BRIEF DESCRIPTION OF THE DRAWINGS
The invention is described in detail hereinafter on the basis of the embodiments represented in the accompanying figures, in which:
FIG. 1A is a side view in partial cross section of a disconnectable mooring system of prior art showing a mooring buoy connected to a vessel and a fluid transfer system;
FIG. 1B is a side view in partial cross section of the prior art disconnectable mooring system of FIG. 1A showing the mooring buoy disconnected from the vessel in the process of mooring;
FIG. 2A is a side view in partial cross section of a later disconnectable mooring system of prior art showing a mooring buoy connected to a vessel and a fluid transfer system;
FIG. 2B is a side view in partial cross section of the prior art disconnectable mooring system of FIG. 2A showing the mooring buoy disconnected from the vessel in the process of mooring;
FIG. 3A is a side view in partial cross section of a disconnectable subsurface buoy mooring system of prior art showing a mooring buoy connected to a vessel;
FIG. 3B is a side view in partial cross section of the prior art disconnectable subsurface buoy mooring system of FIG. 3A showing the mooring buoy disconnected from the vessel;
FIG. 4A is a side view in partial cross section of a disconnectable mooring system of prior art showing a mooring buoy with an onboard turret connected to a vessel;
FIG. 4B is a side view in partial cross section of the prior art disconnectable mooring system of FIG. 4A showing the mooring buoy disconnected from the vessel;
FIG. 5A is a side view of a floating cargo tanker ship moored to a disconnectable geostationary buoy according to an embodiment of the invention;
FIG. 5B is a side view of the cargo tanker ship of FIG. 5A disconnected from the buoy of FIG. 5A;
FIG. 6A is a side view of a floating production system moored by a detachable buoy according to an embodiment of the invention;
FIG. 6B is a side view of the floating production system of FIG. 6A disconnected from the buoy of FIG. 6A;
FIG. 7A is a side view of a floating LNG import/export terminal moored to a disconnectable geostationary buoy according to an embodiment of the invention;
FIG. 7B is a side view of the LNG import/export terminal of FIG. 7A disconnected from the buoy of FIG. 7A;
FIG. 8 is a side view in partial cross section of a mooring and fluid transfer system according to a preferred embodiment of the invention;
FIG. 9A is a side view in partial cross section of the mooring and fluid transfer system of FIG. 8 showing the mooring buoy detached from the vessel and supported by a line as if being retrieved to the ship;
FIG. 9B depicts in partial cross section an array of parts to be assembled onto the mooring buoy prior to disconnection from the vessel;
FIG. 10A is an enlarged side view cross section of the structural connector and buoy bearing assembly of FIG. 8, showing the structural connector connected to the buoy bearing hub;
FIG. 10B is an enlarged side view cross section of the structural connector and buoy bearing assembly of FIG. 8, showing the structural connector disconnected from the buoy bearing hub;
FIG. 11 is a cross section view taken along lines 11-11 of FIG. 8 looking down on the mooring buoy and showing a circumferential arrangement of hydraulic actuators that operate the structural connector;
FIG. 12 is a cross section view taken along lines 12-12 of FIG. 8 looking down on the mooring buoy and showing a circumferential arrangement of collet segments of the structural connector;
FIG. 13 is an enlarged side view exploded diagram of the buoy bearing assembly of FIG. 8 as it would be installed on the buoy;
FIG. 14A is an enlarged top view exploded diagram of the buoy bearing assembly of FIG. 8 showing a segmented ring and bearing hub;
FIG. 14B is an enlarged top view of completed assembly of FIG. 14A showing the segmented bearing ring assembled on the bearing hub;
FIG. 15 is a side view in partial cross section of an arrangement for sealing the opening at the structural connector when the buoy is disconnected therefrom; and
FIG. 16 is a side view in partial cross section of a mooring and fluid transfer system according to an alternative embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION
FIGS. 5A and 5B illustrate an embodiment of the invention used for mooring a cargo tanker ship 1 that is adapted for transporting liquid or pressurized gas hydrocarbon products. Tanker 1 typically requires frequent connection and disconnection from the mooring system and may be equipped with bow thrusters 3 to aid the recurring mooring process.
