CA1197180A - Subsea wellhead connection assembly and a method of installing same - Google Patents

Abstract

SUBSEA WELL COMPLETION SYSTEM, A BASE TEMPLATE FOR THE
SYSTEM AND A METHOD OF ESTABLISHING PRODUCTION CAPABILITY
FROM MULTIPLE SUBSEA WELLHEADS

Abstract A subsea well completion system includes a fluid-tight work enclosure hull 13 containing manifold means and having a plurality of radially-disposed lateral penetration means 38 which extend through the hull 13 and are operatively connected to the manifold means. The system also includes a base template 11 having means 17 for securing the template 11 to the marine floor in a substantially horizontal position and having a lower support structure for supporting the work enclosure hull. The template 11 is further provided with an upper guidance structure comprising a plurality of substantially vertical guide members 19 mounted in spaced radial array, the guide member 19 extending inwardly toward the center of the template and forming an opening at the central portion of the template for receiving the work enclosure hull, a portion 20 of the upper peripheral surface of each guide member 19 sloping downwardly toward the opening for guiding the hull 13 as it is lowered during installation of the hull onto the template.
To establish production capability from multiple subsea wellheads 14 on the template 11, with the template being secured to the marine floor, the work enclosure hull 13 is lowered towards the template 11 from a position directly above the template. The upper guide structure then guides the hull 13 into the central cylindrical opening defined by the guide members 19 and, when the hull is in postion, fluid communication is established between the wellheads 14 and the manifold means through respective penetration means 38.

Description

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F-0981(0983) -1-SUB A WELL COMPLETION SYSTEM9 A ~ASE TEMPLATE FOR THE
SYSTEM AND A METHOD OF ESTA8LISHING PRODUCTION CAPA~ILITY
FROM MULTIPLE SUB A ~ELLHEADS

This invention relates to a subsea well completion system, a base template for the system and a method o~ esta~lishing production c~p~h~l~ty ~rom multiple ~subsea wellheads.
Recent deYelopments in the of~shore oil and gas industry extend production to undersea areas, such as the outer fringes of t~e continental shelves and the continental slopes. A submarine production system is believed to b0 the most practical method o~ reaching the sll~a~lleQIJs deposits. Although hydrocar~ons are the main concern at this time, it is contPmplated that sllh~lleo~lc deposits of sulfur and other minerals can be obtained from beneath the seas. whlle bottom-supported ~~ ~nent surface installations have proved to be econ--ic~lly and technologically feasible in comparatively shallow waters, in deeper waters, such as several hundred to several thousand meters, utilization of such sur~ace installations must be limite~ to very special situations. Installations exten~ing above the water surface are also disadvantageous even in sh~llo~r water wnere there are adverse sur~ace conditions, as in are~s where the bottom-supported structure of the a~ove-surface production platfnrm is su~ect to ice loading.
Su~sea systems are ~easible ~or installing multiple wellheads ln relatively close proxlmity through the use of a drilling templa~e secured on the marine floor. Such systems can be operated from remote, floating sur~ace facilities using electrohydraulic control systems, wlth the subsea systPms being connected to the sur~ace ~acilities by flowlines ~or production ~luids, injection ~lui~s, hydraulic controls, electrical cables, and the like.
Habltable, subsea work enclosures, or satellites, can be maintained adjacent multiple, template-drilled wellheads ~or housing operat1ng and/or maintenance personnel, as ~isrlose~, for example in U.S. Patent No. 3,556,208. In such systems, the subsea satellite is t~

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F-0981(0983) -2-independently connected to a number of surrounding su~sea wellheads and serves to control the production from, an~ maintenance o~, ~he wellheads. The wells are drilled in a circular pattern through a template on the ~arine floor, the template serving also as a ~ase upon which the satellite is installed. The production/control p~sages of each well are connected to production eg~ ,t within the satellite by separate connector units which are independently lowered into place from a surface vessel and form portions o~ the flow pa~hs be~ween the wellheads and the production egll;r- ~t within the satelliteO
- ~hile the a~orementioned subsea satellite systems prove generally satisfactory in water depths of 100 to 150 meters, the use o~
such systems at depths o~ 300 to 750 meters presents certain problems.
For example, the utilization of gl~idelines and diver assistance ~or subsea installation o~ the cc~nents o~ the system becomes more complex with increasing water depths~ In waters o~ such substantial depth, it becomes neces~ry to employ dynamic guidance systems, including remote television and/or sonar monltoring5 during the installation process. Furthermore, subsea installation o~ the satellite on the template in prior systems presents problems in terms of guidance of the satellite into proper position on the template and the need to fasten the satellite to the template. Also~ prior art subsea well completion systems typically utilize s~ ieI~_d work enclosure hulls having vertically arranged hull penetrators. Such an arrangement of the penetrators produces undesira~le hull stress condltions, particularly at depths in excess o~ 150 meters.
It is an objective of the present invention to alleviate the problems and disadvantages of the prior art by providlng an improved subsea well completion system and template therefor capable of simpli~ied installation on the marine floor, as well as an improved subsea satellite installation procedure.
Accordingly, the invention resides in one aspect in a subsea well completion system for multiple subsea wells~ comprising a fluid-tlght work enclosure hull having a plurality of radially~disposed lateral penetration means for esta~lishing rele~c~hle ~luid connectlon 7~0 F-0981(0983) -~

