pass through the centre of the latch assembly so that the latch moves to allow the tip portion to pass through and, once the tip portion has passed the ends of the latch, the latch arms then closed behind the tip portion to thereby retainably engage the spike. In this position, with the latch engaged on the spike, the upper ends of the latch arms are withdrawn inwardly towards the head assembly so that they will disengage from the locking coupling and allow the inner tube assembly to move within the drill tube. This therefore allows the overshot tool to either retrieve an inner tube assembly by unlocking the latch from the locking coupling or lower the inner tube assembly into the drill tube by having the upper ends of the latch arms withdrawn from their latching position.

There will be a number of different circumstances where the spike is to be disengaged from the latch. It will need to occur at the surface when the inner tube assembly is manually removed from the end of the drill tubing or it will need to occur remotely once the inner tube assembly has landed at the end of the drilling tube which is known as a dry release. It may also need to occur when the inner tube assembly is part way into the hole.

In all cases, the latch control means operates to disengage the latch from the spike to thereby allow separation of the overshot tool from the inner tube assembly. In the case of when the overshot tool is delivering the inner tube assembly to the end of the drill string, this must be achieved remotely and at the surface, the manual disengagement must allow for easy and safe disengagement.

Preferably, the movement of the latch control means can be initiated remotely from the surface. When the overshot tool is returned to the surface it can be operated manually in a manner that is quick and convenient for an operator and does not involve any potential for injury to be caused or for any loss of or damage to the inner tube assembly.

The latch control mean means preferably slides along the outer surface of the spike and further, preferably comprises a sleeve journalled for sliding movement along a shaft of the spike. The end of the latch control means preferably engages with the arms of the latch to open the lower ends of the latch arms against the resilient biasing member to thereby allow the tip of the spike to be withdrawn from the latch.

The latch control means may have an arrangement that allows manual positioning at the surface to control movement of the latch control means. This may comprise a retainer which moves within the control slot to control movement of the latch control means in a predetermined way. For example, this allows for remote release of the latch control means so that it can move to a second position where the spike is disengaged from the latch in the head assembly.

Movement of the latch control means may be under the influence of a spring member that provides at least a compressive load to the latch control means. Movement of the latch control means may be further controlled by a retainer that can be moved to a released position to thereby allow the latch control means to move along the spike to a position where it will release the latch. The retainer can be designed so that it can be selectively released either once the inner tube assembly is located at the end of the drill string to provide remote release or when the inner tube assembly is retrieved to the top of the drill tube.

Preferably, the latch control means has an intermediate position between the first and second positions where the latch control means acts to prevent the latch from opening to thereby inadvertently release the spike. Preferably, the latch control means is provided with an abutment surface that locates adjacent the upper ends of the latch arms that thereby prevent inward movement of the upper ends of the latch arms. By preventing this inward movement, the latch cannot be released from the spike.

Further, the abutment surface, when the latch control means moves to its second position, locates within an area where there is sufficient clearance between the upper ends of the latch arm and the abutment surface to allow movement of the upper ends of the latch arms inwardly to thereby release the forward ends of the latch arms from the spike.

FIG. 1shows an overshot assembly which is an assembly of an overshot tool10and valve housing11. The overshot tool10is 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 housing11can be used to pump the overshot tool10through a drill string. This will normally be to retrieve the inner tube assembly. The valve housing11is provided with seals12which provide flexible fluid seals between the valve housing11and the inner wall of the drill tube. An indicator valve13is provided within the valve housing11to provide an indication to the driller when movement of the valve housing11ceases. The indicator valve13is shown inFIG. 1in its open position and comprises a ball14and fluid flow ports15. In its open position, the indicator valve allows fluid that is pumped in behind the valve housing11to flow through opening16and the fluid flow ports15. In its closed position and in order to pump the valve housing11along drill tubing, the ball14is set behind valve seat17which prevents fluid flow through the valve housing11and therefore enables fluid pressure to move the valve housing11along the drill tube (as shown inFIG. 3a).

