GB2294714A - Releasable tool joint assembly - Google Patents

Abstract

A releasable tool joint assembly for oil or gas well operation between a wireline and a tool string comprises a female portion (A) adapted to be connected to the wireline or upper tools in the stool string and a male portion (B) adapted to be attached to the lower tools and adapted to be releasably connected to the female portion. Sustained tension above a predetermined value serves to controllably release the male and female portions thus separating the upper and lower portions of the tool string. A means of energy absorption is provided such that shock loads do not cause release. The releasable connection includes a fluid reservoir (30) with a bleed chamber (31) connected by a passageway to allow fluid displacement to disengage a collet release mechanism. Check valves (13, 15, 16) are provided in the passageway to ensure no fluid flow until the sustained tension is greater than a predetermined threshold value. Alternatively the tool joint can include a plastically compressible component, eg a slotted cylinder of low strength steel, which yields to disengage the collet. <IMAGE>

Description

RELEASABLE TOOL JOINT ASSEMBLY Field of the Invention The present invention relates to releasable tool joint and particularly, but not exclusively to releasable tool joint for use in oil or gas well operations.

Background to the Invention Wireline is a method of lowering specialized equipment into an oil or gas well, or raising specialized equipment from an oil or gas well. The principal of wireline is to attach a toolstring to the end of a reel of wire and by reeling out the wire the toolstring is lowered into the well. By either reeling in or reeling out the wire, the toolstring can be made to perform simple tasks downhole. The toolstring consists of a variable combination of individual tools connected together to form a working unit. The uppermost element of a toolstring is rope socket which connects the wire to the remainder of the tools.

Wireline techniques are used for various operations in the maintenance of oil and gas wells. During wireline work there may be a need to temporarily abandon operations. This requires that the downhole tools are released and the wire reeled back to the surface. There is therefore a need for a rope socket or tool joint mounted high in the string which can be easily and controllably released when in a downhole situation, yet which will not undergo release during normal downhole operations. At present there are very few systems which will allow controlled release from the toolstring. The established method of emergency release is to break or cut the wire. This can be achieved by dropping snippers or cutter bars down the wire. For such devices to work they must have enough energy when they reach the bottom to cut the wire.This works in a vertical well, but for a heavily deviated well the cutter slows down, loses energy and frequently fails to cut the wire, causing more problems. Snippers often cut high on hitting fluid or restrictions such as landing nipples.

The inventor is aware of two types of release tools which attempt to overcome these problems but each suffers from its own inherent disadvantages. One such tool is produced by the company Petroline. This has a release mechanism which requires a drop bar to be run down the wire and when the drop bar contacts a release trigger this unlatches an upper housing of the rope socket, leaving a conventional fishing neck exposed. This method does not always succeed for similar reasons to the cutter bar technique.

A second system, produced by Well-Equip Limited can be released by relaxing the wire or cable for a period of approximately one hour before the release mode is activated. With this system there is no way of knowing if the release mode has been activated until the wire is pulled up, which will reset the tool if it has not released. Valuable time can be lost using this type of tool. Furthermore, it requires the wireline to be kept taut at all times. If the line is allowed to relax inadvertently then the tool may release accidentally.

It is the object of the present invention to provide a releasable tool joint which overcomes or minimises these disadvantages and provides reliable, reproducible release in the extreme, inhospitable conditions found downhole in the oil and gas industry as well as elsewhere.

Summarv of the Invention According to the first embodiment of the present invention, in its broadest sense, there is provided a releasable tool joint assembly comprising: i) a female portion adapted to be connected to a wireline or upper tools in a tool string by a connection means; ii) a male portion adapted to be attached to the lower tools and further adapted to be releasably connected to a female portion; iii) disengagement means adapted to controllably release the male and female portions thus separating the lower and upper portions of the tool string; characterised in that the disengagement means is activated by sustained tension above a pre-determined value, and in that it further comprises a means of energy absorption such that shock loads do not cause release.

Thus no drop bar or other implement is required to effect release, which can now be achieved even when the tool string is displaced from the vertical.

There is also no need to keep the wire taut during normal operations.

Preferably the disengagement means comprises: i) a fluid reservoir; ii) a bleed chamber; iii) a passageway connecting the fluid reservoir and the bleed chamber; iv) a flow restrictor located in the passageway such that fluid flow between the fluid reservoir and the bleed chamber is regulated; v) a collet release mechanism; characterised in that sustained tension above a pre-determined value on the female member causes fluid to flow from the fluid reservoir into the bleed chamber, displacement of this fluid ultimately resulting in disengagement of the collet and further characterised in that release of the sustained tension at any time prior to disengagement results in any fluid in the bleed chamber being forced back into the fluid reservoir.

