Abstract
A method of lowering an apparatus (1) through a body of water comprising lowering a guiding element (25) and a weight (27) through the body of water, the lower end of the guiding (element 25) being attached to the weight (27) such that the guiding element (25) is under tension and is maintained in a generally vertical orientation when in its lowered position, and lowering the apparatus (1) through the body of water whilst being guided by the guiding element.
Claims
1. A method of lowering an apparatus through a body of water comprising lowering a guiding element and a weight through the body of water, the lower end of the guiding element being attached to the weight such that the guiding element is under tension and is maintained in a generally vertical orientation when in its lowered position, and lowering the apparatus through the body of water whilst being guided by the guiding element.
2. A method as claimed in claim 1, wherein the apparatus is subsea equipment-protection apparatus.
3. A method as claimed in claim 1, wherein the apparatus is configured such that it may be subject to greater hydrodynamic forces than the guiding element and weight.
4. A method as claimed in claim 1, wherein the guiding element and weight may be lowered through the water freely.
5. A method as claimed in claim 1, wherein the apparatus is lowered through the water freely.
6. A method as claimed in claim 1, wherein the weight and the apparatus are configured such that the weight supports the apparatus when they are in contact.
7. A method as claimed in claim 1, wherein the weight is configured such that it may optionally pass through the hole.
8. A method as claimed in claim 1, further comprising, once the apparatus has reached the weight, moving the apparatus to its desired position by moving the guiding element and weight vertically and/or laterally.
9. A system for lowering an apparatus through a body of water, the system comprising an apparatus to be lowered, a guiding element for guiding the apparatus as it is lowered and a weight, the lower end of the guiding element being attached to the weight such that the guiding element is under tension and is maintained in a generally vertical orientation when in its lowered position, and the apparatus being arranged to be coupled to the guiding element so that it can be lowered through the body of water whilst being guided by the guiding element.
10. A system as claimed in claim 9, wherein the apparatus is arranged to be coupled to the guiding element so that it can move freely in a vertical direction under the influence of gravity.
11. A system as claimed in claim 9, wherein the system further includes a surface vessel or platform that holds the guiding element.
Description
[0102] Certain preferred embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings in which:
[0103] FIG. 1 shows a prior art shielding structure;
[0104] FIG. 2 is a side cross-section of a subsea equipment-protection apparatus with a cap and sleeve arrangement;
[0105] FIG. 3 shows a similar subsea equipment-protection apparatus to that of FIG. 2 in partial section view;
[0106] FIG. 4 is an exploded view of a subsea equipment-protection apparatus with a cap and a sleeve;
[0107] FIG. 5 is a side cross-section of a subsea equipment-protection apparatus for a manifold or the like;
[0108] FIG. 6 shows a subsea equipment-protection apparatus for a Christmas tree together with a subsea equipment-protection apparatus for a manifold;
[0109] FIG. 7 is a plan view of a layout of a subsea installation;
[0110] FIG. 8 shows a cross section of another embodiment of the protection apparatus;
[0111] FIG. 9 shows a cross section of another embodiment of the protection apparatus;
[0112] FIG. 10 shows a cross section of another embodiment of the protection apparatus; and
[0113] FIGS. 11a, 11b and 11c show an embodiment of one aspect of the invention of a method of lowering an apparatus through a body of water.
[0114] The prior art shielding structures are typically as shown in FIG. 1. A deck structure 10 is supported on legs 12 that are placed on foundations 14. The deck structure 10 shields subsea equipment 16 from falling debris and the legs 12 act as trawl deflectors. It will be appreciated that the prior art structure is large and cumbersome, requires complicated foundations, and also puts constraints on the subsea equipment 16 since it must be supported by the shielding structure in some way.
[0115] FIG. 2 shows a subsea equipment-protection apparatus with a cap and sleeve arrangement. It is shown in side cross-section. The concept is based on a pipe in pipe philosophy where a “dome/cup” protection cap 1 fits within a circumferential sleeve 2. In plan view the cap 1 and sleeve 2 are circular in this example. The cap 1 is restrained from movement in a horizontal direction, and is prevented from rotating/pivoting, by the sleeve 2. The cap 1 is secured in place by its weight and by the corresponding shape of the cap and sleeve. This means that no locking device is required to protect the subsea equipment 16 from lateral trawloads and downwards vertical impact loads.
[0116] The concept can be used on a single suction anchor 6 for protection of a Christmas tree (XT), as shown, or for protecting other structures (manifold, UTA, pumps etc.) where a sleeve ring can be integrated to the foundation support. FIGS. 4 to 6 show other subsea equipment as well as XT. The protection cap 1 can be in one unit or several segments locked in place when fitted inside the sleeve ring 2. The sleeve ring 2 accommodates trawl deflectors 3. In the example of FIG. 1 the trawl deflectors 3 take the form of triangular panels fitted to the side walls of the sleeve 2, these may be mounted about the circumference of the sleeve 2, for example at 90 degree intervals. The trawl deflectors 3 can have holes 8 for reducing their weight and minimising the forces generated by ocean currents. The trawl deflectors may support a flexible flowline 4 during installation. This provides a convenient way to hold the flow line 4 and to transport it to the sea-bed.
