U.S. patent application number 09/915011 was filed with the patent office on 2001-11-15 for emergency dump apparatus for buoyancy air tanks on buoyant riser systems.
Invention is credited to Fisher, Edmund A..
Application Number | 20010041098 09/915011 |
Document ID | / |
Family ID | 23329917 |
Filed Date | 2001-11-15 |
United States Patent
Application |
20010041098 |
Kind Code |
A1 |
Fisher, Edmund A. |
November 15, 2001 |
Emergency dump apparatus for buoyancy air tanks on buoyant riser
systems
Abstract
An apparatus for rapid venting of the compressed air and
deballasting of a buoyant air tank in a positively buoyant riser
system in the event of a premature drive off or a riser section
parting is shown. The rapid venting of the compressed air ensures
that the riser section cannot rapidly ascend to the surface and
damage the drilling rig positioned above. In a first embodiment,
the buoyancy tank or housing includes a circumferentially shaped
channel positioned on its upper end. An annularly shaped ring is
placed over the circumferentially shaped channel and sealed in
place by a frangible weld. A tether line attaches to the annularly
shaped ring and extends to an anchor point on the BOP stack below.
In the event of a catastrophic parting of the riser, as the riser
sections and attached buoyancy tank or housings begin ascending,
the tether line is drawn tight. Further ascension of the buoyancy
tank or housings, causes the frangible weld joints to break and
peel back the annularly shaped ring, exposing the circumferentially
shaped channel. This causes an immediate and complete venting of
the buoyancy tank or housings, rendering them negatively buoyant.
Alternate embodiments using an annularly shaped flange releasable
by toggle clamps or retainer pins are also shown.
Inventors: |
Fisher, Edmund A.; (Houston,
TX) |
Correspondence
Address: |
JACKIE LEE DUKE
1001 WEST LOOP SOUTH
SUITE 100
HOUSTON
TX
77027
|
Family ID: |
23329917 |
Appl. No.: |
09/915011 |
Filed: |
July 25, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09915011 |
Jul 25, 2001 |
|
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|
09753348 |
Jan 2, 2001 |
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Current U.S.
Class: |
405/224.2 ;
166/367 |
Current CPC
Class: |
E21B 17/012
20130101 |
Class at
Publication: |
405/224.2 ;
166/367 |
International
Class: |
E21B 017/01 |
Claims
What is claimed is:
1. An emergency dump apparatus for buoyancy tanks or housings on
buoyant riser systems in a subsea environment, comprising: a
buoyancy housing positioned about a riser section, said buoyancy
housing including a frangible section; a sensing means; a remote
releasing means positioned on said frangible section of said
buoyancy housing and controlled by said sensing means, said sensing
means activating said remote releasing means upon a parting of said
riser to detach said frangible section from said buoyancy housing
and flood said buoyancy housing.
2. An emergency dump apparatus for buoyancy tank or housings used
on buoyant riser systems in a subsea environment according to claim
1 wherein: said frangible section of said buoyancy housing includes
an annular flange sealing the annulus between said riser section
and said buoyancy housing to maintain pressure within said buoyancy
housing prior to detachment of said frangible section.
3. An emergency dump apparatus for buoyancy tank or housings used
on buoyant riser systems in a subsea environment according to claim
2 wherein: said sensing means is responsive to a parting of the
riser.
4. An emergency dump apparatus for buoyancy tank or housings used
on buoyant riser systems in a subsea environment according to claim
3 wherein: said remote releasing means is an explosive bolt
assembly.
Description
[0001] This is a divisional application of application Ser. No.
09/753,348 filed Jan. 2, 2001, hereby incorporated herein by
reference; which is a divisional application of application Ser.
No. 09/339,630 filed Jun. 24, 1999, now U.S. Pat. No. 6,193,441,
hereby incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to a novel apparatus for quickly
releasing the air from buoyancy tanks or housings in those
situations when a quick deballasting of the buoyancy tanks or
housings is required. A typical situation where this might occur is
the case of a free-standing drilling riser that replaces most of
the rig tension with positive buoyancy provided by buoyancy tanks
or housings mounted on the riser sections. In the event of a
catastrophic riser failure, i.e., where the riser below the
buoyancy tanks or housings has parted or a bottom release in a
dynamically positioned vessel drive off, the positively buoyant
riser sections with attached buoyancy tanks or housings would
ascend to the surface with increasing velocity to impact the
drilling rig's or ship's hull with sufficient force to seriously
damage the drilling rig. In the extreme case, the impact of the
riser and buoyancy tank or buoyancy housing could sufficiently
damage the drilling rig or ship to cause it to sink and lives to be
lost.