Transient tension on the wire, even above a threshold value, does not therefore initiate release. This makes the system easier to use under normal operating conditions.

Preferably the passageway between the fluid reservoir and the bleed chamber incorporates high and low pressure differential check valves which ensure that no fluid can pass from the reservoir to the bleed chamber until the sustained tension is greater than a pre-determined threshold value, whilst allowing fluid to return freely to the reservoir when tension is removed.

This ensures that inadvertent tension on the wire, even over a prolonged period, cannot initiate release accidentally.

In a particularly preferred embodiment the disengagement means comprises: i) a plastically compressible component; ii) a collet release mechanism; wherein sustained tension above a pre-determined level on the female portion causes the compressible component to yield, ultimately resulting in disengagement of the collet.

This arrangement avoids the use of hydraulic components and the well known variability in oil viscosity at high temperatures and pressures. It also means that no O-ring seals are required, these being problematic in this type of application.

Preferably the compressible component comprises a slotted cylinder.

This slotted cylinder or other mechanical equivalent then becomes a disposable spare part that should be changed when the tool joint comes to the surface.

Preferably the tool joint assembly further incorporates a safety mechanism such that immediately following release the male member remains captured within the female member, or vice versa, such that the uppermost in use component(s) attached to the wire are prevented from catapulting in the direction of the tension force until substantially all the tension force is released.

Preferably the safety effect is achieved by providing slightly hooked ends on the collet.

This invention is also intended to encompass a rope socket incorporating releasable tool joint assembly of the type herein described.

Brief of the Description of the Drawings Preferred embodiments of the present invention will now be more particularly described by way of example, with reference to the accompanying drawings, wherein: Figure 1 shows a cross-section of a device according to a first embodiment of the present invention with the male and female portions connected; Figure 2 shows a cross-section of the device in Figure 2 with the male and female portions disconnected (to be read in conjunction with Table 1); Figure 3 shows the Belleville disc springs as utilized in the first embodiment of the invention; Figure 4 shows a part cross-section of a device according to a second embodiment (to be read in conjunction with Table 2); Figure 5 shows a valve assembly appropriate to the second embodiment;; Figure 6 shows a part cross-section of a device according to a third embodiment (to be read in conjunction with Table 2).

Description of the Preferred Embodiments The embodiments shown in Figures 1-6 represent currently the best ways known to the applicant of putting the invention into practice. But they are not the only ways in which this could be achieved. They are illustrated, and will now be described, by way of example only.

Figure 1 shows a wireline rope socket consisting of a female portion A and a male portion B. In use a wire is threaded inside the female portion of the tool, starting at the top sub 1 and passing through the swivel shaft 3, spring adjuster 6, spring guide 13, pear drop holder 19 and pear drop sleeve 21. The wire is locked in position between the pear drop sleeve 21 and the pear drop 22.

In use, and when at rest in the configuration shown in Figure 1 oil reservoir 30 is full of oil. Spring means 10 acts to keep the pear drop sleeve 21 engaged with a collet 24 and thus prevents release of portions A and B.

When tension above a set value is applied to the wire, the spring guide 13, pear drop holder 19, pear drop sleeve 21, and pear drop 22 move upwards against the force of the spring means 10. In this example Belleville disc springs are illustrated stacked in parallel pairs. It will be appreciated that this is just one type of spring suitable for this application and this example is not intended to be limiting. As this movement occurs oil in the reservoir 30 is forced through a small diameter orifice leading to the bleed chamber 31.

This action slows the movement of the combination of items 13, 19, 21 and 22 and hence any short term application of a force is unable to release the collet holder 23 and collet 24 from the pear drop 22 and the female bottom body section 18. It is not until substantially all the oil has flowed into the chamber 31 that the position is reached where the collet holder 23 and collet 24 can disengage from the body 18. It should be noted that below the set value of the spring means 10 release cannot occur since the pear drop holder 19 is not sufficiently displaced to allow disengagement of the body 18 from the collet 24.

Disengagement means that the female portion A is now effectively freely suspended which relieves the force that initially caused displacement of items 13, 19, 21 and 22, thereby allowing them to return to their original position.

