nef subsea equipment desription

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OTC 9

Northeast rigg Subsea as Production Systemby laude Duvet lf quitaine Norge

OPYRIGHT 1982 OFFSHOR T HNOLOGY ONF R N

This paper was presented at the 14th Annual OT in Houston, Texas, May 3-6, 1982. The material is subjectto correction by the author. Permission to copy is restricted to an abstract of not more than 300 words.

ABSTRACT

The North E as t F ri gg NEF ga s reservoir i sa smal l s t e l l i t e of th e giant Frigg ga s f i e ld locatedi n th e North Sea i n 100 meters o f w ate r.

NEF ga s reserves are to be developed usinga subsea production system th i s being th e f i r s tmajor u nd er wa te r g as production project ever attemptedin th e North Sea.

The purpose of t h i s paper i s to d es cr ib e t heNEF subsea development concept to e xp la in t he ra t ionafo r i t s se l ec t ion and to mention poss ib le appl icat ions of th i s system in th e development of othermarginal f i e lds .

The NEF subsea production f i l i t i e s comprisesof four major components:

- a s u bs e a t e m pl a te which houses and protectss ix wel ls and a manifold

- a 16 ga s l i ne which l inks th e manifold toth e Frigg Field Treatment platform TCP2

- a Field Control Stat ion FCS whose mainfunction i s to c on tr ol t he subsea equipment

- treatment metering and boosting modulesi n s t a l l ed on th e TCP2 p la tf or m t o processth e 6 mil l ion c ub ic m et er s per day of NEFgas.

Different development schemes were evaluated

during t h e p r el im i n ar y select ion studies :

- conventional fixed s t e e l s t ruc tu re

- subsea wells dr i l l ed and control led froma permanent semisubmersible platform mooredabove th e wel ls

- subsea wells and m a ni f ol d r em o te ly control ledfrom Frigg f i e ld

References and i l l u s t r t i o n s t end o f paper.

- subsea wells remotely control led from anunmanned a r t i cu la t ed column i n s t a l l ed closeto th e w el l c lus t e r

The l s t scheme was se lec ted as being th e bes topt imizat ion in terms of:

- Operational safe ty mainly due t o s ep a ra ti ono f r i t i l functions

- Rel iab i l i t y of ga s production by extensiveus e of conventional and tes ted equipmentalthough assembled in a novel conf igura t ion

- Investment costs

- Poten t i a l adapta t ion o f the concept to fu turedevelopments of marginal f i e lds

To date deta i led engineering of pro jec t components i s completed fabr icat ion and dr i l l ing a rein progress . The production s tar t -up i s scheduledin 1984.

INTRODUCTION

Recent shortages and uncer ta int ies in o i l /gassuppl ies and th e r e l a t ed pr ice increases have t r ansformed some unprof i table marginal and/or d i f f i u l tf i e lds in to commercial ones. In th i s context E lfAquitaine Norge EAN and i t s Par tners i n i t i t e dth e NEF development s tu di es f or producing a s t e l l i t eof the giant Frigg ga s f i e ld . This opportunitycombined with the present necess i ty to develop economically a t t r ac t ive concept fo r p r od u ci ng m a rgi n al

f i e lds a d i f f i u l t environment le d to a n u nc onvent ional approach.

Preliminary s tudies began in 1979 with f ina ldecis ion being made mid 1980. Detailed engineeringdesign o f th e vario us sub-systems i s now completed.Fabr ica t ion of NEF components and the d r i l l i n g o fthe wells a re in progress . Production s t r t upi s expected in 1984.

EAN, as opera tor ha s th e overal l managementr e spons ib i l i t y for project execution ut i l i z ing

233



a combination of expe r t i s e gained from Frigg f i e ldand other subsea developments ca r r i ed out by Socie teNationale E lf A q ui ta in e P r od u ct io n ).

E N pa r tne r s in t h i s p ro je ct a re :

Esso Exploration and ProductionNorway Inc . 40,00 )

Scheme four was s el ec te d f or th e f o ll o wi n g r e a so n s :

1. A permanent support was deemed necessary toobta in a su ff i c i en t l eve l of r e l i a b i l i t y ofproduct ion control , to provide i nh ib i to r ~ n e c -

t ion and a quick means of well control inc ludingwell k i l l i n g . Fo r t h i s reason scheme threewas no t se l ec t ed .

NEF PRODUCTION CONCEPT

The above mentioned pa r tne r s h av e b ee n d i rec t lyinvolved i n pro j ec t management.