[0004] The use of such positively buoyant risers with buoyancy
tanks or housings providing the buoyancy is well known to those of
ordinary skill in the art. Typical use dictates several riser
sections will have buoyancy tanks or housings attached, depending
on the water depth, to leave the riser disconnected and free
standing or at least minimize the load on the rig's tensioner
system while connected. The buoyancy tanks or housings are usually
constructed with an open lower end to facilitate filling of the
buoyancy tanks or housings by compressed air or other suitable gas.
The volume and pressure of the supplied compressed air is
determined by the water depth in which the buoyancy tanks or
housings are to be used. Various methods of filling the buoyancy
tank or housings either individually or in groups are well known to
those of ordinary skill in the art.
[0005] Once the riser sections with attached buoyancy tanks or
housings are in place the present invention has particular
applicability. In the event the riser should fail as noted above, a
particularly hazardous situation is presented by the positively
buoyant tanks or housings. The present invention minimizes this
hazardous situation by allowing a means to vent or deballast the
buoyancy tank or housings in a few seconds. It is the rapid venting
or deballasting of these buoyancy tanks or housings to which the
present invention most closely applies.
[0006] 2. Description of Related Art
[0007] A marine riser with open bottom air cans is shown in U.S.
Pat. No. 4,099,560 (Fischer et al.) The apparatus shown by Fischer
et al. discloses an air dump valve attached to a tether line that
is activated in the event of the riser parting.
[0008] U.S. Pat. No. 4,176,986 to Taft et al. discloses another
type of riser system with buoyancy tanks attached. A dump valve for
rapidly venting the compressed air and controlled by a pilot valve
assembly is shown.
[0009] Another marine riser with buoyancy system is disclosed in
U.S. Pat. No. 4,422,801 (Hale et al.) The system shown by Hale et
al. uses a quarter turn ball valve actuated by a trigger cable and
air cylinder to vent the buoyancy air tanks.
[0010] U.S. Pat. No. 4,646,840 to Bartholomew et al., owned by the
assignee of the current invention, discloses a buoyancy tank or
housing system with a cascading system for supplying air to the
buoyancy tank or housings.
[0011] All these systems are too slow for a dynamically positioned
vessel that must vent in less than thirty seconds to avoid damage
to the drilling vessel.
SUMMARY OF THE INVENTION
[0012] The current invention uses a frangible joint or connection
to allow for rapid venting of the compressed air and deballasting
of a buoyancy tank or housing in a positively buoyant riser system
in the event of a riser section parting. The rapid venting of the
compressed air ensures that the riser section cannot rapidly ascend
to the surface and damage the drill rig positioned above.
[0013] According to the present invention, in a first embodiment of
the invention, the buoyancy tank or housing includes a
circumferentially shaped channel positioned on its upper face. An
annularly shaped cover plate is placed over the circumferentially
shaped channel and sealed in place by a frangible weld. The
annularly shaped cover plate includes a ring positioned on its
lower face to which a tether line is anchored. The tether line
extends downwardly to similarly positioned rings on the subsequent
riser sections and buoyancy tanks or housings. The tether line
extends from the lowermost buoyancy tank or housing and is anchored
on the BOP stack below. In the event of a catastrophic parting of
the riser, as the riser sections and attached buoyancy tanks or
housings begin ascending, the tether line is drawn tight. Further
ascension of the buoyancy tanks or housings, causes the frangible
weld joints to break and peel back the cover plate, exposing the
circumferentially shaped channels. This causes an immediate and
complete venting of the buoyancy tanks or housings, rendering them
negatively buoyant.
[0014] In a second embodiment of the invention, the buoyancy tank
or housing includes an annularly shaped flange positioned on the
top. The annularly shaped flange has a weld joint on its interior
and a seal on its exterior to seal against the riser sections and
buoyancy tank or housing, respectively. The flange is retained by a
plurality of toggle retainer clamps. The toggle retainer clamps are
connected to a tether line that extends from the lowermost buoyancy
tank or housing and is anchored on the BOP stack below. In the
event of a catastrophic parting of the riser, the parting of the
riser causes the tether line to release frangible retainer pins
holding the toggle retainer clamps thereby releasing the annularly
shaped flange from the buoyancy housing. This causes an immediate
and complete venting of the buoyancy tanks or housings, rendering
them negatively buoyant.
