Subsea control pod deployment and retrieval systems and methods

A method for replacing a first control pod of a BOP stack includes (a) lowering a control pod exchange device subsea. In addition, the method includes (b) coupling the control pod exchange device to the BOP stack. Further, the method includes (c) transferring the first control pod from the BOP stack to the control pod exchange device after (b). Still further, the method includes (d) lifting the control pod exchange device to the surface after (c).

Not applicable.

BACKGROUND

Embodiments described herein relate generally to systems and methods for deploying and retrieving subsea control pods. More particularly, embodiments described herein relate generally to systems and methods for deploying and retrieving subsea blowout preventer (BOP) and lower marine riser package (LMRP) control pods in deepwater environments exceeding 5,000 feet independent of subsea remotely operated vehicles (ROVs).

Subsea wells are typically made up by installing a primary conductor into the seabed and securing a wellhead secured to the upper end of the primary conductor at the sea floor. In addition, a subsea stack, also referred to as a blowout preventer (BOP) stack, is installed on the wellhead. The stack usually includes a blowout preventer mounted to the upper end of the wellhead and a lower marine riser package (LMRP) mounted to the upper end of the BOP. The primary conductor, wellhead, BOP, and LMRP are typically installed in a vertical arrangement one-above-the-other. The lower end of a riser extending subsea from a surface vessel or rig is coupled to a flex joint at the top of the LMRP. For drilling operations, a drill string is suspended from the surface vessel or rig through the riser, LMRP, BOP, wellhead, and primary conductor to drill a borehole. During drilling, casing strings that line the borehole are successively installed and cemented in place to ensure borehole integrity.

A subsea control system is used to operate and monitor the BOP stack as well as monitor wellbore conditions. For example, the control system can actuate valves (e.g., safety valves, flow control choke valves, shut-off valves, diverter valves, etc.), actuate chemical injection systems, monitor operation of the BOP and LMRP, monitor downhole pressure, temperature and flow rates, etc. The subsea control system typically comprises control modules or pods removably mounted to the BOP and LMRP. Redundant control pods are typically provided on each BOP and LMRP to enable operation and monitoring functions in the event one of the redundant control pods fails. Control pods mounted to the LMRP are often referred to as “primary” pods, whereas control pods mounted to the BOP are often referred to as “secondary” or “backup” pods. Electrical power, hydraulic power, and command signals are provided to the control pods from the surface vessel or rig. The control pods utilize the electrical and hydraulic power to operate and monitor the BOP stack as well as monitor the wellbore conditions in accordance with the command signals.

In the event of a control pod component failure, it may be desirable to retrieve the control pod to the surface to be repaired or replaced, and then deploy the repaired control pod or a replacement control pod subsea to effectively replace the faulty control pod. Traditionally, there are limited options for doing so, and further, some of the options are only applicable in shallow water environments or require the retrieval of the entire LMRP.

BRIEF SUMMARY OF THE DISCLOSURE

Embodiments methods for replacing a first control pod of a BOP stack are disclosed herein. In one embodiment, a method comprises (a) lowering a control pod exchange device subsea. In addition, the method comprises (b) coupling the control pod exchange device to the BOP stack. Further, the method comprises (c) transferring the first control pod from the BOP stack to the control pod exchange device after (b). Still further, the method comprises (d) lifting the control pod exchange device to the surface after (c).

Embodiments of systems for replacing a first control pod coupled to a subsea BOP stack are disclosed herein. In one embodiment, a system comprises a lifting device coupled to a surface vessel. In addition, the system comprises a control pod exchange device suspended from the lifting device and configured to be raised and lowered subsea by the lifting device. The control pod exchange device comprises a housing configured to receive the first control pod. Still further, the system comprises a BOP stack connection assembly coupled to the control pod exchange device. The BOP stack connection assembly is configured to couple the control pod exchange device to the BOP stack.

Embodiments of methods for replacing a first control pod of a BOP stack are disclosed herein. In one embodiment, a method comprises (a) loading a second control pod onto a control pod exchange device. In addition, the method comprises (b) lowering the control pod exchange device subsea after (a) with a lifting device mounted to a surface vessel. The control pod exchange device is suspended from the lifting device with a first rope or a pipe string. Further, the method comprises (c) coupling a BOP stack connector to the BOP stack after (b). A second rope has a first end coupled to the control pod exchange device and a second end coupled to the BOP stack connector. Still further, the method comprises (d) lowering the first rope or the pipe string to lower the control pod exchange device relative to the first rope or the pipe string to the BOP stack connector after (c).

Embodiments of methods for replacing a first control pod of a BOP stack are disclosed herein. In one embodiment, a method comprises (a) lowering a rope from a lifting device mounted to a surface vessel. In addition, the method comprises (b) coupling a lower end of the rope to the first control pod of the BOP stack after (a). Further, the method comprises (c) removing the first control pod from the BOP stack after (b). Still further, the method comprises (d) lifting the first control pod to the surface with the rope and the lifting device.

Embodiments described herein comprise a combination of features and advantages intended to address various shortcomings associated with certain prior devices, systems, and methods. The foregoing has outlined rather broadly the features and technical advantages of the invention in order that the detailed description of the invention that follows may be better understood. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description, and by referring to the accompanying drawings. It should be appreciated by those skilled in the art that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As previously described, a failing subsea control pod can be retrieved to the surface and replaced with a properly functioning control pod. In shallow water offshore operations (i.e., at water depths up to about 6,000 ft.), guidelines or wires extending vertically from the surface vessel or rig to the subsea template or wellhead are used to guide and land the BOP and LMRP onto the wellhead for the initial assembly of the BOP stack. The guidelines generally remain in place after building up the BOP stack, and thus, are generally considered to be permanently installed. Such guidelines can be used to guide and run control pods to and from the BOP stack. However, this technique is typically limited to shallow water operations (guidelines are usually only installed and available for use in shallow water operations), and further, this technique usually cannot be used to retrieve and deploy control pods mounted to the lower portion of the BOP stack (e.g., control pods mounted to the BOP) because LMRP at the upper end of the BOP stack does not provide sufficient clearance around the guidewires to enable the direct vertical movement of control pods along the guidelines to and from the portions of the BOP stack below the LMRP. Thus, control pods mounted to the lower portion of the BOP stack usually cannot utilize guidelines for retrieval and deployment because the guidelines extend vertically, whereas the control pods must be moved laterally away from the BOP stack before being moved vertically upward to the surface. In deep water offshore operations (i.e., at water depths greater than 6,000 ft.), guidelines are typically not available. In some cases, subsea remotely operated vehicles (ROVs) may be used to facilitate the retrieval, deployment, and installation of subsea control pods. However, operation of subsea ROVs can be negatively impacted by a variety of factors including, without limitation, subsea currents, limitations on visibility, payload limits, thrust capacity and accuracy, and ROV pilot skill and experience. For example, modern control pods are often substantially heavier than shallow water guideline retrievable control pods (e.g., 40,000 lbs. versus 2,000 lbs). Consequently, retrieving, deploying, and installing control pods via subsea ROVs may not be desirable or a viable option. Thus, embodiments of systems and devices described herein enable the retrieval, deployment, and installation of subsea control pods on any part of the BOP stack (e.g., the BOP, LMRP, upper part of the BOP stack, lower part of the BOP stack, etc.) without the use of conventional guidelines and with limited or no reliance on subsea ROVs. Although embodiments described herein reduce and/or eliminate reliance on subsea ROVs to physically manipulate and move the control pods, it should be appreciated that one or more subsea ROVs can be used to visually monitor and verify the subsea retrieval, deployment, and installation of the control pods. Moreover, although this disclosure generally describes the retrieval and replacement of faulty subsea control pods (i.e., with a different control pod), it should be appreciated embodiments described herein can also be used to retrieve a faulty control pod to the surface, rapidly repair of the faulty control pod at the surface, and then deploy the repaired control pod subsea for subsequent installation on the BOP stack.

