Wellhead support structure

Abstract

A wellhead support structure 1 suitable for placing about an existing subsea well 5, wherein the wellhead support structure comprises a suction anchor 2 and a guide device 3. The guide device can be u

Description

The invention relates to method of locating a wellhead support structure about an existing subsea well and a wellhead support structure for location about an existing subsea well. There are sometimes scenarios in which it may be desired to re-enter an existing subsea well and / or provide additional wellhead support. The present invention provides a method and apparatus to facilitate such operations. In a first aspect the present invention provides a method of locating a wellhead support structure about an existing subsea well, the method comprising: providing a wellhead support structure, wherein the wellhead support structure comprises a suction anchor and a guide device; and guiding the wellhead support structure into a position about the subsea well using the guide device. In a second aspect the present invention provides a wellhead support structure for location about an existing subsea well, wherein the wellhead support structure comprises: a suction anchor; and a guide device for guiding the wellhead support structure into a position about the subsea well. The method of the first aspect may use the wellhead support structure of the second aspect and / or the wellhead support structure of the second aspect may be used to perform the method of the first aspect. The content of the following description may be equally applicable to the first and / or second aspect of the invention. The method may comprise providing and / or using the apparatus described below. The apparatus / wellhead support structure may be suitable for performing (and or arranged or configured to perform) the method steps described below. It has been realised that there are scenarios in which it may be beneficial or useful to provide a wellhead support structure about an existing subsea well. By existing subsea well, it is meant a preformed, e.g. predrilled, well. The existing well may be a well in which there is already a hole into the seabed. The existing subsea well may comprise one or more well tubulars. This may include a conductor pipe and / or one or more casings, such as surface casings. The existing subsea well may be a well that has been plugged and / or abandoned. The existing well may have been permanently plugged and be an obsolete well. The existing subsea well may have had its wellhead (which may have comprised a high pressure wellhead housing and / or a low pressure wellhead housing (which may also be referred to as a conductor housing)) removed. The existing well may have been cut (or otherwise broken) below the seabed. The existing well may have had the wellhead (including the conductor housing and / or high pressure wellhead) and also possibly the upper part of well casings and / or conductor removed. The removal of the wellhead may have been by means of cutting, blasting, or exploding the tubulars and / or wellhead. The existing subsea well may be a legacy well. The existing well may also be referred to as a pre-existing well. The wellhead support structure may be a structure for supporting a wellhead (which for example may be a newly installed wellhead) connected to the existing well. The wellhead supported by the wellhead support structure may comprise a high pressure wellhead housing and / or a low pressure wellhead housing (which may also be referred to as a conductor housing). By the wellhead support structure providing support to the wellhead it may be meant that forces exerted on the wellhead are transferred into the support structure and then ultimately into the seabed. The wellhead support structure may be rigidly fixed to the wellhead and / or the seabed. This may be rigid in the context of the expected loads experienced on a subsea wellhead during operations. Rigid connection between the wellhead and the seabed via the wellhead support structure may allow forces exerted on the wellhead to be transferred from the wellhead to the seabed without going via the well tubulars and / or the connection between the wellhead and the tubulars. The position of the wellhead support structure about the subsea well may be the final and / or desired position and may be the position in which the wellhead support structure can provide support to the wellhead and / or to allow forces to be transferred from the wellhead via the wellhead support structure into the seabed. The method may comprise re-establishing connection with an existing (e.g. legacy) subsea well. The wellhead support structure may be for re-establishing connection with an existing (e.g. legacy) subsea well. The existing well may not comprise a wellhead (e.g. there is no low pressure wellhead housing (also known as a conductor housing) and / or no high pressure wellhead housing). In the case that the existing well does not comprise a wellhead, the method may comprise installing a wellhead for connection to the existing well, i.e. the tubulars of the existing well. The wellhead support structure may be for installing a wellhead for connection to the existing well, i.e. the tubulars of the existing well. The installation of the wellhead may be together with the installation of the wellhead support structure or after the installation of the wellhead support structure. The possibility to reuse or reenter an existing subsea well may require a subsea wellhead to which equipment, such as a BOP and drilling riser, can connect. This may be to enable drilling and completion activities, such as providing a reservoir barrier, to be performed. Thus, if the existing well does not comprise a wellhead, the method may comprise providing a wellhead. One reason for re-establishing connection with an existing abandoned subsea well may be to improve the barrier(s) within the well. Increasingly there is interest in storing CO2 in reservoirs or formations. However, it has been found that an existing well that has been plugged and abandoned in a normal manner may have plugging that results in insufficient barriers towards a new planned 002 storage reservoir. This planned 002 storage reservoir may be a different reservoir than was originally targeted by the existing well. However, it has been found that in some cases, to use a geological area for permanent 002 storage there is a need to provide new barriers in one or more existing wells that have been plugged and abandoned. This is because the increased pressure and / or safety constraints caused by a new 002 storage reservoir may not have been envisaged or accommodated when plugging and abandoning a legacy well and hence additional barriers are now required. It may be that equipment, such as a drilling rig with a drilling riser and a BOP connected to the well, is needed to perform additional plugging of the existing well. In which case re-establishing a connection with an existing well may be required. Further, given the equipment required, resulting loads from the work to provide the additional plugging and / or possible limited load carrying capacity of an existing (potentially quite old) well, a wellhead support structure (or additional wellhead support structure) may be required. The method may comprise transferring loads (e.g. substantially all of the loads, or most of the loads) from the wellhead to the seabed (i.e. soil) without going through the existing well tubulars. The wellhead support structure may be arranged to transfer loads (e.g. substantially all of the loads, or most of the loads) from the wellhead to the seabed (i.e. soil) without going through the existing well tubulars. These loads may be vertical and / or lateral loads. Typically, a subsea BOP and riser have large down weight and sideways loads when operated on a subsea well. Therefore, the well supporting structure may be arranged to able to handle loads (e.g. vertical and / or lateral loads) imparted by a typical subsea BOP and / or riser and / or typical operational activities. It has been found that a well located onshore will not usually be associated with the same level of loads as an offshore, subsea well. Further, in some subsea cases, there may be a need for diver less operations in the presence of water, at least for deep water wells. These are some of the constraints that may be faced by subsea wells compared to onshore wells. Thus, it has been realised that there may be a need for a methods and apparatuses specifically designed for use with existing subsea wells. The existing subsea well may comprise a wellhead. The wellhead may comprise a high pressure wellhead housing and / or a low pressure wellhead housing (which may also be referred to as a conductor housing). It has been realised that there may be existing subsea wells with wellheads that require more wellhead support than the current arrangement provides (if any). In which case, it may be beneficial to guide the wellhead support structure into a position about the existing subsea well so that the wellhead support structure can provide support to the existing wellhead. The wellhead support structure may be for providing support, e.g. lateral and / or vertical support, to a wellhead (either existing or newly installed at the time of the wellhead support structure) that is connected to the well. The wellhead support structure may be connected (directly or indirectly) to the wellhead such that forces can be transferred from the wellhead through the wellhead support structure into the seabed. The method may comprise rigidly connecting the wellhead support structure to the wellhead. This may for example be done using a clamping arrangement to clamp the wellhead within the wellhead support structure. The wellhead support structure may be connected to the wellhead before or after the wellhead support structure has been installed in the final desired position for the wellhead support structure, e.g. with the suction anchor sucked, at least mostly into the seabed. The method may comprise guiding and / or locating the wellhead support structure into a position that is concentric and / or coaxial with the existing subsea well, e.g. coaxial with the existing well tubulars and / or existing wellhead (if present). The guide device may be for guiding (and used to guide) the wellhead support structure into a position that is concentric and / or coaxial with the subsea well, e.g. existing well tubulars. This may be as the wellhead support structure is lowered towards the existing well and / or as the wellhead support is installed (e.g. as the suction anchor) is sucked (or otherwise embedded) into the seabed. In the case of an existing well in which the wellhead has been removed, the method may comprise connecting a wellhead to the existing one or more tubulars (e.g. conductor and / or casings). This may require concentric placement of the wellhead relative to the well tubulars. Thus, the method may comprise guiding and / or locating a wellhead (that may comprise the high pressure wellhead housing and / or the low pressure / conductor housing) concentric and / or coaxial with the existing subsea well, i.e. the tubulars of the subsea well. This may be achieved by installing the wellhead together with the wellhead support structure (which is located and / or guided into a position that is concentric with the well), or installing the wellhead after the installation of the wellhead support structure and using the wellhead support structure that has been located concentric and / or co axial with the well tubulars to guide the wellhead into a location that is also concentric and / or coaxial with the well tubular(s). There are known methods for joining well tubulars (e.g. casings) inside an existing well. These solutions may require (substantially) concentric casings. Thus, if the wellhead is located concentric and / or coaxial with the existing well tubular these known methods may be used to connect the wellhead to one or more of the existing well tubulars. The present invention may provide a wellhead support structure that may be coaxially and / or concentrically aligned with an existing well, e.g. one that has been plugged and abandoned, while at the same time have necessary strength to support loads that will arise from subsequent operations, such as drilling operations. This may be achieved by providing a wellhead support structure that comprises a suction anchor (which may for example be a suction anchor foundation) and a guide device for guiding the wellhead support structure (e.g. the suction anchor) into a position about the existing subsea well. The method and apparatus may allow this to be achieved without the use of a drilling rig. The normal procedure is that wellheads are installed by the drilling rig because wellheads are normally connected to the casing which are installed as part of the drilling sequence, however, in the case of an existing well without a wellhead, the casings are already installed and thus a different installation method for the wellhead(s) may be required. The wellhead support structure may comprise only one (i.e. a single) suction anchor. The (e.g. single) suction anchor may be coaxially and / or concentrically aligned with the guide device. When the wellhead support structure comprises a single suction anchor, the central axis of the suction anchor may be coaxial and / or concentric with the central axis of the wellhead support structure. Alternatively, the wellhead support structure may comprise a plurality of suction anchors. If the wellhead support structure comprises a plurality of suction anchors, none of the suction anchors may be coaxial with the axis of the guide device and / or the wellhead support structure as a whole. The wellhead support structure may comprise a wellhead support frame. The wellhead support frame may be connected (directly or indirectly) to the guide device and / or the one or more suction anchors. When the wellhead support structure comprises a plurality of suction anchors, the wellhead support structure may be arranged so that when the wellhead support structure is installed about an existing well, the existing well is not within any of the internal volumes of the suction anchors. In other words, the existing well is located outside of the suction skirt of each of the suction anchors. The wellhead support frame may comprise a plurality of beams. The beams may be rigid. By rigid in this context, it may be meant that the beams do not deform under at least the typical loads expected to be experienced during use of wellhead support structure and / or operation of the well. The beams of the support frame may define an internal space. The internal space of the support frame may be for housing a wellhead. The wellhead may be housed by the support frame when it is coupled to the existing well and the wellhead support structure is installed about the existing well. Providing an internal space in the support frame may allow the wellhead, when installed, to be protected from hazards that may pose a risk to the well. For example, the support frame may protect the installed wellhead from impact with marine vehicles that may otherwise collide with the wellhead. The internal space may be for housing equipment (e.g. well control equipment such as a flow control base, blow out preventer (BOP) and / or Christmas tree etc) mounted on the wellhead. The support frame may act as a trawl deflector and / or protection structure for the wellhead and other components housed within the support frame. The method may comprise locating the existing subsea well (i.e. identifying where it is located). Given that the well is subsea, its precise location may need to be determined. Further, in the case of an abandoned / legacy well that has had the wellhead removed, the top of the remaining well tubulars may not be visible, e.g. it may be buried under the seabed. If the subsea well is buried under the seabed, the method may comprise removing soil covering the existing well. The method may comprise installing a guide element on the existing well. The guide element may be for aiding the guiding of the wellhead support structure about the existing well. For example, the guide element may be for interacting with the guide device of the wellhead support structure. The guide device may be used to provide a shaped upper surface at the top of the existing well that facilitates the guiding of the wellhead support device about the existing well. The guide element may have a lower portion that extends into the existing well and / or the guide element may have an upper portion that protrudes above the top of the existing well. The lower portion may extend a significant distance into the casings of the existing well, for example the lower portion may extend more than 1m, more than 5m, more than 10m and up to 40m into the existing well. The upper portion of the guide element may have an outer diameter that is larger than the outer diameter of the lower portion of the guide element. The upper portion of the guide element may have an outer diameter than is larger than the inner diameter of the casing of the existing well. The lower portion of the guide element may have an outer diameter than is smaller than the inner diameter of the casing of the existing well. This is so that when the guide element is landed on the existing well the lower portion of the guide element may extend into the casings of the existing well whilst the upper portion of the guide element may be supported at the top of the casing. The upper portion of the guide element may have a conical upper surface, e.g. the guide element may taper outwards from the upper tip of the guide element. In this case, the guide element may be referred to as a guide cone. When the guide element has a conical upper surface, the guide device of the wellhead support device may comprise an inverted funnel. In this case, the guide element may be used to guide the guide device of the wellhead support structure