Mooring system 4, generally consisting of a geostationary buoy 5 that is detachably connectable to a structural connector 12 mounted to the bottom of the vessel 1, is adapted to temporarily moor the vessel, allowing the vessel to weathervane around the point of mooring under the influence of wind, waves and currents while it is being loaded. Mooring system 4 preferably includes a number of anchors 6 and anchor legs 7 that moor buoy 5 to the sea floor 9 so that the buoy is essentially geostationary.
The structural connector 12, fixed to vessel 1, is locked in axial engagement with the buoy but is free to rotate about the geostationary buoy. Mooring arrangement 4 provides a fluid flow path between a subsea well, pipeline, or component and the vessel when the vessel is moored to the buoy. The cargo is transported to or from ship 1 by pipeline 11 on seafloor 9, pipeline end manifold (PLEM) 10, flexible conductor 8, and fluid transfer system 13, located on ship 1. However, other fluid flow paths arrangements may be used as appropriate.
FIG. 5B shows ship 1 disconnected from buoy 5. Structural connector 12 remains on the ship. When the buoy 5 is completely detached from the vessel 1, the buoy 5 is designed and arranged to sink to a neutrally buoyant position about 36 meters below sea level 2. Unlike the mooring arrangements of FIGS. 1-3, the vessel 1 used with mooring system 4 does not carry a turret assembly revolvably disposed within the vessel hull. Neither axial bearings nor radial bearings remain on the vessel when the buoy is disconnected therefrom.
FIGS. 6A and 6B illustrate an embodiment of the invention used for mooring a floating production, storage, and offloading (FPSO) vessel 22. Production system 21 may be installed on vessel 22. This type system does not require frequent or rapid disconnection from the buoy. Disconnection and reconnection of this type system generally is done in fairly calm water conditions, but may occur in deteriorating weather conditions from an approaching hurricane. Advantages of quicker construction, less capital expense, and rapid offshore installation of the mooring system are provided by the invention.
Mooring system 26, generally consisting of a geostationary buoy 27 that is detachably connectable to a structural connector 28 mounted to the bottom of the vessel 22, is adapted to moor the vessel, allowing the vessel to weathervane around the point of mooring under the influence of wind, waves and currents. Mooring system 26 preferably includes a number of anchors and anchor legs 23 that moor buoy 27 to the sea floor so that the buoy is essentially geostationary.
In FIG. 6A, the structural connector 28, fixed to vessel 22, is locked in axial engagement with the buoy but is free to rotate about the geostationary buoy. Mooring arrangement 26 provides a fluid flow path between a subsea well 29 and the vessel when the vessel is moored to the buoy. Fluid is transported to FPSO 22 from the subsea well by a subsea manifold 24, flexible conductor 30 and fluid transfer system 25, located on FPSO 22. However, other fluid flow paths arrangements may be used as appropriate.
FIG. 6B shows FPSO 22 disconnected from buoy 27. Structural connector 28 remains on the vessel. When the buoy 27 is completely detached from the vessel 22, the buoy 27 is designed and arranged to sink to a neutrally buoyant position about 36 meters below sea level. Unlike the mooring arrangements of FIGS. 1-3, the vessel 22 used with mooring system 26 does not carry a turret assembly about which the vessel can revolve. Neither axial bearings nor radial bearings remain on the vessel when the buoy is disconnected therefrom.
FIGS. 7A and 7B illustrate an embodiment of the invention used with an LNG import/export terminal 35 including an LNG regas ship 36 that loads or offloads LNG cargo through flexible conductor 41. Mooring system 37, generally consisting of a geostationary buoy 38 that is detachably connectable to a structural connector 45 mounted to the bottom of the vessel 36, is adapted to moor the vessel, allowing the vessel to weathervane around the point of mooring under the influence of wind, waves and currents. Mooring system 37 preferably includes a number of anchors 39 and anchor legs 40 that moor buoy 38 to the sea floor 42 so that the buoy is essentially geostationary.