Referring now toFIG. 1, an embodiment of an offshore system10for drilling and/or producing a subsea well is shown. In this embodiment, system10includes a subsea blowout preventer (BOP) stack11mounted to a wellhead12at the sea floor13. Stack11includes a blowout preventer (BOP)14attached to the upper end of wellhead12and a lower marine riser package (LMRP)15connected to the upper end of BOP14. A marine riser16extends from a surface vessel20at the sea surface17to LMRP15. In this embodiment, vessel20is a floating platform, and thus, may also be referred to as platform20. In other embodiments, the vessel (e.g., vessel20) can be a drill ship or any other vessel disposed at the sea surface for conducting offshore drilling and/or production operations. Platform20includes a drilling derrick21and a lifting device22, which in this embodiment is a full depth crane.

Riser16is a large-diameter pipe that connects LMRP15to floating platform20. During drilling operations, riser16takes mud returns to platform20. A primary conductor18extends from wellhead12into the subterranean wellbore19.

BOP14, LMRP15, wellhead12, and conductor18are arranged such that each shares a common central axis25. In other words, BOP14, LMRP15, wellhead12, and conductor18are coaxially aligned. In addition, BOP14, LMRP15, wellhead12, and conductor18are vertically stacked one-above-the-other, and the position of platform20is controlled such that axis25is vertically or substantially vertically oriented. In general, platform20can be maintained in position over stack11with mooring lines and/or a dynamic positioning (DP) system. However, it should be appreciated that platform20moves to a limited degree during normal drilling and/or production operations in response to external loads such as wind, waves, currents, etc. Such movements of platform20result in the upper end of riser16, which is secured to platform20, moving relative to the lower end of riser16, which is secured to LMRP15. Wellhead12, BOP14and LMRP15are generally fixed in position at the sea floor13, and thus, riser16may flex and pivot about its lower and upper ends as platform20moves at the surface17. Consequently, although riser16is shown as extending vertically from platform20to LMRP15inFIG. 1, riser16may deviate somewhat from vertical as platform20moves at the surface17.

Referring still toFIG. 1, a pair of control pods30are releasably coupled to LMRP15and a pair of control pods31are releasably coupled to BOP14. Pods30are positioned above pods31(pods30are not necessarily directly over pods31), and pods30are coupled to LMRP15, whereas pods31are coupled to BOP14. It should be appreciated that pods30and pods31can control functions in the LMRP15and/or BOP14. For purposes of clarity and further explanation, pods30may also be referred to as “primary” pods30, and pods31may also be referred to as “secondary” pods31. In this embodiment, primary pods30are redundant meaning each primary pod30can perform all of the functions as the other primary pod30, and secondary pods31are backups to the primary pods30, each pod30,31being able to control select functions in LMRP15and BOP14. In general, control pods30,31can perform any of the functions performed by subsea control pods known in the art. For example, each primary control pod30can operate and monitor LMRP15and BOP14, and monitor conditions within LMRP15and BOP14(e.g., temperature, pressure, flow rates, etc.), and each secondary control pod31can operate and monitor LMRP15and BOP14, and monitor conditions within LMRP15and BOP14(e.g., temperature, pressure, flow rates, etc.). Electrical power, hydraulic power, and command signals are provided to primary control pods30from platform20. Secondary control pods31are provided power BOP stack11(e.g., stored power). In addition, the interface between each control pod30,31BOP stack11includes hydraulic and/or electrical couplings that enable pods30,31to control hydraulic and/or electrical functions of LMRP15and BOP14.

As will be described in more detail below, embodiments described and illustrated herein are directed to systems and methods for retrieving a failed or faulty control pod (e.g., control pod30or control pod31), and replacing it with a replacement control pod (e.g., control pod30or control pod31). Although embodiments described herein specifically show and described replacing a control pod30mounted to LMRP15, it is to be understood that embodiments described herein can also be used in the manners described to replace a control pod31mounted to BOP14.

Referring now toFIGS. 2A-2I, an embodiment of a system100for retrieving a failed or faulty control pod30, and replacing it with a replacement control pod30is schematically shown. More specifically, inFIGS. 2A-2D, system100is shown removing the failed or faulty control pod30from BOP stack11; inFIGS. 2D and 2E, system100is shown retrieving the failed or faulty control pod30to vessel20at the surface17; inFIGS. 2F-2H, system100is shown delivering the replacement control pod30subsea to BOP stack11; and inFIGS. 2H and 2I, system100is shown installing replacement control pod30on BOP stack11.

For purposes of clarity and further explanation (e.g., to aid in distinguishing failed or faulty pod30from replacement pod30), in embodiments described herein, the failed or faulty pod30is labeled with reference numeral30′ and the replacement pod30is labeled with reference numeral30″. In general, the replacement pod30″ can be a new pod30or a repaired pod30.

In this embodiment, system100includes lifting device22mounted to surface vessel20and rigging50coupled to lifting device22. In this embodiment, rigging50is rope that extends from lifting device22and can be paid in or paid out from lifting device22to raise or lower loads. As used herein, the term “rope” may be used to refer to any flexible type of rope including, without limitation, wire rope, cable, synthetic rope, or the like. In this embodiment, as well as other embodiments described herein, one or more subsea remotely operated vehicles40are used, to varying degrees, to assist in the retrieval of pod30′ and deployment of pod30″. Each ROV40includes an arm41having a claw42, a subsea camera43for viewing the subsea operations (e.g., the relative positions of LMRP15, BOP14, pods30,31, the positions and movement of arm41and claw42, etc.), and an umbilical44. Streaming video and/or images from cameras43are communicated to the surface or other remote location via umbilical44for viewing on a continuous live basis. Arms41and claws42are controlled via commands sent from the surface through umbilical44.

Referring again toFIGS. 2A-2I, an embodiment of a method for replacing control pod30′ with control pod30″ using system100will be described. In general, the method includes removing control pod30′ from BOP stack11as shown inFIGS. 2A-2E; lifting control pod30′ to vessel20at the surface17as shown inFIGS. 2E and 2F; deploying control pod30″ from vessel20subsea to BOP stack11as shown inFIGS. 2G and 2H; and installing control pod30″ on BOP stack as shown inFIGS. 2H and 2I.

Referring first toFIGS. 2A-2B, rope50is coupled to the failed or faulty control pod30′ In particular, rope50is paid out from lifting device22until the free, subsea end50aof rope50is at a depth equal to or greater than the depth of control pod30′ as shown inFIG. 2A. Next, with sufficient slack in rope50, ROV40grabs end50awith its claw42, moves end50ato control pod30′, and secures end50ato control pod30′ as shown inFIGS. 2B and 2C. If necessary, ROV40can then be used to decouple any connections between pod30′ and BOP stack11(e.g., mechanical and/or hydraulic connections between pod30′ to BOP stack11) as shown inFIG. 2D. Moving now toFIGS. 2E and 2F, ROV40is employed to pull pod30′ from BOP stack11as rope50is paid-in to apply tension to rope50, thereby lifting pod30′ to vessel20.