through the hull and a ~ase template having a lower support structure for supporting the ~ork enclosure hull and means for securing the template to a marine floor so that the lower support structure extends substantially hori ontally, the template ~urther having an upper guidance structure comprising a plurality of guide members extending substantially perpeo~ir~1Ar to the lower support structure and mounted in spaced radial array, the guide members extending inwardly toward the center oF the template and forming an opening at the central portion of the template for receiving the work enclosure hull, a portlon of ~he upper peripheral sur~ace of each guide member sloping downwardly toward the opening for guidins the hull into the opening during installation of the hull ~y lowering the hull onto the template.
In a ~urther asoect the invention resides in a subsea base template for guiding marine ~loor well drilling e~ t at multiple wells and supporting a subsea work enclosure hull and wellheads comprising: a lower support strurture ~c ~L ~ing a substantially horizontally aligned9 open ~ubular f~ crk and a plurality of substantially vertical well Conductor pipes spaced around the peripheral portion of thP f~ c~ k and integral therewith, for aligning well drilling e~ -.,t, the upper section o~ each well conductor pipe terminating in a wellhead, th~ central port~on o~ the frf~ k being adapted to support the subsea work enclosure hull and the peripheral portion being adapted to support the wellheads; and an upper guidance structure comprising a plurality of guide mem~ers rigidly mounted on, and extending vertically from, the lowar support structure in spaced radial array, each gui~e member extending inwardly toward the center of the template, forming a substantially cylindrical opening at the central portion of the fL ?~-k for receiving the work enclosure hu119 a portion of the upper surface of each guide mem~er sloping downwardly toward the cylindrical opening ~or guiding the work enclosure hull as it is low~red during installation thereof on~o the template, the guide members further providing structural protection for the work enclosure hull and the wellheads.

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F-0981(0983) 4-In yet a further aspect, the invention resides in a method of esta~lishing production c~p~hi1ity from multiple subsea wellneads on a base template secured to the marine floor, comprising. providing a work enclosure hull containing a mani~old, the hull having a substantially cylindrical portion with a plurality o~ radially-a1~po~ed lateral hull Penetrators extending therethrough and operatively connected to the manifold; providing an upper guidance structure on the template comprising a plurality of substantially vertical guide members mounted in spaced radial array, each guide member exten~ing inwardly from the outer periphery of the template, th~re~y providing a sub-stantially cylindrical opening at the central portion o~ the template for receiving the work enclosure hull, a portion o~ the upper peripheral surface of each guide mem~er sloping downwardly towar~ the cylindrical opening; lowering the work enolosure hull from a position directly above the template and directing the hull through the upper guidance structure into the cylindrical openlng at the central portion of the template, the work enclosure hull being guided into its resting position on the template by the guide mem~ers; and esta~lishing subsea fluid communication between the subsea wellheads and the work enclosure hull.
In the a~-), aying drawings, Figure l is a perspe~tive view of a su~sea well completion system according tû a ~irst example o~ the present invention for gl~dPlineless installation;
Figure 2 is a pelspective view, in partial phantom, of the system of Figure l, showin~ 9ui~e1~neless installation of one of its components;
Figure 3 is a perspect1ve view of the marine ~loor Dase template of the system of Figure l;
Figure 4 is a plan view o~ the marine ~loor base template shown in Figure 3;
Figure 5 i5 a perspective view of the subsea wor~ enclosure hull of the system of Figure l, showing the attached pipeline boom and pipeline;

F-0981(0983) Figure 6 is a cross-sectional plan view of the upper control section of the work enclosure hull, showing internal monitoring and control e~ nt;
Figure 7 is a cross-sectional si~e elevation vie~q of tne lower service section o~ the work enclosure hull, showing a portion o~ the lnternal fluid handling apparatus;
Figure 8 is a cross~sectional plan view, in partial phantom, of the lower service section shown in Figure 7;
Figure 9 is a perspective view of a ~ellhead connector ~eans and its associated protectiYP alignment ~rame of the system o~ Figure l;
Figure 10 is a perspective view of a master valve assembly and assnciated protective alignment ~rame of the system o~ Figure l;
Figure 11 is a side elevation view of the master valve assembly and associated prot~ctive alignment frame shown in Figure 10;
Figure 12 is a p~rspective view o~ a subsea well completion system according to a secon~ example of the present invention, showing i~1;ne installation o~ one o~ the system ccn,--~ents.
Re~erring to Figure 1, the subsea well completion sys~em o~
the first example is ~epresented generally by the numeral 10 an~
includes a ~ase template, designate~ generally by the numeral 11, having a lower support structure for supporting a work snclosure hull 13, individual ~ellheads 14, and wellhead connector means 15.
Wellheads 14 are mounted on well conductor pipes 16 ~orming a portion o~ the lower support structure o~ base templat2 11.
A SP~;s~ si~le drilling rig (not shown) lowers base template 11 to the marine floor on a drilling riser in a known mannerO
Drilling of each well through base template 11 is a~ 1she~ using a conventional blow out preventer (OOP~ stack and conventional drilling procedures. Preferably, base templa~e 11 is constructed s~ch that a OûP stack will be contained within its designated well location by vertical guides 199 thereby preventing overlap or entry into adjacent well locations. When a well is completed, a master valve assem~ly 50 (described below) is pre~erably lowere~ on a drilling riser (not shown) and operatively connected to wellhead 14 to cap it. ~ork enclosure hull 13 is installed on base template 11 by lowering it on a riser ~rom ~7~

