Subsea technology

Abstract

A system for tethering a subsea blowout preventer (BOP) or well head is disclosed. In at least one embodiment, the system comprises an interface associable with the BOP, and more than one anchors disposed about the BOP. Each anchor is configured to carry or support a tensioning system arranged in operable association with a respective tether. Each tether is arranged so as to link a respective anchor with a respective operable means associated with the BOP. Furthermore, each of the respective operable means are configured in operable association with the interface such that tension in the tethers can be adjustable either individually or together as a group of two or more tethers, by way of the interface.

Claims

1. A system for tethering a subsea blowout preventer (BOP) associated with a well head, the system comprising: a first interface attached or mounted to a portion or region of the BOP; and more than one anchors disposed about the BOP, each anchor configured to carry or support a tensioning system arranged in operable association with a respective tether, each tether arranged so as to link a respective anchor with a respective operable means associated with the BOP, whereby, each of the respective operable means are configured in hydraulic association with the interface such that tension in the tethers can be adjustable either individually or together as a group of two or more tethers, by way of the interface.

2. A system according to claim 1, wherein the hydraulic association between the interface and respective operable means is by way of a fluid circuit assembly arranged such that the tension in the tethers can be adjustable either individually or together as a group of two or more tethers, by way of the interface.

3. A system according to claim 2, wherein the fluid circuit assembly is configured so as to facilitate operation of the or any operable means toward a retracted condition, whereby the retracted condition of the or any operable means can be selectively operable via the interface.

4. A system according to claim 2, wherein the fluid circuit assembly is configured so as to facilitate operation of the or any operable means toward an extended condition, whereby the extended condition of the or any operable means can be selectively operable via the interface.

5. A system according to claim 4, wherein movement toward the retracted condition of the or each operable means is by way of selective operation of one or more valves provided in-circuit with the fluid circuit assembly.

6. A system according to claim 5, wherein movement toward the extended condition of the or each operable means is by way of a check valve and a pilot operated check valve provided in-circuit with the fluid circuit assembly.

7. A system according to claim 2, wherein the interface comprises a port that is capable of engaging with a nozzle provided by way of a remotely operated vehicle (ROV) for the purposes of transferring hydraulic fluid to/from the fluid circuit assembly for facilitating two-way hydraulic fluid transfer.

8. A system according to claim 7, wherein the fluid circuit assembly comprises one or more fluid circuits which allow for fluid to be transferred to/from the operable means respectively by way of the port, and wherein the fluid circuit assembly is configured such that the port is arranged in fluid communication with a first fluid circuit, the first fluid circuit being provided in fluid communication with the operable means respectively.

9. A system according to claim 8, wherein the first fluid circuit comprises one or more first subordinate fluid circuits which fluidly connect the first fluid circuit with a respective first chamber of respective operable means.

10. A system according to claim 9, wherein the fluid circuit assembly is configured such that the port is arranged in fluid communication with a second fluid circuit, the second fluid circuit being provided in fluid communication with the respective operable means.

11. A system according to claim 10, wherein the second fluid circuit comprises one or more second subordinate fluid circuits which fluidly connect the second fluid circuit with a respective second chamber of respective operable means.

12. A system according to claim 11, wherein the first and second chambers of respective operable means are fluidly separated by way of a piston and rod arrangement, whereby the piston and rod are moveable in a substantially selective manner in a first direction by way of fluid filling one of the first or second chambers; or in a second direction by way of fluid filling the alternate chamber.

13. A system according to claim 12, wherein the or each first or second subordinate fluid circuit is in fluid communication with a valve unit provided with the interface.

14. A system according to claim 13, wherein the fluid circuit assembly is configured such that operation of one or more operable means can be caused by way of operating the or each valve units to either an open or closed condition, depending on whether the retracting or extended conditions are required/desired.

15. A system according to claim 13, wherein the fluid circuit assembly is configured such that any of the operable means can be caused to apply or adjust tension to/in each of the respective tethers by all valve units being provided in the open condition.

16. A system according to claim 1, wherein the interface means comprises componentry for monitoring tension in the tethers.

17. A system according to claim 1, wherein each operable means is provided in the form of a hydraulic cylinder.

18. A method for installing a system for use in tethering a subsea blowout preventer (BOP), the blowout preventer being associated with a wellhead, the method comprising: attaching or mounting, or causing to be attached or mounted, to a portion or region of a BOP, a first interface; deploying more than one anchors on the seabed about the BOP or the wellhead, associating, or causing to be associated, a tether with each anchor and a respective operable means associated with the BOP, each operable means being provided in operable association with the interface; and causing a tension in the tethers to be adjusted or adjustable either individually or together as a group of two or more tethers, by way of the interface.

19. A method according to claim 18, wherein the method is carried out in respect of an embodiment of a system arranged in accordance with the system of claim 1.

20. A kit of parts for use in a system for tethering a subsea blowout preventer (BOP) associated with a wellhead, the kit of parts comprising: more than one anchor units configured to carry or support a tensioning system; more than one operable means; a first interface capable of being attached or mounted to a portion or region of a subsea BOP structure; and a fluid circuit assembly suitable for operably associating the interface with each operable means such that each operable means can be operable either individually or together as a group of two or more operable means, by way of the interface.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further features of the inventive principles are more fully described in the following description of several non-limiting embodiments thereof. This description is included solely for the purposes of exemplifying the inventive principles. It should not be understood as a restriction on the broad summary, disclosure or description as set out above. The description will be made with reference to the accompanying drawings in which:

(2) FIG. 1 shows a perspective view of one arrangement of a tethering system operationally associated with a subsea blowout preventer;

(3) FIG. 2 shows a perspective view of one embodiment of an anchor configured in accordance with the principles described herein;

(4) FIG. 3 shows an end view of the embodiment of the anchor shown in FIG. 2;

(5) FIG. 4 shows an elevation view of the embodiment of the anchor shown in FIGS. 2 to 3;

(6) FIG. 5 shows a plan view of the embodiment of the anchor shown in FIGS. 2 to 4;

(7) FIG. 6 shows a section view of region A shown in FIG. 5;

(8) FIG. 7 shows a perspective view of the embodiment of the anchor shown in FIGS. 2 to 7 showing deployment lines (also used for retrieval);

