00013976-Through Bore Subsea XT
00013976-Through Bore Subsea XT
00013976-Through Bore Subsea XT
1.
~~
Ltd~ Ux
INTRODUCTION
The workovers of subsea completed wells are expensive and time consuming
as even the most routine tasks must be carried out by a semi-submersible.
This paper describes the economic, safety and operational advantages which
led to the development
and successful
first installation
of through bore
subsea production trees.
The conventional wet subsea trees have proved to be very reliable over the
past ten years of operation in the Argyll, Duncan and Innes fields, however
the completion
strings require pulling on the average
about once every
three to five years.
The conventional
subsea tree/tubing hanger set up
design requires the tree to be tripped and a rig BOP stack run to pull the
.
n:.
sensitive
and
LSlm Ope?atlcn is time consuming~ very weather
tubing.
leaves the well temporarily without a well control stack on the wellhead.
The 7 1/16 through bore subsea tree was developed
to minimize
the
tubing pulling workover time and several trees have been run successfully
since the latter
part of 1984.
The time saving on a tubing pulling
workover is three days.
In addition, the design considerably
reduces the
hazards and equipment damage risks inherent iii the conventional
design.
Hamilton Brothers and National Supply Company in Aberdeen designed the
equipment which must be considered a new generation of subsea production
trees.
2.
REASON
AND
FREQUENCY
OF WORKOVBRS
Hamilton
Brothers
has
operated
the
Argyll
fields,
a subsea
sy$tem
producing to a floating production facility, for over ten years.
The fields
presently consist of 18 subsea wells including 2 water injectors and 5 gas
form a very high proportion
of the
W=U maintenance
lift WMA.
-. ..-_. _ cost,s
total
field operations
costs~ especially
when comp=ed
to a platform
In
developed
field.
Completions
are designed to last the life of a field.
practice, however, a tubing pulling workover
is required on average
once
per four years per well.
The
reasons
for
workovers
are similar
to a nlatform
or lad
well.
Fourteen tubing pulling workovers have been per~ormed over the past 5
years.
The reasons, in order of frequency, have been:
1.
Repair
problems
2.
Change
3.
Recompletion
4.
Damaged
5.
Seal leaks.
to the DHSV
tubing.
zone.
system.
to include
gas lift
equipment.
SPE13976/2
THROUGH BORE SUBSEA CHRISTMM
TREES
A typical tubing pulling workover requires 12 days and runs out at over a
With such costs at stake, a concerted effort is made to
million dollars.
make the system
as reliable
as possible,
and to ensure that when a
workover is required, a minimum amount of time is spent changing out the
The through bore tree was designed not only to minimize this
system.
time but also to simplify the conventional
design considerably,
and thus
increase the reliability of the system ii&Mkd.
The time saving with the through bore trees is 3 days since the subsea
This is the historical time it has taken
tree does not need to be tripped.
to pull the subsea tree, run the drilling rigs BOP, pull the BOP and re-run
The time can be considerably
longer especially
in marginal
the tree.
weather conditions because of the problems
associated
with handling the
These 3 days of rig time
rigs 300$000 pound BOP stack in rough weather.
The yearly saving would be well over a million
cost about 300,000 USD.
dollars for a subsea field developed
with 15 through bore trees based on
Due to this
the historical
workover
frequency
of once every 4 years.
potential cost saving, a pro~am to develop the idea of through bore trees
was started in the early spring of 1983.
The cost of the two designs of subsea trees is the same.
Although
increasing the valve size from 4 1/16 to 7 1/16 would normally add 152W0
to the cost of a tree, the two trees cost the same because of the
.
--. .:-- simpler =qulp~ a b design.
4.
DESCRIPllON
&
OF SYSTEM
ComwentionalSystem
A schematic
of a single 4 bore, non-orienting,
wet subsea
This conventional
production
tree is included as Figure
2.
tree has not changed significantly
in design over the past 10
years.
The major components are the tree and the tubing hanger.
The
tree
consists
of
a block
section
with
hydraulically
activated
f ail-saf e-dose
production and wing valves, a lower
manual master valve section and a wellhead connector.
The
tubing hanger shown is of the non-orienting
type and has
access
for communication
to the annulus along
with the
facility
for hydraulic
fluid to pass through the hanger
to
function the DHSV.
SPE13976/3
DSHuber,
GFSimmers&CSJ~
b.
BOre System
SPE13976/4
TREES
THROUGH BORE SUBSEA CH RxsTnAAs
The system is flexible to various completion configurations
including
tubing conveyed perforating
guns, hydraulic set packers if the well is
Both the water
completed in 7 casing} or as a gas lift completion.
injection
wells in the Duncan field were completed
with through
bore trees.
5.
The two major advantages of the design have been mentioned previously.
Firstly,
the time/cost
saving is estimated
at 3 days of rig time and
300,000 USD per
workover. .
Secondly,
the equipment
is considerably
simpler by design and with fewer critical pieces of equipment to fail snd
The other advantages
as such the system is judged to be more reliable.
are as follows:
Well Control
&
?2.
P.+-ti.l
- .-
f=
-
f-
Danqe
Handling
the tree can result in damage
especially
in the
moonpool area while pulling the tree through the splash zone.
W-cc
z subsez tree is landed, the safest condition fQr the
tree is to stay latched onto the wellhead.
c.
If the ring
This is the most critical area on the wellhead.
gasket groove on the wellhead
is damaged such that a seal
cannot be maintained, the cost to repair is such that the well
would most likely be abandoned.
kmalusmowilrea
d8
---..1.
- on W=L-. bl.
