U.S. patent application number 14/380720 was filed with the patent office on 2015-01-22 for method and system for providing fuel gas to a topside facility.
The applicant listed for this patent is FMC Kongsberg Subsea AS. Invention is credited to Steinar Eriksen.
Application Number | 20150021235 14/380720 |
Document ID | / |
Family ID | 47790169 |
Filed Date | 2015-01-22 |
United States Patent
Application |
20150021235 |
Kind Code |
A1 |
Eriksen; Steinar |
January 22, 2015 |
METHOD AND SYSTEM FOR PROVIDING FUEL GAS TO A TOPSIDE FACILITY
Abstract
A method for providing fuel gas to a top-side processing system
of a sub-sea well stream is provided. The method comprises
separating the sub-sea well stream in a sub-sea arranged three
phase separator obtaining a crude oil stream, and a crude natural
gas stream, separating acid gasses and/or water from the crude
natural gas, pressurizing the gas stream sub-sea, adding at least
part of the pressurized gas to the crude oil stream subsea,
transporting the added gas together with the oil to the topside,
separating the gas from the oil in a first stabilization stage and
providing the separated gas as fuel gas to a fuel gas system.
Inventors: |
Eriksen; Steinar; (Hokksund,
NO) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FMC Kongsberg Subsea AS |
Kongsberg |
|
NO |
|
|
Family ID: |
47790169 |
Appl. No.: |
14/380720 |
Filed: |
February 21, 2013 |
PCT Filed: |
February 21, 2013 |
PCT NO: |
PCT/EP2013/053415 |
371 Date: |
August 23, 2014 |
Current U.S.
Class: |
208/187 ;
196/46 |
Current CPC
Class: |
E21B 43/36 20130101 |
Class at
Publication: |
208/187 ;
196/46 |
International
Class: |
E21B 43/36 20060101
E21B043/36 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 23, 2012 |
NO |
20120188 |
Claims
1. A method for providing fuel gas to a topside processing system
for a subsea well stream, the method comprising: separating the
subsea well stream in a subsea arranged three phase separator to
thereby obtain a crude oil stream and a crude natural gas stream;
separating at least one of acid gasses and water from the crude
natural gas stream; pressurizing the crude natural gas stream
subsea; adding at least part of the pressurized gas to the crude
oil stream subsea; transporting the added pressurized gas together
with the crude oil to the topside processing system; separating the
pressurized gas from the crude oil in a first stabilization stage;
and providing the separated gas as fuel gas to a fuel gas
system.
2. The method according to claim 1, further comprises removing
water from the crude oil stream subsea to obtain dry crude oil, and
transporting the dry crude oil to the topside processing
system.
3. The method according to claim 2, wherein the step of removing
water from the crude oil stream subsea comprises passing the crude
oil through a subsea arranged electrostatic coalescer.
4. The method according to claim 1, 2 or 3, further comprising
stabilizing the crude oil stream for tanker transport in the
topside, processing system through removal of dissolved gas from
the crude oil stream.
5. The method according to claim 4, wherein the stabilizing step is
performed at a gas pressure equal to a pressure required for the
topside fuel gas system.
6. The method according to claim 4, wherein the crude oil is
stabilized in first and second stages and is heated with interstage
heating.
7. The method according to claim 1, wherein the step of separating
acid gasses or water from the crude natural gas is performed
subsea.
8. A subsea well topside fuel gas-providing system which comprises:
a subsea arranged three phase separator which includes a well
stream inlet, a crude natural gas outlet and a crude oil outlet; a
riser which includes a subsea riser inlet in fluid communication
with the crude oil outlet and the crude natural gas outlet; the
riser further comprising a topside riser outlet in fluid
communication with a topside arranged stabilization unit which
includes a stabilized crude oil outlet and a fuel gas outlet.
9. The system according to claim 8, further comprising a subsea gas
treatment system located downstream of the three phase separator,
the subsea gas treatment system comprising an inlet in fluid
communication with the crude natural gas outlet and a treated gas
outlet in fluid communication with the riser.
10. The system according to claim 8 or 9, further comprising a
subsea arranged water removal unit located downstream of the three
phase separator, the water re oval unit comprising a crude oil
inlet in fluid communication with the crude oil outlet, a dry crude
oil outlet in fluid communication with the riser, and a water
outlet.
11. The system according to claim 10, wherein the water removal
unit comprises an electrostatic coalescer.
12. The system according to claim 8, herein the fuel gas outlet is
in fluid communication with a fuel gas net inlet of a topside
arranged power generating unit.
