Patent Description:
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.

<CIT> discloses a method for retrieving a subsea pod from a lower marine riser package platform by connecting a buoyant pod retriever to the subsea pod and raising the subsea pod to the surface. The method may be is accomplished without an interruption of associated subsea drilling operations and/or without disconnecting the lower marine riser package from an associated subsea stack. The method includes: positioning a retrieval module above the pod container, the retrieval module having a pod holder releasably connected thereto; disconnecting the pod holder from the retrieval module; lowering the pod holder to the pod container and releasably connecting the pod holder to the pod container; releasing the pod container from the subsea lower marine riser platform; raising the pod holder to the retrieval module and releasably connecting the pod holder with the pod container to the retrieval module; and raising the retrieval module with the pod container to a location at the surface.

The invention is as defined in the claims, wherein methods for replacing a first control pod of a BOP stack are defined according to claims <NUM> to <NUM>, and systems for replacing a first control pod coupled to a subsea BOP stack with a second control pod are defined according to claims <NUM> to <NUM>.

For a detailed description of the preferred embodiments of the invention, reference will now be made to the accompanying drawings in which:.

The following discussion is directed to various exemplary embodiments. However, one skilled in the art will understand that the examples disclosed herein have broad application, and that the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to suggest that the scope of the disclosure, including the claims, is limited to that embodiment.

Certain terms are used throughout the following description and claims to refer to particular features or components. As one skilled in the art will appreciate, different persons may refer to the same feature or component by different names. This document does not intend to distinguish between components or features that differ in name but not function. The drawing figures are not necessarily to scale. Certain features and components herein may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in interest of clarity and conciseness.

In the following discussion and in the claims, the terms "including" and "comprising" are used in an open-ended fashion, and thus should be interpreted to mean "including, but not limited to. " Also, the term "couple" or "couples" is intended to mean either an indirect or direct connection. Thus, if a first device couples to a second device, that connection may be through a direct connection, or through an indirect connection via other devices, components, and connections. In addition, as used herein, the terms "axial" and "axially" generally mean along or parallel to a central axis (e.g., central axis of a body or a port), while the terms "radial" and "radially" generally mean perpendicular to the central axis. For instance, an axial distance refers to a distance measured along or parallel to the central axis, and a radial distance means a distance measured perpendicular to the central axis.

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 <NUM>,<NUM> 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 <NUM>,<NUM> 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., <NUM>,<NUM> lbs (<NUM> lbs = <NUM>,<NUM>) versus <NUM>,<NUM> 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 to <FIG>, an embodiment of an offshore system <NUM> for drilling and/or producing a subsea well is shown. In this embodiment, system <NUM> includes a subsea blowout preventer (BOP) stack <NUM> mounted to a wellhead <NUM> at the sea floor <NUM>. Stack <NUM> includes a blowout preventer (BOP) <NUM> attached to the upper end of wellhead <NUM> and a lower marine riser package (LMRP) <NUM> connected to the upper end of BOP <NUM>. A marine riser <NUM> extends from a surface vessel <NUM> at the sea surface <NUM> to LMRP <NUM>. In this embodiment, vessel <NUM> is a floating platform, and thus, may also be referred to as platform <NUM>. In other embodiments, the vessel (e.g., vessel <NUM>) can be a drill ship or any other vessel disposed at the sea surface for conducting offshore drilling and/or production operations. Platform <NUM> includes a drilling derrick <NUM> and a lifting device <NUM>, which in this embodiment is a full depth crane.

Riser <NUM> is a large-diameter pipe that connects LMRP <NUM> to floating platform <NUM>. During drilling operations, riser <NUM> takes mud returns to platform <NUM>. A primary conductor <NUM> extends from wellhead <NUM> into the subterranean wellbore <NUM>.

BOP <NUM>, LMRP <NUM>, wellhead <NUM>, and conductor <NUM> are arranged such that each shares a common central axis <NUM>. In other words, BOP <NUM>, LMRP <NUM>, wellhead <NUM>, and conductor <NUM> are coaxially aligned. In addition, BOP <NUM>, LMRP <NUM>, wellhead <NUM>, and conductor <NUM> are vertically stacked one-above-the-other, and the position of platform <NUM> is controlled such that axis <NUM> is vertically or substantially vertically oriented. In general, platform <NUM> can be maintained in position over stack <NUM> with mooring lines and/or a dynamic positioning (DP) system. However, it should be appreciated that platform <NUM> moves 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 platform <NUM> result in the upper end of riser <NUM>, which is secured to platform <NUM>, moving relative to the lower end of riser <NUM>, which is secured to LMRP <NUM>. Wellhead <NUM>, BOP <NUM> and LMRP <NUM> are generally fixed in position at the sea floor <NUM>, and thus, riser <NUM> may flex and pivot about its lower and upper ends as platform <NUM> moves at the surface <NUM>. Consequently, although riser <NUM> is shown as extending vertically from platform <NUM> to LMRP <NUM> in <FIG>, riser <NUM> may deviate somewhat from vertical as platform <NUM> moves at the surface <NUM>.

Referring still to <FIG>, a pair of control pods <NUM> are releasably coupled to LMRP <NUM> and a pair of control pods <NUM> are releasably coupled to BOP <NUM>. Pods <NUM> are positioned above pods <NUM> (pods <NUM> are not necessarily directly over pods <NUM>), and pods <NUM> are coupled to LMRP <NUM>, whereas pods <NUM> are coupled to BOP <NUM>. It should be appreciated that pods <NUM> and pods <NUM> can control functions in the LMRP <NUM> and/or BOP <NUM>. For purposes of clarity and further explanation, pods <NUM> may also be referred to as "primary" pods <NUM>, and pods <NUM> may also be referred to as "secondary" pods <NUM>. In this embodiment, primary pods <NUM> are redundant meaning each primary pod <NUM> can perform all of the functions as the other primary pod <NUM>, and secondary pods <NUM> are backups to the primary pods <NUM>, each pod <NUM>, <NUM> being able to control select functions in LMRP <NUM> and BOP <NUM>. In general, control pods <NUM>, <NUM> can perform any of the functions performed by subsea control pods known in the art. For example, each primary control pod <NUM> can operate and monitor LMRP <NUM> and BOP <NUM>, and monitor conditions within LMRP <NUM> and BOP <NUM> (e.g., temperature, pressure, flow rates, etc.), and each secondary control pod <NUM> can operate and monitor LMRP <NUM> and BOP <NUM>, and monitor conditions within LMRP <NUM> and BOP <NUM> (e.g., temperature, pressure, flow rates, etc.). Electrical power, hydraulic power, and command signals are provided to primary control pods <NUM> from platform <NUM>. Secondary control pods <NUM> are provided power BOP stack <NUM> (e.g., stored power). In addition, the interface between each control pod <NUM>, <NUM> BOP stack <NUM> includes hydraulic and/or electrical couplings that enable pods <NUM>, <NUM> to control hydraulic and/or electrical functions of LMRP <NUM> and BOP <NUM>.

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 pod <NUM> or control pod <NUM>), and replacing it with a replacement control pod (e.g., control pod <NUM> or control pod <NUM>). Although embodiments described herein specifically show and described replacing a control pod <NUM> mounted to LMRP <NUM>, it is to be understood that embodiments described herein can also be used in the manners described to replace a control pod <NUM> mounted to BOP <NUM>.

Referring now to <FIG>, an embodiment of a system <NUM> for retrieving a failed or faulty control pod <NUM>, and replacing it with a replacement control pod <NUM> is schematically shown. More specifically, in <FIG>, system <NUM> is shown removing the failed or faulty control pod <NUM> from BOP stack <NUM>; in <FIG> and <FIG>, system <NUM> is shown retrieving the failed or faulty control pod <NUM> to vessel <NUM> at the surface <NUM>; in <FIG>, system <NUM> is shown delivering the replacement control pod <NUM> subsea to BOP stack <NUM>; and in <FIG> and <FIG>, system <NUM> is shown installing replacement control pod <NUM> on BOP stack <NUM>.

