WO2010062184A2

WO2010062184A2 - System and method for anchor monitoring and verification

Info

Publication number: WO2010062184A2
Application number: PCT/NO2009/000388
Authority: WO
Inventors: Sigmund Andre Hertzberg
Original assignee: Tristein As
Priority date: 2008-11-25
Filing date: 2009-11-12
Publication date: 2010-06-03
Also published as: NO20084947L; WO2010062184A3; NO332343B1

Abstract

A system for monitoring and verification of an anchor (10) for placement on a seabed below a body of water (W). A position monitoring and control apparatus (29) is located at a distance from the anchor (10), and sensing and transmitting means (20) attached to the anchor (10) and adapted for transmission of data, continuously or at selected intervals, between the anchor (10) and the position monitoring and control apparatus (29).

Description

System and method for anchor monitoring and verification

Field of the Invention The invention concerns the monitoring and control of anchors. More specifically, it concerns a system and a method for monitoring and verification of an anchor for placement on a seabed below a body of water, both during installation and after the anchor has been set.

Background of the Invention Drilling rigs are normally moored using an 8 to 12 line anchor spread. The anchors are installed one by one in predetermined positions on the seabed using anchor handling tugs (AHT). Correct position, orientation and seabed penetration are crucial factors for a safe and reliable mooring and to verify that input data correspond to the approved mooring analysis. In the current state of the art, anchor orientation, penetration and position can today only be confirmed by use of submersible "Remotely Operated Vehicles" (ROV) after installation. The pertinent data for each anchor may also be estimated purely on theoretic drag and penetrations- charts or be based on vessel position, chain length and tension readings. Anchor penetration can be estimated based on analysis. There are systems available which can give anchor penetration data to a type of "black box", and the data can be processed after the anchor is retrieved onto the deck. However, such devices are only used for prototype testing of new anchors and are not suitable for use in anchor handling operations since they do not provide online and real-time data, and as they do not provide global position data. New rules and regulations issued from the Norwegian Maritime Directorate, and stricter administration by the Norwegian "Petroleumstilsynet" (PTIL) have increased the requirements for documentation. The process of anchoring a rig on the Norwegian shelf includes drag analysis, ROV checks and extreme tension pull on the rig to verify the holding capacity, and to verify that a set anchor is not moving. It is therefore a need for a system and a method for providing accurate online and real-time positioning, orientation and load data for rig anchors during anchor handling operations and anchor penetration.

Summary of the Invention

The invention is set forth and characterized in the independent claims, while the dependent claims describe other characteristics of the invention.

The purpose of the invention is to achieve a system and a method of monitoring and verification of an anchor for placement on a seabed below a body of water. The system according to the invention is characterized by a position monitoring and control apparatus located at a distance from the anchor, and sensing and transmitting means attached to the anchor and adapted for transmission of data, including transmission of spatial data (x-y-z), continuously or at selected intervals, between the anchor and the position monitoring and control apparatus.

The sensing and transmitting means may be placed in a protective housing which, alternatively via housing attachment means, is attached to the anchor. Preferably, the sensing and transmitting means is attached to a part of the anchor which is not intended for exposure to materials in the seabed, preferably in the shank of the anchor.

In an embodiment, load sensing means are mechanically attachable to the anchor, preferably the shank of the anchor, and to the anchor chain, wherein the load sensing means is adapted for transmission of data, continuously or at selected intervals, between the load sensing means and sensing and transmitting means. The data transmission between the load sensing means and sensing and transmitting means may be provided by a cable or by wireless devices.

The load sensing means may comprise a load cell, strain gauge, or similar. The sensing and transmitting means and the position monitoring and control apparatus may comprise hydroacoustic units, such as sonar. The position monitoring and control apparatus is preferably positioned on a vessel for placing the anchor on the seabed.

The method of setting an anchor from a floating vessel to a position on a seabed below a body of water by means of the system according to the invention, comprises the following steps: a) Positioning the vessel in proximity to said position; b) Deploying the anchor into the water; c) Receiving data signals from the sensing and transmitting means to the position monitoring and control apparatus; further characterized by the following steps: d) Deploying the anchor onto the seabed; e) Applying tension to the anchor chain connected to the anchor while monitoring the data from the sensing and transmitting means, until a pre-determined penetration depth into the seabed has been achieved.