13. The system according to claim 8, further comprising a subsea
natural gas compressor with an inlet in fluid communication with
the natural gas outlet and a pressurized gas outlet in
communication with the riser.
Description
[0001] The present invention relates to an offshore processing
method, especially the present invention relates to an offshore
processing method for providing fuel for an offshore processing
system which can be combined with a method for stabilization of oil
for tanker transport.
BACKGROUND
[0002] The exploitation of subsea wells has gone through
considerable developments since the start of the offshore era. The
location of the wells has changed both with respect to sea depth as
well as distance to shore. This has resulted in new systems for
handling the well streams. One such system includes a subsea
installation near the well head combined with a topside platform,
which can be a floating processing platform. Transportation of the
well products can take place either through subsea pipelines or via
tanker transport. Due to the limited space on a floating platform
generally the amount of process equipment need to be adjusted to
the available space. Transport of crude oil on tankers requires
that the crude oil has been stabilized to an extent that gas which
can be released from the oil during transport is limited. The
release of gas during transport is a result of changes in the
conditions for instance due to changes in the temperatures of the
surroundings, but also a result of settlement over time during
transport.
[0003] Stabilization of crude oil for tanker transport comprises
controlled degasification of the crude oil.
[0004] The offshore top side processing equipment requires power
for driving mechanical equipment and for providing heat.
[0005] The power can be provided through electrical cables
connected to onshore power plants or be generated offshore through
combustion of fuel or a combination thereof.
PRIOR ART
[0006] Stabilisation of crude oil through degasification is well
known in the art, and WO 03/033872 is mentioned as an example.
[0007] WO 03/033872 relates to an installation arranged on the sea
bed for the separation of fluids, comprising at least one separator
that is connected to one or more wells, each via an associated well
head or similar, and a pipeline. The components separated, oil,
gas, water or combinations of these substances, are fed fully or
partially from the installation to a platform, vessel etc. on the
surface via collecting pipelines onto shore, or are re-injected
into the formation beneath the sea bed. Each separator consist of a
long pipe (pipe separator) that may form a major or minor part of
the transport pipeline from the well and has a diameter that is
mainly equal to or slightly larger that the diameter of the
transport pipeline.
OBJECTIVES OF THE INVENTION
[0008] An aim of the present invention is to provide a method for
providing fuel to a topside platform from a subsea well which
utilizes equipment mainly provided for other purposes.
[0009] Another aim is to provide a method for stabilisation of oil
for tanker transport.
[0010] The present invention provides a method for providing fuel
gas to a top-side processing system of a sub-sea well stream, where
the method comprises separating the sub-sea well stream in a
sub-sea arranged three phase separator obtaining a crude oil
stream, and a crude natural gas stream, separating acid gasses
and/or water from the crude natural gas, pressurizing the gas
stream sub-sea, adding at least part of the pressurized gas to the
crude oil stream subsea, transporting the added gas together with
the oil to the topside, separating the gas from the oil in a first
stabilization stage and providing the separated gas as fuel gas to
a fuel gas system.
[0011] In one aspect of method according to the present invention
the method further comprises removing water from the crude oil
stream subsea to obtain dry crude oil, transporting the dry crude
oil to the topside processing system. Removing water from the crude
oil stream subsea may in another aspect comprise passing the crude
oil trough a subsea arranged electrostatic coalescer.
[0012] In a further aspect of the method according to the present
invention the crude oil stream is stabilized for tanker transport
in the top-side processing system through removal of dissolved
gas.
[0013] In yet another aspect of the method according to the present
invention the first stabilization stage operates at a gas pressure
equal to a pressure required for the topside fuel gas system.
[0014] In an additional aspect of the present invention the crude
oil is stabilized in the first stage and in a second stage with
interstage heating.
[0015] In a further aspect of the method according to present
invention the step of separating acid gasses and/or water from the
crude natural gas is performed subsea.
[0016] Further the present invention provides a subside well,
topside fuel gas providing system comprising a sub-sea arranged
three phase separator with a well stream inlet and at least a crude
natural gas outlet and a crude oil outlet, a riser with a subsea
riser inlet in fluid communication with the crude oil outlet and in
fluid communication with the crude natural gas outlet and a topside
riser outlet in fluid communication with a topside arranged
stabilization unit comprising a stabilized crude oil outlet and a
fuel gas outlet.
[0017] In one aspect of the system according to the present
invention, the system further comprises a subsea gas treatment
system down stream the three phase separator with an inlet in fluid
communication with the crude natural gas outlet and with a treated
gas outlet in fluid communication with the riser.