The Fr igg f i e ld i s th e l a rges t na tu ra l ga ss t ruc tu re developed in North Sea with proven recovera b le r es er ve s exceeding 200 b i l l i o n cubic meters.

I t dwarfs the NEF f i e ld whose recoverable reservesare approximately 8 b i l l i o n cubic meters, allowing

a da i ly average p ro d uc ti o n o f 6 mi l l i on c u bi c m e te rsover the f iv e year l i f e o f the f i e ld .

The favourable reservoir c on ditio ns o f th eNEF f i e ld and th e p ro xi mi ty o f ava i l ab l e process ing ,boosting and t r anspo r t a t i on f a c i l i t i e s a t th e mainFrigg f i e ld le d E N to invest igate th e f e a s i b i l i t yof th e pro jec t . Furthermore th e f l e x i b i l i t y ofth e sa l e s g as n et wo rk t hr ou gh a banking mechanismbased upon th e Frigg f i e l d s l a rge ga s accumulationto compensate poss ib le NEF product ion shut downs,was an a d d i ti o n a l i n c en t iv e . s a consequence unconvent ional development schemes c ould be consideredas more su i t ab l e to the smal l s ize o f the reservesthan a more c l a s s i c a l concept.

The following d e sc ri be s t he four main componentso f the pro jec t Fig. 1)

- Subsea wells , template and manifold

- Fie ld Control Sta t i on

Scheme four was se lec ted in preference to schemeon e because favourable condi t ions a t NEF made

an i dea l oppor tuni ty to use a subsea productionconcept. Both technical and economical evaluat ionsindica ted th e v i a b i l i t y o f scheme four.

2. A semisubmers ib le permanent ly posi t ioned above

producing wel ls and s ub je ct to a d v er s e w e at h ercondi t ions was not considered as su ff i c i en t lyre l i ab le for a ga s appl ica t ion. The economicalunce r t a in i t i e s at tached to the a d ap ta ti on o fth e v es se l to th e specif ica t ions o f the projectwere also taken in to considera t ion .

Production Phi losophy

The NEF philosophy i s character ized by i t s unmanne

o p e ra ti n g c o n di ti o n and i s based upon th e assumptiont ha t r e l i ab le equipment and exis t ing technologypermi t th e us e o f a quasiautomatic opera t ing systemfo r subsea ga s production. Rel iab i l i t y w i l l beachieved by using simple systems an d f i e ld provenequipment with b u i l t - i n redundancy. F or componentswhich are not f i e ld proven, comprehensive t e s t i ngwi l l be carr ied ou t to compensate fo r th e lack o fexper ience .

3,00 )

19,72 )

12,42 )

Norsk Hydro Produksjon A/S

Tota l M ar in e N or sk A/S

Den Norske Sta t s OljeselskapA/S S t a to i l )

Concept select ion

From many poss ib le solut ions , four bas i c developm en t s ch em es were se lec ted fo r de t a i l ed evaluat ioni n terms of cos t s , s af e c on tr ol of the wel ls andr e l i a b i l i t y of th e production.

1 . A conventional solut ion with th e wel ls d r i l l e dfrom an unmanned fixed s t e e l p la tf orm , t heproduct ion being remotely control led fromth e main Frigg f i e ld . Assistance of a semisubmersible tender v es se l f or d r i l l i n g opera t ionswas assumed.

2. Subsea w el ls w ith a semisubmersible supportvesse l permanently anchored above th e wel l

c lus t e r, p r od u ct i on b e in g control led from th evesse l through f l ex ib l e r i s e r s .

3 . Subsea w el ls w it h no permanent surface support,p r od u ct io n b ei ng r em ot el y control led from Friggthrough a sub-marine e l e ct r o -h y d r au l ic m u l t iplex system.

4. Subsea w el ls w ith an a r t i cu la t ed column as al oca l Field Contro l Sta t i on FCS), product ionbeing control led through f l ex ib l e umbilicalsand monitored from Frigg through a radio l i nk .

- Subsea ga s l i n e , methanol l i ne and e l e c t r i c a lcable

- Treatment an d metering modules

SU SE EQUIPMENT

Subsea production concept

The NEF Field i s developed with s ix product ionwel ls c lus t e r ed in to a template i n s t a l l ed on th ese a bottom. One wel l i s v e r t i c a l and f i ve a re d ir ect i ona l . Each Xmas t r ee i s connected to a manifoldthrough a f lowl ine i n s t a l l ed on th e template andi s control led from th e Field Control Sta t i on through

a control /service umbi l ica l .A ll ~ u b s ecomponents inc luding th e subsea d r i l l i n g

completion and product ion equipment a re designedfo r r e l i a b i l i t y easy o f control an d maintenance.Standard offshore d r i l l i n g and completion techniquesw i l l be used, i n par t i cu la r th e wel ls w i l l be dr i l l edand completed from a conventional semisubmersibled r il li ng r ig us ing f i e ld proven explora tory d r i l l i n gtechniques.

