Patent Description:
Mooring and anchoring systems are critical to ensure reliable station keeping of floating objects such as floating wind turbines or floaters used in petroleum production. Many solutions exist for this purpose, such as suction bucket moorings, embedded anchors, torpedo anchors, etc. With the increasing development of, for example, offshore renewable energy and the exploration of more remote and environmentally challenging areas for natural resources exploration, there is a continuous need for improved mooring and anchoring technology. Improved mooring and anchoring technology is also relevant for various other offshore applications.

Documents which may be useful for understanding the field of technology include <CIT>, which describes an anchor adapted to be sunk in the ocean floor and left there in the event that it is necessary to disconnect the anchor line and move an anchored vessel or other structure to another location; <CIT>, which describes a method of sinking boreholes using a driven rotary tool carrying cutters; <CIT>, which describes a method of anchoring floating structures at sea; <CIT>; <CIT> and <CIT>.

The present disclosure has the objective to provide improved technology for mooring and anchoring, or at least alternative solutions to the state of the art.

According to the invention, there is provided a method for installing a sea floor anchor, the method comprising the steps: (a) building a drill string from a vessel, (b) drilling a hole in the sea floor, (c) lowering an anchor member from the vessel and into the hole, and (d) cementing the anchor member in place in the hole via a cementing hose from the vessel. After carrying out steps (a)-(d), the vessel is moved to a new drilling location with the drill string hung off from the vessel.

The detailed description below and appended claims outline further embodiments.

These and other characteristics will become clear from the following description of illustrative embodiments, given as non-restrictive examples, with reference to the attached drawings, in which.

The following description may use terms such as "horizontal", "vertical", "lateral", "back and forth", "up and down", "upper", "lower", "inner", "outer", "forward", "rear", etc. These terms generally refer to the views and orientations as shown in the drawings and that are associated with a normal use of the invention. The terms are used for the reader's convenience only and shall not be limiting.

<FIG> illustrate an example installation which may utilise embodiments described below. A floating structure <NUM> is moored to a sea floor <NUM> by means of a plurality of anchors <NUM> (in <FIG>, only one anchor <NUM> is shown but it is to be understood that further anchors will usually be present). Mooring lines <NUM> connect the floating structure <NUM> to the anchors <NUM>. The floating structure <NUM> may, for example, be a floating wind power generator, as illustrated. The floating structure <NUM> is moored at a location with a water depth x (the vertical distance between a waterline <NUM> and the sea floor <NUM>). As illustrated in <FIG>, the anchor <NUM> may be installed at a horizontal distance y away from the floating structure <NUM> to provide a so-called catenary mooring. Alternatively, as illustrated in <FIG>, the mooring lines <NUM> may extend substantially vertically to provide a vertical mooring system. The mooring system may, for example, comprise three anchors <NUM> and three mooring lines <NUM>.

The sea floor <NUM> may comprise a soft soil layer <NUM> and a hard soil layer <NUM>. The soft soil layer <NUM> may have a lower density or hardness compared to the hard soil layer <NUM>. The soft soil layer <NUM> and the hard soil layer <NUM> may combined make up a rock formation, or the sea floor <NUM> may comprise only a rock formation, only a soft soil layer <NUM> or only a hard soil layer <NUM>.

According to an embodiment, there is provided a method for installing a sea floor anchor <NUM>, the method comprising the steps.

<FIG> illustrate a method for installing a sea floor anchor <NUM>. A vessel <NUM> is provided and positioned above a location at which the sea floor anchor <NUM> is to be installed. A drill string <NUM> is built on the vessel <NUM>, for example by a plurality of individual drill string segments (for example so-called joints or stands) connected together and lowered towards the sea floor <NUM>. The drill string <NUM> comprises a drilling head for engaging the sea floor <NUM> and drilling a hole <NUM>, as illustrated in <FIG>.

When the hole <NUM> is completed, for example after drilling the hole <NUM> to a depth of a few meter, the drill string <NUM> is lifted out of the hole <NUM> and may be hung off from the vessel <NUM> instead of being retrieved fully back onto the vessel <NUM>. In such a case, the drill string <NUM> can remain hung off from the vessel <NUM> while carrying out steps (c) and (d). If using a vessel <NUM> having a moon pool (see below), the drill string <NUM> may be hung off through the moon pool <NUM>. The vessel <NUM> may be provided with a skidding arrangement or equivalent mechanism to allow the drill string <NUM> to be moved to the side or sideways within the moon pool prior to carrying out steps (c) and (d). Moving or skidding the drill string <NUM> to the side may comprise moving or skidding the drill string <NUM> away from a vertical axis extending through the drilling machine <NUM> (described below). This may be done, for example, by means of a trolley or skid arranged in or adjacent the moon pool. In this way, the drill string <NUM> may, in a first position, be positioned vertically below the drilling machine <NUM> and in a second position be spaced from a vertical axis extending through the drilling machine <NUM>.