over and / or around the existing well. The upper portion of the guide element may comprise a funnel. In this case the guide element may be used to guide the guide device of the wellhead support structure into the existing well. In the case that the method comprises installing a wellhead (e.g. in the case that the existing well does not comprise a wellhead, e.g. the well has had its wellhead removed), the method may comprise providing a wellhead in the wellhead support structure (e.g. in the receptacle, if present). This step may be before or after the wellhead support structure has been installed, i.e. located, about the existing subsea well in the seabed. The method may comprise deploying the wellhead support structure subsea. The wellhead support structure may be held from a surface vessel, e.g. a ship. The wellhead support structure may be held, suspended and / or lowered subsea using a lifting arrangement. The lifting arrangement may comprise lifting wires and / or a crane. The method may comprise lowering the wellhead support structure towards the existing subsea well. This step of lowering the wellhead support structure may be through the water. The method may comprise lowering the wellhead support structure towards the existing well until the guide device reaches the existing subsea well. The guide device may be designed / arranged to reach, contact, surround and / or enter the existing well before the suction anchor reaches the well and / or seabed. Thus, the method may comprise lowering the wellhead support structure towards the existing well until the guide device reaches, contacts, surrounds and / or enters the existing subsea well but before the suction anchor(s) of the wellhead support structure reaches and / or contacts the seabed and / or well. Additionally or alternatively, the guide device may be designed / arranged to reach, contact, surround and / or enter an additional component coupled to the top of the existing well, for example a guide element, before the suction anchor(s) of the wellhead support structure reaches and / or contacts the seabed and / or well. If entrance, surrounding and / or contact of the well by the guide device is unsuccessful, i.e. not achieved as desired, the wellhead support structure may be lifted to a higher position and the lowering procedure may be repeated until the guide device does successfully enter, surround and / or contact the well and / or guide element. The step of guiding the wellhead support structure into a position about the subsea well using the guide device may comprise aligning the wellhead support structure and / or the guide device (and wellhead, if being installed together with the wellhead support structure) with, e.g. concentric and / or coaxial to, the existing well tubulars. This may be performed whilst the suction anchor is not in contact with the subsea well and / or seabed. Thus, there may be a stage of the method in which the wellhead support structure is suspended above the existing well with the guide device in contact with and / or entered into the well (or in contact with, entered into and / or surrounding the guide element) and the suction anchor is not in contact with the well or the seabed. This may be the position of the wellhead support structure when it is being aligned (e.g. made coaxial and / or concentric) with the existing well, e.g. tubulars of the existing well. The method may comprise lowering the wellhead support structure through the water (e.g. by means of a crane and lifting wires) until the guide device enters the existing well, e.g. enters the well tubular(s) of the existing well, contacts or surrounds the existing well. Once the guide device has contacted, e.g. entered or surrounded the existing well, the guide device may be arranged (e.g. located and / or with sufficient stiffness) such that this causes alignment of the wellhead support structure, e.g. suction anchor of the wellhead support structure, about the existing well. The guide device may be concentric and / or coaxial with the suction anchor. Thus, contact of the guide device with the existing well (or guide element), e.g. entry of the guide device into the existing well, may cause the suction anchor of the wellhead support structure to be coaxial with the existing well. The method may comprise lowering the wellhead support structure through the water (e.g. by means of a crane and lifting wires) until the guide device contacts and / or surrounds the well tubular(s) and / or the guide element coupled to the well tubular(s) of the existing well. Once the guide device has contacted and / or surrounded the existing well and / or guide element, the guide device may be arranged (e.g. located and / or with sufficient stiffness) such that this causes alignment of the wellhead support structure about the existing well. In this arrangement, the guide device may not be concentric and / or coaxial with the suction anchor(s). Instead, the wellhead support structure may comprise a plurality of suction anchors arranged in an area surrounding the well when the wellhead support structure is installed, as discussed above. Once the suspended wellhead support structure has been aligned with the existing well using the guide device, the wellhead support structure may be lowered further towards the existing well and / or seabed until the suction anchor(s) (e.g. outer suction skirt(s)) contacts the seabed. The guide device may move down within or around the well as the wellhead support structure is lowered towards the seabed, as a result the concentric guiding and positioning and / or alignment of the suction anchor(s) by the guide device can be provided at least until the bottom of the suction anchor(s) reaches the seabed and optionally until the suction anchor(s) is embedded into the seabed to its / their final desired location. When the wellhead support device comprises a support frame, the suction anchors may be sunk into the seabed until a desired gap between the support frame and the seabed is achieved. Before the suction anchor reaches the seabed, the wellhead support structure may be rotated about its vertical axis. This may be by rotation of the lifting wires and / or ROV manipulation. If the wellhead support structure comprises a plurality of suction anchors, vertical alignment of the wellhead support structure may be achieved after the suction anchors reach the seabed by embedding each suction anchor to a different depth in the seabed. The method may comprise adjusting the verticality and / or alignment of the wellhead support structure. The method may comprise independently controlling the depth of each of the plurality of suction anchors of the wellhead support structure. The existing subsea well may have a vertical inclination away from the true vertical. The guiding by the guide device may help ensure that the suction anchor(s) installation into the seabed / soil will start along a similar inclination out of true vertical. After the suction anchor has reached the seabed, the method may comprise forcing the suction anchor (i.e. outer suction skirt) into the seabed (e.g. under gravity by its own weight, suction and / or piling etc) in a position (e.g. concentric and / or coaxial) about the existing well. Once the wellhead support structure is fully installed (i.e. once the suction anchor reaches a desired installation depth in the seabed and / or until the wellhead support structure (e.g. an internal pipe) stops against the existing well), the suction anchor, e.g. outer suction skirt of the suction anchor, may surround, e.g. circumscribe, at least part of the existing well, e.g. it may be located about (such as on the same horizontal plane) of the top of the one or more tubulars of the existing well. When the wellhead support structure comprises a plurality of suction anchors, once the wellhead support structure is fully installed (i.e. installed into the desired position about the existing well), the suction anchors may be located in an area surrounding the existing well such that the existing well is not located within the internal volume of any of the suction anchors. Whether the wellhead support structure comprises a single suction anchor or a plurality of suction anchors, the position in which the wellhead support structure is fully installed may be the final desired position of the wellhead support structure. This may be the position in which the suction anchor(s) is at least mostly sucked into the seabed, the position in which the wellhead support structure is at the correct height for supporting a wellhead connected to the existing well and / or the position in which the wellhead support structure is rigidly fixed to the seabed. The method may comprise fluidly connecting the wellhead and the existing well tubulars. This may be once the wellhead support structure is fully installed. The method may comprise engaging the wellhead support structure with the wellhead such that loads (vertical and / or lateral loads) can be transferred from the wellhead into the wellhead support structure (and then ultimately into the seabed), preferably without going via the well tubular(s). The suction anchor(s) may comprise an outer suction skirt and a top lid. The top lid may be perpendicular to the wall of the outer suction skirt. The top lid may be substantially parallel to the seabed and / or rest on or near the top of the seabed when the suction anchor is installed. The top lid of the suction anchor may comprise one or more laterally extending load bearing means, such as I-beams. These load bearing means may be provided so that the suction anchor can accommodate lateral loads imparted on and transferred through the wellhead support structure. These load bearing means (e.g. beams) may be regarded as providing a support frame. The wellhead support structure (e.g. the suction anchor of the wellhead support structure and / or the support frame) may comprise a receptacle for receiving the wellhead. The receptacle may be a tubular component. The receptacle may be referred to as a wellhead housing receptacle. The receptacle may be provided in a location at, or towards, the top of the wellhead support structure, e.g. at, or near, or through the top lid of the suction anchor and / or through the support frame, if present. The receptacle may be provided coaxially and / or concentrically with the wellhead support structure, e.g. the outer suction skirt of the suction anchor of the wellhead support structure and / or the guide device. This receptacle may be arranged so that when the wellhead is located in the receptacle the wellhead is concentric and / or coaxial with the wellhead support structure, the guide device, and / or the outer suction skirt of the suction anchor of the wellhead support structure. The wellhead support structure, e.g. suction anchor and / or support frame, may comprise an aperture, e.g. central aperture. The aperture may extend through the top lid and / or receptacle of the suction anchor and / or support frame. The aperture may be an aperture through which the fully formed subsea well extends (i.e. the well with the wellhead attached). For example, the wellhead (comprising the low pressure and / or the high pressure wellheads) may be received in and / or through the aperture. The aperture may be bounded by the receptacle for receiving the wellhead. The wellhead support structure may be arranged so that forces experienced by the wellhead, e.g. lateral and / or vertical forces, can be transferred to the suction anchor (e.g. via the receptacle, top lid and / or outer suction skirt) to the seabed. The wellhead may be mechanically fixed, e.g. clamped, directly or indirectly to the suction anchor(s), e.g. to / in the receptacle for receiving the wellhead. This may allow the forces (e.g. vertical and / or lateral forces) to be transferred from the wellhead to the suction anchor(s) as mentioned above. Alternatively, a plurality of suction anchors may be provided in an area surrounding the existing well when the wellhead support structure is installed. In this alternative, it is not necessary to provide an aperture on the suction anchors since the existing well does not need to extend through the suction anchors. Instead the aperture for the well may be provided through a support frame (which is may be for transferring forces from the wellhead to the suction anchors). The aperture may be arranged so that it can be sealed or otherwise fixed to the existing well. The suction anchor may comprise an internal pipe. The internal pipe may be connected (directly or indirectly) to the top lid of the suction anchor. The internal pipe may be for connection to the existing well, e.g. the top of one of the tubulars of the existing well. The internal pipe may be arranged to be located above the top of the existing well, abut the top of the existing well and / or overlap the top of the existing well, when the suction anchor is fully installed. For example, the internal pipe may be for connection to the conductor of the existing well. The internal pipe may have substantially the same diameter as one of the tubulars of the existing well, such as the conductor pipe of the existing well. The internal pipe may be a central pipe, i.e. located such that the central axis of the internal pipe is the same as the central axis of the suction anchor. In cases where the internal pipe is planned to contact, be located just above, and / or overlap the existing well it may be possible to establish a fluid (i.e. liquid and / or gas) tight connection between the internal pipe and at least one of the well casings. Thus, the method may comprise establishing a fluid (i.e. liquid and / or gas) tight connection between the internal pipe and at least one of the well casings. The diameter of the internal pipe may be smaller than the diameter of the conductor of the existing well. This may be so that the internal pipe may be received inside the existing well conductor casing. If the existing well comprises a surface casing, and the internal pipe diameter is such that it can enter in the annulus formed by the conductor and surface casing, provided that a significant overlap between the internal pipe and the existing well tubulars (conductor casing and surface casing) is obtained, it may be possible to make a fluid tight connection by cementing the internal pipe of the wellhead support device in the annulus. The cementing may be done after the guide device has been removed. The internal pipe may be substantially parallel and / or coaxial with the outer suction skirt of the suction anchor. The internal pipe may extend from, or near, the top of the suction anchor (e.g. the top lid of the suction anchor) in a direction towards the bottom of the suction anchor. The internal pipe may extend from the bottom of the receptacle. The internal pipe may be fixed, e.g. mechanically fixed or welded, to the suction anchor, such as to the bottom of the receptacle. Whilst the receptacle and internal pipe could be two distinct components, the receptacle (for receiving the wellhead), if present, and the internal pipe may be integrally formed and / or provided by the same part, i.e. there may be a single integrally formed pipe that at a top end provides the function of the receptacle for receiving the wellhead and at its bottom end provides the internal pipe for connection to the existing well. The receptacle may be connected to the existing well. This may for example be in arrangements in which an internal pipe is not present. The method may comprise, once the wellhead support structure has been installed on the seabed, connecting the internal pipe (and / or receptacle) to the existing well, e.g. to one or more of the tubulars of the existing well. The connection between the internal pipe (and / or receptacle) and the existing well, once made, may be a fluid tight and / or pressure tight connection (i.e. pressure tight to the usual maximum pressure experienced within a typical subsea well). Once the internal pipe (and / or receptacle) is connected to the existing well, the internal pipe may form part of the tubulars of the subsea well. The internal pipe may be shorter than the outer suction skirt. This means that the bottom of the internal pipe does not protrude beyond the bottom of the outer suction skirt. The internal pipe may be significantly shorter than the outer suction skirt. The length of the internal pipe may be less than 50%, 25% or 10%, of the length of the outer suction skirt. The internal pipe may extend only within the top half, quarter or tenth of the internal volume of the suction anchor. The length of the internal pipe may such that, when the suction anchor is in the (final desired) location for providing wellhead support (e.g. fully embedded in the seabed or embedded sufficiently to provide the required lateral and / or vertical support) about the existing well, e.g. with the suction anchor and / or internal pipe coaxial with the tubular(s) of the existing well, the bottom of the internal pipe is above, or at, the height of the top of the existing well, i.e. the top of the existing well tubulars. Thus, the length of the internal pipe may be designed to prevent contact between the internal pipe and the existing well, e.g. tubulars and cement, that could interfere with installation of the suction anchor around the existing well. The internal pipe may be made sufficiently short relative to the suction skirt length such that, with a complete suction of the suction anchor into the soil, the internal pipe will not contact the well. Alternatively, it may be desirable for the internal pipe to make contact to the top of the existing well prior to a complete skirt suction into soil and / or to overlap with the top of the existing well. For abandoned wells, there are different solutions used for cutting wells for removal of the wellhead. These include machined cuts with a predictable, known and / or straight top surfaces to more violent methods, such as use of explosives and abrasive waterjet cutters, that may