GB2504104A

GB2504104A - Wellhead assembly for downhole tool deployment.

Info

Publication number: GB2504104A
Application number: GB201212697A
Authority: GB
Inventors: Philip Head
Original assignee: Artificial Lift Co Ltd
Current assignee: Artificial Lift Co Ltd
Priority date: 2012-07-17
Filing date: 2012-07-17
Publication date: 2014-01-22
Also published as: GB201212697D0

Abstract

Wellhead assembly comprising a tubular string (8, FIG 5) suspended from a wellhead casing. There is a cable 60 including a conductor 61 hanging from a cable hanger 40. Bypass passage 33 is arranged to fluidly connect a central bore 5 below the cable hanger with an outlet 9 above the cable hanger. Connection path 72 passing through the wellhead connects the conductor with surface equipment. The bypass passage is arranged between the casing hanger and tubular outer wall and radially outward / offset from the longitudinal central axis X X of the borehole. The cable hanger 40 may form part of an insert which can be received supported by a seat in the wellhead. The bypass passage may be divided into a plurality of parallel channels. The conductor may be an electrical conductor to power a tool suspended from the cable.

Description

Welihead assembly for downhole tool deployment This invention relates to the deployment of dowrihole tools, particularly but not exclusively in a hydrocarbon well, via a wellhead.

D

An oil or gas well comprises a borehole having at least one, more usually two or more concentric tubular strings which are sealingly connected to a wellhead (which is to say, a wellhead assembly) at the earth's surface. The wellhead is commonly a vertical assembly of short, flanged tubular elements or spools, with an internal diameter not less than that of the well casing so that production tubing or other smaller diameter tubular elements can bc run into the casing via the wellhead. Each spool may incorporate a hanger from which a respective one of the tubular strings is sealingly suspended, or a valved port extending through the side wall of the spool which provides fluid communication to the annulus between two respective tubular strings, either for injection of fluid into the well or for production of fluid from the well. The central bore of the uppermost spool is fluidly connected with the bore of the innermost tubular string, usually the production tubing which carries the principal fluid production of the well and provides a path through which tools such as electric submersible pumps or sensing (logging) devices may be lowered down the borehole to the productive formation.

In order to control the flow of well fluid from the production tubing, an assembly of intercommunicating valves known as a Christmas tree is sealingly mounted on top of the wellhead. The Christmas tree typically includes redundant, upper and lower master valves arranged in series at its lower end, which can be closed to shut off the flow from the production tubing; lateral wing valves above the master valves, which are used respectively for carrying the well fluid produced from the well and for injecting kill fluid into the well; and, at its upper end, a swab valve.

Usually at least one blowout preventer is also arranged in line with the wellhead and the Christmas tree.

The swab valve is axially aligned with the wellbore and master valves, providing a route through which coiled tubing or small diameter tools can be lowered into the well via the production tubing. It is possible to provide for the swab and master valves and connecting vertical pipework of the Christmas tree to have a diameter corresponding to that of the wellhead, so that larger diameter tools, such as electric submersible pump assemblies (ESPs), may also be deployed in the well via the swab valve. This however considerably increases the cost of the Christmas tree. Moreover, it is undesirable for cables or conductors to extend in use through I 0 the master valves and so prevent them from being filly closed.

It is known, for example from US 4289199 and US 5732771 to suspend a string of production tubing from a tubing hanger in the wellhead. and to provide conductors extending down the annulus external to the production tubing which exit the wellhead via a penetration in the tubing hanger, either laterally through a tubular sidewall of the wellhead (US 4289199) or upwardly via a bulkhead at the upper end of the wellhead (US 5732771), Although these arrangements provide a means whereby power, sensing and control lines arranged in the annulus can be brought out of the wellhead without fouling the master valves, the problem remains of how to deploy tools suspended on cables within the production tubing and to terminate the cables extending therefrom.

It is the object of the present invention to provide a more convenient way of deploying tools in a hydrocarbon well without the use of an oversized Christmas tree and without obstructing the master valves.

According to the present invention there is provided a wellhead assembly as defined in the claims.