(9) FIG. 8 shows a perspective view of the embodiment of the anchor shown in FIGS. 2 to 7, illustrating the fleet angle;

(10) FIG. 9 shows a perspective view of a region of the embodiment of the blowout preventer shown in FIG. 1;

(11) FIG. 10A shows a perspective view of one embodiment of a (hydrualic) tensioning cylinder described herein;

(12) FIG. 10B shows a close up perspective view of one embodiment of a saddle mount assembly provided at a region of a blowout preventer frame;

(13) FIG. 11 shows another close up perspective view of the saddle mount assembly shown in FIG. 10B;

(14) FIG. 12 shows a perspective schematic view of the saddle mount assembly shown in FIGS. 10B and 11, whereby the gate is shown in a closed condition;

(15) FIG. 13 shows a perspective schematic view of the saddle mount assembly shown in FIGS. 10B and 11, whereby the gate is shown in an open condition;

(16) FIG. 14 shows a close up perspective view of the control panel located on a region of the frame of the blowout preventer;

(17) FIG. 15 shows a further close up perspective view of the control panel shown in FIG. 14;

(18) FIG. 16 shows a top view of the control panel shown in FIGS. 14 and 15;

(19) FIG. 17 shows a side view of the control panel shown in FIGS. 14 to 16;

(20) FIG. 18 shows a rear view of the control panel shown in FIGS. 14 to 17;

(21) FIG. 19 shows a schematic of the fluid circuit assembly operated by way of the control panel shown in FIGS. 14 to 18;

(22) FIG. 20A shows a first stage in a deployment process whereby the embodiment of the anchor shown in FIGS. 2 to 6 is deployed for operational use in a subsea environment;

(23) FIG. 20B shows a second stage in deployment process initiated by the stage shown in FIG. 20A;

(24) FIG. 20C shows a third stage in deployment process initiated by the stage shown in FIG. 20A;

(25) FIG. 20D shows a fourth stage in deployment process initiated by the stage shown in FIG. 20A;

(26) FIG. 21A shows a first stage of one example installation process whereby the embodiment of the anchor shown in FIGS. 2 to 7 is installed for operational use with a blow-out preventer (BOP) in a subsea environment;

(27) FIG. 21B shows a second stage in the example installation process initiated by the stage shown in FIG. 21A;

(28) FIG. 21C shows a third stage in the example installation process initiated by the stage shown in FIG. 21A;

(29) FIG. 21D shows a fourth stage in the example installation process initiated by the stage shown in FIG. 21A;

(30) FIG. 22 shows a perspective view of a further arrangement of a tethering system operationally associated with a subsea blowout preventer arranged in accordance with the principles described herein; and

(31) FIG. 23 shows a perspective view of another arrangement of a tethering system operationally associated with a subsea blowout preventer also arranged in accordance with the principles described herein.

(32) In the figures, like elements are referred to by like numerals throughout the views provided. The skilled reader will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and/or relative positioning of some of the elements in the figures may be exaggerated relative to other elements to facilitate an understanding of the various embodiments exemplifying the principles described herein. Also, common but well understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to provide a less obstructed view of these various embodiments. It will also be understood that the terms and expressions used herein adopt the ordinary meaning as is accorded to such terms and expressions with respect to their corresponding respective areas of inquiry and study except where specific meanings have otherwise been set forth herein.

(33) It should be noted that the figures are schematic only and the location and disposition of the components can vary according to the particular arrangements of the embodiment(s) as well as of the particular applications of such embodiment(s).

(34) Specifically, reference to positional descriptions, such as ‘lower’ and ‘upper’, and associated forms such as ‘uppermost’ and ‘lowermost’, are to be taken in context of the embodiments shown in the figures, and are not to be taken as limiting the scope of the principles described herein to the literal interpretation of the term, but rather as would be understood by the skilled reader.

(35) Embodiments described herein may include one or more range of values (eg. size, displacement and field strength etc). A range of values will be understood to include all values within the range, including the values defining the range, and values adjacent to the range which lead to the same or substantially the same outcome as the values immediately adjacent to that value which defines the boundary to the range.

(36) Other definitions for selected terms used herein may be found within the detailed description and apply throughout. Unless otherwise defined, all other scientific and technical terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which the embodiment(s) relate.

DETAILED DESCRIPTION

(37) The words used in the specification are words of description rather than limitation, and it is to be understood that various changes may be made without departing from the spirit and scope of any aspect of the invention. Those skilled in the art will readily appreciate that a wide variety of modifications, alterations, and combinations can be made with respect to the above described embodiments without departing from the spirit and scope of any aspect of the invention, and that such modifications, alterations, and combinations are to be viewed as falling within the ambit of the inventive concept.

(38) Throughout the specification and the claims that follow, unless the context requires otherwise, the word “comprise” or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

(39) Furthermore, throughout the specification and the claims that follow, unless the context requires otherwise, the word “include” or variations such as “includes” or “including”, will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

(40) FIGS. 1 to 21 show one embodiment of a system 5 used for tethering a subsea blowout preventer (BOP) 10 attached to a wellhead 12. In at least one embodiment, the system 5 comprises an interface (provided in the form of a control panel 15) provided with the BOP 10, and four anchors 20 disposed about the BOP. Each anchor 20 is configured to carry or support a tensioning system 25 which is arranged in operable association with a respective tether 30. Each tether 30 is arranged so as to link a respective anchor 20 with a respective operable means, which is provided in the form of a hydraulic cylinder 35, provided with the BOP 10 by way of the cylinder's cylinder rod 38. Furthermore, each respective hydraulic cylinder 35 is configured in operable association with the interface 15 such that tension in each of the respective tethers 30 can be adjustable either individually or together as a group of two or more tethers by way of the interface 15.

(41) The interface 15, in the context of the present description provides, in at least one embodiment, an arrangement allowing the tension in each of the tethers 30 to be adjustable when a common or centralised location (by way of the interface 15), for example, from a location such as a region or portion of the BOP 10. In this manner, the hydraulic cylinders 35 can be operated (for example, by way of a remotely operated vehicle ROV 40—see FIGS. 21A to 21D) so as to adjust or control the tension in any of the tethers 30 separately and/or together as a group of two or more tethers.