F-09Bl(0983) -6-a s~- 'sllh~ersi~le ~rilling vessel and oriented by rotating ~he riser9 uslng television cameras or sonar to ostermine the orientation.
Installation o~ ~ork enclosure hull 13 on ~ase template 11 is preferably performed without the use o~ g~ es. Wellh~ad connector means 15 are then lowered ~rom the drllllng rig on a drill Pipe and operatively connerted ~etween each master valve assem~ly an~ mani~old means housed within ~ork enclosure hull 13 via lateral penetratlon means 38 extending through the hUll. The msni~old means, in turn, connects to pipelines aod flow lines extending tnrough work enclo~ure hull 13. Work enclosure hull 13 must land and lock on ~ase template 11 within a determined rotational aæimuth tolerance to allow lat~ral penetration means 38 to be ~ith~n an arcPpt~hla reach of the c~r~e~pond~ng wellhead connector mPans 15.
The well completlon system 10 is operated from a remote sur~ace production ~acility througn the use of conventlonal electrohydraulic aontrol systems, with ~he well completion sy~em Deing connected to the sur~ace ~acility ~y pipelines, ~luid service lines~
hy~raulic lines, and electrical ca~les. Production and control enu~r~eot inside work enclosu~e hull 13 is m~intained by pelsonnel ~rought ~o the ~ham~r in a ~u~mersi~le or teth~re~ tran~r vehicle.
Well re~oair i5 p~r~ormed either by vertical reentry techniques ~rom a ~loating dri~lin~ rig; or through the use o~ pump~down tools (PDT) launched ~rom ins~d2 work enclosure hull 13 and controlled ~rom the remote sur.~ace facility.
~ here desirable, e.g. for deeper water applications, all subsea co~onehts of the well completion system are installe~ on ~he base t~nplate 11 ~ithout the use o~ gil~del~nes~ Wellhead conneotor means 157 master valve as~ PS 50, and blow cut preventer stacks (not shDwn) are pre~erably eml~red wlth a ~ec~Ally deslgned ~u~per ~tructure (~esrri~ed in detail ~elow) to mate wlth a ~peri~lly d~signe~
upper guidance structure section of ~ase template 11.
Re~erring to Figure 2, the ~ ,~nent, in this case a wellhead connector assembly 15, tQ ~e landed on base te~plate 11 is lowered ~y drill pipe 61 to a point preferably outslde the well bay, ~or safety in the event the ~nl-nent ~hould be aocidentally dropped, and is oriented by rDtating the drill pipe using remote televlsioll or sonar to monitor .

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F-0981(0983) -7=

the operation. Then the component is moved horizontally into the well bay structure and lowered for landing on ~ellhead 14 or master valve assem~ly 50, using running tools similar to those conventionally used for installing wet su~sea trees.
Re~erring to Figures 1-4, the lower support structure of base template 11 also includes means ~or securing the template to the marine floor in a substantially horizontal position. As shown in Figure 4, the securing means includes conventional leveling pile guides 17 spaced about the periphery of the template and extending coaxially with well conductor pipes 16 for rigidly atta~hing base template 11 to the marine floor in a substantially horizontal positionO Wellheads 14 and well conductor pipes 16 are of conventional construction.
Base template 11 fu~ther includes an upper gu1~ance structure comprised of a plurality of substantially vertically extending guide members 19 mounted on the template in spaced radial array. Each vertical gui~ member 19 extends from the outer periphe~y o~ the ~ase template inwardly, leaving a substantially cylindrical opening at the central ,oortion o~ the templatP, de~ined ~y the respective vertical inner legs 21 o~ each guide member 19, for receiving the work enclosure hull 1~. A portion 20 of the upper peripheral surface o~ each guide member 19 slopes r, I ~ dly towards the cylindrical opening to serve as a ~unnel or guid~way. Pre~ersbly, sloplng portion 20 ~e~ines an angle of about 45 to the horizontal.
To install work enclosure hull 1~ on the central portion of basè template 119 the hull is lowered ~y a conventional drill string or riser (not shown) from a floating or semî-submersible vessel (not shown) above the template. The drill string may ~e connected to work enclosure hull 13 using a connector 18 (see Figure 12) CO~x~ y secured to an upper portion of the hull. As work enclosure hull 13 contacts the upper guidance structure of base template 11, sloping portions 2Q will serve to guide the hull 13 into the substantially cylindrical opening defined by legs 21 of the template upper guidance structure at the central portion of the template, thus ensuring proper positioning o~ the hull at khe central po~tion o~ the template.

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F-0981(0983) -8-In addition to providing guidance to work enclosure hull 13 during guidelineless installation onto base template 11, the upper guidan~e structure of base template 11 provides protection against damage to the hull~ As a result of its rigid construction, this structure serves as a protective cage surrounding work enclosure hull 13. Base template 11 is preferably constructed from rigid structural piping, using an open frame construction, as shown. In ad~ition to its ~relly~ such piping permits control of the buoyancy of the template, to aid in its installation on the marine floor.
Further guidance and orientation ~or the hull 13 is prefera~ly provided by guide flange 22 (Figure 3) on the template 11, which extend radially inwardly from legs 21 and have downwardly inclined upper surface portions 230 While other shapes are pns-~ih~e, base template 11 is preferably circular in shape, when viewed from above, ~lth wellheads 14 and well conductor pipes 16 spaced about its circumference, preferably at a common radial distance from the center of the template. In such a system, vertical guide members 19 are preferably spaced apart equidistantly.
The upper guidance structure of base template ll also prcferably possessPs cros~rieces 24 (Figure 1) of structural piplng extending betw~en adjac~nt vertical legs 21, and rigidly secured thereto. As will be explained below, crosspiece~s 24 serve as bloc~ing means, whereby the ~-ls~sion of a cros~p~ece 24 between a preselected pair of legs 21 further facilitates alignment and orientation o~ work enclosure hull 1~ in its desired position during installation on base template 11.
Base template 11 may be provided with ballast tanks (not shown) for ease of handling during towing and installation of the structure. Preferably~ base template 11 ls an open, welded metal structure with a tubular metal frame, cross-braced for strength.
Referring now to Figures 1 and 5, as mentioned~ work enclosure hull 13 is installed on the subsea base template 11 by lowering it on a drill string without the use of gll~delines. To furth0r assist in '7~

