GB2258675A - Workover system with multi bore converter - Google Patents

Abstract

A workover system suitable for subsea oil and/or gas wells has a convertor allowing the system to be used to access any of the bores of a parallel, multiple bore well. The convertor has an outer housing 10 and movable bored inner portion 35, the movement lining the bore up in succession with one of the parallel bores 22, 23. The bore(s) not lined up have outlet(s) through the convertor for circulation of fluids. The inner portion 35 may move rotatably or be swung pendulum fashion. A workover system can be used with the convertor, the system having a pressure resistant riser to a surface vessel and a second pressure resistant communication with the surface vessel, which may be a second riser concentric with the first or the kill and choke lines of a drilling riser. The convertor and workover system form standardised equipment which can be used on a variety of wells with differing bore sizes and configurations. <IMAGE>

Description

WORKOVER SYSTEM WITH MULTI BORE CONVERTOR This invention relates to a workover system with a multi-bore convertor for changing a concentric workover system to one capable of use with parallel bore wells. It is particularly, but not exclusively, suitable for use on sub-sea oil and/or gas wells.

Introduction Oil and/or gas wells commonly have two or more flow bores within their casings. These bores may be concentric (ie a central bore with one or more surrounding annuli) or parallel (ie two or more separate side-by-side bores).

Concentric bores have advantages over parallel bores in simplicity of conRstruction and positioning and in greater capacity, but are less well proven. Multiple parallel bores are in extensive use with well proven safety records. In the future it is probable that both systems will be in use depending on the particular circumstances of any given oil or gas field and the preferences of the operator.

Background Any well whatever its bore system may require a so-called "workover" from time to time. A workover means gaining access to one of the bores for testing and servicing or to carry out remedial work on the well. Workovers may be carried out on completion of a well or at any time during its productive life. The types of work involved in a workoever are well known to oilfield operators and may include: Wire line work, cable logging and perforating, intervention with coiled tubing or narrow diameter drill pipe, and removal and replacement of tubing.

During, or as part of, a workover, fluids may need to be circulated down one bore and up another.

Sometimes it is necessary to pull a completion to effect a workover (ie to remove the well tree and sometimes even the internal tubing hangers and tubing of the well) but this should obviously be avoided if possible because of the high cost and the time lost. The more intervention or remedial work that can be carried out without going to this extreme the better, and it is much preferable to leave the well tree in place and carry out the workover through the bores of the tree.

Access may be required to any of the bores of a multi-bore well and, for sub-sea wells, it has, in the past, been the practice to use workover riser systems that match the type of completion, eg a dual bore riser and dual bore BOP for a dual bore well - two of everything, in fact, for the rated size and pressure. Such duplication is very costly.

However, an important point to note is that, at any one time, physical access to only one bore is required. Only the capability of fluid flow from the other bore or bores is required without direct physical access. Duplication of the workover system for a multibore well could be avoided, therefore, if the system had means for switching to the well bore being worked over below the riser and BOP.

Although only access to one bore is required at any one time, the need to circulate fluids implies that the means for switching should include an outlet for the bore not being directly accessed so that fluid can be circulated down one bore and out the other.

Another practical factor in the cost of workovers is the tendency of oilfield operators to synchronise workovers in a number of fields owned or operated by them. A surface vessel or rig has to be hired so it makes sense to use it to carry out as many workovers as possible.

However, the oil fields may have a variety of different types of trees and completions so the surface vessel or rig may need to carry a number of different workover systems, each one being specially designed to suit a particular oilfield. The advantages of synchronising workovers in a number of fields will be partly nullified by the need for the vessel or rig to carry a number of workover systems and to change the system when moving from field to field.

Operational requirement From the above discussion, it will be apparent that there would be advantages in having a standardised workover system capable of servicing a variety of different types of well completions. This standardised system should avoid the duplication hitherto needed for multi-bore wells by having a single bore BOP and a single main pressure resistant riser extending up to the surface vessel or rig, with means, below the BOP, for switching to whichever bore of the well needs to be accessed. To give the standardised system the capacity for circulating fluids there should be a circulation return facility from the non-accessed bore or bores through the switching means and up to the surface vessel or rig.

The standardised system will thus be essentially a concentric workover system, with the switching means providing the capability for it to operate on parallel multi-bore wells.

