OTC 5402

Gullfaks A Subsea Wells SystemProduction Startup

by O. Inderberg and T.W. Knudsen, Statoil

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Development, Completion, and

Copyright 1987 Offshore Technology Conference

This paper was presented at the 19th Annual OTC in Houston,Texas, April27-30, 1987. The material iSsubjectto correctionby the author.permissionto COPY is restricted to an abstract of not more than 300 words.

ABSTRACT

This paper deals with the Gullfaks A Subsea

Production Systems: Philosophy, development

plan, technical and functional descriptions

and Statoil’s experience to date in the

various phases, including start up. The

wells are connected to the Gullfaks A plat-

form, which is a PDQ (processing, Dri~lin9

and Living Quarters) Platform. Subsea

operation were accomplished.

THE GULLFAKS FIELD

The

the

The

Gullfaks field is situated 140 km from

Norwegian mainland (Figure No. 1) .

field appraisal drilling showed that the

reservoirs are heavily faulted with a main

north-south fault through the whole field.

Recoverable reserves of the Gullfaks field

are assumed to be 210xI06 Sm3 (1,320x106

Bbls) of oil and 23X109 Sm3 (812x109 SCF) o~

gas.

The water depth at the field varies from 13(

to 220 meters.

GULLFAKS A SUBSEA DEVELOPMENT PLAN

Illustrations at end of paper

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,a~n objectives for incorporating subsea

‘ells as part of the field development are:

Develop reservoirs

cient reach of the

Figure No. 2.

outside the effi-

platform wells.

Accelerate production and improve

economic returns.

Gain information and experience for

future field developments.

I’hescope of the subsea part of the GullfakS

A Project has changed from:

STATUS AT FEBRUARY 1984 : 5

-V~- APRIL 1985 : 3

1

-tl- _*r_ 1986 : 4.1

PRODUCERS

PRODUCERS &

WATER INJECTOR

PRODUCERS &

WATER INJECTOR

These changes are due to increased knowledg

from the drilling of the subsea wells and

new reservoir simulations.

The subsea wells are of a wet satellite typ

non-TFL (non-thru-flowline) ; However~

wireline serviceable.

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I‘he same Christmas tree is used both for I Wellhead & Tubing Hanger

production and water injection. Each well

.s connected to the platform with a separate

Flexible flowline, a hydraulic umbilical and

m electrical umbilical.

!he system is designed to be diverless, i.e.

Prior to start of drilling operations, the

protective roof is removed by a guideline

establishment tool. In a single run, the

tool establishes guidelines to the four main

guideposts and retrieves the protective

111 tools required for installation and I roof.

vorkover are non-diver assisted. I An 18 3/4”, 10,000 psi CAMERON WS-11 weight

?he design life of the subsea production

;Ystem is 10 years.

set wellhead system is used in the subsea

wells. A 5-string casing programme is used,

comprising 30”, 20”, 16”, 13 3/8” and 10

?he plan for the development, installation I 3/4” casing strings.

md start-up of the Gullfaks A subsea

;ystems are shown in Figure No. 3.

;ATELLITE SYSTEM

The tubing hanger system allows the tubing

hanger to be run, orientated, tested and

locked in one trip.

?he main components of the satellite system I Christmas Tree System

me shown in Figure No. 4. They consist of:

protective structure

Christmas tree System

satellite control module

workover system

tools allowing for diverless

installation and workover.

The Christmas tree System (Figure No. 4)

contains the following:

Christmas tree

Christmas tree cap

Christmas tree and tree cap running

tool .

I The Christmas tree valve block is forged as

The Gullfaks A satellite system is a new Ia single block.

development

Protective Structure

The guide frame provides protection for the

valve operators. The valves are fitted for

ROV override through an extension shaft

The protective structure is an open framesupported by the frame work.

type structure allowing ROV access. It has

been designed to deflect fishing gear, with

a high probability, and is piled to absorb

100 tons anchor dragging loads. A removable

roof is fitted to the structure to provide

overhead protection.

The structure is shown in Figure No. 5.

Additional protection is installed in the

pull in areas after pull in and connection.

The Christmas tree running tool is used to

run or retrieve either the Christmas tree a

the Christmas tree cap.

Satellite Control Module

This unit (Figure No. 4) contains all activ

components of the control system installed

subsea. All hydraulic connections are via

the bottom of the satellite control module

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SCM) . The electrical connectors are via

,nductive couplers on the outboard side of

.he SCM.

