U.S. patent application number 12/720737 was filed with the patent office on 2010-12-16 for method and system for subsea intervention using a dynamic seal.
Invention is credited to Yves LeMoign, Keith A. Moriarty, Andrea Sbordone, Rene Schuurman.
Application Number | 20100314122 12/720737 |
Document ID | / |
Family ID | 42136759 |
Filed Date | 2010-12-16 |
United States Patent
Application |
20100314122 |
Kind Code |
A1 |
Sbordone; Andrea ; et
al. |
December 16, 2010 |
METHOD AND SYSTEM FOR SUBSEA INTERVENTION USING A DYNAMIC SEAL
Abstract
A system for performing intervention operations in subsea
installations, including a tubular which connects a subsea
installation to a surface vessel, a conveyance designed to enter
subsea installation to perform an intervention, and a
non-retrievable subsea dynamic seal, which prevents hydrocarbons
from reaching the vessel. A surface dynamic seal can be provided. A
method for subsea intervention using the system and a corresponding
subsea dynamic seal apparatus are provided.
Inventors: |
Sbordone; Andrea; (Rio de
Janeiro, BR) ; Moriarty; Keith A.; (Sugar Land,
TX) ; LeMoign; Yves; (Tanglin Park, SG) ;
Schuurman; Rene; (Hafrsfjord, NO) |
Correspondence
Address: |
SCHLUMBERGER OILFIELD SERVICES
200 GILLINGHAM LANE, MD 200-9
SUGAR LAND
TX
77478
US
|
Family ID: |
42136759 |
Appl. No.: |
12/720737 |
Filed: |
March 10, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61159111 |
Mar 11, 2009 |
|
|
|
61159227 |
Mar 11, 2009 |
|
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Current U.S.
Class: |
166/345 ;
166/85.3 |
Current CPC
Class: |
E21B 33/076
20130101 |
Class at
Publication: |
166/345 ;
166/85.3 |
International
Class: |
E21B 33/035 20060101
E21B033/035 |
Claims
1. A system for subsea intervention, the system comprising: at
least one non-retrievable subsea dynamic seal provided between a
surface vessel and a subsea well or a subsea installation; a
tubular extending between the at least one subsea dynamic seal and
the surface vessel; and a toolstring coupled to a conveyance and
lowered through the tubular to the subsea well or the subsea
installation, the toolstring passing through the at least one
subsea dynamic seal, wherein the at least one subsea dynamic seal
establishes a dynamic, pressure tight seal on the conveyance to
prevent the entry of borehole fluids into the tubular.
2. The system of claim 1, further comprising: an intervention
package located between the surface vessel and above the subsea
well or the subsea installation.
3. The system of claim 2, further comprising: at least one subsea
lubricator located above the intervention package.
4. The system of claim 1, further comprising: at least one surface
dynamic seal located on or in proximity of the surface vessel for
establishing a dynamic, pressure tight seal on the conveyance at an
upper end of the tubular and so as to pressurize an annulus between
the conveyance and the tubular.
5. A method for subsea intervention, the method comprising:
installing at least one non-retrievable subsea dynamic seal between
a surface vessel and a subsea well or a subsea installation;
installing a tubular extending between the subsea dynamic seal and
the surface vessel; lowering a toolstring coupled to a conveyance
through the tubular from the vessel into the subsea well or the
subsea installation and passing the toolstring through the subsea
dynamic seal; and establishing a dynamic, pressure tight seal with
the at least one subsea dynamic seal on the conveyance for
preventing borehole fluids from entering into the tubular.
6. The method of claim 5, further comprising: installing an
intervention package between the surface vessel and above the
subsea well or the installation.
7. The method of claim 6, further comprising: lowering the
toolstring into a subsea lubricator before the toolstring is
lowered into the subsea well or the subsea installation, the subsea
lubricator located above the intervention package.
8. The method of claim 7, further comprising: establishing a
dynamic, pressure tight seal on the conveyance at an upper end of
the tubular so as to pressurize an annulus between the conveyance
and the tubular with at least one surface dynamic seal located on
or in proximity of the surface vessel.
9. The method of claim 8, further comprising: equalizing the
pressure above well barriers in the intervention package with the
pressure below the well barriers; opening the well barriers in the
intervention package; performing an intervention operation;
retrieving the toolstring into the lubricator; closing the well
barriers in the intervention package; bleeding off pressure from
the lubricator and from the tubular; opening the subsea dynamic
seal; and retrieving the toolstring to the surface through the
tubular.