Upon the valve housing11becoming stationary as would be the case when the overshot tool10engages an inner tube assembly, an increase in fluid pressure will cause the ball14to move through the valve seat17from the position ofFIG. 3ato its position ofFIG. 1so that the fluid ports15are now open and allow fluid to freely flow forward of the valve housing11and around the overshot tool10. This change in pressure provides an indication at the surface to the drill operator that the overshot tool10has landed. The valve housing11has a wire rope connector18to which a retrieval wire rope is secured. This enables the overshot tool10and valve housing11combination to withdraw an inner tube assembly from the drill hole. The valve housing11is secured to the overshot tool10either threadably or by a pin or both. The overshot tool10comprises a spike20and a latch control means21. The latch control means21has an axial bore through which a portion of the shaft of the spike20locates. The spike20and latch control means21are located within a housing22and the housing22is in turn located within a cover member23.

The latch control means21comprises a sleeve within which a portion of the shaft of spike20is slidably journalled. As will be explained below, the latch control means21moves to various positions along the spike20to control operation of a latch, and that movement is controlled by a retainer24which is threadably mounted with respect to the latch control means21. An end25of the retainer24projects from the inner bore of the latch control mean21and is selectively locatable within either a longitudinal slot26or circumferential slot27which are both located on the spike20as shown inFIG. 8. The shaft of the retainer24locates within a control slot29which is located within the wall of the housing22. The head30of the retainer24projects above the outer surface of the housing22and locates generally within a cut out31within the cover member23. As will be explained below, the head30will in certain circumstances abut against an edge of the cut out31.

A spring32is connected to both the housing22and the latch control means21. It provides both a compressive and torsional force to the latch control means21. The spring32is compressed and normally provides a force that pushes the latch control means21away from the housing22. The spike20has a tip35that comprises a conical portion36and a circumferential ledge37. The conical portion36and ledge37are designed to engage with the latch in the inner tube assembly.

The spike20is journalled for sliding movement within a bearing39in the housing22. The spike20is retained within the housing22via a pair of bolts40that threadably engage the end of the spike20. The heads of the bolts40are located within slots41which in turn allows a small amount of longitudinal movement of the spike20with respect to the housing22. When the end25of the retainer24is located within the circumferential slot27on the shaft of the spike20then the spring32acting on the latch control means21will in turn bias the spike20into its forward position shown inFIG. 2. When the end25of the retainer24is located within the longitudinal slot26on the spike20, the spring32will push the latch control means21forward so that the bell portion43locates over the head portion44of the spike20. The latch control means21has an abutment collar45which cooperates with the latch in the head assembly and its operation is described below.

The cover member23is journalled for rotation on the housing22. Detent balls58locate within detent apertures57to hold the cover member23in one of two positions. This is to position the cut out31in relation to the head30of the retainer24to either arrest movement of the retainer24or to allow movement to a predetermined extent.

Figure groups4to7show the engagement of the overshot tool10with an inner tube assembly. The Figures show a head assembly47and do not include the inner tube in which the sample is collected. The inner tube is threadably connected to an end of the head assembly47. The head assembly47combined with the inner tube is referred to as the inner tube assembly.

FIGS. 4aand 4bshow the overshot tool10that has been pumped into a hole and has just engaged with the latches48of the head assembly. The latches48comprise a pair of arms49that are pivotally connected to the head assembly47via pivots50. The inner ends51of the latch arms49locate behind the ledge37on the spike20. An elastomeric o-ring52locates around the inner ends51and bias the inner ends51so that they engage against the head portion44of the spike20. This holds the inner ends against the ledge37to thereby hold the latch48in a closed position with respect to the spike20. The arms49have upper ends53which abut with the locking coupling of a drill string (not drawn) to hold the head assembly47, in its drilling position where it is positioned to receive core sample as drilling progresses. In order for the upper ends53of the latch48to engage with locking coupling in the core barrel, the upper ends53need to project radially outward to a greater extent than what is shown inFIG. 4b. The diameter of the head portion44of the spike20is sized so that the inner end51are pushed outwardly against the O ring52to thereby retract the upper ends53to the position shown inFIG. 4b. This retracted position of the upper ends53provides clearance both with respect to the locking coupling and the inner wall of the drill tubing.