Iorkover Control System

This system (Figure No~ 6) ‘s ‘Seal ‘0

:un/rekrieve and operate the following

;omponents:

T?he

Christmas tree and tree cap

Tubing hanger

pull-in and connecting tools

control of Christmas tree valves are

transferred from the Gullfaks A platform to

:he workover rig during workover of the

~ell. This is achieved after removal of thf

Lree cap and rerunning the Christmas tree

cunning tool.

Pull-in and Connection System

Each satellite well has three lines to be

pulled in and connected (Flowline, hydrauli~

umbilical and electrical umbilical).

The pull-in and connection tools are shown

on Figure No. 4. The tools are run on dril

pipe.

SUBSEA CONTROL SYSTEM

The subsea control system (Figure No. 7)

provides pressure, temperature and

hydrocarbon leakage monitoring and control c

the satellite failsafe valves during

start-up, production and shut down

operations.

All computer commands, instructions and

monitoring are performed within the main

control room of the platform from the

dedicated subsea master control station.

Manual operation of the control system is

directed from the well control modules on

the platform deck.

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‘here is a dedicated uninterruptible power

:upply (UPS) incorporated in the system to

insure the capability of a controlled shut

lown sequence in the event of loss of

)rimary platform power.

?he subsea control system is designed to

>perate from either a discrete piloted

,lydraulic signal system or from a

m

s

multiplexed electro/hydraulic control

;ystern.

!he complete subsea control and monitoring

;ystem is contained within the satellite

:ontrol module (SCM) , which is retrievable

Zrom the surface.

Fhe subsea control system utilizes a 10W

?iscosity water-based hydraulic fluid for

~uicker response times over oil-based

fluids.

The fluid in the hydraulic control lines car

be displaced.

FLOWLINES AND UMBILICALS

The reservoir fluid composition and

consolidation of the oil producing sands

justify a single flowline concept. The

flexible flowlines chosen have an ID of 6“

and a pressure rating of 4,000 psi. A

special difficulty has been to provide

relevant inspection/testing possibilities.

Test spools of the flexible pipe have been

installed on the platform above the termina

tion of the J-tubes. The test spools will

be replaced with new ones each time a test

and inspection program is exercised. The

result from the test/ inspection will

determine the length of recertification tin

for the flowline.

The umbilicals are standard flexible

cables/hose bundles.

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igure No. 8 shows how congested the seabed

asily can become with anchors over

“lowlines, etc. The protection of the

!Iowlines and umbilicals is achieved by

.renching or overlay with mattresses.

‘ROJECT EXECUTION

!he overall project execution plan is shown

.n Figure No. 3. The main activities are:

Engineering and fabrication

Integration Testing

Drilling and Completion

Offshore Construction

Phe following factors have

in the project execution.

been highlighted

Prototype development

High complexity of equipment

Uncertainties with respect ko certain

reservoir properties.

Strong requirements on reliability and

safety.

Several simultaneous offshore

operations during installation and

completion.

A thorough debugging/verification of

equipment and offshore procedures

through an extensive Integration Test

(.IT)program.

Important factors to ensure an efficient

project execution are:

Definition of field data

Authorities requirements

Technology status/development

Systems for project control both

in-house and for contractors

Clear contract plan/strategy

Activity plans at required levels

(Note: early planning of offshore work)

Verification of design by analysisand

test

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A prerequisite for the above is a clear

definition of scope and requirements.

Engineering and Fabrication

The subsea production system was added to

the Gullfaks A Project in early 1984. Main

contracts were established in April 1984.

A main contractor was chosen to be

responsible for detail engineering,

fabrication and the first phase of the

integration testing. The total platform

based control system and the first set of

subsea equipment were assembled early June

1985, and integration testing started.

Integration Testinq

The purpose of integration testing is to

prepare equipment, procedures and personnel

for efficient and safe offshore operations.

This is achieved by:

The

Make adjustments proven necessary or

highly desirable while the equipment i~

easily accessible.

Gain experience in running tools for

diverless operation on TV control.

Test the installation and operating

procedures.

Added safety in a debugged and verifiec

system prior to going offshore.

Train personnel

integration testing was divided into

four phases lasting over a year. The

original plan was for one year duration.

This was extended due to late delivery of

the last Christmas tree and the extent of

debugging found necessary. The integration

testing phases were:

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The

system integration test of the control

system and first set of subsea

equipment.

