U.S. patent application number 11/387378 was filed with the patent office on 2006-07-27 for system and method of installing and maintaining an offshore exploration and production system having an adjustable buoyancy chamber.
Invention is credited to Charles H. King, Eric E. Maidla, Keith K. Millheim.
Application Number | 20060162933 11/387378 |
Document ID | / |
Family ID | 37193951 |
Filed Date | 2006-07-27 |
United States Patent
Application |
20060162933 |
Kind Code |
A1 |
Millheim; Keith K. ; et
al. |
July 27, 2006 |
System and method of installing and maintaining an offshore
exploration and production system having an adjustable buoyancy
chamber
Abstract
A system and method of establishing an offshore exploration and
production system is disclosed, in which a well casing is disposed
in communication with an adjustable buoyancy chamber and a well
hole bored into the floor of a body of water. A lower connecting
member joins the well casing and the chamber, and an upper
connecting member joins the adjustable buoyancy chamber and a well
terminal member. The chamber's adjustable buoyancy enables an
operator to vary the height or depth of the well terminal member,
and to vary the vertical tension imparted to drilling and
production strings throughout exploration and production
operations. Also disclosed is a system and method of adjusting the
height or depth of a wellhead while associated vertical and lateral
forces remain approximately constant. A variety of well isolation
members, lateral stabilizers and anchoring means, as well as
several methods of practicing the invention, are also
disclosed.
Inventors: |
Millheim; Keith K.; (The
Woodlands, TX) ; Maidla; Eric E.; (Sugar Land,
TX) ; King; Charles H.; (Austin, TX) |
Correspondence
Address: |
ARNOLD & FERRERA, L.L.P.
2401 FOUNTAIN VIEW DRIVE
SUITE 630
HOUSTON
TX
77057
US
|
Family ID: |
37193951 |
Appl. No.: |
11/387378 |
Filed: |
March 23, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10994799 |
Nov 22, 2004 |
|
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11387378 |
Mar 23, 2006 |
|
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60606335 |
Sep 1, 2004 |
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Current U.S.
Class: |
166/344 |
Current CPC
Class: |
E21B 17/012 20130101;
E21B 33/035 20130101; E21B 33/064 20130101; E21B 17/07 20130101;
E21B 41/0007 20130101 |
Class at
Publication: |
166/344 |
International
Class: |
E21B 34/04 20060101
E21B034/04 |
Claims
1. A method of transferring fluid flow initiated from a subsurface
wellhead disposed beneath the surface of a body of water to a fluid
retention vessel disposed nearer the surface of said body of water,
said method comprising: buoyantly supporting a well control system
within said body of water; positioning said well control system
through said subsurface wellhead; initiating a fluid flow from said
subsurface wellhead; receiving said fluid flow from said subsurface
wellhead using a fluid flow receiving means; transferring said
fluid flow from said fluid flow receiving means to said well
control system; and transferring said fluid flow from said well
control system to said fluid retention vessel.
2. The method of transferring fluid flow initiated from a
subsurface wellhead of claim 1, wherein said method further
comprises: buoyantly supporting said well control system within
said body of water using a buoyancy chamber.
3. The method of transferring fluid flow initiated from a
subsurface wellhead of claim 1, wherein said method further
comprises: positioning said well control system through said
subsurface wellhead using a stress joint.
4. The method of transferring fluid flow initiated from a
subsurface wellhead of claim 3, wherein said method further
comprises: receiving said fluid flow from said subsurface wellhead
using said stress joint.
5. The method of transferring fluid flow initiated from a
subsurface wellhead of claim 1, wherein said method further
comprises: transferring said fluid flow from said fluid flow
receiving means to said well control system using production
casing.
6. The method of transferring fluid flow initiated from a
subsurface wellhead of claim 1, wherein said method further
comprises: transferring said fluid flow from said well control
system to said fluid retention vessel using at least one of a
production tree, a blowout preventer, and a wellhead disposed
nearer the surface of said body of water than said subsurface
wellhead.
