Buoyancy tensioning systems for offshore marine risers and methods of use
Devices and methods for the enhanced assembly and disassembly of offshore marine risers through the use of a combination of passive and active buoyancy elements in a marine riser. Methods for assembling passive buoyancy joints comprise providing disc handling devices capable of simultaneously manipulating a plurality of buoyancy discs capable of nesting and interlocking with one another. The combination of passive and active buoyancy elements along with a near surface disconnect package allow for quicker upper riser recovery especially in the event of an approaching tropical storm.
This nonprovisional patent application claims priority to and the benefit of U.S. Provisional Patent Application Ser. No. 60/964,473, titled “Sea Hook Free Standing Riser (FSR),” which is hereby incorporated by reference.
BACKGROUNDThe present invention generally relates to buoyancy tensioning systems and methods for offshore marine risers and more particularly, buoyancy tensioning systems for marine offshore riser systems that incorporate passive and active buoyancy elements and corresponding methods of use.
Offshore drilling for hydrocarbons typically involves an offshore drilling rig that connected to a wellhead via a marine riser.
It is often desirable that a riser and correspondingly elements of riser, are negatively buoyant (i.e. sinks without assistance). Negatively buoyant riser elements are easier to install because they float down of their own volition, thus not needing an additional force to displace them to their installed position. Additionally, negative buoyancy acts to reduce the effects of currents and wave motion on the lateral motion of the riser. Nevertheless, a riser string that is too negatively buoyant will be too heavy for a rig to provide support, that is, the tension necessary to prevent the riser from collapsing under its own weight. Thus, it is desirable to counteract a large portion of the negative buoyancy to avoid a riser string that is “too heavy.” In some cases, operators will typically design riser elements as only slightly negatively buoyant. This slight negative buoyancy is usually accomplished by the incorporation of one of more passive buoyancy elements to somewhat offset the heavy weight of each riser element. For example, passive buoyancy elements 4 surround each joint of riser 2. Here each passive buoyancy element is shown as a syntactic foam element.
Conventional buoyancy elements such as those depicted in
Occasionally, an operator may wish to move riser 2 to another wellhead location. With such a conventional system, riser 2 must be disconnected at wellhead 3, and then, retrieved joint-by-joint in a painstaking time-consuming process. Indeed, retrieving an entire riser often involves several days of intensive labor to successfully retrieve the entire length of an offshore marine riser. Where sufficient warning time is not available, operators are sometimes forced to abandon an entire riser string to allow departure of an offshore rig, resulting in significant capital loss. Thus, the conventional method of retrieving riser 2 is costly and time-consuming.
Alternatively, in the event of some emergency, such as an approaching hurricane, offshore rig 1 may need to be evacuated if moored, or moved out of the path of dangerous weather patterns to a safe location if dynamically-positioned. Again, in such a conventional system, entire riser string 2 would need to be retrieved joint-by-joint before being able to evacuate offshore rig 1. The conventional system of removing riser 2 to allow movement of rig 1 is costly and time-consuming. Frequently, it is difficult to predict the path of a hurricane or other weather emergencies. Some weather or meteorological/oceanographic emergencies such as loop or eddy currents or other fast-developing weather patterns may not afford an operator the necessary time to retrieve riser 2 by conventional methods to allow evacuation of or, in the case of non-moored, dynamically-positioned mobile offshore drilling units, evasive movement by rig 1. Additionally, a great deal of productive operational time is lost by the conventional systems because of the long duration required to retrieve riser 2. Moreover, cost and time is often expended for the retrieval of riser string that ultimately proves unnecessary given the changing path of a hurricane. In addition to the time and cost involved in retrieving the entire length of riser string, such a process involves additional safety risks, including the risks involved with manipulating the pipe being disassembled and handling the large volume of riser pipe at the rig.
Some operators have sought to address these disadvantages through the use of a “free-standing riser” design. An example of a free-standing riser design is depicted in
Such a design involves numerous disadvantages. Some of these disadvantages, which are enumerated by Chau Nguyen in Storm-Safe Deepwater Drilling (IADC/SPE 10338), include the necessity of modifying the rig to provide additional space to store, transport, and install the bulky aircan or aircans, which are integrally installed into the riser. Furthermore, additionally handling equipment on the rig is necessary to adequately deal with the bulky aircans. Compounding the problem of dealing with the volume of bulky aircans is the inability to install the integral aircans above the rotary table. Because of their large size, aircans must often be installed within the moonpool area below the rotary table. Dealing with this bulky equipment is problematic not only during initial installation of a riser string having aircans, but also during retrieval of a riser string. The large volume occupied on the rig by the bulky handling equipment and the bulky aircans pose not only serious safety risks but increase operational costs as well. Moreover, it slows down the process of inserting pipe joints into the riser.
Accordingly, it would be desirable to provide buoyancy tensioning systems that address one or more disadvantages of the prior art.
SUMMARYThe present invention generally relates to buoyancy tensioning systems and methods for offshore marine risers and more particularly, buoyancy tensioning systems for marine offshore riser systems that incorporate passive and active buoyancy elements and corresponding methods of use.