[0018] In a further aspect the system comprises a sub-sea arranged
water removal unit arranged downstream the three phase separator
with a crude oil inlet in fluid communication with the crude oil
outlet, a dry crude oil outlet in fluid communication with the
riser and a water outlet. In one aspect of the system the water
removal unit comprises an electrostatic coalescer.
[0019] In yet another aspect the system according to the present
invention the fuel gas outlet is in fluid communication with a fuel
gas inlet to a topside arranged power generating unit.
[0020] In an additional aspect of the system according to the
present invention the system further comprises a subsea natural gas
compressor with an inlet in fluid communication with the natural
gas outlet and a pressurized gas outlet in communication with the
riser.
[0021] The term "topside" as used here refers to a position in
proximity of the sea level. For floating topside installations part
of the equipment may be installed above or below the sea level but
with in or on the floating vessel or platform. For platforms with
one or more legs connected to the seabed the term "topside" should
be interpreted to refer to any position on the platform above sea
level.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The present invention will be discussed in further detail
with reference to the enclosed figures where:
[0023] FIG. 1 schematically illustrates a first embodiment of the
present invention.
[0024] FIG. 2 schematically illustrates a second embodiment of the
present invention.
[0025] FIG. 3 schematically illustrates a third embodiment of the
present invention.
[0026] FIG. 4 illustrates the process scheme of a fourth embodiment
of the present invention.
PRINCIPAL DESCRIPTION OF THE INVENTION
[0027] The figures illustrated different embodiments of the present
invention. The same reference numbers are used to refer to equally
elements within the different embodiments. It should be understood
that features of the different embodiments may be combined to
provide additional embodiments of the present invention.
[0028] FIG. 1 illustrates a first embodiment of the present
invention. A well stream 1 is fed to a subsea three-phase separator
2, to obtain a water stream 19, a crude oil stream 13 and a gas
stream 3. The water stream 19 is transferred to a produced water
treatment system 4. The gas stream 3 is past through a heat
exchanger 8 to obtain a cooled gas 5. The cooling results in
condensation of higher hydrocarbons which are separated in
separator 10. The liquid stream 7 is via pump 12 and pipe 9 mixed
with the main oil stream from the separator 2. The gas 11 leaving
over the top of the separator 10 is subject to a treatment system
22 conditioning the gas for pipeline transport. The conditioned gas
51 is pressurized in subsea compressor 52 to obtain pressurised gas
53.
[0029] The oil stream 81 comprising the main crude oil stream 13
and the condensed oil 9 is transported via a pump 80 and a pipeline
83. A part 57 of the pressurized gas is added to the oil before the
oil is transferred to top side via line 85. The rest of the gas is
transferred via heat exchanger 54 and pipeline 55 to shore.
[0030] The mixture of gas and oil is transported to a topside
installation 90 in riser 85. Within the oil treatment system 6' the
oil is dehydrated and gas initially present as well as the added
gas is removed in a first stabilization step 84. Stream 87 is
stabilized oil, depending on the restrictions for tanker transport
additional oil treatment may if necessary be performed on the
topside installation. Stream 89 comprises the added gas stream 57
as well as any additional gas released from the crude oil. This
stream 89 is fed as fuel gas to a topside gas fuel power providing
system 86.
[0031] FIG. 2 illustrates an alternative embodiment of the present
invention, wherein the at least partly stabilized crude oil 87 is
returned from the topside installation to subside, and transported
to shore together with the compressed gas 55 as stream 65 via a
subsea pipeline. In this embodiment the crude oil is transferred to
the topside installation to be dried. For pipeline transport
together with the crude gas both the gas and the oil need to be
dried to avoid hydrate formation.
[0032] FIG. 3 illustrates a further embodiment of the present
invention. Here also the initial oil treatment system 6 is arranged
subsea. Here the crude oil is dehydration for instance by use of
electrostatic coalescers. Separated water is past as stream 15 to
the produced water treatment system 4. The dehydrated oil 81 is via
pump 80 transferred to the topside installation 90 together with
treated gas 57. The stabilization system 84 comprises one or more
stabilization steps where gas is flashed of from the crude oil. The
first step is preferably performed at a pressure equal to the
pressure required by the fuel gas system 86 so that it is not
required to compressed the fuel gas 89 before feeding it to the
fuel gas system 86. The fuel gas is a combination of the added gas
57 and the gas present in the crude oil prior to stabilization.
Additional stabilization steps may be included within unit 84 to
allow for removal of additional gas to secure quality applicable
for tanker transport. These additional steps will be performed at a
lower pressure than the pressure of the fuel gas. If significant
amounts of gas are released at a lower pressure, then the treatment
system may also comprise a compressor to increase the pressure of
the removed gas to the pressure required by the fuel system.