For purposes of clarity and further explanation (e.g., to aid in distinguishing failed or faulty pod <NUM> from replacement pod <NUM>), in embodiments described herein, the failed or faulty pod <NUM> is labeled with reference numeral <NUM>' and the replacement pod <NUM> is labeled with reference numeral <NUM>". In general, the replacement pod <NUM>" can be a new pod <NUM> or a repaired pod <NUM>.

In this embodiment, system <NUM> includes lifting device <NUM> mounted to surface vessel <NUM> and rigging <NUM> coupled to lifting device <NUM>. In this embodiment, rigging <NUM> is rope that extends from lifting device <NUM> and can be paid in or paid out from lifting device <NUM> to 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 vehicles <NUM> are used, to varying degrees, to assist in the retrieval of pod <NUM>' and deployment of pod <NUM>''. Each ROV <NUM> includes an arm <NUM> having a claw <NUM>, a subsea camera <NUM> for viewing the subsea operations (e.g., the relative positions of LMRP <NUM>, BOP <NUM>, pods <NUM>, <NUM>, the positions and movement of arm <NUM> and claw <NUM>, etc.), and an umbilical <NUM>. Streaming video and/or images from cameras <NUM> are communicated to the surface or other remote location via umbilical <NUM> for viewing on a continuous live basis. Arms <NUM> and claws <NUM> are controlled via commands sent from the surface through umbilical <NUM>.

Referring again to <FIG>, an embodiment of a method for replacing control pod <NUM>' with control pod <NUM>" using system <NUM> will be described. In general, the method includes removing control pod <NUM>' from BOP stack <NUM> as shown in <FIG>; lifting control pod <NUM>' to vessel <NUM> at the surface <NUM> as shown in <FIG> and <FIG>; deploying control pod <NUM>" from vessel <NUM> subsea to BOP stack <NUM> as shown in <FIG> and <FIG>; and installing control pod <NUM>" on BOP stack as shown in <FIG> and <FIG>.

Referring first to <FIG>, rope <NUM> is coupled to the failed or faulty control pod <NUM>' In particular, rope <NUM> is paid out from lifting device <NUM> until the free, subsea end 50a of rope <NUM> is at a depth equal to or greater than the depth of control pod <NUM>' as shown in <FIG>. Next, with sufficient slack in rope <NUM>, ROV <NUM> grabs end 50a with its claw <NUM>, moves end 50a to control pod <NUM>', and secures end 50a to control pod <NUM>' as shown in <FIG> and <FIG>. If necessary, ROV <NUM> can then be used to decouple any connections between pod <NUM>' and BOP stack <NUM> (e.g., mechanical and/or hydraulic connections between pod <NUM>' to BOP stack <NUM>) as shown in <FIG>. Moving now to <FIG> and <FIG>, ROV <NUM> is employed to pull pod <NUM>' from BOP stack <NUM> as rope <NUM> is paid-in to apply tension to rope <NUM>, thereby lifting pod <NUM>' to vessel <NUM>.

Referring now to <FIG>, replacement pod <NUM>" is deployed subsea from vessel <NUM> and attached to BOP stack <NUM> to replace pod <NUM>' by effectively performing the steps of the retrieval process shown in <FIG> in reverse order. Namely, as shown in <FIG>, the free end 50a of rope <NUM> is attached to replacement pod <NUM>" on vessel <NUM>, and lifting device <NUM> is used to lower replacement pod <NUM>" subsea. Using lifting device <NUM>, replacement pod <NUM>" is lowered to a depth that is equal to or slightly greater than the depth at which pod <NUM>" is to be installed on BOP stack <NUM> as shown in <FIG>. Moving now to <FIG> and <FIG>, ROV <NUM> pushes pod <NUM>" into place on BOP stack <NUM>. If necessary, ROV <NUM> can then be used to make up any connections between pod <NUM>' and BOP stack <NUM> (e.g., mechanical and/or hydraulic connections between pod <NUM>' to BOP stack <NUM>). Once replacement pod <NUM>" is properly installed on BOP stack <NUM>, ROV <NUM> disconnects end 50a of wire from pod <NUM>", and lifting devices pays-in rope <NUM> to lift end 50a back to the surface <NUM>.

In the manner described and shown in <FIG>, system <NUM> can be used to retrieve control pod <NUM>' and replace it with control pod <NUM>''. During retrieval of pod <NUM>' to the surface <NUM>, ROV <NUM> is used to connect rope <NUM> to pod <NUM>', disconnect pod <NUM>' from BOP stack <NUM>, and move pod <NUM>' from BOP stack <NUM>. During deployment of pod <NUM>" from the surface <NUM>, ROV <NUM> is used to move pod <NUM>" onto BOP stack <NUM>, connect pod <NUM>' to BOP stack <NUM>, and disconnect rope <NUM> from pod <NUM>". It should be appreciated that rope <NUM> is different from a conventional guideline as rope <NUM> is not permanently installed and used to assemble the BOP stack (e.g., BOP stack <NUM>). Rather, rope <NUM> can be deployed for use with system <NUM> on an as needed basis after BOP stack <NUM> is installed and mounted to wellhead <NUM>. In addition, ROV <NUM> can be used to guide and/or monitor pod <NUM>" as it is lifted, lowered, or otherwise moved subsea. However, it should be appreciated that during both the retrieval of pod <NUM>' and the deployment of pod <NUM>", the weight of pod <NUM>' and pod <NUM>", respectively, is supported by rope <NUM>, thereby reducing the payload lifting requirements for ROV <NUM>.

A rough alignment system such as a stabbing spear and mating guide or funnel can be included in system <NUM> to assist in guiding pod <NUM>' as it is removed from BOP stack <NUM> and assist in guiding pod <NUM>" as it is advanced to BOP stack <NUM>. For example, a stabbing spear extending from BOP stack <NUM> and a funnel slidingly disposed about the spear and attached to pod <NUM>' can be used to guide pod <NUM>' as it is pulled from BOP stack <NUM>, and a funnel attached to pod <NUM>" can be used to slidingly receive the spear as pod <NUM>" is moved to BOP stack <NUM>. It should be appreciated that one benefit of such a rough alignment system is a reduction in the demands placed on the ROV <NUM> in terms of the precision needed in positioning and aligning pod <NUM>" with BOP stack <NUM>.

Referring now to <FIG>, an embodiment of a system <NUM> for retrieving a failed or faulty control pod <NUM>', and replacing it with a replacement control pod <NUM>" is schematically shown. More specifically, in <FIG>, system <NUM> is shown delivering replacement control pod <NUM>" subsea to BOP stack <NUM>; in <FIG>, system <NUM> is shown removing the failed or faulty control pod <NUM>' from BOP stack <NUM> and replacing it with control pod <NUM>"; and in <FIG>, system <NUM> is shown retrieving control pod <NUM>' to vessel <NUM> at the surface <NUM>.

In this embodiment, system <NUM> includes lifting device <NUM> mounted to surface vessel <NUM>, rigging <NUM> coupled to lifting device <NUM>, control pod exchange device <NUM>, and BOP stack connection assembly <NUM> coupled to device <NUM>. Lifting device <NUM> and rigging <NUM> are as previously described. Namely, lifting device <NUM> is a heavy lift crane disposed on vessel <NUM>, and rigging <NUM> is rope that extends from lifting device <NUM> and can be paid in or paid out from lifting device <NUM> to raise or lower loads. In this embodiment, one or more ROV <NUM> as previously described is used to assist in the retrieval of pod <NUM>' and deployment of pod <NUM>". As will be described in more detail below, control pod exchange device <NUM> delivers replacement pod <NUM>" to BOP stack <NUM>, automates the exchange of pods <NUM>', <NUM>" (i.e., removes pod <NUM>' from stack <NUM> and installs pod <NUM>" in stack <NUM>), and delivers pod <NUM>' to the surface <NUM>. Connection assembly <NUM> facilitates the alignment of device <NUM> relative to BOP stack <NUM> and coupling of device <NUM> to BOP stack <NUM> such that pods <NUM>', <NUM>" can be exchanged.

