United States Patent
`
`[19]
`
`[11] Patent Number:
`
`5,544,707
`
`US0055447O7A
`
`[45] Date of Patent:
`
`Aug. 13,1996
`
`......................... .. 166/348
`1/1967 Brown et al.
`3/1967 Yancey . ... .. . . . ..
`.. .. .... 166/348
`11/1970 Sizer ..................
`166/368 X
`8/1971 Kenneth et al.
`..... .. 166/368
`5/1972 Wakefield, Jr.
`................... .. 166/368 X
`
`
`
`3,295,600
`3,310,107
`3,542,125
`3,602,303
`3,662,822
`
`FOREIGN PATENT DOCUMENTS
`
`8601852
`
`3/1986 WIPO.
`
`'
`
`Primary Examiner—Hoang C. Dang
`_ Attorney, Agent, or Firm——Conley, Rose & Tayon
`
`[57]
`
`ABSTRACT
`
`A wellhead having, instead of a conventional Christmas tree,
`a spool
`tree in which a tubing hanger is landed at a
`predetermined angular orientation. The tubing string can be
`pulled without disturbing the tree and access may be had to
`the production easing hanger for monitoring production
`casing annulus pressure and for the introduction of larger
`tools into the well hole without breaching the integrity of the
`well. In the embodiment described, a valve is used to open
`and close a fluid pressure passage between the production
`casing annulus and a production casing annulus monitoring
`port in the spool tree.
`
`Hopper et al.
`
`[54] WELLHEAD
`
`[75]
`
`Inventors: Hans P. Hopper, Aberdeen, Scotland;
`Thomas G. Cassity, Cobham, England
`
`[73] Assignec: Cooper Cameron Corporation,
`Houston, Tex.
`'
`
`[21] Appl. No.:
`
`204,397
`
`[22] PCT Filed:
`
`May 28, 1993
`
`[86] PCT No.:
`
`PCT/US93l052.46
`
`§ 371 Date:
`
`Mar. 16, 1994
`
`§ 102(c) Date: Mar. 16, 1994
`
`[87] PCT Pub. No.: W093l2.4730
`
`PCT Pub. Date: Dec. 9, 1993
`
`Foreign Application Priority Data
`[30]
`Jun. 1, 1992
`[EP]
`European Pat. Off.
`
`92305014
`
`Int. Cl.5 ...................................................... E2113 33/03
`[51]
`
`[52] U.S. Cl.
`............. ..
`.. 166/382; 166/368
`[58] Field of Search ..................................... 166/348, 339,
`166/368, 341, 347, 382, 88, 89, 95, 208
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`2,889,886
`
`6/1959 Gould ........................................ 166/89
`
`13 Claims, 16 Drawing Sheets
`
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`U.S. Patent
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`Aug.13, 1996
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`5,544,707
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`1
`WELLHEAD
`
`BACKGROUND OF THE INVENTION
`
`Conventionally, wells in oil and gas fields are built up by
`establishing a wellhead housing, and with a drilling blow out
`preventer stack (BOP) installed, drilling down to produce
`the well hole whilst successively installing concentric casing
`strings, which are cemented at the lower ends and sealed
`with mechanical seal assemblies at their upper ends. In order
`to convert the cased well for production, a tubing string is
`run in through the BOP and a hanger at its upper end landed
`in the wellhead. Thereafter the drilling BOP stack is
`removed and replaced by a Christmas tree having one or
`more production bores containing actuated valves and
`extending vertically to respective lateral production fluid
`outlet ports in the wall of the Christmas tree.
`This arrangement has involved problems which have,
`previously, been accepted as inevitable. Thus any operations
`down hole have been limited to tooling which can pass
`through the production bore, which is usually no more than
`five inch diameter, unless the Christmas tree is first removed
`and replaced by a BOP stack. However this involves setting
`plugs or valves, which may be unreliable by not having been
`used for along time, down hole. The well is in a vulnerable
`condition whilst the Christmas tree and BOP stack are being
`exchanged and neither one is in position, which is a lengthy
`operation. Also, if it is necessary to pull the completion,
`consisting essentially of the tubing string on its hanger, the
`Christmas tree must first be removed and replaced by a BOP
`stack. This usually involves plugging and/or killing the well.