7. A means for transferring fluid flow initiated from a subsurface
wellhead disposed beneath the surface of a body of water to a fluid
retention vessel disposed nearer the surface of said body of water,
said means comprising: means for buoyantly supporting a well
control system within said body of water; means for positioning
said well control system through said subsurface wellhead; means
for initiating a fluid flow from said subsurface wellhead; means
for receiving said fluid flow from said subsurface wellhead; means
for transferring said fluid flow from said subsurface wellhead to
said well control system; and means for transferring said fluid
flow from said well control system to said fluid retention
vessel.
8. The means for transferring fluid flow initiated from a
subsurface wellhead disposed beneath the surface of a body of water
of claim 7, wherein said means further comprises: a buoyancy
chamber for supporting said well control system within said body of
water.
9. The means for transferring fluid flow initiated from a
subsurface wellhead disposed beneath the surface of a body of water
of claim 7, wherein said means further comprises: a stress joint
for positioning said well control system through said subsurface
wellhead.
10. The means for transferring fluid flow initiated from a
subsurface wellhead disposed beneath the surface of a body of water
of claim 9, wherein said stress joint is also used for receiving
said fluid flow from said subsurface wellhead.
11. The means for transferring fluid flow initiated from a
subsurface wellhead disposed beneath the surface of a body of water
of claim 7, wherein said means further comprises: a length of
production casing for transferring said fluid flow from said
subsurface wellhead to said well control system.
12. The means for transferring fluid flow initiated from a
subsurface wellhead disposed beneath the surface of a body of water
of claim 7, wherein said means further comprises: at least one of a
production tree, a blowout preventer, and a wellhead disposed
nearer the surface than said subsurface wellhead used for
transferring said fluid flow from said well control system to said
fluid retention vessel.
13. A system for transferring fluid flow initiated from a
subsurface wellhead disposed beneath the surface of a body of water
to a fluid retention vessel disposed nearer the surface of said
body of water, said system comprising: a buoyancy chamber for
buoyantly supporting a well control system within said body of
water; a means for positioning said well control system through
said subsurface wellhead; a means for initiating a fluid flow from
said subsurface wellhead; a fluid flow receiving means for
receiving said fluid flow from said subsurface wellhead; a length
of production casing for transferring said fluid flow from said
fluid flow receiving means to said well control system; and at
least one of a production tree, a blowout preventer and a wellhead
disposed nearer the surface of said body of water used for
transferring said fluid flow from said well control system to said
fluid retention vessel.
14. The system for transferring fluid flow initiated from a
subsurface wellhead disposed beneath the surface of a body of water
of claim 13, wherein said means for positioning said well control
system through said subsurface wellhead further comprises a stress
joint.
15. The system for transferring fluid flow initiated from a
subsurface wellhead disposed beneath the surface of a body of water
of claim 14, wherein said stress joint is also used to receive said
fluid flow from said subsurface wellhead.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The instant application is a divisional of prior
non-provisional application Ser. No. 10/994,799, filed Nov. 22,
2004, still pending, which claims the benefit of prior provisional
application No. 60/606,335.
FIELD OF THE INVENTION
[0002] The present invention relates generally to oil and gas
exploration and production, and in a specific, non-limiting
embodiment, to a system and method of installing and maintaining an
offshore exploration and production system having an adjustable
buoyancy chamber.
BACKGROUND OF THE INVENTION
[0003] Innumerable systems and methods have been employed in
efforts to find and recover hydrocarbon reserves around the world.
At first, such efforts were limited to land operations involving
simple but effective drilling methods that satisfactorily recovered
reserves from large, productive fields. As the number of known
producing fields dwindled, however, it became necessary to search
in ever more remote locales, and to move offshore, in the search
for new resources. Eventually, sophisticated drilling systems and
advanced signal processing techniques enabled oil and gas companies
to search virtually anywhere in the world for recoverable
hydrocarbons.
[0004] Initially, deepwater exploration and production efforts
consisted of expensive, large scale drilling operations supported
by tanker storage and transportation systems, due primarily to the
fact that most offshore drilling sites are associated with
difficult and hazardous sea conditions, and thus large scale
operations provided the most stable and cost-effective manner in
which to search for and recover hydrocarbon reserves. A major
drawback to the large-scale paradigm, however, is that explorers
and producers have little financial incentive to work smaller
reserves, since potential financial recovery is generally offset by
the lengthy delay between exploration and production (approximately
3 to 7 years) and the large capital investment required for
conventional platforms and related drilling and production
equipment. Moreover, complex regulatory controls and industry-wide
risk aversion have led to standardization, leaving operators with
few opportunities to significantly alter the prevailing paradigm.