The drilling (step (b)) may be carried out through the moon pool <NUM> of the vessel <NUM>.

Illustrated in <FIG>, after drilling of the hole <NUM> has been completed, the vessel <NUM> may move slightly off the drilling position and/or the drill string <NUM> may be skidded or moved away from the drilling position. Illustrated in <FIG> and <FIG>, an anchor member <NUM> is then lowered from the vessel <NUM> and into the hole <NUM>. The anchor member <NUM> may be lowered by means of a winch and an elongate lifting member <NUM> (see <FIG>), such as a rope or a wire. Supporting the anchor member <NUM> from the vessel <NUM> during lowering may be done via a crane <NUM> (see <FIG>). The anchor member <NUM> may be lowered through a moon pool <NUM> of the vessel <NUM> or, optionally, over a side (<NUM>) of the vessel <NUM>. If the lowering of the anchor member <NUM> is supported by the crane <NUM>, the elongate lifting member <NUM> may be a rope or a wire arranged on the crane <NUM> (such as on a winch drum on the crane <NUM>), or it may be a rope or a wire arranged in connection with a separate winch on the vessel <NUM> and wherein the rope or wire is led via a sheave or the like held by the crane <NUM>. If lowering the anchor member <NUM> over a side of the vessel <NUM>, a cantilever structure <NUM> (see <FIG>) may optionally be used for guidance or support.

Also illustrated in <FIG> and <FIG>, a cementing hose <NUM> may be lowered together with the anchor member <NUM> and fixed to the anchor member <NUM>. The cementing hose <NUM> may be a tube or pipe operable to carry cement from the vessel <NUM> in order to fill voids between the anchor member <NUM> and the walls of the hole <NUM> so as to cement the anchor member <NUM> in place in the hole <NUM>.

Alternatively, the cementing hose <NUM> can be provided separately from the anchor member <NUM>, for example in that the cementing hose <NUM> is lowered separately from the vessel <NUM>.

The cementing hose <NUM> may be handled by an ROV <NUM> which is controlled via a control umbilical <NUM> from the vessel <NUM> (see <FIG>).

After pumping cement into the hole <NUM>, the cementing hose <NUM> can be detached from the anchor <NUM>. This can, for example, be done by an ROV <NUM>. An ROV <NUM> may also, additionally or alternatively, detach the lifting member <NUM>. Alternatively, the cementing hose <NUM> and/or the lifting member <NUM> may be detached for example via a release mechanism which activates by applying tension from the vessel <NUM>, for example via a sideways or vertical tension applied to the cementing hose <NUM> and/or the lifting member <NUM>.

After carrying out steps (a)-(d), the vessel <NUM> moves to a new drilling location with the drill string <NUM> hung off from the vessel <NUM>, as illustrated in <FIG>. The anchor <NUM> has been installed and may be connected up to a floating object by another vessel, if necessary after a period of time to allow the cement to settle. Optionally, the vessel <NUM> may connect up the anchor <NUM> to a mooring line or to a floating object before moving away.

<FIG> illustrates an anchor member <NUM>. The anchor member <NUM> is preferably cylindrical, and may have a varying cross-sectional diameter. For example, the anchor member <NUM> may have a smaller diameter at a lower part 14a and larger diameter at an upper part 14b thereof.

The hole <NUM> may advantageously be drilled with a diameter of more than <NUM>, more than <NUM>, more than <NUM> or more than <NUM>.

The anchor member <NUM> may advantageously have a length of more than the diameter of the hole <NUM>, more than <NUM>% of the diameter of the hole <NUM>, or more than <NUM>% of the diameter of the hole <NUM>.

<FIG> illustrate a drilling machine <NUM> suitable for use on a vessel <NUM>. The vessel <NUM> may have a support structure <NUM>, such as a rig or tower structure, for holding the drilling machine <NUM>. The drilling machine <NUM> and/or the support structure <NUM> may be positioned on a deck of the vessel <NUM>. The drilling machine <NUM> can be a drilling machine operable to rotate the drill string <NUM>.