`A further dilficulty which exists, particularly with subsea
`wells, is in providing the proper angular alignment between
`the various functions, such as fluid flow bores, and electrical
`and hydraulic lines, when the wellhead equipment, including
`the tubing hanger, Christmas tree, BOP stack and emergency
`disconnect devices are stacked up. Exact alignment is nec-
`essary if clean connections are to be made without damage
`as the devices are lowered into engagement with one
`another. This problem is exacerbated in the case of subsea
`wells as the various devices which are to be stacked up are
`run down onto guide posts or a guide funnel projecting
`upwardly from a guide base. The post receptacles which ride
`down on to the guide posts or the entry guide into the funnel
`do so with appreciable clearance. This clearance inevitably
`introduces some uncertainty in alignment and the aggregate
`misalignment when multiple devices are stacked, can be
`unacceptably large. Also the exact orientation will depend
`upon the precise positions of the posts or keys on a particular
`guide base and the guides on a particular running tool or
`BOP stack and these will vary significantly from one to
`another. Consequently it is preferable to ensure that the same
`running tools or BOP stack are used for the same wellhead,
`or a new tool or stack may have to be specially modified for
`a particular wellhead. Further misalignments can arise from
`the manner in which the guide base is bolted to the conduc-
`tor casing of the wellhead.
`
`SUMMARY OF THE INVENTION
`
`In accordance with the present invention, a wellhead
`comprises a wellhead housing; a spool tree fixed and sealed
`to the housing, and having at least a lateral production fluid
`outlet port connected to an actuated valve; and a tubing
`hanger landed within the spool
`tree at a predetermined
`angular position at which a lateral production fluid outlet
`
`2
`port in the tubing hanger is in alignment with that in the
`spool tree.
`With this arrangement, the spool tree, takes the place of a
`conventional Christmas tree but diifers therefrom in having
`a comparatively large vertical
`through bore without any
`internal valves and at least large enough to accommodate the
`tubing completion. The advantages winch are derived from
`the use of such spool tree are remarkable, in respect to safety
`and operational benefits.
`Thus, in workover situations the completion, consisting
`essentially of the tubing string, can be pulled through a BOP
`stack, without disturbing the spool
`tree and hence the
`pressure integrity of the well, whereafter full production
`casing drift access is provided to the well through the large
`bore in the spool tree. The BOP can be any appropriate
`workover BOP or drilling BOP of opportunity and does not
`have to be one specially set up for that well.
`Preferably, there are complementary guide means on the
`tubing hanger and spool tree to rotate the tubing hanger into
`the predetermined angular position relatively to the spool
`tree as the tubing hanger is lowered on to its landing. With
`this feature the spool tree can be landed at any angular
`orientation onto the wellhead housing and the guide means
`ensures that the tubing string will rotate directly to exactly
`the correct angular orientation relatively to the spool tree
`quite independently of any outside influence. The guide
`means to control rotation of the tubing hanger into the
`predetermined angular orientation relatively to the spool tree
`maybe provided by complementary oblique edge surfaces
`one facing downwardly on an orientation sleeve depending
`from the tubing hanger the other facing upwardly on an
`orientation sleeve carried by the spool tree.
`Whereas modern well
`technology provides continuous
`access to the tubing annulus around the tubing string, it has
`generally been accepted as being diflicult, if not impossible,
`to provide continuous venting and/or monitoring of the
`pressure in the production casing annulus, that is the annulus
`around the innermost casing string. This has been because
`the production casing annulus must be securely sealed whist
`the Christmas tree is fitted in place of the drilling BOP, and
`the Christmas tree has only been fitted after the tubing string
`and hanger has been run in, necessarily inside the production
`casing hanger, so that the production casing hanger is no
`longer accessible for the opening of a passageway from the
`production casing annulus. However, the new arrangement,
`wherein the spool tree is fitted before the tubing string is run
`in provides adequate protected" access through the BOP and
`spool tree to the production casing hanger for controlling a
`passage from the production casing annulus.