F-0981(0983) -9-aligning and orienting work enclosure hull 13 in the desired position at the central portion of base template 11, alignment means 25 (Figure 5) preferably extends from the periphery D~ work enclosure hull 13. As ~ ed herein, the alignment means 25 ro~p~i~es a pipeline ~oom, within which are disposed one or more pipelines and flow lines Z6 extending through work enclosure hull 13 to its interior (~i~c~ssed in greater detail below). The external dimensions of pipeline boom 25 are selected so as to provide a close fit between the ooom and adjacent vertical legs 21 of the upper guide structure o~ base template 11.
During installation, the crosspi~ces 24 serve as boom blocking meansl precluding the lowering of pipeline boom 25, so that the pipeline boom may only be lowered between the single pai~ of vertical legs 21 having no cross~iRcP 24, thereby ensuring the desired orientation o~ work enclosure hull 13.
As best shown in Figures 1 and 3, base template 11 prefPra~ly further comprises pipeline ~oom alignment bumpers 27 for providing finer alignment of boom 25 between the correct vertical guide mem~ers 19. Pipeline boom 25 pre~erably tapers toward a narrower end portion 25l, and bumpers 27 are spaced along the periphery o~ base template 11 at a distance designed to ensure a close ~it of this nalLu:.er end portion~ As shown, bumpers 27 also pref~rably include downwardly sloping portions adapted to guide en~ portion 25' as it ls lowered during installation on ~ase template 11.
As shown in Figure 5, at least one laterally exten~in~
position~ng stop 29 is preferably secured to the outer perlph~ry of the cylindrical portion of work enclosure hull 13 for con~acting vertical leg 21 of a guide member 19 to b'ock movement of the hull when it is rotated during installation nf the hull on ~ase template 11, thus further facilitating orientation o~ the hull with respect to the template. ~ositioning stops 23 may also se~ve as lifting tabs or gussets for surface handling of work enclosure hull 13.
Utilizing the procedures ~1souss~d above, a work enclosure hull may be installed on a marine floor base template ~ithout the !Ise of gl~id~lines at water depths of 750 meters. Acoustic beacons and 37~81~

F-0981 (0983) -10-snnar re~lectors, as well as remote tel~vision cameras m~y be used to monitor the position and orientatlon of the ~ork enclosure hull relatlve to the base template during in5tallation.
Re~err~ng now to F~gures 5 7, the work e~rlos~re hull 13 prel~erably comprises a v~rtically orlented, stspped cylinder, The upper, s~aller cylindrical section 30, together with a c-.n, ~ E ~tary hemispherical end section 31 house a control section 32. The lower, larger cylindrical section 33 is topped by a c~,le ~tary hemispherical section 3~, ~hi~h joins the lower ~nd of the smaller cylindr$cal section 30. A ~urther hemispherlcal section 35 extends ~rom the bo~tom o~ cylindrical sectlon 33 and completes the enclosure ~or a servlce section 36, ~hiCh is su~ported by skirt mem~er 37 having the ~low llne boom 25 extendin~ there~ron.
Spaced about the periphery o~ cylindrical section 33, and extending generally horizontally there~rom9 are lateral penetration means 3~, for establishlng.well n u~d communication throu~h work enclosure hull 1~. Hbrizontal alignment o~ lateral p@netration means ~8 through hull 13 provldes signi~icantly improved hull stress ~el~e~
when comp~red ~ith vertical slignment throu~h upper hemispherlcal sectiQn ~1. ~
Service section 36 (Figure 7) hous~s production manifbld 39 whidh is operatively connected to sne or more pipelines ~6 ~xtending through ~ork enclosure hull 13, as shown in Figure ~.
A portion o~ the internal Pluid hand1ing system o~ a typlcal service section 3~, as shown in Figures 7 and 8, operatlvely connects the man~old 39 to the lntgrnal terminations 40 o~ the integrally welded penetration means 38~ Various produced petroleum streams, gas^
streams7 water streams, ~h-TI;C~1 injection streams, test streams and hydraulic lin~s can b~ mani~olded through their resp~rtive lines and valves individually according to the desir~d production schedules~ The mani~olding and valving are pre~erably de-~igned ~o permit the passage o~ pump-down tools (PDT) ~rom the subsea work enclosure out to and down the invidual ~ells. In such a case, a lubricator, to permit loa~ing the pump-down tools into the system piping, must b~ connected to a ~ L9~7~8~

F-0981 ( 0983) power fluid cupply line from a surface facility to satisfy the requlrement for large pumping C~p~hi 1 ;ty, metering, fluid treating and storage. C~hility is preferably provided to allnw switching between the individual well ~unctions (from production to test to service) during the operating life of tne well. Internal valve means permit sequencing or combining fluids according to the desired production schedules. Remotely-actuated and/or manual valve operatlons are employed, as desired.
Figures 7 and 8 illustrate relevant portions o~ a typical syst~m of internal piping and valving~ including PDT c~p~hil~ty~ for establishing fluid ~low between a single penetration means 38 and manifold means ~9. Substantially i~entical systems are provided for connecting each of the individual penetration means 38 spac~d a~out work enclosure hull 13 to mani~ol~ means 39. The complete details o~
such other systems have been omitted ~rom Figures 7 and 8 for clarity.
PDT servicing requires that at least a 1.52 meter bending radius be maintained on all piping bends through which pump-down tools will pass.
Service section 36 is provided with an PYp~os~on~inhibiting inert atmosphere, such as nitrogen. Q structural bulkh~ad and purgable compartment 42 are provided for trans~erring personnel between service sectlon ~6 and control section 32, while keeping the two atmospheres in the respective sections separated and ~ree from mixing through the use o~ conventional air lock transfer techniques. Plug-in type breathing eqll~pr~ ~t is utilized by personnel in service section 36.
Control section 32 (Figuxe 6) is provided with a breathahle atmosphere~ rendering the control section habitable~ The life support systems for habitable control section 32, as well as the re~uired remote controls and the like, may be connected to a remote surface facility by one or more conduits for providing air, exhaust, communications, power, and the like. These conduits may piggyback with or be within pipeline 26.
Control section 32 ~Figure 6) is provided with a personnel transfer bell, or "teacup"~ 41 ~or transferring operating and maintenance personnel ~rom a conventional s~ -rine vessel (not shown) using atmospheric pressure trans~er techniques.