leave a less clean and predictable top surface to the existing well. At least for these reasons it may be desirable in some cases to avoid any direct contact and / or overlap between the wellhead support structure (i.e. internal pipe) and the existing subsea well at the final installation stages. The method may comprise determining the position of the top of the existing well relative to the seabed, and providing the wellhead support structure with an internal pipe and / or receptacle for connection to the existing well that is sized based on the position of the top of the existing well. Alternatively, when the wellhead support structure is arranged such that the well does not extend through a suction anchor, it is not necessary to include an internal pipe connected to the top lid of the suction anchors. Instead, a wellhead housing (i.e. conductor housing and / or high pressure wellhead housing) and / or wellhead housing receptacle may be provided concentric and / or coaxial to the guide element. The wellhead housing and / or wellhead housing receptacle may be arranged to be located above or around the existing well when the wellhead support device is fully installed. For example, the wellhead housing and / or wellhead housing receptacle may have an inner diameter that is larger than the outer diameter of the existing well. In addition, whilst the guide element and wellhead housing and / or wellhead housing receptacle could be two distinct components, the guide element (for guiding the wellhead support structure into alignment with the existing well) and the wellhead housing and / or wellhead housing receptacle may be integrally formed and / or provided by the same part, i.e. there may be a single integrally formed component that at a bottom end provides the function of the guide element for guiding the wellhead support structure and at its top end provides the wellhead housing (i.e. conductor housing and / or high pressure wellhead housing) and or wellhead housing receptacle for connection to the existing well. The method may comprise, once the wellhead support structure has been installed on the seabed, connecting the wellhead housing and / or wellhead housing receptacle to the existing well, e.g. to one or more of the tubulars of the existing well. The connection between the wellhead housing and / or wellhead housing receptacle and the existing well, once made, may be a fluid tight and / or pressure tight connection (i.e. pressure tight to the usual maximum pressure experienced within a typical subsea well). Once the wellhead housing and / or wellhead housing receptacle is connected to the existing well, the wellhead housing and / or wellhead housing receptacle may form part of the tubulars of the subsea well. The wellhead support structure may comprise a closure for providing a closed volume within the suction anchor. This may be a closed volume relative to the surrounding seawater. The closed volume may be when the suction anchor has been landed on the seabed and the suction skirt created a seal with the seabed, e.g. when the suction anchor has been allowed to at least partly self-penetrate the seabed under its own weight. The installation of the suction anchor may be performed by lowering the suction anchor towards the seabed until it contacts the seabed. The suction anchor (i.e. outer suction skirt of the suction anchor) may be allowed to partly embed into the seabed first under its own weight (i.e. by way of gravity). Further embedding of the suction anchor into the seabed may be performed using suction. This may be achieved by generating a lower pressure inside the suction anchor. This may be done by evacuating (e.g. pumping) fluid (typically seawater) from the inside volume of the suction anchor. This may only possible if the internal volume of the suction anchor is closed towards the surrounding water by the wellhead support structure being closed and pushed into soil. The closure may be required because the suction anchor comprises a short internal pipe, or no internal pipe at all. This means that even when the suction anchor has landed on, and partially self embedded in the seabed under its own weight, the aperture though which the subsea well will extend (if it extends through the suction anchor) may not be sealed. Hence a closure may be needed to seal the aperture. The closure may be for sealing the aperture, receptacle and / or internal pipe of the wellhead support structure (i.e. of the suction anchor). The closure may be a temporary closure, i.e. one that is releasable. The closure may be a plug, cap or lid, e.g. a pressure cap. The closure may be releasably attached to the suction anchor, e.g. top of the aperture, receptacle and / or internal pipe or inside the aperture or anywhere along within the length of the receptacle or internal pipe. After the suction anchor has been installed the closure may be removed. This is so that a well can extend through the suction anchor without being blocked by the closure. The closure may be arranged so that it can seal the aperture. The closure may be able to sustain a differential pressure acting from the outside (i.e. a lower pressure inside the suction anchor compared to the external environment) sufficient for installation of the suction anchor. The closure may be a plug that fits the aperture and provides a seal. The closure may be held in place by gravity and differential pressure alone. Alternatively, the closure may be arranged to also seal and resist a differential pressure acting from inside (i.e. a higher pressure inside the suction anchor compared to the external environment). This is because it may be desirable to remove the entire wellhead support device at a later point in time. This may be achieved by inverting the suction process to one of pumping fluid into the suction anchor(s) to force the assembly out from the soil. It may also be necessary to reverse the direction of differential pressure during installation, e.g. due to damage or failure of parts the assembly, for instance to bring the suction anchor(s) back for surface for repair or alterations. The method may comprise partially reversing the suction of the suction anchor(s) into the seabed to improve the installation. This may for example be if the suction anchor(s) is(are) at an undesired installation inclination (e.g. not coaxial with the existing well) and / or is heading towards one or more obstacles such as boulders in the soil and / or to achieve the soil penetration benefits of “stroking” the suction anchor(s) up and down during installation. Thus, the closure may be locked in a sealing position. This may be by means of a locking mechanism holding it in a sealing position. Thus, the closure may provide a two-way sealing plug that can withstand both a high and low differential pressure inside the suction anchor compared to the external environment. This may have the benefit of avoiding the need to change between one-way type plugs if there is a need to change the direction of pressure differential within the suction anchor. The closure may be a known WH High Pressure Cap. This is an existing (e.g. off the shelf) device for sealing a high pressure wellhead housing to resist pressures from the inside and outside at significantly higher pressures than required when installing a suction anchor. The known WH High Pressure Cap may lock and seal to the wellhead in the same manner as BOPs and xmas trees. If the wellhead support structure comprises a wellhead, the closure may utilise the wellhead top mandrel locking profile (i.e. that on the outside of the wellhead) for locking with a separate seal ring (VX seal) at the top / inside of the wellhead. This may be used when the wellhead is received in a sealing manner in the top of the suction anchor. Such a WH High Pressure Cap may be used if a wellhead (e.g. high pressure wellhead) is installed in the suction anchor (i.e. in the receptacle) in a sealing manner, before the step of sucking the suction anchor into the seabed. The suction anchor(s) may comprise a further opening (additional to the aperture through which the well will extend), such as a vent hatch. This may be an openable, closable and / or sealable opening. This opening may be in the top lid of the (each) suction anchor. The opening may be to allow gas, e.g. air, out of the suction anchor as and / or after it is deployed subsea. This is so that gas does not get trapped inside the suction anchor(s) which may impede the lowering of the wellhead support device (i.e. suction anchor) towards the seabed. Once the gas has been released so that the suction anchor(s) can be lowered through the water to the seabed, the opening may be closed and / or sealed. This is to provide a closed volume within the suction anchor(s) so that it can be sucked into the seabed as described above. Evacuation of fluid out of the suction anchor(s) to force it into the seabed may be performed through the opening (i.e. vent hatch) and / or the aperture (i.e. the central aperture) of the suction anchor (if present). The guide device may be connected to and / or arranged to be connected (directly or indirectly) to the suction anchor. The guide device when connected to the suction anchor may extend beyond the bottom of the suction anchor, e.g. beyond the bottom of the outer suction skirt of the suction anchor. The guide device may be connected and / or arranged to be connected (directly or indirectly) to a support frame of the wellhead support structure. The guide device may be an elongate member. The guide device may guide the wellhead support structure into a position about the existing subsea well by itself entering the subsea well, i.e. entering the tubulars of the subsea well. The guide device may be an inverted funnel shape. That is, the guide device may be substantially conical in shape. The guide device may comprise a first opening at the top and a second opening at the bottom. The second opening in the bottom may have a larger diameter than the first opening in the top. The guide device may taper inward towards the top of the guide device. The installation may comprise a guide element for installing on the existing well. The guide element may be arranged such that when the wellhead support structure (and hence the guide device) is lowered towards the existing well, the guide device contacts the guide element and they act to aid bringing the wellhead support structure into alignment with the well. The guide element may be a tubular member with a conical upper end. The maximum outer diameter of the guide element may be smaller than the minimum inner diameter of the guide device, the wellhead housing and / or wellhead housing receptacle. This is so that the guide device, the wellhead housing and / or wellhead housing receptacle may be lowered around the guide element during installation of the wellhead support structure. The guide element may be arranged so that in use the angled surface of the conical upper end may contact the angled surface of the funnel of the guide device (if it is a funnel) to aid bringing the guide device and guide element into coaxial alignment. As mentioned above, alternatively the guide element may comprise a funnel that is arranged to guide a guide device of the wellhead support structure into the existing well. The guide element may be installed on the existing well prior to installation of the wellhead support structure on the seabed. Installation of the guide element may be performed using a crane and lifting cables from the surface of the water. Additionally, an ROV may be used to aid the installation of the guide element by guiding the guide element into position on the existing well. The guide element may be fixed to the existing well and / or may be held in place on the existing well using only its own weight. The guide element may be removable from the existing well. The guide element may be removed after installation of the wellhead support structure, e.g. using lifting cables and cranes and / or an ROV. The guide device may extend along the central axis of the wellhead support structure. When the guide device is attached to the suction anchor (directly or indirectly), the guide device may extend along the central axis of the suction anchor. When the guide device is attached to the suction anchor (directly or indirectly), the outer suction skirt of the suction anchor may be coaxial and / or concentric with the guide device and the outer suction skirt may surround at least part of the guide device. When the guide device is attached to the suction anchor (directly or indirectly), the guide device may extend from a top end, at or near the top of the suction anchor, to a bottom end below the bottom of the suction skirt of the suction anchor. When the guide device is attached to the support frame (directly or indirectly), the guide device may extend from a bottom surface, or near the bottom surface of the support frame. The guide device may extend along the central axis of the support frame. The guide device may be for being inserted into or around a well tubular of the existing well. The guide device may be configured to enter or surround an existing well along the central axis of the well. The guide device may be rigidly connected to the suction anchor(s) and / or the support frame and / or itself may be, at least along part of its length, substantially rigid when subjected to the forces experienced subsea as the guide device enters or surrounds and is lowered through or around a subsea well. This may mean that the position of the wellhead support structure (e.g. suction anchor and / or support frame) is adjusted as the guide device enters or surrounds and follows the central shaft of the subsea well. The guide device may be designed to reach, contact, surround and / or enter the existing well before the suction anchor(s) (i.e. outer suction skirt) reaches the well and / or seabed. The guide device may be releasable and / or retrievable from the suction anchor. The guide device may comprise an initial well entry portion and / or an aligning portion and / or an internal portion. The initial well entry portion may be provided at the bottom of the guide device, the aligning portion may be a middle portion of the guide device and the internal portion may be an upper part of the guide device. The initial well entry portion may be the part of the guide device that is for entering the existing well first. The initial well entry portion may be at the lowermost tip of the guide device when the guide device is connected to the suction anchor. The initial entry portion may be the part of the guide device that is furthest from the top lid of the suction anchor. The initial entry portion may be the lowermost 20%, 10% or 5% of the length of the guide device. For example, the initial entry portion may be the lowermost 1m, 2m, 5m of the guide device. When the guide device is connected to the suction anchor the initial well entry portion may be located below the bottom of the suction anchor. This is so that the initial well entry guiding portion can enter the well before the suction anchor contacts the seabed. The function of the initial well entry portion may be to aid entry of the guide device into the existing subsea well. The initial well entry portion may be a portion of the guide device with the lowest lateral stiffness. The initial well entry portion may have an outer diameter that is less than the outer diameter of the aligning portion of the guide device. The initial well entry portion may be more flexible and / or less stiff than the aligning portion. The initial well entry portion may have a lower lateral stiffness compared to the aligning portion of the guide device. The initial well entry portion may comprise a flexible section such as a wire and / or rope section. For example, it may comprise a steel wire, chain and / or fibre rope section, e.g. a whip wire. This may be the part that allows the initial well entry part to be relatively flexible. The initial well entry portion may be provided by a bottom section of a pull in wire. For example, the pull in wire may be connected to the lower part of the guide device such that a lowermost section of the pull in wire protrudes from the bottom of the aligning portion of the guide device. This protruding section of the pull in wire may provide an initial well entry portion. The initial well entry portion may be attached to the bottom of the aligning portion of the guide device. The initial well entry portion may be retractable inside the aligning portion of the guide device. The initial well entry portion and aligning portion may be movable axially relative to each other. The initial well entry portion may have an adjustable length. This may be achieved by retracting and extending at least a portion of the initial well entry portion inside the aligning portion. The aligning portion may be formed from a tube or pipe (e.g. drill pipe) into which the initial well entry portion can be retracted. The initial well entry portion may be fixable and / or fixed to the end of the aligning portion. The initial well entry portion may be arranged to be removable and / or retracted into the aligning portion. This may be after entry of the aligning portion into the subsea well, when the initial well entry portion may no longer be required (because its main function may be to help guide the aligning portion into the subsea well). The initial well entry portion may comprise a weight, such as a clump weight. The weight, may for example, be provided by a spelter socket. This weight may be provided to hold the flexible portion taut and vertical. This may be when the wellhead support structure is suspended subsea but before the guide device reaches the existing well. The weight may be provided at the bottom of the flexible portion, i.e. the bottom of the wire, chain and / or rope. The initial well entry portion may be provided by a pipe section with a knuckle joint. The initial well entry portion may be connected to the aligning portion via the knuckle