Referring now toFIGS. 2F-2I, replacement pod30″ is deployed subsea from vessel20and attached to BOP stack11to replace pod30′ by effectively performing the steps of the retrieval process shown inFIGS. 2A-2Ein reverse order. Namely, as shown inFIG. 2F, the free end50aof rope50is attached to replacement pod30″ on vessel20, and lifting device22is used to lower replacement pod30″ subsea. Using lifting device22, replacement pod30″ is lowered to a depth that is equal to or slightly greater than the depth at which pod30″ is to be installed on BOP stack11as shown inFIG. 2G. Moving now toFIGS. 2H and 2I, ROV40pushes pod30″ into place on BOP stack11. If necessary, ROV40can then be used to make up any connections between pod30′ and BOP stack11(e.g., mechanical and/or hydraulic connections between pod30′ to BOP stack11). Once replacement pod30″ is properly installed on BOP stack11, ROV40disconnects end50aof wire from pod30″, and lifting devices pays-in rope50to lift end50aback to the surface17.

In the manner described and shown inFIGS. 2A-2I, system100can be used to retrieve control pod30′ and replace it with control pod30″. During retrieval of pod30′ to the surface17, ROV40is used to connect rope50to pod30′, disconnect pod30′ from BOP stack11, and move pod30′ from BOP stack11. During deployment of pod30″ from the surface17, ROV40is used to move pod30″ onto BOP stack11, connect pod30′ to BOP stack11, and disconnect rope50from pod30″. It should be appreciated that rope50is different from a conventional guideline as rope50is not permanently installed and used to assemble the BOP stack (e.g., BOP stack11). Rather, rope50can be deployed for use with system100on an as needed basis after BOP stack11is installed and mounted to wellhead12. In addition, ROV40can be used to guide and/or monitor pod30″ as it is lifted, lowered, or otherwise moved subsea. However, it should be appreciated that during both the retrieval of pod30′ and the deployment of pod30″, the weight of pod30′ and pod30″, respectively, is supported by rope50, thereby reducing the payload lifting requirements for ROV40.

A rough alignment system such as a stabbing spear and mating guide or funnel can be included in system100to assist in guiding pod30′ as it is removed from BOP stack11and assist in guiding pod30″ as it is advanced to BOP stack11. For example, a stabbing spear extending from BOP stack11and a funnel slidingly disposed about the spear and attached to pod30′ can be used to guide pod30′ as it is pulled from BOP stack11, and a funnel attached to pod30″ can be used to slidingly receive the spear as pod30″ is moved to BOP stack11. It should be appreciated that one benefit of such a rough alignment system is a reduction in the demands placed on the ROV40in terms of the precision needed in positioning and aligning pod30″ with BOP stack11.

Referring now toFIGS. 3A-3N, an embodiment of a system200for retrieving a failed or faulty control pod30′, and replacing it with a replacement control pod30″ is schematically shown. More specifically, inFIGS. 3A-3C, system200is shown delivering replacement control pod30″ subsea to BOP stack11; inFIGS. 3D-3K, system200is shown removing the failed or faulty control pod30′ from BOP stack11and replacing it with control pod30″; and inFIGS. 3L-3N, system200is shown retrieving control pod30′ to vessel20at the surface17.

In this embodiment, system200includes lifting device22mounted to surface vessel20, rigging50coupled to lifting device22, control pod exchange device210, and BOP stack connection assembly220coupled to device210. Lifting device22and rigging50are as previously described. Namely, lifting device22is a heavy lift crane disposed on vessel20, and rigging50is rope that extends from lifting device22and can be paid in or paid out from lifting device22to raise or lower loads. In this embodiment, one or more ROV40as previously described is used to assist in the retrieval of pod30′ and deployment of pod30″. As will be described in more detail below, control pod exchange device210delivers replacement pod30″ to BOP stack11, automates the exchange of pods30′,30″ (i.e., removes pod30′ from stack11and installs pod30″ in stack11), and delivers pod30′ to the surface17. Connection assembly220facilitates the alignment of device210relative to BOP stack11and coupling of device210to BOP stack11such that pods30′,30″ can be exchanged.

Referring briefly toFIGS. 4A-4C, control pod exchange device210and BOP stack connection assembly220coupled to device210are shown. In this embodiment, exchange device210includes an outer housing211and a control pod transfer assembly230moveably disposed in housing211. In this embodiment, housing211is a rectangular frame having a top211a, a bottom211b, a front211c, a back211d, and lateral sides211e,211f. A connector213is provided on the top211aof housing211for coupling housing211and device210to the free end50aof rope50. The front211cof housing211is open to allow control pods30,31to be transferred therethrough into and out of housing211. As best shown inFIGS. 4A and 4B, the interior of housing211includes three areas or bays212a,212b,212c(schematically shown with dashed lines) horizontally arranged side-by-side between lateral sides211e,211f. Each bay212a,212b,212cis sized to accommodate one control pod30,31. In this embodiment, connection assembly220includes a pair of parallel arms221coupled to housing211proximal the top211a. Arms221extend horizontally outward from the front211cof housing211. As shown inFIG. 3C, arms221are sized, shaped, and positioned to mate and engage with the BOP stack11(e.g., the outer frame of the BOP stack11) with middle bay212baligned with and adjacent the control pod30,31to be replaced.

Referring still toFIGS. 4A-4C, control pod transfer assembly230automates the transfer of control pod30′ from BOP stack11into housing211and the transfer of control pod30″ from housing211into BOP stack11. In this embodiment, transfer assembly230includes a tray231moveably disposed in housing211proximal the bottom211band a pair of control pod supports232a,232bmoveably coupled to tray231. Supports232a,232bare arranged laterally side-by-side on tray231—inFIGS. 4A and 4B, support232ais positioned on the left side of tray231and support232bis positioned on the right side of tray231. Each support232a,232bis sized to support one control pod30,31thereon.

Tray231is controllably moved laterally within housing211between sides211e,211fas represented by arrows233, and supports232a,232bare controllably moved forward and backward relative to tray231as represented by arrows234. Each support232a,232bcan extend from tray231and housing211to retrieve pod30′ from BOP stack11and install pod30″ into BOP stack11when that particular support232a,232bis aligned with the middle bay212b(i.e., disposed immediately below the middle bay212b). In general, any suitable means or devices known in the art can be used to controllably move tray231laterally relative to housing211and move supports232forward and back relative to tray231including, without limitation, hydraulic cylinders, electric actuators, and the like.

As previously described, tray231can be moved laterally within housing211in the direction of arrows233. In particular, tray231can be moved laterally between a first position (shown inFIGS. 4A and 4B) with tray231positioned adjacent side211fand distal side211ewith support232aaligned with middle bay212band support232baligned with bay212c(the rightmost bay inFIGS. 4A and 4B); and a second position with tray231positioned adjacent side211eand distal side211fwith support232aaligned with bay212a(the leftmost bay inFIGS. 4A and 4B) and support232baligned with bay212b. Further, as previously described, each support232a,232bcan be moved forward and backward relative to tray231in the direction of arrows234when the particular support232a,232bis aligned with middle bay212b. Thus, when a given support232a,232bis aligned with middle bay212b, that support232a,232bhas a withdrawn position disposed within housing211and an extended position extending from tray231and the front211cof housing211.