Referring briefly to <FIG>, control pod exchange device <NUM> and BOP stack connection assembly <NUM> coupled to device <NUM> are shown. In this embodiment, exchange device <NUM> includes an outer housing <NUM> and a control pod transfer assembly <NUM> moveably disposed in housing <NUM>. In this embodiment, housing <NUM> is a rectangular frame having a top 211a, a bottom 211b, a front 211c, a back 211d, and lateral sides 211e, 211f. A connector <NUM> is provided on the top 211a of housing <NUM> for coupling housing <NUM> and device <NUM> to the free end 50a of rope <NUM>. The front 211c of housing <NUM> is open to allow control pods <NUM>, <NUM> to be transferred therethrough into and out of housing <NUM>. As best shown in <FIG>, the interior of housing <NUM> includes three areas or bays 212a, 212b, 212c (schematically shown with dashed lines) horizontally arranged side-by-side between lateral sides 211e, 211f. Each bay 212a, 212b, 212c is sized to accommodate one control pod <NUM>, <NUM>. In this embodiment, connection assembly <NUM> includes a pair of parallel arms <NUM> coupled to housing <NUM> proximal the top 211a. Arms <NUM> extend horizontally outward from the front 211c of housing <NUM>. As shown in <FIG>, arms <NUM> are sized, shaped, and positioned to mate and engage with the BOP stack <NUM> (e.g., the outer frame of the BOP stack <NUM>) with middle bay 212b aligned with and adjacent the control pod <NUM>, <NUM> to be replaced.

Referring still to <FIG>, control pod transfer assembly <NUM> automates the transfer of control pod <NUM>' from BOP stack <NUM> into housing <NUM> and the transfer of control pod <NUM>" from housing <NUM> into BOP stack <NUM>. In this embodiment, transfer assembly <NUM> includes a tray <NUM> moveably disposed in housing <NUM> proximal the bottom 211b and a pair of control pod supports 232a, 232b moveably coupled to tray <NUM>. Supports 232a, 232b are arranged laterally side-by-side on tray <NUM> - in <FIG>, support 232a is positioned on the left side of tray <NUM> and support 232b is positioned on the right side of tray <NUM>. Each support 232a, 232b is sized to support one control pod <NUM>, <NUM> thereon.

Tray <NUM> is controllably moved laterally within housing <NUM> between sides 211e, 211f as represented by arrows <NUM>, and supports 232a, 232b are controllably moved forward and backward relative to tray <NUM> as represented by arrows <NUM>. Each support 232a, 232b can extend from tray <NUM> and housing <NUM> to retrieve pod <NUM>' from BOP stack <NUM> and install pod <NUM>" into BOP stack <NUM> when that particular support 232a, 232b is aligned with the middle bay 212b (i.e., disposed immediately below the middle bay 212b). In general, any suitable means or devices known in the art can be used to controllably move tray <NUM> laterally relative to housing <NUM> and move supports <NUM> forward and back relative to tray <NUM> including, without limitation, hydraulic cylinders, electric actuators, and the like.

As previously described, tray <NUM> can be moved laterally within housing <NUM> in the direction of arrows <NUM>. In particular, tray <NUM> can be moved laterally between a first position (shown in <FIG>) with tray <NUM> positioned adjacent side 211f and distal side 211e with support 232a aligned with middle bay 212b and support 232b aligned with bay 212c (the rightmost bay in <FIG>); and a second position with tray <NUM> positioned adjacent side 211e and distal side 211f with support 232a aligned with bay 212a (the leftmost bay in <FIG>) and support 232b aligned with bay 212b. Further, as previously described, each support 232a, 232b can be moved forward and backward relative to tray <NUM> in the direction of arrows <NUM> when the particular support 232a, 232b is aligned with middle bay 212b. Thus, when a given support 232a, 232b is aligned with middle bay 212b, that support 232a, 232b has a withdrawn position disposed within housing <NUM> and an extended position extending from tray <NUM> and the front 211c of housing <NUM>.

Referring again to <FIG>, an embodiment of a method for replacing control pod <NUM>' with control pod <NUM>" using system <NUM> will be described. In <FIG>, control pod <NUM>" is shown being deployed subsea to BOP stack <NUM>; in <FIG>, control pod <NUM>' is shown being removed from BOP stack <NUM> and transferred to exchange device <NUM>; in <FIG>, control pod <NUM>" is shown being transferred from exchange device <NUM> to BOP stack <NUM> and installed on BOP stack <NUM>; and in <FIG>, control pod <NUM>' is shown being retrieved to the surface <NUM> and vessel <NUM>.

Referring first to <FIG>, control pod <NUM>" is disposed within exchange device <NUM> on vessel <NUM>, and the free end 50a of rope <NUM> is attached to connector <NUM> on vessel <NUM>. Pod <NUM>" is positioned on one of the supports 232a, 232b within housing <NUM>. The support 232a, 232b on which pod <NUM>" is disposed is preferably aligned with middle bay 212b to balance the weight of device <NUM> with pod <NUM>" therein. In this embodiment, pod <NUM>" is positioned on support 232a. Next, lifting device <NUM> lowers exchange device <NUM> (carrying pod <NUM>") subsea. As shown in <FIG>, rope <NUM> is paid out from lifting device <NUM> until pod <NUM>" is at a depth generally equal to the depth of control pod <NUM>'. Moving now to <FIG> and <FIG>, ROV <NUM> moves exchange device <NUM> to BOP stack <NUM> immediately adjacent control pod <NUM>', and device <NUM> is mounted to BOP stack <NUM> with connection assembly <NUM>. During this process, lifting device <NUM> is used to control and adjust the vertical position of device <NUM> relative to BOP stack <NUM> while ROV <NUM> generally provides the lateral force to move device <NUM> to BOP stack <NUM>. It should be appreciated that rope <NUM> may need to be paid out to allow device <NUM> to be moved to BOP stack <NUM>, however, rope <NUM> remains in tension, and thus, supports the weight of device <NUM> and pod <NUM>" therein.

As previously described and best shown in <FIG>, arms <NUM> of connection assembly <NUM> are sized, shaped, and positioned to mate and engage with the BOP stack <NUM> (e.g., the outer frame of the BOP stack <NUM>) with middle bay 212b aligned with and adjacent the control pod <NUM>' to be replaced. With device <NUM> coupled to BOP stack <NUM>, pods <NUM>', <NUM>" can be swapped. In particular, as shown in <FIG> and <FIG>, tray <NUM> is translated laterally to move replacement control pod <NUM>" out of middle bay 212b and align the empty support 232a, 232b with control pod <NUM>'. In this embodiment, pod <NUM>" is seated on support 232a, and thus, tray <NUM> is moved laterally to move pod <NUM>" and support 232a from middle bay 212b to bay 212a while simultaneously moving empty support 232b from bay 212c to middle bay 212b. Next, as shown in <FIG> and <FIG>, the empty support 232b is extended from tray <NUM> and the front 211c of housing <NUM> to pod <NUM>'. In this embodiment, support 232b is sized and positioned to slide under pod <NUM>'. With support 232b slidingly engaging the bottom of pod <NUM>', and thus, positioned to support the weight of pod <NUM>', ROV <NUM> can be used to decouple any connections between pod <NUM>' and BOP stack <NUM> (e.g., mechanical and/or hydraulic connections between pod <NUM>' to BOP stack <NUM>). Then, with pod <NUM>' sitting on support 232b, support 232b is withdrawn back into housing <NUM>, thereby positioning pod <NUM>' in middle bay 212b.

Referring now to <FIG>, once pod <NUM>' is removed from BOP stack <NUM>, pod <NUM>" can be installed. First, as shown in <FIG> and <FIG>, with both pods <NUM>', <NUM>" disposed in housing <NUM> on trays 232b, 232a, respectively, tray <NUM> is moved laterally to move control pod <NUM>' out of middle bay 212b and move replacement control pod <NUM>" into middle bay 212b. Next, support 232a is extended from tray <NUM> and the front 211c of housing <NUM> to install pod <NUM>' on BOP stack <NUM>. ROV <NUM> can be used to make up any connections between pod <NUM>" and BOP stack <NUM> (e.g., mechanical and/or hydraulic connections between pod <NUM>' to BOP stack <NUM>). Moving now to <FIG>, with replacement control pod <NUM>" installed on BOP stack <NUM>, support 232a is withdrawn back into housing <NUM>, thereby completing the exchange of pods <NUM>', <NUM>". To balance the weight of exchange device <NUM> following the installation of pod <NUM>", tray <NUM> is preferably moved laterally to position pod <NUM>' in middle bay 212b to balance the weight of device <NUM> with pod <NUM>' therein.