An example of a method of retrieving a marine riser system between an offshore rig at the surface of an ocean and a wellhead adjacent the ocean floor comprises the steps of: providing a marine riser system comprising: a riser comprising an upper riser and a lower riser, a disconnect joint removably attaching the upper riser to the lower riser, and a second buoy having at least one chamber into which buoyancy fluid may be introduced wherein the second buoy is non-integral to the lower riser and removably attached to the lower riser; introducing a buoyancy fluid into the at least one chamber of the second buoy; and disconnecting the upper riser from the lower riser at the disconnect joint.
An example of a buoyancy tensioning system for a marine riser comprises: a riser string defined by a first end and a second end; a disconnect joint disposed in said riser string; a blow out preventer stack attached to said second end of said riser string; a first buoy attached to said riser string adjacent to said disconnect joint; a landing ring attached to said riser string between said first buoy and said second end; and a second buoy seated on said landing ring is seated, said second buoy comprising at least one chamber for receipt of a buoyancy fluid.
A buoy system for an oil and gas marine riser string comprises: a first housing comprised of buoyant material, said first housing defined by a top wall, a bottom wall and a side wall joining said top and bottom walls, said walls defining an interior compartment within said housing, wherein said top wall is provided with an aperture and an opening is provided in at least a side wall or the bottom wall; and a second housing comprised of buoyant material, said second housing sized to pass through said opening in a wall of said first housing, said second housing having an aperture passing axially therethrough and at least one chamber for receipt of a buoyancy fluid.
An example of a buoyancy system for use with an offshore oil and gas riser string comprises: a buoyant collar comprising: an upper surface and a lower surface and a bore extending therebetween; a keyway disposed in said collar, substantially parallel to said bore, said keyway extending from said upper surface to said lower surface; and at least one chamber into which buoyancy fluid can be pumped.
An example of a method for installing an offshore oil and gas riser string between a rig at the surface of the ocean and a wellhead adjacent the ocean floor comprises: securing a first buoy having a second buoy removably disposed therein adjacent the ocean floor; attaching a blowout preventer to the lower end of a riser string; attaching a landing ring on said riser string above said blowout preventer; attaching a third buoy on said riser string above said landing ring; attaching a riser disconnect joint in said riser string above said third buoy; attaching riser joints above said riser disconnect joint; positioning said riser string adjacent said first buoy; moving said riser string so as to engage the second buoy; moving said riser string with the engaged second buoy away from said first buoy; and attaching said blowout preventer adjacent a wellhead on the ocean floor.
An example of a method for moving an offshore oil and gas rig attached to a riser extending down to the ocean floor and attached to a blowout preventer comprises: providing a riser with a first buoy secured adjacent a disconnect joint and a second buoy secured to said riser below said first buoy, wherein said riser system has an upper riser portion above said disconnect joint and a lower riser portion below said disconnect joint; pumping a fluid into said second buoy so as to increase the buoyancy of said second buoy and thereby the tension on the lower riser portion of said riser string; and disconnecting said rig and upper riser portion from said lower riser portion at said disconnect joint.
An example of a passive buoyancy system for attaching to and providing buoyancy for a marine riser comprises: a support mandrel wherein the support mandrel is capable of integrally attaching to a marine riser; a plurality of stackable elements stacked on the support mandrel; wherein each stackable element comprises a buoyant material; and wherein each stackable element is substantially in the shape of a disc with a bore therethrough and a keyway for allowing each stackable element to slide onto the support mandrel to affix to the support mandrel.
An example of a method for assembling a passive buoyancy system for integration of the passive buoyancy system into a marine riser comprises: providing a disc handling device wherein the disc handling device comprises a frame, and a plurality of lifting arms attached to the frame with a means for interfacing with, retrieving, lifting, and rotating a plurality of stackable elements from a support spool and a means for rotating and lowering the stackable elements onto a support mandrel; providing a transport spool; providing a support mandrel wherein the support mandrel is capable of integrally attaching to a marine riser; providing a plurality of stackable elements stacked on the transport spool wherein each stackable element comprises a buoyant material wherein each stackable element is substantially in the shape of a disc with a bore therethrough and a keyway for allowing each stackable element to slide onto a shaft wherein each stackable element comprises an orientation element for interfacing and locking with an adjacently stacked stackable element; interfacing each stackable element with the plurality of lifting arms; lifting each stackable element a distance apart from each adjacently stacked stackable element; rotating each stackable element so as to configure each keyway into alignment with one another; sliding the support mandrel through the aligned keyways of each stackable element so as to dispose the support mandrel substantially within the bore of each stackable element; rotating each stackable element to an angle that allows the orientation notch of each stackable disc to interface and lock with each adjacently stacked stackable element; and lowering and loading each stackable element onto the support mandrel.