[0117] FIG. 2 also shows the use of a sensor 5 for detecting build-up of gas or pressure leakage from the subsea equipment 16 or from any other source. The Figure further illustrates the way that a pipeline 7 can be drilled through the suction anchor foundation 6.
[0118] Another example is shown in FIG. 3. This has the same basic features as the example of FIG. 2, with a cap 1, sleeve 2, trawl deflector 3 and foundation 6. In this example the trawl deflector 3 uses an angled beam rather than a triangular plate. This Figure also illustrates additional optional features, including an access hatch 9 in the upper part of the cap 1 and holes 10 in the sleeve 2. The holes 10 in the sleeve can be used to allow access to the subsea equipment 16. The hatch 9 has a similar purpose. FIG. 3, as compared with FIG. 2, also shows how the cap 1 can be supported by an upper part of the sleeve ring (in FIG. 3) or by sitting at the base of the sleeve ring 2 (in FIG. 2).
[0119] The basic main elements are shown in two further examples in FIG. 4, in exploded view. On the left of the Figure a protection apparatus for a manifold or similar structure is shown. The cap 1 is non-circular in plan view in order to accommodate the rectangular shape of a manifold. The sleeve 2 has a similar shape to the cap 1. The cap 1 fits into the sleeve 2 and the sleeve 2 has trawl protectors 3. On the right of FIG. 4 an XT protection apparatus for XT is shown. In both cases, a flexible flow line 4 can be wrapped around the sleeve 2 as discussed above. A further feature shown in FIG. 4 is a frustoconical element 11 for trawl deflection. Thus, with these examples the trawl deflector can be made up of the angle plate 3 and the frustoconical element 11. Of course, with the manifold protection apparatus the frustoconical element 11 is not a true cone since it must also follow the non-circular shape of the cap 1.
[0120] FIG. 5 shows another example protection apparatus, similar to that on the left of FIG. 4. The subsea equipment 16 may be a manifold. The apparatus of FIG. 5 is similar in form to that of FIG. 2 aside from that the shape in plan view would be non-circular, for example a stadium shape or an oval, so that it fits closely around generally rectangular subsea equipment 16.
[0121] The cap and sleeve protection apparatus can be used in a subsea installation to protect various different parts of subsea equipment, as shown in FIG. 6 and FIG. 7.
[0122] In FIG. 6 a CAN and XT on the left are protected by a first cap 1 and sleeve 2 arrangement, which would be generally circular in plan view, and a manifold on the right is protected by a second cap 1 and sleeve 2 arrangement, which would be non-circular in plan view. The XT protection apparatus is shown in side cross-section. The manifold protection apparatus is shown in partial side cross-section. In FIG. 7 a subsea installation is shown in plan view. Three Christmas trees with circular caps 1 are connected to a manifold with a stadium shaped cap 1.
[0123] The subsea equipment is connected together by line 13, which can be protected by a concrete mattress 15. Since the various elements of subsea equipment 16 are separated apart and have separate protection then they can be placed freely wherever is most convenient, and also it is possible to easily remove and add elements in a modular fashion. Intervening elements could also be easily added later on, for example a booster pump 17 as shown in FIG. 6. This type of flexible approach is not possible with prior art shielding structures where multiple pieces of equipment are combined together under one shield.
[0124] With reference to FIG. 8, in contrast to FIGS. 2 and 6, the sensor 5 is fixed to the subsea equipment 16 via support 18, such that the sensor is suspended above the subsea equipment 16 in an upper region of the cap 1. Thus, the sensor 5 is not fixed to the cap 1.
[0125] With reference to FIG. 9, in contrast to the previously described embodiments, the cap 101 comprises a hole 121 in an upper portion of the cap 101. The hole 121 is provided at a centre of symmetry of the cap 101. A tubular portion 122 extends from the hole 121 and into the upper portion of the cap 101. Thus, a cavity 123 is formed between the tubular portion 122 and the cap 101. The leak-monitoring device 5 is positioned in this cavity 123 and is attached to the cap 101.
[0126] FIG. 10 shows is a similar embodiment to FIG. 9, except that the sensor 105 is fixed to subsea equipment 116 via support 118, similarly as shown in FIG. 8.
[0127] FIGS. 11a and 11b illustrate an embodiment of a method of lowering an apparatus through a body of water. As shown in FIG. 11a, the method comprises suspending the cap 1 above a sea surface 24. The cap 1 is supported by retractable protrusions 29 of a weight 27 which is connected to a lower end of a cable 25. The cable 25 is connected to a crane 23 located on a vessel 21.
[0128] The method further comprises releasing the cable 25 by fast pay out. Thus, the cap 1 and the weight 27 begin to free fall. Due to their respective shapes, the weight 27 is subject to smaller hydrodynamic forces than the cap 1. Thus, the weight 27 sinks faster than the cap 1.
[0129] As shown in FIG. 11b, once the weight 27 has reached its desired depth, the fast pay-out is ceased and the weight 27 is suspended by the cable 25. The weight 27 causes the cable 25 to be under tension, and hence held in a generally vertical direction.
[0130] Due to interaction between the cap 1 and the cable 25 (e.g. via hole 121 discussed above), the cap 1 may descend whilst being guided by the cable 25. As shown in FIG. 11c, once the cap 1 reaches the weight 27, the protrusions 29 again support the cap 1 and prevent the cap 1 from descending further.