10. A non-retrievable subsea dynamic seal apparatus for subsea
intervention, the apparatus comprising: at least one
non-retrievable subsea dynamic seal adapted to be coupled between a
surface vessel and a subsea well or a subsea installation; the at
least one subsea dynamic seal adapted to be coupled to a tubular
extending to the surface vessel; the at least one subsea dynamic
seal adapted to allow a toolstring to pass therethrough, the
toolstring coupled to a conveyance and lowered through the tubular
to the subsea well or the subsea installation; and the at least one
subsea dynamic seal configured to establish a dynamic, pressure
tight seal on the conveyance to prevent the entry of borehole
fluids into the tubular.
11. The apparatus of claim 10, wherein an intervention package is
located between the surface vessel and above the subsea well or the
subsea installation.
12. The apparatus of claim 11, wherein at least one subsea
lubricator is located above the intervention package.
13. The apparatus of claim 10, wherein at least one surface dynamic
seal is located on or in proximity of the surface vessel for
establishing a dynamic, surface tight seal on the conveyance at an
upper end of the tubular and so as to pressurize an annulus between
the conveyance and the tubular.
14. The apparatus of claim 10, further comprising: a set of one or
more ram-type devices coupled to least one non-retrievable subsea
dynamic seal and configured to cause the at least one
non-retrievable subsea dynamic seal to form a dynamic, pressure
tight seal on the conveyance.
15. The apparatus of claim 14, wherein the set of one or more
ram-type devices is configured to open the at least one
non-retrievable subsea dynamic seal so as to allow the toolstring
to pass therethrough, and close the at least one non-retrievable
subsea dynamic seal so as to establish the dynamic seal on the
conveyance.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present disclosure claims benefit of priority to U.S.
Provisional Patent Application Ser. No. 61/159,227 and U.S.
Provisional Patent Application Ser. No. 61/159,111, both of Andrea
Sbordone et al., and both entitled "METHOD AND SYSTEM FOR SUBSEA
INTERVENTION USING A DYNAMIC SEAL," each of which was filed on Mar.
11, 2009, the entire contents of each are hereby incorporated by
reference herein.
TECHNICAL FIELD
[0002] The present disclosure generally relates to methods and
systems for subsea intervention, and more particularly to a method
and system for subsea intervention using a tubular, e.g., a riser,
having one or more dynamic seals.
DISCUSSION OF THE BACKGROUND
[0003] In the field of subsea intervention, it is of particular
interest to perform intervention operations into a subsea
installation (e.g., well, flowline, etc.) from a support unit,
typically a ship-shaped vessel smaller than normal drilling rigs
and drillships.
[0004] Normal operations from rigs and drillships include the use
of a riser, which is a tubular which connects the subsea
installation with the surface vessel and which is exposed to
borehole fluids. The possibility of pressurized borehole fluids
reaching the surface vessel imposes additional safety constraints
which could be quite onerous to implement on a small vessel, on
which the distance between the living quarters of the vessel and
the surface end of the riser would be smaller than on rigs and
drillships.
[0005] It is therefore of particular interest to avoid the
extension of the borehole to a surface vessel by having one or more
subsea dynamic seals, which seal on a conveyance during
intervention operations and prevent borehole pressure and fluids
from reaching the surface vessel. Such seals are called subsea
dynamic seals because they are located in the water column
somewhere between the subsea well or a subsea installation and the
vessel and because they allow the conveyance to be moved up and
down through the seal while still maintaining a pressure tight
seal.
SUMMARY OF THE DISCLOSURE
[0006] There exists a need to provide a system and method for
performing intervention operations into subsea installations (e.g.,
wells, flowlines, etc.) using a tubular. The above and other needs
and problems are addressed by the exemplary embodiments of the
present disclosure. The system includes a tubular connecting the
subsea installation to a surface vessel, and at least one
non-retrievable subsea dynamic seal (also referred to herein as a
"subsea dynamic seal" or "SDS") in proximity of the lower end of
the tubular or anywhere within the tubular in the water column. The
subsea dynamic seal provides a sealed connection on the conveyance
and prevents fluids from the well(s), flowline(s) or other subsea
installations from entering the tubular and possibly reaching the
vessel. At least one surface dynamic seal, which allows for the
controlled pressurization of the tubular, can also be included in
the system. The at least one surface dynamic seal (which may also
be referred to herein as "a surface dynamic seal") may be placed at
any suitable location, e.g., above the surface vessel.