F-0981(0983) -12-Work enclosure hull 13 must ~e of sufficient strength to withstand the extremely high pressure at water depths up to 750 meters. It has been found that work enclosure hull 13 may be constructed so as to possess negative buoyancy, through pxoper ~eighting and ballasting. Such a construction avoids the necessity ~or any latching e~ir~nt to hold down the hull once it is installed on the marine floor base templateO Preferably, work enclosure hull 13 includes slips (not shown~, which may be of conventional construction, and the base template 11 includes a centrally located manarel 9 (see Figures 3 and 4) extending substantially vertically upward~ In this -nt, work enclosure hull 13 is retained on base template 11 by the force of gravity and by the slips attaching to mandrel 9.
Referring to Figures 1 and 9, the well completion system of the present invention further comprises wellhead connertor means 15 for connecting a wellhead 14 to a work enclosure hull penetration means 38 to establish fluld communication therebetween. As -~iP~ herein, ~ellhead connector means 15 c:n, ises a fluid connection assembly 49, and a conventional hydraulic conr,ector (not shown), extending substantially vertically ~rom the lower enr~ of the assem~ly for operatively connecting it to wellhead 14. In a preferred ~ - ~ent~
the hydraulic connector does not attach directly to wellhead 14, but is connected to a master valve assembly 50, secured to wellhead 14 ~or providing well shut-in c~rahility an~ protection before the well is connect~d to work enclosure manifold 39. Master valve assembly 50, which may be of conventional construction~ is installer~ on base template 11 before work enclosure hull 13 is installed. Master valve assembly 50 will be ~lscus~e~ in grrater detail below.
Fluid connection assembly 49 also preferably includes a wye spool 51 extending from a diverter 52, which provides fluid communication between conventional swa~ valves 53 and the hydraulic connector. Swab valves 53 are pre~erably included for maintenance pllrposes, commonly referred to as "workover". In the preferred er ~rir-~t shown in Figure 9, swab valves 53, as well as the down hole production and service bores, may be vertically ~r~cPssed from the o F-0981(0983) -13-surface or a submersible work vehicle via conventional connector mandrel 54 and piping 55. In order to provide ~or pump~down tool ca~hility, wye spool 51 must be curved on a radius of at least 5 ~eet. Wye spool 51 is connected to th~ associated lateral penetration means ~8 through the use o~ a suitable penetrator connector 56, with a mechanical linkage 57 being provided for movement o~ penetrator connector 56 onto operative connection with the penetration meansO For a more complete description of the construction and operation o~
penetrator connector 56 and lateral penetration means 38, attention is invited to U.S. Patent No. 4,191,256.
Upon coupling the hydraulic connector of the wellhead connector means 15 to wellhead 14, or master valve assembly 50, and coupling o~ penetrator connector 56 to lateral penetration means 38, well fluids exiting wellhead 14 may be communicated through work enclosure hull 13 and into mani~old means 39J thus establishlng production c~pahility. The wellhead connector means 15 shown in Figure 9, in combination with horizontal penetration means 38, permit signi~icant reduction in the si~e of the wellhesd connector means, wh~n c~m, ed with prior structures, while still providing external production piping which is re~ovable for maintenance.
~ ellhead connector means 15 preferably ~urther comprises a guide ~rame 60 for support and protection o~ the fluid communication assembly 49, which is rigidly secur~d thereto. As shown in Figure 2 wellhead connector means 15 may be installed on base template 11 by lowering it on a riser 61, connected to upper mandrel 54 by conventional running tool connectors. In water depths o~ 750 meters, conventional gu~dPline installation may9 however3 not ~e possihle.
Consequently, in one pre~erred ~ ir lt of the invention! a ~pecially-designed guide frame 60 serves not only as a protective cage ~or the connector means 15, but also ~acilitates installation o~
connector means 15 on base template llo Speci~ically, in the ~ - r- ~t shown in Figures 2 and 9, guide frame 60 is constructed as an open, wedge-shaped bumper structure designed to mate with a well bay ~efine~ by adjacent vertical guides 19 ~7~8~