The example shown inFIGS. 4a, 4b, 4c, 5a, 5b, 5cand 5dare where the overshot tool10is 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.

FIG. 4cillustrates the setting of the cover member23for retrieval.FIGS. 4aand 4bshow the overshot tool10just as it connects to the head assembly47that is to be retrieved. The tip35of the spike20pushes through the inner ends51of the arms49to thereby unlatch the head assembly47from the locking coupling of the core barrel. The latch48is now engaged with the spike20with the inner ends51of the arms49located behind the ledge37.

Prior to sending the overshot tool10into the drill tube to retrieve the head assembly47the latch control means21is positioned with respect to the housing22so that the retainer24is in the position shown inFIG. 4c. In addition, the cover member23is rotated so that a slot61in the cover member23is not aligned with the slot60of the control slot29. This is a pre-loaded position so that the spring32holds the retainer24in this position. When the spike20engages with the latch48the fluid pressure continues to act on the valve housing11and there is simultaneous operation of both the indicator valve13and the retainer24associated with the latch control means21. Both of these things occur substantially simultaneously.

In the case of the indicator valve13, the pressure will be sufficient to force the ball14through the valve seat17to the position shown in4a,3band3c. The valve seat17is a polymer and is sufficiently resilient to enable movement of the ball14at a predetermined pressure. This release of the ball14opens the fluid ports15which will enable fluid to flow through the valve housing11. The valve arrangements within the head assembly47will be closed which will prevent fluid flow and allow the overshot tool10and valve housing11to be pumped through the drill string. Upon reaching a halt, the ball14moves through the valve seat17and causes a momentary pressure spike which provides an indication to the operator at the surface that the overshot tool10has landed.

At the same time, the spike in fluid pressure results in the valve housing11pushing the housing22and cover member23forward towards the head assembly47so that the housing22is caused to move in relation to both the latch control means21and spike20. Engagement of the end25of the retainer24within the circumferential slot27results in the spike20and latch control means21moving rearwardly as is shown inFIG. 5d. This in turn causes the spring32to be compressed and for the retainer24to be moved rearwardly in relation to the control slot29. It reaches the end of edge end55of the control slot29and the torsional force exerted by spring32causes the latch control means21to rotate so that retainer24moves into slot portion60. This is illustrated inFIG. 5dwhere the latch control means21is now able to move longitudinally with respect of spike20as a result of the end25now engaging the longitudinal slot26. This moves the latch control means21to the positions shown inFIG. 5bwhere the abutment collar45blocks any further inward movement of the upper ends53of the latch arms49. This is the intermediate position of the latch control means21and physically prevents any movement of the outer ends of the latch53inwardly and thereby prevents any disengagement of the inner ends51of the latch arms49from the tip35of the spike20.

Once the latch control means21rotates so that the retainer24is within slot60of the control slot29, the spring32acts to push the latch control means21forward and the retainer24slides within slot60until it abuts against edge62of the cut out31in the cover member23. This is illustrated inFIG. 5d. In this position, the spring32continues to apply force to the latch control means21so as to hold the retainer24against the edge62.

The release of the indicator valve13provides an indication to the driller at the surface that the overshot tool10has engaged the head assembly47. As the latch control means21will have operated automatically, then the combination of the overshot tool10, valve housing11and inner tube assembly will be ready for removal. In order to release the overshot tool10from the head assembly47upon arrival of the combination of the overshot tool10, valve housing11and inner tube assembly to the surface, the cover member23is rotated so that the slot61and the cover member23aligns with slot60in the housing22. This results in spring32pushing the latch control means21fully forward to its second position where it disengages the spike20from the latch as previously described above. The rotation of the cover member23is illustrated inFIG. 6cand the release position is shown inFIGS. 6aand6b.