As a result, offshore drilling operations have traditionally been
burdened with long delays between investment and profit, excessive
cost overruns, and slow, inflexible recovery strategies dictated by
the operational environment.
[0005] More recently, deepwater sites have been found in which much
of the danger and instability present in such operations is
avoided. For example, off the coast of West Africa, Indonesia and
Brazil, potential drilling sites have been identified where
surrounding seas and weather conditions are relatively mild and
calm in comparison to other, more volatile sites such as the Gulf
of Mexico and the North Sea. These recently discovered sites tend
to have favorable producing characteristics, yield positive
exploration success rates, and admit to production using simple
drilling techniques similar to those employed in dry land or
near-shore operations.
[0006] However, since lognormal distributions of recoverable
reserves tend to be spread over a large number of small fields,
each of which yield less than would normally be required in order
to justify the expense of a conventional large-scale operation,
these regions have to date been underexplored and underproduced
relative to its potential. Consequently, many potentially
productive smaller fields have already been discovered, but remain
undeveloped due to economic considerations. In response, explorers
and producers have adapted their technologies in an attempt to
achieve greater profitability by downsizing the scale of operations
and otherwise reducing expense, so that recovery from smaller
fields makes more financial sense, and the delay between investment
and profitability is reduced.
[0007] For example, in published Patent Application No. US
2001/0047869 A1 and a number of related pending applications and
patents issued to Hopper et al., various methods of drilling
deepwater wells are provided in which adjustments to the drilling
system can be made so as to ensure a better recovery rate than
would otherwise be possible with traditional fixed-well
technologies. However, the Hopper system cannot be adjusted during
completion, testing and production of the well, and is especially
ineffective in instances where the well bore starts at a mud line
in a vertical position. The Hopper system also fails to support a
variety of different surface loads, and is therefore self-limiting
with respect to the flexibility drillers desire during actual
operations.
[0008] In U.S. Pat. No. 4,223,737 to O'Reilly, a method is
disclosed in which the problems associated with traditional,
vertically oriented operations are addressed. The method of
O'Reilly involves laying out a number of interconnected,
horizontally disposed pipes in a string just above the sea floor
(along with a blow out preventer and other necessary equipment),
and then using a drive or a remote operated vehicle to force the
string horizontally into the drilling medium. The O'Reilly system,
however, is inflexible in that it fails to admit to practice while
the well is being completed and tested. Moreover, the method
utterly fails to contemplate functionality during production and
workover operations. In short, the O'Reilly reference is helpful
only during the initial stages of drilling a well, and would
therefore not be looked to as a systemic solution for establishing
and maintaining a deepwater exploration and production
operation.
[0009] Other offshore operators have attempted to solve the
problems associated with deepwater drilling by effectively "raising
the floor" of an underwater well by disposing a submerged wellhead
above a self-contained, rigid framework of pipe casing that is
tensioned by means of a gas filled, buoyant chamber. For example,
as seen in prior U.S. Pat. No. 6,196,322 B1 to Magnussen, the
Atlantis Deepwater Technology Holding Group has developed an
artificial buoyant seabed (ABS) system, which is essentially a gas
filled buoyancy chamber deployed in conjunction with one or more
segments of pipe casing disposed at a depth of between 600 and 900
feet beneath the surface of a body of water. After the ABS wellhead
is fitted with a blowout preventer during drilling, or with a
production tree during production, buoyancy and tension are
imparted by the ABS to a lower connecting member and all internal
casings. The BOP and riser (during drilling) and production tree
(during production), are supported by the lifting force of the
buoyancy chamber. Offset of the wellhead is reasonably controlled
by means of vertical tension resulting from the buoyancy of the
ABS.
[0010] The Atlantis ABS system is deficient, however, in several
practical respects. For example, the '322 Magnussen patent
specifically limits deployment of the buoyancy chamber to
environments where the influence of surface waves is effectively
negligible, i.e., at a depth of more than about 500 feet beneath
the surface. Those of ordinary skill in the art will appreciate
that deployment at such depths is an expensive and relatively
risk-laden solution, given that installation and maintenance can
only be carried out by deep sea divers or remotely operated
vehicles, and the fact that a relatively extensive transport system
must still be installed between the top of the buoyancy chamber and
the bottom of an associated recovery vessel in order to initiate
production from the well.