joint. When the wellhead support structure and hence guide device is being lowered towards the existing well, a guiding ROV may be used to guide the bottom of guide device, e.g. the initial well entry portion, if present, into the existing subsea well. The initial well entry portion (e.g. being flexible, narrow and having a weight on the end) and / or the use of the guiding ROV, may increase the chance of the guide device successfully entering the subsea well and reduce the need for repeated lifting and lowering of the wellhead support structure that may undesirably increase the offshore operation time. The part of the guide device that is designed to enter an existing well (e.g. the initial well entry portion and the aligning portion) may have a maximum outer diameter that is less than the inner diameter of the upper part of the existing subsea well that will receive the guide device. This may be to allow this guide device to enter the inside of the upper part of the well. The guide device (e.g. the initial well entry portion) may have a maximum outer diameter that is significantly less than the inner diameter of the upper part of the existing subsea well. For example, the maximum outer diameter of the guide device that in use will enter the subsea well may be 90%, 75%, 50% or 25% of the inner diameter of the upper part of the existing subsea well in which the guide device will be received. This may facilitate the entry of the guide device into the existing well. The initial well entry portion may guide the aligning portion into the existing well. This is because the initial well entry portion being more flexible and / or smaller maximum outer diameter than the aligning portion may mean that it is easier to get that part of the guide device into the existing well, and once the initial well entry portion is in the well, it may be used to guide the aligning portion into the well. The aligning portion may be the portion of the guide device that is used to guide the wellhead support structure into the desired position about the subsea well, e.g. into a position in which the wellhead support structure is coaxial with the existing well. The maximum outer diameter of the aligning portion may be less than the minimum inner dimension of the existing well. This is so that the guide device, e.g. the aligning portion of the guide device, can enter the subsea well. However, the maximum outer diameter of the aligning portion may only be slightly less than the minimum inner dimension of the existing well. This is so that the alignment device can be used to fairly accurately locate (i.e. make coaxial) the wellhead support structure relative to the existing well. The guide device may comprise one or more centralisers. These centraliser(s) may be the part of the guide device with the maximum outer diameter. The guide device may comprise one or more guiding centralisers. These are centraliser(s) that are on a lower part of the guide device, e.g. below the bottom of the suction skirt when the guide device is attached to the suction anchor. The guiding centralisers may be arranged and positioned to enter the existing well as the wellhead support structure is guided into position about the subsea well. The guiding centraliser(s) may be provided on the aligning portion of the guide device. The guiding centraliser(s) may have a maximum outer diameter that is only slightly smaller than the minimum inner diameter of the existing well. The guide device may comprise a plurality of, e.g. at least two, guiding centralisers. The two guiding centralisers may be spaced along the length of the guide device, e.g. at least 5m apart. The presence of a plurality of guiding centralisers may increase the reliability of the guide device being coaxial with the existing well and hence make the internal pipe, aperture, wellhead, suction anchor and / or wellhead support device coaxial with the existing well. When a plurality of guiding centralisers is provided, the centralisers may each have different maximum outer diameters. For example, in a direction from the bottom of the guide device to the top of the guide device, the centralisers may have an increasing maximum outer diameter. This may be so the first part of the lowering is done with a less guiding and subsequently more and more centralising and concentricity occurs as the suction anchor gets closer to the seabed. This may have the advantage that any necessary adjustment of the lifting arrangement (e.g. crane and lifting wires which may be used to adjust the position of the wellhead support structure relative to the existing well) can be done gradually, e.g. in steps as the lowering of the wellhead support structure occurs. Additionally, or alternatively, provision of a plurality of guiding centralisers may have the effect of more reliably (compared to an arrangement with only one guiding centraliser) transferring any vertical misalignment of the well to the suction anchor. If the virtual centreline of the upper part of the well is not perfectly straight the guiding centralisers placed at discrete locations along the length of the guide device may allow installation while obtaining and maintaining concentricity. Use of guiding centralisers may be a preferred alternative over having a guide device with an outer diameter slightly less than that of the inner diameter of the well. This is because the centralisers may be less prone to jamming the two tubulars (the well tubular and the guiding device) as they are inserted into each other. Such jamming may occur if either of these two tubulars have geometrical imperfections, such as ovality, out of roundness, deviations in straightness and / or diameter variations (tolerances) that in sum exceeds the diameter differences at any point along the interaction sliding distance, or by simultaneous surface contact at a plurality of locations along the overlapping length of the well and the guide device. Additionally, since the purpose of the guide device may be to guide the wellhead support device into a coaxial and / or concentric position, it is likely that the guide device will contact the inner wall of the well as a result of the guiding and this contact increases the risk of jamming the guide device inside the well. Use of centralisers may reduce this risk while still providing the desired guiding. The guiding centraliser(s) may be arranged to keep the guide device concentric with the existing well while the guide device is being moved (e.g. lowered) inside the existing well tubular. The initial well entry portion may be considered as a coarse alignment part and the aligning portion may be considered a finer alignment part. Whilst part of the guide device, (e.g. the initial well entry portion of the guide device) may have an outer diameter significantly less than the inner diameter of the well so as to ease the task of entering the well with the guide device, provision of one or more centralisers may allow obtaining of the desired concentricity as the guide device is inserted further into the well (as the wellhead support structure is lowered further towards the seabed). The guide device may comprise one or more upper centralisers. The upper centraliser(s) may be used to ensure the upper (e.g. internal) portion of the guide device remains in the desired position (e.g. coaxial and concentric) with the suction anchor. The upper centraliser(s) may be provided on an internal portion of the guide device, i.e. an upper part that is within the suction skirt when the guide device is attached to the suction anchor. The upper centraliser(s) may be located within the internal pipe and / or the receptacle of the suction anchor and / or wellhead (if present) when the guide device is attached to the suction anchor. The upper centraliser(s) may aid an improved transfer of lateral (sideways) loads from the guide device to the suction anchor. This is because it may result in at least two points of contact between the guide device (e.g. the upper attachment and the upper centraliser(s) that contact the internal pipe internal wall). When the guide device is being attached to the suction anchor, it may be pulled and / or pushed though the internal pipe, receptacle and / or wellhead. The one or more upper centralisers may facilitate the relative movement of the guide device relative to the internal pipe, receptacle and / or wellhead and / or reduce the risk of the components jamming. The centraliser(s) (guiding centraliser(s) and / or upper centraliser(s)) may be used to make the guide device coaxial with the existing well and keep the guide device coaxial with the suction anchor and hence make the internal pipe, aperture, wellhead, suction anchor and / or wellhead support device coaxial with the existing well. The centraliser(s) may be a known centraliser(s) used in the field of downhole operations, e.g. on drill pipes. The centraliser(s) may be radially flexible, may comprise roller bearings or wheels, and / or may be collapsible. For example, the centraliser(s) may be an inflatable type. The centraliser(s) may comprise a plurality of ball bearings on its outer surface. This may reduce the risk of jamming as the guide is inserted into the well and / or fixed to the suction anchor. The guiding centraliser(s) and the upper centraliser(s) may be the same type of centralisers. Alternatively, the guiding centraliser(s) and the upper centraliser(s) may be different types of centralisers. This is because the upper centralisers may not have the same risk of jamming as the guiding centralisers because they may not be moving within the tubular in which they are located and / or the tubular in which they are located is less likely to comprise defects that increase the risk of jamming. It may be the case that the upper end of the guide device is not sliding relative to the internal pipe of the suction anchor in which it is located while performing the intended load transfer function. The guide device may be removed after the suction anchor is installed. In this case, there may be a need for relative movement between the guide device and the internal pipe. Similarly, there may be relative movement between the guide device and the internal pipe as the guide device is being installed in the suction anchor. Thus, there may still be a benefit in having an upper centraliser of a type that may reduce the risk of jamming such that it does not prevent the desired removal. This may include the centraliser(s) being radially flexible, comprising roller bearings or wheels, and / or being collapsible. The internal portion of the guide device may be a portion of the guide device that is located within the suction anchor, e.g. within the suction skirt. The internal portion may extend from at or near the top of the suction anchor down towards the bottom of the suction anchor / suction skirt. The internal portion may be the same length as, or shorter than, the suction skirt of the suction anchor. The internal portion of the guide device may extend through the internal pipe, receptacle, wellhead and / or aperture. When the guide device is connected to the suction anchor, the aligning portion may be located below, or mainly below, the bottom of the suction anchor. This is so that the aligning portion can enter the well and perform its aligning / guiding function before the suction anchor contacts the seabed. The guide device may comprise a drill pipe. At least a portion of the central part of the guide device may comprise a drill pipe. For example, the aligning portion and / or the internal portion may comprise and / or be formed from a drill pipe. A drill pipe may be used as these are well known to be run (passed, slid or installed) into well casings. Additionally, drill pipes are a “commodity” within the drilling industry, are easily obtainable in a range of lengths and diameter sizes, material grades and with connections (e.g. threaded connections), that may be used for joining the portions of the guide device. The guide device may be retrievable. For example, the guide device may be connectable to and / or separable from the wellhead support device, e.g. the suction anchor. The guide device may be provided for the steps of aligning and / or installing the wellhead support device, e.g. the suction anchor. After this, the guide device may be retrieved from the seabed. Thus, the method may comprise removing the guide device from the wellhead support structure. This step may be after the suction anchor has reached the seabed, after the suction anchor has been sucked into the seabed, and / or after the wellhead support structure is in the final desired position. The guide device may be removed by attaching a lifting arrangement, e.g. lifting wire(s) and a vessel crane to the guiding tail pipe and lifting the guide device up away from the installed wellhead support device. In some arrangements the guide device may not be removed. In other words, the guide device may remain in place even once the well is in operation. The closure may also be removed, e.g. after the suction anchor has been sucked into the seabed. The closure may be removed by releasing the closure (e.g. pressure cap) by means of an ROV and attaching a lifting arrangement, e.g. lifting wire(s) and a vessel crane to the closure and lifting the closure up away from the installed wellhead support device. The guide device may be connected to and / or retrievable with the closure. The upper part of the guide device may be connected to the inside and / or underside of the closure. The connection of the guide device to the closure may be a releasable and / or temporary attachment. This allows the possibility of using a different guide device of different length and / or diameter as desired for a specific well. An advantage of attaching the guide device to the cap (e.g. high pressure cap) is that it may provide an efficient means to allow for removal of the closure and the guide device in one operational step after the suction anchor installation has been completed. Another advantage is that the closure may provide a convenient means for releasably attaching the guide device to the suction anchor. Alternatively, the upper end of the guide device may be attached to another part of the wellhead support device such that it is independent of the closure. In either case, the attachment of the guide device to the wellhead support structure (i.e. suction anchor) may be of sufficient strength to accommodate the forces expected during the guiding operation. In either case, it is beneficial for the attachment to be a temporary attachment to allow for a different guide device to be used with the suction anchor so that geometrical adjustments can be made from well to well. The guide device may be a single integrally formed piece. This may be a single piece along its length from the top where it is attached to the suction anchor (directly or indirectly) down to or towards the bottom of the guide device at its bottom end. For example, the guide device may be formed from a single length of drill pipe. The single integrally formed guide device may have the flexible wire and / or centralisers attached thereto. The guide device may be a multi part (e.g. two or more parts) device, wherein the parts (i.e. lengths of pipe) are disconnectable and / or connectable to each other. Connecting the parts together may form the elongate guide device. The wellhead support structure and / or the guide device may be arranged so that the parts of the guide device are disconnectable and / or connectable to each other after the wellhead support device has been deployed subsea. The guide device may comprise an upper part and a lower part. The upper part and the lower part may be disconnectable and / or connectable to each other. Alternatively, the upper part and the lower part may be integrally formed parts and / or joined together before the wellhead support structure is deployed subsea. The upper part may comprise the internal portion of the guide device. The lower part may comprise the aligning portion and / or the initial well entry portion. When the upper and lower parts of the guide device are connected together and the guide device is attached to the suction anchor, the upper part may (at least primarily) be located within the suction anchor and / or above the top lid of the suction anchor. The guide device may be arranged so that when the guide device is attached to the suction anchor, the upper part does not protrude beyond the bottom of the suction anchor. When the upper and lower parts of the guide device are connected together and the guide device is attached to the suction anchor, the lower part may (at least primarily) be located below the suction anchor. When the guide device is attached to the wellhead support structure, e.g. the suction anchor, in position to perform its guiding function (e.g. fully assembled if the guide device is a multipart device and ready to be used), this may be referred to as the operational guiding position. When the guide device is in the operational guiding position the guide device may extend along the central axis of the suction anchor, through the inner volume of the suction anchor, and / or from a top end at or near the top of the suction anchor to a bottom end below the bottom of the suction anchor. This may make transportation of the wellhead support structure to the installation site difficult and risks the guide device (particularly the part extending below the bottom of the suction skirt) getting damaged, such as bent. One option is to transport the guide device and the suction anchor to the installation site without the guide device in its operational guiding position attached to the suction anchor. This may for example be by transporting the guide device separately or transporting the guide device in a stowed position (i.e. not the operational guiding position) on the suction anchor, such as attached (e.g. strapped) to the outside of the suction skirt. When the guide device is in the stowed position it may not protrude beyond