Referring again toFIGS. 3A-3N, an embodiment of a method for replacing control pod30′ with control pod30″ using system200will be described. InFIGS. 3A-3C, control pod30″ is shown being deployed subsea to BOP stack11; inFIGS. 3D-3G, control pod30′ is shown being removed from BOP stack11and transferred to exchange device210; inFIGS. 3H-3J, control pod30″ is shown being transferred from exchange device210to BOP stack11and installed on BOP stack11; and inFIGS. 3L-3N, control pod30′ is shown being retrieved to the surface17and vessel20.

Referring first toFIGS. 3A-3C, control pod30″ is disposed within exchange device210on vessel20, and the free end50aof rope50is attached to connector213on vessel20. Pod30″ is positioned on one of the supports232a,232bwithin housing211. The support232a,232bon which pod30″ is disposed is preferably aligned with middle bay212bto balance the weight of device210with pod30″ therein. In this embodiment, pod30″ is positioned on support232a. Next, lifting device22lowers exchange device210(carrying pod30″) subsea. As shown inFIG. 3A, rope50is paid out from lifting device22until pod30″ is at a depth generally equal to the depth of control pod30′. Moving now toFIGS. 3B and 3C, ROV40moves exchange device210to BOP stack11immediately adjacent control pod30′, and device210is mounted to BOP stack11with connection assembly220. During this process, lifting device22is used to control and adjust the vertical position of device210relative to BOP stack11while ROV40generally provides the lateral force to move device210to BOP stack11. It should be appreciated that rope50may need to be paid out to allow device210to be moved to BOP stack11, however, rope50remains in tension, and thus, supports the weight of device210and pod30″ therein.

As previously described and best shown inFIG. 3C, arms221of connection assembly220are sized, shaped, and positioned to mate and engage with the BOP stack11(e.g., the outer frame of the BOP stack11) with middle bay212baligned with and adjacent the control pod30′ to be replaced. With device210coupled to BOP stack11, pods30′,30″ can be swapped. In particular, as shown inFIGS. 3D and 3E, tray231is translated laterally to move replacement control pod30″ out of middle bay212band align the empty support232a,232bwith control pod30′. In this embodiment, pod30″ is seated on support232a, and thus, tray231is moved laterally to move pod30″ and support232afrom middle bay212bto bay212awhile simultaneously moving empty support232bfrom bay212cto middle bay212b. Next, as shown inFIGS. 3E and 3F, the empty support232bis extended from tray231and the front211cof housing211to pod30′. In this embodiment, support232bis sized and positioned to slide under pod30′. With support232bslidingly engaging the bottom of pod30′, and thus, positioned to support the weight of pod30′, ROV40can be used to decouple any connections between pod30′ and BOP stack11(e.g., mechanical and/or hydraulic connections between pod30′ to BOP stack11). Then, with pod30′ sitting on support232b, support232bis withdrawn back into housing211, thereby positioning pod30′ in middle bay212b.

Referring now toFIGS. 3G-3K, once pod30′ is removed from BOP stack11, pod30″ can be installed. First, as shown inFIGS. 3G and 3H, with both pods30′,30″ disposed in housing211on trays232b,232a, respectively, tray231is moved laterally to move control pod30′ out of middle bay212band move replacement control pod30″ into middle bay212b. Next, support232ais extended from tray231and the front211cof housing211to install pod30′ on BOP stack11. ROV40can be used to make up any connections between pod30″ and BOP stack11(e.g., mechanical and/or hydraulic connections between pod30′ to BOP stack11). Moving now toFIG. 3J, with replacement control pod30″ installed on BOP stack11, support232ais withdrawn back into housing211, thereby completing the exchange of pods30′,30″. To balance the weight of exchange device210following the installation of pod30″, tray231is preferably moved laterally to position pod30′ in middle bay212bto balance the weight of device210with pod30′ therein.

Referring now toFIGS. 3L-3N, after swapping pods30′,30″, exchange device210is decoupled from BOP stack11by applying tension to rope50with lifting device22to lift exchange device210while ROV40pulls and/or guides exchange device210laterally away from BOP stack11. Rope50remains in tension during this process, and thus, supports the weight of device210and pod30″ therein, while ROV40generally provides the lateral force to guide device210away from BOP stack11.

In the manner described and shown inFIGS. 3A-3M, system200can be used to deploy control pod30″, exchange or swap control pods30′,30″ at BOP stack11, and retrieve control pod30′ to the surface17in a single subsea trip. During deployment of pod30″ and retrieval of pod30′, ROV40is used to laterally move and/or guide exchange device210to and from BOP stack11, respectively. In addition, ROV40can be used to guide and/or monitor exchange device210(and pod30′, pod30″ disposed thereon) as it is lifted, lowered, or otherwise moved subsea. However, it should be appreciated that during deployment of pod30″, exchanging of pods30′,30″ at BOP stack11, and retrieval of pod30′, the weight of exchange device210(and any pod30′,30″ thereon) is supported by rope50and/or BOP stack11, thereby reducing the payload lifting requirements for ROV40.

Referring now toFIGS. 5A-5J, an embodiment of a system300for retrieving a failed or faulty control pod30′, and replacing it with a replacement control pod30″ is schematically shown. More specifically, inFIGS. 5A-5E, system300is shown delivering replacement control pod30″ subsea to BOP stack11; inFIGS. 5E and 5F, system300is shown removing the failed or faulty control pod30′ from BOP stack11and replacing it with control pod30″; and inFIGS. 5G-5J, system300is shown retrieving control pod30′ to vessel20at the surface17.

In this embodiment, system300is substantially the same as system200previously described except that BOP stack connection assembly220is replaced with BOP stack connection assembly240. Thus, in this embodiment, system300includes lifting device22mounted to surface vessel20, rigging50coupled to lifting device22, control pod exchange device210, and BOP stack connection assembly240coupled to device210.

In this embodiment, BOP stack connection assembly240is a winch mounted to exchange device210, and more specifically, fixably attached to the top211aof housing211of exchange device210. Accordingly, connection assembly240may also be referred to as winch240. As will be described in more detail below, winch240can pay in and pay out a rope51. In this embodiment, one or more ROV40as previously described is used to assist in the retrieval of pod30′ and deployment of pod30″.

In the same manner as previously described with respect to system200, control pod exchange device210delivers replacement pod30″ to BOP stack11, automates the exchange of pods30′,30″ (i.e., removes pod30′ from stack11and installs pod30″ in stack11), and delivers pod30′ to the surface17. However, in this embodiment, winch240facilitates the alignment of device210relative to BOP stack11, the coupling of device210to BOP stack11such that pods30′,30″ can be exchanged, and the movement of device210to and away from BOP stack11.

Referring still toFIGS. 5A-5J, an embodiment of a method for replacing control pod30′ with control pod30″ using system300will be described. InFIGS. 5A and 5B, control pod30″ is shown being deployed subsea; inFIGS. 5C-5E, control pod30″ is shown being moved to BOP stack11; inFIGS. 5E and 5F, control pod30′ is shown being removed from BOP stack11and transferred to exchange device210while control pod30″ is transferred from exchange device210to BOP stack11and installed on BOP stack11; and inFIGS. 5G-5J, control pod30′ is shown being retrieved to the surface17and vessel20.