[0007] Accordingly, in one exemplary aspect of the present
disclosure there is provided a system for subsea intervention,
including at least one non-retrievable subsea dynamic seal provided
between a surface vessel and a subsea well or a subsea
installation; a tubular extending between the at least one subsea
dynamic seal and the surface vessel; and a toolstring coupled to a
conveyance and lowered through the tubular to the subsea well or
the subsea installation, the toolstring passing through the at
least one subsea dynamic seal, wherein the at least one subsea
dynamic seal establishes a dynamic, pressure tight seal on the
conveyance to prevent the entry of borehole fluids into the
tubular.
[0008] The system can further include an intervention package
located between the surface vessel and above the subsea well or the
subsea installation.
[0009] The system can further include at least one subsea
lubricator located above the intervention package.
[0010] The system can further include at least one surface dynamic
seal located on or in proximity of the surface vessel for
establishing a dynamic, pressure tight seal on the conveyance at an
upper end of the tubular and so as to pressurize an annulus between
the conveyance and the tubular.
[0011] In another exemplary aspect of the present disclosure there
is provided a method for subsea intervention, including installing
at least one non-retrievable subsea dynamic seal between a surface
vessel and a subsea well or a subsea installation; installing a
tubular extending between the subsea dynamic seal and the surface
vessel; lowering a toolstring coupled to a conveyance through the
tubular from the vessel into the subsea well or the subsea
installation and passing the toolstring through the subsea dynamic
seal; and establishing a dynamic, pressure tight seal with the at
least one subsea dynamic seal on the conveyance for preventing
borehole fluids from entering into the tubular.
[0012] The method can further include installing an intervention
package between the surface vessel and above the subsea well or the
installation.
[0013] The method can further include lowering the toolstring into
a subsea lubricator before the toolstring is lowered into the
subsea well or the subsea installation, the subsea lubricator
located above the intervention package.
[0014] The method can further include establishing a dynamic,
pressure tight seal on the conveyance at an upper end of the
tubular so as to pressurize an annulus between the conveyance and
the tubular with at least one surface dynamic seal located on or in
proximity of the surface vessel.
[0015] The method can further include equalizing the pressure above
well barriers in the intervention package with the pressure below
the well barriers; opening the well barriers in the intervention
package; performing an intervention operation; retrieving the
toolstring into the lubricator; closing the well barriers in the
intervention package; bleeding off pressure from the lubricator and
from the tubular; opening the subsea dynamic seal; and retrieving
the toolstring to the surface through the tubular.
[0016] In another exemplary aspect of the present disclosure there
is provided non-retrievable subsea dynamic seal apparatus for
subsea intervention, including at least one non-retrievable subsea
dynamic seal adapted to be coupled between a surface vessel and a
subsea well or a subsea installation; the at least one subsea
dynamic seal adapted to be coupled to a tubular extending to the
surface vessel; the at least one subsea dynamic seal adapted to
allow a toolstring to pass therethrough, the toolstring coupled to
a conveyance and lowered through the tubular to the subsea well or
the subsea installation; and the at least one subsea dynamic seal
configured to establish a dynamic, pressure tight seal on the
conveyance to prevent the entry of borehole fluids into the
tubular.
[0017] An intervention package can be located between the surface
vessel and above the subsea well or the subsea installation.
[0018] At least one subsea lubricator can be located above the
intervention package.
[0019] At least one surface dynamic seal can be located on or in
proximity of the surface vessel for establishing a dynamic, surface
tight seal on the conveyance at an upper end of the tubular and so
as to pressurize an annulus between the conveyance and the
tubular.
[0020] The apparatus can further include a set of one or more
ram-type devices coupled to least one non-retrievable subsea
dynamic seal and configured to cause the at least one
non-retrievable subsea dynamic seal to form a dynamic, pressure
tight seal on the conveyance.
[0021] The set of one or more ram-type devices is configured to
open the at least one non-retrievable subsea dynamic seal so as to
allow the toolstring to pass therethrough, and close the at least
one non-retrievable subsea dynamic seal so as to establish the
dynamic seal on the conveyance.