(42) As noted, U.S. Pat. No. 9,359,852 ('852) describes an existing tethering system used for tethering a BOP. However, in the system described, adjustment of the tension in each of the (what appear to be essential to the operation of the system) pile-top assemblies must be undertaken in turn (which could require multiple iterations of adjustment) in order to configure the system appropriately—this onerous requirement represents a significant disadvantage in that it can take a substantial amount of time to configure the system for appropriate and safe operation; thereby incurring high installation cost, and increasing unnecessary safety risks (ie. a larger window of time for safe installation is needed in an environment in which the inherent conditions are continually changing, ie. the marine/subsea environment).

(43) In stark contrast to the system described and shown in '852, the embodiment of the system 5 described herein seeks to provide adjustment of the tension in each of the tethers at a centralised location; for example, at a selected region of the BOP 10 (ie. where the interface 15 is provided). This therefore provides a significant advantage in that requisite tension in each of the tethers can be sought/adjusted at a common location (either separately and/or together as a group of two or more tethers).

(44) The embodiment of the various components of the system 5 will be described below, commencing with the anchors 20.

(45) FIG. 2 shows a perspective view of an embodiment of an improved anchor 20 configured for use with the system 5. Broadly, the embodiment of the anchor 20 in FIG. 2 comprises a body 45 having a portion 50 thereof configured capable of supporting or carrying a device (such as, for example, the tensioning system 25); and a guard means having a pair of guard elements 52A, 52B (collectively, 52). In the embodiment shown, the guard means is provided in the form of a pair of skids 55A, 55B (collectively, 55). In the embodiment shown, the skids 55 are associated with the body 45 and configured so that a portion of each skid (55A, 55B) is provided more distal of the body 45 than one or more portions of the device (in the instance shown, the tensioning system 25). In this manner, the risk of the tensioning system 25 becoming subject to interference during handling (which may, for example, include deployment/retrieval of the anchor 20 into/from a subsea environment onto the deck of, for example, a marine vessel) of the anchor is sought to be reduced.

(46) As noted above, the term “device” is intended to refer to any appropriate resource or equipment required for the application at hand. For the purposes of the description herein, the device comprises the tensioning system 25 which is configured operable with a respective tether 30, or tether arrangement. It will be appreciated by the skilled reader that the device could be exemplified by any other like/related equipment/machinery, such as for example, hydraulic cylinders, airbags, pneumatic cylinders, chain gypsies, and the like.

(47) In its simplest form the body 45 comprises a number of generally rectangular plates 60A, 60B, 60C, and 60D (collectively, plates 60) configured in a stacked relationship, and which make up the general profile of the body. As is shown in FIGS. 2, 6, 7, and 8, opposing sides of the body 45 provide support for respective skids 55A, 55B.

(48) In the embodiment shown in FIG. 2, each skid 55 comprises a pair of contact faces 61A, 61B (upper/lower contact faces of skid 55A) and 61C, 61D (upper/lower contact faces of skid 55B)(collectively, 61) respectively and arranged with the body 45 and between which the tensioning system 25 can be supported or carried by the body. The contact faces 61 are aligned so as to be substantially parallel to each other and, in the embodiment shown, arranged so as to be substantially symmetrical about a central axis X of the body 45. Furthermore, as shown in FIG. 4, the contact faces 61 are arranged so as to be substantially symmetric about a plane P (which extends through the body 45 at about the mid-height of the skids 55).

(49) Contact faces 61A, 61C provide the outer facing surfaces of upper flange portions 65A, 65B, one or more portions of which are provided more distal of the body 45 than at least one or more of the operational components (see discussion below) of the tensioning system 25. Lower contact faces 61B, 61D, are provided by way of the lower most plate 60A.

(50) Curved flanges 75A, 75B, 75C, and 75D (including flange elements 70A and 70B) are provided in a web-flange like construction and are connected to respective skids 55A, 55B as shown. Flange portions 65A, 65B each have a width dimension which is aligned in a lateral direction of the body (ie. the lateral direction being substantially transverse to the central axis X of the body 45). In this manner, the lateral direction is orthogonal to a lengthwise dimension (being aligned with the forward-aft direction) of the body/anchor. As clearly shown in FIG. 2, the lengthwise dimension of each flange portion 65 is larger in magnitude than its respect width dimension.

(51) In substance, the outer facing surfaces of the skids 55A, 55B serve to function, at least in part, as protective guards during handling operations of the anchor 20, such as for example, deployment/retrieval of the anchor to/from a subsea environment. In at least one respect, the symmetrical nature/configuration of the skids 55A, 55B relative to the body 45 about the central axis X, and about mid-plane P, facilitates, at least in part, reduced complexity of handling of the anchor 20 during deployment/retrieval operations. In this regard, the risk of adverse interference occurring to the tensioning system 25 such as, for example, damaging the tensioning system when retrieving the anchor back onto the deck of a marine vessel is sought to be reduced. In this manner, during the retrieval process it is often not possible to control with sufficient precision the orientation of the anchor 20 when seeking to load the anchor back aboard the relevant marine vessel. Accordingly, the configuration of the skids 55A, 55B serve to, at least in part, protect the tensioning system 25 from making contact with the deck during such an operation (and therefore seek to reduce the risk of damage occurring to the tensioning system).

(52) With further reference to FIG. 2, a first side 80 of the body 45 is configured so that a region 85 thereof is capable of carrying a portion of the tensioning system 25. A second side 90 of the body 45 is provided opposite the first side 80 of the body. In a first orientation of the body 45, the first side 80 of the body is or faces uppermost. In this manner, the tensioning system 25 is provided in an operable state when the anchor 20 is positioned on the seafloor such that its second side 90 is adjacent or proximal the seafloor.

(53) The body 45 of the anchor 20 comprises first 95 and second 100 ends. As shown in FIG. 2, a portion of the tensioning system 25 is configured so as to be provided near the first 95 end of the body 45. The tensioning system 25 comprises a first operative assembly 115, and a second operative assembly 120. The first operative assembly 115 comprises a winch drum 125 (provided near the first 95 end of the body 45). The first operative assembly 115 further comprises winch mounting brackets 130A, 130B configured so as to support, at least in part, the winch drum 125 near the first 95 end of the body 45. The winch mounting brackets 130A, 130B are attached to the body 45 by way of an appropriate fastening system (such as, for example, a nut and bolt fastening system 135A, 135B as shown in FIG. 3).