The wel l completion scheme Fig. 2) i s basedon th e experience gained in th e F rig g f i e ld . In

4



In addi t ion , th e sand screen hanger-packer assemblyhas an ex t r a landing nipple /p lug f or i nc re as ed sa fe tyduring th e running of th e production s t r ing . Two

tubing r e t r i evab le safe ty v al ve s a re used i n tandemand i ~ e t l ycontrol led from th e FCS, these beingse lec ted because o f sa fe ty and r e l i a b i l i t y considerat ions although a workover opera t ion w i l l be requi redto replace them i f they f a i l

Due to th e f ac t tha t th e r e se rvo i r cha rac t e r i s

t i c s a re w el l known, t he w el ls wi l l no t be i nd iv idual ly t e s t ed and no control choke w i l l be i n s t a l l ed .

Well heads an d Xmas t r ee s

The wellhead i s a conventional 13 3/8 - 5000p s i working pressure w e ll h ea d h o us i ng with a 9 5/8c as in g h an ge r;

The Xmas t r ee Fig. 4) i s a we t monob1ock uni ti nc lu d in g t he wing valve . I t ha s been designedto meet th e f o ll ow i ng r e qu i re m e nt s :

- Compliance with API l4D spec i f i ca t ions

- 5000 P SI w or ki ng pressure an d 10 000 PS I

t e s t pressure

- Valves a re 4 1/8 and 2 1/16 -5000 PSI gatevalves with hydraul ic , f a i l s af e c lo se ,opera tor and manual overr ide .

- Ver t i ca l access to 4 1 / 8 p r od u c ti o n b o reand 2 1/16 annulus bore fo r wire l i n e operat ions

- Sof t landing jacks and p r ot e ct iv e s h ie ld

The t ree connector i s an hydraul ica l ly actuated13 3/8 - 5000 p si c ol le t connector.

Template

The t em pl at e F ig . 3) accommodates s ix wel lsp lus two spare s l o t s necessary manifold pipingand con t ro l valves . The template measures 17 Mx 30 M x 8 M high and weighs approximately 350 T.I t h as been fixed to the sea bed by four cornerp i l e s

The template system incorpora tes s t ruc tu reand a l l n e c es s a ry s u b- s ys t em s , i n par t i cu la r : al eve l l i ng d ev ic e, w e ll guide funnels , manifold piping,p r o du c ti o n h e a de r, 16 p ipe l ine connector and ananchoring device.

The template i s m ai nl y u se d fo r supportingconductor pipes an d guide bases , protect ing Xmas

t r ee s and manifold, during th e producing l i f e of

th e f i e l d

Manifold

The template manifold incorpora tes p ~ p ~ n gtoc on ne ct e ac h Xmas t r ee to th e 16 p ipe l ine . Eachhor izonta l 4 1/2 flowline i s connected to a Xmas

t r ee by a v e r t i c a l spoolpiece , t h i s arrangementproviding necessary f l e x i b i l i t y to accommodate poss ible expansion or subsea i n s t a l l a t i o n problems. Thes p o ol p i ec e c o nn e ct i on s wi l l be made by divers withconventional f langes .

A 4 1/2 - 5000 p s i remotely control led i so la t ionvalve connects each f lo wl in e t o a 16 header whichi s subsequently connected to th e 16 ga s pipel inev ia a 16 - 5000 p si b al l valve . I f required , apig launcher ca n be i n s t a l l ed on th e opposi te en dof th e header.

FIELD CONTROL ST TION FeS)

FCS Concept

The FCS i s designed to control subsea equipmentduring normal unmanned production opera t ion an dto accommodate personnel in manned s i tua t ions suchas rout ine maintenance, spec i a l opera t ions and t e s t i ngof subsea valves . This concept emphasizes u t i l i z a -t i on o f a u to m a ti c al ly control led , high r e l i a b i l i t yequipment together with redundant c r i t i c a l systemssuch as the power supply and th e i n h ib i to r i n je c t io n .Safety i s maintained by automatic safe ty loops.