The present invention According to the present invention a convertor for a workover system allowing a concentric bore workover system to have access to any one of a number of parallel bores in an oil and/or gas well comprises: an outer housing adapted to form part of a concentric workover package, said outer housing having, at its top, a single opening and at its base, two or more parallel openings, a movable inner portion within the housing with a bore which mates at its top end with the single opening but which, on movement of the portion, can mate with any one of the parallel openings, means for moving the inner portion, and a pressure-tight outlet from the opening or openings not mated with the bore of the inner portion.

The convertor may be placed within the workover package below the workover BOP and above a well tree connector which will be a parallel bore connector. It is preferably removably joined into the package to allow a number of different convertors to be used depending on the type of well completion being worked over. Thus the convertor could be a dual bore or triple bore with variations in the sizes of the bores and the pressures to be resisted. In the event of the workover package being required to operate on a concentrically completed well the convertor can be removed altogether with the workover BOP being joined directly to a well tree connector. With concentrically completed wells it is only possible to have direct access into the central bore so there is no need for any convertor with such wells.

The movement of the inner portion may be rotational or of the swinging pendulum type.

With rotational movement the rotation may be around the vertical axis of the convertor, although the axis of rotation may be offset with respect to the centre line of the convertor. There may be bearings between the inner portion and the housing, and seals at appropriate points to ensure that the inner portion is fluid and pressure tight. The parallel bore or bores not lined up with the bore of the inner portion must be sealed against access to the main bore but should have access for circulating fluids. Thus the inner portion may have a passage or passages separate from the main bore providing a pathway from a non-lined up bore to a side outlet or outlets in the outer housing.

The inner portion may be rotated by any convenient means, eg an axially movable, toothed rod cooperating with a toothed ring on the inner portion, or a rotatable screw threaded rod meshing with the toothed ring. The former ram type gearing is preferred to the latter worm gearing as being more positive and easily reversible.

Worm gearing tends to require a higher torque to unlock it than to drive it. The power for the gearing may be hydraulic, electrical or mechanical and the power supply and controls should be such that the inner portion can be rotated when in place sub-sea. Thus after carrying out a workover operation on one bore of a well, it should be possible to withdraw the wireline, coiled tubing, or whatever workover equipment is being used, to seal the well by actuating the tree valves, to depressurise the workover system, to switch the convertor to another bore, to repressurise the system and reopen the tree and carry out a workover on another bore.

To ensure proper alignment of the bore and passages of the inner portion with the openings of the housing, the housing may have stops to limit the rotational movement of the inner portion.

A rotational convertor can be relatively simple in design and easy to machine accurately. The bores can be effectively isolated from one another and sealed even against large pressure differences between them. It can be designed to be free of cavities or pockets where corrosive fluids or erosive substances such as sand or grit could collect.

The inner portion of a swinging pendulum convertor may be a tube within the housing with, at its top, a ball joint fitting closely within a spherical hollow of the housing. The housing should have sufficient space to allow the tube to swing pendulum fashion and the bottom of the housing, which has the parallel openings, may be curved so that the bottom end of the tube is always hard up against the housing.

The tube may be swung by means of horizontal rams passing through the housing and contacting the outside of the tube. The contact may be through a yoke and collar which is gimballed so that the moving force is always horizontal irrespective of the swing of the tube. The motive power may be hydraulic, electrical or mechanical with the power supply and the controls being arranged so that the pendulum tube can be swung with the convertor in place sub-sea.

With the pendulum convertor it is less easy to provide pressure tight sealing between the inner portion and the housing and hence between the parallel bores Preferably, therefore, the parallel openings in the bottom of the housing extend down through the housing for a sufficient distance to allow the insertion of a valve in each parallel bore, these valves being the means for sealing the bore or bores not being worked over. Below these valves each bore may have a side outlet through the housing, each outlet also having a valve to allow for and control the circulation of fluids through the non-worked over bore.

In either type of convertor the passage through the convertor and its inner portion can be made substantially vertical although some slight deflection may have to be tolerated. The deflection can, however, be kept to a limit such that it does not impede the passage of wire line tools or instruments, coiled tubing, or narrow diameter drill pipe.

The workover system into which the convertor fits may itself require some variations from conventional workover systems, the object being to have a standard, versatile system capable of being used with a variety of different well trees and completions.