(54) An end 140 of the winch drum 125 is supported at a portion of the skid 55A, near first end 95 of the body 45 by way of sleeve 145. As shown, sleeve 145 is attached to face 150 of web 155A which is bounded substantially by curved flange 75A (and flange element 70A) of skid 55A. Engagement between end 140 of the winch drum 125 and sleeve 145 is at least supportive in nature, such that end 140 is supported so that an axis A of the winch drum 125 is orthogonal to axis X of the body 45. Similar construction is shown for skid 55B whereby web 155B is bounded substantially by curved flange 75B (and flange element 70B).

(55) The first operative assembly 115 of the tensioning system 25 comprises a ratchet drive 160 and an associated drive pawl arrangement 165. The ratchet drive 160 is provided concentric with the axis A of the winch drum 125, and the drive pawl 165 is provided eccentric of the axis A of the winch drum. As the skilled reader will appreciate, the drive pawl arrangement 165 is provided in operable association with the ratchet drive 160. The first operative assembly 115 further comprises a winch pawl rod 170 and associated handle 175 (see FIG. 4) configured so that the drive pawl arrangement 165 can be operated as appropriate (eg. by way of a ROV). The first operative assembly 115 also comprises a locking mechanism (not shown) which is arranged operable so as to cease movement (ie. rotational movement) of the winch drum 125.

(56) The second operative assembly 120 comprises an annulus or aperture provided in the form of an opening or an eyelet 180 formation (shown in clearer detail in FIG. 7) through which a portion of a respective tether 30 may pass, and which is provided generally distal of the winch drum 125. The eyelet 180 is provided at a free end of a cover 185 which is arranged to provide, at least in part, a cover for a portion of tether 30 extending between the winch drum 125 and passing through the eyelet 180. The arrangement of a spool region 195 (see below) on the winch drum 125 and the eyelet 180 is configured to limit the fleet angle to ensure proper spooling of the tether/fibre-rope on the winch drum 125 (discussed below). The cover portion 185 generally comprises an opening 190 through which a portion of the tether 30 passes (enroute to eyelet 180), and further comprises a shape which tapers substantially toward the eyelet 180; the shape serving to assist in, if needed, focusing or converging the covered portion of the tether 30 toward the eyelet 180 (eg. if the tether becomes slack). The cover portion 185 is connected to the body 45 by way of any appropriate connecting or fastening assembly (eg. an appropriate nut/bolt fastening assembly), or welding process.

(57) With regard to FIGS. 3 and 5, a region (hereinafter, spool region 195) of the winch drum 125 is configured so as to allow a spool of material (such as, for example, a spool of a substantially flexible material such as a portion of tether 30) to be carried/stored appropriately by the winch drum 125. An axial dimension of the spool region 195 (relative to axis A of the winch drum 125) is, at least in part, determined such that an internal angle θ of an apex A.sub.p created by converging lines L.sub.1, L.sub.2 which extend from opposite ends of the spool region 195 to the eyelet 180 (which is configured to limit the fleet angle to ensure proper spooling of the tether/fibre-rope) is not greater than about 10 degrees; this being the addition of angles α.sub.1 (preferably no greater than about 5 degrees in the embodiment shown in FIG. 5) and α.sub.2 (similarly, preferably no greater than about 5 degrees in the embodiment shown in FIG. 5) formed at the intersection of lines L.sub.1, L.sub.2 with centre line L.sub.c (which aligns substantially with the axis X) respectively. The spool region 195 is configured so as to allow sufficient storage capacity of a portion of length of the tether 30 so as to allow for acceptable operation of the tensioning system 25.

(58) The anchor 20 further comprises a half round section of pipe 198 which is associated with the body 45 for the purpose of preventing the tether 30 from abrading on the edge of the body.

(59) The body 45 is configured such that the anchor 20 is portable. In this manner, the body 45 is configured such that the anchor 20 can be easily transportable by ship, road, or train.

(60) FIG. 9 shows a region of the embodiment of the BOP 10 shown in FIG. 1. Shown on the front right hand side of the BOP 10 is the interface 15 (hereinafter, control panel 15). In effect, the control panel 15 serves as the primary means by which each of the hydraulic cylinders 35 (hereinafter, tensioning cylinders 35) can be activated. The control panel 15 (ie. the components provided therewith) and each of the tensioning cylinders 35 are arranged in operable association with each by way of a fluid circuit assembly 312 (shown in detail in FIG. 19) comprising a number of fluid circuits (for example, hydraulic fluid circuits) to be discussed in further details below. Broadly, the control panel 15 hosts (eg. carry or support) componentry which can be manipulated by way of, for example, a ROV to operate each of the tensioning cylinders 35. In this manner, each of the tensioning cylinders 35 can be operated from a centralised location (ie. the control panel 15) either separately or together as a group of two or more.

(61) An overview of a tensioning cylinder 35 (shown in the retracted condition) is shown in FIG. 10A. Shown in FIG. 10A is a cylinder barrel 200 (of the tensioning cylinder 35), an end 205 of the cylinder rod 38 (slightly exposed), and an end 210 of the cylinder barrel 200. At or near the end 205 of the cylinder rod 38 is provided an attachment point to which first shackle 215 can attach to connection point 217 (which comprises the ability to rotate about axis T of the tube 200) of the cylinder rod 38 end 205. Similarly, the end 210 of the cylinder barrel 200 also provides an attachment point 218 where shackle 222 attaches to shackle 220 (which, as shown, is restrained from rotation about axis T) via chain link 223.

(62) When connected to a respective tether 30, the tensioning cylinders 35 operate to provide or impart a tensile force (within the respective tether 30) between the BOP 10 and the anchors 20 to mitigate fatigue of the wellhead 12. Each tensioning cylinder 35 has a stroke, for example, of about 1,500 mm, and are double acting in nature so that they can be extended (by way of the ROV 40) prior to connection with the relevant tether 30, and then operable so as to use the retraction stroke to tension the tether. The tensioning cylinders 35 also comprise a pilot operated check valve 225 (provided near end 210 of the cylinder) that acts as a safety mechanism to prevent the hydraulic pressure on the retraction side of the cylinder 35 from being vented accidentally.