An example of a method of assembling a marine riser system between an offshore rig at the surface of an ocean and a wellhead adjacent the ocean floor comprises the steps of: providing a marine riser system comprising: a riser comprising an upper riser and a lower riser, a disconnect joint removably attaching the upper riser to the lower riser, and a hang-off ring attached to the lower riser; providing a second buoy having at least one chamber into which buoyancy fluid may be introduced wherein the second buoy is moored to the seabed by one or more mooring lines wherein the second buoy is configured to mate with the hang-off ring of the lower riser; mating the marine riser system to the second buoy via the hang-off ring; introducing a buoyancy fluid into the at least one chamber of the second buoy; and disconnecting the upper riser from the lower riser at the disconnect joint.
The features and advantages of the present invention will be apparent to those skilled in the art. While numerous changes may be made by those skilled in the art, such changes are within the spirit of the invention.
A more complete understanding of the present disclosure and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying figures, wherein:
The Figures depicted herein are schematic depictions, and it is recognized that not all of the components depicted therein are drawn to scale.
While the present invention is susceptible to various modifications and alternative forms, specific exemplary embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
DESCRIPTION OF PREFERRED EMBODIMENTSThe present invention generally relates to buoyancy tensioning systems for offshore marine risers and more particularly, buoyancy tensioning systems for marine offshore riser systems that incorporate passive and active buoyancy elements and corresponding methods of use.
Generally, certain embodiments of the present invention provide devices and methods for the enhanced assembly and disassembly of offshore marine risers through the use of a combination of passive and active buoyancy elements in a marine riser. Individual elements of this overall system form additional embodiments of the present invention. Methods of use and corresponding methods of operation are also provided herein.
Advantages of the devices of the present invention include, but are not limited to, enhanced assembly and disassembly of offshore risers, particularly in the event of an emergency evacuation. Additionally, in certain embodiments, devices and methods of the present invention allow offshore rigs to be evacuated from an offshore riser without having to disassemble the entire riser or otherwise abandon the riser in place, which allows for a quicker disconnect and reconnect times. Furthermore, methods of certain embodiments of the present invention avoid the necessity of active buoyancy modules to be handled and stored on an offshore rig.
To facilitate a better understanding of the present invention, the following examples of certain embodiments are given. In no way should the following examples be read to limit, or define, the scope of the invention.
I. Overview of Elements of Buoyancy Tensioning SystemRiser 271 is a marine riser that extends from rig floor 251 to wellhead 277. Riser 271 allows hydrocarbons and drilling fluids to flow between wellhead 277 and an to an offshore rig at the ocean surface. Tensioning system 252 provides an upward tension on riser 271 so as to maintain riser 271 in a substantially vertical orientation and to prevent excessive bending loads on the wellhead 277.
Riser 271 is comprised of upper riser section 271A and lower riser section 271B. Near surface disconnect package (NSDP) 210 allows upper riser section 271A to be disconnected from lower riser section 271B. NSDP 210 is comprised of upper NSDP 210A and lower NSDP 210B. In the event of a disconnect, upper NSDP 210A remains with upper riser section 271A, whereas lower NSDP 210B remains with lower riser section 271B. Thus, in the event of an evacuation of an offshore rig and its corresponding upper riser section, for example, upper riser section 271A may be moved to another location independently of lower riser section 271B, which may be left in place. As lower riser section 271B is at a sufficient depth where it is not exposed to significant lateral water currents, it may safely be abandoned in place until upper riser section 271A can return and join again with lower riser section 271B.
For lower riser section 271B to be abandoned in place, however, lower riser section 271B requires additional buoyancy to prevent it from essentially “falling over,” which would constitute a catastrophic failure, likely resulting in significant loss of or damage to equipment and possible environmental exposure of hydrocarbons to the environment.
Lower riser section 271B is supported vertically in part by both passive buoyancy joint 220 and submerged riser tensioning buoy (SRTB) 230. SRTB 230 comprises an active buoyancy element, which comprises a buoyancy chamber which may be charged with a gas or other buoyant fluid. In normal use, while upper riser 271A and lower riser 271B are connected, SRTB 230 may be left deactivated (e.g. by flooding its chambers with seawater). In such a configuration, buoyancy is provided by tensioning system 252, passive buoyancy joint 220, and any other passive buoyancy elements incorporated into or on riser 271.
In the event of a planned disconnect of upper riser 271A and lower riser 271B, passive buoyancy joint 220 may be sized to maintain lower riser 271B in a substantially vertical position while additional buoyancy may be provided by SRTB 230 so as to reduce bending loads on wellhead 277. In this way, the combination of passive buoyancy joint 220 and SRTB 230 provides buoyancy to maintain lower riser 271B in a substantially vertical position regardless of whether lower riser 271B is connected to tensioning system 252 by way of upper riser 271A. In certain embodiments, SRTB may also comprise one or more passive buoyancy elements. In certain other embodiments, the SRTB may be used without passive buoyancy joint 220 if use of the passive buoyancy joint is deemed unnecessary.