[0015] In a third embodiment of the invention, the buoyancy tank or
housing includes an annularly shaped flange positioned on the top.
The annularly shaped flange has a weld joint on its interior and a
seal on its exterior to seal against the riser sections and
buoyancy tank or housing, respectively. The flange is retained by a
plurality of retainer pin assemblies. The retainer pin assemblies
are connected to a tether line that extends from the lowermost
buoyancy tank or housing and is anchored on the BOP stack below. In
the event of a catastrophic parting of the riser, the parting of
the riser causes the tether line to release removable retainer pins
thereby releasing the annularly shaped flange from the buoyancy
tank or housing. This causes an immediate and complete venting of
the buoyancy tanks or housings, rendering them negatively
buoyant.
[0016] In a fourth embodiment of the invention, the buoyancy tank
or housing includes an annularly shaped flange positioned on the
top. The annularly shaped flange has a weld joint on its interior
and a seal on its exterior to seal against the riser sections and
buoyancy tank or housing, respectively. The flange is retained by a
plurality of explosive bolt assemblies. The explosive bolt
assemblies are connected to a transceiver box connected to the
explosive bolt assemblies. In the event of a catastrophic parting
of the riser, a signal is transmitted to the transceiver box that
in turns fires the explosive bolt assemblies. The release of the
explosive bolt assemblies allows the annularly shaped flange to be
released from the buoyancy tank or housing. This causes an
immediate and complete venting of the buoyancy tanks or housings,
rendering them negatively buoyant.
[0017] A principal object of the present invention is to provide an
apparatus to quickly vent the air from buoyancy tanks or housings
thereby preventing their uncontrolled and rapid ascension to the
surface.
[0018] Another object of the present invention is to provide an
apparatus to quickly vent the air from buoyancy tanks or housings
without requiring any operator intervention in the event the riser
parts.
[0019] These with other objects and advantages of the present
invention are pointed out with specificness in the claims annexed
hereto and form a part of this disclosure. A full and complete
understanding of the invention may be had by reference to the
accompanying drawings and description of the preferred
embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] These and other objects and advantages of the present
invention are set forth below and further made clear by reference
to the drawings, wherein:
[0021] FIG. 1 is an elevation view of a riser system with buoyancy
tank or housings used in subsea oil and gas drilling operations
that incorporates the emergency dump apparatus of the present
invention
[0022] FIG. 2 is an isometric view of the first embodiment of the
emergency dump apparatus prior to being activated.
[0023] FIG. 3 is an isometric view of the first embodiment of the
emergency dump apparatus after activation.
[0024] FIG. 4 is a sectional view of the second embodiment of the
emergency dump apparatus prior to being activated.
[0025] FIG. 5 is a sectional view of the second embodiment of the
emergency dump apparatus after activation.
[0026] FIG. 6 is a sectional view of the third embodiment of the
emergency dump apparatus prior to being activated.
[0027] FIG. 7 is a sectional view of the third embodiment of the
emergency dump apparatus after activation.
[0028] FIG. 8 is a sectional view of the fourth embodiment of the
emergency dump apparatus prior to being activated.
[0029] FIG. 9 is a sectional view of the fourth embodiment of the
emergency dump apparatus after activation.
DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS
[0030] With reference to the drawings, and particularly to FIG. 1,
subsea drilling riser system 100 is shown in an elevation view.
Subsea drilling riser system 100 extends from floating drilling rig
or vessel 102 to BOP stack 104 located on ocean floor 106. Subsea
drilling riser system 100 is composed of a plurality of riser
sections 108 connected in end to end relationship by suitable
mechanical means as end connections 110 which may be threaded
connections, flanged end connections or clamp hub connections as is
well known to those of ordinary skill in the art. Some of riser
sections 108 have buoyancy tank or housings 112 clamped thereon or
they may be integrally formed therewith without departing from the
scope of the invention. Buoyancy tank or housings 112 air filled
with compressed air to provide buoyancy to subsea drilling riser
system 100 thereby lessening or obviating the need for a riser
tensioner system. Upper riser connector 114 is provided near the
upper end of riser system 100 to allow drilling rig 102 to
disconnect from riser system 100 in the event of a drive off or
inclement weather that necessitates the suspension of drilling
operations. Tether line 116, of suitable material as chain, wire or
polyester rope, extends from buoyancy tank or housings 112 to BOP
stack 104 below the lower marine riser package where it is anchored
for purposes that will be explained hereinafter.