Further features and advantages will become apparent from the following illustrative embodiment of the invention which will now be described, purely by way of example and with reference to the accompanying drawings, in which: Fig. 1 shows a tool suspended in a borehole from a first wellhead assembly surmounted by a Christmas tree, the welihead assembly being shown in longitudinal section and including a cable hanger supported in an insert, the longitudinal section being taken at I -I of Fig. 3; Fig. 2 is a longitudinal section through the first wellhead assembly with the cable hanger removed; Fig. 3 is a plan view of the cable hanger received in the insert; Fig. 4 is a side view of the cable hanger; Fig. S is an enlarged view of part of Fig. 1; and Fig. 6 is an enlarged view of part of Fig. 5.

Corresponding reference numerals indicate the same features in each of the figures.

Referring to the figures, a wellhead assembly I comprises a vertical assembly of axially aligned flanged tubular elements or spools 2, 3, 4 which together form a tubular outer wall 1' defining a generally vertical, central bore 5 which is arranged above the wellbore 6 of the borehole 6' in axial alignment with its longitudinal central axis X -X. The tubular outer wall I' forms together with an upper plate I" the outer casing of the wellhead which contains the pressure from the productive formation. A lower one of the spoo1s (not shown) is sealingly connected in fluid communication with the well casing 7 which is cemented into the ground to define the outermost wall of the borehole.

in the illustrated embodiment, the radially innermost tubular string (i.e. string of tubing) 8 suspended from the wellhead casing and extending down the borehole coaxially with its longitudinal central axis X -X and having an open upper end 8 fluidly communicating with the central bore 5 comprises production tubing for conveying oil, gas or water from the well to surface, The innermost tubular string 8 thus forms the major flowpath from the well, and may be of a diameter sufficient to convey large tools such as ESPs into the well down to the productive formation. Alternatively, it could be used to convey fluids into the well, with the produced well fluid being conveyed to surface via the annulus outside it. The tubular string 8 is sealingly suspended from the tubular outer wall I' of the wellhead easing via an uppermost tubing hanger 4! in an upper one of the spools 4 so that it extends down the borehole concentrically within the well casing 7.

Typically the innermost tubular string 8 is arranged concentrically within progressively radially larger tubular strings (not shown) which are suspended from corresponding radially larger tubing hangers mounted lower down in the tubular outer wall I' oithe wellhead casing. Similarly to the well casing 7, these radially larger tubular strings do not have open upper ends fluidly communicating with the central bore, but rather define the outer walls of respective annuli which are fluidly connected to lateral flow lines (not shown) via valves in the tubular outer wall 1 of the wellhead casing.

The central bore terminates at the upper end of the wellhead assembly at an outlet 9 which is axially aligned with the central bore 5 and fluidly communicates with a Christmas tree 20 mounted above the wellhead assembly on the uppermost spool 2. The Christmas tree comprises an assembly of valves including upper and lower master valves 21, 22, wing valves 23, 24 and a swab valve 25, the master and swab valves 21. 22, 25 being axially aligned with the central bore S of the

S

welihead assembly on the axis X -X of the weilbore so that small diameter tools can be run into the well via the swab valve. The pipework of the Christmas tree connecting the master and swab valves is of conventional diameter, being substantially less than that of the central bore 5 of the welihead assembly.

The central bore 5 includes a first seat 10 and a second seat 32. The first seat 10 comprises an inner wall of an upper portion 5' of the central bore S formed in the cylindrical, tubular outer wall 2' of the uppermost spool 2 which fornis part of the tubular outer wall 1' of the wellhead assembly 1 * The first seat 10 includes an internal shoulder 10' and has an internal diameter Dl which is enlarged relative to the diameter 1)2 of a relatively lower portion 5" of the central bore below the scat, the diameter 1)2 being not less than the inner diameter D3 of the production tubing 8.

The second seat 32 defines a bore 37 formed in an insert 30 having an external shoulder 31, the insert being releasably received in the first seat 10 and supported by its external shoulder 31 which abuts against the internal shoulder 1 o' of the first seat, and retained by retaining screws 11. The second seat also has an internal shoulder 32'. A bypass passage 33 is formed in the insert 30 so that it extends in parallel with the bore 37.

A cable hanger 40 having an external shoulder 41 is releasably received in the second seat 32 and supported by its external shoulder 41 which abuts against the internal shoulder 32' of the second seat so that the cable hanger forms a releasable part of the insert 30. The cable hanger is thus axially interposed between the open upper end 8' of thc innermost string of production tubing S and the outlet 9, %vhich is to say that when considered in the axial direction X X of the borehole, i.e. in plan view, the cable hanger is seen to be arranged at least partially in-between the upper end 8' and the outlet 9. In the illustrated embodiment, when considered in plan view the cable hanger is advantageously arranged within the outer circumference of the outlet 9 and coaxially with the central axis X -X of the borehole and tubular string 8 and outlet 9.