the bottom of the suction anchor. This may require the guide device in the stowed position to protrude beyond the top of the suction anchor. The is because in the case of a single piece guide device the entire overall length of the guide device may be attached at the outside of the suction anchor. This is during transportation (e.g. shipment) and optionally as the wellhead support device is lifted into the water. This is because the guide device may be longer than the height of the suction anchor. The guide device may be attached to the suction anchor in its operational guiding position when the wellhead support device is offshore, e.g. on a vessel near the installation site or after the suction anchor has been deployed subsea. Another option, when the guide device is a multipart device, is to connect the guide device to the suction anchor onshore with the upper and lower parts disconnected. The upper part may be connected to the suction anchor in the position in which it will be used when performing its guiding function, e.g. to the top of the suction anchor with the upper part extending within the suction skirt of the suction anchor. This may be referred to as its operating and / or guiding position. The lower part may be connected to the to the suction anchor in the position that is different to the position it will be in when performing its guiding function. This different position may be referred to as a stowed position. For example, the lower part may be connected (e.g. directly connected) to the outside of the suction skirt of the suction anchor. The lower part may be connected to the outside of the suction anchor by means of straps that can be released when it is desired to move the lower part from the stowed position. The wellhead support structure may be transported to the installation site with the upper part in its operating position and the lower part in the stowed position. The lower part of the guide device may be released from the stowed position and moved (e.g. by falling) to a suspended position underneath the suction anchor. This may be performed when the wellhead support structure is subsea in a suspended position above the seabed. The wellhead support structure may comprise one or more pull in wires. The pull in wire may be a flexible length such as a chain, rope, and / or wire etc. It may be a steel wire and / or a fibre rope. The pull in wire may be for connecting the guide device, or part of the guide device, to the suction anchor (directly or indirectly). This may be when the wellhead support structure is subsea, such as suspended subsea above the seabed. The pull in wire may be used to hold the guide device, or a lower part of the guide device, in a suspended position underneath the suction anchor after it has been released from the stowed position. The pull in wire may be used to pull the guide device towards the top of the suction anchor to allow the guide device to be connected to the suction anchor. This may be an indirect connection via a closure to which the guide device is connected. The pull in wire may be used to pull the lower part of the guide device towards the upper part to allow the lower part and upper part to be connected together. Once the guide device is in its operating guide position or the lower part of the guide device is connected to the upper part in its operating position, the pull in wire may be tensioned and locked to hold the guide device in its desired position, or lower part of the guide device and the upper part of the guide device together. The pull in wire may extend from a first end connected (directly or indirectly) to the top of suction anchor, e.g. at a position at, near and / or above the suction anchor to a second end connected to the guide device or lower part of the guide device. The pull in wire may be connected to the guide device or lower part of the guide device when it is in the stowed position. The connection between the pull-in wire and the guide device or the lower part of the guide device may be made when the wellhead support structure is onshore. As a result, moving of the guide device or the lower part of the guide device from the stowed position to the suspended position underneath the suction anchor to a pulled in position in which it is in its operational guiding position may be a relatively simple operation to perform when the wellhead support structure is subsea. This is because it is facilitated by means of a preconnected pull in wire. The pull in wire may have an adjustable length between the top of the suction anchor and the bottom of the pull-in wire. The pull in wire may be pulled from the first end to pull the guide device into connection with the top of the suction anchor (e.g. via a closure) or the lower part up into connection with the upper part. The first end of the pull in wire may be attached to an actuator, such as a winch, for pulling in and paying out the pull in wire. The actuator may be a component of the wellhead support structure and / or provided by an external ROV. The pull in wire may extend through the closure (if present). The closure may have sealing arrangement around the pull in wire that extends through the closure. This is so the closure can maintain its function of sealing the inner volume of the suction anchor. However, if the top of the guide device is sealingly attached to the closure around the pull in wire, the pull in wire may extend through an opening in the closure without any sealing arrangement around the pull in wire. This because after the guide device, e.g. upper part of the guide device, has been installed and attached to the closure, the unsealed opening that the pull in wire extends through may be only in communication with the inside volume of the guide device and not in fluid communication with the internal volume of the suction anchor once the outer suction skirt has landed on the seabed, thus removing the need for a sealing against the pull in wire. The pull in wire may be connected to the top of the guide device. The pull in wire may extend through the upper part (e.g. through the internal portion of the guide device). The upper part may be a hollow tubular part, e.g. drill pipe, through which the pull in wire extends. The pull in wire may be movable relative to the upper part. This is so that the pull-in wire can be pulled in or payed out through the upper part. The pull in wire may be connected to the lower part. The connection between the pull in wire and the guide device and the pull in wire itself may be sufficiently strong so that the guide device or lower part of the guide device can be held by the pull in wire alone when suspended under the suction anchor and the pull in wire can be used to pull the guide device into connection with the suction anchor and / or closure or the lower part into connection with the upper part of the guide device. The connection between the pull in wire and the guide device, e.g. lower part of the guide device, may allow the pull in wire to move freely relative to the guide device, e.g. lower part, in a downward direction relative to the guide device. This may for example be by means of providing a one-way stop, ratchet or no go solution etc for attaching the pull in wire into the guide device, e.g. lower part. This may ease the installation of pull-in wire during pre-deployment assembly and / or allow for the possibility to remove the wire from the assembly after the guide device has been attached to the suction anchor and / or the lower and upper parts have been attached to each other. The ability to remove the pull in wire once the guide device is in its operational guiding position may help simplify the design of wellhead support structure as it does not need a means to seal around the pull-in wire during suction of the suction anchor into the seabed. The pull in wire may be connected to the guide device at or near the top of the lower part. Alternatively, the pull in wire may extend through at least a portion of the lower part (e.g. through the aligning portion). The lower part may at least partially be a tubular part, e.g. drill pipe, through which the pull in wire extends. The second end of the pull in wire may be connected to the top of the initial well entry portion. If the pull in wire is connected to the initial well entry portion of the guide device, the initial well entry portion of the guide device may be fixed e.g. to the bottom of the aligning portion. The pull in wire may be removable. For example, after the pull in wire has been used to pull the guide device into connection with the suction anchor and / or used to pull together the lower part and the upper part of the guide device, the pull in wire may be removed. The pull in wire may be removed before the suction anchor is sucked into the seabed. This may avoid the need for a cap or other sealing arrangement that can seal around the pull in wire. The guide device may be connected to the wellhead support structure, e.g. suction anchor and / or support frame, so that lateral loads may be transferred from the guide device to the wellhead support structure, e.g. suction anchor(s) and / or support frame. This is so that the guide device may guide the position of the suction anchor(s) and / or support frame and as such guide the entire wellhead support structure. The lower part and / or upper part of the guide device may be connected by a connector that allows lateral loads to be transferred between the lower and upper parts of the guide device. This is so that the lower part may transmit its guiding action to the upper part and as such guide the entire wellhead support structure. The wellhead support structure, e.g. the closure, and / or the top of the guide device may comprise a connector for connecting the guide device to the suction anchor. The suction anchor and / or closure and the guide device may be arranged so that they latch together automatically as they are pulled towards each other. The lower part and / or upper part of the guide device may comprise a connector for connecting the lower part to the upper part. The upper and lower part may be arranged so that they latch together automatically as they are pulled towards each other. The connector for connecting the guide device to the suction anchor and / or the lower part to the upper part of the guide device may comprise any known pipe connector such as a j-slot, grapple or threaded connector. If the guide device, e.g. upper part and / or lower parts, comprise drill pipes the parts may be connected by means of the threaded connection. In the case of a threaded connection, the connector may be provided by corresponding screw threads connected to or on the suction anchor and guide device or upper and lower parts that can interact with each when the guide device and suction anchor or upper and lower parts are brought together. The top end of the guide device and the the part to which it connects on the suction anchor, e.g. the closure, may be arranged to stab into each other. The guide device and the suction anchor may be rotated relative to each other to make up the threaded connection. The top end of the lower part and the bottom end of the upper part may be arranged to stab into each other. The lower part and upper part may be rotated relative to each other to make up the threaded connection. For example, the guide device or the lower part of the guide device may be rotated by help of a ROV operating a suitable tool. For example, traction wires may be spun a few turns around the lower pipe part and pulled by a subsea winch or by a winch located at the installation vessel. If the upper part of the guiding device is rotated to achieve the threaded connection, the wellhead support structure may be arranged so that the attachment of the upper part relative to the suction anchor is able to rotate. The upper part may be rotated from above or inside the suction anchor, e.g. by means of a motor. If the upper part is rotated to make up the threaded connection, there may be a need for an anti-rotation feature arresting the rotation of the lower part. This is to ensure that there is relative rotation between the upper and lower parts of the guide device. The anti-rotation feature may be a traction wire that has been spun around the lower part and attached to the suction anchor e.g. the lower end of the suction skirt. The connector may be provided by the lower part and / or the upper part comprising an overlap section. This overlap section is a portion at the top of the lower part, or bottom of the upper part that overlaps the other of the upper or lower part when the two parts are brought together. The pipe overlap section may have an inner diameter that is slightly larger and / or substantially the same as the outer diameter of the upper or lower part it is overlapping. The inner diameter of the overlap section and the outer diameter of the part it overlaps may be sufficiently similar such that lateral loads can be transferred between the lower and upper parts of the guide device without any significant axial deviation (e.g. more than 1 or 2 degrees) between the two parts. The guide device and closure may together provide a closure and guide device. The closure (or some other connection means) may be used to connect the guide device to the suction anchor. This connection may be via the aperture, receptacle, internal pipe and / or wellhead (if present). The closure and guide device may be arranged so that release and retrieval of the closure from the suction anchor results in release and retrieval of the guide device from the closure. The guide device may be connected to the closure by means of a connector. This may for example be a threaded connector and / or pipe overlap section as described above. The guide device may extend through the aperture, receptacle, wellhead and / or internal pipe (if present). The guide device may be coaxial with the aperture, receptacle, wellhead and / or internal pipe (if present), when the guide device is connected to the suction anchor in its operational guiding position. If the guide device and / or wellhead support structure is retrievable, the guide device and / or wellhead support structure may be used on several different wells. The method may comprise retrieving the guide device from the seabed. The guide device may be retrieved whilst leaving the suction anchor(s) in position about the subsea well. This may be after the guide device has been used to guide the wellhead support structure into a position about the subsea well, after the suction anchor(s) has partially embedded into the seabed under its own weight and / or after the suction anchor(s) has been fully installed (i.e. into its desired position to provide wellhead support). The guide device dimensions, (e.g. the outer diameter, inner diameter and / or length of the guide device) may be chosen based on the existing well the wellhead support structure is to be used with. The suction anchor(s) dimensions (e.g. the diameter and / or length of the suction skirt) may be chosen based on the well the wellhead support structure is to be used with. The method may comprise obtaining information about the existing well. This may comprise obtaining information about one or more of the minimum internal diameter of the existing well, the depth of any existing plug within the existing well, the distance between the top of the existing well and the seabed, the geology of the seabed surrounding the existing well, the location of any other parts such as concrete in the seabed. The method may comprise using a guide device and / or suction anchor(s) that is selected based on the information about the existing well. The method may comprise providing a plurality of suction anchors of different designs (e.g. different diameter, length, and / or thickness of the outer suction skirt and / or different thickness of the top plate) and / or providing a plurality of guide devices of different designs (e.g. different maximum outer diameter, length, and / or flexibility). The method may comprise selecting one of the plurality of suction anchors and / or one of the plurality of guide devices to provide the wellhead support structure. The selection of the suction anchor and / or guide device may be based on information about the existing well. The method may comprise connecting the selected guide device to the selected suction anchor to provide the wellhead support structure for location about the existing well. A kit of parts for providing the wellhead support structure may be provided. The kit of parts may comprise one or more suction anchors and one or more guide devices. The kits of part may comprise a plurality of suction anchors of different designs (e.g. different diameter, length, and / or thickness of the outer suction skirt and / or different thickness of the top plate) and / or a plurality of guide devices of different designs (e.g. different maximum outer diameter, length, and / or flexibility etc). The wellhead support structure may comprise one of the guide devices connected to one of the suction anchors. The method may comprise attaching the guide device (directly or indirectly) to the suction anchor. The guide device may be attached to the suction anchor such that the guide device extends along the central axis of the suction anchor and / or protrudes beyond the bottom of the suction anchor. At least the lower part of the guide device may be attached to the suction anchor to provide the guide device in its operational guiding position when the wellhead support structure is subsea. Once a wellhead support structure is provided with the guide device in the operational guiding position, the wellhead support structure may be lowered towards the existing well. The method may then comprise inserting the bottom of the guide device into the existing well, e.g. one or more tubulars of the existing well. The method may comprise inserting the bottom of the guide device into the existing well before the bottom of the suction anchor reaches the seabed. The method