`For this purpose, the wellhead may include a production
`casing hanger landed in the wellhead housing below the
`spool tree; an isolation sleeve which is sealed at its lower
`end to the production casing hanger and at its upper end to
`the spool tree to define an annular void between the isolation
`sleeve and the housings and an adapter located in the annular
`space and providing part of a passage from the production
`casing annulus to a production casing annulus pressure
`monitoring port in the spool tree, the adapter having a valve
`for opening and closing the passage, and the valve being
`operable through the spool
`tree after withdrawal of the
`isolation sleeve up through the spool tree. The valve may be
`provided by a gland nut, which can be screwed up and down
`within a body of the adapter to bring parts of the passage
`formed in the gland nut and adapter body, respectively, into
`and out of alignment with one another. The orientation
`sleeve for the tubing hanger maybe provided within the
`isolation sleeve.
`
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`5,544,707
`
`3
`Production casing annulus pressure monitoring can then
`be set up by method of completing a cased well in which a
`production casing hanger is fixed and sealed by a seal
`assembly to a wellhead housing, the method comprising,
`with BOP installed on the housing, removing the seal
`assembly and replacing it with an adapter which is manipu-
`latable between configurations in which a passages from the
`production casing annulus up past the production easing
`hanger is open or closed; with the passage closed, removing
`the BOP and fitting to the housing above the production
`casing hanger a spool tree having an internal landing for a
`tubing hanger; installing a BOP on the spool trees running
`a tool down through the BOP and spool tree to manipulate
`the valve and open the passage; inserting through the BOP
`and spool tree an isolation sleeve, which seals to both the
`production casing and spool tree and hence defines between
`the sleeve and easing an annular void through which the
`passage leads to a production casing annulus pressure moni-
`toring port in the spool tree; and running a tubing string
`down through the BOP and spool tree until the tubing hanger
`lands in the spool tree with lateral outlet ports in the tubing
`hanger and spool tree for production fluid flow, in alignment
`with one another.
`
`According to a further feature of the invention the spool
`tree has a downwardly depending location manure] which is
`a close sliding fit within a bore of the wellhead housing. The
`close fit between the location mandrel of the spool tree and
`the wellhead housing provides a secure mounting which
`transmits inevitable bending stresses to the housing from the
`heavy equipment, such as a BOP, which projects upwardly
`from the top of the wellhead housing, without the need for
`excessively sturdy connections. The location mandrel may
`be formed as an integral part of the body of the spool tree,
`or maybe a separate part which is securely fixed, oriented
`and sealed to the body.
`Pressure integrity between the wellhead housing and
`spool tree may be provided by two seals positioned in series
`one forming an environmental seal (such as an AX gasket)
`between the spool tree and the wellhead housing, and the
`other forming a production seal between the location man-
`drel and either the wellhead housing or the production
`casing hanger.
`During workover operations, the production casing annu-
`lus can be rescaled by reversing the above steps, if necessary
`after setting plugs or packers down hole.
`When production casing pressure monitoring is unneces-
`sary, so that no isolation sleeve is required, the orientation
`sleeve carried by the spool tree for guiding and rotating the
`tubing hanger down into the correct angular orientation
`maybe part of the spool tree location mandrel itself.
`Double barrier isolation, that is to say two barriers in
`series, are generally necessary for containing pressure in a
`well. If a spool
`tree is used instead of a conventional
`Christmas tree,
`there are no valves within the vertical
`production and annulus fluid flow bores within the tree, and
`alternative provision must be made for sealing the bore or
`bores through the top of the spool tree which provide for
`wire line or drill pipe access.
`In accordance with a further feature of the invention, at
`least one vertical production fluid bore in the tubing hanger
`is scaled above the respective lateral production fluid outlet
`port by means of a removable plug, and the bore through the
`spool tree being scaled above the tubing hanger by means of
`a second removable plug.
`With this arrangement, the first plug, takes the function of
`a conventional swab valve, and may be a wireline set plug.
`
`4
`The second plug could be a stopper set in the spool tree
`above the tubing hanger by, e.g., a drill pipe running tool.
`The stopper could contain at least one wireline retrievable
`plug which would allow well access when only wire line
`operations are called for. The second plug should seal and be
`locked internally into the spool tree as it performs a barrier
`to the well when a BOP or intervention module is deployed.
`A particular advantage of this double plug arrangement is
`that, as is necessary to satisfy authorities in some jurisdic-
`tions, the two independent barriers are provided in mechani-
`cally separate parts, namely the tubing hanger and its plug
`and the second plug in the spool tree.