Referring now to <FIG>, after swapping pods <NUM>', <NUM>", exchange device <NUM> is decoupled from BOP stack <NUM> by applying tension to rope <NUM> with lifting device <NUM> to lift exchange device <NUM> while ROV <NUM> pulls and/or guides exchange device <NUM> laterally away from BOP stack <NUM>. Rope <NUM> remains in tension during this process, and thus, supports the weight of device <NUM> and pod <NUM>" therein, while ROV <NUM> generally provides the lateral force to guide device <NUM> away from BOP stack <NUM>.

Once exchange device <NUM> is removed from BOP stack <NUM>, lifting device <NUM> lifts exchange device <NUM> (carrying pod <NUM>') to vessel <NUM> at the surface <NUM> as shown in <FIG> and <FIG>.

In the manner described and shown in <FIG>, system <NUM> can be used to deploy control pod <NUM>", exchange or swap control pods <NUM>', <NUM>" at BOP stack <NUM>, and retrieve control pod <NUM>' to the surface <NUM> in a single subsea trip. During deployment of pod <NUM>" and retrieval of pod <NUM>', ROV <NUM> is used to laterally move and/or guide exchange device <NUM> to and from BOP stack <NUM>, respectively. In addition, ROV <NUM> can be used to guide and/or monitor exchange device <NUM> (and pod <NUM>', pod <NUM>" disposed thereon) as it is lifted, lowered, or otherwise moved subsea. However, it should be appreciated that during deployment of pod <NUM>", exchanging of pods <NUM>', <NUM>" at BOP stack <NUM>, and retrieval of pod <NUM>', the weight of exchange device <NUM> (and any pod <NUM>', <NUM>" thereon) is supported by rope <NUM> and/or BOP stack <NUM>, thereby reducing the payload lifting requirements for ROV <NUM>.

Referring now to <FIG>, an embodiment of a system <NUM> for retrieving a failed or faulty control pod <NUM>', and replacing it with a replacement control pod <NUM>" is schematically shown. More specifically, in <FIG>, system <NUM> is shown delivering replacement control pod <NUM>" subsea to BOP stack <NUM>; in <FIG> and <FIG>, system <NUM> is shown removing the failed or faulty control pod <NUM>' from BOP stack <NUM> and replacing it with control pod <NUM>"; and in <FIG>, system <NUM> is shown retrieving control pod <NUM>' to vessel <NUM> at the surface <NUM>.

In this embodiment, system <NUM> is substantially the same as system <NUM> previously described except that BOP stack connection assembly <NUM> is replaced with BOP stack connection assembly <NUM>. Thus, in this embodiment, system <NUM> includes lifting device <NUM> mounted to surface vessel <NUM>, rigging <NUM> coupled to lifting device <NUM>, control pod exchange device <NUM>, and BOP stack connection assembly <NUM> coupled to device <NUM>.

In this embodiment, BOP stack connection assembly <NUM> is a winch mounted to exchange device <NUM>, and more specifically, fixably attached to the top 211a of housing <NUM> of exchange device <NUM>. Accordingly, connection assembly <NUM> may also be referred to as winch <NUM>. As will be described in more detail below, winch <NUM> can pay in and pay out a rope <NUM>. In this embodiment, one or more ROV <NUM> as previously described is used to assist in the retrieval of pod <NUM>' and deployment of pod <NUM>''.

In the same manner as previously described with respect to system <NUM>, control pod exchange device <NUM> delivers replacement pod <NUM>" to BOP stack <NUM>, automates the exchange of pods <NUM>', <NUM>" (i.e., removes pod <NUM>' from stack <NUM> and installs pod <NUM>" in stack <NUM>), and delivers pod <NUM>' to the surface <NUM>. However, in this embodiment, winch <NUM> facilitates the alignment of device <NUM> relative to BOP stack <NUM>, the coupling of device <NUM> to BOP stack <NUM> such that pods <NUM>', <NUM>" can be exchanged, and the movement of device <NUM> to and away from BOP stack <NUM>.

Referring still to <FIG>, an embodiment of a method for replacing control pod <NUM>' with control pod <NUM>" using system <NUM> will be described. In <FIG> and <FIG>, control pod <NUM>" is shown being deployed subsea; in <FIG>, control pod <NUM>" is shown being moved to BOP stack <NUM>; in <FIG> and <FIG>, control pod <NUM>' is shown being removed from BOP stack <NUM> and transferred to exchange device <NUM> while control pod <NUM>" is transferred from exchange device <NUM> to BOP stack <NUM> and installed on BOP stack <NUM>; and in <FIG>, control pod <NUM>' is shown being retrieved to the surface <NUM> and vessel <NUM>.

Referring first to <FIG> and <FIG>, control pod <NUM>" is disposed within exchange device <NUM> on vessel <NUM>, and the free end 50a of rope <NUM> is attached to connector <NUM> on vessel <NUM>. Pod <NUM>" is positioned on one of the supports 232a, 232b within housing <NUM>. The support 232a, 232b on which pod <NUM>" is disposed is preferably aligned with middle bay 212b to balance the weight of device <NUM> with pod <NUM>" therein. Next, lifting device <NUM> lowers exchange device <NUM> (carrying pod <NUM>") subsea. As shown in <FIG>, rope <NUM> is paid out from lifting device <NUM> until pod <NUM>" is at a depth less than the depth of control pod <NUM>'.

Moving now to <FIG>, rope <NUM> is paid out from winch <NUM>, and with sufficient slack in rope <NUM>, ROV <NUM> grabs the free end 51a of rope <NUM> with its claw <NUM>, moves end 51a to BOP stack <NUM>, and secures end 51a to BOP stack <NUM>, thereby coupling exchange device <NUM> with BOP stack <NUM>. Free end 51a is attached to BOP stack <NUM> at a particular position that allows winch <NUM> to pull exchange device <NUM> to BOP stack <NUM> with middle bay 212b aligned with and immediately adjacent control pod <NUM>'. Next, as shown in <FIG> and <FIG>, winch <NUM> is operated to pay in rope <NUM>, thereby applying tension to rope <NUM> and pulling exchange device <NUM> to BOP stack <NUM>. Due to the attachment point of end 50a on BOP stack <NUM>, bay 212b is aligned with and adjacent to control pod <NUM>' when exchange device <NUM> is pulled to BOP stack <NUM> with winch <NUM>. Although rope <NUM> may need to be paid out to allow device <NUM> to be pulled to BOP stack <NUM> with winch <NUM>, rope <NUM> remains in tension, and thus, supports the weight of device <NUM> and pod <NUM>" therein. Thus, lifting device <NUM> primarily supports the weight of exchange device <NUM> and pod <NUM>' therein, while winch <NUM> provides the lateral force to move device <NUM> to BOP stack <NUM>.

As shown in <FIG> and <FIG>, with device <NUM> coupled to BOP stack <NUM> with middle bay 212b aligned with and adjacent the control pod <NUM>', pod <NUM>' is removed from BOP stack <NUM> and then pod <NUM>" is installed in BOP stack <NUM> (i.e., pod <NUM>' is replaced with pod <NUM>"). In this embodiment, exchange device <NUM> replaces pod <NUM>' with pod <NUM>" in the same manner as previously described and shown in <FIG>.