Advantageously, the drill string <NUM> is suspended from the vessel <NUM> from a heave compensated drilling machine <NUM>. This can be achieved may making the drilling machine heave compensated in the support structure <NUM>.

Advantageously, the anchor member <NUM> is suspended from the vessel <NUM> from a heave compensated winch or crane <NUM>. The winch or crane <NUM> may be independent of the drilling machine <NUM>.

Optionally, the drill string <NUM> may be hung off from the vessel <NUM> as described above by leaving the drill string <NUM> hanging from the drilling machine <NUM> while operating the winch or crane <NUM> to carry out the steps relating to lowering and cementing the anchor member <NUM>.

As described above, the sea floor may comprise a soft soil layer <NUM> (see <FIG>) and a hard soil layer <NUM>, wherein the hard soil layer <NUM> is more compact than the soft soil layer <NUM>. The method may comprise drilling into the hard soil layer <NUM> and cementing the anchor member <NUM> at least partly in the hard soil layer <NUM>.

The method may comprise removing a part of the soft soil layer <NUM> prior to step (b). The soft layer <NUM> may be removed by drilling through the soft soil layer <NUM> prior to drilling into the hard soil layer <NUM>. The vertical thickness of the soft soil layer <NUM> may be less than <NUM>, less than <NUM>, less than <NUM> or less than <NUM>.

Any embodiments of the method described herein may comprise lowering a guide base with guide wires to the sea floor <NUM> and drilling through the guide base. The guide wires may also be used for quick access to the drilled hole when running and landing the anchor member.

<FIG> illustrate a vessel <NUM> which may be suitable for carrying out a method according to embodiments described herein. The vessel <NUM> comprises components described above, including a support (rig or tower) structure <NUM> with a drilling machine <NUM> and a crane <NUM>, which in this example is a knuckle-boom crane. The vessel <NUM> has a moon pool <NUM> (see <FIG>) in its hull, through which the drill string <NUM> and other components (such as wire/rope elongate lifting member <NUM>) may be lowered.

The vessel <NUM> has a deck <NUM> on which associated components and equipment can be stored during operation. Particularly, the vessel <NUM> may have storage, on the deck <NUM> or elsewhere, for a plurality of anchor members <NUM> for installation. In this way, a large number of anchor members <NUM> may be available and ready for installation on the vessel <NUM>, such as to allow efficient operation.

The vessel <NUM> may also comprise fluid handling systems <NUM> (see <FIG>) for handling of drilling fluid and/or cement, as may be required during the abovementioned operations.

The anchors <NUM> can be designed for the expected soil conditions and operational conditions, for example in view of their diameter, length, materials properties, etc. The anchors <NUM> may support one mooring line <NUM> (see <FIG>) or, optionally, more than one mooring line <NUM>. For example, in a wind park with a number of floating wind turbine generators, one anchor <NUM> may provide support to more than one floating wind turbine generator, thereby reducing the total number of anchors required.

Advantageously, if allowing for the drill string <NUM> to be hung off from the vessel <NUM>, the drill string <NUM> may be built and tripped in once per location, and hung off in a parking position, for example in the moon pool, while carrying out other activities. The other activities may be carried out by a crane or winch, or a combined crane and winch. When finished with such other activities, such as steps (c) and (d) described above, the vessel <NUM> may move to the next installation location and start the next drilling operation without having to build and trip in the entire drill string <NUM>.

In any of the embodiments described here, the diameter of the hole <NUM> may, for example, be in the order of <NUM> and the anchor member <NUM> may be in the order of <NUM>-<NUM> for an anchor <NUM> suitable for use with a wind energy floater. Various other sizes may, however, be relevant for other applications, depending on the demands and requirements in any particular case.

Prior to commencing the drilling operation, an onboard ROV may be deployed to inspect and, if required, measure inclination or other parameters of the sea floor <NUM>.

Optionally, the vessel <NUM> may have the functionality to skid or tilt the drilling machine <NUM> and associated components away from the moon pool area. This is illustrated in <FIG> (see also <FIG>). The drilling machine <NUM> may be arranged supported by a support structure <NUM> which is movable in relation to the rest of the vessel <NUM> structure. For example, the support structure <NUM> may be skiddable or tiltable in relation to the moon pool <NUM>.

This is illustrated in <FIG>, wherein the support structure <NUM> with the drilling machine <NUM> can be skidded in relation to the moon pool <NUM>. The support structure <NUM> may be skidded completely away from an opening defined by the moon pool <NUM>, as illustrated in <FIG>, or only partially away from the opening. For example, if the drill string <NUM> remains suspended from the drilling machine <NUM> during for example the lowering of the anchor member <NUM>, the support structure <NUM> may be skidded only sufficiently far to provide more space for other operations through the moon pool <NUM>, but so that the drill string <NUM> may remain suspended from the drilling machine <NUM>, through the moon pool <NUM>, and into the water below the vessel <NUM>.