`A further advantage arises if a workover port extends
`laterally through the wall of the spool tree from between the
`two plugs; a tubing annulus fluid port extends laterally
`through the wall of the spool tree from the tubing annulus;
`and these two ports through the spool tree are interconnected
`via an external flow line containing at least one actuated
`valve. The bore from the tubing annulus can then terminate
`at the port in the spool tree and no wireline access to the
`tubing annulus bore is necessa.ry through the spool tree as
`the tubing annulus bore can be connected via the interplug
`void to choke or kill lines,
`i.e. a BOP annulus, so that
`downhole circulation is still available. It is then only nec-
`essary to provide wireline access at workover situations to
`the production here or bores. This considerably simplifies
`workover BOP andlor riser construction. When used in
`conjunction with the plug at the top of the spool tree, the
`desirable double barrier isolation is provided by the spool
`tree plug over the tubing hanger, or workover valve from the
`V production flow.
`When the well is completed as a multi production bore
`well, in which the tubing hanger has at least two vertical
`production through bores each with a lateral production fluid
`flow port aligned with the corresponding port in the spool
`tree, at least two respective connectors may be provided for
`selective connection of a single bore wire line running tool
`to one or other of the production bores, each connector
`having a key for entering a complementary fonnation at the
`top of the spool tree to locate the connector in a predeter-
`mined angular orientation relatively to the spool tree. The
`same type of alternative connectors may be used for pro-
`viding wireline or other running tool access to a selected one
`of a plurality of functional connections, e.g. electrical or
`hydraulic couplings, at the upper end of the tubing hanger.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The development and completion of a subsea wellhead in
`accordance with the present invention are illustrated in the
`accompanying drawings, in which:
`FIGS. 1 to 8 are vertical axial sections showing successive
`steps in development and completion of the wellhead, the
`Figure numbers bearing the letter A being enlargements of
`part of the corresponding Figures of same number without
`the A:
`
`FIG. 9 is a circuit diagram showing external connections
`to the spool 3;
`FIG. 10 is a vertical axial section through a completed
`dual production bore well in production mode;
`FIGS. 11 and 12 are vertical axial sections showing
`alternative connectors to the upper end of the dual produc-
`tion bore wellhead during work over; and,
`FIGS. 13, 13A and 13B show the seating of one of the
`connectors in the spool tree.
`
`10
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`30
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`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`FIG. 1 shows the upper end of a cased well having a
`wellhead housing 20, in which easing hangers, including an
`uppermost production casing hanger 21 for, for example, 9
`5/s" or 10%" production casing is mounted in conventional
`manner. FIG. 1 shows a conventional drilling BOP 22
`having rams 23 and kill and choke lines 24 connected to the
`upper end of the housing 20 by a drilling connector 25.
`As seen in more detail in FIG. 1A, the usual mechanical
`seal assemblies between the production casing hanger 21
`and the surrounding Wellhead housing 20 have been
`removed and replaced through the BOP with an adapter 26
`consisting of an outer annular body part 27 and an inner
`annular gland nut 28 which has a screw threaded connection
`to the body 27 so that it can be screwed between a lowered
`position shown on the right hand side of FIG. 1A, in which
`radial ducts 29 and 30, respectively in the body 27 and nut
`28, are in communication with one another, and a raised
`position shown on the left hand side of FIG. 1A, in which the
`ducts are out of communication with one another. The duct
`
`29 communicates through a conduit 31 between a depending
`portion of the body 27 and the housing 20, and through a
`conduit 32 passing through the production casing hanger 21,
`to the annulus surround the production casing. The duct 30
`communicates through channels 33 formed in the radially
`inner surface of the nut 28, and hence to a void 10 be
`described. The cooperation between the gland nut 28 and
`body 27 of the adapter therefore acts as a valve which can
`open and close a passage up past the production casing
`hanger from the production casing annulus. After "appropri-
`ate testing, a tool is run in through the BOP and, by means
`by radially projecting spring lugs engaging in the channels
`33, rotates the gland nut 28 to the valve closed position
`shown on the right hand side on FIG. 1A. The well is thus
`resealed and the drilling BOP 22 can temporarily be
`removed.
