WO2016170310A1

WO2016170310A1 - Monitoring of floating production, storage and offload facilities

Info

Publication number: WO2016170310A1
Application number: PCT/GB2016/051071
Authority: WO
Inventors: Carl Tiltman; Andrew Clayson
Original assignee: Subsea Asset Location Technologies Limited; Ftl Subsea Limited
Priority date: 2015-04-20
Filing date: 2016-04-19
Publication date: 2016-10-27
Also published as: GB2556456A; KR20180015626A; AU2016251385A1; GB201506623D0; GB201717502D0

Abstract

A system for monitoring a floating production, storage and offload facility which is anchored by mooring lines comprises one or more of acoustic reflectors attached to one of more or the mooring lines. A vertical sonar system comprising a floating body and one or more sonars mounted below the floating body. The sonars scan the acoustic reflectors, receive the reflected acoustic signals. Each acoustic reflector is identified and its position transmitted to a user

Description

MONITORING OF FLOATING PRODUCTION, STORAGE AND OFFLOAD FACILITIES

Technical Field

This invention relates to systems for monitoring floating production, storage and offload (FPSO) facilities. Such facilities are normally used at sea as floating platforms for oil and/or gas exploration and extraction but may in future also be used also for exploration for and extraction of other minerals and materials. Such facilities are normally anchored to the sea bed using mooring lines for example in the form of cables, chains or other catenaries.

Background Art

GB2458810A (The Secretary of State for Defence) and WO2011/012877, and WO2012/007742 (both Subsea Asset Location Technologies Limited) all of whose contents are incorporated herein by reference, describe acoustic reflectors for underwater use. Broadly, an acoustic reflector for underwater use comprising a shell surrounding a core, the shell permits incident acoustic radiation, at certain frequencies, in part to pass through an acoustic window, into the core to be reflected back from the back of the shell opposite said window(s). The shell also conducts some of the incident acoustic radiation around the core to interfere constructively with the reflected radiation, the combined radiation being reradiated from the reflector towards the source of the incident radiation.

In WO2012/101423 (Subsea Asset Location Technologies Limited) – the contents of which are incorporated herein by reference - a method a method of identifying and locating an underwater acoustic reflector of a kind described in the previous paragraph comprises acoustically interrogating an underwater search area in which such an acoustic reflector may be present, identifying an object that apparently reflects the acoustic interrogation with a double echo, measuring the acoustic diameter of the object, and comparing that diameter with known acoustic diameters for underwater acoustic reflectors that may be present in the search area: thus accepting or rejecting the reflected acoustic wave as one being one potentially of interest.

That method may be further elaborated by including further steps including

a. measuring the target strength of the echoes in a double echo received from an object and rejecting the object as one of interest if the target strength in the first echo of a double echo exceeds that of the second echo;
b. measuring the total target strength of an echo from an object, the object being rejected as being a potential underwater acoustic reflector of interest if the target strength is less than a predetermined minimum;
c. measuring the acoustic width of an object and comparing that with the acoustic width of known acoustic reflectors, the object being rejected as being potentially an underwater acoustic reflector of interest if the acoustic width is not that of a known underwater acoustic reflector;
d. measuring the frequency response of an object, the object being accepted or rejected as being potentially an acoustic reflector of interest if the frequency response corresponds to the known frequency response of such an underwater reflector; and
e. measuring the phase response of an object, the object being accepted or rejected as potentially an underwater acoustic reflector of interest if the phase response corresponds to the known phase response of such an underwater acoustic reflector.

There is an issue associated with the anchoring of with floating production, storage and offload facilities in that at present it is difficult and expensive to monitor the anchor arrangements for deterioration and movement, especially movement which could give rise the facility concerned being dragged from its location or in an extreme case breaking away entirely. Existing methods require detailed analysis of results obtained from scanning using underwater remotely operated vehicles (ROVs) to inspect the anchor arrangements. Such methods are time consuming, expensive, and not entirely reliable.

Disclosure of Invention

According to the present invention a system of monitoring a floating production , storage and offload facility which is anchored by mooring lines comprises one or a plurality of acoustic reflectors attached to mooring lines of the floating production , storage and offload facility, and a sonar system; the sonar system comprises a floating body and one or more sonars mounted below the floating body, the vertical sonar system scanning the acoustic reflectors and receive the reflected acoustic signals, identifying the acoustic reflectors and their position transmitting the information to a user.

In one embodiment the sonar system comprises a plurality of sonars suspended in a vertical array below the floating body.

In another embodiment the sonar system is attached to the floating body which can be the floating production, storage and offload facility itself.

By using acoustic reflectors of the kind described in WO2012/007742 and the method set out in WO2012/101423, the acoustic reflectors can be distinguished positively from other reflectors in the neighbourhood and furthermore the acoustic reflectors are robust for use in severe environments.

The sonar system is preferably self-powered, for example using a stored energy source such as lithium-ion batteries. Preferably the sonars have steerable sonar beams.