[0022] These together with other aspects, features, and advantages
of the present disclosure, along with the various features of
novelty, which characterize the disclosure, are pointed out with
particularity in the claims annexed to and forming a part of this
disclosure. The above aspects and advantages are neither exhaustive
nor individually or jointly critical to the spirit or practice of
the disclosure. Other aspects, features, and advantages of the
present disclosure will become readily apparent to those skilled in
the art from the following description of exemplary embodiments in
combination with the accompanying drawings. Accordingly, the
drawings and description are to be regarded as illustrative in
nature, and not restrictive.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The disclosure will be better understood and aspects other
than those set forth above will become apparent when consideration
is given to the following detailed description thereof.
[0024] Such description of the present disclosure is illustrated by
way of example, and not by way of limitation, to the annexed
pictorial illustrations, graphs, drawings, and appendices, in which
like reference numerals refer to similar elements, and in
which:
[0025] FIG. 1 illustrates an exemplary system for subsea
intervention; and
[0026] FIG. 2 is used to illustrate an exemplary non-retrievable,
ram-type dynamic seal for the system of FIG. 1 for subsea
intervention.
DETAILED DESCRIPTION
[0027] Specific embodiments of the present disclosure will now be
described in detail with reference to the accompanying drawings.
Further, in the following detailed description of embodiments of
the present disclosure, numerous specific details are set forth in
order to provide a more thorough understanding of the disclosure.
However, it will be apparent to one of ordinary skill in the art
that the embodiments disclosed herein may be practiced without
these specific details. In other instances, well-known features
have not been described in detail to avoid unnecessarily
complicating the description.
[0028] In the context of the present disclosure, a subsea
installation includes any kind of subsea equipment or artifact in
which it might be of interest to gain access thereto in order to
perform some kind of intervention, maintenance, repair, and similar
conduits. The subsea installation can include a subsea well, a
subsea flowline, a Christmas tree, and the like.
[0029] A tubular can include any kind of a conduit that connects a
subsea installation to a surface vessel, for example, including a
tensioned riser, an attached riser, a pull tube riser, a steel
catenary riser, a buoyant riser, a production riser, a riser tower,
a flexible riser (e.g., Coflexip hose), a jointed pipe riser, a set
of casing joints, a set of drillpipe joints, tensioned coiled
tubing, and similar conduits. The tubular is preferably adapted to
safely conduct well fluids between the surface vessel and subsea
installation.
[0030] A conveyance can include any device designed to enter a
subsea installation and perform some kind of intervention,
including lowering an intervention toolstring into the
installation, pumping fluids into the installation, circulating
fluids, locating and/or removing an item or items from inside the
installation, pushing hardware inside the installation, activating
a device inside the installation, and the like. The conveyance also
can include a cable, an electrical cable (e.g., a wireline), a
slickline, coiled tubing, a coiled rod, composite coiled tubing, a
composite cable, a fiber optic cable, a heavy-duty line, a
combination of any of the above or any other suitable means of
conveyance, and similar devices.
[0031] The present disclosure includes recognition that there are
various technologies directed to the use of retrievable dynamic
seals for subsea installations. For example, U.S. Pat. No.
4,905,763 is directed to a method and system for servicing an
offshore well, including a sealing nipple lowered into a blowout
preventer (BOP) and held by rams of the BOP to pressurize a
borehole. U.S. Pat. No. 6,321,846 is directed to a sealing device
for use in subsea wells, including a dynamic seal that is lowered
into BOP rams and is actuated by hydraulic pressure applied between
two sets of rams. U.S. Patent Application Publication 20080060816
is directed to a wellhead seal unit, including a retrievable
dynamic seal for a drill pipe to be held by BOP rams.
[0032] However, the above technologies employ a retrievable seal,
which is lowered from the surface to the seabed to then establish a
seabed dynamic seal. By contrast, the exemplary system of the
present disclosure employs a non-retrievable subsea dynamic seal,
which can be engaged on a conveyance and advantageously is operable
without the need for deployment of any sealing part from the
surface.
[0033] Commonly assigned U.S. Patent Application 20080185152,
incorporated by reference herein, is directed to a system and
method for pressure control with a compliant guide, which may also
be referred to as a spoolable compliant guide (SCG), including a
system and method to intervene in a subsea installation with the
compliant guide. The system and method include a subsea dynamic
seal, preventing the entrance of borehole fluids into the compliant
guide, and a means allowing the pressurization of the compliant
guide to facilitate well control with the subsea dynamic seal.
[0034] Commonly assigned U.S. Pat. No. 6,386,290, by Headworth,
also incorporated by reference herein, is directed to a spoolable
compliant guide (as briefly described above) for accessing seabed
installations.