The oil then displaces back to the reservoir through the valve in the mid body 25 and the releasable rope socket is ready for reuse.

The rate at which tension-induced release takes place will depend in part on the viscosity of the oil used. In this example SHELL OMALA 320 (TM) oil is used. The more viscous the oil the slower the release action and vice versa.

Oil is just one fluid that can be used in this context. The term fluid is intended to cover any liquid, liquid mixture, gas or gas mixtures suitable for use in this assembly.

Once the release has taken place the top section of the tool A is retrieved to the surface on the wire enabling another toolstring to be made up to fish out the tools which are left downhole. To facilitate this operation the collet holder 23 and collet 24 have a standard fishing profile.

It will be appreciated that in the embodiment illustrated, once the female portion A has been released as a result of a sustained force applied to the wireline, it will tend to move with some momentum up the well. To prevent this happening a further embodiment of the invention provides for a safety catch mechanism such that after its release female portion A can only travel a short distance before being brought to a stop. This type of safety mechanism could be likened to that used in the bonnet catch of a motor car wherein the bonnet is released against the force of the spring and it is then restrained from flying open. Such catch and latch mechanisms are known in other fields of engineering and an example is shown in Figure 5 where the collet has slightly hooked ends (see below).

Figures 4 and 5 show a cross section of a second, embodiment of the invention with male and female components in engagement. In normal use, male component bottom sub 28, 29 is locked into the female assembly terminating in a rope socket body 1 or top sub 4, 5. The locking component is collet 26. The collet 26 is maintained in engagement with the bottom sub 28,29 by the close fitting bore in lower body 22. The collet is prevented from moving downwards by hydraulic oil trapped in the cylinder 12 by the HP valve 13. The valve is set by preloading the Belleville spring washers 30 with the Belleville adjuster 11.

Sufficient tension between bottom sub 28, 29 and rope socket body 1 or top sub 4,5, above the set value of the HP valve, initiates release. When release has begun, the HP valve passes oil and the internal assembly of mandrel 18 and collet 26 etc moves downwards relative to the external assembly. The rate of movement is controlled both by the throttling effect of the valve assembly and by restricting the oil flow through orifice(s) in the HP valve component. When the full travel is achieved, the internal assembly locks out by a lock button 24 protruding through a hole (not shown) in the lower body.

At any time after initiation, but before the lock button locks out, applied tension may fall below the set value. In this case movement of the internal assembly will cease and the bottom sub will remain locked in place.

Substantially releasing the tension (slacking off line) will result in the return spring 20 forcing the internal assembly back to its start position. The oil is allowed to pass back through the LP valve 15, 16, which offers little resistance to flow. The tool is thus reset and the release process must begin again from scratch.

Note that a force exceeding a threshold value over the full length of travel is needed to achieve the lock button lockout position. In this way the tool can be set so that normal toolstring operations do not cause any initiation of release, and short unexpected shock loads do not complete release.

When the lock button locks out, the bottom sub will remain hanging in the collet as long as significant tension is maintained on the tool. This is because the collet 26 has slightly hooked ends engaging it with the bottom sub 28, 29.

In this way the female assembly is not catapulted up the hole by the release of energy stored in wire stretch. With all significant tension removed, the collet springs open into the clearance diameter of the lower body. A positive set-down will ensure that the collet is unhooked and open. The male bottom sub is thus free of the female upper assembly and release is completed by lifting away the female assembly.

The bottom sub leaves a standard fishing profile facing up to facilitate later retrieval.

The type of valve assembly used in this second embodiment contributes significantly to the performance of the releasable tool joint and is shown in more detail in Figure 5. The assembly consists essentially of two moving components, the HP valve 13 and the LP valve assembly 15, 16. The valves are held together and sealed by spring force. The HP valve receives a high force from the Belleville spring washers 30, the LP valve assembly a low force from coil spring 17. Since the spring forces are not in equilibrium, a net force exists and this is reacted by the valve stop 14, assembled onto mandrel 8. In normal use, oil is prevented from passing the HP/LP valve assembly by the three sealing elements, namely 0-rings 35, 37 and 39. Tension in the tool is resisted hydraulically by the HP valve.A form of hydraulic gearing exists since the piston face of the lower end cap 21 is larger than the piston face of the HP valve. In this way, the preload force provided by the Belleville washers is considerably less than the tension on the tool required to overcome it. When an applied tension does overcome the preload on the Belleville washers, the HP valve moves away from the valve stop. The LP valve soon comes to rest against the valve stop and further movement of the HP valve opens a gap between the valves and allows the flow of oil through the assembly. The flow is damped by throttling between the HP and the LP valves and by having to pass through orifices in the HP valve. The damping ensures that a significant time is required to pass the volume of oil necessary to complete the travel to the lockout point of the tool.If, at any point during the travel, the applied tension drops below the set point of the HP valve, then the HP valve will close and travel will cease. Further reduction in tension allows the return spring 20 to start building pressure above the LP valve, a small amount of pressure will open the LP valve and allow the return of oil through the valve assembly, and thus return the whole internal assembly to its start position.