In certain embodiments, buoyancy elements incorporated into riser 271 are sized such that riser 271 is slightly negatively buoyant or neutrally buoyant. Such a configuration is usually desirable to avoid the undesirable consequences that would result from a failure of a riser joint or connection with a positively buoyant riser upon 252. That is, if riser 271 were significantly positively buoyant, riser 271 could “rocket” or “shoot” upwards through the offshore rig upon failure, i.e., separation of a riser joint or riser connection which at the time of the failure is being held under high tension by tensioning system 252.
Lower Marine Riser Package 275 (LMRP) provides a surface-operable connection to blow out preventer (BOP) stack 276. Blow out preventer (BOP) stack 276 in turn interfaces with wellhead 277 and provides fluid isolation between riser 271 and wellhead 277 as desired.
Garage buoy 260 provides a housing for SRTB 230 for storage and constrains SRTB 230 when SRTB 230 is not in use. Garage buoy, sometimes referred to herein as the “third buoy,” houses SRTB 230 before SRTB 230 is installed on lower riser 271B or any other time when storage of SRTB 230 is desired. Additionally, garage buoy 260 houses SRTB 230 after removal of SRTB 230 from lower riser 271B. Garage buoy may be fixed in proximity to wellhead 277 by mooring lines 279 attached to anchors 278.
Each component of marine buoyancy marine tensioning system 200 is explained in more detail below. Methods of corresponding use are also provided below in more detail below.
II. Submerged Riser Tensioning Buoy (SRTB) and Garage Buoy ConceptSubmerged riser tensioning buoy (SRTB) 230 comprises an active buoyancy component, which provides additional buoyancy to a riser when connected thereto. In this example, the active buoyancy components are air chambers 320, which may be “activated” by charging with a gas or other buoyant fluid to provide additionally buoyancy to SRTB 230. Alternatively, air chambers 320 may be flooded with seawater to “deactivate” SRTB 230 so as to neutralize the positive buoyancy of SRTB 230. Charging of air chambers 320 may be accomplished through valves 310. Ports 331 allow communication among air chambers 320 or to the environment (e.g. nitrogen or air may be released through an egress port). Ports 331 may also allow each air chamber to be isolated from one another to allow independent charging or operation of each air chamber.
Generally, SRTB 230 provides additionally buoyancy during various uses of riser 271. For example, SRTB 230 may be activated in the event of a disconnect of upper riser 271A and lower riser 271B. SRTB 230 may be activated at any time when additional buoyancy to lower riser 271B is desired. In certain embodiments, SRTB 230 may also incorporate passive buoyancy components into its structure. For example, SRTB 230 may include passive buoyancy components in walls 350.
SRTB 230 mates or otherwise interfaces with lower riser 271B by landing profile 340. Landing profile 340 is a seat that is adapted to mate with a hang-off ring (see e.g., 480 of
SRTB 230 features keyway 360, which provides a slot for unidirectionally interfacing with lower riser 271B.
In certain embodiments, garage buoy 703 has a positive buoyancy and is moored to the ocean floor or other fixed structure in proximity to the ocean or sea floor. Garage buoy 703 may be preinstalled well before the arrival or assembly of a corresponding marine riser. This preinstallation of the SRTB allows the SRTB to be delivered and installed by a vessel separate from the offshore rig containing the marine riser elements. As mentioned previously, this preinstallation of garage buoy 703 and its corresponding SRTB is advantageous in that the garage buoy and the SRTB need not be stored on the offshore rig, which in effect eliminates a significant volume of equipment from the offshore rig.
In certain embodiments, SRTBs of the present invention are one or more gas chambers integrally formed as one unit or buoyancy module with an overall diameter or overall size of about 24 feet to about 48 feet, and in certain embodiments, about 28 feet. Because SRTBs of the present invention are deployed separately from the marine riser, i.e. not from the rig itself, SRTBs of the present invention are logistically much simpler and safer due to this reduction in equipment handling on the rig.
Anti-rotation blocks 905 may take any shape suitable for constraining the rotational movement of an SRTB disposed in garage buoy 905.
For certain deepwater wells, the submerged riser tensioning buoy may be moored directly over or in close proximity to the well location as an alternative to deploying the SRTB from a moored garage buoy. In this embodiment, mooring lines 979 could remain attached to SRTB 901 throughout the period of operations, especially for exploration or appraisal wells where operating at the well location is not complicated by the installation or existence of subsea facilities, and where there is not a need for intense, multiple ROV support.
So as not to affect the proper functioning of an emergency disconnect system (EDS), a weak-point 936 or disconnect 936 could be introduced into each mooring line 979 to ensure that if moorings lines 979 failed, before any damage is done to riser 971 and/or SRTB 901 in the event of a drive-off/drift-off. Alternately, mooring lines 979 may be disconnected upon mating of riser 971/SRTB 901 and then later reconnected when LMRP 975 is pulled.
III. Passive Buoyancy Joint and Disc Handling DevicePassive buoyancy joint 1020 aids in maintaining a lower riser in the vertical position. In certain embodiments, passive buoyancy joint 1020 is placed in proximity to the top of the lower riser. The passive buoyancy joint 1020 is optional and may be excluded from certain embodiments of the present invention.