[0035] International Patent Application WO 2009/061211 is directed
to a riser system comprising at least one riser extending from a
subsea wellhead to a surface vessel, tension means, and an upper
workover riser package located at the upper section of the riser
and arranged to seal off the riser passage.
[0036] The exemplary system of the present disclosure can be
employed with any kind of a tubular, as defined herein, connecting
a subsea installation to a surface vessel. In one embodiment, the
tubular includes a riser, a drill pipe, a jointed pipe, coiled
tubing, flexible hose, flexible pipe, or a mix of the above, but it
is not included in a riser system used to transfer liquid/gas from
the well to the surface vessel. The at least one non-retrievable
subsea dynamic seal employed in the tubular substantially prevents
any hydrocarbons or other well fluids from reaching the vessel.
Thus, the interior of the tubular is substantially free of any
hydrocarbons or other well fluids. In an exemplary embodiment, the
tubular extends through the water column, and need not be included
in any other pipe or riser, such that its exterior is exposed to
the environment above the subsea installation, e.g., water. In
another embodiment, the tubular (or "a first tubular") may be
included within a second tubular. The first tubular includes at
least one non-retrievable subsea dynamic seal, and optionally, at
least one surface dynamic seal. The second tubular would is also
equipped with its own, separate at least one non-retrievable subsea
dynamic seal and, optionally, a separate at least one surface
dynamic seal.
[0037] Referring now to the drawings, wherein like reference
numerals designate identical or corresponding parts throughout the
several views, and more particularly to FIG. 1 thereof, there is
illustrated an exemplary system 100 configuration for performing an
intervention operation into a subsea well 102. In FIG. 1, the
exemplary system 100 includes a non-retrievable subsea dynamic seal
104 (e.g., a ram energized seal, etc.) that can be a fixed, self
contained seal in which a sealing element of the subsea dynamic
seal 104 remains in the body of the SDS 104 at all times. The
subsea dynamic seal 104 is placed in proximity of the subsea well,
and it is placed at a location substantially remote from the
intervention vessel 110. Thus, the subsea dynamic seal can be
positioned above an optional lubricator 112, which is located
within a tubular 114 and/or the SDS can be placed above an
intervention package 116 located above a subsea wellhead 118
(referred to also as a Christmas (x-mas) tree) at the seabed 120.
Intervention packages are known in the art, and any suitable
intervention package can be used in the system, of this disclosure,
such as that described in U.S. Pat. No. 7,578,349, incorporated
herein by reference. The exemplary system 100 can further include
at least one surface dynamic seal 122, which can be any
conventional surface dynamic seal, also referred to in the art as a
"stuffing box" or "stripper."
[0038] By contrast, heretofore-known conventional systems employ a
dynamic seal which is retrievable, i.e., which is lowered from the
surface, installed subsea, and then retrieved again to the surface
when the intervention operation has been performed and the
toolstring is retrieved to the surface. In the exemplary system
100, however, the subsea dynamic seal 104 is advantageously not
retrievable, but rather is deployed in a subsea location as a fixed
part of the subsea intervention hardware. FIG. 2 is used to
illustrate an exemplary non-retrievable, ram-type, subsea dynamic
seal 104 for subsea intervention. In FIG. 2, the non-retrievable
subsea dynamic seal 104 can include a set of one or more ram-type
devices 202 configured to cause a seal 204 to provide a dynamic
pressure tight seal on the conveyance 106, while the conveyance 106
is moving up and down inside the tubular 114. In order to allow the
intervention toolstring 108 to pass through the subsea dynamic seal
104, the non-retrievable subsea dynamic seal 104 can open via the
ram-type devices 202 to let the toolstring 108 pass through and
then close via the ram-type devices 202 on the conveyance 106 to
establish a dynamic, pressure tight seal in order to prevent
leakage or to prevent the entry of borehole fluids into the
tubular. For example, the subsea dynamic seal 104 can be configured
to open to the full size of the lubricator 112, so that any tool
which can fit through the lubricator 112 can also fit through the
open subsea dynamic seal 104.
[0039] Advantageously, the same subsea dynamic seal 104 can be
configured to be able to seal on different types of conveyances 106
of different sizes, eliminating the need to replace a component of
the system. Otherwise, the exemplary system can be configured with
different sets of non-retrievable subsea dynamic seals 104, each of
them configured for a certain set of conveyances 106.