`
`As shown in FIGS. 2 and 2A, the body of a tree spool 34
`is then lowered on a tree installation tool 35, using conven-
`tional guide post location, or a guide funnel in case of deep
`water, until a spool tree mandrel 36 is guided into alignment
`with and slides as a close machined fit, into the upper end of
`the wellhead housing 20, to which the spool tree is then fixed
`via a production connector 37 and bolts 38. The mandrel 36
`is actually a separate part which is bolted and sealed to the
`rest of the spool tree body. As seen particularly in FIG. 2A
`a weight set AX gasket 39, forming a metal
`to metal
`environmental seal is provided between the spool tree body
`and the wellhead housing 20. In addition two sets of sealing
`rings 40 provide, in series with the environmental seal, a
`production fluid seal externally between the ends to the
`spool
`tree mandrel 36 to the spool tree body and to the
`wellhead housing 20. The intervening cavity can be tested
`through a test part 40A. The provision of the adapter 26 is
`actually optional, and in its absence the lower end_of the
`spool tree mandrel 36 may form a production seal directly
`with the production easing hanger 21. As is also apparent
`from reasons which will subsequently become apparent, the
`upper radially inner edge of the spool tree mandrel projects
`radially inwardly from the inner surface of the spool tree
`body above, to form a landing shoulder 42 and at least one
`machined key slot 43 is formed down through the landing
`shoulder.
`'
`
`As shown in FIG. 3, the drilling BOP 22 is reinstalled on
`the spool tree 34. The tool 44 used to set the adapter in FIG.
`1, having the spring dogs 45, is again run in until it lands on
`
`the shoulder 42, and the spring dogs 45 engage in the
`_ channels 33. The tool is then turned to screw the gland nut
`28 down within the body 27 of the adapter 26 to the valve
`open position shown on the right hand side in FIG. 1A. It is
`now safe to open the production casing annulus as the well
`is protected by the BOP.
`The next stage, shown in FIGS. 4 and 4A, is to run in
`through the BOP and spool tree on an appropriate tool 44A
`a combined isolation and orientation sleeve 45. This lands
`on the shoulder 42 at the top of the spool tree mandrel and
`is rotated until a key on the sleeve drops into the mandrel key
`slot 43. This ensures precise angular orientation between the
`sleeve 45 and the spool tree 34, which is necessary, and in
`contrast to the angular orientation between the spool tree 34
`and the wellhead casing, which is arbitrary. The sleeve 45
`consists of an external cylindrical portion, an upper external
`surface of which is sealed by ring seals 46 to the spool tree
`34, and the lower external surface of which is sealed by an
`annular seal 47 to the production casing hanger 21. There is
`thus provided between the sleeve 45 and the surrounding
`wellhead casing 20 a void 48 with which the channels 33,
`now defined radially inwardly by the sleeve 45, communi-
`eate. The void 48 in turn communicates via a duct 49
`through the mandrel and body of the spool tree 34 to a lateral
`port. It is thus possible to monitor and vent the pressure in
`the production easing annulus through the passage provided
`past the production casing hanger via the conduits 32, 31 the
`ducts 29 and 30, the channels 33, shown in FIG. 1A, the void
`48, the duct 49, and the lateral port in the spool tree. In the
`drawings, the radial portion of the duct 49 is shown appar-
`ently communicating with a tubing annulus, but this is
`draughtsman’ s licence and the ports from the two annuli are,
`in fact, angularly and radially spaced.
`Within the cylindrical portion of the sleeve 45 is a lining,
`which may be fixed in the cylindrical portion, or left after
`internal machining of the sleeve. This lining provides an
`orientation sleeve having an upper/edge forming a cam 50.
`The lowermost portion of the cam leads into a key slot 51.