The modular design utilizing stackable buoyancy discs facilitates easier handling and storage of the discs at the rig and allows for easier reconfiguration of the total buoyancy of passive buoyancy joint 1020. Additionally, each buoyancy disc 1021 is formed so as to allow an interlocking fit with an adjacent buoyancy disc.
Although passive buoyancy joint 1020 is depicted herein as formed of a plurality of buoyancy discs 1021, it is explicitly recognized that passive buoyancy joint 1020 may be formed of one integral component. Passive buoyancy joint 1020 may be constructed out of any material suitable for providing a positive buoyancy, including, but not limited to, foam, closed-cell foam, any lightweight material having a density less than that of seawater, or any combination thereof.
In this way, each adjacent buoyancy disc may be rotated in an alternating fashion so as to allow each adjacent disc to be positioned to facilitate each buoyancy disc nesting and interlocking with one another. That is, raised sections 1068 of buoyancy disc 1021A interface with keyway 1063 of buoyancy disc 1021B when each alternating buoyancy disc is stacked on top of an adjacent disc. Likewise, raised sections 1068 of buoyancy disc 1021B interface with keyway 1063 of buoyancy disc 1021A.
In certain embodiments, a buoyancy wedge (not shown), constructed of buoyant material, may be added to fill in the void space of keyway 1063.
Orienting protrusion 1072, as previously explained, provides a rotational stop or limit to assist in orienting each disc to its final desired rotational position.
With reference to
As each buoyancy disc 1021 has been rotated in an alternating fashion, the series of discs 1021 cannot all be removed simultaneously from transport spool 1073 by simultaneously displacing all buoyancy discs 1021 in one direction. This configuration, where each alternating buoyancy disc is rotated in an alternating fashion such that each keyway is not aligned with the keyways of adjacent discs, may be referred to herein as the “closed configuration” or “nested configuration.” The simultaneous removal of buoyancy discs 1063 is prevented because keyways 1063 of each disc 1021 are not aligned with one another as shown in
After removal from a transport spool, buoyancy discs may be installed on a mandrel joint with all of the buoyancy discs in the open configuration. After mounting each buoyancy disc onto the mandrel joint, each disc may then be rotated in an alternating fashion so as to place the buoyancy discs in a closed configuration. As an example of such a closed configuration,
Although each buoyancy disc may be individually handled and manipulated, in certain embodiments, it is advantageous and more efficient to manipulate multiple buoyancy discs simultaneously. Examples of operations suitable for multiple simultaneous disc manipulation include, but are not limited to transferring buoyancy discs from a transport spool to a riser and vice-versa.
An example of a device suitable for simultaneously manipulating a plurality of buoyancy discs is shown in
Turning back to
Lifting plates 2083 are raised and lowered by lifting pistons 2082. Lifting pistons 2082 may be hydraulically or mechanically actuated. In this way, lifting plates 2083 are capable of lifting adjacent, nested buoyancy discs 2021 so as to separate them.
Normally, when each disc rests on a transport spool, each buoyancy disc is nested and interlocked with adjacent discs (refer to
The buoyancy discs, however, are prevented from rotating in their nested configuration because of the interlocking of the raised sections of each buoyancy disc with the keyways of adjacent buoyancy discs. Accordingly, before the buoyancy discs can be rotated, each disc must be raised and separated from adjacent buoyancy discs. Accordingly, to effect the simultaneous removal of a plurality of buoyancy discs from a transport spool for installation on a mandrel joint or riser, the buoyancy discs on the transport spool must be raised and separated from one another. Each disc must then be rotated in an alternating fashion so as to align their keyways. This permits the buoyancy discs to be removed from the transport spool and mounted on the mandrel joint. Each disc may then be rotated in an alternating fashion until the raised section of each buoyancy disc aligns with the keyways of adjacent discs. Finally, each disc is lowered onto one another so that each buoyancy disc interlocks with adjacent discs in a nested configuration.
In
Now, buoyancy discs 2021 are ready for simultaneous installation on a mandrel joint as keyways 2063 are commonly aligned.
Each of the steps described in
As is apparent in
As explained previously, garage buoy 3260 and SRTB 3230 have been previously been located in position ready to interact with buoyancy tensioning riser system 3200. This preinstallation may be accomplished by the same offshore rig 3251 or may be accomplished by a separate vessel. Preinstalling SRTB 3230 reduces the critical path for assembling buoyancy tensioning riser system 3200 and further reduces the volume of equipment that must be handled on offshore rig 3251.
In
More particularly,
Once SRTB 3230 is charged, either fully or partially, near surface disconnect package (NDSP) 3210 can be disconnected so as to release upper riser 3271A from lower riser 3271B. In this way, SRTB 3230 provides the additional buoyancy support required to support lower riser 3271B in the upright, vertical position, plus any additional extra tension deemed necessary to maintain bending moments on the subsea wellhead at an acceptable magnitude.
