# US 2013/0239649 A1 · Method of determining the tension in a mooring line

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- Number: US 2013/0239649 A1
- Document ID: US20130239649A1
- Status: Published application
- Kind: A1
- Application number: 13/823,490
- Filed: 2011-09-15
- Published: 2013-09-19
- Earliest claimed: 2010-09-15
- Assignees: Catenary Testing Limited
- Inventors: Angus Jamieson
- Web page: https://patentgrep.com/patent/US20130239649A1

## CPC

- G01N 3/08: by applying steady tensile or compressive forces (G01N3/28 takes precedence)
- B63B 21/00: Tying-up; Shifting, towing, or pushing equipment; Anchoring ({of buoys B63B22/04;} dynamic anchoring B63H25/00 {; equipment for shipping on coasts, in harbours or on other fixed marine structures, e.g. for landing purposes, E02B})
- B63B 21/50: Anchoring arrangements {or methods} for special vessels, e.g. for floating drilling platforms or dredgers
- G01L 5/102: using sensors located at a non-interrupted part of the flexible member
- G01L 25/00: Testing or calibrating of apparatus for measuring force, torque, work, mechanical power, or mechanical efficiency
- B63B 2021/008: {Load monitors}
- G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q)
- B63B: SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING (arrangements of vessel ventilation, heating, cooling, or air-conditioning B63J2/00; floating substructures as supports of dredgers or soil-shifting machines E02F9/06)
- G01L: MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE (weighing G01G)

## Abstract

A method of calibrating a tension meter arranged to measure the tension in a mooring line of a marine asset is described. The method comprises the step of determining at least one characteristic of the catenary trajectory formed by the mooring line, and determining the tension in the mooring line based on the at least one characteristic. The characteristic may be, for example, shape of the catenary trajectory or elastic response of the mooring line. The determined tension is compared with a corresponding tension measurement from the tension meter to allow the tension meter to be calibrated. The method may be carried out during normal operations of the marine asset, such as drilling or hydrocarbon production. Computer implemented methods are described, as are methods of deriving a position map of the mooring lines. The invention may be implemented in a real-time monitoring system which forms a long-term or permanent feature of the marine asset.

## Claims

### Claim 1

A method of calibrating a tension meter arranged to measure the tension in a
mooring line of a marine asset, the method comprising:
determining at least one characteristic of the catenary trajectory formed by the mooring line;
determining the tension in the mooring line based on the at least one characteristic; and
comparing the determined tension with a corresponding tension measurement from the tension meter.

### Claim 2 (depends on 1)

The method of claim 1, wherein determining the characteristic of the catenary trajectory formed by the mooring line comprises determining a shape of the catenary trajectory.

### Claim 3 (depends on 2)

The method of claim 2, wherein determining the shape of the catenary trajectory comprises:
calculating a set of catenary trajectories between a connection point of the asset and an anchor point of the mooring line for a particular seabed profile;
measuring a depth of the mooring line at a known distance from the connection point; and
identifying a catenary trajectory corresponding to the known distance and measured depth.

### Claim 4 (depends on 2)

The method of claim 2, wherein determining the shape of the catenary trajectory comprises:
measuring a first depth of the mooring line at a first known distance from a connection point;
measuring a second depth of the mooring line at a second known distance from the connection point; and
identifying a catenary trajectory corresponding to the first and second known distances and measured depths.

### Claim 5 (depends on 4)

The method of claim 4, wherein determining the shape of the catenary trajectory further comprises measuring a third depth of the mooring line at a third known distance from the connection point.

### Claim 6 (depends on 1)

The method of claim 1, wherein determining the characteristic of the catenary trajectory formed by the mooring line comprises determining an elastic response of the mooring line.

### Claim 7 (depends on 6)

The method of claim 6, wherein determining the elastic response of the mooring line comprises:
calculating a set of elastic response profiles for the mooring line and a particular seabed profile for a range of mooring line tensions;
measuring the elastic response profile of the mooring line; and
comparing the measured elastic response profiles with the set of calculated elastic response profiles.

### Claim 8 (depends on 6)

The method claim 6, wherein measuring the elastic response profile of the mooring line comprises:
measuring the relative displacement of a connection point of the mooring line from an anchor point;
measuring the change in tension induced by the relative movement.

### Claim 9

(canceled)

### Claim 10 (depends on 1)

The method of claim 1, further comprising:
determining the characteristic of the catenary trajectory formed by the mooring line to identify the tension in the mooring line after a change in the tension in the mooring line; and
comparing the calculated tension with that observed from the tension meter.