Referring now to <FIG>, after swapping pods <NUM>', <NUM>", exchange device <NUM> is decoupled from BOP stack <NUM>. In particular, the tension in rope <NUM> is increased with lifting device <NUM> to pull exchange device <NUM> away from BOP stack <NUM> while winch <NUM> pays out rope <NUM> as shown in <FIG> and <FIG>. ROV <NUM> can be employed to assist in guiding exchange device <NUM> away from BOP stack <NUM>. Next, slack is provided in rope <NUM>, and then ROV <NUM> decouples end 51a of rope <NUM> from BOP stack <NUM> as shown in <FIG> and <FIG>. Moving now to <FIG>, once exchange device <NUM> is decoupled from BOP stack <NUM>, lifting device <NUM> lifts exchange device <NUM> (carrying pod <NUM>') to vessel <NUM> at the surface <NUM>.

In the manner described and shown in <FIG>, system <NUM> can be used to deploy control pod <NUM>", exchange or swap control pods <NUM>', <NUM>" at BOP stack <NUM>, and retrieve control pod <NUM>' to the surface <NUM> in a single subsea trip. During deployment of pod <NUM>" and retrieval of pod <NUM>', winch <NUM> and associated rope <NUM> are used to laterally move exchange device <NUM> to and from BOP stack <NUM>. In addition, ROV <NUM> can be used to guide and/or monitor exchange device <NUM> (and pod <NUM>', pod <NUM>" disposed thereon) as it is lifted, lowered, or otherwise moved subsea. However, it should be appreciated that during deployment of pod <NUM>", exchanging of pods <NUM>', <NUM>" at BOP stack <NUM>, and retrieval of pod <NUM>', the weight of exchange device <NUM> (and any pod <NUM>', <NUM>" thereon) is supported by rope <NUM>, thereby reducing the payload lifting requirements for ROV <NUM>.

In this embodiment, BOP stack connection assembly <NUM> includes a pulley or sheave <NUM> rotatably coupled to the lower end 50a of rope <NUM>, a guide member <NUM> mounted to exchange device <NUM>, and a rope <NUM>. In this embodiment, assembly <NUM> is made up or constructed prior to deploying exchange device <NUM> and control pod <NUM>" subsea. In particular, rope <NUM> is passed over sheave <NUM> and through a guide passage <NUM> in guide member <NUM>. One free end 52a of rope <NUM> is coupled to connector <NUM> of exchange device <NUM>, and the other free end 52b of rope <NUM> is coupled to BOP stack <NUM> with ROV <NUM>. In this embodiment, the lower portion of passage <NUM> defines a guide or funnel and a stabbing spear <NUM> is provided at the end 52b of rope <NUM>. ROV <NUM> couples spear <NUM> to BOP stack <NUM>, and rope <NUM> extends from spear <NUM> through passage <NUM> and over sheave <NUM> to exchange device <NUM>. As will be described in more detail below, the lower portion of passage <NUM> is configured to slidingly receive spear <NUM> as exchange device <NUM> approaches BOP stack <NUM> to guide and align exchange device <NUM> to the desired position and orientation relative to BOP stack <NUM>.

In the same manner as previously described with respect to system <NUM>, control pod exchange device <NUM> delivers replacement pod <NUM>" to BOP stack <NUM>, automates the exchange of pods <NUM>', <NUM>" (i.e., removes pod <NUM>' from stack <NUM> and installs pod <NUM>" in stack <NUM>), and delivers pod <NUM>' to the surface <NUM>. However, in this embodiment, assembly <NUM> facilitates the alignment of device <NUM> relative to BOP stack <NUM>, the coupling of device <NUM> to BOP stack <NUM> such that pods <NUM>', <NUM>" can be exchanged, and the movement of device <NUM> to and away from BOP stack <NUM>.

Referring still to <FIG>, an embodiment of a method for replacing control pod <NUM>' with control pod <NUM>" using system <NUM> will be described. In <FIG>, control pod <NUM>" is shown being deployed subsea and moved to BOP stack <NUM>; in <FIG> and <FIG>, control pod <NUM>' is shown being removed from BOP stack <NUM> and transferred to exchange device <NUM> while control pod <NUM>" is transferred from exchange device <NUM> to BOP stack <NUM> and installed on BOP stack <NUM>; and in <FIG>, control pod <NUM>' is shown being retrieved to the surface <NUM> and vessel <NUM>.

Referring first to <FIG> and <FIG>, control pod <NUM>" is disposed within exchange device <NUM> on vessel <NUM>. In particular, pod <NUM>" is positioned on one of the supports 232a, 232b within housing <NUM>. The support 232a, 232b on which pod <NUM>" is disposed is preferably aligned with middle bay 212b to balance the weight of device <NUM> with pod <NUM>" therein. Next, lifting device <NUM> raises sheave <NUM> to lift device <NUM> from vessel <NUM>, and then lowers sheave <NUM> to lower device <NUM> (carrying pod <NUM>") subsea. Rope <NUM> extends over sheave <NUM> with end 52b attached to the tip of spear <NUM>, which in turn is coupled to BOP stack <NUM>, and the other end 52a attached to exchange device <NUM>. Consequently, rope <NUM> remains in tension as sheave <NUM> is lowered subsea with lifting device <NUM> (the weight of exchange device <NUM> continuously pulls on rope <NUM>). As shown in <FIG>, lifting device <NUM> continues to lower sheave <NUM> to lower exchange device <NUM> towards BOP stack <NUM>. In essence, as sheave <NUM> is lowered by lifting device <NUM>, exchange device <NUM> is controllably lowered under its own weight. Rope <NUM> passes through guide passage <NUM>, and thus, as exchange device <NUM> is lowered, guide member <NUM> slides along rope <NUM> toward end 52a. Guide member <NUM> is attached to exchange device <NUM>, and thus, as guide member <NUM> moves along rope <NUM>, exchange device <NUM> also moves toward BOP stack <NUM>. As best shown in <FIG>, spear <NUM> is attached to BOP stack <NUM> at a particular position that enables alignment of exchange device <NUM> and BOP stack <NUM>. As exchange device <NUM> is lowered to BOP stack <NUM>, the lower portion of passage <NUM> slidingly receives spear <NUM>, thereby guiding exchange device <NUM> to the desired positions relative to BOP stack <NUM>. Thus, the funnel at the lower portion of passage <NUM> and spear <NUM> enable alignment of exchange device <NUM> relative to BOP stack <NUM>, thereby allowing guide member <NUM> to mate and engage with the BOP stack <NUM> (e.g., the outer frame of the BOP stack <NUM>) with middle bay 212b aligned with and adjacent to the control pod <NUM>' to be replaced.

As shown in <FIG> and <FIG>, with device <NUM> coupled to BOP stack <NUM> with middle bay 212b aligned with and adjacent the control pod <NUM>', pod <NUM>' is removed from BOP stack <NUM> and then pod <NUM>" is installed in BOP stack <NUM> (i.e., pod <NUM>' is replaced with pod <NUM>"). In this embodiment, exchange device <NUM> replaces pod <NUM>' with pod <NUM>" in the same manner as previously described and shown in <FIG>. Since guide member <NUM> mates and engages BOP stack <NUM> in this embodiment, slack can be provided in rope <NUM> as BOP stack <NUM> supports and maintains the position of guide member <NUM> and exchange device <NUM> attached thereto.

Moving now to <FIG> and <FIG>, after swapping pods <NUM>', <NUM>", sheave <NUM> is raised with lifting device <NUM> to apply and/or increase tension in rope <NUM>, and lift guide member <NUM> and exchange device <NUM> from BOP stack <NUM>. Sheave <NUM> is raised by lifting device <NUM> to lift exchange device <NUM> and pod <NUM>" to the surface <NUM> and vessel <NUM>. Once exchange device <NUM> (carrying pod <NUM>") is disposed on vessel <NUM>, end 52b of rope <NUM> can be decoupled from BOP stack <NUM> with ROV <NUM>.