Alternatively, if there are two fuel gas systems topside; 1) for
feeding the generator turbine (high pressure) and 2) one for
feeding a direct fired heater to provide heating medium, then the
gas released at lower pressure is fed to the fuel system for the
direct fired heater. Alternatively if the pressure of the removed
gas obtained in the first step is larger than the pressure needed
for the fuel system. The two gas streams, from the first step with
to high pressure and from the additional step with to low pressure
may be combined before they are fed to the fuel gas system with the
correct pressure.
[0033] FIG. 4 illustrated an embodiment of the present invention in
further detail. The well fluid 1 enters a phase separator 2, where
the gas stream 3 is separated from the liquid. In the illustrated
embodiment a water stream 19 is passed to a produced water
treatment system 4, and the oil stream 13 is past to an oil
treatment system 6. The gas 3 is initially cooled by cooler 8 to
obtain cooled gas 5. The cooling results in condensation of higher
hydrocarbons which are separated in separator 10. The liquid stream
7 is via pump 12 and pipe 9 mixed with the main oil stream from the
separator 2. The gas 11 leaving over the top of the separator 10 is
subject to a gas treatment system. In FIGS. 1-3 this was referred
to as system 22 whereas here one embodiment of this system is
disclosed in detail. However it should be noted that other subsea
systems for gas conditioning are equally applicable. The crude gas
stream 11 comprising a compound to be removed such as CO.sub.2
and/or other acid gasses is fed to a contactor system 14, 16
arranged subsea. In the illustrated embodiment the contactor system
is a 2 stage process with an initial direct contactor 14 and a
traditional contactor column 16. However the present invention is
not limited to this embodiment but any contactor system applicable
for subsea arrangement may be employed. In the direct contactor the
gas stream is brought in contact with a treatment solution stream
fed trough pipe 23. The obtained gas treatment solution mixture
proceeds as stream 17 into the contactor column 16. Lean treatment
solution is provided to the column from pipe 21. In the illustrated
embodiment the treatment solution for the direct contactor is
obtained from the column 16 at a level above the gas inlet, however
the present invention is not limited to this solution as lean
treatment solution could also be fed to the direct contactor as
well as the column. The treatment solution comprises one or more
species that at least with some selectivity absorb the compound to
be removed from the crude gas stream. A species and solvent/diluent
applicable for forming an effective treatment solution can be
selected by the user depending on the compound to be removed and
the prevailing conditions within the system. During contact with
the treatment solution the compound to be removed is absorbed in
the solution. The crude gas accordingly at least partly depleted
from the compound to be removed leaves over the top of the column
trough pipeline 31. The main crude gas stream accordingly stays
subsea during the treatment process. The rich treatment solution
leaves the contactor 16 trough the bottom outlet pipeline 25.
[0034] In the illustrated embodiment a pump 18 is provided to force
the rich treatment solution 25 to proceed up through the riser or
pipeline 27. The is only an illustration of one possible way of
securing transport of the rich treatment solution up trough the
pipeline 27 other methods of providing the needed pressure and flow
can equally be employed. On a topside facility 90 a regeneration
system 20 is installed. The system receives the rich solution from
pipeline 27, desorbes and separates the absorbed compound there
from and obtains a depleted treatment solution which is send back
to the subsea contactor system trough pipeline/riser 21. The
desorbed compound leaves the regeneration unit 20 as stream 29. If
the compound is CO.sub.2 the stream 29 may be treated and
compressed in unit 60 and from there transported via pipeline 61 to
a subsea injection well (not shown).
[0035] The obtained treated gas 31 enters a second system for
removal of a second compound, such as water. The system comprises a
direct contactor 34, where the gas is brought in contact with a
treatment solution stream 43. The obtained mixture is fed to a
contactor column 36. The rich treatment solution leaves via the
bottom as stream 45, via pump 38 and is transported via pipeline 47
to a top side installation 90 and a regeneration unit 40. Here the
compound absorbed in the rich treatment solution is released
resulting in a compound stream 49 and a lean treatment solution 41
being returned to the subsea contactor 36. If the compound is water
the stream 49 is steam that can be released to the atmosphere.
[0036] The treated gas stream 51 leaving over the top of 36 can be
compressed in compressor 52 and the temperature of the compressed
gas 53 controlled by heat exchanger 54. Hereby providing a treated
gas stream 55 adjusted for subsea pipeline transport.
* * * * *