The present invention includes, therefore, a workover system comprising: a pressure resistant riser deployable from a surface vessel to a subsea well, a single bore workover BOP connected to the riser, means for attaching a convertor below the workover BOP, a connector for attaching the package to a well tree or well head, and a second pressure resistant means of communication between the surface vessel and the well tree or well head capable of conveying fluids to or from the surface vessel.

The pressure resistant riser provides the means of access to the well bore to be worked over, the second means of communication allowing fluids to be circulated to or from a well bore not being worked over.

One embodiment which provides both the means of access to one well bore while providing means of fluid communication with another well bore may be a relatively large diameter pressure resistant riser with a smaller diameter pressure resistant tubing run concentrically within the large diameter riser. The two concentric risers thus provide two means of pressure-resistant communication, a central bore and an annular flow path.

In another embodiment the main access may be a pressure resistant riser formed of eg a tubing hanger running string within a non-pressure resistant conventional drilling riser, and the second means of communication may be the conventional kill and choke lines normally associated with such drilling risers.

With either embodiment a second riser BOP may be required suspended below the surface vessel at the top of the workover system. The pressure resistant riser through which the workover tools are deployed has to be sealed at its top end and a second riser BOP may be the most convenient form of control and isolation of the system.

Means of access on the drill floor and moon pool of the surface vessel may be the normal type of intervention workface allowing wireline tools or instruments, coiled tubing, or narrow diameter drill pipe to be inserted into the workover package.

Either embodiment could form a standard package with a number of convertors, the precise convertor selected being adapted for the bore sizes and pressures of the parallel bore well. Thus using a rotational convertor attached to a standard package with a 7 inch BOP, access could be had into a 5 inch x 2 inch or a 4 inch x 2 inch dual parallel bore well or into a 3 inch x 3 inch x 2 inch triple parallel bore well. The pendulum convertor may be limited to use with dual bore wells only but could accommodate a variety of different dual bore sizes, using a standard package with a 7 inch or 5 inch BOP.

The invention is illustrated with reference to the following drawings in which Figure 1 is a vertical section through a rotational convertor according to the present invention.

Figure 2 is a horizontal section through the rotational convertor of Figure 1, the left hand side being along line A-A of Figure 1, and the right hand side along line B-B of Figure 1.

Figure 3 is a vertical section through a pendulum convertor according to the present invention, and Figure 4 is a representation of a standard workover package using a drilling riser which may be used in association with the convertor of either Figures 1 and 2 or Figure 3.

In Figure 1 the convertor has an outer housing formed in two parts, upper body 10 and lower body 11. The casing is made in two parts for ease of assembly, the parts being held together by a number of bolts 12, and with a BX ring gasket 13 between the bodies to ensure a pressure tight seal. The top of upper body 10 has a releasable connector (not shown) for attachment to the bottom of a BOP, and the bottom of lower body 11 has a releasable connector (not shown) for attachment to a multi-bore parallel bore well tree.

Upper body 10 has a circular opening 14 at its top. As shown it is 7 inches in diameter for use with a 7 inch BOP, but a smaller diameter 5 inch opening for use with a 5 inch BOP could be used and is shown by dotted lines 15. Openings 14, 15 are concentric with the centre line of the convertor, which is also the centre line of the BOP and well tree. The centre line is indicated at 16.

Within upper body 10, however, opening 14 widens out and becomes off-centre with respect to centre line 16, this off-set centre line being indicated at 17. Off-set circular passage 18 is lined with a sleeve 19A having ring seals 20 and metal lip seals 21 at top and bottom. Indicated by dotted lines is the position of sleeve 19B which would be used with a 5 inch diameter BOP.

At the bottom of lower body 11 are two parallel openings 22, 23 both of the same 5 inch diameter initially, but one narrowing down to 2 inch diameter. As previously indicated, the larger opening could be 4 inches and it could be possible to have three parallel openings of 3 inches, 3 inches and 2 inches respectively. Whatever the number of openings and whatever their eventual diameters it is important that their initial diameters should be the same.

Each opening is lined with a sleeve 24, 25 similar to sleeve 19A of upper body 10 with side ring seals 26 and metal lip seals 27 at the bottom. Instead of upper lip seals, however, the top of each sleeve has a ring seal 28. Below each sleeve is an energising spring 29.

Springs 29 and the pressure within the system when in use tend to force the sleeves upwardly so that seals 28 form a pressure tight seal where they contact cylindrical member 35, described hereafter.