(63) In practice, the end 205 of the cylinder rod 38 is attached to the free end of the tether 30 by way of the first shackle 215, and the end 210 of the cylinder barrel 200 is connected to the frame of the BOP 10 by way of shackle 222. For the embodiment shown, during normal operation, the tensioning cylinders 35 will be used to apply a tension of up to about 5 tonnes, which equates to a hydraulic pressure of about 670 psi in the retract side of the tensioning cylinders. The system 5 components provided with the BOP 10 have a maximum safe working pressure of about 3,000 psi, which means that each tensioning cylinder 35 is capable of applying a tension of approximately 22.4 tonnes if required.

(64) The cylinder rods 38 are manufactured from stainless steel for long term corrosion protection while the cylinder barrel 200 is painted alloy steel. The painting coat is sufficient to protect the cylinders against corrosion, however, an anode could be attached to the barrel of the cylinder barrel 200 to prevent corrosion if the coating is, for any reason, damaged.

(65) As will be described, the tensioning cylinders 35 are operably associated with the control panel 15 (located on the frame of the BOP 10) and actuated via a ‘hot stab’ (320) from the ROV 40. The tensioning cylinders 35 can be operated individually or as a group.

(66) During deployment and recovery of the BOP 10 the tensioning cylinders 35 are secured within a respective saddle assembly 230 that are mounted on the BOP 10. Once the BOP 10 has been landed on the seabed, the ROV 40 is able to open a gate 244 (made from high density polyethylene (HPDE)) provided on each saddle assembly 230 to stow the cylinder barrel 200 when the tensioning cylinder 35 is not in use. The gate 244 is arranged so as to pivot about an axis defined by nut/bolt arrangement 246 so that the gate can swing between open and closed conditions as shown in FIGS. 12 (open condition) and 13 (closed condition) for capturing/releasing the cylinder barrel 200.

(67) FIG. 10B shows a close up perspective view of a portion of a frame member 235 of the BOP 10 in which a portion of the tensioning cylinder 35 (near end 205 of the cylinder rod 38) is captured by way of a respective saddle mount assembly 230. As shown, the saddle mount assembly 230 attaches to the frame member 235 by way of a clamp plate 238 engaging with a body 240 of the saddle mount assembly 230. The body 240 serves as a bridge joining first semi-round form 241 (which provides a mounting point for the clamping plate 238) and second semi-round form 242 (within which the cylinder barrel 200 can be captured and restrained). The engagement/connection between the clamp plate 238 and the saddle mount assembly 230 body 240 is by way of a nut/bolt fastening assembly as shown.

(68) In order to protect the cylinder barrel 200 of the tensioning cylinders 35, a protector 248 (see FIG. 11) is installed on each of the tensioning cylinders at a location on the cylinder barrel 200 that corresponds with its contact with the saddle mount assembly 230 (as shown in FIG. 11). The protector 248 is appropriately configured so as to minimise any damage occurring to the cylinder barrel 200 due its contact with the saddle mount assembly 230.

(69) FIGS. 12 and 13 show a locking arrangement 250 provided with the saddle mount assembly 230 which is configured so as to be operable with the gate 244 for affirmatively confirming the gate in the closed condition when capturing a portion of the cylinder barrel 200. The locking arrangement 250 comprises an open elongate barrel housing 255 which is configured to house (concentrically therewith) an elongate locking pin 260 which is configured having an end (not shown) which is moveable by way of handle 261 to register within aperture 262 (of the gate 244) and an aperture 263 of the locking arrangement 250 so as to restrain movement of the gate and therefore capture the cylinder barrel 200 sufficiently in the second semi-round form 242. As shown in FIGS. 12 and 13, the open barrel housing 255 is configured having a shaped channel 270 within which the handle 261 can be moved within (both in translation and rotation) so as to actuate either of the open/closed conditions of the gate 244. The gate 244 is configured having a handle portion 290 which can be operated so as to move the gate about nut/bolt arrangement 246. As noted, operation of the handle 261 and the gate 244 is, in practice, by way of remote control of a ROV (40).

(70) As shown in FIGS. 12 and 13, the body 240 of each saddle assembly 230 is comprised of first 275 and second 280 portions, each of which face opposite sides of an intermediate portion 285 and held together by way of a plurality of nut/bolt fastening assemblies. The shapes of the first 275, second 280, and intermediate 285 portions are configured so as to correspond with each other. The first 275 and second 280 portions are made from stainless steel, and the intermediate portion 285 is made from HDPE.

(71) FIGS. 14 (in-situ schematic view), 15 (perspective front view), 16 (top view), 17 (side view), and 18 (rear view), show the general configuration of the control panel 15. The control panel 15 (in practice, provided with the frame of the BOP 10) is used by the ROV 40 to control the extension and retraction of each of the tensioning cylinders 35 using a single dual port hot-stab 320 (such as for example, an ISO 13628-8 Type dual port Hot-stab). Provided on the control panel 15 is also an isolation valve (315) which is arranged in-line (hydraulically) on the retraction side of each tensioning cylinder 35 that allows a respective tensioning cylinder to be isolated to prevent creep and/or allow specific tensioning cylinders to be actuated as required (discussed in further detail below).

(72) With reference to FIG. 15, the control panel 15 comprises a generally planar face 300 which serves to provide four pressure gauges (such as for example, 0-5,000 psi subsea pressure gauges) 305A, 305B, 305C, and 305D (or collectively, 305), each of which displays the respective retraction pressures of four subordinate (sub) fluid circuits 375A, 375B, 375C, and 375D (collectively, 375) of a fluid circuit assembly 312 (see FIG. 19), whereby each of the sub fluid circuits 375 of the fluid circuit assembly are operably associated with tensioning cylinders 35 (35A, 35B, 35C, and 35D) respectively. The control panel 15 also provides four retraction isolation valves 315A, 315B, 315C, and 315D which are associated with respective sub fluid circuits 375 of the fluid circuit assembly 312. The control panel 15 also comprises an actuable element which is provided in the form of a single dual port hot-stab 320 which is used by the ROV 40 to operate the tensioning cylinders 35. The single dual port hot-stab 320 provides a means of transferring fluid subsea to/from the ROV 40.