This allows a very convenient and safe release of the overshot tool10from the head assembly47. This release is illustrated progressively inFIGS. 7a, 7b, 7cand 7dwhere the bell portion43of the latch control means21locates over the head portion44of the spike20such that the end of the bell portion43abuts against the ledge37. In this position, the outer surface of the bell portion43abuts against the inner surfaces of the latch arms49adjacent the inner ends51of the latch arms49so that the inner ends51move away from the head portion44and out of engagement with the ledge37. Once the inner ends51of the arms49no longer engage the ledge37then as seen inFIGS. 7a, 7b, 7cand 7d, the overshot tool10can be withdrawn from the latch48and the end of the head assembly47.

FIGS. 8 and 9show more clearly the relationship of the longitudinal slot26, circumferential slot27and retainer24. As can been seen in, for example,FIG. 12c, when the retainer24is located in the three shorter lengths of the control slot29, that are parallel and proceed slot60that cause back and forth movement of the retainer24portion of the control slot29, the end25of the retainer24will be in the circumferential slot27and thereby lock movement of the latch control means21with respect to the spike20. However, when the retainer moves into slot60out of the three shorter lengths of the control slot29(as shown inFIG. 9), then the end25aligns with the longitudinal slot26which then frees the latch control means21to move longitudinally with respect of the spike20. This enables the latch control means21to move between its first and second position and also an intermediate position as will be described below.

It may also be possible to use the overshot tool10and valve housing11to 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 tool10connected to the head assembly47as shown inFIGS. 10aand 10bit would be possible to deliver an inner tube assembly to the end of the drill rods if required. The part conical portion36bears against a surface54within the head assembly47. This enables the overshot tool10to push against the head assembly47while the latch48prevents release of the overshot tool10. In this position, the overshot tool10combined with the valve housing11could 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.

In order to achieve this, the retainer24is placed within the control slot29in the position shown inFIG. 10c. The retainer24is held in this position by the compressive action of spring32pushing the latch control means21with respect to the housing22to thereby hold the retainer24in the position shown inFIG. 10c. In addition, the end25of the retainer24is located within the circumferential slot27on the spike20. This in turn forces the spike20forward so that the bolts40are in the forward portion of their slots41. Further, the spring32provides a torsional load to the latch control means21which in turn means that the retainer24is pushed against the edge end55of the control slot29.

In this configuration, the combination of the inner tube assembly, overshot tool and valve housing11can 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 housing11. The stuffing box is designed to allow a wire rope connected to the wire rope connector18to be fed into the drill tube as the combination advances to the end of the drill tube.

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 housing11will increase and exert pressure which will result in both operation of the indicator valve13in the valve housing11and forward movement of the housing22with respect to the spike20. Both of these operations occur substantially simultaneously.

In relation to the indicator valve13, the fluid pressure is sufficient to push the ball14through the valve seat17to thereby open the fluid flow ports15this is as previously described and illustrated inFIGS. 3a, 3band 3c. At the same time, the housing22moves with respect of the spike20. The spike20is in the position shown inFIG. 6b. In this position, the bolts40are at the upper ends of the slots41. As the end25of the retainer24is located within the circumferential slot27, then movement of the spike20also results in movement of the latch control means21which is effectively locked with respect to the spike20. This causes movement of the retainer24so that the head abuts against the end55of the control slot29. Once the retainer24reaches the end55of the control slot29the torsional force applied to the latch control means21by the spring32causes the latch control means21to rotate so that the retainer24locates within slot portion60. In this position, the end25of the retainer24aligns with the longitudinal slot26in the spike20and allows the latch control means to slide forwardly with respect to the spike20.