[0031] As best seen in FIGS. 2 and 3, the first embodiment of the
present invention includes buoyancy tank or housing 210 attached to
riser section 108. Buoyancy tank or housing 210 includes frangible
section 212 to which actuation ring 214 is attached. Tether line
116 is connected to actuation ring 214 and extends downwardly to
BOP stack 104 as previously noted. Frangible section 212 includes
circumferentially shaped channel 216 in buoyancy tank or housing
210 that is sealed by annularly shaped ring 218.
[0032] Annularly shaped ring 218 is sealed by frangible welded
joint 220. Annularly shaped ring 218 extends circumferentially
around buoyancy tank or housing 210 and is sealed completely around
its periphery by frangible welded joint 220. Frangible welded joint
220 is sized to break when a suitable predetermined force is
applied by tether line 116. Restraining line 222 extends between
buoyancy tank or housing 210 and riser section 108 and connects to
restraining hoops 224 that are welded to buoyancy tank 210 and
riser section 108. In the event of a catastrophic riser failure,
i.e., where the riser below the buoyancy tanks or housings has
parted, the positively buoyant riser sections 108 with attached
buoyancy tank or housings 210 will ascend to the surface with
increasing velocity unless the compressed air in buoyancy tank or
housings 210 is vented immediately. As positively buoyant riser
sections 108 with attached buoyancy tank or housings 210 start to
ascend toward the surface, tether line 116 is drawn taut and begins
pulling on actuation ring 214. As best seen in FIG. 3, continued
ascent of riser sections 108 with attached buoyancy tank or
housings 210 causes frangible welded joint 220 to break and peel
annularly shaped ring 218 from buoyancy tank or housings 210. This
detachment of annularly shaped ring 218 leaves circumferentially
shaped channel 216 open to sea water and thereby venting the
compressed air from buoyancy tank or housings 210 and rendering
riser sections 108 negatively buoyant. Restraining line 222 ensures
that buoyancy tank or housing 210 does not completely separate from
riser section 108 and thereby aids in salvage operations.
[0033] A second embodiment of the present invention is shown in
FIGS. 4 and 5. Those items that are the same as in the first
embodiment retain the same numeric designation. As in the first
embodiment, riser section 108 has buoyancy tank or housing 310
attached thereto. Buoyancy tank or housing 310 has toggle clamp
assembly 312 positioned at its upper end to which actuation arm 314
is attached. Tether line 116 is connected to actuation arm 314 and
extends downwardly to BOP stack 104 as previously noted. Toggle
clamp assembly 312 holds toggle retainer clamps 322 in engagement
retaining annularly shaped flange 316 that seals inside the top of
buoyancy tank or housing 310 with an annular seal ring 320.
Annularly shaped flange 316 is attached and sealed against riser
section 108 by welds 318.
[0034] Rapidly removable section such as annularly shaped flange
316 is held by in sealing engagement with buoyancy tank or housing
310 by toggle retainer clamps 322. Toggle retainer clamps 322
include a frangible retainer pin 324. Frangible retainer pin 324 is
sized to break when a suitable predetermined force is applied by
tether line 116. Restraining line 326 extends between buoyancy tank
or housing 310 and riser section 108 and connects to restraining
hoops 328 that are welded to buoyancy tank 310 and riser section
108. As in the previous embodiments when a catastrophic riser
failure occurs the ascent of positively buoyant riser sections 108
with attached buoyancy tank or housings 310 causes tether line 116
to be drawn taut and begins pulling on actuation arm 314. As best
seen in FIG. 5, continued ascent of riser sections 108 with
attached buoyancy tank or housings 310 causes frangible retainer
pin 324 to break and toggle retainer clamps 322 to release
annularly shaped flange 316 from buoyancy tank or housings 310.
This detachment of annularly shaped flange 316 allows buoyancy tank
or housing 310 to vent the compressed air therein and render riser
sections 108 negatively buoyant. Restraining line 326 ensures that
buoyancy tank or housing 310 does not completely separate from
riser section 108 and thereby aids in salvage operations.