As a result of these features this second embodiment is more compact, less complicated and therefore easier and cheaper to make and use than the first embodiment. It is hydraulically damped at all times.

A third embodiment is illustrated in Figure 6. Here the hydraulic valve mechanism is replaced by a plastically compressible component 19. For example, and in this illustration, the component is a slotted cylinder made of a low strength steel. The cylinder is a disposable component which acts as an energy absorber, much like the convoluted or slotted metal cylinder employed as a safety device in the steering column of motor cars. The cylinder has a yield force which is carefully calculated from its wall thickness and slot pattern. Because of the ductility of the material employed and the design of the cylinder, the force needed to start yielding is required throughout the working deflection of the component.Since the units of energy are the product of force and distance it will be seen that a specific and calculable amount of energy is required to deflect the cylinder and so release the tool. Various yield strengths of cylinder are to be provided to allow accurate setting of the tool appropriate to the working conditions. In use, when the cylinder is yielded, the internal components of the tool (mandrel 18, collet 26 etc) move downwards towards the release position and the slack left by the cylinder's compression is taken up by the return spring 20. If a brief impact causes the cylinder to yield, the short duration of the force ensures a low energy input and therefore the cylinder will not have compressed enough to allow release of the collet. In this way short shock loads do not release the tool.Compare this action to that of an alternative potential solution, that of a pin in perfect shear. Here the material strain on yielding is immense for a small distance travelled and so the pin will reach its failure strain and break at a fraction of the input energy for the cylinder, even when the yielding load is the same. A shear pin is thus prone to shock load failure and must be rejected as unsuitable. The lower part in use of the third embodiment is seen to be identical to the second embodiment. Full compression of the slotted cylinder 19 allows the collet tips 26 to pass into the larger diameter in the lower body 22. Release of tension (set down) allows the collet tips to slip out of engagement with the undercut on the fishneck 28, 29 and so, on picking up weight, the tool will separate as required.

It will be seen that, in this third embodiment, the tool's release load is set and assured by the exchange of the disposable slotted cylinder, pre-calibrated by the manufacturer. This embodiment does not therefore require the use of special calibration and adjustment tools as do the first and second embodiments. Also this embodiment disposes completely of the necessarily expensive and delicate hydraulic components seen in the previous embodiments.

However, no recovery of deflection is seen if the tool in this embodiment is slacked off after a partial release. Partial releases during one trip downhole may thus sum to result in inadvertent separation for this tool that would not occur for the previous embodiments. The fact that partial release has occurred can easily be determined by visual inspection of the tool, specifically by the relative position of the spigot 27 and bottom sub 28. That is to say there is no need to dismantle the tool to determine if partial release has occurred.

In summary the present invention offers the following advantages: * all wire is retrieved undamaged; * the tool cannot release accidentally under jarring forces due to the specific energy input required to effect release; * the tool can be externally adjusted and calibrated to suit various wires and conditions, either by setting the springs and valving or by interchanging the collapsible component; * time and labour costs can be saved compared with other known types of releasable rope socket connectors and as against wire cutting operations; operation of the system does not require a vertical or substantially vertical configuration and will therefore operate effectively in a heavily deviated well.

ITEM DESCRIPTION 1 TOP SUB 2 /4" 28UNF GRUB SCREW 3 SWIVEL SHAFT 4 BODY ADAPTER 5 BODY 6 SPRING ADJUSTER 7 UNF SOCKET SCREW 8 KEY 9 DUST SEAL 10 BELLEVILLE WASHER 11 'O'-RING 12 'O'-RING 13 SPRING GUIDE 14 'O'-RING 15 N.P.T PLUG (FLUSH) 16 'O'-RING 17 N.P.T PLUG (FLUSH) 18 BOTTOM BODY SECTION 19 PEAR DROP HOLDER 20 'O'-RING 21 PEAR DROP SLEEVE 22 PEAR DROP 23 COLLET HOLDER 24 COLLET 25 MID BODY 26 UNC GRUB SCREW 27 BALL BEARING 28 SPRING TABLE 1: KEY TO FIGS 1 1 & 2