[0011] The Magnussen system also fails to contemplate multiple
anchoring systems, even in instances where problematic drilling
environments are likely to be encountered. Moreover, the system
lacks any control means for controlling adjustment of either
vertical tension or wellhead depth during production and workover
operations, and expressly teaches away from the use of lateral
stabilizers that could enable the wellhead to be deployed in
shallower waters subject to stronger tidal and wave forces.
[0012] Thus, there is plainly a widespread need for a system and
method of disposing an offshore wellhead in a manner such that
drillers can adjust both the depth of a wellhead and the vertical
tension applied to associated pipe casing throughout the duration
of exploration and production operations. There is also a need for
an adjustable buoyancy chamber system capable of maintaining
approximately constant vertical tension on an associated drilling
or production string, and adjusting either the height of a wellhead
at any time during exploration and production by releasing
additional lengths of tension line from a buoyancy chamber height
adjustment member. There is also a need for an offshore exploration
and production system that flexibly admits to use in connection
with both deepwater and shallow target horizons, without
necessarily being configured to conform to any particular
operational depth.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a side view of an offshore exploration and
production system in which an adjustable buoyancy chamber is
employed to adjust the height or depth of an associated well
terminal member.
[0014] FIGS. 2A and 2B are side views of an offshore exploration
and production system, in which lateral and vertical forces on an
adjustable buoyancy chamber are held approximately constant while
the height of an associated well terminal member is adjusted by
releasing additional lengths of tension line.
SUMMARY OF THE INVENTION
[0015] A system and method of establishing an offshore exploration
and production system is provided, in which a well casing is
disposed in communication with an adjustable buoyancy chamber and a
well hole bored into the floor of a body of water. A lower
connecting member joins the well casing and the chamber, and an
upper connecting member joins the adjustable buoyancy chamber and a
well terminal member. The chamber's adjustable buoyancy enables an
operator to vary the height or depth of the well terminal member,
and to vary the vertical tension imparted to drilling and
production strings throughout exploration and production
operations. Also provided is a system and method of adjusting the
height or depth of a wellhead while associated vertical and lateral
forces remain approximately constant. A variety of well isolation
members, lateral stabilizers and anchoring means, as well as
several methods of practicing the invention, are also
disclosed.
DETAILED DESCRIPTION
[0016] Referring now to the specific, non-limiting embodiment of
the invention depicted in FIG. 1, an offshore exploration and
production system is provided, comprising a well casing 2 installed
in communication with a submerged well 1 and an adjustable buoyancy
chamber 9, wherein a lower connecting member 5 is disposed between
the well casing and the adjustable buoyancy chamber. In a presently
preferred embodiment, the well 1 is accessed from above by means of
a well hole 3 that has been bored into an associated sea floor
surface. In a typical embodiment, a well casing 2 is set into the
hole in a firm and secure manner, and then cemented into place
using known downhole technology. In other embodiments, a well
casing is securely set into the well hole 3, and a fluid transport
member, such as a smaller-diameter pipe or pipe casing, is inserted
into well casing 2. Once a desired fit has been achieved, the outer
surface of the fluid transport member is cemented or set with a
packer to the inner surface of the well casing. Those of ordinary
skill in the art will appreciate that while the embodiment
described above refers to but a single well, the offshore
exploration and production system disclosed herein can be readily
adapted to simultaneously work multiple neighboring wells without
departing from the scope or spirit of the invention.
[0017] According to a one embodiment, a well isolation member 4 is
disposed between well casing 2 and a lower connecting member 5. In
some embodiments, well isolation member 4 comprises one or more
ball valves, which, if lower connecting member 5 is removed, can be
closed so that the well is effectively shut in. In further
embodiments, well isolation member 4 comprises a blowout preventer
or a shear ram that can be maintained in either an open or closed
position in order to provide access to, or to instead shut in, the
contents of well 1.