Referring first toFIGS. 5A and 5B, control pod30″ is disposed within exchange device210on vessel20, and the free end50aof rope50is attached to connector213on vessel20. Pod30″ is positioned on one of the supports232a,232bwithin housing211. The support232a,232bon which pod30″ is disposed is preferably aligned with middle bay212bto balance the weight of device210with pod30″ therein. Next, lifting device22lowers exchange device210(carrying pod30″) subsea. As shown inFIG. 5B, rope50is paid out from lifting device22until pod30″ is at a depth less than the depth of control pod30′.

Moving now toFIG. 5C, rope51is paid out from winch240, and with sufficient slack in rope51, ROV40grabs the free end51aof rope51with its claw42, moves end51ato BOP stack11, and secures end51ato BOP stack11, thereby coupling exchange device210with BOP stack11. Free end51ais attached to BOP stack11at a particular position that allows winch240to pull exchange device210to BOP stack11with middle bay212baligned with and immediately adjacent control pod30′. Next, as shown inFIGS. 5D and 5E, winch240is operated to pay in rope51, thereby applying tension to rope51and pulling exchange device210to BOP stack11. Due to the attachment point of end50aon BOP stack11, bay212bis aligned with and adjacent to control pod30′ when exchange device210is pulled to BOP stack11with winch240. Although rope50may need to be paid out to allow device210to be pulled to BOP stack11with winch240, rope50remains in tension, and thus, supports the weight of device210and pod30″ therein. Thus, lifting device22primarily supports the weight of exchange device210and pod30′ therein, while winch240provides the lateral force to move device210to BOP stack11.

As shown inFIGS. 5E and 5F, with device210coupled to BOP stack11with middle bay212baligned with and adjacent the control pod30′, pod30′ is removed from BOP stack11and then pod30″ is installed in BOP stack11(i.e., pod30′ is replaced with pod30″). In this embodiment, exchange device210replaces pod30′ with pod30″ in the same manner as previously described and shown inFIGS. 3D-3K.

Referring now toFIGS. 5F-5I, after swapping pods30′,30″, exchange device210is decoupled from BOP stack11. In particular, the tension in rope50is increased with lifting device22to pull exchange device210away from BOP stack11while winch240pays out rope51as shown inFIGS. 5F and 5G. ROV40can be employed to assist in guiding exchange device210away from BOP stack11. Next, slack is provided in rope51, and then ROV40decouples end51aof rope51from BOP stack11as shown inFIGS. 5H and 5I. Moving now toFIG. 5J, once exchange device210is decoupled from BOP stack11, lifting device22lifts exchange device210(carrying pod30′) to vessel20at the surface17.

In the manner described and shown inFIGS. 5A-5J, system300can be used to deploy control pod30″, exchange or swap control pods30′,30″ at BOP stack11, and retrieve control pod30′ to the surface17in a single subsea trip. During deployment of pod30″ and retrieval of pod30′, winch240and associated rope51are used to laterally move exchange device210to and from BOP stack11. In addition, ROV40can be used to guide and/or monitor exchange device210(and pod30′, pod30″ disposed thereon) as it is lifted, lowered, or otherwise moved subsea. However, it should be appreciated that during deployment of pod30″, exchanging of pods30′,30″ at BOP stack11, and retrieval of pod30′, the weight of exchange device210(and any pod30′,30″ thereon) is supported by rope50, thereby reducing the payload lifting requirements for ROV40.

Referring now toFIGS. 6A-6E, an embodiment of a system400for retrieving a failed or faulty control pod30′, and replacing it with a replacement control pod30″ is schematically shown. More specifically, inFIGS. 6A-6C, system400is shown delivering replacement control pod30″ subsea to BOP stack11; inFIGS. 6C and 6D, system400is shown removing the failed or faulty control pod30′ from BOP stack11and replacing it with control pod30″; and inFIG. 6E, system400is shown retrieving control pod30′ to vessel20at the surface17.

In this embodiment, system400is substantially the same as system200previously described except that BOP stack connection assembly220is replaced with BOP stack connection assembly250. Thus, in this embodiment, system400includes lifting device22mounted to surface vessel20, rigging50coupled to lifting device22, control pod exchange device210, and BOP stack connection assembly250coupled to device210.

In this embodiment, BOP stack connection assembly250includes a pulley or sheave251rotatably coupled to the lower end50aof rope50, a guide member252mounted to exchange device210, and a rope52. In this embodiment, assembly250is made up or constructed prior to deploying exchange device210and control pod30″ subsea. In particular, rope52is passed over sheave251and through a guide passage253in guide member252. One free end52aof rope52is coupled to connector213of exchange device210, and the other free end52bof rope52is coupled to BOP stack11with ROV40. In this embodiment, the lower portion of passage253defines a guide or funnel and a stabbing spear255is provided at the end52bof rope52. ROV40couples spear255to BOP stack11, and rope52extends from spear255through passage253and over sheave251to exchange device210. As will be described in more detail below, the lower portion of passage253is configured to slidingly receive spear255as exchange device210approaches BOP stack11to guide and align exchange device210to the desired position and orientation relative to BOP stack11.

In the same manner as previously described with respect to system200, control pod exchange device210delivers replacement pod30″ to BOP stack11, automates the exchange of pods30′,30″ (i.e., removes pod30′ from stack11and installs pod30″ in stack11), and delivers pod30′ to the surface17. However, in this embodiment, assembly250facilitates the alignment of device210relative to BOP stack11, the coupling of device210to BOP stack11such that pods30′,30″ can be exchanged, and the movement of device210to and away from BOP stack11.

Referring still toFIGS. 6A-6E, an embodiment of a method for replacing control pod30′ with control pod30″ using system400will be described. InFIGS. 6A-6C, control pod30″ is shown being deployed subsea and moved to BOP stack11; inFIGS. 6C and 6D, control pod30′ is shown being removed from BOP stack11and transferred to exchange device210while control pod30″ is transferred from exchange device210to BOP stack11and installed on BOP stack11; and inFIG. 6E, control pod30′ is shown being retrieved to the surface17and vessel20.

Referring first toFIGS. 6A and 6B, control pod30″ is disposed within exchange device210on vessel20. In particular, pod30″ is positioned on one of the supports232a,232bwithin housing211. The support232a,232bon which pod30″ is disposed is preferably aligned with middle bay212bto balance the weight of device210with pod30″ therein. Next, lifting device22raises sheave251to lift device210from vessel20, and then lowers sheave251to lower device210(carrying pod30″) subsea. Rope52extends over sheave251with end52battached to the tip of spear55, which in turn is coupled to BOP stack11, and the other end52aattached to exchange device210. Consequently, rope52remains in tension as sheave251is lowered subsea with lifting device22(the weight of exchange device210continuously pulls on rope52). As shown inFIG. 6B, lifting device22continues to lower sheave251to lower exchange device210towards BOP stack11. In essence, as sheave251is lowered by lifting device22, exchange device210is controllably lowered under its own weight. Rope52passes through guide passage253, and thus, as exchange device210is lowered, guide member252slides along rope52toward end52a. Guide member252is attached to exchange device210, and thus, as guide member252moves along rope52, exchange device210also moves toward BOP stack11. As best shown inFIG. 6C, spear55is attached to BOP stack11at a particular position that enables alignment of exchange device210and BOP stack11. As exchange device210is lowered to BOP stack11, the lower portion of passage253slidingly receives spear255, thereby guiding exchange device210to the desired positions relative to BOP stack11. Thus, the funnel at the lower portion of passage253and spear255enable alignment of exchange device210relative to BOP stack11, thereby allowing guide member252to mate and engage with the BOP stack11(e.g., the outer frame of the BOP stack11) with middle bay212baligned with and adjacent to the control pod30′ to be replaced.