[0040] Advantageously, the system 100 can be used with a variety of
subsea installations, for example, depending on a particular
environment and type of intervention operation, and similar
factors. Where such a subsea installation is the subsea well 102,
including the Christmas tree 118 coupled to the subsea well 102,
the subsea dynamic seal 104 is positioned generally at the bottom
of the tubular 114 to help block incursion of well fluids into the
interior 124 of the tubular 114. The interior 124 can be filled
with a buffer fluid used to regulate the pressure differential
acting on the subsea dynamic seal 104, which is permanently placed
in the lower part of the tubular 114. In this embodiment, the
subsea dynamic seal 104 opens and closes around the conveyance 106
to let the tool string 108 pass during, for example, deployment.
Furthermore, the pressure within the tubular 114 can be adjusted to
control the desired pressure differential over the subsea dynamic
seal 104, which can be useful in assisting with various
intervention operations. Advantageously, reducing the pressure
differential across the subsea dynamic seal 104 provides for easier
sealing, reduced friction forces on the conveyance 106, and reduced
wear of the subsea dynamic seal 104 resulting in an increased
useful life of the subsea dynamic seal 104.
[0041] The subsea dynamic seal 104 is generally positioned at the
top end of a subsea lubricator 112. In some applications, a lower
portion of the tubular 114 also can be utilized as part of the
lubricator 112 to enable the use of much longer intervention
toolstring (or tool strings) 108 and/or provide a reduction in
length of the subsea lubricator 112. By way of example, the subsea
dynamic seal 104 can be attached at the lower end of the tubular
114, or it can be mounted at the top of the subsea lubricator 112.
The subsea lubricator 112 can be used to deploy tools that have a
relatively large outside diameter.
[0042] In operation, the subsea dynamic seal 104 is designed to
prevent the escape of borehole fluids from a borehole of the subsea
well 102. This prevents the mixing of the borehole fluids with
buffer fluids within the tubular 114. The subsea dynamic seal 104
seals against the conveyance 106, and may be designed to seal
against a variety of conveyances, discussed herein, including
coiled tubing, coiled rod, wireline, slickline, heavy-duty line,
and other cable-type conveyances. The subsea dynamic seal 104 also
can be designed with an active system that may be controlled to
selectively open and close its sealing surfaces to accommodate the
passage of larger tools.
[0043] The subsea dynamic seal 104 enables the selective
pressurization of a buffer fluid disposed in interior 124 of the
tubular 114. The ability to pressurize a buffer fluid enables, for
example, control over differential pressures exerted on the subsea
dynamic seal 104, thereby improving the life of the seal 104 and/or
lowering the required functional specifications for the seal 104.
Pressure control equipment can be positioned at any suitable
location, e.g., at a surface location to provide adjustable control
over the pressure of a buffer fluid, and thus over the pressure
acting on the borehole fluids. In some applications, the pressure
control equipment also can be used to deliver a buffer fluid into
the tubular 114. The pressure control equipment can be mounted, for
example, on the surface intervention vessel 110.
[0044] In this manner, the tubular 114 is used in conjunction with
subsea dynamic seal 104 to prevent the borehole fluids from
escaping the borehole by forming a connection with the wellhead 102
and by filling the tubular 114 with buffer fluid. In this
particular embodiment, the tubular 114 can be coupled to the
wellhead 102 through a blowout preventer (not shown) and the subsea
lubricator 112. The subsea dynamic seal 104 is present between the
wellhead 102 and the low side of the tubular 114 to prevent
borehole fluids from migrating into the tubular 114. The pressure
of a buffer fluid within the tubular 114 can be easily adjusted by
the pressure control equipment, e.g., from the surface location.
With this arrangement, the borehole fluids are prevented from
moving up the tubular 114 by virtue of the cooperation between the
subsea dynamic seal 104 and the buffer fluid. The buffer fluid
counterbalances the borehole pressure via appropriate
pressurization with pressure control equipment located on, for
example, a surface vessel 110. A lower end of the tubular 114 forms
a dynamic pressure tight seal with the subsea installation or the
well 102, for example, the top of the subsea lubricator 112 or at a
blowout preventer. In some embodiments, the subsea lubricator 112
can be formed as part of the tubular 114, which is then connected
to the top of a blowout preventer stack (not shown).