F-0981 ( 0983) -14-of base template 11 for ~acilitating approximate alignment and orientation of wellhead connector means 15 on the template. This bumper structure preferably extends the full height of fluid connection assembly 49, and is preferably comprised o~ heavy structural piping.
In the preferred i bc' r~nt shown in Figure 9, guide ~rame 60 comprises substantially symmetrical top and bottom support mem~ers 65, 66, with ~luid connection assem~ly 49 aligned for inward, substantially horizontal connection to a mating lateral penetration means on work enclosure hull 13, an~ for downward, substantially vertical connectîon to a mating wellhead 14, either directly or via a master valve assembly 50. Top and bottom support members 65, 66 are vertically connected by substantially vertical structural members 67, 68, 69, 709 71, 72, 739 74, and have an inwardly-tapering outer dimension to faoilitate alignment of guide frame 60 within a col-lespondingly tapered well ~ay section. AlthouQh the tr~re70id~1 shape o~ top and bottom support members 65, 66, shown in Figure 9 is well-suited to provide the desired inwardly-tapering outer dimension o~ guide frame 60, it is by no means the only suitable shape. The important factor is that guide frame 60 has opposing side portions which are tapered similarly to the tapered sides o~ the well bay in which wellhead connector means 15 is to be mounted (as de~ined by adjac0nt vertical guide members 1~), and which are suf~iciently spaced apart and extend for a su~ficient length and height to provide alignment o~ gul~e ~ramP 60 in the well bay as it is moved laterally inwardly during installation on ~ase template 11. In addition9 the tapered side portions o~ guide frame 60 must taper to a narrow end width which is su~iciently narrow to permit the guide frame to fully enter the well bay? and thus position wellhead connector means 15, and particularly penetrator connector 56, sufficiently close to work enclosure hull 13, ana particularly to penetration means 383 to permlt their operative connection. Thus, the narrow end width defined by bumper members 75, 763 77 must ~e small enough to be received adjacent to the work enclosure hull 13, as guide frame 60 is moved toward the center of base template 11 during installation.

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F-0981(0983) -15-In general, the desired orientation of well connector means 15 in the well bay may be achieved by ma~ing the width dimension of the radially outermost portion o~ guide frame 60, with respect to the center o~ base template 11, su~iciently large to prevent misorientation of guide frame 60. In the c -1im~nt shown in Figure 9, this width dimension is defined by bumper members 78, 79. In such an alternative construction, radial positioning of wellhead connector means 15 is preferably asslsted by ma~ing the width dimension o~ the radially innermost portion of guide frame 60 (de~ined ~y bumper members 759 76, 77 in Figure 9~ suf~iciently small to ~e unobstructed ~y vertical guides 19~ so as to be receive~ adjacent work enclosure hull 13, and ~y proper radial positioning of fluid connection assembly 50 on guide ~rame 60, with respect to end bu~per mem~ers 75, 76, 77.
~ neless installation of wellhead connector ~eans 15 is achieved by first lowering the connector to a depth which permits contact between guide ~rame 60 and the upper guidance structure of ~ase template 11. For safety reasons, wellhead connector means 15 is preferably not lowered direotly over the template. This reduces the risk9 should the lowering riser ~ail or a mishap oocur, resulting in the e~ui~ ~t being dropped. Having reache~ the proper depth in the general vicinity of ~ase template 11, wellhead connector means 15 is moved laterally in the general direction o~ the cer,ter o~ base template 11. Monitoring of its movement may be by remote television cameras, sona~, submarihes, etc. Euide frame 60 will contact one or more vertical guide members 19 o~ base template 11, and will b~ guided into the well bay between ad~acent vertical guide members 19, thus insuring proper orientation o~ wellhead connector means 15~
Referring again to Figure 1, in the pre~erred ~ t shown, the vertical guide members 19 of the base template 11 are space~
equidistantly around the template so as to divide it into equally-slzed, inwardly tapered well bays9 all but one of which arP
adapted to receive corle~polldlngly tapered wellhead connector means 15. Each o~ the lateral penetration means 38 are situate~ on work enclosure hull 13 so as to be aligned with a wellhead connector means 8~

F-0981(0983) -16-15, with the horizontal spacing between all but two of the lateral penetration means being equal. Such an arrangement, together with the arrangement of wellheads 14 at a common radial distance, permits the use of equally sized and shaped well connector means 15 and provides for improved utilization of space withln service section 36 of work enclosure hull 13, in terms of the arrangement o~ the nPress~ry production, testing and service intervals.
Referring now to Figures 2, 9 and 10, final alignment and operative connection of wellhead connector means 15 with wellhead 14, or preferably with master valve assem~ly 50 which is coupled to wellhead 14, is preferably achieved using conventional funneling alignment techniques. One such technique employs a large diameter, downwardly directed funnel 8û (Figure 9) connected to the bottom of fluid connection asse~bly 49 and/or guide frame 60. As wellhead connector means 15 is lowered, funnel 80 is guideo over a mating alignment structure, e.g. ring 81 (Figure 2), and the wellhea~
connector means is rotated into the final, aligned position. Funnel 80 is then retracted upward, allowing well connector means 15 to operatively engage the mandrel of wellhead 14 (or master valve assembly 50~ thereby establishing fluid communication.
Such a guide funnel technique may also be used to connect wellhead conneotor means 15 to drilling riser 61, with funnel 62 (Figure 2) being secured to the riser, or a running tool, and guided over lan~ing ring 62 on the wellhead cnnnector means.
Master valve assembly 50, as shown in Figures 1, 2, 10 and 11, is generally of convsntional construction to provide well shut-in ra~h~lity after drilling is completed and protection before the well is connected to work enclosure manifold 39. It is installed after drilling and completing the well, but before work enclosure hull 13 is installed on base template 11. Master valve assem~ly 50 typically comprises a lower connector 82 to be attached to the wellhsad, a master valve 83 in each string, and a top mandrel 84. A guide funnel technique, as descri~ed a~ove in connection with wellhead connector means 15, is pre~erably utilized to guide master valve assembly 50 onto ~97~8~