In the manner described and shown in <FIG>, system <NUM> can be used to deploy control pod <NUM>", exchange or swap control pods <NUM>', <NUM>" at BOP stack <NUM>, and retrieve control pod <NUM>' to the surface <NUM> in a single subsea trip. During deployment of pod <NUM>" and retrieval of pod <NUM>', lifting device <NUM> is used to lower and raise exchange device <NUM>, respectively, while guide member <NUM> simultaneously slides along rope <NUM> to move exchange device laterally to and from BOP stack <NUM>. In addition, ROV <NUM> can be used to guide and/or monitor exchange device <NUM> (and pod <NUM>', pod <NUM>" disposed thereon) as it is lifted, lowered, or otherwise moved subsea. However, it should be appreciated that during deployment of pod <NUM>", exchanging of pods <NUM>', <NUM>" at BOP stack <NUM>, and retrieval of pod <NUM>', the weight of exchange device <NUM> (and any pod <NUM>', <NUM>" thereon) is supported by rope <NUM> and rope <NUM>, thereby reducing the payload lifting requirements for ROV <NUM>.

In this embodiment, system <NUM> includes lifting device <NUM> mounted to surface vessel <NUM>, rigging <NUM> coupled to lifting device <NUM>, control pod exchange device <NUM>, and a BOP stack connection assembly <NUM> coupled to device <NUM>. Lifting device <NUM>, rigging <NUM>, and exchange device <NUM> are each as previously described, however, BOP stack connection assembly <NUM> is different than connection assemblies <NUM>, <NUM>, <NUM>, <NUM> previously described.

Referring briefly to <FIG> and <FIG>, BOP stack connection assembly <NUM> releasably couples control pod exchange device <NUM> to BOP stack <NUM>, controllably lowers and raises control pod exchange device <NUM> to and from BOP stack <NUM>, and guides control pod exchange device <NUM> as it moves to and from BOP stack <NUM>. In this embodiment, BOP stack connection assembly <NUM> includes a housing connector <NUM> coupled to the top 211a of housing <NUM>, a connection assembly <NUM> releasably connected to housing connector <NUM>, a winch <NUM> coupled to the top 211a of housing <NUM>, a first pair of sheaves <NUM> rotatably coupled to housing <NUM> and connector <NUM>, a second pair of sheaves <NUM> rotatably coupled to housing <NUM> and connector <NUM>, a pair of BOP stack connection members <NUM>, a pair of tubular guides <NUM> coupled to housing <NUM>, and a pair of ropes <NUM> extending from winch <NUM> to stack connection members <NUM>. Guides <NUM> are positioned proximal the top 211a and the front 211c of housing <NUM>. As will be described in more detail below, the forward lower ends of guides <NUM> comprise funnels that function to slidingly receive and guide connection members <NUM> into guides <NUM>. In this embodiment, connection assembly <NUM> is releasably coupled to housing connector <NUM>, and hence housing <NUM>, with a pin <NUM>. However, in other embodiments, the connection assembly (e.g., assembly <NUM>) can be releasably coupled to housing connector (e.g., housing connector <NUM>) and housing (e.g., housing <NUM>) by other mechanisms or devices such as a ratcheting mechanism.

Housing connector <NUM> is a rigid structure extending vertically upward from the top 211a of housing <NUM>. In particular, housing connector <NUM> has a lower end 261a fixably secured to housing <NUM> and an upper end 261b distal housing <NUM>. Upper end 261b includes a through bore that slidingly receives pin <NUM>.

Referring still to <FIG> and <FIG>, connection assembly <NUM> releasably couples housing connector <NUM> and exchange device <NUM> to rigging <NUM>. In this embodiment, connection assembly <NUM> includes a base member <NUM>, a sheave support <NUM> pivotally coupled to base member <NUM>, and a pair of laterally spaced sheaves <NUM> rotatably coupled to support <NUM> on opposite lateral sides of base member <NUM> in front view (<FIG>). Base member <NUM> is a rigid structure having a lower end 271a pivotally coupled to housing connector <NUM> with pin <NUM> and an upper end 271b comprising a connector <NUM>. Lower end 271a includes a through bore that slidingly receives pin <NUM>, thereby pivotally and releasably coupling base member <NUM> to housing connector <NUM>. Connector <NUM> couples connection assembly <NUM>, housing connector <NUM>, and exchange device <NUM> to rigging <NUM>. As will be described in more detail below, each rope <NUM> extends from winch <NUM> over one sheave <NUM>, over one sheave <NUM>, and through one guide <NUM> to the corresponding connection member <NUM>.

Referring still to <FIG> and <FIG>, BOP stack connection members <NUM> releasably couples connection assembly <NUM> and exchange device <NUM> to BOP stack <NUM>, and guide exchange device <NUM> such that bay 212b is aligned with and adjacent to control pod <NUM>'. In this embodiment, each connection member <NUM> is an elongate stabbing spear having a first or upper end 290a and a second or lower end 290b. Lower end 290b is provided with a foot <NUM> sized and shaped to releasably engage a mating profile on BOP stack <NUM>. One end of each rope <NUM> is mounted to winch <NUM> and the opposite end of each rope <NUM> is attached to upper end 290a of one connection member <NUM>.

Connection members <NUM> are movably coupled to exchange device <NUM> with ropes <NUM> and winch <NUM>. More specifically, when connection members <NUM> are disposed in guides <NUM>, ropes <NUM> can be paid out from winch <NUM> to allow connection members <NUM> to slide downward out of guides <NUM>, thereby enabling BOP stack connection members <NUM> to be controllably lowered from exchange device <NUM>; and when connection members <NUM> are spaced apart from exchange device <NUM>, ropes <NUM> can be paid in to winch <NUM> to pull connection members <NUM> upward toward exchange device <NUM> and into guides <NUM>.

Referring again to <FIG>, an embodiment of a method for replacing control pod <NUM>' with control pod <NUM>" using system <NUM> will be described. In <FIG>, control pod <NUM>" is shown being deployed subsea and moved to BOP stack <NUM>; in <FIG> and <FIG>, control pod <NUM>' is shown being removed from BOP stack <NUM> and transferred to exchange device <NUM> while control pod <NUM>" is transferred from exchange device <NUM> to BOP stack <NUM> and installed on BOP stack <NUM>; and in <FIG>, control pod <NUM>' is shown being retrieved to the surface <NUM> and vessel <NUM>.

Referring first to <FIG>, control pod <NUM>" is disposed within exchange device <NUM> on vessel <NUM>. In particular, pod <NUM>" is positioned on one of the supports 232a, 232b within housing <NUM>, and the free end 50a of rope <NUM> is attached to connector <NUM> on vessel <NUM>. The support 232a, 232b on which pod <NUM>" is disposed is preferably aligned with middle bay 212b to balance the weight of device <NUM> with pod <NUM>" therein. In addition, connection assembly <NUM> is pivotally coupled to housing connector <NUM>, and hence exchange device <NUM>, with pin <NUM>. Next, lifting device <NUM> lowers exchange device <NUM> (carrying pod <NUM>") subsea via rope <NUM> and connection assembly <NUM>. As shown in <FIG>, ropes <NUM> are paid out from winch <NUM> at the surface <NUM> such that stack connection members <NUM> hang from exchange device <NUM>.

Moving now to <FIG>, ropes <NUM> are paid out from winch <NUM> at the surface <NUM> such that connection members <NUM> are lowered to a depth equal to or greater than the depth of control pod <NUM>' as exchange device <NUM> is lowered subsea with lifting device <NUM>. Next, stack connection members <NUM> are attached to BOP stack <NUM> with ROV <NUM>. Feet <NUM> are sized, shaped, and positioned to mate and engage with BOP stack <NUM>, while simultaneously aligning bay 212b with pod <NUM>' when received by guides <NUM> upon arrival of exchange device <NUM>.

Referring now to <FIG>, once stack connection members <NUM> are secured to BOP stack <NUM>, lifting device <NUM> pays in rope <NUM> to pull any slack from ropes <NUM> and place ropes <NUM> in tension. Next, ROV <NUM> pulls pin <NUM> from base member <NUM> and housing connector <NUM>, thereby decoupling exchange device <NUM> from connection assembly <NUM> so that exchange device <NUM> can be lowered to BOP stack <NUM>. To enable ROV <NUM> to easily remove pin <NUM> from the throughbores in member <NUM> and connector <NUM>, the shear loads acting on pin <NUM> by member <NUM> and connector <NUM> are preferably eliminated.