[0035] A third embodiment of the present invention is shown in
FIGS. 6 and 7. Those items that are the same as in the first
embodiment retain the same numeric designation. As in the first
embodiment, riser section 108 has buoyancy tank or housing 410
attached thereto. Buoyancy tank or housing 410 has retainer pin
assembly 412 positioned at its upper end to which actuation arm 414
is attached. Tether line 116 is connected to actuation arm 414 and
extends downwardly to BOP stack 104 as previously noted. Retainer
pin assembly 412 holds retainer arm 416 in engagement retaining
annularly shaped flange 418 that seals inside the top of buoyancy
tank or housing 410 with an annular seal ring 420. Rapidly
removable section such as annularly shaped flange 418 is attached
and sealed against riser section 108 by welds 422.
[0036] Annularly shaped flange 418 is held by in sealing engagement
with buoyancy tank or housing 410 by retainer arm 416. Retainer arm
416 is held in position by retainer pin assembly 412 that includes
removable retainer pin 424. Removable retainer pin 424 is released
when a suitable predetermined force is applied by tether line 116
to actuation arm 414 and pivoting retainer pin assembly 412
outwardly. Restraining line 426 extends between buoyancy tank or
housing 410 and riser section 108 and connects to restraining hoops
428 that are welded to buoyancy tank 410 and riser section 108. As
in the previous embodiments when a catastrophic riser failure
occurs the ascent of positively buoyant riser sections 108 with
attached buoyancy tank or housings 410 causes tether line 116 to be
drawn taut and begins pulling on actuation arm 414. As best seen in
FIG. 7, continued ascent of riser sections 108 with attached
buoyancy tank or housings 410 causes retainer pin assembly 412 to
pivot outward and withdraw retainer pin 424 from retainer arm 416
to release annularly shaped flange 418 from buoyancy tank or
housings 410. This detachment of annularly shaped flange 418 allows
buoyancy tank or housing 410 to vent the compressed air therein and
render riser sections 108 negatively buoyant. Restraining line 426
ensures that buoyancy tank or housing 410 does not completely
separate from riser section 108 and thereby aids in salvage
operations.
[0037] A fourth embodiment of the present invention is shown in
FIGS. 8 and 9. Those items that are the same as in the first
embodiment retain the same numeric designation. As in the first
embodiment, riser section 108 has buoyancy tank or housing 510
attached thereto. Buoyancy tank or housing 510 has explosive bolt
assembly 512 positioned at its upper end. A sensing means such as
transceiver box 514 is attached to buoyancy tank or housing
adjacent explosive bolt assembly 512. Control lead 516 connects
transceiver box 514 to a remote releasing means such as explosive
bolt assembly 512. Explosive bolt assembly 512 retains annularly
shaped flange 518 that seals inside the top of buoyancy tank or
housing 510 with an annular seal ring 520. Annularly shaped flange
518 is attached and sealed against riser section 108 by welds
522.
[0038] Rapidly removable section such as annularly shaped flange
518 is held in sealing engagement with buoyancy tank or housing 510
by explosive bolt assembly 512. Explosive bolt assembly 512 is
activated when upon detection of a parting of the riser a signal is
sent to a sensing means such as transceiver box 514. Such signal
could be mechanical, electrical, acoustic or hydraulic without
departing from the scope of the present invention. Restraining line
524 extends between buoyancy tank or housing 510 and riser section
108 and connects to restraining hoops 526 that are welded to
buoyancy tank 510 and riser section 108. When a catastrophic riser
failure occurs a signal is transmitted to transceiver box 514 that
in turns fires explosive bolt assembly 512 through control lead
516. As best seen in FIG. 9, the release of explosive bolt assembly
512 allows annularly shaped flange 518 to be released from buoyancy
tank or housings 510. This detachment of annularly shaped flange
518 allows buoyancy tank or housing 510 to vent the compressed air
therein and render riser sections 108 negatively buoyant.
Restraining line 524 ensures that buoyancy tank or housing 510 does
not completely separate from riser section 108 and thereby aids in
salvage operations.
[0039] My improved apparatus to provide for rapid venting of the
compressed air and deballasting of a buoyant air tank in a
positively buoyant riser system in the event of a riser section
parting and the methods of its application will be readily
understood from the foregoing description. Furthermore, while the
invention has been shown and described with respect to certain
preferred embodiments, it is obvious that equivalent alterations
and modifications will occur to others skilled in the art upon the
reading and understanding of the specification. The present
invention includes all such equivalent alterations and
modifications, and is limited only by the scope of the appended
claims.
* * * * *