Finally, as regards the housing, lower body 11 has a circular groove 30 on its inside having side outlet 31. Bolted by bolts 32 to lower body 11 at outlet 31 is a Dipe 33, with BX gaskets 34 between the parts to form a pressure tight seal. Pipe 33 can convey fluids to or from the convertor as will be described hereafter.

Within the upper and lower bodies 10, 11 of the housing, is a generally cylindrical member 35 capable of limited rotation about off set centre line 17. It has a tapering passage 36 through it leading from passage 18 to opening 23 as shown, but on rotation of the member, passage 36 could also link passage 18 to opening 22.

Opening 22, as shown, lines up with another passage 41 leading to groove 30 of lower body 11 and hence to side outlet 31. Rotation of member 35 will link opening 23 with groove 30 through passage 41.

Member 35 rotates on bearings 37, 38-at top and bottom, with upper bearing 37 held by a circlip 39. Three sets of double seals 40 seal member 35 against lower body 11.

Rotation of member 35 is effected by a toothed ring 42 on the member cooperating with a toothed ram 43 on upper body 10.

An upward extension of part of ring 42 forms a key 44 which extends upwardly into a circular recess of upper body 10. Key 44 holds and locates ring 42 with respect to member 35.

The limits of rotational movement of member 35 are controlled by rotation stop rods 45, 46 in upper body 10. Only one is shown in Figure 1 and that is diagrammatic since the stops are not in the plane of the section. Ram 43 and stop rods 45, 46 are better seen and will be described in more detail with reference to Figure 2.

To complete the description of Figure 1, where passage 41 of rotatable member 35 meets groove 30 of lower body 11, a fluid tight junction is ensured by upper and lower ring seals. Upper ring seal 47 has a metal lip seal 48 and is held by a circlip 49. The lower ring seal has two spacers 50, 51 each held by a circlip 52, 53 and with a metal lip seal 54 between them. There is one further metal lip seal 55 at the outside bottom edge of member 35.

Figure 2 is a composite section, the left hand side being along plane A-A of Figure 1 (ie the plane of the rotation stop rods) and the right hand side being along plane B-B of Figure 1 (ie the plane of toothed ring 42 and toothed ram 43). Parts already described in Figure 1 have the same reference numerals.

Taking the left hand side of Figure 2 first, stop rod 45 limits the anti-clockwise rotation of member 35 and stop rod 46 the clockwise rotation. Their ends are within a recess formed between upper body 10 and member 35 (see Figure 1) with seals 56 to make them pressure tight within upper body 10. Each stop rod is adjustable, adjustment thread 57 and lock nut 58 being shown as part of stop rod 45. A removable isolation plug 59 plugs the point of insertion of stop rod 45 into upper body 10. An upward stepped extension of ring 42 in the vicinity of key 44 has faces 60 and 61.

Face 60 is shown contacting the end of clockwise rotational stop rod 46 (ie as shown member 35 is at its clockwise limit of rotation).

If member 35 is rotated anticlockwise for 180 , face 61 will contact the end of anti-clockwise rotational stop rod 45 and so limit the anti-clockwise rotation.

The right hand side of Figure 2 shows how ram 43 fits within a groove of upper body 10 with ram housings 63 on the outside of body 10, each housing held by bolts 64 and having BX ring seals 65. Ram 43 is a toothed rack and toothed ring 42 a pinion so axial movement of ram 43 will move ring 42 and hence member 35 either clockwise or anti-clockwise to an extent governed by stop rods 45, 46. &commat; As previously explained ram 43 could be replaced by a rotating screw, but a ram is preferred as being more positive.

From Figure 1 and 2 it will be seen that the passage from opening 14 through the convertor to either opening 22 or 23 does deviate from the vertical but that this deviation is relatively small.

A convertor for a triple parallel bore well (eg a 3" x 3" x 2" well) would have three parallel outlets instead of the two outlets 22, 23, each outlet having an initial diameter of 3 inches but one of them narrowing down to 2 inches. The third outlet would mate with a second passage in member 35 similar to passage 41 but with a separate side groove and side outlet below groove 30 and outlet 31.

This further groove and outlet would be made pressure tight with seals.

Member 35 could thus access any one of the three bores with the other two, each having their own separate, isolated, fluid outlets.