Referring briefly to <FIG>, a schematic free body diagram of the forces acting on pin <NUM> under static conditions are shown. For purposes of clarity and simplicity, sheaves <NUM>, ropes <NUM>, and connection members <NUM> are represented by a single sheave <NUM>, a single rope <NUM>, and a single connection member <NUM>, respectively, in <FIG>. The weight of exchange device <NUM> (including any pod <NUM> disposed thereon) is represented with reference numeral "W<NUM>," the tension in rope <NUM> is represented with reference numeral "T<NUM>," the tension in the portion of rope <NUM> extending between sheave <NUM> and stack connection member <NUM> is represented with reference numeral "T<NUM>-<NUM>," and the tension in the portion of rope <NUM> extending between sheave <NUM> and winch <NUM> is represented with reference numeral "T<NUM>-<NUM>.

Under static conditions, when there is no tension in rope <NUM> (i.e., T<NUM>-<NUM> = <NUM> and T<NUM>-<NUM> = <NUM>), the forces applied to pin <NUM> include the weight W<NUM> acting through connector <NUM> and the tension T<NUM> acting through member <NUM>. In such case, the downward force acting on pin <NUM> through connector <NUM> due to the weight W<NUM> is laterally spaced from and opposed by the upward force acting on pin <NUM> through member <NUM> due to tension T<NUM>, thereby resulting in shear loads being applied to pin <NUM>. However, with stack connection members <NUM> secured to BOP stack <NUM> and ropes <NUM> and rope <NUM> in tension, when the tension T<NUM> applied to rope <NUM> is equal to twice the weight W<NUM>, the downward force acting on pin <NUM> due to weight W<NUM> goes to zero (the weight W<NUM> is offset and balanced by tension T<NUM>-<NUM>) and the upward force acting on pin <NUM> due to tension T<NUM> goes to zero (the tension T<NUM> is offset and balanced by tensions T<NUM>-<NUM>, T<NUM>-<NUM>). When tension is applied to rope <NUM> and assuming static conditions, T<NUM> = T<NUM>-<NUM> + W<NUM>, and thus, when T<NUM>-<NUM> = W<NUM>, tension T<NUM> = <NUM> * W<NUM>. Thus, when lifting device <NUM> increases the tension in rope <NUM> (i.e., tension T<NUM>-<NUM>, which equals tension T<NUM>-<NUM>) to the weight W<NUM>, pin <NUM> is no longer in shear and can be pull with ROV <NUM>, and the tension in rope <NUM> (i.e., tension T<NUM>) will be twice the weight W<NUM>.

Referring still to <FIG>, the foregoing relationships between the tension in rope <NUM>, the tension in ropes <NUM>, and the weight of exchange device <NUM> can be utilized to control and time the removal of pin <NUM> with ROV <NUM>. Namely, once stack connection members <NUM> is secured to BOP stack <NUM>, lifting device <NUM> is operated to pay in rope <NUM> until the tension in rope <NUM> (measured at lifting device <NUM>) is twice the weight of exchange device <NUM>, at which point - pin <NUM> is no longer in shear and ROV <NUM> can remove pin <NUM>.

Moving now to <FIG> and <FIG>, upon removal of pin <NUM>, exchange device <NUM> is decoupled from connection assembly <NUM> and is lowered by paying out rope <NUM> from lifting device <NUM>. As rope <NUM> is paid out, ropes <NUM> move around sheaves <NUM> as exchange device <NUM> slides along ropes <NUM> extending through guides <NUM> towards connection members <NUM> and BOP stack <NUM>. As exchange device <NUM> approaches BOP stack <NUM>, connection members <NUM> are slidingly received into guides <NUM>, thereby aligning exchange device <NUM> in the desired positon relative to BOP stack <NUM> (i.e., with bay 212b aligned with and adjacent to control pod <NUM>').

As previously described, in this embodiment, pin <NUM> is removed by ROV <NUM> once the shear loads acting on pin <NUM> are sufficiently reduced and/or eliminated. However, in other embodiments, the pin (e.g., pin <NUM>) 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 pin <NUM> are sufficiently reduced and/or eliminated.

Referring now to <FIG>, after swapping pods <NUM>', <NUM>", exchange device <NUM> is lifted from BOP stack <NUM>. In particular, lifting device <NUM> is operated to pay in rope <NUM>, thereby pulling exchange device <NUM> upward toward the surface <NUM> and connection assembly <NUM>. As rope <NUM> is paid in, ropes <NUM> move around sheaves <NUM> as exchange device <NUM> slides along ropes <NUM> extending through guides <NUM> away from stack connection members <NUM> and BOP stack <NUM>. As shown in <FIG>, upon arrival at connection assembly <NUM>, the throughbores in member <NUM> and connector <NUM> are aligned and ROV <NUM> inserts pin <NUM> therethrough, thereby pivotally coupling exchange device <NUM> and connection assembly <NUM>.

Moving now to <FIG> and <FIG>, after coupling exchange device <NUM> and connection assembly <NUM>, the weight of exchange device <NUM> is supported by rope <NUM> while lifting device <NUM> is operated to pay out rope <NUM>, thereby removing any tension in ropes <NUM>. Next, ROV <NUM> decouples stack connection members <NUM> from BOP stack <NUM>. At this point, winch <NUM> can be operated to pay in ropes <NUM> and pull stack connection members <NUM> upward to exchange device <NUM>, or alternatively, ropes <NUM> can be left hanging while exchange device <NUM>. Lifting device <NUM> can then be used to lift exchange device <NUM> (carrying pod <NUM>') to vessel <NUM> via rope <NUM> and connection assembly <NUM>.

In the manner described and shown in <FIG>, system <NUM> can be used to deploy control pod <NUM>", exchange or swap control pods <NUM>', <NUM>" at BOP stack <NUM>, and retrieve control pod <NUM>' to the surface <NUM> in a single subsea trip. During deployment of pod <NUM>" and retrieval of pod <NUM>', lifting device <NUM> pays out and pays in rope <NUM> to move exchange device <NUM> to and from BOP stack <NUM>. Thus, in this embodiment, control over the deployment and retrieval of exchange device <NUM> is primarily controlled from the surface with lifting device <NUM>. For example, winch <NUM> need not be operated to lower and raise exchange device <NUM> to and from, respectively, BOP stack <NUM>. In addition, ROV <NUM> can be used to guide and/or monitor exchange device <NUM> (and pod <NUM>', pod <NUM>" disposed thereon) as it is lifted, lowered, or otherwise moved subsea. However, it should be appreciated that during deployment of pod <NUM>", exchanging of pods <NUM>', <NUM>" at BOP stack <NUM>, and retrieval of pod <NUM>', the weight of exchange device <NUM> (and any pod <NUM>', <NUM>" thereon) is supported by rope <NUM> and/or ropes <NUM>, thereby reducing the payload lifting requirements for ROV <NUM>.

System <NUM> is similar to system <NUM> previously described with the exception that system <NUM> relies on a different lifting device mounted to surface vessel <NUM> to deploy and retrieve control pod exchange device <NUM>. In this embodiment, the lifting device is an offset derrick <NUM>' mounted to surface vessel <NUM> instead of lifting device <NUM> (e.g., a crane), and further, a pipe string <NUM> (e.g., a drill string) suspended from derrick <NUM>' is used instead of rigging <NUM>. Thus, in this embodiment, system <NUM> includes offset derrick <NUM>' mounted to surface vessel <NUM>, pipe string <NUM> suspended from derrick <NUM>', control pod exchange device <NUM>, and BOP stack connection assembly <NUM> coupled to device <NUM>. Control pod exchange device <NUM> and BOP stack connection assembly <NUM> are each as previously described. Connector <NUM> of connection assembly <NUM> is releasably attached to the lower end of pipe string <NUM> (instead of the lower end of rigging <NUM>). Thus, in this embodiment of system <NUM>, using offset derrick <NUM>' and pipe string <NUM>, control pod exchange device <NUM> delivers replacement pod <NUM>" to BOP stack <NUM>, automates the exchange of pods <NUM>', <NUM>" (i.e., removes pod <NUM>' from stack <NUM> and installs pod <NUM>" in stack <NUM>), and delivers pod <NUM>' to the surface <NUM>. Connection members <NUM>, guides <NUM>, and ropes <NUM> facilitate the alignment of device <NUM> relative to BOP stack <NUM>, the coupling of device <NUM> to BOP stack <NUM> such that pods <NUM>', <NUM>" can be exchanged, and the movement of device <NUM> to and away from BOP stack <NUM>. One or more subsea remotely operated vehicles <NUM> as previously described are used, to varying degrees, to assist in the retrieval of pod <NUM>' and deployment of pod <NUM>".