Preferably, between step c) and step d), the vessel position is adjusted based on information in said data signals, in order to ensure that the anchor is set in the desired position on the seabed.

The invention thus provides a sensor based system for safe and reliable real-time anchor handling, rendering analyses and ROV surveys superfluous. With the present invention having a sensor mounted on the anchor, anchor handling vessels, drilling rigs and oil companies will get accurate and reliable distance, orientation, position, penetration and tension data from the anchor, through equipment already installed on the anchor handling vessels. Brief description of the drawings

These and other characteristics of the invention will be clear from the following description of an embodiment, given as a non-restrictive example, with reference to the attached drawings wherein:

Figure 1 is a perspective view illustrating an embodiment of the invention in association with an anchor;

Figure 2 is a perspective view of the embodiment illustrated by figure 1, in a different assembly state;

Figure 3 is a perspective view of the embodiment illustrated by figures 1 and 2, where the anchor is placed on a seabed; Figure 4 is a perspective view of the embodiment illustrated by figures 1, 2 and 3, where the anchor is embedded in a seabed;

Figure 5 is a perspective view of the embodiment of the invention, the anchor being deployed from a vessel;

Figure 6 is a perspective view of an embodiment of a housing according to the invention;

Figure 7 is a schematic illustration of an embodiment of a position monitoring and control apparatus;

Figure 8 is an exploded view of an alternative embodiment of the transponder housing; Figure 9 is a perspective view of the transponder housing shown in figure 8;

Figure 10a is a perspective view of the transponder housing shown in figures 8 and 9, installed on an anchor; and

Figure 10b is an enlarged view of a portion of figure 10a. Detailed description of a preferential embodiment The system according to the invention comprises an anchor 10 for placement on a seabed S below a body of water W, and penetration and embedment into the soil E below the seabed. The anchor may in principle be any known rig anchor, typically comprising one or more flukes 12 for penetration into the seabed, connected to a shank 14 to which an anchor chain 22 may be connected, as illustrated by figure 2. It is not uncommon that the anchor flukes and shank are connected via a hinge arrangement, such that the angle between the shank and the flukes may be adjusted depending on soil conditions and/or desired penetration angle. A transponder 20 is mechanically attached to the anchor 10, preferably to a part of the anchor 10 which is not intended for exposure to materials in the seabed, for example to the shank 14. In the illustrated embodiment, the transponder is attached substantially inside the structural elements of the shank. The transponder 20 may comprise any hydro acoustic transponder compatible with commercially available high precision acoustic positioning systems (HIPAP).

As illustrated by figure 1, the transponder 20 is placed in a heavy duty mounting bracket or housing 18, purpose-built to suit the chosen transponder dimensions and anchor installation method. The transponder bracket must be mounted to allow for the most optimal transmitting direction ("line of sight") to the HIPAP transceiver, hence the mounting angle must be adjusted according to seabed penetration angle. The housing 18 is also illustrated by figure 6, showing also brackets 19 for attachment to the anchor.

The housing 18 is mounted on the anchor in the most protected location (depending on the type of anchor), possible but still retaining communication capabilities. Prior to the anchor 10 being deployed into the water, the transponder 20 is installed in the housing 18, and the transponder is activated.

Turning now to figure 5, the anchor 10 is shown suspended by a deployment wire 24, in the water below an anchor handling vessel 26 (In a practical application, the deployment wire 24 may be connected to the anchor via a separate element known in the art as a "chaser"). This is a typical scenario in the deployment and installation of an anchor. Although not shown on figure 5, the skilled person will know that the anchor chain 22 is normally attached to the anchor 10 even at this stage. The anchor handling vessel 26 is equipped with a high precision acoustic positioning system (HIPAP) transceiver 29, schematically illustrated by figure 7. A standard (HIPAP) transceiver configuration comprises the transceiver unit 36, an operator station 38 and a hull unit 32. The hull unit 32 comprises a hoist control unit 32, and an antenna 30 penetrating the ship's hull 28. The transceiver may be a standard HIPAP500, which is commonly known in the art.