ITEM DESCRIPTION 1 ROPE SOCKET BODY 2 PEAR DROP SLEEVE 3 PEAR DROP 4 SAFE JOINT TOP SUB (ORJ) 5 SAFE JOINT TOP SUB (THREAD) 6 END CAP UPPER 7 ADJUSTER LOCK 8 ADJUSTER LOCK PIN 9 LOCK PIN SLEEVE 10 ADJUSTER LOCK SPRING 11 BELLEVILLE ADJUSTER 12 CYLINDER 13 H.P. VALVE 14 VALVE STOP 15 L.P. VALVE OUTER 16 L.P. VALVE INNER 17 L.P. VALVE SPRING 18 MANDREL 19 COLLAPSABLE CYLINDER 20 RETURN SPRING 21 END CAP LOWER 22 LOWER BODY 23 PROTECTION SLEEVE 24 LOCK BUTTON 25 LOCK BUTTON SPRING 26 COLLET 27 SPIGOT 28 BOTTOM SUB (THREAD) 29 BOTTOM SUB (ORJ) 30 BELLEVILLE WASHER 31 GRUB SCREW l/4UNF '/aLONG 32 GRUB SCREW l/4UNF 3/8LONG 33 FLUSH TYPE PLUG l/aNPT 34 DOUBLE DELTA RING S-55403 35 'O'-RING BS 016 36 'O'-RING BS 114 37 'O'-RING BS 125 38 'O'-RING BS 127 39 'O'-RING BS 212 TABLE 2: KEY TO FIGS 4 5 & 6

Claims (9)

1. CLAIMS 1. A releasable tool joint assembly comprising:

   i) a female portion adapted to be connected to a wire line or upper tools in a tool string by a connection means;

   ii) a male portion adapted to be attached to the lower tools and further adapted to be releasably connected to the female portion;

   iii) disengagement means adapted to controllably release the male and female portions thus separating the upper and lower portions of the tool string; characterised in that the disengagement means is activated by sustained tension above a pre-determined value, and in that it further comprises a means of energy absorption such that shock loads do not cause release.
2. 2. A releasable tool joint assembly according to Claim 1 wherein the disengagement means comprises:

   i) a fluid reservoir;

   ii) a bleed chamber;

   iii) a passageway connecting the fluid reservoir and the bleed chamber;

   iv) a flow restrictor located in the passageway such that fluid flow between the fluid reservoir and the bleed chamber is regulated;

   v) a collet release mechanism; characterised in that sustained tension above a pre-determined value on the female member causes fluid to flow from the fluid reservoir into the bleed chamber, displacement of this fluid ultimately resulting in disengagement of the collet and further characterised in that release of the sustained tension at any time prior to disengagement results in any fluid in the bleed chamber being forced back into the fluid reservoir.
3. 3. A releasable tool joint assembly as claimed in Claim 2 wherein the passageway between the fluid reservoir and the bleed chamber incorporates high and low pressure differential check valves which ensure that no fluid can pass from the reservoir to the bleed chamber until the sustained tension is greater than a pre-determined threshold value, whilst allowing fluid to return freely to the reservoir when tension is removed.
4. 4. A releasable tool joint assembly as claimed in Claim 1 characterised in that the disengagement means comprises:

   i) a plastically compressible component;

   ii) a collet release mechanism; wherein sustained tension above a pre-determined level on the female portion causes the compressible component to yield, ultimately resulting in disengagement of the collet.
5. 5. A releasable tool joint assembly as claimed in Claim 4 wherein the compressible component comprises a slotted cylinder.
6. 6. A releasable tool joint assembly as claimed in any preceding claim which further incorporates a safety mechanism such that immediately following release the male member remains captured within the female member, or vice versa, such that the uppermost in use component(s) attached to the wire is prevented from catapulting in the direction of the tension force until substantially all of the tension force is released.
7. 7. A releasable tool joint assembly as claimed in Claim 6 wherein the safety effect is achieved by providing slightly hooked ends on the collet.
8. 8. A releasable tool joint assembly substantially as herein described with reference and as illustrated in any combination of the accompanying drawings.
9. 9. A rope sock incorporating a releasable tool joint assembly as claimed in any preceding claim or substantially as herein described.