-.. -k
lsfi.a
~~ee
ne Criticai FLOW area to the ixnnuxb
L&wu5AS
UUA =
This is
about four times the area for a conventional tree.
is
important
for
gas
lift
considerations
to
decrease
the
possibility of hydrate formation and erosion.
1
e.
Presaue
-
Testing
The pressure
testing
procedures
for
the system
sre
not
However a major advantage
of the
addressed in this paper.
through bore system is that all the critical seals are installed
on the tubing hanger.
These are tested as soon as the tubing
is landed and repairs can be made if required by pulling out
On the conventional
Systemt the
of the hoie immediately.
tree is landed after the tubing hanger and must be tripped to
Test ports between
each
repair seals on the tubing hanger.
set of seals on the through tubing tree hanger are included so
that seals sre not tested in sequence.
SPE13976/5
DSEuber$
GFSimmera&C
Shhuscm
Des@
Production Facilities
DESCRIPTION
a8
OF TREE
~a~
SPE13976/6
THROUGH BORE SUBSEA CHRISTMAS
TREEs
The
block
valves
are
lower
master
valve
and composite
essentially the same standard designs which have proved to be
However, the internals have been refined
reliable ~ the past.
to prevent damage to the valves and the seals on the tubing
hanger when the hanger is run through the tree.
The valve
bodies have been made stronger
to accept
the
riser and BOP.
The
higher loads imposed by the workover
pressure and temperature
ratings for the existing system are
5000 psi Normal 6000 psi Fracturing and up to 300F.
b.
Seal Area
Teat Ports
Lock
Down&ea
. -.
SPE13$176/7
DSHuber,
&
GFSimmers
&C
SJohnson
valves
The 7 1/16 EM lower master valve and composite valves are
However,
an extension of existing designs for 4 1/16 valves.
the external
loads
imposed
on these
components
by the
workover riser and BOP has meant that these two valves have
had to be analysed
for loads not normally
encountered
by
Detailed changes have been
made to
these types of valves.
the valve internals to ensure that seals on tubing hangers and
will not be damaged when run through both
running
tools
valves.
The size of 7 1/16 was selected as the most convenient size
to take a tubing hanger with 4 1/2 tubing and still allow
room for the DHSV control line.
Adysis
Although the through bore tree has been run without a special
workover riser, a dedicated workover riser and BOP have been
designed and built as part of an integrated equipment system.
Figure 5 shows the subsea set-up.
The system comprises a workover BOP package, a taper joint,
several riser joints, a tension collar, and a surface tree and a
bell mouth joint.
11
The BOP package
consists of a 13 5/8 5M connector,
10M pipe ram, 11 10M shear ram and an annular BOP.
The
BOP is split to allow handling by a crane of 14 ton capacity.
A taper joint was chosen in preference
to other alternatives
such as ball joints snd elastomeric
flex joints because
the
taper joint deflects through a smooth curve when the riser is
at an angle to the BOP.
This smooth curve allows the tubing
hanger and workover tools to be run without damage to seals.
However, one of the consequences of choosing a taper joint is
that higher bending loads are fed back into the tree than
. would be the case for a ball or flex joint.
A non-rotating
preloaded
connector is used to join the riser
These
connectors
provide
quick
make up, high
sections.
bending moment capacity and resistance
to fatigue.
In this
AL --->-2
->
elon
1 l~n
-11
Cnnc
--- 1: --.:-_
w aAL
a --72
Lne
y
Llk
appucalun
are
uemJIJnmA
-h
8
319
x
pipe.
During a workover the external loads imposed on t??e TBT are
higher than for a conventional
tree.
This is because
in a
workover
of a conventional
tree the riser is of a smaller
diameter.
Consequently
site specific analysis was carried out
for the complete system to determine the operating envelope
for the installation.
Included in this was a fatigue analysis
which took account of the fact that the system would be used
intermittently
(10-12 days at a time).
envelope
developed
field
was:
f.
New
Developments
~~~~i~~~
SPE13976/9
DSHuber,
GFSimmers&CSJobmmn
~t
Society
1985
This paper
was prepared
for the Offshore
Europe
85 Conference
in
conjunction
with the Society of Petroleum
Engineers
of ~E,
held in
Permission
to copy is restricted to MI
Aberdeen,
10-13 September
1985.
abstract of not more than 300 words.
Illustrations
may not be copied.
~.e abstract sho~d contti
conspicuous acknowledgement
of where and by
Publication
elsewhere
is usually granted
whom the paper is presented.
upon request provided agreement to give proper credit is made
TABLE 1
RUIMMMGPROCEDURES
F~
CC)NWI(IWL
e.
~+
SUBSEATREE IJESIGMS
THWWH BORETREE
ilESk34
RunnIng Procedure
Al
Run production
A2
Dlsplaca
f I !tarad
A3
casing.
ecd Iar.
A!S
Pull
AS
Run the
the
rlg
8(JP.
uorkovor W
Run tha
gWOdUdlOIt
*SO.
and rlsar.
Parf orate
A8
1%1
II
C2
C3
C4
C5
(%
Parf orate
C7
Pul
casing.
product Ion.
cd Iar.
sat packer.
tree.
and rl ser.
product Ion.
nlppla.
A7
Run production
nOWdSM)gl Og
A4
cl
Wall
Is ready for
RE-ENTRY
. 7i
T
HUB
ALvE\
q--.
uPPER
1.
-WIN6
/-Production
LINE
MASTER~
1-
LOUER MASTERVALVE
I9
DHSV
r
I
I
,1OLATIOh
VALVE
ANNULUS
LINE
TYPICAL
SUBSEA
TREE
SCHEMATIC
FIG. 1
w
$
El
iii
5
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au
I.u
FIG .2
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GUIDE
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FIG. 5