After successful over-boarding of the anchor 10 from the anchor handling ship 26 and lowering to a predetermined depth in the water (e.g. 50 metres), the hydro acoustic signal/communication between the transponder 20 and the HIPAP 29 is tested. Thereafter, spatial data for the anchor 10 may be transmitted from the transponder 20 to the HIPAP 29 on a continuous basis, if desired, thereby ensuring a real-time, online, monitoring of the anchor 10. The anchor 10 is lowered by the deployment wire 24 until it is landed in a correct orientation and in the desired position on a seabed S. Loss of signals from the transponder 20 during this phase could e.g. indicate that the anchor has been landed upside down, in which case it should be redeployed until in correct position. Figure 3 illustrates the anchor 10 placed on the seabed S, prior to penetration. The deployment wire 24 has been removed, the anchor chain 22 is attached to the anchor shank 14, and the anchor is ready to be set. This is performed by the applying a controlled tension to the anchor chain 22, whereby the flukes 12 of the anchor will penetrate into the soil E underneath the seabed S. The anchor chain tension is applied by suitable pull-in equipment on the vessel (rig, etc., not shown in the figures) which is to be moored or anchored by the anchor 10. This is a procedure well known in the art, and will therefore not be discussed further. However, with the real-time monitoring system according to the invention, the pull-in operation may be controlled based on online data received from the transponder 20. In addition to the spatial data mentioned above (x-y-z position), the system according to the invention also allows for a monitoring of the tension applied by the anchor chain to the anchor. This is illustrated in particular by figure 2, schematically showing a load cell 16 attached at one end to the anchor 10 and a second end to the anchor chain 22. The load cell may be substituted by a strain gauge arrangement in the attachment pin 15 on the anchor, or similar. The tension load data is transmitted to the transponder 20 via a cable 17 connecting the load cell 16 to the transponder. Other means for transferring data from the load cell to the transponder (e.g. wireless) may be considered as equivalents.

When using the system according to the invention, the following main activities may be carried out: a) Positioning the anchor handling vessel 26 in close proximity to the final anchor position; b) Placing the transponder 20 in the receptacle 18 on the anchor 10; c) Lowering the anchor 10 into the water W, e.g. by means of a deployment wire 24 over the stern roller; d) Moving the vessel 26 into a desired and pre-determined run-line position; e) Lowering the anchor down a predetermined depth (e.g. 50 metres) in the water, optionally minimizing vessel to ensure best possible hydro acoustic send/receive conditions, interrogating transponder 20 and verify acceptable signal; f) Continuing movement of vessel 26 to above intended anchor position on seabed; g) Lowering the anchor 10 to a pre-determined distance above the seabed S (e.g. 10 metres); verifying position on seabed S given by transponder 20 to HIPAP 29; h) Deploying the anchor 10 to seabed S, and reducing tension in the deployment wire 24; i) When the anchor 10 is in the correct position and the heading on the seabed, and orientation is acceptable, the HIPAP 29 system will receive signals from the transponder 20. If there is no signal or if the signals are week, the vessel 26 may be moved for optimal heading to ensure signal strength (If necessary, ensuring sufficient slack on the deployment wire 24 in order not to move the anchor unintentionally); j) When optimal signal from transponder 20 has been obtained, commence pre- tensioning the anchor 10 while constantly monitoring the data from the transponder 20; k) When acceptable penetration depth into the seabed has been achieved and verified by the transponder 20, and anchor holding capacity has been verified by the rig, the deployment wire may be disconnected from the anchor. The system according to the invention is using the signals from a conventional hydro acoustic transponder, transmitted through an ordinary HIPAP sensor to determine the exact position, orientation and penetration of an offshore rig anchor. The invented Advanced Distance and Positioning System - ADAPS) gives precise and reliable data to the operators about anchor position, orientation penetration and tension during anchor handling operations and the mooring period at location.

Although the invention has been described with reference to hydro-acoustic signals transmitted from a transponder mounted on a rig anchor, the skilled person will understand that the inventive concept embraces also other means of wireless communication.

The skilled person will also understand that the data between the load cell 16 and the transponder 20 may be provided by a wireless application, instead of the cable 17.