### Claim 11 (depends on 1)

The method of claim 1, wherein calibrating the tension meter comprises determining a scale factor correction for the tension meter.

### Claim 12 (depends on 1)

The method of claim 1, wherein calibrating the tension meter comprises determining a bias error for the tension meter.

### Claim 13 (depends on 1)

The method of claim 1, wherein determining the tension of the mooring line comprises comparing the at least one characteristic of the catenary trajectory with an appropriate look-up table.

### Claim 14 (depends on 1)

The method of claim 1, wherein determining the tension of the mooring line comprises:
capturing an image of a portion of a mooring line between a connection point on the marine asset and a surface of the water;
analysing the image in a computer processor to determine the angle subtended by the mooring line at the connection point;
determining the tension in the mooring line from the determined angle.

### Claim 15 (depends on 14)

The method of claim 14 comprising determining the vertical height of the connection point of the mooring line;
determining the length of the mooring line between the connection point and the water surface; and
calculating the angle subtended by the mooring line at the connection point from the height and the length.

### Claim 16 (depends on 14)

The method of claim 14 comprising determining the length of the mooring line between the connection point and the water surface by analysing the image in the computer processor to count the number of chain links between the connection point and the water surface.

### Claim 17 (depends on 14)

The method of claim 14 comprising analysing the foreshortening of the chain links in the computer processor to determine the angle subtended by the mooring line at the connection point.

### Claim 18 (depends on 1)

The method of claim 1, wherein the method is repeated periodically.

### Claim 19

(canceled)

### Claim 20 (depends on 1)

The method of claim 1, wherein the method is carried out during normal operations of the marine asset.

### Claim 21 (depends on 1)

The method of claim 1, wherein the method is carried out during one or more operations selected from the group consisting of: drilling; wellbore construction and/or completion of a well; well clean-up; well intervention and/or workover; well stimulation and/or reservoir stimulation; wellbore and/or reservoir injection; well testing; or hydrocarbon production.

### Claim 22 (depends on 1)

A computer program for instructing a computer to perform the method of claim 1 when executed.

### Claim 23 (depends on 22)

The computer program of claim 22, wherein the computer program comprises a
generation module configured to generate a set of catenary trajectories, a
measurement module configured to provide a measurement of at least one characteristic of the catenary trajectory formed by the mooring line, and a processing module adapted to determine which generated trajectory corresponds to the at least one characteristic and output a corresponding tension value.

### Claim 24 (depends on 22)

The computer program of claim 22, wherein the computer program comprises a measurement module configured to provide a measurement of at least two characteristics of the catenary trajectory formed by the mooring line, and a processing module adapted to identify a catenary trajectory that corresponds to the at least two characteristics and output a corresponding tension value.

### Claim 25 (depends on 22)

The computer program of claim 22, wherein the computer program comprises a measurement module configured to provide a measurement of displacement of the asset and a measurement of a corresponding change in tension, a generation module configured to generate a set of elastic profiles, and a processing module configured to determine an elastic profile of the mooring line and to determine which generated elastic profile corresponds to the determined elastic profile and output a corresponding tension value.

### Claim 26 (depends on 22)

The computer program of claim 22, wherein the computer program comprises a seabed profile module configured to provide information relating to a seabed profile.

### Claim 27

(canceled)

### Claim 28

(canceled)

### Claim 29

A method of calibrating a tension meter arranged to measure the tension in a
mooring line of a marine asset, the method comprising:
determining at least one characteristic of a catenary trajectory formed by the mooring line to generate catenary characteristic data;
receiving the catenary characteristic data in one or more computer processors;
processing the catenary characteristic data using the one or more computer processors to determine the tension in the mooring line; and
comparing the determined tension with corresponding tension measurement data from the tension meter to generate calibration data.

### Claim 30 (depends on 29)

The method of claim 29, comprising outputting and/or displaying the calibration data from at least one of the one or more computer processors.

### Claim 31

A method of determining the tension in a mooring line of a marine asset, the method comprising:
determining an elastic response of the mooring line; and
determining the tension in the mooring line from the elastic response of the mooring line.

### Claim 32 (depends on 31)

The method of claim 31, wherein determining an elastic response of the mooring line comprises generating a set of elastic response profiles for a range of tension values, measuring an elastic response profile of the mooring line, and identifying a generated elastic response profile that corresponds with the measured elastic response profile.