Rotating member 35 by 135 would select the next bore, member 35 having an overall rotation of 270' instead of 180'.

Instead of two stop rods 45, 46, the stops may be three spring loaded, hydraulically released, vertical pins co-operating with three slots on the top of ring 42. The spring loading means that the pins will automatically enter the slots on rotation and the hydraulic release and withdrawal means that no mechanical lock up can occur.

A longer axially movable ram 43 could be used, but this would need to be rather long for a ring rotation of 270'. A rotatable screw rod would, therefore, be preferable.

Figure 3 is a vertical section through a pendulum convertor.

With this unit the housing has a lower body 70 forming most of the casing with upper body 71 being little more than a cover. Upper body 71 is bolted on to lower body 70 with bolts 72 and there is a BX ring gasket 73 between the bodies to make a fluid tight seal. A socket plate 74 is let into the top of lower body 70 below upper body 71, which has a 7 inch opening 75. This opening is concentric with the centre line of the convertor.

Dotted lines indicate the size and position of an alternative 5 inch opening. As with the rotational convertor upper body 71 has a releasable connector (not shown) to a 7 inch (or 5 inch) BOP, and lower body 70 a releasable connector (not shown) to a dual parallel bore well tree.

Upper body 71 and socket plate 74 are shaped to give a truncated spherical socket below opening 75, this socket housing a ball 76 which forms the top of pendulum selector sleeve 77. The ball and socket joint allows sleeve 77 to swing as a pendulum within lower body 70 between two positions, one as shown in the drawing and the other indicated by dotted lines. It can thus line up with either of two parallel openings 78, 79 in the bottom of lower body 70. Both start as 5 inch bores but one narrows down to 2 inches and, through a well tree connector, they lead into 5 inch and 2 inch parallel bores of a well tree. Lower body 70 has a curved surface of contact with the end of sleeve 77 to ensure close contact.The positions of openings 78, 79 with respect to the centre line of the convertor are such that, depending on the position of sleeve 77, there is a passage from opening 75, through sleeve 77 to either the 5 inch or 2 inch bores which deviates as little as possible from the vertical. The bore not lined up with sleeve 77 is open to the chamber of lower body 71 within which sleeve 77 swings, so each bore has a valve 80, 81. This can be any convenient type of remotely controlled shut off valve. Each bore also has a side outlet 82, 83 with a remotely controlled shut off valve 84, 85. As shown in the drawing, if valve 80 is open and valve 81 closed, there will be direct access through the convertor to the 2 inch well tree bore with the 5 inch bore sealed. Moving the sleeve 77, and shutting valve 80 and opening valve 81, gives access to the 5 inch well tree bore while sealing the 2 inch bore.The side valve of the open bore will normally be closed, but opening the valve of the sealed bore would allow controlled fluid flow into or out of the sealed bore.

Sleeve 77 is swung between its two positions by two selector rams 86, 87. They have ring seals where they pass through lower body 71, one seal for ram 87 being shown at 88. Each ram bears on sleeve 77 through a yoke 89, and a collar 90 with a split gimbal insert 91 held by circlip 92. Sleeve 77 has a curved surface 93 where collars 90 contact it. This arrangement allows the rams to move horizontally while the sleeve swings, collars 90 moving around curved surface 93 and up or down yokes 89 as sleeve 77 swings.

The rams of both types of convertor are preferably driven by hydraulic pistons but they could be driven by electric motors or mechanically by an ROV. They may be controlled from a surface rig or vessel using the hydraulic control system of the workover BOP.

Figure 4 is a view of a standard workover package which may be used with the rotational convertor of Figures 1 and 2 or the pendulum convertor of Figure 3.

The convertor is shown at 100, with a releasable connector 101 locking it to a subsea multiple parallel bore well tree 102. Below the tree is well head 103 with tubing hangers supporting two parallel bores 104, 105 extending down into the well.

Above convertor 100 is workover BOP 106. For convenience Figure 4 is sub-divided by side-lines into a series of modular packages, the workover BOP 106, convertor 100, and releasable connector 101 being combined as a workover BOP package 107.

Workover BOP package 107 is hung on the end of a basically conventional drilling riser assembly, but which has been modified to accept and service package 107.