<FIG> illustrates how the support structure <NUM> or a part of the support structure <NUM> can be tilted in order to provide more space above the moon pool area. Optionally or additionally, the entire platform as shown in <FIG> can be arranged with capability to be skidded sideways, similarly as illustrated in <FIG>.

Step (b) of the method may thus comprise operating a drilling machine <NUM> to drill the hole in the sea floor <NUM>, as described above, and thereafter skidding or tilting a support structure <NUM> supporting the drilling machine <NUM>. In this manner, the support structure <NUM>, the drilling machine <NUM> or other associated components may be moved out of the way in order that other operations through the moon pool <NUM> can be carried out more easily.

Illustrated in <FIG>, the method may comprise creating a liquid flow from a drill string head <NUM>' and upwardly inside the drill string <NUM> to the vessel <NUM>. In this embodiment, the method may include receiving soil particles or cuttings <NUM> on the vessel <NUM> via the liquid flow. The soil particles or cuttings <NUM> may be received on the vessel <NUM> for storage, processing or transport away. In this manner, the soil particles or cuttings <NUM> need not be dumped on the sea floor <NUM>.

Carrying out the drilling as a reverse circulation drilling (RCD) process provides advantages that soil particles or cuttings <NUM> can be transported away from the site at or around the hole <NUM>.

The liquid flow in the drill string <NUM> may, for example, be created by gas lift, i.e. by injecting gas (such as air) into the drill string <NUM>. The liquid flow, including soil particles or cuttings <NUM>, if present, may be received via a return pipe <NUM> arranged in association with the drilling machine <NUM>, as can be seen in <FIG>. The return pipe <NUM> may be connected to a liquid handling system, for example for separating liquid and soil particles or cuttings <NUM>, other processing of the liquid, or discharge of the liquid.

Advantageously, a part of the soft layer <NUM> can be removed at a sea floor area larger than a cross-section area of the drill string head <NUM>' or larger than a cross-section area of the drill string <NUM>. This is indicated in <FIG>, wherein a reverse circulation flow may be used to remove soil particles from the soft layer <NUM> over a larger area than the cross-sectional area required for the hole <NUM>. This provides the advantage that the hole <NUM> may have less risk of collapsing or that the risk of operational disturbance is reduced.

The method may comprise positioning a lower end, such as a drill string head <NUM>', of the drill string <NUM> above and adjacent the soft layer <NUM> or into the soft layer <NUM> while suspending the drill string <NUM> from the vessel <NUM> and creating a liquid flow upwardly inside the drill string <NUM> to the vessel <NUM>. In this embodiment, one may, for example, hover the lower end above the soft layer <NUM> while moving the vessel <NUM> in order that a larger area of the soft layer <NUM> is removed and transported to the vessel <NUM> via the liquid flow in the drill string <NUM>.

As can be seen in e.g. <FIG>, the drilling machine <NUM> can be supported by a support structure <NUM> on the vessel <NUM>. The support structure <NUM> can provide rotational support to the drilling machine <NUM> in a horizontal plane when the drilling machine <NUM> imposes a moment on the drill string <NUM> for rotating the drill string <NUM>, and thus hold the drilling machine <NUM> rotationally fixed in relation to the vessel <NUM>. Advantageously, the support structure <NUM> comprises a heave compensated frame <NUM>' supporting the drilling machine <NUM>. The heave compensated frame <NUM>' may, for example, comprise vertically arranged hydraulic cylinders which allows for vertical motion of the drilling machine <NUM> in response to vessel heave.

Alternatively, the drilling machine <NUM> may be suspended by a heave compensated crane <NUM> (see <FIG>). In such an arrangement, the crane <NUM> can be arranged to hold the drilling machine <NUM> vertically, e.g. by suspending the drilling machine <NUM> from the crane via a hook or the like. The support structure <NUM> may be arranged to provide rotational support to the drilling machine <NUM>, as described above, but to allow the drilling machine <NUM> to move freely in the vertical direction, e.g. along tracks or support rods. A movable frame, similar to frame <NUM>', may be used for this purpose. The crane <NUM> may be operated in heave compensation mode to hold the drilling machine <NUM>, in order to provide heave compensation capability of the drilling machine <NUM>.