may comprise lowering the wellhead support structure further towards the seabed so that the guide device enters the existing subsea well further and the bottom of the suction anchor contacts the seabed. The guide device may be arranged so that as the suction anchor is lowered towards the seabed and / or the existing well, the wellhead support structure is guided into a position so that it can provide lateral and / or vertical support to a wellhead connected (or to be connected) to the existing well. This may be a position with the suction anchor coaxial and / or concentric with at least the top of the existing well. The guide device may be attached to the suction anchor such that the guide device does not extend along the central axis of the suction anchor and / or does not protrude beyond the bottom of the suction anchor(s). The method may comprise allowing the suction anchor(s) to at least partially embed into the seabed under its own weight, i.e. under the action of gravity alone. The method may comprise providing a sealed volume within the suction anchor(s). This may be provided by sealing the central aperture of the suction anchor, sealing any other openings in the suction anchor such as a vent hatch, sealing the bottom opening of the suction anchor by the suction anchor being partially imbedded in the seabed and / or sealing the existing well. The method may comprise reducing the pressure inside the suction anchor(s) (e.g. by pumping fluid out of the suction anchor, such as through the vent hatch) so as to force the suction anchor further into the seabed. The method may comprise forcing the suction anchor(s) into the seabed until it is in position for the wellhead support structure to provide lateral and / or vertical support to a wellhead connected to the existing well. The method may comprise forcing the suction anchor into the seabed until at least a bottom portion of the suction anchor encircles a top portion of the existing well. The method may comprise forcing the suction anchor into the seabed until the internal pipe of the suction anchor and / or aperture of the suction anchor is in a position above the top of the existing well to be fluidly connected thereto. The method may comprise releasing and / or retrieving the guide device (and closure if present) from the wellhead support structure (i.e. from the suction anchor). The method may comprise providing a wellhead (either for installation with the suction anchor(s) or into the wellhead support structure after the wellhead support structure has been positioned about the existing subsea well). The wellhead may comprise a low pressure wellhead and / or a high pressure wellhead. The method may comprise fluidly connecting the wellhead to the existing well, e.g. one or more tubulars of the existing well. The method may then comprise performing desired operations, e.g. re-entry operations, on the existing well. The wellhead support structure and / or suction anchor(s) may be retrievable. This may mean that once the desired operations in the well have been performed, e.g. additional plugging of the well, the wellhead support structure and / or suction anchor(s) may be retrieved from the seabed. This may comprise breaking the connection between the internal pipe and / or aperture and the well tubular(s) (e.g. by cutting), increasing the pressure inside the suction anchor(s) to force it out of the seabed, and / or lifting the wellhead support structure and / or suction anchor(s) away from the seabed. Once retrieved the wellhead support structure may be used with a different existing subsea well. If the guide device had previously been removed, the method may comprise reconnecting a guide device (either the same guide device as used previously or a different guide device) to the suction anchor before it is used with another existing well. The wellhead support structure may comprise a single suction anchor or may comprise a plurality of suction anchors, for example four suction anchors, as discussed above. The well may be (or have been in the case of a legacy well) an exploration well, production well, keeper well (in which an exploration well is converted to a production well), injection well, relief well, monitoring well (e.g. pressure monitoring well), controlling well and / or well for CO2 injection for carbon storage (CCS). In the case of a CCS well, the well may be for direct or indirect injection of CO2. The well may be (or have been) a hydrocarbon well, an oil and / or gas well, a water and / or gas injection well, a dry exploration well, a CO2 disposal well, and / or a gas hydrate production well. The well may be converted one or more times between different types of wells, such as those listed above. For example, an exploration well may be converted to a production well, a production and / or exploration well may be converted to a CCS well, and / or a CCS well may be converted to a monitoring well etc. The requirement for a wellhead support structure on an existing well may be to assist and / or allow the conversion of one type of well to another type of well. The well may have been a CCS well. The well may be a well that is leaking, i.e. leaking liquid and / or gas. For example, the well may be a legacy CCS well that is now leaking CO2. The method and / or apparatus may be to facilitate operations to increase the leak resistance of the well, i.e. increase the resistance of the well to leaking CO2 and / or any other liquid or gases. The well may be a satellite well, stand-alone well, one or more of a cluster well arrangement (e.g. connected to a central manifold), one or more of a series of daisy-chained wells, one or more template wells etc. The well may be an existing single subsea well. The well may have been a previously operational well (of any known type) that has been plugged and abandoned and the need to re-establish connection may be to further plug the well, i.e. not to make it operational again. Whilst the well is referred to as a subsea well, the well may be under any body of water, e.g. a lake, reservoir, ocean etc. Thus, references herein to a subsea well should be understood to mean a well that is located under a body of water. Similarly, the references herein to seabed should be understood to mean waterbed, i.e. bottom surface of the body of water under which the well is located. Certain preferred embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which: Figure 1 shows a wellhead support structure with a suction anchor and guide device in an operational guiding position; Figure 2 shows the wellhead support structure with a lower part of the guide device in a stowed position; Figure 3 shows the wellhead support structure above an existing well; Figure 4 shows the wellhead support structure with the guide device entering the existing well; Figure 5 shows the wellhead support structure in a position about the subsea well; Figure 6 shows the guide device being retrieved; Figure 7 shows an alternative wellhead support structure with the guide device in a stowed position; Figure 8 illustrates schematically a way of connecting the lower part of the guide device to an upper part of a guide device; Figure 9 shows an option for connecting an internal pipe of the suction anchor to the tubulars of the existing well; Figure 10 shows a centraliser; Figure 11 shows another type of centraliser; Figure 12 shows an existing well with a guide element installed; Figure 13 shows the installation of a second type of wellhead support structure above an existing well; Figure 14 shows the installation of the second type of wellhead support structure into the seabed; Figure 15 shows the second type of wellhead support structure when installed; and Figure 16 shows an isometric view of another wellhead support structure. Figure 1 shows a wellhead support structure 1 which is for positioning about an existing subsea well. This is so that the wellhead support structure 1 can provide lateral and vertical support to a wellhead connected to the subsea well. The wellhead support structure 1 comprises a suction anchor 2 and a guide device 3. The suction anchor 2 is for embedding in the seabed to provide a large and rigid connection to the seabed. The guide device 3 is rigidly connected to the suction anchor 2 and is for guiding the wellhead support structure 1 into a position about the existing subsea well so that it can be connected thereto and provide the required support. The suction anchor 2 comprises an annular top lid 4 and cylindrical outer suction skirt 6 that bound an internal volume 7 of the suction anchor 2. The top lid 4 extends from the top of the outer suction skirt 6 to a central aperture 8. The central aperture 8 is an aperture through which the top of a well, e.g. a wellhead, can extend. The top lid 4 may be reinforced, such as with I-beams. This is so the top lid 4 can withstand forces expected during installation of the suction anchor 2 and during operation of the well. The suction anchor 2 comprises a vent hatch 10. The vent hatch 10 can be open when the suction anchor 2 is deployed subsea so as to allow air to escape from the internal volume 7 of the suction anchor 2. The vent hatch 10 can also be connected to, and sealed with, a pump (not shown) to allow fluid to be sucked out of (and optionally into) the internal volume 7 to allow the suction anchor 2 to be forced into (and optionally out of) the seabed as described in greater detail below. The suction anchor 2 comprises an internal pipe 12. The internal pipe 12 is attached (directly or indirectly) to the top lid 4 and is coaxial with the centre axis of the suction anchor 2. The internal pipe 12 is for fluid connection to one or more tubulars of the existing subsea well. Once connected to the existing subsea well, the internal pipe 12 may form part of a tubular, e.g. conductor or casing, of the subsea well. The internal pipe 12 extends at least partially into the internal volume 7 of the suction anchor 2. The internal pipe 12 is significantly shorter than the length of the suction skirt 6 and, in the arrangement shown in the figures, is provided within the top quarter of the suction anchor 3. The reason for the internal pipe 12 being short is that it is for connection to the top of one or more tubulars of the existing well whilst the suction skirt 6 is for embedding into the seabed around the existing well and below the top of the existing well. The internal pipe 12 is short so that it does not impede the installation of the suction anchor 2 due to contacting the top of the existing well. The position and / or diameter of the top of the existing subsea well may be known and the length and / or diameter of the internal pipe 12 may be chosen accordingly. Although in the figures the internal pipe 12 is shown schematically as extending up though the aperture 8 of the top lid 4 to above the top of the suction anchor 2 as one continuous member with a constant diameter, the top part of the internal pipe 12 may comprise a receptacle for receiving a wellhead (which may be a low pressure wellhead and / or a high pressure wellhead), and / or a wellhead. In any event, the aperture 8 of the suction anchor 2 is designed to receive a wellhead such that lateral and / or vertical support can be provided to the wellhead. This is so that forces experienced by the wellhead, e.g. during downhole operations, can be transferred from the wellhead to the suction anchor 2 and ultimately into the seabed rather than the well tubulars below the wellhead. The wellhead support structure 1 comprises a closure 14. This is a closure 14 for sealing the aperture 8 at the top of the suction anchor 2. This is so that the internal volume 7 can be a closed volume as required during sucking in or out of the suction anchor 2 from the seabed. If the top of the suction anchor 2 is provided with a wellhead during installation, the closure 14 may be a high pressure wellhead cap as known in the field of subsea wells. The guide device 3 comprises an upper part 16 and a lower part 18. As shown in figures 1 to 6, the upper part 16 and lower part 18 may be separable parts. Alternatively, the guide device 3 may be a single part as shown in figure 7. The upper part 16 comprises an internal portion 20. This is a portion 20 of the guide device 3 that extends from the top of the suction anchor 2 through the internal volume 7 towards the bottom of the suction skirt 6. In this arrangement the internal portion is connected to the underside of the closure 14. When the guide device 3 is attached to the suction anchor in its operational guiding position as shown in figure 1, the lower part 18 primarily extends beyond the bottom of the suction anchor 2. The lower part comprises an aligning portion 22 and an initial well entry portion 24. The aligning portion 22 is for entering a tubular of the existing well and has the function of guiding the suction anchor 2 into the desired position about the subsea well. The aligning portion 22 comprises centralisers 26. The centralisers 26 may be of the type shown in figures 10 and 11. For example the centraliser(s) 26 may be radially flexible as shown in figure 10 which may allow the centraliser(s) to adapt to the required outer diameter depending on the internal diameter of the well. The centraliser(s) may have ball bearings on the outer surface as shown in figure 11. This may reduce the risk of the guide device 3 getting jamed in the subsea well 5. The centralisers 26 may have a maximum outer diameter that is substantially the same as the inner diameter of the tubular of the existing well into which the guide device 3 will in use enter. This is so that the central axis of the guide device 3 may be aligned with the central axis of the existing subsea well and hence cause alignment between the wellhead support structure 1 and the existing well. The initial well entry portion 24 is for helping guide the aligning portion into the subsea well. The initial well entry portion 24 has a lateral stiffness that is less than the lateral stiffness of the aligning portion 22. This greater flexibility at its bottom end can make it easier to get the guide device 3 into the existing well. The initial well entry portion 24 comprises a wire 28 that provides the flexibility and a clump weight 30 (which in this example is a spelter socket). The initial well entry portion 24 is connected to the bottom of the well aligning portion 22. The lower part 18 is connected to the upper part 16 of the guide device 3 by a pipe overlap sleeve 32. This sleeve 32 is provided at the top end of the lower part 18 (although it could equally be provided at the bottom end of the top part 16) and has an inner diameter which is substantially the same as the outer diameter of the bottom of the upper part 16. When the lower part 18 is pulled towards the upper part 16 the sleeve 32 will slide over the bottom of the upper part 16 and provide a connection between the upper and lower parts 16, 18 that can rigidly hold the two parts together when subjected to lateral forces. The lower part 18 may be pulled towards the upper part 16 by means of a pull-in wire 34. The pull in wire 34 is connected to the lower part 18 at the top end of the initial well entry portion 24 and extends through the aligning portion 22 and the internal portion 20 (i.e. upper part 16) and through the closure 14. The pull in wire 34 can be used to pull the lower part 18 towards the upper part 16 and held and / or locked with the pull in wire 34 in tension to hold and lock the upper and lower parts 16, 18 together to provide a rigid guide device 3 that can perform the desired guiding function. Other connection means between the upper and lower parts 16, 18 may be used, such as a threaded connection. The aligning portion 22 and the internal portion 20 could for example be made from drill pipes. These are well known, off the shelf components, commonly used in the drilling industry. Typically, lengths of drill pipes are joined by a threaded connection and hence a threaded connection may be used here. A threaded connection may also be used to connect the internal portion 20 to the underside of the closure 14 as shown schematically in figure 7. As illustrated in figure 8, if the upper and lower parts 16, 18 of the guide device 3 are joined by a threaded connection 38, they may be joined by rotating the lower part 18 relative to the upper part 16. For example, the lower part 18 of the guide device 3 may be rotated by help of a ROV (not shown) operating a suitable tool. For example, traction wires 40 may be spun a few turns around the lower part 18 and pulled by a subsea winch (not shown) or by a winch located at the installation vessel. This may rotate the lower part 18 relative to the upper part 16 to make the threaded connection 38. As shown in figures 1 to 5, the wellhead support structure 1 can be held suspended subsea and lowered towards the seabed and existing well using lifting wires 36 and a lifting apparatus (not shown) such as a crane on a surface vessel. The lifting wires 36 may be any known lifting wires such as ropes, chains, wires etc. The lifting wires 36 may comprise one, two, three or more wires / chains / ropes to stably and / or securely hold the structure. The lifting wires 36 may be attached by any known means, such as clips and / or hooks, to the wellhead support structure 1. Figure 2 shows the wellhead support structure 1 with the lower part 18 in a stowed position. In the stowed position the lower part 18 is fixed, e.g. strapped, to the outside of the suction skirt 6. This may be the configuration of the wellhead support structure 1 during transportation from onshore to subsea above the existing well. The wellhead support structure 1 may be built onshore with the upper part 16 of the guide device attached (e.g. by means of threaded connection) to the underside of the closure 14, and the closure 14 fixed in a sealing manner to the top of the internal pipe 12 (e.g. via a receptacle and / or wellhead) to seal the central aperture 8 of the suction anchor 2. The pull in