F-0981(098~) -17-wellhead 14, if ~ dPlineless installation is employed. Furthermore, guidelineless installation o~ master valve assembly 5û on base template 11 is preferably facilitated by incorporating a wedge-shaped, protective ~umper structure, or guide frame, 9û into the master val~e assembly. Except for obvious changes resulting from differences in size, the structure and functioning of guide frame 90 are substantially identical to guide ~rame 60, ~escribed above in connection with the installation of wellhead connector means 15, with the vertical guides 19 serving to direct guide frame 90 into position as it ~s moved laterally during its installation on base template 11.
As shown in Figure l? to assist in g~ plineless installation o~ master valve assembly 5û, and to provide increased structural ~rotection, base template 11 preferably ~urther comprises bumpers 95 extending along the outer periphery of the template. The vertical height of bumpers 95 should approximate the height of master valve assembly 50. Installation of master valve assembly 50 requires that the assembly ~irst ~e lowered to a ~epth no greater than the top of bumpers 19, then laterally moved into position over wellhead 14, and finally lowered the remaining ~istance to esta~lish contact with wellhead 14. Master valve assembly 50 is then operatively connected to wellhead 14 via its lower connector 82.
Figure 12 illustrates an ~ t o~ the invention in whlch a conventional gui~Pline technique is used for installing wellhead connector means 15. In this technique, gl~idelines 100 are affixed to a gu~de frame 101 secured in a well bay on base template 11, strung through vertical piping which forms the corner posts of the ~ellhead connector frame 60, and then placed under high tension Wellhead connector means 15 is then lowered along ~ delines 100 Dy riser 61.
Xn such a system, the structure of base template 11 is essentially as described aoove ~or gll~del~neless installation (except ~or the presence of guide frame 101), and the procedure for installing subsea work enclosure 13 on the template is substantially unchanged ~rom that already described.

~ ~.97~

F-0981(0983) -18-Illustrative ex Fl~rY parameters for various system 5~ e"~s of the present invention are ~iscussed below.
The upper guidance structure of ~ase template 11 is prefera~ly sized and constructed such that, upon lowering, work enclosure hull 11 can be 1.8 meters off center in any lateral direction and will still be directed on target by the upper guidance structure, or up to 15 o~f in -rotational orientation and will still be properly oriented ~y the upper guidance structure. Of course, the more offset hori~ontally the work enclosure hull 13 is, the smaller the orientation ~ nment that can be tolerated. Once the work enclosure hull 13 is within the portion of base template 11 ~ormed by vertical legs 21, additional flanges or gussets 22 pre~erably align the hull within 7.6 cm o~ the desired alignment. When work enclosure ~ull 13 is ~ully lowered o~ base template 11, preferably only a 15~2 cm clearance will exist between pipeline ~oom 25 and alignment bum~ers 27 at the ~ree end o~ the boom.
This is su~ficient to orient work enclos~re hull 13 to within plus or minus one-half degree in rotation.
The lower support system of ~ase template 11 is pre~era~ly leveled to within plus or minus one-half degree of horizontal.
With a 22~ angular spacing of blow out preventer t~OP) envelopes around a circular base template 11 ~uring drilling of the wells, and assuming the envelopes to be 3.7m X 4.6m9 the envelopes need not overlap each other~ which is pre~erable. With such a 80P envelope spacing, a base template diameter o~ 18 meters is prefera~ly the minimum diameter for the template.
In the present invention, for water ~epths in ~xcess o~ 300 meters, the ~ells are spaced about base template 11 at a co~mon radius ~rom the center of the template.
In one practical ~ ~ ~ o~ a well completion system designed for operatlon at water depths of 750 meters, base template 11 is circular in shape and has a diameter of 19.5 meters and an overall height (bottom of lowPr support structure to top o~ upper guidance structure) of 13.7 meters. Such a template, designed for up to 8 wells, has a weight o~ about 2 X 105 Kg an~ a well spacing of 6.7 '7~

F-0981(0983) -19-meters radially. The well to well spacing is 4.6 meters. The upper guidance structure is 9.8 meters in height9 while the lower support structure has a height of 3.96 metersO The structural members ~orming the uPper guidance structure of the base template 11 comprise 50.8 cm outer diameter by 0.750 cm Wall structural tubing while those forming the template lower support structure are 76.2 c~ outer diameter by 0.500 cm Wall structural tubing. Typically the wellhea~s o~ such a system are 42.5 cm and the leveling pile guides utilize three 106.7 om outer diameter piles. The su~sea work enclosure hull 13 has an overall height of 17045 meters and an overall outer diameter o~ 7.4 meters, with the outer diameter o~ the cylindrical section 30 of control section 32 being 3.7 meters~ The outside radius of h~mispherical sectiDn 31 is 182 cm and the outside radius of hemispherical sectinns 34, 35 is 370 cm. The weight of work enclosure hull 13 is 2û3,000 Kg (less the weight of skirt 37) boom 25 ana the internal piplng and e~l~1r~~nt)~ and the total outfitted weight is 457,000 Kg. Sufficient ballast is added within cham~ers (not shown) in skirt 37 to make the su' -. ged hull (ov,erall) about 45,000 Kg heavy~

Claims (15)

CLAIMS:

1. A subsea well completion system for multiple subsea wells, comprising:
a fluid-tight work enclosure hull having a plurality of radially-disposed lateral penetration means for establishing releasable fluid connection through the hull, and a base template having a lower support structure for supporting the work enclosure hull and means for securing the template to a marine floor so that the lower support structure extends substantially horizontally, the template further having an upper guidance structure comprising a plurality of guide members extending substantially perpendicular to the lower support structure and mounted in spaced radial array, the guide members extending inwardly toward the center of the template and forming an opening at the central portion of the template for receiving the work enclosure hull, a portion of the upper peripheral surface of each guide member sloping downwardly toward the opening for guiding the hull into the opening during installation of the hull by lowering the hull onto the template.