In FIG. 7A, the structural connector 45, fixed to vessel 36, is locked in axial engagement with the buoy but is free to rotate about the geostationary buoy. Mooring arrangement 37 provides a fluid flow path between a pipeline or component and the vessel when the vessel is moored to the buoy. Fluid is transported to or from LNG carrier ship 36 by pipeline 44 on seafloor 42, pipeline end manifold (PLEM) 43, flexible conductor 41, and fluid transfer system 46, located on vessel 36. However, other fluid flow paths arrangements may be used as appropriate.
FIG. 7B shows LNG carrier ship 36 disconnected from buoy 38. Structural connector 45 remains on the ship. When the buoy 38 is completely detached from the vessel 36, the buoy 38 is designed and arranged to sink to a neutrally buoyant position about 36 meters below sea level. Unlike the mooring arrangements of FIGS. 1-3, the vessel 36 used with mooring system 37 does not carry a turret assembly revolvably disposed within the vessel hull. Neither axial bearings nor radial bearings remain on the vessel when the buoy is disconnected therefrom.
FIG. 8 illustrates the improved mooring and fluid transfer system 151 of the invention in partial cross-section according to a preferred embodiment. Detachable buoy 162 is rotatively fastened to the keel 166 of vessel 152 by bearing hub 167, buoy bearing 170, and structural connecter 161. Rubber fenders 165 are provided on buoy 162 to cushion the mooring process, and a water seal 168 is provided to maintain watertight integrity of the vessel fluid transfer system (FTS) compartment. Buoy 162 is geostationarily moored above the sea floor by anchor legs 164 and anchor leg connectors 163. Center post 184 serves the dual purpose of driving swivel torque tube 158 and providing the attachment point for pulling head 182 as shown in FIG. 9.
A flexible fluid conduit 169 is suspended by buoy 162 to provide a fluid flow path between a subsea well, pipeline or component and vessel 152, when moored to buoy 162. Bend restrictor 174 is preferably disposed about flexible conduit 169 at the buoy/conduit interface to prevent bend radii of flexible conduit 169 smaller than allowable limits. Flexible conductor 169 connects to the vessel fluid transfer system (FTS) 153. The fluid path of FTS 153 includes fluid swivel 154, upper flexible conductor 155, conductor elbow 156, isolation valve 173, and geostationary conductor 171. Conductor water seal 172 is provided to maintain watertight integrity of the vessel FTS compartment. The axial geostationary part of swivel 154 is attached to buoy 162 by torque tube 158. The weight of swivel 154 and the geostationary fluid conductors 156, 173, 171 and 169 are carried by swivel bearing 159. A swivel rotary drive 160 is also provided.
FIG. 9A illustrates mooring buoy 162 detached from vessel 152 and supported by hawser 176, as if being retrieved to the ship. Fluid swivel 154 has been moved aside on trolley 186. A fixed retrieval guide unit 177 centers line 176 and provides for centralized alignment of pulling head 182 as buoy 162 approaches vessel bottom 166. Retrieval guide unit 177 includes a central guide sleeve 179 and rubber shock absorber elements 178 to allow impact loading by pulling head 182. Guide sleeve 179 and shock absorbers 178 are disposed within a cylindrical guide housing 180. Guide housing 180 has an upper flange 300 that vertically supports retrieval guide unit 177 on connector cover 191 when installed. Retrieval guide unit 177 is secured in place by guide latches 181, which are ideally fastened to connector cover 191. After buoy 162 is fully connected, retrieval guide 177 is removed in preparation for lifting conductors 169, 171, and 173 toward swivel 154.
FIG. 9B depicts the array of parts to be assembled onto buoy 162 prior to buoy disconnection. After torque tube 158 is retracted from engagement with center post 184 (see FIG. 8), cover 183 is lowered into position on post 184. Pulling head 182 with attached line 176 is then lowered and locked onto post 184.