Figures 8, 9, 10a and 10b illustrate an alternative embodiment of a transponder housing 18'. The housing 18' comprises in this embodiment a hollow cylindrical body having an opening in a first end for insertion of a transponder. A detachable clamping portion 46 is fastened to the housing by means of bolts 50a extending through corresponding holes 52 and secured by nuts 50b. When the transponder 20 is installed in the housing 18', the clamping portion 46 may thus be bolted to the housing in order to exert a suitable pressure on the transponder and in that way keep it in position within the housing. As shown in figure 8, a rubber sheet (e.g. 2 mm thickness) is placed inside the clamping portion 46 and/or inside the corresponding area in the housing (not shown) in order to increase friction between the transponder and housing.

The housing 18' is connected to the anchor by means of two connection bars 44a,b, e.g. each 50xl0x500mm steel flat bar, preferably welded to the housing. As shown in figures 10a,b, the connection bars are attched (e.g. by welding) to the anchor and provides an extremely strong connection and at the same time deflects passing stones and debris which will have less possibility to get stuck in the transponder system.

In the illustrated embodiment, the housing 18' is attached substantially inside the structural elements of the shank 14, a part of the anchor 10 which is not intended for exposure to materials in the seabed. Additional protection may be provided by the stiffeners 42 inside the shank.

The transponder housing 18' serves the following purposes:

1. Fixing the transponder to the anchor in the correct angled position for optimal transmission of hydro-acoustic signals during all phases of the anchor installation;

2. Giving the transponder sufficient protection against the violent forces from the soil while transponder is penetrating through the seabed and down to final depth;

3. Influencing neither the holding capacity nor the structural integrity of the anchor; and

4. Enabling easy and rapid installation and retrieval of the transponder.

The bracket and associated clamping portion and connection bars may be made of ordinary construction steel quality.

Claims

1. A system for monitoring and verification of an anchor (10) for placement on and below a seabed below a body of water (W), characterized by a position monitoring and control apparatus (29) located at a distance from the anchor (10), and sensing and transmitting means (20) attached to the anchor (10) and adapted for transmission of data, including transmission of spatial data (x-y-z), continuously or at selected intervals, between the anchor (10) and the position monitoring and control apparatus (29).

2. The system of claim 1 , wherein the sensing and transmitting means (20) is placed in a protective housing (18; 18') which, alternatively via housing attachment means (19), is attached to the anchor (10).

3. The system of claim 1 or 2, wherein the sensing and transmitting means (20) is attached to a part of the anchor (10) which is not intended for exposure to materials in the seabed, preferably in the shank (14) of the anchor.

4. The system of any of the preceding claims, further comprising load sensing means (16) mechanically attachable to the anchor (10), preferably the shank of the anchor, and to the an anchor chain (22), wherein the load sensing means (16) is adapted for transmission of data, continuously or at selected intervals, between the load sensing means and sensing and transmitting means (20).

5. The system of claim 4, wherein the data transmission between the load sensing means (16) and sensing and transmitting means (20) is provided by means of a cable (17).

6. The system of claims 4 or 5, wherein the load sensing means (16) comprises a load cell, strain gauge, or similar.

7. The system of any of the preceding claims, wherein the sensing and transmitting means (20) comprise a hydroacoustic transponder, and the position monitoring and control apparatus (29) comprise a hydroacoustic transceiver in a high-precision acoustic positioning system.

8. The system of any of the preceding claims, wherein the position monitoring and control apparatus (29) is positioned on a vessel (26) for placing the anchor (10) on the seabed.

9. A method of setting an anchor (10) from a floating vessel (26) to a position on a seabed (S) below a body of water (W) by means of the system of any one of claims 1 - 7, comprising the following steps: a) Positioning the vessel (26) in proximity to said position; b) Deploying the anchor (10) into the water; c) Receiving data signals from the sensing and transmitting means (20) to the position monitoring and control apparatus (29), characterized by the following steps: d) Deploying the anchor (10) onto the seabed (S); e) Applying tension to the anchor chain (22) connected to the anchor (10) while monitoring the data from the sensing and transmitting means (20), until a predetermined penetration depth into the seabed has been achieved.

10. The method of claim 9, wherein between step c) and step d), the vessel (26) position is adjusted based on information in said data signals, in order to ensure that the anchor is set in the desired position on the seabed (S).

11. The system of claim 2, wherein the protective housing (18') comprises fastening means (46) for the sensing and transmitting means (20) and elongate attachment elements (44a,b) for attachment to the anchor.