The above steps may be reversed to reconnect rig 3251 and upper riser 3271A to lower riser 3271B so as to put buoyancy tensioning riser system 3200 in operation. Additionally, if desired, SRTB 3230 may be detached from lower riser 3271B as desired by reversing the steps detailed above as well.
As used herein, the terms “join,” “affix to,” “connect to,” and “attach to” do not require elements to be directly connected to other elements and include elements indirectly connected to one another so as to communicate mechanical forces.
It is explicitly recognized that any of the features, elements, and steps of each embodiment described herein may be combined with any other embodiment described herein.
Therefore, the present invention is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the present invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular illustrative embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the present invention. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee.
Claims
1. A method of retrieving a marine riser system between an offshore rig at the surface of an ocean and a wellhead adjacent the ocean floor, the method comprising the steps of:
- providing a marine riser system comprising: a riser comprising an upper riser and a lower riser, a disconnect joint removably attaching the upper riser to the lower riser, and a second buoy having at least one chamber into which buoyancy fluid may be introduced wherein the second buoy is non-integral to the lower riser and removably attached to the lower riser;
- introducing a buoyancy fluid into the at least one chamber of the second buoy; and
- disconnecting the upper riser from the lower riser at the disconnect joint.
2. The method of claim 1 wherein the marine riser system further comprises a first buoy attached to the lower riser.
3. The method of claim 1 wherein a sufficient quantity of buoyancy fluid is introduced into the second buoy to maintain the lower riser in a substantially vertical position to prevent the lower riser from collapsing.
4. The method of claim 1 further comprising:
- retrieving the upper riser; and
- leaving the lower riser in place.
5. The method of claim 1 further comprising:
- retrieving the upper riser;
- retrieving and disassembling the lower riser while simultaneously expelling the buoyancy fluid from the second buoy; and
- detaching the second buoy from the lower riser.
6. The method of claim 1 further comprising:
- retrieving the upper riser;
- disconnecting the lower riser from the wellhead;
- displacing the lower riser to a second wellhead location; and
- attaching the lower riser to the second wellhead location.
7. The method of claim 5 further comprising providing a third stand-alone buoy disposed for receipt of the second buoy when the second buoy is detached from the lower riser.
8. The method of claim 5 further comprising storing the second buoy in the third stand-alone buoy.
9. The method of claim 8 wherein the third stand-alone buoy comprises a passively buoyant material and wherein the third stand-alone buoy is secured to the ocean floor by a plurality of mooring cables.
10. The method of claim 2 wherein the first buoy is attached at substantially the top of the lower riser.
11. The method of claim 10 wherein the first buoy is attached at the top of the lower riser.
12. The method of claim 2 wherein the first buoy is attached to within about 100 feet of the top of the lower riser.
13. The method of claim 10 wherein the second buoy is substantially adjacent the first buoy.
14. The method of claim 13 wherein the second buoy is below the first buoy.
15. The method of claim 13 wherein the second buoy further comprises a passive buoyancy element.
16. The method of claim 13 wherein the first buoy comprises a passive buoy.
17. The method of claim 16 wherein the first buoy is a passive buoy and wherein the first buoy is integrally attached to the lower riser.
18. The method of claim 1 further comprising providing a landing ring wherein the landing ring is attached to the lower riser, and wherein the second buoy is adapted to seat on the landing ring by virtue of upward buoyancy.
19. The method of claim 18 wherein the second buoy comprises a buoyant collar wherein the buoyant collar comprises:
- an upper surface and a lower surface and a bore extending therebetween;
- a keyway disposed in the collar, substantially parallel to the bore, the keyway extending from the upper surface to the lower surface.
20. The method of claim 19 wherein the buoyancy collar is formed of a buoyant material.
21. The method of claim 19 wherein the bore has a diameter and said keyway has a width and the bore diameter is equal to the keyway width.
22. The method of claim 19 wherein the bore has a diameter and the keyway has a width and the bore diameter is larger than the keyway width.
23. The method of claim 19 wherein the at least one chamber is open to the lower surface.
24. The method of claim 19 further comprising a recess disposed in the upper surface of the buoyant collar.
25. The method of claim 19 further comprising an orientation notch disposed in the upper surface of the buoyant collar.
26. The method of claim 19 wherein the buoyant collar is disc shaped.
27. The method of claim 19 wherein the buoyant collar is spherical in shape.
28. The method of claim 19 wherein the buoyant collar is cylindrical in shape.
29. The method of claim 19 wherein the buoyant collar is asymmetrical in shape.
30. The method of claim 19 further comprising providing a centralizer element wherein the centralizer element is attached to the lower riser.
31. The method of claim 30 wherein the centralizer element is a centralizer ring.
32. The method of claim 1 wherein the buoyancy fluid comprises a gas wherein the gas is air or nitrogen.
33. The method of claim 30 wherein the disconnect joint comprises an upper disconnect joint and a lower disconnect joint and further comprising providing a blow out preventer stack wherein the blow out preventer stack is attached to the lower riser.