[0018] In other embodiments, lower connecting member 5 further
comprises one or more receiving members disposed to receive an
attachment member disposed on well isolation member 4. In an
alternative embodiment, lower connecting member 5 comprises an
attachment member for attaching said lower connecting member 5 to a
receiving member disposed on well isolation member 4. Methods and
means of securely fastening lower connecting member 5 to well
isolation member 4 are known to those of ordinary skill in the art,
and may comprise one or more of a wide variety of fastening
techniques, e.g., hydraulic couplers, various nut and bolt
assemblies, welded joints, pressure fittings (either with or
without gaskets), swaging, etc., without departing from the scope
or spirit of the present invention.
[0019] Likewise, lower connecting member 5 may comprise any known
connecting means appropriate for the specific application
contemplated by operators. For example, in various embodiments,
lower connecting member 5 comprises one or more of segments of
riser, riser pipe, and/or pipe casing. In some embodiments, lower
connecting member 5 comprises a concentric arrangement, for
example, a fluid transport member having a smaller outer diameter
than the inner diameter of a pipe casing in which the fluid
transport member is housed.
[0020] In further embodiments, lower connecting member 5 is
disposed in communication with one or more lateral stabilizers 6,
which, when deployed in conjunction a plurality of tension lines 7,
effectively controls horizontal offset of the system. By utilizing
the buoyant forces of adjustable buoyancy chamber 9, lower
connecting member 5 is drawn taut and held in a stable
position.
[0021] In an alternative embodiment, one or more stabilizers 6
control horizontal offset of lower connecting member 5, and the
height or depth of an associated well terminal member 14 is
adjusted by varying the length of upper connecting member 12. In
some embodiments, the vertical tension of lower connecting member 5
is held approximately constant while the height or depth of well
terminal member 14 is adjusted. In further embodiments, the height
or depth of well terminal member 14 is held approximately constant,
while the vertical tension imparted by adjustable buoyancy chamber
9 on lower connecting member 5 is adjusted. In still further
embodiments, the height or depth of well terminal member 14 and the
vertical tension applied to lower connecting member 5 are held
approximately constant, while lateral adjustments are performed
using lateral stabilizer 6 and one or more of tension lines 7.
[0022] In certain embodiments, one or more lateral tension lines 7
are individually adjustable, whereas in other embodiments, the
tension lines 7 are collectively adjustable. In further
embodiments, one or more tension lines 7 are both individually and
collectively adjustable. In still further embodiments, the one or
more lateral stabilizers 6 are disposed in communication with a
tension measuring means, so that a fixed or predetermined amount of
lateral tension can be applied to lower connecting member 5 in
order to better control system offset. In some embodiments, the
tension lines 7 are anchored to the sea floor by means of an
anchoring member 8, for example, a suction type anchor, or
alternatively, a mechanical or conventional deadweight type
anchor.
[0023] In a presently preferred embodiment, adjustable buoyancy
chamber 9 is approximately annular in shape, so that lower
connecting member 5 can be passed through a void longitudinally
disposed in a central portion of the device. In further
embodiments, adjustable buoyancy chamber 9 further comprises a
plurality of inner chambers. In still further embodiments, each of
the chambers is independently operable, and different amounts of
air or gas (or another fluid) are disposed in the chambers to
provide greater adjustable buoyancy control. In one example
embodiment, adjustable buoyancy chamber 9 further comprises a fluid
ballast that can be ejected from the chamber, thereby achieving
greater chamber buoyancy and lending additional vertical tension to
lower connecting member 5. Those of ordinary skill in the art will
appreciate that many appropriate fluid ballast can be used to
increase or retard buoyancy; for example, compressed air is an
appropriate fluid that is both inexpensive and readily
available.
[0024] In some embodiments, adjustable buoyancy chamber 9 further
comprises a ballast input valve, so that a fluid ballast can be
injected into the chamber from an external source, for example,
through an umbilical line run to the surface or a remote operated
vehicle, so that an operator can deliver a supply of compressed gas
to the chamber via the umbilical, thereby adjusting buoyancy
characteristics as desired. In other embodiments, the fluid input
valve is disposed in communication with one or more pumps or
compressors, so that the fluid ballast is delivered to the chamber
under greater pressure, thereby effecting the desired change in
buoyancy more quickly and reliably.