wire 34 extends through the closure 14, through the internal portion 20 of the guide device 3 and is connected to the lower part 18 of the guide device 3. The wellhead support structure 1 may be transported to the installation location, e.g. by a surface vessel such as a ship, and then lifted and lowered subsea as shown in figure 3. The vent hatch 10 is opened to let any air or other gases out of the internal volume 7 suction anchor 2 so that the wellhead support structure 1 can be lowered towards the seabed 9. Once subsea, the lower part 18 can be released from the outside of the suction anchor 2, e.g. by cutting straps (not shown). The lower part 18 can then fall down into a position below the bottom of the suction anchor 2 and be held and suspended there by means of connection to the pull-in wire 34. The top end 42 of the pull in wire 34 may be pulled, e.g. by a winch or ROV (not shown), to pull the pull in wire 34 up through the internal portion 20 and up through the closure 14 to pull the lower part 18 of the guide device 16 towards the upper part of the guide device until they are mated together by means of the pipe overlap sleeve 32. The pull in wire 34 may be held and / or locked in tension to hold the upper and lower parts 16, 18 of the guide device 3 together to create the arrangement as shown in figure 1. The wellhead support structure is then lowered towards the seabed 9 and existing subsea well 5 with the aim of getting the guide device 3 into the tubular of the existing well 5. This can be achieved by getting the initial well entry portion 24 into the subsea well 5. This may for example be achieved by guiding the initial well entry portion using an ROV (not shown). Once the initial well entry portion 24 is in the well 5, the wellhead support structure 1 is lowered further towards the seabed 9 and well 5 until the aligning portion 22 enters the subsea well 5. The relatively flexible initial well entry portion 24 guides the stiffer aligning portion 22 into the well 5. Once the aligning portion 22 is in the well 5 the centralisers 26 on the aligning portion 22 contact with the inside surface of the well tubular of the well 5 so as to align the guide device 3 with the well. The guide device 3 is rigidly fixed to the suction anchor 2 such that this alignment also has the effect of aligning and positioning the suction anchor 2 relative to the well 5. The suction anchor 2 is positioned by the guide device 3 relative to the well 5 such that as the wellhead support structure 1 is lowered the suction anchor 2 is located around the top of the subsea well 5 and has its central aperture 8, receptacle and wellhead (if present) aligned and coaxial with the tubulars of the subsea well 5. The guide device 3 extends beyond the bottom of the suction anchor 2 such that the suction anchor can be positioned relative to the well 5 before the bottom of the suction skirt 6 contacts the seabed. The wellhead support structure 1 is then lowered further until the bottom of the suction anchor 2 suction skirt 6 contacts the seabed. The suction anchor 2 is then allowed to partially penetrate the seabed under its own weight. This creates a sealed volume within the suction anchor 2, or further sealing can be made, such as over the existing well 5, to create a sealed volume within the suction anchor 2. At this point fluid, e.g. seawater, can be pumped out of the suction anchor 2 via the vent hatch 10 to cause the suction anchor 2 to be sucked into the seabed 9. The suction anchor 2 may be sucked into the seabed until the top 4 of the suction anchor 2 is level with the top of the seabed and / or the bottom of the internal pipe 12 is just above or abutting the top of the existing well for connection thereto, as shown for example in figure 5. The guide device 3 may be of a length such that when the wellhead support device 1 is in its desired installation position, e.g. with the suction anchor 2 embedded into the sea bed with the internal pipe 12 abutting or just above the top of the existing well, the bottom of the guide device 3 is above or at the top surface of a cement plug 11 within the subsea well 5. Once the suction anchor 2 is in the desired position about the subsea well 5 as shown in figures 5 or 6 the closure 14 and guide device 3 may be removed and retrieved to the surface. This may be achieved by releasing the connection between the closure 14 and the suction anchor 2 (if there is a connection) and lifting the closure 14 and guide device 3 together by means of lifting the top 42 of the pull-in wire 34. By lifting the guide device 3 out by the pull-in wire 34 the upper and lower parts 16, 18 of the guide device 3 may be retrieved together with the closure 14. The guide device 3 and closure 14 may be used with another suction anchor to facilitate re-entry with another existing subsea well. Once the guide device 3 and closure 14 have been removed, a wellhead (low pressure wellhead and / or high pressure wellhead) can be installed in the top of the wellhead support structure 1 if the structure was installed without a wellhead (low pressure wellhead and / or high pressure wellhead) therein. The wellhead is received in the central aperture 8 of the suction anchor 2. For example, the wellhead may be received at the top of the internal pipe 12, e.g. a wellhead receptacle. At this point (before or after the wellhead is installed) the internal pipe 12 can be fluidly connected to one or more tubulars of the existing well to provide a connection (e.g. a pressure tight connection) to the existing well up through the top of the suction anchor 2 to the wellhead. At this point use of the well in the desired (usual) manner may be performed. For example, a BOP may be connected to the top of the wellhead and desired downhole operations such as additional plugging can be performed. Once the desired well operations have been completed, the connection between the internal pipe 12 may be cut, the central aperture 8 sealed, e.g. with a closure 14, and the suction anchor 2 pumped out of the seabed 9 by pumping fluid in through the vent hatch 10. Once the suction anchor 2 has been forced out of the seabed by increasing the pressure inside the suction anchor 2, it can be retrieved to the surface. The suction anchor 2 can be again connected up with a guide 3 and used on another subsea well. As mentioned above, figure 7 shows an arrangement in which the guide device 3 is a single piece. In this case the entire length of the guide device 3 is attached to the outside of the suction skirt 6 of the suction anchor 2 in a stowed position. In this stowed position the guide device 3 does not protrude beyond the bottom of the suction anchor 2 but due to the length of the entire guide device 3 it does extend beyond the top of the suction anchor. The guide device 3 may be released from the outside of the suction skirt to hang below the suction anchor 2 and be pulled in by the pull-in wire 34 as described above in relation to the two part guide device 3. The guide device 3 can be fixed to the underside of the closure 14. This may be by a threaded connection, particularly if the guide device 3 is made from a drill pipe. The guide device 3 may be rotated relative to the suction anchor 2 by a traction wire arrangement similar to that shown in figure 8. The pull-in wire 34 may extend through the entire length of the guide device 3 as shown in figure 7. In this case the lower end of the pull-in wire 34 may be allowed to protrude from the bottom of the suction anchor 2 to act as the initial well entry portion of the guide device 3. Such an arrangement with the pull-in wire 34 acting as the initial well entry portion of the guide device 3 may also be present in a multi part (e.g. two part) guide device as described above. The guide device 3 may also comprise one or more upper centralisers 26’ as shown in figure 7 (in which one upper centraliser 26’ is shown). This centraliser 26’ may be sized to sit within and interact with the internal pipe 12 of the suction anchor 2. This centraliser 26’ may help guide the guide device into the internal pipe 12 as the guide device 3 is pulled towards the top of the suction anchor 2 by the pull-in wire. This upper centraliser 26’ may also provide a second contact point between the guide device 3 and the suction anchor 2 such that the position of the guide device 3 may be more rigidly held in position relative to the suction anchor 2. Thus, the multi part (e.g. two part) guide device as described above may also comprise one or more upper centralisers 26’. The upper centraliser 26’ may also be one of the types of centralisers shown in figures 10 or 11. Although above it is disclosed that the internal pipe 12 may sit above or abut the top of the existing well 5 tubulars, it could alternatively overlap the existing well 5 tubulars as shown in figure 9. As shown in figure 9, the existing well 5 may comprise an outer conductor tubular 45 and an inner surface casing 47. The length of the internal pipe 12 of the suction anchor 2 (not shown in figure 9), may be such that when the suction anchor is positioned in the seabed in its desired position, the internal pipe 12 overlaps the top of the conductor 45 and the surface casing 47. Further the diameter of the internal pipe 12 is such that it sits in the annulus between the conductor 45 and the surfacing casing 47. The internal pipe 12 may be connected to the surface casing 47 of the existing well 5 by cement 49. Figure 13 shows a second type of wellhead support structure 101 for positioning about an existing subsea well. The wellhead support structure 101 is for providing support (e.g. lateral and / or vertical support) to a wellhead connected to the subsea well 5. This means that forces exerted on the wellhead can be transferred into the support structure 101 and then ultimately into the seabed when the support structure is installed. The wellhead support structure 101 comprises a plurality of (in this case four) suction anchors 102 and a support frame 103. The support frame 103 comprises (e.g. is formed from) a plurality of connected rigid beams 104. The beams 104 may for example be metal beams. These beams 104 define an internal space between them. This internal space may be for housing the wellhead and equipment (e.g. well control equipment such as a flow control base, blow out preventer (BOP) and / or Christmas tree etc) mounted on the wellhead. The support frame 103 may act as a trawl deflector and / or protection structure for the wellhead and other components housed within the support frame 103. As shown in figure 16, the beams 104 are arranged to provide a frame that is substantially square or rectangular in shape when viewed from above. Four lower beams 104a are provided forming an X shape. The lower beams 104a define a lower plane of the support frame 103. An upper plane of the support frame 103 is defined by four upper beams 104b arranged in a rectangular (or square) shape. Four (e.g. obliquely extending) side beams 104c are provided, each coupled between one of the beams 104a of the lower plane of the support frame and one of the beams 104b of the upper plane of the support frame. As shown in this embodiment, the side beams 104c may extend between the outer end of at least one of the beams 104a of the lower plane and a corner between two beams 104b of the upper plane of the support frame 103. The suction anchors 102 are for securing the support frame 103 rigidly to the seabed. The suction anchors 102 each comprise an annular top lid 105 and a cylindrical outer suction skirt 106 that bounds an internal volume 107 of the suction anchors. The top lid 105 of each suction anchor 102 is affixed to the support frame 103 such that the interior volume 107 of the suction anchors 102 is below the lower plane of the support frame 103. As shown in figures 13 to 15, each suction anchor 102 is affixed to the lower plane of the support frame 103 at or towards the outer end of a respective lower beam 104a. This allows for a wide base by which the suction anchors 102 can stabilise the wellhead support structure 101 and secure it to the seabed. As shown, in this type of wellhead support structure, the well does not extend through a suction anchor itself, but instead extends through part of the support frame 103 rigidly secured by the suction anchors 102 to the seabed. The wellhead support structure 101 further comprises a guide device 108 in the form of an inverted conical funnel. The guide device 108 is shaped such that the upper portion of the guide device 108 has a smaller diameter than the lower portion. That is, the guide device 108 tapers towards the top of the guide device 108. The guide device 108 is fixed to the lower plane of the support frame 103 such that it is located below the lower plane of the support frame 103. Integrally formed with the guide device 108 is a wellhead housing receptacle 109. The wellhead housing receptacle 109 comprises (e.g. is formed from) a cylindrical casing attached to the top of the guide device 108. The wellhead housing receptacle 109 is for receiving a wellhead housing (e.g. conductor housing and / or high pressure wellhead housing). The wellhead housing (not shown in figures 13 to 15) may be mounted in the wellhead housing receptacle 109 before or after the wellhead support frame 101 is installed on the sea bed. In order to aid correct location of the wellhead support structure 101 about the existing well 5, the existing well 5 is fitted with a guide element 110. The guide element 110 comprises a cylindrical body formed with a conical tip. An installation cable 111 is connected to the conical tip of the guide element 110 to allow the guide element 110 to be lowered from the surface of the water to the existing well 5. The cylindrical body of the guide element 110 is sized so that when installed it engages with the interior (e.g. the internal diameter of the uppermost casing) of the existing well 5. The guide element 110 is positioned on the existing well 5 either using the cable 111 or by an ROV. The guide element 110 may be held in place only by its own weight, e.g. there may be no means to lock or secure the guide element 110 to the existing well 5. This may simplify the design of the system and / or ease retrieval of the guide element 110 after the wellhead support structure 101 has been installed. The method of installing the wellhead support structure 101 comprises first installing the guide element 110 on the existing well 5. Figure 12 shows the guide element 110 installed on the existing wellhead 5. The installation of the guide element 110 may comprise lowering the guide element 110 from the surface of the sea to the existing well 5 using a crane and lifting wires 111. The guide element 110 is installed on top of the existing well 5 with the help of a guiding ROV. The guide element 110 is not otherwise secured to the existing well and, as mentioned above, is held in place using its own weight alone. Once the guide element 110 has been installed on the existing well, the wellhead support structure 101 is lowered towards the guide element 110. This may for example be by use of a crane and lifting wires 112. As the wellhead support structure 101 is being lowered towards the existing well, the angled surface (i.e. the lower conical funnel) of the guide device 108 contacts the angled surface (i.e. conical tip) of the guide element 110 and together they act to bring the guide device 108 (and hence wellhead support structure 101) into coaxial alignment with the existing well 5 on the seabed. The wellhead support structure 101 is lowered further towards the sea bed such that the wellhead housing receptacle 109, provided above the guide device 108, is lowered around the existing well 5 in a position that is coaxial and concentric with the well 5. As the wellhead support structure 101 is lowered, the suction anchors 102 contact the seabed. The suction anchors 102 are then forced into the sea bed. The suction anchors 102 may be forced into the seabed by their own weight and the weight of the wellhead support structure 101, and / or by actively removing (e.g. pumping out) fluid from the cavity 107 within them until the wellhead support structure 101 is at a desired / chosen height from the seabed as shown in figure 14. The removal of fluid from each of the plurality of suction anchors 102 may be independently controlled. This allows control over the verticality of the wellhead support structure 101. Once the wellhead support structure 101 has been guided into position about the existing well 5, the guide element 110 is removed from the existing well 5 using the crane and lifting cables 111. The wellhead housing receptacle 109 is sealingly connected to the existing well 5, e.g. by cementing and other known sealing means. The wellhead support structure 101 remains securely and rigidly fixed to the seabed as shown in Figure 15. This is achieved by the use of suction anchors 102. A wellhead (e.g. conductor housing and / or high pressure wellhead housing) (not shown) is then landed on the wellhead support structure 101 in the wellhead housing receptacle 109. The wellhead is then sealingly and / or rigidly coupled to the wellhead housing receptacle 109. When the wellhead is installed and rigidly connected to the wellhead support structure 101 (e.g. via the wellhead housing receptacle 109), forces exerted on the wellhead may be transferred into the wellhead support structure and ultimately into the seabed. Forces acting on the wellhead may be transferred sequentially to the wellhead housing receptacle 109, into the support frame 103 and into the suction anchors 102 and then ultimately to the seabed. The wellhead housing receptacle 109 is not designed to bear pressure but is designed to withstand all mechanical loads transferred by the wellhead (along with the associated casing). The installed wellhead including wellhead support from the wellhead support structure 101 means that operations for re-entry into the existing well 5 can be safely and / or reliably performed.