As shown inFIGS. 6C and 6D, with device210coupled to BOP stack11with middle bay212baligned with and adjacent the control pod30′, pod30′ is removed from BOP stack11and then pod30″ is installed in BOP stack11(i.e., pod30′ is replaced with pod30″). In this embodiment, exchange device210replaces pod30′ with pod30″ in the same manner as previously described and shown inFIGS. 3D-3K. Since guide member252mates and engages BOP stack11in this embodiment, slack can be provided in rope52as BOP stack11supports and maintains the position of guide member252and exchange device210attached thereto.

Moving now toFIGS. 6D and 6E, after swapping pods30′,30″, sheave251is raised with lifting device22to apply and/or increase tension in rope52, and lift guide member252and exchange device210from BOP stack11. Sheave251is raised by lifting device22to lift exchange device210and pod30″ to the surface17and vessel20. Once exchange device210(carrying pod30″) is disposed on vessel20, end52bof rope52can be decoupled from BOP stack11with ROV40.

In the manner described and shown inFIGS. 6A-6E, system400can be used to deploy control pod30″, exchange or swap control pods30′,30″ at BOP stack11, and retrieve control pod30′ to the surface17in a single subsea trip. During deployment of pod30″ and retrieval of pod30′, lifting device22is used to lower and raise exchange device210, respectively, while guide member252simultaneously slides along rope52to move exchange device laterally to and from BOP stack11. In addition, ROV40can be used to guide and/or monitor exchange device210(and pod30′, pod30″ disposed thereon) as it is lifted, lowered, or otherwise moved subsea. However, it should be appreciated that during deployment of pod30″, exchanging of pods30′,30″ at BOP stack11, and retrieval of pod30′, the weight of exchange device210(and any pod30′,30″ thereon) is supported by rope50and rope52, thereby reducing the payload lifting requirements for ROV40.

Referring now toFIGS. 7A-7J, an embodiment of a system500for retrieving a failed or faulty control pod30′, and replacing it with a replacement control pod30″ is schematically shown. More specifically, inFIGS. 7A-7E, system500is shown delivering replacement control pod30″ subsea to BOP stack11; inFIGS. 7E and 7F, system500is shown removing the failed or faulty control pod30′ from BOP stack11and replacing it with control pod30″; and inFIGS. 7G-7J, system500is shown retrieving control pod30′ to vessel20at the surface17.

In this embodiment, system500includes lifting device22mounted to surface vessel20, rigging50coupled to lifting device22, control pod exchange device210, and a BOP stack connection assembly260coupled to device210. Lifting device22, rigging50, and exchange device210are each as previously described, however, BOP stack connection assembly260is different than connection assemblies220,230,240,250previously described.

Referring briefly toFIGS. 8A and 8B, BOP stack connection assembly260releasably couples control pod exchange device210to BOP stack11, controllably lowers and raises control pod exchange device210to and from BOP stack11, and guides control pod exchange device210as it moves to and from BOP stack11. In this embodiment, BOP stack connection assembly260includes a housing connector261coupled to the top211aof housing211, a connection assembly270releasably connected to housing connector261, a winch280coupled to the top211aof housing211, a first pair of sheaves281rotatably coupled to housing211and connector261, a second pair of sheaves282rotatably coupled to housing211and connector261, a pair of BOP stack connection members290, a pair of tubular guides295coupled to housing211, and a pair of ropes285extending from winch280to stack connection members290. Guides295are positioned proximal the top211aand the front211cof housing211. As will be described in more detail below, the forward lower ends of guides295comprise funnels that function to slidingly receive and guide connection members290into guides295. In this embodiment, connection assembly270is releasably coupled to housing connector261, and hence housing211, with a pin262. However, in other embodiments, the connection assembly (e.g., assembly270) can be releasably coupled to housing connector (e.g., housing connector261) and housing (e.g., housing211) by other mechanisms or devices such as a ratcheting mechanism.

Housing connector261is a rigid structure extending vertically upward from the top211aof housing211. In particular, housing connector261has a lower end261afixably secured to housing211and an upper end261bdistal housing211. Upper end261bincludes a through bore that slidingly receives pin262.

Referring still toFIGS. 8A and 8B, connection assembly270releasably couples housing connector261and exchange device210to rigging50. In this embodiment, connection assembly270includes a base member271, a sheave support272pivotally coupled to base member271, and a pair of laterally spaced sheaves273rotatably coupled to support272on opposite lateral sides of base member271in front view (FIG. 8A). Base member271is a rigid structure having a lower end271apivotally coupled to housing connector261with pin262and an upper end271bcomprising a connector213. Lower end271aincludes a through bore that slidingly receives pin262, thereby pivotally and releasably coupling base member271to housing connector261. Connector213couples connection assembly270, housing connector261, and exchange device210to rigging50. As will be described in more detail below, each rope285extends from winch280over one sheave273, over one sheave281, and through one guide295to the corresponding connection member290.

Referring still toFIGS. 8A and 8B, BOP stack connection members290releasably couples connection assembly270and exchange device210to BOP stack11, and guide exchange device210such that bay212bis aligned with and adjacent to control pod30′. In this embodiment, each connection member290is an elongate stabbing spear having a first or upper end290aand a second or lower end290b. Lower end290bis provided with a foot291sized and shaped to releasably engage a mating profile on BOP stack11. One end of each rope285is mounted to winch280and the opposite end of each rope285is attached to upper end290aof one connection member290g.

Connection members290are movably coupled to exchange device210with ropes285and winch280. More specifically, when connection members290are disposed in guides295, ropes285can be paid out from winch280to allow connection members290to slide downward out of guides295, thereby enabling BOP stack connection members290to be controllably lowered from exchange device210; and when connection members290are spaced apart from exchange device210, ropes285can be paid in to winch280to pull connection members290upward toward exchange device210and into guides295

In the same manner as previously described with respect to system200, control pod exchange device210delivers replacement pod30″ to BOP stack11, automates the exchange of pods30′,30″ (i.e., removes pod30′ from stack11and installs pod30″ in stack11), and delivers pod30′ to the surface17. However, in this embodiment, assembly260facilitates the alignment of device210relative to BOP stack11, the coupling of device210to BOP stack11such that pods30′,30″ can be exchanged, and the movement of device210to and away from BOP stack11.

Referring again toFIGS. 7A-7J, an embodiment of a method for replacing control pod30′ with control pod30″ using system500will be described. InFIGS. 7A-7D, control pod30″ is shown being deployed subsea and moved to BOP stack11; inFIGS. 7E and 7F, control pod30′ is shown being removed from BOP stack11and transferred to exchange device210while control pod30″ is transferred from exchange device210to BOP stack11and installed on BOP stack11; and inFIG. 7G-7J, control pod30′ is shown being retrieved to the surface17and vessel20.