FCS g en er al l ay ou t

The FCS F ig . 5) i s an a r t i cu l a t ed column. Aconcrete gravi ty b ase F ig. 6) supports th e universa lj o i n t The concrete base measures 45 m x 42 m x

6, 5 m high. I t ha s a dry weight o f 6800 metrictons and a submerged weight o f 4500 m e tr ic t on s .Due to good s o i l condi t ions , no spec i f i c anchoringor grouting device proved necessary. The base i sprovided with a ba l l a s t ing system and necessarysupports fo r a l l f le x ib le l in e s connected to th eFes.

A universa l j o i n t connects th e base to th e lowerpar t o f the column. I t weighs 150 metric tons andca n b e c on ne ct ed or disconnected from th e base orth e column by a remotely control led hydraul ic lockingsystem. Specia l ant icorros ion and w ear protect ionhave been included in th e design.

8 meter diameter, cy l ind r i ca l , s t e e l columni s th e l a rges t component i n th e FCS. I t ha s a dr yweight of approximately 4500 metric tons and anet buoyancy of about 500 m e tr ic t on s. The columnconta ins heavy b a l l a s t mater ia l a t i t s lower par tand tanks fo r b uo ya nc y a nd s t a b i l i t y a t i t s upperpar t . I ns id e t he column, a u t i l i t y sha f t housesth e water systems and other auxi l iary equipment.The column also supports the r i s e r s for th e u m bi lica l s , a fendering system a t sea l eve l , an d th e FCS

head on the top .

4. - A head Fig. 7) h ou se s a lm os t a l l u t i l i t i e sand control equipment. I t weighs approximately630 metr ic tons . The FCS head cons i s t s mainlyof four decks: a methanol deck with methanolpumps and s to ra g e t an k s, a main deck withm a ch in e ry a nd th e w ell control manifold, al iv ing quar ters deck with control rooms an da hel ideck.

The FCS i s th e cen t r a l contro l un i t fo r th ega s production and a l l FCS subsystems a re designedto ensure a safe and r e l i ab le service . I t s mostimportant syb-systems a re described herea f t e r.

Remote control system

The remote control system i s s p li t in to twosepara te sub-systems: 1) th e hydraul ic system

235



for subsea well control/monitoring and 2 the communi- to correct ive action through a logic network. There

cation system between the main Frigg Field and theFCS.

will be automatic shut down when no correction ispossible for cr it ical systems such as fire detect ion,gas detect ion and low gas pressure detect ion during

The funct ions of the hydraul ic control system unmanned operation.are to open or close the subsea valves, to shutdown all wells in an emergency, to monitor the well Redundancy is also part of the safety philosophy.pressures tubing and annulus and to monitor the Back-up solut ions have been provided to crit icalstatus of the sand probe. This hydraulic control systems, such as methanol inject ion system, powersystem is self operating, but the subsea valve con- supply, telecommunication system, lighting etc...f igurat ion can be changed by direct manual control In addition, emergency safety systems complete thefrom the hydraulic control panels in the column. whole safety concept.

The control/monitoring link between each subsea Preventive maintenance and periodic surveyswell and the hydraulic system on the FCS is an umbili- have been taken into consideration, in part icularcal which includes a bundle of 20 x 1/2” stainless with regard to the structural integrity. All ballastlines placed around a 2“ flexible service line. f loats and tanks can be periodically surveyed.This umbilical will be connected to the Xmas treewith a semiautomatic connector. SEALINES AND CABLES

Functions of the communicat ion system are to The NEF installation is connected to TCP2 plat-transmit to the main FRIGG field all signals from form by a 16” sealine, a 1 1/4” supply line, anFCS sensors and to send commands from Frigg field electrical and a communication cable.to the FCS. Automatic or voluntary shut down ofthe wells can be initiated from Frigg through this ~61, gas l inecommunication system.

This line transports the gas to FRIGG platformInhibitor injection system for treatment. It has the fol lowing characterist ics:

Methanol is stored on TCP2 platform and pumped - Pipe: concrete coated 16” OD, 5/8” w ll

through a 1 1/ 4” line to storage tanks on the FCS, thickness, API 5LX-X60 steelfrom where it is injected into each Xmas tree throughone of the 1/2” line contained in each umbilical - Length: 18 kmto prevent hydrate formation in Xmas trees, manifoldand sea line. - Working pressure: 170 bars

Kill ing and service system - The line will not be trenched

The killing and service system is designed 1 1/4” Inhibitor supply line.to inject special fluids ki ll ing of wells or methano :. massive hydrate destruction into the wells and ~This line supplies the FCS at a daily rate ofto test the subsea safety valves. Injection can 8 m of methanol. It has the following characteris-be made through the 2“ killing and service line tics:which connects the Xmas trees to the FCS auxiliaryproduct ion equipment , mud pump and tank. In addition, - Pipe: 1 1/4” OD, 3/8 wall thickness, APIthis 2“ line can also be used to bleed-off the well. grade B st l

Utilities - Length: 18 km

The FCS is equipped with all necessary titilities - Working pressure: 20 barsfor manned and unmanned working conditions. Powerwill be supplied to the I?CSfrom the FRIGG field - The line will be layed with 16” lineby an electrical subsea cable. Diesel generatorsinstalled column will provide power in case of damage Electrical cableto the electrical cable.