2. A subsea well completion system as claimed in claim 1, wherein the work enclosure hull includes alignment means extending laterally from the periphery of the work enclosure hull and the upper template guidance structure further comprises blocking means rigidly mounted between each, but one, pair of adjacent guide members, whereby said blocking means can only be received between said one pair of adjacent guide members as the hull is lowered during installation of the hull onto the template, thereby orienting the hull.

3. A subsea well completion system as claimed in claim 2, wherein the free end of the hull alignment means is smaller than the opposite end thereof, and the base template further comprises a pair of substantially vertically extending bumpers spaced along the periphery of the template at a distance permitting close fitting of said free end therebetween, the vertically extending bumpers having facing portions sloping downwardly for guiding the alignment means as the work enclosure hull is lowered during installation onto the template.

4. A subsea well completion system as claimed in claim 1 wherein the lower support structure of the template includes a plurality of well conductor pipes which extend substantially vertically in use and which are spaced around the template at a common radial distance from the center of the template for aligning the individual wells during drilling, the upper section of each conductor pipe terminating in a wellhead.

5. A subsea well completion system as claimed in claim 4, further comprising wellhead connector means for releasably connecting a wellhead to one of the lateral penetration means to establish fluid communication therebetween, and wherein the vertical guide members are situated such that adjacent members define a radially inwardly tapered well bay for each wellhead.

6. A subsea well completion system as claimed in claim 5, wherein the wellhead connector means comprises a fluid connection assembly adapted for mounting in a well bay and a rigid, open guide frame surrounding and rigidly secured to the fluid connection assembly, the frame having opposing side portions which are tapered similarly to the radially aligned sides of the well bay in which the wellhead connector means is to be mounted, the tapered side portions being sufficiently spaced apart and extending for a sufficient length and height to provide alignment of the frame in the well bay as it is moved laterally during installation of the wellhead connector means onto the template, whereby a desired orientation of the fluid connection assembly can be achieved.

7. A subsea well completion system as claimed in claim 6, wherein the guide frame comprises substantially symmetrical upper and lower support members and open, vertical structural members connected between the upper and lower support members, the fluid connection assembly being aligned for inward horizontal connection to a mating lateral penetration means and downward vertical connection to a mating wellhead.

8. A subsea well completion system as claimed in claim 5, further comprising at least one master valve assembly for providing fluid communication between a wellhead and the associated wellhead connector means, the master valve assembly including a rigid guide frame having opposing side portions which are tapered similarly to the radially aligned sides of the well bay into which the assembly is to be mounted, the tapered side portions being sufficiently spaced apart and extending for a sufficient length and height to provide alignment of the guide frame in the well bay as it is moved laterally during installation onto the template, whereby a desired orientation of the assembly can be achieved.

9. A subsea well completion system as claimed in claim 8, wherein the upper structure of the template further comprises substantially vertical bumpers extending along the outer periphery of the template for radially guiding and positioning the master valve assembly as it is lowered during installation onto the template, the vertical bumpers providing structural protection and alignment of the assembly.

10. A subsea well completion system as claimed in claim 1, 2 or 3, wherein the work enclosure hull is divided into an upper control section having a breathable atmosphere and a lower service section having an inert, non-combustible, and substantially dry atmosphere, the service section having a substantially cylindrical portion and the penetration means extending laterally through the wall of said cylindrical portion, and the guide members forming a substantially cylindrical opening at the central portion of the template.

11. A subsea base template for guiding marine floor well drilling equipment at multiple wells and supporting a subsea work enclosure hull and wellheads, comprising:
a lower support structure comprising a substantially horizontally aligned, open tubular framework and a plurality of substantially vertical well conductor pipes spaced around the peripheral portion of the framework and integral therewith, for aligning well drilling equipment, the upper section of each well conductor pipe terminating in a wellhead, the central portion of the framework being adapted to support the subsea work enclosure hull and the peripheral portion being adapted to support the wellheads; and an upper guidance structure comprising a plurality of guide members rigidly mounted on, and extending vertically from, the lower support structure in spaced radial array, each guide member extending inwardly toward the center of the template, forming a substantially cylindrical opening at the central portion of the framework for receiving the work enclosure hull, a portion of the upper surface of each guide member sloping downwardly toward the cylindrical opening for guiding the work enclosure hull as it is lowered during installation thereof onto the template, the guide members further providing structural protection for the work enclosure hull and the wellheads.

12. A subsea base template as claimed in claim 11, further comprising means for securing the template to the marine floor in a substantially horizontal position.

13. A method of establishing production capability from multiple subsea wellheads on a base template secured to the marine floor, comprising:
providing a work enclosure hull containing a manifold, the hull having a substantially cylindrical portion with a plurality of radially-disposed lateral hull penetrators extending therethrough and operatively connected to the manifold;
providing an upper guidance structure on the template comprising a plurality of substantially vertical guide members mounted in spaced radial array, each guide member extending inwardly from the outer periphery of the template, thereby providing a substantially cylindrical opening at the central portion of the template for receiving the work enclosure hull, a portion of the upper peripheral surface of each guide member sloping downwardly toward the cylindrical opening;
lowering the work enclosure hull from a position directly above the template and directing the hull through the upper guidance structure into the cylindrical opening at the central portion of the template, the work enclosure hull being guided into its resting position on the template by the guide members; and establishing subsea fluid communication between the subsea wellheads and the work enclosure hull.

14. A method as claimed in claim 13, wherein the fluid communication between the work enclosure hull and the wellheads is established by operatively connecting a wellhead connector therebetween within a well bay defined by adjacent vertical guide members.

15. A method as claimed in claim 14, including the step of lowering the wellhead connector in the vicinity of the template and laterally moving the wellhead connector into the well bay, the wellhead connector being guided into its resting position on the template by the adjacent vertical guide members defining the well bay.