`As shown in FIGS. 5, 6 and 6A a tubing string of
`productionitubing 53 on a tubing hanger 54 is run in through
`the BOP 22 and spool tree 34 on a tool 55 until the tubing
`hanger lands by means of a keyed shoulder 56 on a landing
`in the spool
`tree and is locked down by a conventional
`mechanism 57. The tubing hanger 54 has a depending
`orientation sleeve 58 having an oblique lower edge forming
`a cam 59 which is complementary to the cam 50 in the sleeve
`45 and, at the lower end of the cam, a downwardly project-
`ing key 60 which is complementary to the key slot 51. The
`effect of the earns 50 and 59 is that, irrespective of the
`angular orientation of the tubing string as it is run in, the
`cams will cause the tubing hanger S4 to be rotated to its
`correct angular orientation relatively to the spool tree and
`the engagement of the key 60 in the key slot 51 will lock this
`relative orientation between the tubing hanger and spool
`tree, so that lateral production and tubing annulus fluid flow
`ports 61 and 62 in the tubing hanger 54 are in alignment with
`respective lateral production and tubing annulus fluid flow
`ports 63 and 64 through the wall of the spool tree. Metal to
`metal annulus seals 65, which are set by the weight of the
`tubing string, provide production fluid seals between the
`tubing hanger 54 and the spool tree 34. Provision is made in
`the top of the tubing hanger 54 for a wireline set plug 66. The
`keyed shoulder 56 of the tubing hanger lands in a comple-
`mentary machined step in the spool
`tree 34 to ensure
`ultimate machined accuracy of orientation between the
`tubing hanger 54 and the spool tree 34.
`FIG. 7 shows the final step in the completion of the spool
`tree. This involves the running down on drill pipe 67 through
`
`16
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`5,544,707
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`7
`the BOP, an internal isolation stopper 68 which seals within
`the top of the spool tree 34 and has an opening closed by an
`in situ wireline activated plug 69. The BOP can then be
`removed leaving the wellhead in production mode with
`double barrier isolation at the upper end of the spool tree
`provided by the plugs 66 and 69 and the stopper 68. The
`production fluid outlet is controlled by a master control
`valve 70 and pressure through the tubing annulus outlet
`ports 62 and 64 is controlled by an annulus master valve 71.
`The other side of this valve is connected, through a work-
`over valve 72 to a lateral workover port 73 which extends
`through the wall of the spool tree to the void between the
`plugs 69 and 66. With this arrangement, wireline access to
`the tubing annulus in and downstream of a tubing hanger is
`unnecessary as any circulation of fluids can take place
`through the valves 71 and 72, the ports 62, 64 and 73, and
`the kill or choke lines of any BOP which has been installed.
`The spool tree in the completed production mode is shown
`in FIG. 8.
`
`FIG. 9 shows valve circuitry associated with the comple-
`tion and, in addition to the earlier views, shows a production
`fluid isolation valve 74, a tubing annulus valve 75 and a
`cross over valve 76. With this arrangement a wide variety of
`circulation can be achieved down hole using the production
`bore and tubing annulus, in conjunction with choke and kill
`lines extending from the BOP and through the usual riser
`string. All the valves are fail/safe closed if not actuated.
`The arrangement shown in FIGS. 1 to 9 is a mono
`production bore wellhead which can be accessed by a single
`wireline or drill pipe, and the external loop from the tubing
`annulus port to the void between the two plugs at the top of
`the spool tree avoids the need for wireline access to the
`tubing annulus bore.
`FIG. 10 corresponds to FIG. 8 but shows a 55/: inch X23/la
`inch dual production bore wellhead with primary and sec-
`ondary production tubing 53A and 53B. Development and
`completion are carried out as with the monobore wellhead
`except that the spool tree 34A and tubing hanger 54A are
`elongated to accommodate lateral outlet ports 61A, 63A for
`the primary production fluid flow from a primary bore 80 in
`the tubing hanger to a primary production master valve 70A,
`and lateral outlet ports 62A,64A for the secondary produc-
`tion fluid flow from a secondary bore 81 in the tubing hanger
`to a secondary production master valve 70B. The upper ends
`of the bores 80 and 81 are closed by wireline plugs 66A and
`66B. A stopper 68A, which closes the upper end of the spool
`tree 34A has openings, in alignment with the plugs 66A and
`66B, closed by wireline plugs 69A a.r1d 69B.
`FIGS. 11 and 12 show how a wireline 77 can be applied
`through a single drill pipe to activate selectively one or other
`of the two wireline plugs 66A and 66B in the production
`bores S0 and 81 respectively. This involves the use of a
`selected one of two connectors 82 and 83. In practice, a
`drilling BOP 22 is installed and the stopper 68A is removed.
`Thereafter the connector 82 or 83 is run in on the drill pipe
`or tubing until it lands in, and is secured and sealed to the
`spool
`tree 34A. FIGS. 13, 13A and 13B show how the
`c