### Claim 33 (depends on 31)

The method of claim 31, further comprising calculating a set of elastic response profiles for the mooring line and a particular seabed profile for a range of mooring line tensions;
measuring the elastic response profile induced upon the mooring line; and comparing the measured elastic response profiles with the set of calculated elastic response profiles

### Claim 34 (depends on 33)

The method of claim 33, wherein measuring an elastic response profile comprises determining a displacement between a connection point on the asset at one end of the mooring line and an anchor point at the opposite end of the mooring line, and determining the change in tension on the mooring line effected by the displacement.

### Claim 35

(canceled)

### Claim 36

(canceled)

### Claim 37 (depends on 31)

The method of claim 31, wherein the method is repeated periodically.

### Claim 38

(canceled)

### Claim 39 (depends on 31)

The method of claim 31, wherein the method is carried out during normal operations of the marine asset.

### Claim 40 (depends on 31)

The method of claim 31, wherein the method is carried out during one or more operations selected from the group consisting of: drilling; wellbore construction and/or completion of a well; well clean-up; well intervention and/or workover; well stimulation and/or reservoir stimulation; wellbore and/or reservoir injection; well testing; or hydrocarbon production.

### Claim 41 (depends on 31)

A computer program for instructing a computer to perform the method of claim 31 when executed.

### Claim 42 (depends on 41)

The computer program of claim 41, wherein the computer program comprises a measurement module configured to provide a measurement of displacement of the asset and a measurement of a corresponding change in tension, a generation module configured to generate a set of elastic response profiles, and a processing module configured to determine an elastic response profile of the mooring line and to determine which generated elastic response profile corresponds to the determined elastic response profile and output a corresponding tension value.

### Claim 43 (depends on 41)

The computer program of claim 41, wherein the computer software comprises a seabed profile module configured to provide information relating to a seabed profile.

### Claim 44

(canceled)

### Claim 45

(canceled)

### Claim 46 (depends on 1)

A method of determining the position of one or more mooring lines of a marine asset, the method comprising carrying out the method of claim 1, and deriving the position of the one or more mooring lines from a determined tension.

### Claim 47 (depends on 46)

The method of claim 46, further comprising generating a display of the position of the one or more mooring lines.

### Claim 48 (depends on 46)

The method of claim 46, wherein the method is carried out during normal operations of the marine asset.

### Claim 49 (depends on 46)

The method of claim 46, wherein the method is carried out during one or more operations selected from the group consisting of: drilling; wellbore construction and/or completion of a well; well clean-up; well intervention and/or workover; well stimulation and/or reservoir stimulation; wellbore and/or reservoir injection; well testing; or hydrocarbon production.

### Claim 50 (depends on 1)

A method of monitoring the position of one or more mooring lines of a marine asset, the method comprising:
calibrating a tension meter of the marine asset according to the methods of claim 1 at a first time;
determining the position of the one or more mooring lines at the first time;
recalibrating the a tension meter of the marine asset according to the methods of claim 1 at a second later time; and
determining the position of the one or more mooring lines at the second later time.

### Claim 51 (depends on 50)

A method of producing a real-time representation of the position of one or more mooring lines of a marine asset, the method comprising repeating the method of claim 50 at a plurality of time intervals.

### Claim 52 (depends on 50)

The method of claim 50, wherein the method is carried out during normal operations of the marine asset.

### Claim 53 (depends on 50)

The method of claim 50, wherein the method is carried out during one or more operations selected from the group consisting of: drilling; wellbore construction and/or completion of a well; well clean-up; well intervention and/or workover; well stimulation and/or reservoir stimulation; wellbore and/or reservoir injection; well testing; or hydrocarbon production.

### Claim 54 (depends on 50)

A computer program for instructing a computer to perform the method of claim 50 when executed.

### Claim 55 (depends on 29)

A method of determining the position of one or more mooring lines of a marine asset, the method comprising carrying out the method of claim 29 and deriving the position of the one or more mooring lines from a determined tension.

### Claim 56 (depends on 55)

The method of claim 55, further comprising generating a display of the position of the one or more mooring lines.

### Claim 57 (depends on 55)

The method of claim 55, wherein the method is carried out during normal operations of the marine asset.

### Claim 58 (depends on 55)

The method of claim 55, wherein the method is carried out during one or more operations selected from the group consisting of: drilling; wellbore construction and/or completion of a well; well clean-up; well intervention and/or workover; well stimulation and/or reservoir stimulation; wellbore and/or reservoir injection; well testing; or hydrocarbon production.