In any of the embodiments herein, the heave compensation may be passive heave compensation or active heave compensation.

Illustrated in <FIG>, in any of the embodiments described herein the method may, optionally, be carried out over a side of the vessel via a cantilever structure <NUM> extending outwardly from a side <NUM> of the vessel. This may include building the drill string <NUM> from the cantilever structure <NUM>, such that the drill string <NUM> is (directly or indirectly) suspended from the cantilever structure <NUM>.

Additionally, or alternatively, the anchor member <NUM> may be lowered from the vessel <NUM> via a cantilever structure <NUM>, for example by suspending the anchor member <NUM> directly or indirectly from the cantilever structure <NUM> while lowering it or by for example lateral support of the lifting member <NUM> while lowering it.

<FIG> illustrate various embodiments of an anchor member <NUM> suitable for use with the method described herein. The anchor member <NUM> may have a suspension member <NUM>, for example a shackle or a hook, from which it can be suspended and lowered from the vessel <NUM> via the lifting member <NUM>.

Advantageously, the anchor member <NUM> may have a perforated lower part 14a. This may allow for cement to be distributed in and around the anchor member <NUM> in a manner beneficial for the anchor member <NUM> to be fixed reliably in the hole <NUM>.

The lower part 14b may be formed as a hollow, elongate tube, see for example <FIG>, <FIG>.

The anchor member <NUM> may comprise an inlet tube probe <NUM> arranged for injection of cement into an internal part of the anchor member <NUM>. The anchor member <NUM> may be arranged hollow for this purpose, for example in an elongate cylindrical form, whereby an internal volume of the anchor member <NUM> may be filled with cement via the inlet tube probe <NUM>. The inlet tube probe <NUM> may extend downwardly inside the anchor member <NUM>.

The cementing hose <NUM> may be connected to the inlet tube probe <NUM> before the anchor member <NUM> is lowered to the sea floor <NUM>. Alternatively, the cementing hose <NUM> may be connected to the inlet probe <NUM> after lowering of the anchor member <NUM>, for example by assistance of an ROV <NUM>. In this manner, cementing of the anchor member <NUM> may be done by filling cement into an inside volume of the anchor member <NUM> in addition to filling an annulus volume around the anchor member <NUM> in the hole <NUM>. Optionally, the anchor member <NUM> may be cemented in place in the hole <NUM> by filling the annulus around the anchor member <NUM> in the hole <NUM> with cement.

If the inlet tube probe <NUM> extends into the interior volume of the anchor member <NUM>, the method may comprise retracting the inlet tube probe <NUM> from inside the anchor member <NUM> during the cementing operation to achieve enhanced cement distribution, both inside the anchor member <NUM> and the annulus around the anchor member <NUM> by use of an onboard cement reel and assisted by ROV <NUM>.

<FIG> illustrates an embodiment of a vessel <NUM> having an alternative support structure <NUM> for holding and suspending the drilling machine <NUM>.

Embodiments described herein may, for example, be suitable for installation of floating renewable energy installations such as floating wind turbine units. According to embodiments, a more flexible installation of the mooring and anchoring systems can be achieved. For example, a structurally reliable mooring in different or varying soil conditions can be obtained, and operations may be less sensitive to water depth. Additionally, or alternatively, a high installation efficiency can be obtained, allowing the use of less specialized installation vessels and/or reducing dependency on weather windows. This may be advantageous for example in the installation of large renewable energy parks, with a high number of mooring points required.

Advantageously, the vessel <NUM> may additionally be equipped for installing suction anchors. Having the possibility to carry out such "dual" operations can give advantages of more efficient operations for example in areas with varying soil conditions, where a combination of suction anchors and cemented anchors may be used.

The system and method may be employed using lighter vessels than would normally be used for subsea drilling operations. For example, such vessels known as offshore service vessels may be suitable for this purpose.

Claim 1:
A method for installing a sea floor anchor (<NUM>), the method comprising the steps
(a) building a drill string (<NUM>) from a vessel (<NUM>),
(b) drilling a hole (<NUM>) in the sea floor (<NUM>),
(c) lowering an anchor member (<NUM>) from the vessel (<NUM>) and into the hole (<NUM>), and
(d) cementing the anchor member (<NUM>) in place in the hole (<NUM>) via a cementing hose (<NUM>) from the vessel (<NUM>),
characterized by, after carrying out steps (a)-(d), moving the vessel (<NUM>) to a new drilling location with the drill string (<NUM>) hung off from the vessel (<NUM>).