Deep water test. Main components

tested in this phase were tubing

hanger, the integral workover riser and

the workover control system.

Shallow water test of Christmas tree

and running tools together with pull-in

and connection tools.

Land integration test of all subsea

equipment, excluding the platform

control system equipment.

last three integration test phases were

<

performed by Statoil.

[sin experiences gained in the test phases

rere:

Lack of verification in the engineering<

phase caused a higher amount of

debugging than anticipated.

Lack of proper configuration control

both with respect to hardware and

documentation caused extra work.

The testing was necessary in order to

place TV cameras properly on diverless

tools and develop proper marking.

Testing proved necessary in order to

develop all operational requirements.

The extension of the integration test did

not cause any delay on the offshore

completion program. This is due to the

fact, that a decoupling of these activities

was achieved.

rilling, Completion and Commissioning

Irilling and completion was performed

‘ithout interfering with the Gullfaks A

}latform tow-out installation in 1986.

:ompletion comprises of the following

Activities:

Well completion

Pull-in and connection of flowline and

umbilicals

rhis work was performed without the use of

livers. It clearly supported the necessity

>f an integration test in order to achieve a

iiverless performance offshore. The

~iverless operations proved to be very

efficient.

Commissioning of the wells was done as part

of a verification of the connection

operations. A close communication between

the rig over the well and the platform is

necessary in this phase. A clear definition

of organizational interfaces is essential to

have cleared before starting such

operations.

Offshore Construction

In addition to the completion program,

offshore installation of subsea equipment

was organized in two contracts:

Installation of Protective Structures

Fabrication of Flowlines, and

Installation and Protection of

Flowlines and Umbilicals.

Installation of Protective Structures was

done in JulylAugust 1985. This installation

was diver assisted, but could easily have

been a diverless operation.

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Phe laying and trenching of flowline and These problems were solved after the first

.unbilicals was done simultaneously by the day, and were due to restricted gas flow in

lse of a combined laying and mechanical the l’st stage separator. All wells were

trenching machine. It is important to be brought on production in the multiplex

ible to plan these and other offshoxe secondary control mode.

~perations so as to have flexibility if

unforeseen incidents occur. The capability The hydraulic temperature sensor located at

of handling simultaneous operations is the subsea Christmas tree has not performed

required. satisfactorily. During normal flowing

conditions (12,000 BPD) , the subsea wellhead

Production Start-Up temperature indicated a temperature far

below that read at the platform choke. The

First oil was produced December 22, 1986, measured temperature profiles have matched

approximately 7 months before scheduled. very well with design criteria for the

The extensive testing and offshore training buriedjinsulated flowline.

programs proved to be very valuable, as the

start-up went very smoothly. SUMNARY OF EXPERIENCE

Due to the experience gained, during commis- -Development of a subsea production

sioning with hydrocarbon alarms, swamp gas system, with high requirements for

seepages did not disturb the production verification prior to deployment,start-up or have they been a problem for require good project managementoperations to date. systems.

Each subsea well was brought on production -Configuration control of equipment and

by pressurizing the flowline to open the documentation is a strict requirement

subsea tree valves and to shear a pump-open to ensure that the equipment is

plug in the tubing. This plug was installed installed correctly.

as an extra safety barrier during temporary

abandonment. Integration testing is a usefull and

necessary part of the total project

Production was brought on from each of three execution plan.

subsea wells within 24 hours after each had

been cleaned up to mud burners for removal The drilling plan is based on reservoir

of glycol and diesel in the flcwline and evaluations which changes and improves

tubing, respectively. The wells were flowedas the geologists receive new data.

to the burners for approximately 6 hours, to The subsea concept plans must be

allow them to heat up before they were flexible enough to incorporate this.

turned into the production train.

Subsea offshore work required careful

Some problems during initial start-up were: planning at an early stage to ensure

flexibility. Gullfaks A Project

1) skimming/carry-over in the process started to develop a marine interface

train plan, including all offshore

2) indication of slug flow in the flowlin e activities, in October 1983.

394

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,cKNoWLEDG~NT

!he authors would like to express their

Appreciation to the management of Statoil

md the other partners in the Gullfaks Field

Eor allowing this paper to be presented, so

that others who have an interest in this

subject, maY avoid some of the problems that

have been observed.

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Fig.l—Gullfaksfieldlocation.

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Fig. 6—Workover control system.

Fig, 7—subse* cOntrol system.

Fig, 8- flowllne/anchor pattern.

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