Claims

1. Method of locating a wellhead support structure about an existing subsea well, the method comprising:providing a wellhead support structure, wherein the wellhead support structure comprises a suction anchor and a guide device; andguiding the wellhead support structure into a position about the subsea well using the guide device.

2. The method according to claim 1, wherein the method comprises lowering the wellhead support structure towards the existing well, and wherein the guide device reaches the existing subsea well before the suction anchor of the wellhead support structure reaches the seabed.

3. The method according to claim 1 or 2, wherein the suction anchor comprises an internal pipe.

4. The method according to claim 3, wherein the method comprises installing the wellhead support structure on the seabed, and then connecting the internal pipe to the existing well.

5. The method according to claim 3 or 4, wherein the method comprises determining the position of the top of the existing well relative to the seabed, and providing the internal pipe for connection to the existing well that is sized based on the position of the top of the existing well.

6. The method according to any preceding claim, wherein the method comprises providing a wellhead in the wellhead support structure.

7. The method according to claim 6, wherein the method comprises fluidly connecting the wellhead to one or more well tubulars of the existing well.

8. The method according to any preceding claim, wherein the method comprises removing the guide device from the wellhead support structure after the suction anchor has reached the seabed.

9. A wellhead support structure for location about an existing subsea well, wherein the wellhead support structure comprises:a suction anchor; anda guide device for guiding the wellhead support structure into a position about the subsea well.

10. The wellhead support structure according to claim 9, wherein the guide device extends beyond the bottom of the suction anchor.

11. The wellhead support structure according to claim 9 or 10, wherein the suction anchor comprises an internal pipe for connection to the existing well.

12. The wellhead support structure according to claim 11, wherein the length of the internal pipe is such that, when the suction anchor is in a location for providing wellhead support about the existing well, the bottom of the internal pipe is above, or at, the height of the top of the existing well.

13. The wellhead support structure according to any of claims 9 to 12, wherein the guide device is releasable and / or retrievable from the suction anchor.

14. The wellhead support structure according to any of claims 9 to 13, wherein the guide device comprises an initial well entry portion and an aligning portion.

15. The wellhead support structure according to claim 14, wherein the initial well entry portion has a lower lateral stiffness than the aligning portion.

16. The wellhead support structure according to any of claims 9 to 15, wherein the guide device comprises one or more guiding centralisers, wherein the one or more guiding centralisers is arranged and positioned to enter the existing subsea well as the wellhead support structure is guided into position about the existing subsea well.

17. The wellhead support structure according to claim 16, wherein the guide device comprises a plurality of guiding centralisers, and wherein in a direction from the bottom of the guide device towards the top of the guide device, the guiding centralisers have an increasing maximum outer5 diameter.

18. The wellhead support structure according to any of claims 9 to 17, wherein the wellhead support structure is arranged to perform the method of any of claims 1 to 8.

019. The method according to any of claims 1 to 8, wherein the method is performed using the wellhead support structure of any of claims 9 to 18.A

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