Referring first toFIG. 7A, control pod30″ is disposed within exchange device210on vessel20. In particular, pod30″ is positioned on one of the supports232a,232bwithin housing211, and the free end50aof rope50is attached to connector213on vessel20. The support232a,232bon which pod30″ is disposed is preferably aligned with middle bay212bto balance the weight of device210with pod30″ therein. In addition, connection assembly270is pivotally coupled to housing connector261, and hence exchange device210, with pin262. Next, lifting device22lowers exchange device210(carrying pod30″) subsea via rope50and connection assembly270. As shown inFIG. 7A, ropes285are paid out from winch280at the surface17such that stack connection members290hang from exchange device210.

Moving now toFIG. 7B, ropes285are paid out from winch280at the surface17such that connection members290are lowered to a depth equal to or greater than the depth of control pod30′ as exchange device210is lowered subsea with lifting device22. Next, stack connection members290are attached to BOP stack11with ROV40. Feet291are sized, shaped, and positioned to mate and engage with BOP stack11, while simultaneously aligning bay212bwith pod30′ when received by guides295upon arrival of exchange device210.

Referring now toFIG. 7C, once stack connection members290are secured to BOP stack11, lifting device22pays in rope50to pull any slack from ropes285and place ropes285in tension. Next, ROV40pulls pin262from base member271and housing connector261, thereby decoupling exchange device210from connection assembly270so that exchange device210can be lowered to BOP stack11. To enable ROV40to easily remove pin262from the throughbores in member271and connector261, the shear loads acting on pin262by member271and connector261are preferably eliminated.

Referring briefly toFIG. 8C, a schematic free body diagram of the forces acting on pin262under static conditions are shown. For purposes of clarity and simplicity, sheaves273, ropes285, and connection members290are represented by a single sheave273, a single rope285, and a single connection member290, respectively, inFIG. 7C. The weight of exchange device210(including any pod30disposed thereon) is represented with reference numeral “W210,” the tension in rope50is represented with reference numeral “T50,” the tension in the portion of rope285extending between sheave273and stack connection member290is represented with reference numeral “T273-290,” and the tension in the portion of rope285extending between sheave273and winch280is represented with reference numeral “T273-280.”

Under static conditions, when there is no tension in rope285(i.e., T273-280=0 and T273-290=0), the forces applied to pin262include the weight W210acting through connector261and the tension T50acting through member271. In such case, the downward force acting on pin262through connector261due to the weight W210is laterally spaced from and opposed by the upward force acting on pin262through member271due to tension T50, thereby resulting in shear loads being applied to pin262. However, with stack connection members290secured to BOP stack11and ropes285and rope50in tension, when the tension T50applied to rope50is equal to twice the weight W210, the downward force acting on pin262due to weight W210goes to zero (the weight W210is offset and balanced by tension T273-280) and the upward force acting on pin262due to tension T50goes to zero (the tension T50is offset and balanced by tensions T273-280, T273-290). When tension is applied to rope285and assuming static conditions, T50=T273-290+W210, and thus, when T273-290=W210, tension T50=2*W210. Thus, when lifting device22increases the tension in rope285(i.e., tension T273-290, which equals tension T273-290) to the weight W210, pin262is no longer in shear and can be pull with ROV40, and the tension in rope50(i.e., tension T50) will be twice the weight W210.

Referring still toFIG. 7C, the foregoing relationships between the tension in rope50, the tension in ropes285, and the weight of exchange device210can be utilized to control and time the removal of pin262with ROV40. Namely, once stack connection members290is secured to BOP stack11, lifting device22is operated to pay in rope50until the tension in rope50(measured at lifting device22) is twice the weight of exchange device210, at which point—pin262is no longer in shear and ROV40can remove pin262.

Moving now toFIGS. 7D and 7E, upon removal of pin262, exchange device210is decoupled from connection assembly270and is lowered by paying out rope50from lifting device22. As rope50is paid out, ropes285move around sheaves273as exchange device210slides along ropes285extending through guides295towards connection members290and BOP stack11. As exchange device210approaches BOP stack11, connection members290are slidingly received into guides295, thereby aligning exchange device210in the desired position relative to BOP stack11(i.e., with bay212baligned with and adjacent to control pod30′).

As previously described, in this embodiment, pin262is removed by ROV40once the shear loads acting on pin262are sufficiently reduced and/or eliminated. However, in other embodiments, the pin (e.g., pin262) may be biased out of the corresponding throughbores (e.g., spring loaded) such that the pin automatically moves out of the aligned throughbores once the the shear loads acting on pin262are sufficiently reduced and/or eliminated.

As shown inFIGS. 7E and 7F, with device210coupled to BOP stack11with middle bay212baligned with and adjacent the control pod30′, pod30′ is removed from BOP stack11and then pod30″ is installed in BOP stack11(i.e., pod30′ is replaced with pod30″). In this embodiment, exchange device210replaces pod30′ with pod30″ in the same manner as previously described and shown inFIGS. 3D-3K.

Referring now toFIGS. 7F-7H, after swapping pods30′,30″, exchange device210is lifted from BOP stack11. In particular, lifting device22is operated to pay in rope50, thereby pulling exchange device210upward toward the surface17and connection assembly270. As rope50is paid in, ropes285move around sheaves273as exchange device210slides along ropes285extending through guides295away from stack connection members290and BOP stack11. As shown inFIG. 7H, upon arrival at connection assembly270, the throughbores in member271and connector261are aligned and ROV40inserts pin262therethrough, thereby pivotally coupling exchange device210and connection assembly270.

Moving now toFIGS. 7I and 7J, after coupling exchange device210and connection assembly270, the weight of exchange device210is supported by rope50while lifting device22is operated to pay out rope50, thereby removing any tension in ropes285. Next, ROV40decouples stack connection members290from BOP stack11. At this point, winch280can be operated to pay in ropes285and pull stack connection members290upward to exchange device210, or alternatively, ropes285can be left hanging while exchange device210. Lifting device22can then be used to lift exchange device210(carrying pod30′) to vessel20via rope50and connection assembly270.

In the manner described and shown inFIGS. 7A-7I, system500can be used to deploy control pod30″, exchange or swap control pods30′,30″ at BOP stack11, and retrieve control pod30′ to the surface17in a single subsea trip. During deployment of pod30″ and retrieval of pod30′, lifting device22pays out and pays in rope50to move exchange device210to and from BOP stack11. Thus, in this embodiment, control over the deployment and retrieval of exchange device210is primarily controlled from the surface with lifting device22. For example, winch280need not be operated to lower and raise exchange device210to and from, respectively, BOP stack11. In addition, ROV40can be used to guide and/or monitor exchange device210(and pod30′, pod30″ disposed thereon) as it is lifted, lowered, or otherwise moved subsea. However, it should be appreciated that during deployment of pod30″, exchanging of pods30′,30″ at BOP stack11, and retrieval of pod30′, the weight of exchange device210(and any pod30′,30″ thereon) is supported by rope50and/or ropes285, thereby reducing the payload lifting requirements for ROV40.

Referring now toFIGS. 9A-9J, an embodiment of a system600for retrieving a failed or faulty control pod30′, and replacing it with a replacement control pod30″ is schematically shown. More specifically, inFIGS. 9A-9E, system600is shown delivering replacement control pod30″ subsea to BOP stack11; inFIGS. 9E and 9F, system600is shown removing the failed or faulty control pod30′ from BOP stack11and replacing it with control pod30″; and inFIGS. 9G-9J, system600is shown retrieving control pod30′ to vessel20at the surface17.