The bypass passage 33 is arranged between the cable hanger 40 and the tubular outer wall 1 (more specifically, radially inwardly of the cylindrical, tubular outer wall 2' of the spool 2) and radially outwardly of the longitudinal central axis X -X of the borehole so as to fluidly connect the lower portion 5" of the central bore below the cable hanger 40 and below the first seat 10 with the outlet 9 above the cable hanger when the insert 30 is received in the first seat 10 and the cable hanger 40 is received in the second seat 32 as shown.

An electric submersible pump assembly (ESP) 50 is deployed into the borehole by suspending it from the cable 60 which subsequently supplies it with power. The cable 60 has three self supporting insulated electrical conductors 61, each conductor including a respective steel core 62 with a copper cladding 63 and an insulating sheath 64, the conductors being enclosed in an outer sheath 65. The steel cores arc mcchanically anchored in thc cable hanger 40 with their respective copper claddings 63 bcing electrically conncctcd to thrcc rcspcctive connectors 42 which terminate in an enclosed intcrnal compartment 43 of the cable hanger, which may be filled with potting compound.

Each connector 42 is connected to a respective conductor 71 of an upper cable 70 which connects the respective conductor 61 and hence the ESP 50 with surface equipment 80 external to the wellhead. The conductors 71 of the upper cable exit the welihead assembly via a connection path 72 passing through an aperture 2" in the casing F, 1" of the wellhead assembly, specifically in the external tubular wall 2' of the uppermost spool 2 forming part of the tubular outer wall 1' and through corresponding bores 34, 44 which cxtcnd radially outwardly respectively through an outer wall portion 35 of the insert 30 and through an outer wall portion 45 of the cable hanger 40, the radial bore 44 communicating with the internal compartment 43 ol' the cable hanger so that the connection path extends from the internal compartment 43 out through the outer wall 2 of the uppermost spool.

In order to deploy the ESP in the weilbore, the well is killed by injecting a dense fluid via one of the wing valves, and then the Christmas tree is removed from the wellhead assembly to expose the outlet 9. The cable 60 connected at its lower end to the ESP 50 is introduced through the bore 37 of the insert 30 and supported by a sheave (not shown) which lowers the ESP through the outlet 9 and ccntral bore 5 down inside the production tubing 8 into the welibore 6. Once the ESP has been lowered beneath the wellhead assembly, the insert 30 is arranged in the first seat with its bore 34 aligned with the aperture 2" and captured by the retaining screws 11. l'he upper end of the cable 60 is connected to the cable hanger 40, which has a threaded socket 47 at its upper end for connection to lifting equipment above the wellhead. When the ESP has been run to its target depth, the cable hanger is lowered into the second seat 32 with its radial bore 44 aligned with the radial bore 34 in the insert, so that the ESP is suspended from the cable, the cable being suspended from thc cable hangcr 40 so that it extends through the central bore 5 down the borchoic 6' within thc tubular string 8, as shown in Fig. I. Thc radial bores 34, 44 are thus aligned as shown with the aperture 2" to define the connection path 72 which extends through a first interface 73 between the outer wall 36 of the insert and the first seat 10 and through a second interface 74 between the outer surface 46 of the cable hanger 40 and the second seat 32. The upper cable 70 is protected by a rigid tubular sheath 75 which extends through the first interface 73 and is sealed in the aperture 2" by an annular sea] 76.

A pair of upper and lower flrst annular seals 77, 77' are arranged between the insert 30 and the first seat 10, respectively above and below the radial bore 34, and another pair of upper and lower second annular seals 78, 78' arc arranged between the cable hanger 40 and the second seat 32, respectively above and below the radial bore 44. Each pair of first and second seals define an isolated annular portion of the respective interface 73. 74 so that together the first and second seals isolate the connection path from the central bore 5. In alternative but less preferred embodiments, each pair of seals could be substituted by just one seal arranged coaxially with the respective radial bore 34, 44 to seal the respective interface.

II will he noted that the aperture 2" is isolated from the wellhore by a system of redundant seals including the seal 76 and the upper and lower first seals 77, 77'.