Thus above package 107, is a lower riser package 108. This has a releasable connector 109 for joining the lower riser package 108 to the work over BOP package 107. Above connector 109 is an isolation and test block 110, which has valves to control the kill and choke lines of the riser assembly. As described hereafter these kill and choke lines are used for the flow of fluids from the well through convertor 100, hence the need for block 110, to control the flow for either isolation or testing purposes. Above block 110 is a shear off safety connection 111, which as its name implies, will shear in an emergency and so prevent damage to the packages and well head below it. Running string anchor housing 112 anchors running string 119 (described hereafter) into package 108, which is completed by a flex joint 113 and a riser adaptor 114 which holds drilling riser 116.

The next package 115 is a drilling riser package with drilling riser 116, kill and choke lines 117, and control umbilical 118. For the purposes of the present invention, within the drilling riser is a further concentric pressure resistant completion running string 119 which provides the pathway for workover tools into the lower riser package 108 and the workover BOP package 107. This pressure resistant string 119 is as previously stated held in the lower riser package 108 by the running string anchor housing 112.

Drilling riser 116 can be of moderate diameter, eg 7 5/8 or 11 inch and need not be one of the more conventional 21 or 16 inch diameter drilling risers. The internal running string 119 can be 5 inch diameter within a 7 5/8 inch riser or 7 inch diameter within an 11 inch riser.

Drilling riser package 115 extends up almost to the surface vessel or rig, where suspended below the vessel or rig is a riser isolation package 120 held by rig tensioners 121. The components of this package are a tension adjuster 122 for running string 119, a riser BOP 123, and tension ring 124. There is a feed line 125 for the control umbilical, and also pressure resistant lines 126, 127 and 128. Riser BOP 123 is needed in the riser isolation package 120 because running string 119 is a pressure resistant line which may be flowing high pressure fluid. It need not, however, be as complex as a conventional BOP but of any form which will provide a safe shut off in an emergency.

Pressure resistant line 126 is connected to either the kill or the choke line and is for the return flow of fluid from convertor 100. Test line 128 is connected to whichever of the kill or choke lines is not being used for fluid return flow from convertor 100, and is, as its name implies, a line which can be used for any testing purposes prior to operation. Line 127 connects into running string 119 and exists for general monitoring.

Riser isolation package 120 has a telescopic joint 130 and flex joint 131 where it leads up into the surface vessel, these being known types of joint to allow for limited movement of the surface vessel. Shown diagrammatically are the drill floor datum 132 and drill floor substructure 133, with divertor 134 and divertor line discharge 135. Finally above the drill floor are a workover extension joint 136 and intervention interface 137, these being the point of entry for workover or logging tools.

Any surface rig or vessel would carry a drilling riser assembly as standard equipment and Figure 4 shows how such an assembly may be modified to double up as a workover assembly. The drilling riser, being itself not pressure resistant, is the mechanical support between the surface vessel or rig and the workover BOP package 107, the lower riser package 108 being modified to have connection 109 onto package 107 rather than a connection onto a well head. The assembly is also modified by having a pressure resistant running string 119 concentrically within the riser. The string extends from intervention interface 137 on the drill floor through the riser isolation package 120 and its BOP 123, then within the drilling riser 116 to anchor housing 112 in lower riser package 108 and thence into the workover BOP 106.Convertor 100 then allows this pathway to be directed to either of the two parallel well bores 104, 105 so that there is a continuous pathway for workover equipment from intervention interface 137 to either bore 104 or bore 105.

The kill and choke lines 117 of the riser assembly, not being required for their normal purpose, are utilised to provide a path for circulating fluids from the well bore not being accessed. The side outlets of the convertor (31 of Figure 1, or 82, 83 of Figure 3) are connected through workover BOP package 107 and lower riser package 108 to whichever of the kill and choke lines is connected to outlet line 126. Fluid under pressure can thus be sent down running string 119, and through connector 100, into the well bore 104 or 105 being worked over or tested, then back to connector 100 and its side outlet, up the kill or choke line and so out through line 126. In this embodiment the other kill and choke line is used solely for test purposes.

However, since there are two kill and choke lines, it would be possible to use one line for down fluid flow and the other for return fluid flow, thereby obviating the need to send fluid down the inner pressure resistant running string 119. The connections in lower riser package 108 would need to be modified to connect the down kill or choke line into the main bore of the convertor, but this could be the simpler embodiment when using running string 112 for wireline work, since the need for a wireline BOP would be obviated.