Referring first to <FIG>, control pod <NUM>" is disposed within exchange device <NUM> on vessel <NUM>. In particular, pod <NUM>" is positioned on one of the supports 232a, 232b within housing <NUM>, and the lower end of pipe string <NUM> is coupled to connector <NUM> on vessel <NUM>. The support 232a, 232b on which pod <NUM>" is disposed is preferably aligned with middle bay 212b to balance the weight of device <NUM> with pod <NUM>" therein. In addition, connection assembly <NUM> is pivotally coupled to housing connector <NUM>, and hence exchange device <NUM>, with pin <NUM>. Next, derrick <NUM>' lowers exchange device <NUM> (carrying pod <NUM>") subsea via pipe string <NUM> and connection assembly <NUM>. As shown in <FIG>, ropes <NUM> are paid out from winch <NUM> at the surface <NUM> such that stack connection members <NUM> hang from exchange device <NUM>.

Moving now to <FIG>, ropes <NUM> are paid out from winch <NUM> at the surface <NUM> such that connection members <NUM> are lowered to a depth equal to or greater than the depth of control pod <NUM>' as exchange device <NUM> is lowered subsea with derrick <NUM>' and pipe string <NUM>. Next, stack connection members <NUM> are attached to BOP stack <NUM> with ROV <NUM>. Feet <NUM> are sized, shaped, and positioned to mate and engage with BOP stack <NUM>, while simultaneously aligning bay 212b with pod <NUM>' when received by guides <NUM> upon arrival of exchange device <NUM>.

Referring now to <FIG>, once stack connection members <NUM> are secured to BOP stack <NUM>, derrick <NUM>' applies a lifting force to pipe string <NUM> to pull any slack from ropes <NUM> and place ropes <NUM> in tension. Next, ROV <NUM> pulls pin <NUM> from base member <NUM> and housing connector <NUM>, thereby decoupling exchange device <NUM> from connection assembly <NUM> so that exchange device <NUM> can be lowered to BOP stack <NUM>. To enable ROV <NUM> to easily remove pin <NUM> from the throughbores in member <NUM> and connector <NUM>, the shear loads acting on pin <NUM> by member <NUM> and connector <NUM> are eliminated as previously described. In particular, the tension in pipe string <NUM>, the tension in ropes <NUM>, and the weight of exchange device <NUM> can be utilized to control and time the removal of pin <NUM> with ROV <NUM>. Namely, once stack connection members <NUM> is secured to BOP stack <NUM>, derrick <NUM>' is operated to lift pipe string <NUM> until the tension pipe string <NUM> (measured at derrick <NUM>') is twice the weight of exchange device <NUM>, at which point - pin <NUM> is no longer in shear and ROV <NUM> can remove pin <NUM>.

Moving now to <FIG> and <FIG>, upon removal of pin <NUM>, exchange device <NUM> is decoupled from connection assembly <NUM> and is lowered by lowering pipe string <NUM> with derrick <NUM>'. As pipe string <NUM> is lowered, ropes <NUM> move around sheaves <NUM> as exchange device <NUM> slides along ropes <NUM> extending through guides <NUM> towards connection members <NUM> and BOP stack <NUM>. As exchange device <NUM> approaches BOP stack <NUM>, connection members <NUM> are slidingly received into guides <NUM>, thereby aligning exchange device <NUM> in the desired positon relative to BOP stack <NUM> (i.e., with bay 212b aligned with and adjacent to control pod <NUM>').

Referring now to <FIG>, after swapping pods <NUM>', <NUM>", exchange device <NUM> is lifted from BOP stack <NUM>. In particular, derrick <NUM>' is operated to lift pipe string <NUM>, thereby pulling exchange device <NUM> upward toward the surface <NUM> and connection assembly <NUM>. As pipe string <NUM> is lifted, ropes <NUM> move around sheaves <NUM> as exchange device <NUM> slides along ropes <NUM> extending through guides <NUM> away from stack connection members <NUM> and BOP stack <NUM>. As shown in <FIG>, upon arrival at connection assembly <NUM>, the throughbores in member <NUM> and connector <NUM> are aligned and ROV <NUM> inserts pin <NUM> therethrough, thereby pivotally coupling exchange device <NUM> and connection assembly <NUM>.

Moving now to <FIG>, after coupling exchange device <NUM> and connection assembly <NUM>, the weight of exchange device <NUM> is supported by pipe string <NUM> while derrick <NUM>' is operated to lower pipe string <NUM>, thereby removing any tension in ropes <NUM>. Next, ROV <NUM> decouples stack connection members <NUM> from BOP stack <NUM>. At this point, winch <NUM> can be operated to pay in ropes <NUM> and pull stack connection members <NUM> upward to exchange device <NUM>, or alternatively, ropes <NUM> can be left hanging while exchange device <NUM>. Derrick <NUM>' can then be used to lift exchange device <NUM> (carrying pod <NUM>') to vessel <NUM> via pipe string <NUM> and connection assembly <NUM>.

Claim 1:
A method for replacing a first control pod (<NUM>, <NUM>') of a BOP stack (<NUM>), the method comprising:
(a) lowering a control pod exchange device (<NUM>) subsea with a second control pod (<NUM>, <NUM>") positioned on the control pod exchange device (<NUM>), wherein the control pod exchange device (<NUM>) comprises:
a housing (<NUM>) including a first bay (212a), a second bay (212b) horizontally adjacent the first bay (212a), and a third bay (212c) horizontally adjacent the second bay (212b), wherein the second bay (212b) is horizontally positioned between the first bay (212a) and the third bay (212c), wherein each bay (212a, 212b, 212c) is sized to receive the first control pod (<NUM>, <NUM>') or the second control pod (<NUM>, <NUM>") from the BOP stack (<NUM>) and transfer a second control pod (<NUM>, <NUM>") to the BOP stack (<NUM>);
a control pod transfer assembly (<NUM>) moveably disposed in the housing (<NUM>), wherein the control pod transfer assembly (<NUM>) is configured to move the second control pod (<NUM>, <NUM>") horizontally from the first bay (212a) to the second bay (212b) and move the first control pod (<NUM>, <NUM>') horizontally from the first bay (212a) to third bay (212c);
(b) coupling the control pod exchange device (<NUM>) to the BOP stack (<NUM>);
(c) transferring the first control pod (<NUM>, <NUM>') from the BOP stack (<NUM>) to the control pod exchange device (<NUM>) and transferring the second control pod (<NUM>, <NUM>") from the control pod exchange device (<NUM>) to the BOP stack (<NUM>) while the control pod exchange device (<NUM>) is coupled to the BOP stack (<NUM>), wherein (c) comprises:
(c1) receiving the first control pod (<NUM>, <NUM>') from the BOP stack into the second bay (212b) with the second control pod (<NUM>, <NUM>") in the first bay (212a);
(c2) moving the first control pod (<NUM>, <NUM>') laterally from the second bay (212a) to a third bay (212c) after (c1);
(c3) moving the second control pod (<NUM>, <NUM>") laterally from the first bay (212a) to the second bay (212b) after (c2); and
(c4) moving the second control pod (<NUM>, <NUM>") from the second bay (212b) to the BOP stack (<NUM>) after (c3);
(d) decoupling the control pod exchange device from the BOP stack after (c); and
(e) lifting the control pod exchange device (<NUM>) and the first control pod (<NUM>, <NUM>') disposed thereon to the surface (<NUM>) after (c) and (d).