(73) The control panel 15 is mounted directly to a region of the BOP 10 frame and allows a single/common point tensioning, release, and monitoring point via the single dual port hot-stab 320, the four pressure gauges 305, and the isolation valves 315. Pilot operated check valves 225A, 225B, 225C, and 225D (collectively check valves 225) provide primary pressure holding, while secondary pressure holding and independent cylinder control is by way of respective isolation valves 315.

(74) A support 318 is also provided with the control panel 15 for use by the ROV 40 for stabilisation purposes while operating the hot-stab 320 at the control panel 15.

(75) FIG. 19 shows a schematic diagram of the fluid circuit assembly 312 associating the hot-stab port 320 with each of the tensioning cylinders 35. Each of the tensioning cylinders (noted as 35A, 35B, 35C, and 35D) are shown, each having a piston 353, first fluid chamber 352, and a second fluid chamber 355. The fluid circuit 312 further shows a first fluid circuit 350, which is configured to supply fluid to each of the tensioning cylinders 35 by way of sub fluid circuits 351A, 351B, 351C, and 351D (collectively 351) for extending respective cylinder rods 38 by way of filling respective first fluid chambers 352 (ie. whereby the working fluid acts on piston 353 so as to extend the respective cylinder rod 38); and a second fluid circuit 370 which is configured to supply fluid to each of the tensioning cylinders 35 by way of the sub fluid circuits 375 for retracting respective cylinder rods 38 by way of filling respective second fluid chambers 355A, 355B, 355C, and 355D (collectively, 355) (ie. whereby the working fluid acts on piston 353 so as to retract the respective cylinder rod 38). Each sub fluid circuit 375 is fluidly connected to a respective fluid pressure gauge 305 by a respective fluid line 380.

(76) Thus, when a tensioning cylinder 35 is to be operated, the ROV 40 will engage the hot-stab port 320 by way of its on-board hot-stab port engagement device. For causing the cylinder rod 38 to extend (which causes any tension already present in a respective tether 30 to reduce), fluid (for example, suitable hydraulic fluid) will be caused to transfer from the ROV 40 by way of the hot-stab engagement arrangement to flow through the first fluid circuit 350 which, as shown in FIG. 19, is in fluid communication with each of sub fluid circuits 351. Each of sub fluid circuits 351 is fluidly connected to respective first fluid chambers 352 of the respective tensioning cylinders 35. In this manner, fluid flowing through the first fluid circuit 350 and any or one of sub fluid circuits 351, will cause fluid to fill the respective first fluid chambers 352 thereby serving to extend the relevant cylinder rod 38 (by way of the fluid acting on the piston 353) outward (ie. downward in FIG. 19).

(77) For causing the cylinder rod 38 to retract (which introduces or increases tension in a respective tether 30), fluid will transfer from the ROV 40 by way of the hot-stab engagement arrangement to flow through the second fluid circuit 370 which is in fluid communication with each of sub fluid circuits 375. Each of sub fluid circuits 375 is fluidly connected to respective second fluid chambers 355 of respective tensioning cylinders 35. In this manner, and with valves 315 in the open condition, fluid flowing through the second fluid circuit 370 and any or one of sub fluid circuits 375, will cause fluid to fill the respective second chambers 355 thereby serving to retract the relevant cylinder rod 38 (by way of the fluid acting on the piston 353) inward (ie. upward in FIG. 19).

(78) As an extension of the cylinder rod 38 is occurring, and with respective valves 315 in the open condition, fluid residing in the second fluid chambers 355 is pushed through sub fluid circuit 375 and subsequently the second fluid circuit 370. Conversely, when the cylinder rod 38 is being caused to retract, fluid residing in the first chambers 352 is pushed through sub fluid circuit 351 and subsequently the first fluid circuit 350.

(79) As shown in FIG. 19, each of the sub fluid circuits 375 comprise respective isolation valves 315 (which are accessible by way of the control panel 15). In the arrangement shown, the control panel 15 can be used as a centralised interface for controlling each of the tensioning cylinders, either separately or together as a group of two or more. The valves 315 are placed in the respective fluid circuits associated with the second fluid chamber 355 of the tensioning cylinders 35 as filling of these chambers causes retraction of the cylinder rods 38 which, in turn, tensions the tether 30 when connected thereto.

(80) For example, with all valves 315 open, fluid transferred from the ROV 40 into second fluid circuit 370 flows into each of sub fluid circuits 375 so as to fill second fluid chambers 355 of the tensioning cylinders 35 and causing each of the cylinder rods 38 to retract. In this manner, all tensioning cylinders 35 can be operated so as to retract their respective cylinder rods 38 together.

(81) Using the fluid circuit assembly 312, any of the tensioning cylinders 38 can be selectively isolated for independent operation (retraction or extension) by way of operation of the respective valves 315 and pilot operated check valves 225.

(82) For example, if valves 315B, 315C, and 315D are closed, and valve 315A left open, incoming fluid flowing through second fluid circuit 370 will be prevented from flowing into sub fluid circuits 375B, 375C, and 375D and caused to only flow into sub fluid circuit 375A, thereby causing a retraction of the cylinder rod 38A in tensioning cylinder 35A. The skilled reader will appreciated that each of valves 315 can be open or closed depending on what tensioning cylinders, or combination of tensioning cylinders, are needed to be operated.

(83) Extension of the tensioning cylinders 35 can be executed in the same manner as retraction—this is achieved by way of pilot operated check valves 225A, 225B, 225C, and 225D. As the skilled person will be aware, pilot operated check vales allow free flow through the check valve; in the present instance, for example, hydraulic fluid flowing along sub fluid circuit 351A—with valve 315A open—will flow into first chamber 352A). The pilot operated valve 225A inherently blocks flow from the second chamber 355A until it feels a pilot pressure (in this case, by way of respective pilot line 228A). Thus, extension of the tensioning 35 cylinder rod 38 can be achieved by way of hydraulic fluid flowing through sub fluid circuit 351A and through pilot operated check valve 225A. As fluid flows through pilot operated check valve 225A, the fluid also flows through pilot line 228A which serves to open the valve and allow fluid to empty from second chamber 355A as fluid pressure builds in first chamber 352A. In this manner, cylinder rod 38A extends. It will be appreciated that similar functionality occurs in respect of the tensioning cylinders 35B, 35C, and 35D.