FIGS. 10A and 10B are enlarged side view cross sections of structural connector 161 and buoy bearing assembly 170, connected and disconnected respectively, and FIGS. 11 and 12 are top view cross sections of structural connector 161 looking down at lines 11, 12 of FIG. 8. Structural connector 161 preferably includes a cylindrical connector housing 192 connected to a cylindrical retainer ring 193 by bolts 301. Retainer ring 193 includes an upper flange 302 that vertically supports structural connector 161 on a lip 303 of a cylindrical vessel structural bulkhead 304. Housing 192 is secured in place by a cylindrical rim 305 that extends downwardly from connector cover 191, which in turn is bolted to the cylindrical vessel bulkhead 304 by bolts 306. Housing 192 has an integral internal shelf 307 formed therein, the interior circumference 308 of which acts as a lower guide for movable connector sleeve 189 to slide axially therein. Connector cover 191 includes a downwardly extending ring 313 that fits within the interior of connector sleeve 189 and provides an upper guide for connector sleeve 189 to slide within.
The upper surface 309 of housing shelf 307 supports a circular hydraulic pressure manifold 187 thereon. Manifold 187 supplies pressurized hydraulic fluid to a plurality of hydraulic piston/cylinder actuators 188 that are circumferentially arranged about connector sleeve 189 and seated on manifold 187. Preferably, twelve actuators 188 are used, but any suitable number may be used. The upper ends of actuators 188 are connected to connector sleeve 189 at an integral external upper flange 310. Below shelf 307, a plurality of circumferentially arranged collet segments 190 are captured between a lower interior lip 311 of housing 192 and a lower exterior lip 312 of connector sleeve 189. Ideally, two dozen collet segments 190 are used, but any suitable number may be used.
Each collet segment 190 has a profile that vertically captures it between lips 311, 312 of connector housing 192 and connector sleeve 189, respectively, yet forces the lower end of the collet segment 190 to pivot radially in and out as connector sleeve 189 is moved up and down axially within housing 192 by actuators 188. The lower end of each collet segment 190 has a radially-outward facing lip 314 that engages an interior groove 315 of buoy bearing hub 167. Thus, when connector sleeve 189 is moved downwardly, lip 312 forces the lower ends of collet segments 190 to pivot radially outward, thereby securely dogging buoy bearing hub 167 against housing 192. Alternatively, when connector sleeve 189 moves upwardly, the lower ends of collet segments 190 pivot radially inward, thereby disconnecting bearing hub 167 from the vessel.
Although connector 161 is described and illustrated herein as being generally cylindrical, it is not limited to a cylindrical configuration. For example, octagonal, hexagonal, or even a square-shaped structural connector 161 may be used. Also, although the movable connector sleeve 189 is preferred to be coaxially disposed within housing 192, it may be disposed coaxially outside of housing 192, if desired.
Bearing hub 167 is rotatively captured by buoy bearing assembly 170 so that hub 167 can rotate with respect to buoy 162 when the buoy is connected to the seabed and the hub 167 is connected to the connector 161. A water seal 168 prevents water ingress into the structural connector compartment after the buoy 162 is connected to the vessel.
FIG. 13 is an enlarged side view exploded diagram illustrating buoy bearing assembly 170 as it is completely constructed for installation on buoy 162. FIG. 10B shows a side view cross section of the assembled and mounted bearing assembly 170 of FIG. 13. FIGS. 14A and 14B are a top view exploded diagram and a plan view of bearing assembly 170, respectively. Referring to FIGS. 10B, 13, 14A, and 14B collectively, bearing hub 167 is rotatively captured in a tongue and groove arrangement by bearing ring 203. Bearing hub 167 slidingly rotates within segmented bearing ring 203 by means of upper and lower axial bushing segments 206, 207 and radial bushing segments 208. Upper and lower bushing segments 206, 207 are captured between bearing ring 203 and bearing hub 167. Bearing ring 203 is manufactured in segments and is dimensioned so that when the segments are assembled they form a true circular ring that fits closely into pilot bore 205 (FIG. 13) yet allow a circumferential gap 211 (FIG. 10B) between bearing ring 203 and bearing hub 167. Gap 211 minimizes any sliding contact between hub 167 and ring 203 even after wear of radial bushing 208. Bearing ring segments 203 preferably include alignment pins 216 and alignment pin holes 217 (FIG. 14A) to maintain proper alignment during assembly. Joining plates 204 are used to hold bearing ring segments 203 together during assembly, and they also assure alignment and flatness at the segment joints within bearing ring 203. Radial bushing segments 208 circumferentially fit outside the lower portion of bearing hub 167 at radial bushing 209 and fit within radial bushing seat 210 of the bearing module 200 on buoy 162. Bushing segments 206, 207, 208, 209 are preferably made of non-metallic low-friction bushing material, such as Orkot brand or a similar material. Such materials are readily available for submerged service exposed directly to the seawater. The sliding bearing surfaces of bearing ring 203, bearing hub 167, and bearing module 200 that are in contact with bushing segments 206, 207, 208, and 209 are made of non-corrosive wear resistant materials such as stainless steel or Inconel. Grease suitable for use in salt water may advantageously be applied between bushings 208, 209 and between segments 206 and 207 and surfaces of hub 167. Bearing assembly 170 is mounted to the bearing module 200 on buoy 162 by threaded studs or other fasteners 202.
