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Transcript of OTC-5402-MS
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
389
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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.
I 391
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
392
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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rEl
<z N’”s .
3 .m——_ .___ _ _
oz
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396
Fig. 6—Workover control system.
Fig, 7—subse* cOntrol system.
Fig, 8- flowllne/anchor pattern.
397
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