(84) The skilled reader would appreciate that similar architecture could be developed and realised for selective control of the extension of the tensioning cylinders 35.

(85) In at least one practical embodiment, the system 5 is provided as a kit or set of components comprising, for example, a suitable number of anchors 20 (for example, 4 units arranged as described herein), a suitable number of tensioning cylinders 35 (for example, 4 units arranged as those described herein, a control panel 15 (for example, 1 unit arranged as described herein), and a fluid circuit assembly 312 like that described herein.

(86) Installation of the system 5 involves, broadly, deploying the control panel 15 at a region of the BOP 10 (for example, a region of the frame of the BOP), deploying the hydraulic cylinders 35 at regions of the BOP (similarly, for example, a region of the frame of the BOP), and deploying the anchors 20 about the wellhead 10 on the seabed 1000 (see FIGS. 21A-21D). The installation method further involves, broadly, setting the desired tension in each of the tethers 30, as will be described below.

(87) Deployment of the control panel 15 and the tensioning cylinders 35 to regions of the BOP 10 is done prior to the BOP being deployed in position with the target wellhead.

(88) A method for deploying each of the anchors 20 is shown in schematic sequence in FIGS. 20A to 20D, and a method of installing the embodiment of the system 5 is shown in schematic sequence in FIGS. 21A to 21D.

(89) The anchor 20 comprises means for facilitating deployment and/or retrieval (hereinafter, deployment/retrieval means 1005) of the anchor to/from a subsea environment. As shown in FIG. 7, the deployment/retrieval means 1005 is configured so as to be operable about a generally central region of the body 45 of the anchor 20.

(90) The deployment/retrieval means 1005 comprises one or more annuli provided in the form of eyelets or pad-eyes 1010 and each configured for operable association with respective ropes or lines 1015. As shown, a first pair of pad-eyes 1010A, 1010B are provided at or near the first 95 end of the body 45, and a second pair of pad-eyes 1010C, 1010D are provided at or near the second 100 end of the body. FIG. 7 shows the general arrangement of the cables 1015 when the anchor 20 is being deployed (as will be discussed below). In the arrangement shown, lines 1015 serve to provide a four leg sling 1020 for deployment purposes.

(91) The anchor 20 also provides a further pair of pad-eyes 1012A, 1012B which allows a two leg sling arrangement (reference 1045 as shown in FIGS. 20A to 20D) to attach to the anchor for (a) initial deployment purposes (overboard from the deck of a marine vessel before transitioning to use of the four leg sling 1020), and (b) retrieval purposes.

(92) For example, FIGS. 20A-20D show various stages of the anchor 20 when being deployed from the aft deck 1025 of a marine vessel 1030 to the seafloor 1032 (see FIGS. 21A-21D).

(93) FIG. 20A shows the anchor 20 sitting on the aft deck 1025 of the marine vessel 1030 ready for deployment. As shown, the anchor 20 is connected to a launch winch 1035 mounted on the aft deck 1025 by way of a primary line 1040. Primary line 1040 provides a two leg sling 1042 arrangement at its end which connects with the anchor 20. Further, the four leg sling 1020 formed by way of lines 1015 is attached to a line 1045 (not shown in FIG. 20A, see FIGS. 20C and 20D).

(94) At FIG. 20B, the launch winch 1030 is operated so as to feed out primary line 1040 in the aft direction so that anchor 20 is moveable toward the aft most edge 1050 of the aft deck 1025. As will be clear from FIG. 20B, further extension of the primary line 1040 will allow the anchor 20 to be moved overboard toward the water surface 1052.

(95) It is during this step (as well as when retrieving the anchor 20 from operation) that the configuration of the skids 55A, 55B comes into advantageous practical effect. In this manner, during the deployment (and retrieval) process it is often not possible to control with sufficient precision the orientation of the anchor 20 when held by the relevant support lines. Accordingly, the configuration of the skids 55A, 55B serve to, at least in part, protect the tensioning system 25 from making contact with the deck (or any of the sides of the marine vessel) during such an operation and risking damage occurring to the tensioning system. In the embodiment of the anchor 20 shown, the risk of adverse contact occurring is reduced regardless of the orientation of the anchor when being deployed over side, or when being loaded back aboard the marine vessel 1030.

(96) FIG. 20C shows an advancement of the position of the anchor 20 from that shown in FIG. 20B. As can be seen, the anchor 20 is now beyond the aft most edge 1050 and is provided in a substantially vertical orientation being supported by the two leg sling line 1042 and line 1040.

(97) FIG. 20D shows advancement of the orientation of the anchor 20 whereby cables 1015 now deploy in the four leg sling 1020 arrangement (consistent with that shown in FIG. 7), and are supported by line 1045. Line 1045 is also operable by way of winch 1035. At this point, the two leg sling line 1042 is released thereby allowing the anchor 20 to be completely supported by way of the four leg sling 1020 arrangement (by way of line 1045). Thus, the support for the anchor 20 is therefore transitioned from the two leg sling line 1042 (and line 1040) to the four leg sling 1020 arrangement. Continued ease of pendant line 1045 (by the winch 1035) will cause the anchor 20 to be lowered toward the seafloor 1032 in substantially the orientation shown in FIG. 20D (and FIG. 7). Buoyancy device 1055 is also deployed.

(98) The method of retrieval of the anchor 20 from the subsea environment involves, broadly, using the two leg sling line 1042 by way of line 1040. In this manner, line 1040 is tensioned so as to raise or lift the end of the anchor 20 where the two free ends of the two leg sling line 1042 are attached. Initial tensioning of the two leg sling line 1042 serves to assist in reducing a suction force which can sometimes be present between the underside of the anchor 20 and the seafloor. This initial tensioning action could be undertaken in an iterative manner until the suction force is reduced sufficiently so as to begin raising or lifting the anchor 20 in earnest.

(99) The anchor 20 is then raised toward the water's surface and above as appropriate by way of the two leg sling line 1042 using primary line 1040. As discussed herein, during this time, no substantive consideration needs to be had to the specific orientation of the anchor 20 as it is hoisted about edge 1050 (which is the point at which contact/interference with the tensioning system 25 is most likely to occur if the anchor is hoisted in an upside down orientation) given the configuration of the skids 55A, 55B.