Once in the slot portion60, the compressive force applied by spring32pushes the latch control means21forward and as the end25of the retainer24is in the longitudinal slot26and the head30locates within slot61of the cover member23, then the latch control means21moves from its first position as shown inFIGS. 10aand 10bto a second position where the latch control means21acts to open the latch48to thereby release the spike20as previously described and with reference toFIGS. 7a, 7b, 7cand 7d. The overshot tool10and valve housing11are then free to be returned to the surface by winching in the wire which is connected to the wire rope connector18. The core barrel assembly is now latched in position where the upper ends53of the arms49are now engaged with the locking coupling and thereby latch the inner tube assembly into place. With the overshot tool10released from the latch48, then it is free to be returned to the surface.

The overshot tool10may 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 housing11a free fall attachment65is connected to the overshot tool10. This is illustrated inFIG. 11. The free fall attachment65has a series of guide rollers66that assist movement of the combination through the drill tube. Importantly, the weight of the free fall attachment65is sufficient to compress the spring32. Accordingly, when the inner tube assembly latches in place, the weight of the free fall attachment65will cause movement of the housing22and cover member23with respect to the latch control means21and spike20. However, while the combination of the free fall attachment65, overshot tool10and inner tube assembly is suspended from the winch wire (attached to wire rope connector18) there will be no relative movement between the housing22and the latch control means21.

Prior to inserting the inner tube assembly into the drill tube, the position of the latch control means21is pre-set to the extreme end of the control slot29as shown inFIG. 12c. This position provides a degree of safety as it will require two separate operations to release the overshot tool10from the head assembly47. This prevents accidental release of the overshot tool10in the case where the progress of the inner tube assembly through the drill tube is interrupted. Clearance between the landing seal56and 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 attachment65will be applied to the overshot tool10which will result in the latch control means21indexing through the first section of the control slot29. The first application of the weight of the free fall attachment65will result in the housing22moving downwardly which in turn results in the retainer24moving to end67of the control slot29as seen inFIG. 12c. Once in this position, the torsional force applied by spring32will result in the latch control means21rotating and bearing against end67of the control slot29as seen inFIG. 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 attachment65is removed from the overshot tool10. However, the retainer24goes to the position shown inFIG. 4cand the overshot tool10is not released from the head assembly47. 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 attachment65will act to release the overshot tool10from connection to the head assembly47. In this case at least the overshot tool10and free fall attachment65can be recovered and then an attempt can be made to retrieve the inner tube assembly.

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 attachment65are 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.

At the same time, the weight of the free fall attachment65and overshot tool will operate the latch control by indexing it through the first section of the control slot29. 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 tool10and free fall attachment65which 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 tool10by winching it out of the hole. This will obviously save some time as the overshot tool10may be out of the drill tube by the time the inner tube assembly latches into the core barrel.

In a fully dry hole, the inner tube assembly will latch into drilling position with the latch control means21and retainer24in the position shown inFIG. 12c. Once in this position, then it will be necessary for the driller to lift the free fall attachment65and overshot tool10twice in order to release the overshot tool10from the latch48as the process of attachment will have resulted in the weight of the overshot tool10and free fall attachment65already indexing the retainer once as shown inFIG. 13c. This release is illustrated progressively inFIGS. 13a, 13band 13cwhereFIG. 13cshows the retainer24located at the end of both slot60and61which results in the latch control means21moving to its second position as shown inFIG. 13bwhere it releases the overshot tool from the head assembly47. This then allows the overshot tool10and free fall attachment65to be retrieved to the surface.

The free fall attachment65combined with the overshot tool10can 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 tool10, free fall attachment65and 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 tool10and free fall attachment65connected. Similarly, the weight of the free fall attachment65will be sufficient to operate the latch control means21and retainer24in the matter described above when the inner tube assembly reaches the core barrel.

As will be appreciated from the above description, the invention provides useful means of controlling the operation of an overshot tool10to 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.

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.

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.