System600is similar to system500previously described with the exception that system600relies on a different lifting device mounted to surface vessel20to deploy and retrieve control pod exchange device210. In this embodiment, the lifting device is an offset derrick21′ mounted to surface vessel20instead of lifting device22(e.g., a crane), and further, a pipe string150(e.g., a drill string) suspended from derrick21′ is used instead of rigging50. Thus, in this embodiment, system600includes offset derrick21′ mounted to surface vessel20, pipe string150suspended from derrick21′, control pod exchange device210, and BOP stack connection assembly260coupled to device210. Control pod exchange device210and BOP stack connection assembly260are each as previously described. Connector213of connection assembly270is releasably attached to the lower end of pipe string150(instead of the lower end of rigging50). Thus, in this embodiment of system600, using offset derrick21′ and pipe string150, control pod exchange device210delivers replacement pod30″ to BOP stack11, automates the exchange of pods30′,30″ (i.e., removes pod30′ from stack11and installs pod30″ in stack11), and delivers pod30′ to the surface17. Connection members290, guides295, and ropes290facilitate the alignment of device210relative to BOP stack11, the coupling of device210to BOP stack11such that pods30′,30″ can be exchanged, and the movement of device210to and away from BOP stack11. One or more subsea remotely operated vehicles40as previously described are used, to varying degrees, to assist in the retrieval of pod30′ and deployment of pod30″.

Referring still toFIGS. 9A-9J, an embodiment of a method for replacing control pod30′ with control pod30″ using system600will be described. InFIGS. 9A-9D, control pod30″ is shown being deployed subsea and moved to BOP stack11; inFIGS. 9E and 9F, control pod30′ is shown being removed from BOP stack11and transferred to exchange device210while control pod30″ is transferred from exchange device210to BOP stack11and installed on BOP stack11; and inFIGS. 9G-9J, control pod30′ is shown being retrieved to the surface17and vessel20.

Referring first toFIG. 9A, control pod30″ is disposed within exchange device210on vessel20. In particular, pod30″ is positioned on one of the supports232a,232bwithin housing211, and the lower end of pipe string150is coupled to connector213on vessel20. The support232a,232bon which pod30″ is disposed is preferably aligned with middle bay212bto balance the weight of device210with pod30″ therein. In addition, connection assembly270is pivotally coupled to housing connector261, and hence exchange device210, with pin262. Next, derrick21′ lowers exchange device210(carrying pod30″) subsea via pipe string150and connection assembly270. As shown inFIG. 9A, ropes285are paid out from winch280at the surface17such that stack connection members290hang from exchange device210.

Moving now toFIG. 9B, ropes285are paid out from winch280at the surface17such that connection members290are lowered to a depth equal to or greater than the depth of control pod30′ as exchange device210is lowered subsea with derrick21′ and pipe string150. Next, stack connection members290are attached to BOP stack11with ROV40. Feet291are sized, shaped, and positioned to mate and engage with BOP stack11, while simultaneously aligning bay212bwith pod30′ when received by guides295upon arrival of exchange device210.

Referring now toFIG. 9C, once stack connection members290are secured to BOP stack11, derrick21′ applies a lifting force to pipe string150to pull any slack from ropes285and place ropes285in tension. Next, ROV40pulls pin262from base member271and housing connector261, thereby decoupling exchange device210from connection assembly270so that exchange device210can be lowered to BOP stack11. To enable ROV40to easily remove pin262from the throughbores in member271and connector261, the shear loads acting on pin262by member271and connector261are eliminated as previously described. In particular, the tension in pipe string150, the tension in ropes285, and the weight of exchange device210can be utilized to control and time the removal of pin262with ROV40. Namely, once stack connection members290is secured to BOP stack11, derrick21′ is operated to lift pipe string150until the tension pipe string150(measured at derrick21′) is twice the weight of exchange device210, at which point—pin262is no longer in shear and ROV40can remove pin262.

Moving now toFIGS. 9D and 9E, upon removal of pin262, exchange device210is decoupled from connection assembly270and is lowered by lowering pipe string150with derrick21′. As pipe string150is lowered, ropes285move around sheaves273as exchange device210slides along ropes285extending through guides295towards connection members290and BOP stack11. As exchange device210approaches BOP stack11, connection members290are slidingly received into guides295, thereby aligning exchange device210in the desired positon relative to BOP stack11(i.e., with bay212baligned with and adjacent to control pod30′).

As previously described, in this embodiment, pin262is removed by ROV40once the shear loads acting on pin262are sufficiently reduced and/or eliminated. However, in other embodiments, the pin (e.g., pin262) may be biased out of the corresponding throughbores (e.g., spring loaded) such that the pin automatically moves out of the aligned throughbores once the the shear loads acting on pin262are sufficiently reduced and/or eliminated.

As shown inFIGS. 9E and 9F, with device210coupled to BOP stack11with middle bay212baligned with and adjacent the control pod30′, pod30′ is removed from BOP stack11and then pod30″ is installed in BOP stack11(i.e., pod30′ is replaced with pod30″). In this embodiment, exchange device210replaces pod30′ with pod30″ in the same manner as previously described and shown inFIGS. 3D-3K.

Referring now toFIGS. 9F-9H, after swapping pods30′,30″, exchange device210is lifted from BOP stack11. In particular, derrick21′ is operated to lift pipe string150, thereby pulling exchange device210upward toward the surface17and connection assembly270. As pipe string150is lifted, ropes285move around sheaves273as exchange device210slides along ropes285extending through guides295away from stack connection members290and BOP stack11. As shown inFIG. 9H, upon arrival at connection assembly270, the throughbores in member271and connector261are aligned and ROV40inserts pin262therethrough, thereby pivotally coupling exchange device210and connection assembly270.

Moving now toFIGS. 9H-9J, after coupling exchange device210and connection assembly270, the weight of exchange device210is supported by pipe string150while derrick21′ is operated to lower pipe string150, thereby removing any tension in ropes285. Next, ROV40decouples stack connection members290from BOP stack11. At this point, winch280can be operated to pay in ropes285and pull stack connection members290upward to exchange device210, or alternatively, ropes285can be left hanging while exchange device210. Derrick21′ can then be used to lift exchange device210(carrying pod30′) to vessel20via pipe string150and connection assembly270.

In the manner described and shown inFIGS. 9A-9J, system600can be used to deploy control pod30″, exchange or swap control pods30′,30″ at BOP stack11, and retrieve control pod30′ to the surface17in a single subsea trip. During deployment of pod30″ and retrieval of pod30′, derrick21′ raises and lowers pipe string150to move exchange device210to and from BOP stack11. Thus, in this embodiment, control over the deployment and retrieval of exchange device210is primarily controlled from the surface with derrick21′. For example, winch280need not be operated to lower and raise exchange device210to and from, respectively, BOP stack11. In addition, ROV40can be used to guide and/or monitor exchange device210(and pod30′, pod30″ disposed thereon) as it is lifted, lowered, or otherwise moved subsea. However, it should be appreciated that during deployment of pod30″, exchanging of pods30′,30″ at BOP stack11, and retrieval of pod30′, the weight of exchange device210(and any pod30′,30″ thereon) is supported by pipe string150and/or ropes285, thereby reducing the payload lifting requirements for ROV40.