[0025] In other embodiments, adjustable buoyancy chamber 9 further
comprises a ballast output valve, so that ballast can be discharged
from the chamber. In instances where air or another light fluid is
injected into the chamber while water or another heavy liquid is
discharged, the chamber will become more buoyant and increase
vertical tension on lower connecting member 5. Conversely, if water
or another heavy liquid is injected into the chamber while air is
bled out, the chamber will lose buoyancy, thereby lessening
vertical tension on lower connecting member 5.
[0026] In alternative embodiments, the ballast output valve is
disposed in communication with one or more pumps or compressors, so
that ballast is ejected from the chamber in a more reliable and
controlled manner. In some embodiments, the ballast output valve is
disposed in communication with an umbilical, so that ballast
ejected from the chamber can be recovered or recycled at the
surface. In any event, a principle advantage of the present
invention is that adjustments to the chamber's buoyancy and
tensioning properties, and the ability to control the height of the
well terminal member 14, can be performed at any time during either
exploration or production, due to the various ballast input and
output control means disposed about the body of the chamber.
[0027] In further embodiments, adjustable buoyancy chamber 9 is
further disposed in communication with one or more tension lines 10
provided to anchor the adjustable buoyancy chamber to the sea
floor. As before, tension lines 10 are anchored to the sea floor
using known anchoring technology, for example, suction anchors or
dead weight type anchors, etc. The one or more tension lines 10 can
also provide additional lateral stability for the system,
especially during operations in which more than one well is being
worked. In one embodiment, the one or more tension lines 10 are run
from the adjustable buoyancy chamber 9 to the surface, and then
moored to other buoys or a surface vessel, etc., so that even
greater lateral tension and system stability are achieved. In
further embodiments, the tension lines 10 are individually
adjustable, whereas in other embodiments, the tension lines 10 are
collectively controlled. In still further embodiments, the one or
more tension lines 10 are both individually and collectively
adjustable.
[0028] In one example embodiment, adjustable buoyancy chamber 9 is
disposed in communication with a vertical tension receiving member
11. In another embodiment, the vertical tension receiving member 11
is equipped with a tension measuring means (e.g., a load cell,
strain gauge, etc.), so that vertical tension applied to lower
connecting member 5 is imparted in a more controlled and efficient
manner. In another embodiment, the buoyant force applied to tension
receiving member 11 is adjusted by varying the lengths of tension
lines 10, while the buoyancy of adjustable buoyancy chamber 9 is
held approximately constant. In a further embodiment, the buoyancy
of adjustable buoyancy chamber 9 is controlled by means of one or
more individually selectable ballast exhaust ports disposed about
the body of the chamber, which vent excess ballast fluid to the
surrounding sea. In still further embodiments, the open or closed
state of the ballast exhaust ports are individually controlled
using port controllers known to those of ordinary skill in the art
(e.g., plugs, seacocks, etc.)
[0029] In a presently preferred embodiment, the system is disposed
so that a well terminal member 14 installed above buoyancy chamber
9 is submerged to a depth at which maintenance and testing can be
carried out by SCUBA divers using lightweight, flexible diving
equipment, for example, at a depth of about 100 to 300 feet beneath
the surface. In some embodiments, the well terminal member 14 is
submerged only to the minimum depth necessary to provide topside
access to the hulls of various surface vessels servicing the well,
meaning that well terminal member 14 could also be disposed at a
much shallower depth, for example, a depth of about 50 to 100 feet.
In alternative embodiments, well terminal member 14 is disposed at
depths of less than 50 feet, or greater than 300 feet, depending
upon the actual conditions surrounding operations. In still further
embodiments, well terminal member 14 is disposed either at the
surface or above the surface of the water, and a blowout preventer
or a production tree is installed by workers operating aboard a
service platform or surface vessel. This "damp tree" model avoids
the need to assemble long subsurface riser stacks, as would
generally be required during deepwater operations. Moreover,
disposing the well terminal member at or near the surface also
permits testing and maintenance to be carried out by SCUBA divers
or surface crews, without the need for expensive and time-consuming
remote operated vehicle operations.
[0030] In some embodiments, well terminal member 14 further
comprises either a blowout preventer or a production tree. In a
presently preferred embodiment, however, well terminal member 14
further comprises a combined blowout preventer and production tree
assembly configured so as to facilitate simplified well
intervention operations.