The bypass passage 33 has an internal cross sectional area at least 65%, preferably at least 90% of that of the internal bore (defined by diameter D3) of the production tubing 8. In the example shown, the bypass passage 33 is divided into a plurality of parallel channels which when considered in cross section (i.e. a section transverse to the longitudinal central axis X -X of the borehole) define sectors 33' 1 5 separated by radial walls 38 and by the circumferentially wider outer wall portion containing the bore 34 which extends radially between the second seat 32 and the outer wall 36 of the insert to form part of the connection path 72.

The sectors 33' together with the radial walls 38 and the portion 35 occupy an annular portion of the insert 30 defincd between the radially inner 39 and outer 39' walls of each sector. If the annular portion were entirely open (i.e. if the radial walls 38 and portion 35 were removed) then it would form an annular bypass passage having an internal cross sectional area of about 163% of the internal cross sectional area of the production tubing 8.

Advantageously, the bypass passage extends for at least 1 80 degrees around the vertical axis Y -Y of the cable hanger, with the load applied to the hanger by the cable and suspended tool being transferred to the casing of the wellhead assembly by the radial walls 38. This maximises the available area of the ilowpath without increasing the overall diameter and hence the cost of the wellhead assembly. In the example shown, the five sectors of the bypass passage occupy about 260 degrees of the circumference of the annular portion of the insert and so advantageously have a combined cross sectional area of about 118% of the internal cross sectional area of the production tubing, which ensures that the well fluid produced via the production tubing can flow freely through them past the cable hanger. This is made possible by the enlarged internal diameter Dl of the upper portion of the central bore 5 forming the first seat 10 in which the insert 30 is arranged. At the same time, the cable 60 is conveniently connected to the surface equipment 80 external to the wellhead via the connection path which is safely isolated from the central bore by multiple, redundant scals.

In summary, a wellhead assembly preferably comprises an internal cable hanger arranged axially above the borehole, a bypass passage through which the fluid produced from the well can flow past the cable hanger to an outlet axially above it, and a connection path isolated from the weilbore through which a cable suspended from the hanger is connected to surface equipment external to the wellhead. The eahlc hanger may be releasably mounted in the wellhead and may comprise part of an insert including the bypass passage. An electrical submersible pump assembly may be suspended from the cable.

In alternative embodiments, the central bore need not include a removable insert separate from the cable hanger, in which case the cable hanger may be releasably received in a seat formed directly in one of the spools defining the tubular outer wall of the wellhead casing. For example, the insert 30 including the bypass passage 33 and second seat 32 could be formed as an integral part of the spool 2, with the cable hanger 40 being releasably received in and supported by the second seat 32 as shown. The spooi 2 including the integral insert portion 30 would then have to be removed to obtain full bore access to the borehole 6.

In yet further alternative embodiments, instead of forming a removable part of the insert 30 as shown, the cable hanger 40 could form an integral part of the insert 30 including the bypass passage 33, both integral parts 40, 30 being releasably received in and supported by the first seat 10.

In alternative embodiments, the connection path could pass axially upwardly through an upper end of the outer easing of the wellhead assembly, e.g. through the upper plate 1", rather than laterally through the tubular outer wall I' as shown.

In the illustrated embodiment the longitudinal central axis X -X of the borehole extends through the cable hanger and the outlet. Specifically, the vertical central axis Y -Y of the cable hanger is aligned with the longitudinal central axis X -X of the borehole which also forms the central axis of the outlet 9, so that the outlet, the cable hanger and the cable are all coaxial with the borehole and the central bore 5. This makes it easier to deploy the cable and suspended tool in the borehole via the outlet and avoids damage to the cable by keeping its upper end clear of the innermost string of production tubing when it is suspended from the cable hanger while avoiding the substantial cost of increasing the diameter of the wellhead. In less preferred embodiments the cable hanger 40 and/or the outlet 9 could be offset somewhat From the ccntral axis X -X of the borehole, however still being interposed between the outlet and the upper end 8' of the tubular string so that tooling may be deployed on cable via the outlet 9 and tubular string 8, the cable subsequently being suspended from the cable hanger.

In the illustrated embodiment, the cable 60 advantageously comprises three electrical conductors, each conductor having a steel core and copper cladding, the steel core conferring sufficient tensile strength to support the weight of the cable plus an electrically powered tool suspended from it over the substantial depth of the boreholc.