(100) Thus, an advantage of the configuration of the anchor 20 is seen in that the skids 55A, 55B serve to assist in reducing the risk that any adverse interference or contact will impact on the tensioning system 25 when the anchor is retrieved back onto the deck 1025 of the marine vessel 1030, regardless of the orientation of the anchor 20 during the raising process. In this manner, no undue delay needs to be incurred during the loading process thereby allowing the recovery to be as efficient as possible (ie. reducing safety risks) in view of the prevailing circumstances.

(101) Operation of the tensioning system 25 of the anchor 20 is part of the overarching method for installing the system 5 for use with, for example, a blowout preventer (used with a wellhead). Broadly, tension in each of the associated tethers 30 is adjusted by way of a multi stage tether adjustment method in which an initial adjustment is made which serves as a ‘course’ adjustment of the tether, and at least one further adjustment of the tether which serves as a ‘fine’ adjustment. Further or subsequent adjustments of the respective tethers 30 tend to be comparatively less than that of the initial or ‘course’ adjustment of the tether.

(102) Thus, following deployment of the anchors 20, the ROV 40 is appropriately configured for assisting in the set-up of the system 5 with the BOP.

(103) FIGS. 21A-21D show various stages of one embodiment of an installation process where the anchor 20 is to be placed in operable association with a BOP 1065. In practice, installation of the anchor 20 for operational use with the BOP 1065 is assisted by the ROV 40 (which is itself operated by personnel stationed remotely on the marine vessel 1030). Operation of the tensioning system 25 of the anchor 20 by the ROV 40 is by way of manipulating the winch pawl rod handle 175. In this manner, the tensioning system 25 can be operated so as to assist in the adjustment of the tether 30 as appropriate.

(104) FIG. 21A shows the anchor 20 at a position prior to contact with the seafloor 1032, and within the vicinity of the BOP 1065. The BOP 1065 is arranged so as to be provided with a number of tension cylinders 35 (four in the arrangement shown) that can be controlled by the control panel 15 provided with the BOP 1065. The tether 30 associated with each anchor 20 will be placed in operable association with a respective tension cylinder 35 (provided at the BOP 1065).

(105) Prior to contact with the seafloor 1032 the ROV 40 is operated so as to align the orientation of the anchor 20 as appropriate. Generally, the anchor 20 is aligned so that its second 100 end faces the tension cylinder 35 that it is to be arranged in operation with. Once done, the anchor 20 is lowered to the seafloor 1032 and secured in position by way of its self-weight.

(106) With reference to FIG. 21B, once the anchor 20 is resting on the seafloor 1032 (following deployment from the vessel 1030), the ROV 40 is operated so as to release the locking mechanism of the tensioning system 25 so as to allow the pulling out of a free end 1061 of the tether 30 (by way of the ROV) for attachment to the end of a respective rod cylinder 38 of a respective tensioning cylinder 35.

(107) With regard now to FIG. 21C, once all the tethers 30 (of all respective anchors 20) have been connected to respective tension cylinders 35), the ROV 40 is operated so as to remove or reduce any slack or catenary in the respective tethers 30 by powering the tensioning system 25 on the respective anchors 20. Winch motivation is applied by the ROV 40 with the interface being by way of a standard ROV torque bucket. In practice, this adjustment represents, in effect, a ‘course’ adjustment of the tether where it is reasonably expected that large amounts of slack or catenary in the tether will be reduced or removed.

(108) Turning now to FIG. 21D, with each of the tensioning systems 25 of the anchors 20 having been operated to remove or reduce any slack or catenary in the respective tethers 30, the ROV 40 is then moved to the control panel 15 from which (via the hot-stab port 320 in the control panel 15) the ROV can be operated so as to retract the tension cylinders 35 so as to apply the required tension. In the embodiment described herein, the required pre-tension is about 5,000 kgf. This subsequent adjustment represents, in effect, a ‘fine’ adjustment of the tether where it is reasonably expected that comparatively small adjustments, in comparison with the initial ‘course’ adjustment, will be required.

(109) FIGS. 22 and 23 both show different embodiments of tethering systems 500 and 600 where, primarily, further embodiments of anchor units are shown. FIG. 22 shows tethering system 500 employing 4 x anchor units 510 tethered to a BOP 520 by way of respective tethers 530. FIG. 23 shows tethering system 600 employing 4 x anchor units 610 tethered to a BOP 620 by way of respective tethers 630. The skilled reader would readily appreciate different way in which the principles of the anchor 20 could be exemplified in other embodiments or forms.

(110) The skilled reader will appreciate that the embodiment of the anchor 20 described herein may be configured (which could comprise an appropriate modification) for operational use with an existing tethering system. Furthermore, a tethering system (existing or otherwise) may be comprised of one or more of the embodiments of the anchor 20 described herein. Thus, a number of methods could be realised which comprise operably configuring (modifying or otherwise) an embodiment of a tethering system (existing or otherwise) so as to embody the principles described herein. Furthermore, a number of methods could also be realised which comprise operably configuring (modifying or otherwise) embodiments of an anchor (existing or otherwise) so as to embody the principles described herein. The skilled reader will appreciate that any such anchor so configured could include any existing gravity anchor.

(111) The system 5 could be supplied as a kit of parts comprising a suitable number (depending on the application/circumstances) of anchors (for example, anchors 20), a suitable number of operable means (for example, hydraulic cylinders 35), and a fluid circuit assembly (for example, fluid circuit assembly 312) suitable for operably associating an interface (such as for example, a control panel 15) with each operable means such that each operable means can be operable either individually or together as a group of two or more operable means, by way of the interface. Tether like components (for example, tethers 30) could also be supplied as part of the kit, or could be provided as a separate component.

(112) The skilled reader would readily appreciate the nature of the materials appropriate for making the embodiment described herein. Materials such as stainless steel, having an appropriate self-weight and/or corrosive avoiding components would find ready application. Other materials, or methods for modifying such materials, could be employed for application.

(113) Future patent applications maybe filed in Australia or overseas on the basis of, or claiming priority from, the present application. It is to be understood that the following claims are provided by way of example only, and are not intended to limit the scope of what may be claimed in any such future application. Features may be added to or omitted from the provisional claims at a later date so as to further define or re-define the invention or inventions.