34. The method of claim 3 further comprising:
- wherein the marine riser system further comprises a first buoy attached to the lower riser;
- providing a landing ring wherein the landing ring is attached to the lower riser, and wherein the second buoy is adapted to mate with and removably attach to the landing ring so as to enable the second buoy to removably affix to the lower riser;
- wherein the second buoy is non-integral to the lower riser and wherein the second buoy is removably attached to the lower riser;
- wherein the second buoy is substantially adjacent the first buoy;
- wherein the first buoy comprises a passive buoy;
- wherein the first buoy is attached at substantially the top of the lower riser retrieving the upper riser;
- wherein the disconnect joint comprises an upper disconnect joint and a lower disconnect joint and further comprising providing a blow out preventer stack wherein the blow out preventer stack is attached to the lower riser;
- detaching the second buoy from the lower riser;
- providing a third stand-alone buoy disposed for receipt of the second buoy when the second buoy is detached from the lower riser wherein the third stand-alone buoy comprises a passively buoyant material and wherein stand-alone buoy is secured to the ocean floor by a plurality of mooring cables;
- retrieving and disassembling the lower riser;
- storing the second buoy in the third stand-alone buoy;
- wherein the second buoy comprises a buoyant collar that is formed of buoyant material wherein the buoyant collar comprises: an upper surface and a lower surface and a bore extending therebetween; and a keyway disposed in the collar, substantially parallel to the bore, the keyway extending from the upper surface to the lower surface.
35. The method of claim 1 wherein the lower riser and any other devices connected thereto are together substantially neutrally buoyant before the step of disconnecting the upper riser from the lower riser so as to prevent the lower riser from forcefully rising up upon disconnecting the upper riser from the lower riser.
36. A buoyancy tensioning system for a marine riser, said buoyancy system comprising:
- a riser string defined by a first end and a second end;
- a disconnect joint disposed in said riser string;
- a blow out preventer stack attached to said second end of said riser string;
- a first buoy attached to said riser string adjacent to said disconnect joint;
- a landing ring attached to said riser string between said first buoy and said second end; and
- a second buoy seated on said landing ring is seated, said second buoy comprising at least one chamber for receipt of a buoyancy fluid.
37. The system of claim 36, further comprising a third stand alone buoy disposed for receipt of said second buoy when said second buoy is not mounted on by said landing ring.
38. The system of claim 36, further comprising a centralizer mounted on said riser string between said landing ring and said second end of said riser string.
39. A buoy system for an oil and gas marine riser string, said buoy system comprising:
- a first housing comprised of buoyant material, said first housing defined by a top wall, a bottom wall and a side wall joining said top and bottom walls, said walls defining an interior compartment within said housing, wherein said top wall is provided with an aperture and an opening is provided in at least a side wall or the bottom wall; and
- a second housing comprised of buoyant material, said second housing sized to pass through said opening in a wall of said first housing, said second housing having an aperture passing axially therethrough and at least one chamber for receipt of a buoyancy fluid.
40. A buoyancy system for use with an offshore oil and gas riser string, said buoyancy system comprising:
- a buoyant collar comprising:
- an upper surface and a lower surface and a bore extending therebetween;
- a keyway disposed in said collar, substantially parallel to said bore, said keyway extending from said upper surface to said lower surface; and
- at least one chamber into which buoyancy fluid can be pumped.
41. The system of claim 40 wherein said buoyant collar is formed of buoyant material.
42. The system of claim 40 wherein said bore has a diameter and said keyway has a width and said bore diameter is equal to said keyway width.
43. The system of claim 40 wherein said bore has a diameter and said keyway has a width and said bore diameter is larger than said keyway width.
44. The system of claim 40 wherein said chamber is open to said lower surface.
45. The system of claim 40 further comprising a seat disposed in the top surface of said collar.
46. The system of claim 40 further comprising an orientation notch disposed in the surface of said collar.
47. The system of claim 40 wherein said buoyant collar is disc shaped.
48. The system of claim 40 wherein said buoyant collar is spherical in shape.
49. The system of claim 40 wherein said buoyant collar is cylindrical in shape.
50. The system of claim 40 wherein said buoyant collar is asymmetrical in shape.
51. A method for installing an offshore oil and gas riser string between a rig at the surface of the ocean and a wellhead adjacent the ocean floor, said method comprising the steps of:
- securing a first buoy having a second buoy removably disposed therein adjacent the ocean floor;
- attaching a blowout preventer to the lower end of a riser string;
- attaching a landing ring on said riser string above said blowout preventer;
- attaching a third buoy on said riser string above said landing ring;
- attaching a riser disconnect joint in said riser string above said third buoy;
- attaching riser joints above said riser disconnect joint;
- positioning said riser string adjacent said first buoy;
- moving said riser string so as to engage the second buoy;
- moving said riser string with the engaged second buoy away from said first buoy; and
- attaching said blowout preventer adjacent a wellhead on the ocean floor.
52. The system of claim 51 wherein the step of moving the riser string to engage the second buoy comprises passing the riser string through a slot in the first buoy, axially aligning said riser string with a bore defined in said first buoy and causing said riser string to move axially downward until said second buoy seats against said landing ring.