A submarine cable supplies the electr ical powerThe living quarters are designed for 6 persons to the FCS and provides a secondary communicat ion

in manned conditions and could accommodate 12 persons link between the FCS and the FRIGG control room.

in emergency conditions. It e liminates the need for act ive power generationon board the FCS.

The helicopter deck is designed for a SIKORSKYS 61 N. After an evaluation of the FCS motions, TREATMENT AND METERING MODULESwind or fog conditions, it was calculated that heli-copter landings would be restricted from 5 to 15 Process descriptiondays a year.

The gas is processed compression and dehydration~ together with FRIGG gas after passing through a

slug catcher, a scrubber and a gas meter. LiquidSafety and rel iabi li ty of the installa tion effluents from slug catcherlscrubber are separated

are particularly dependent on the correct operation and condensate is pumped into the FRIGG system afterof the FCS systems. The automatic safety systems being metered. The water and methanol mixture isare based upon self-actuated loops linking detection flashed and stored before disposal. ?

9clR



The NEF gas treatment modules are planned tobe located on TCP2 FRIGG Field treatment platf rm.They are designed ijoprocess 6 to 7 millions mg3of gas, 35 to 40 m of condensate and about 18mof water/methanol on a dai ly basi s.

CONCLUSION

As described, this concept is a suitable solution

fo r the present NEF gas fi eld characte rist ics andenvironmental condi tions. However, with l imitedchanges the NEF configura tion could be adapted toother s ituations were marginal reserves requirea safe and economically att ract ive system. In addi-tion, articulated structures can provide suitableand rel iable r iser protect ion, support necessarylocal facilities and are well adapted to deeperwater which fur ther extend the possibili ties ofthis concept.

In 1984, this unique produc tion system shouldbe operational. Although known techno logy was pre-ferred and used where possible, in some cases newsolut ions had to be appl ied. This challenge impliespotential risks, but it will reward all parties

concerned by providing needed experience with advancedtechnological solutions for producing hydrocarbonsfrom marginal offshore f ields in an adver se environ-ment.

ACKNOWLEDGEPDZNT _ . .._

The Author and MN express their appreciationto thei r partners ESSO PRODUCTION NORWAY, NORSKHYDRO, TOTAL, and STATOIL for their cont inued suppor twhich has resulted in the present status of theproject.

We also wish to thank the Norwegian authorities,and participating contractors and consultants, whoseunderstanding and constant effort have contributedgreatly to the quality and progress of the Work.

9Q7



_—— ——-4s3 ? NORTH EAST FRIGG FIELD— —— — — —GENERAL ARRANGEMENT

—

2 FLATFCRM

,.cTRKALABL&k:.\ ”

OL STATI ON

I

Fig.1 — Northeast Frigg — general arrangement



NORTH EAST FRIGG

DRILLING COMPLETION SCHEME

/ TUBI NG HANGER

7UDLI NE

30” COND. PI PE

20”CSG.

d

13 3/ 8” CSG —

\

9 5/ 8” CSG

TOP NEF SAND4

I PPLE I N

c =- OVER

LANDI NG NI PPLE

kANDI NG NI PPLE

SEAL RECEPTACLE

PRODUCTI ON PACKER

N ING NI PPLE

SCREEN HANGER PACKER

mHEAR J OI NTPUMP-OUT FLAPPER PLUG

SAND SCREEN

Fig. 2 — NEF drilling and completion scheme



Fig 3 — NEF template with xmas trees and equipment as instalied



NORTH EAST F RIGG

\

WELLHEAD X-MAS TREEAND

UMBI LI CALCONNECTI ON

Fig. 4 — NEF wellhead and xmas tree with an umbilical connected



NORTH EAST FRI=G FIELD CONTROL STATION

HELl DECK

LI VI NGQUARTERS

MAI NWORK DECK

METHANOLDECK

Fig. 5 — NEF field control station



Fig 6 — FCS ooncrete base with umbilical supports



HEAD

Fig. 7 — FCS head — southeast side

nef subsea equipment desription

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