An advantage of the bearing assembly 170 is the prevention of radial loading of the studs 202. The radial load path passes directly through the radial bushing seat 210, radial bushing segment 208 and segment 209 of bearing hub 167. Segmented bearing ring 203 carries only the axial forces and moment loads acting on buoy 162. A second advantage is minimization of weight of the bearing components by providing a two-or-more-piece segmented bearing ring 203. This feature eliminates additional bolted or keyed joints that require additional parts.
Although a bearing assembly 170 is described where bearing ring 203 forms the tongue and bearing hub 167 includes the groove in the tongue and groove capturing arrangement, an opposite bearing arrangement may be used. In other words, bearing hub 167 may have a circumferential tongue (not illustrated) instead of a circumferential groove, which is received into a groove (not illustrated) formed in the interior of bearing ring 203.
FIG. 15 shows an arrangement for sealing the central opening of connector 161 when buoy 162 is disconnected. Guide unit 177 remains in place inside connector sleeve 189 of structural connector 161. Guide unit 177 is raised to a position flush with the vessel bottom 166 and is secured by a guide latch 236. Plug 235 is lowered and secured into guide unit 177 to complete the flush bottom arrangement. Seal 237 around the upper circumference of plug 235 prevents water entry into the vessel FTS compartment. Other seals (not shown) prevent water entry through structural connector 161.
FIG. 16 illustrates a mooring and fluid transfer system 220 according to an alternative embodiment of the invention that is suitable for applications requiring only infrequent disconnection of the vessel 152 from the mooring buoy 224. A lower cost mooring system is provided by the arrangement of FIG. 16 as compared to that of FIG. 8, et al. Unlike the mooring and fluid transfer system 151 of FIGS. 8-15 having a quick-disconnect structural connector 161, the mooring and fluid transfer system 220 of FIG. 16 simply has a cylindrical connector member 221 that is fastened directly to bearing hub 201 of the disconnectable buoy 224 by fasteners 223. The fastener may be disconnected for separation of the buoy 224 from connector member 221 and vice-versa. Connector member 221 has a lower internal flange 222 that forms a seat for the upper end of bearing hub 201. A connector retaining ring 230 secures connector member 221 to the cylindrical vessel structural bulkhead 304. Bearing hub 201 of FIG. 16 is similar to bearing hub 167 of FIG. 10B, except that it substitutes a circumferential pattern of threaded holes along the top of the hub to receive threaded studs 223 in place of the internal groove 315 that is engaged by collet segments 190. Ideally, bearing assembly 170 is structured and functions identically for both embodiments. Buoy 224 supports the static weight of anchor legs 164, although in some cases it may be desirable and readily possible also to support the weight of fluid conductors 169 and fluid transfer system 153 on the buoy.
The Abstract of the disclosure is written solely for providing the United States Patent and Trademark Office and the public at large with a way to determine quickly from a cursory reading the nature and gist of the technical disclosure, and it represents solely a preferred embodiment and is not indicative of the nature of the invention as a whole.
While some embodiments of the invention have been illustrated in detail, the invention is not limited to the embodiments shown; modifications and adaptations of the above embodiment may occur to those skilled in the art. Such modifications and adaptations are in the spirit and scope of the invention as set forth herein:
Patent Application
20070264889