53. A method for moving an offshore oil and gas rig attached to a riser extending down to the ocean floor and attached to a blowout preventer, said method comprising the steps of:
- providing a riser with a first buoy secured adjacent a disconnect joint and a second buoy secured to said riser below said first buoy, wherein said riser system has an upper riser portion above said disconnect joint and a lower riser portion below said disconnect joint;
- pumping a fluid into said second buoy so as to increase the buoyancy of said second buoy and thereby the tension on the lower riser portion of said riser string; and
- disconnecting said rig and upper riser portion from said lower riser portion at said disconnect joint.
54. A passive buoyancy system for attaching to and providing buoyancy for a marine riser comprising:
- a support mandrel wherein the support mandrel is capable of integrally attaching to a marine riser;
- a plurality of stackable elements stacked on the support mandrel;
- wherein each stackable element comprises a buoyant material; and
- wherein each stackable element is substantially in the shape of a disc with a bore therethrough and a keyway for allowing each stackable element to slide onto the support mandrel to affix to the support mandrel.
55. The passive buoyancy system of claim 54 wherein each stackable element has an upper surface and a lower surface and wherein each upper surface comprises a raised section for interfacing and interlocking with an adjacent disc.
56. The passive buoyancy system of claim 55 wherein each stackable element comprises a mesh netting having a buoyant material within the mesh netting.
57. The passive buoyancy system of claim 55 wherein the plurality of stackable elements comprise:
- a plurality of clockwise stackable elements;
- a plurality of counterclockwise stackable elements.
58. The passive buoyancy system of claim 57 wherein each of the clockwise stackable elements are adapted to mate with each of the counterclockwise stackable elements when each of the clockwise stackable elements is stacked adjacent to each of the counterclockwise stackable elements and when each of the clockwise stackable elements is rotated to mate and lock with each of the counterclockwise stackable elements.
59. The passive buoyancy system of claim 55 wherein each stackable disc further comprises a plurality of lifting pockets for receiving a lifting arm for manipulating and orientating each stackable disc onto the support mandrel.
60. A disc handling device for assembling a passive buoyancy system for integration of the passive buoyancy system into a marine riser
- a frame; and
- a plurality of lifting arms attached to the frame with a means for interfacing with, retrieving, lifting, and rotating a plurality of stackable elements from a transport spool and a means for rotating and lowering the stackable elements onto a support mandrel.
61. A method for assembling a passive buoyancy system for integration of the passive buoyancy system into a marine riser comprising:
- providing a disc handling device wherein the disc handling device comprises a frame, and a plurality of lifting arms attached to the frame with a means for interfacing with, retrieving, lifting, and rotating a plurality of stackable elements from a support spool and a means for rotating and lowering the stackable elements onto a support mandrel;
- providing a transport spool;
- providing a support mandrel wherein the support mandrel is capable of integrally attaching to a marine riser;
- providing a plurality of stackable elements stacked on the transport spool wherein each stackable element comprises a buoyant material wherein each stackable element is substantially in the shape of a disc with a bore therethrough and a keyway for allowing each stackable element to slide onto a shaft wherein each stackable element comprises an orientation element for interfacing and locking with an adjacently stacked stackable element;
- interfacing each stackable element with the plurality of lifting arms;
- lifting each stackable element a distance apart from each adjacently stacked stackable element;
- rotating each stackable element so as to configure each keyway into alignment with one another;
- sliding the support mandrel through the aligned keyways of each stackable element so as to dispose the support mandrel substantially within the bore of each stackable element;
- rotating each stackable element to an angle that allows the orientation notch of each stackable disc to interface and lock with each adjacently stacked stackable element; and
- lowering and loading each stackable element onto the support mandrel.
62. The method of claim 61 further comprising integrally attaching the lower end of the support mandrel to the marine riser.
63. The method of claim 62 further comprising integrally attaching the upper end of the support mandrel to a disconnect joint.
64. A method of assembling a marine riser system between an offshore rig at the surface of an ocean and a wellhead adjacent the ocean floor, the method comprising the steps of:
- providing a marine riser system comprising: a riser comprising an upper riser and a lower riser, a disconnect joint removably attaching the upper riser to the lower riser, and a hang-off ring attached to the lower riser;
- providing a second buoy having at least one chamber into which buoyancy fluid may be introduced wherein the second buoy is moored to the seabed by one or more mooring lines wherein the second buoy is configured to mate with the hang-off ring of the lower riser;
- mating the marine riser system to the second buoy via the hang-off ring;
- introducing a buoyancy fluid into the at least one chamber of the second buoy; and
- disconnecting the upper riser from the lower riser at the disconnect joint.
65. The method of claim 64 further comprising a spring buoy attached to at least one of the mooring lines.
Type: Application
Filed: Aug 13, 2008
Publication Date: Feb 19, 2009
Inventor: Paul R. Boudreau (Austin, TX)
Application Number: 12/228,452
International Classification: E21B 17/01 (20060101); B63B 22/00 (20060101);