The control umbilical 118 of the riser assembly can be used to provide all the control functions required not only in lower riser package 108 but also in workover BOP package 107 including operation the rams of the convertor 100 to change the well bore being accessed.

With a drilling riser of 11 or 7 5/8 inch diameter, there will be room inside for a 7 inch or 5 inch diameter running string 119, which with correspondingly sized BOPs and convertors will allow workovers to be carried out on a variety of different well bore sizes and configurations.

As an alternative to using a drilling riser assembly as the mechanical support for the workover package, a different concentric arrangement of pipes could be used. The outer pipe would not be a drilling riser but a pressure resistant pipe similar to running string 119 anchored at either end to lower riser package 108 and riser isolation package 120 by pressure resistant housings. Within this outer pipe a further concentric pressure resistant housing inner pipe would be deployed between riser BOP 123 and workover BOP 106 and sealed by annulars. By this use of two concentric pressure resistant risers, a central bore and an annulus are provided, the central bore providing a pathway for workover equipment and the annulus a pathway for the return of circulating fluids, without the need for kill and choke lines as the circulating fluid pathway. A control umbilical similar to 118 will still be needed for control functions and the lower riser package 108 will need to be modified so that the side outlets of the convertor 100 feed to the annulus.

The riser isolation package 120 will also be modified to provide an outlet from the annulus to line 126. Test line 128 will also connect to the annulus.

The outer pressure resistant riser may be 7 5/8 inch diameter and the inner concentric riser 5 inch.

Claims (15)

Claims

1. A convertor for a workover system allowing a concentric bore workover system to have access to any one of a number of parallel bores in an oil and/or gas well comprising: an outer housing adapted to form part of a concentric workover package, said outer housing having, at its top, a single opening and at its base, two or more parallel openings, a movable inner portion within the housing with a bore which mates at its top end with the single opening but which, on movement of the portion, can mate with any one of the parallel openings, means for moving the inner portion, and a pressure-tight outlet from the opening or openings not mated with the bore of the inner portion.

2. A convertor as claimed in claim 1 wherein the convertor has releasable connectors allowing it to be removably joined into the workover system.

3. A convertor as claimed in claim 1 or 2 placed within the workover system below a workover BOP and above a parallel bore well tree connector.

4. A convertor as claimed in claim 1, 2 or 3 which is a rotational convertor wherein the inner portion is rotatable about a vertical axis of the convertor.

5. A convertor as claimed in claim 4 wherein the inner portion has a passage or passages separate from the main bore providing a pathway for the parallel opening or openings not lined up with the main bore to the side outlet or outlets of the outer housing.

6. A convertor as claimed in claim 4 or 5 wherein the inner portion is rotated by a toothed ring cooperating with an axially movable toothed ram or a rotatable screw threaded rod.

7. A convertor as claimed claim 1, 2 or 3 which is a pendulum convertor wherein the inner portion is a tube with, at its top, a ball joint fitting within the outer housing.

8. A convertor as claimed in claim 7 wherein the parallel openings of the outer housing have valves and below the valves side outlets also with valves.

9. A convertor as claimed in claim 7 or 8 wherein the inner portion is swung by rams passing through the outer housing and contacting the tube through a yoke and gimballed collar.

10. A convertor as claimed in any of claims 1 to 9 wherein the means for moving the inner portion is hydraulic, electrical or mechanical actuation with remote control to enable the inner portion to be moved when the convertor is in place in a workover system.

11. A workover system suitable for use with a convertor as claimed in any of claims 1 to 10 comprising: a pressure resistant riser deployable from a surface vessel to a subsea well, a single bore workover BOP connected to the riser, means for attaching a convertor below the workover BOP, a connector for attaching the package to a well tree or well head, and a second pressure resistant means of communication between the surface vessel and the well tree or well head capable of conveying fluids to or from the surface vessel.

12. A workover system as claimed in claim 11 having two concentric pressure resistant risers, the annulus between the risers being the second pressure resistant means of communication.

13. A workover system as claimed in claim 11, having a pressure resistant riser within a non-pressure resistant drilling riser with kill and choke lines, the kill and choke lines being the second pressure resistant means of communication.

14. A workover system as claimed in claim 11, 12 or 13 having a riser BOP at the top of the workover system.

15. A convertor for a workover system according to claim 1 as hereinbefore described with reference to the accompanying drawings.