In alternative embodiments, the cable could comprise one or more electrical conductors of conventional constrnction (not necessarily having steel cores). The cable might comprise optical fibres, hydraulic lines or other non-electrical conductors instead of or in addition to electrical conductors, which may be connected to logging tools or any other downhole tools suspended from and/or connected to the cable.

Many other adaptations will be evident to those skilled in the art, and it will be understood that the invention is limited only by the claims.

Claims

CLAIMS1. A welihead assembly including: a welihead easing including a tubular outer wall, the tubular outer wall defining a generally vertical, central bore arranged above a borehole, the borehole having a longitudinal central axis; a tubular string suspended from the wellhead casing and extending down the borehole coaxia.lly with the longitudinal central axis and having an open upper end fluidly communicating with the central bore; a cable hanger; a cable suspended from the cable hanger and including at least one conductor; a bypass passage arranged to fluidly connect the central bore below the cable hanger with an outlet above the cable hanger; and a connection path passing through the wellhead casing, the at least one conductor being connected with surface equipment via the connection path; characterised in that the cable hanger is axially interposed between the open upper end of the tubular string and the outlet, the cable extends through the central bore down the borehole within the tubular string, and thc bypass passage is arranged between the cable hanger and the tubular outer wall and radially outwardly of the longitudinal central axis of the borehole.
2. A wellhead assembly according to claim 1, wherein the]ongitudinal central axis of the borcholc extends through the cable hanger and the outlet.
3. A welihead assembly according to claim I or claim 2, wherein the connection path passes through the tubular outer wall of the wcllhead assembly.
4. A welihead assembly according to any preceding claim, wherein the connection path is isolated from the cennal bore and communicates with an internal compartment of the cable hanger.
5. A welihead assembly according to any of claims 1 -4, wherein the central bore includes at least one seat, the cable hanger being releasably received in and supported by the seat, and the bypass passage is arranged to fluidly connect a lower portion of the central bore below the seat with the outlet when the cable hanger is received in the seat.
6. A welihead assembly according to claim 5, wherein thc connection path extends through an interface between the cable hanger and the seat.
7. A welihead assembly according to claim 6, wherein at least one seal is arranged between the cable hanger and the seat to isolate the connection path from the central bore.
8. A welihead assembly according to any of claims 5 -7, wherein the cable hanger forms part of an insert, the insert being releasably received in and supported by the seat, and the bypass passage is arranged in the insert.
9. A wellhead assembly according to any of claims 1 -4, wherein the central bore includes a first seat and a second seat; the first seat comprising an inner wall of an upper portion of the central bore, the second seat and the bypass passage being formed in an insert; the insert being releasably received in and supported by the first seat, the cable hanger being releasably received in and supported by the second seat; and the bypass passage is arranged to fluidly connect a lower portion of the central bore below the first seat with the outlet when the insert is received in the first seat and the cable hanger is received in the second seat.
10. A wellhcad assembly according to claim 9, wherein the connection path extends through a first interface between the insert and the first seat and through a second interface between the cable hanger and the second scat.
11. A wellhead assembly according to claim 10, wherein at least one first seal is arranged between the insert and the first scat and at least one second seal is arranged between the cable hanger and the second seat, the first and second seals isolating the connection path from the ecntral bore.
12. A wellhcad assembly according to any of claims 1 11, wherein the bypass passage has an internal cross sectional area at least 65% of that of the tubular string.
13. A welihead assembly according to any of claims 1 -11, wherein the bypass passage has an internal cross sectional area at least 90% of that of the tubular string.
14. A welihead assembly according to any of claims I. -13, wherein the bypass passage extends at least 1 80 degrees around a vertical axis of the cable hanger.
15. A welihead assembly according to claim 14, wherein the bypass passage is divided into a plurality of parallel channels.
16. A welihead assembly according to any preceding claim, wherein a Christmas tree is mounted above the wellhead assembly in fluid communication with the outlet.
17. A wellhead assembly according to any preceding claim, vhcrcin the or each conductor is an insulated electrical conductor and includes a respective steel core.
18. A welihead assembly according to any preceding claim, wherein an electrically powered tool is suspended from the cable during deployment of the tool in the borehole and supplied with power via the at least one conductor.D
19. A wellhead assembly according to claim 18, wherein the tool is an electric submersible pump assembly.
20. A wellhead assembly substantially as described with reference to the accompanying drawings.