[0031] In some embodiments, lower connecting member 5 terminates
within the void formed in a center portion of the annular chamber
9, at which point an upper connecting member 12 becomes the means
by which fluids are transported up to the wellhead. In other
embodiments, lower connecting member 5 does not terminate within
the void formed in a center portion of the annular chamber, but
instead runs through the void and is subsequently employed as an
upper connecting member 12 disposed between the chamber and the
wellhead. In other embodiments, a vertical tension receiving member
11 is disposed between the buoyancy chamber 9 and upper connecting
member 12, so that the chamber's buoyant forces are transferred to
the vertical tension receiving means 11, thereby applying vertical
tension to the drilling or production string extended below the
chamber.
[0032] In further embodiments, upper connecting member 12 further
comprises a well isolation member 13, e.g., one or more ball valves
or blowout preventers, used to halt fluid flow in the event that
well terminal member 14 is either removed or disabled, for example,
during testing and maintenance operations. Those of ordinary skill
in the art will appreciate that the precise types and exact
locations of isolation valves 13 employed in the system are
variable and flexible, the only real requirement being that the
valves are capable of allowing or preventing fluid flow from the
well 1 during periods in which testing or maintenance, or even an
emergency safety condition, are present.
[0033] For example, well terminal member 14 can be equipped with a
production tree so that a production hose disposed on a surface
vessel can be attached to the system and production can commence.
Alternatively, well terminal member 14 can terminate in a blowout
preventer, so that the well will not blow out during drilling
operations. In other embodiments, well terminal member 14
terminates in a combined production tree and blowout preventer
assembly to facilitate simplified well intervention operations.
[0034] Turning now to the specific, non-limiting embodiments of the
invention depicted in FIGS. 2A and 2B, a system and method of
establishing a height-variable well terminal member is provided,
comprising a lower fluid transport pipe 21, an inner well casing
22, an outer well casing 23, and a wellhead 24. In some
embodiments, a well isolation member 25 is disposed above the
wellhead 24, so that the well can be closed off or shut in if
desired.
[0035] In the example embodiment depicted in FIG. 2A, well
isolation member 25 further comprises one or more ball valves that
can be adjustably opened or closed as desired by an operator. A
lower connecting member 26 having one or more interior seals 27 and
an interior polished bore 28 houses a fluid transport member 29
such that the height of fluid transport member 29 is variably
adjustable within a body portion of lower connecting member 26 in
response to vertical lifting forces imparted by adjustable buoyancy
chamber 30. Various lengths of pipe define the height of an upper
connecting member disposed between the buoyancy chamber 30 and a
well terminal member 36. In some embodiments, an upper well
isolation member 35, such as a ball valve or a blowout preventer,
is disposed in communication with the upper connecting member
between buoyancy chamber 30 and well terminal member 36.
[0036] In some embodiments, the system is moored to the sea floor
using one or more mooring lines 31 connected to a first vertical
tension receiving means 32a, while buoyancy chamber 30 is raised or
lowered by either spooling-out or reeling-in lengths of one or more
tension lines 37 disposed between a second vertical tension
receiving means 32b and a chamber height adjustment means 33. As
adjustable buoyancy chamber 30 rises, vertical tension is applied
to vertical tension receiving member 34, which in turn lifts well
terminal member 36 up toward the surface.
[0037] As seen in the example embodiment depicted in FIG. 2B, the
height of both the well terminal member 36 and fluid transport
member 29 are vertically adjusted by increasing the length of
tension lines 37 using chamber height adjustment means 33, even as
vertical and lateral tension on mooring lines 31 and tension lines
37 remains approximately constant. In one embodiment, vertical
tension on lower connecting member 26 is also kept approximately
constant during this process, since fluid transport member 29 is
moved vertically within a body portion of lower connecting member
26. In another embodiment, a second, lower adjustable buoyancy
chamber is added to the system to maintain tension on lower
connecting member 26, while the height of the well terminal member
is adjusted as described above.
[0038] The foregoing specification is provided for illustrative
purposes only, and is not intended to describe all possible aspects
of the present invention. Moreover, while the invention has been
shown and described in detail with respect to several exemplary
embodiments, those of ordinary skill in the pertinent arts will
appreciate that minor changes to the description, and various other
modifications, omissions and additions may also be made without
departing from either the spirit or scope thereof.
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