[0045] A surface dynamic seal 122 can be included at the top of the
tubular 114 to allow the pressurization of the tubular 114, in
order to facilitate subsea dynamic sealing by reducing the
differential pressure across the subsea dynamic seal 104 and to
limit the buckling of any flexible conveyance 106 subjected to an
extrusion force due to pressure below the subsea dynamic seal 104
that may be higher than above the subsea dynamic seal 104. In
addition, the tubular 114 can be filled with a buffer fluid
configured, for example, to prevent hydrate formation, to lubricate
the movement of the conveyance 106 inside the tubular 114,
advantageously, minimizing friction and wear, to disperse traces of
hydrocarbon possibly leaking into the tubular 114 from the subsea
dynamic seal 104, to facilitate detection of leaks into the sea by
fluorescence detection methods or other similar systems, or
accomplish any other similar tasks. A suitable buffer fluid can
include sea water or other buffer fluids, e.g., environmentally
friendly greases for friction reduction; fluids designed for
hydrate prevention; weighted mud; and other appropriate buffer
fluids. The level and pressure of buffer fluid can be controlled
from the surface.
[0046] The exemplary intervention system 100 can include an
intervention package 116, the lubricator 112, which is optional,
one or more subsea dynamic seals 104 between the vessel 110 and the
subsea well or installation 102, the tubular 114 extending between
the subsea dynamic seal 104 and the surface vessel 110, the surface
dynamic seal 122, which is optional, and the conveyance 106 lowered
through the tubular 114 into the subsea installation 102, e.g., a
subsea well.
[0047] The exemplary intervention method can include installing the
intervention package 116, the lubricator, which is optional, the
one or more subsea dynamic seals 104, and the tubular 114 between
the vessel 110 and the subsea installation 102. The method then
includes lowering the toolstring (or tool) 108 and the conveyance
106 through the tubular 114 from the vessel 110 into the subsea
lubricator 112. Then, a dynamic, pressure tight seal is established
with the one or more subsea dynamic seals 104 on the conveyance 106
to prevent the entrance of borehole fluids into the tubular 114. If
needed, a dynamic pressure tight seal is established with the
surface dynamic seal 122 on the conveyance 106 to pressurize an
annulus 124 between the conveyance 106 and the tubular 114.
[0048] Then, well barriers used to prevent the entering of borehole
fluids are opened and the intervention operation is performed. Such
well barriers may be provided in the Christmas tree 118 and/or in
the intervention package 116, for example, depending on the tree
type (e.g., vertical or horizontal). In addition, before opening
the well barriers, the pressure is equalized between the lubricator
112 (or a part of the tubular 114 between the well barriers and the
subsea dynamic seals 104) and the subsea installation 102.
[0049] Upon completion of the intervention, the intervention
toolstring 108 is retrieved into the lubricator 112 and the well
barriers are closed. Pressure from the lubricator 112 and from the
tubular 114 is bled, if needed. The one or more subsea dynamic
seals 104 are opened, and the toolstring 108 is retrieved to
surface through the tubular 114.
[0050] The exemplary embodiments of the present disclosure prevent
borehole fluids from entering into a riser. This is advantageous
insofar that such fluids contain corrosive agents, e.g., CO.sub.2,
and/or H.sub.2S, and similar fluids, which are often found in many
oilfields. Hence, a tubular, such as a riser with a subsea dynamic
seal need not be made of materials resistant to such corrosive
agents. Accordingly, the engineering and manufacturing of such a
riser with a subsea dynamic seal can be made in a cost effective
and simpler manner, and the riser itself can have a longer useful
life before needing replacement. By contrast, without such a subsea
dynamic seal, the riser would be exposed to such corrosive agents
and would have to be made from materials resistant to the corrosive
agents.
[0051] Although the exemplary embodiments are described with
respect to employing tubulars that need not be included inside of
another pipe or riser, the exemplary embodiments of the present
disclosure can be adapted to work with any suitable structures,
including tubulars that are included inside of another tubular,
e.g., a pipe or a riser, or a similar structure, as will be
appreciated by those of ordinary skill in the relevant art(s).
[0052] Although the present disclosure has been described with
reference to exemplary embodiments and implementations thereof, the
present disclosure is not to be limited by or to such exemplary
embodiments and/or implementations. Rather, the systems and methods
of the present disclosure are susceptible to various modifications,
variations and/or enhancements without departing from the spirit or
scope of the present disclosure. Accordingly, the present
disclosure expressly encompasses all such modifications, variations
and enhancements within its scope.
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