Brief Description of Drawings

In order that the invention might be more fully understood, examples will be described with reference to the accompanying drawings in which:

Figure 1 shows a schematic perspective view of a floating production, storage and offload facility monitored in accordance with the invention:

Figure 2 shows a closer view of the facility of figure 1;

Figure 3 shows detail of the sonar and signal transmission arrangements of the invention; and

Figures 4A and 4B are plots of recorded transmissions from a system as illustrated in figures 1 to 3.

Description of Examples

In figures 1 to 3 a floating production, storage and offload facility (FPSO) comprises a platform 1 floating on the sea surface S and anchored to the seabed with mooring lines in the form of cables or catenaries 2. The mooring lines 2 pass through a turret 12 extending below the platform 1. A pipe 4, passing through the turret 12 connects the platform to a pipeline (not shown). Acoustic reflectors 3 are attached to the catenaries either individually or in hanging strings, likewise further acoustic reflectors 5 are hung from the pipe.

The acoustic reflectors used in the example are spherical reflectors with a glass fibre reinforced polyphthalamide shell comprising such as Zytel® HTN51G25HSL with a RTV12 core as described in WO2012/007742. The reflectors are readily deployable and can be retrofitted to exiting production, storage and offload facilities using an underwater remotely operated vehicle. Once in place reflectors of that kind can be left for very many years requiring no maintenance or sources of power. They have no effect on the mooring lines 2. The population of reflectors and their spacing is matched to the area of interest and the monitoring requirement.

A number of sonars 6 are suspended vertically one below another on a cable 7 from spar buoy 10 floating on the sea surface S and held vertically by clump weight 9 at the end of cable 7. The combination of buoy 10 and sonars 6 is self-powered, for example by rechargeable lithium-ion batteries on board the buoy and electrically connected to the sonars 6. The sonars 6 have steerable beams 8 which are reflected from the reflectors 3 and 5 enabling their individual positions to be identified automatically using systems as described tin WO2012/101423. The data is transmitted by an antenna 11 to a user on board the production, storage and offload facility or nearby in a ship, land, aircraft or helicopter.

Figures 4A and 4B illustrate transmitted traces from sonar scans carried out using the invention. The scans are from taken from a sonar array comprising sonars 6 mounted on a vertical cable 7 from a spar buoy 10 , As can be seen in figure 4A the reflectors 2 are substantially aligned with clear double echoes as is characteristic of the reflectors of WO2012/007742. However, as can be seen in figure 4B a scan taken a few seconds later, shows that one of the reflectors in particular has moved quite significantly, and the mooring line in the form of a cable or catenary to which it is attached has possibly become slack.

The sonar array comprising the buoy 10, sonars 6 and cable 7 with its clump weight 9, is rapidly deployable and required no external power source. It allows for on board processing on the buoy providing the operator, wherever the operator is located, with the information that the operator needs and reduces or eliminates the need for or additional data analysis , which has been the situation until now using conventional ways of monitoring floating production, storage and offload facilities. The sonar array comprising the buoy 10, sonars 6 and cable 7 with its clump weight 9, is rapidly deployable and required no external power source. It allows for on board processing on the buoy providing the operator, wherever the operator is located, with the information that the operator needs and reduces or eliminates the need for or additional data analysis , which has been the situation until now using conventional ways of monitoring floating production, storage and offload facilities.

In an alternative configuration, acoustic reflectors 3 are attached to each mooring line 2 near to the hull of platform 1. The acoustic reflectors 3 are attached singly or in a cluster to each mooring line 3. One or more sonars 8 are mounted below the floating body and have their sonar heads directed at each individual acoustic reflector cluster or cluster (typically there are four clusters) typically located on the mooring lines at each quarter of the FPSO at bow and stern. The sonar heads can be attached to the hull of the floating production, storage and offload facility, for example, magnetically. Connecting cables will need to be routed down the hull of the floating production, storage and offload facility. The output of the sonars will be monitored as described with reference to figures 1 to 4.

In a similar configuration, the connecting cable to the sonars is routed through guide tubes in the turret 12 (this is not only practical in all some but not all set ups) - again the sonar(s) would be attached to the platform 1 hull for example, magnetically.

Claims

A system for monitoring a floating production, storage and offload facility which is anchored by mooring lines comprising one or a plurality of acoustic reflectors attached to one or more mooring lines of the floating production , storage and offload facility, and a vertical sonar system comprising a floating body and one or more of sonars mounted below the floating body, the sonars scanning the acoustic reflectors and receiving the reflected acoustic signals, identifying the acoustic reflectors and their position transmitting the information to a user
A system according to claim 1 in which the one or more sonars comprise a plurality of sonars suspended in a vertical array below the floating body.
A system according to claim 1 in which the floating production, storage and offload facility and floating body are the same body.
A system according to claim 3 in which the one are a cluster of sonar reflectors is attached to one or more of the mooring lines and one or more sonars attached below the floating production , storage and offload facility is directed at each of the acoustic reflectors or cluster of reflectors.
A system according to claim 3 or 4 in which the mooring lines and connecting cables to the sonars pass through the turret of the floating production, storage and offload facility.
A system according to any one of claims 3 to 5 in which the sonars are attached to the hull of the floating production, storage and offload facility magnetically.
The system according to any preceding claim in which the vertical sonar system is self-powered.
The system according to any preceding claim in which the sonars have steerable sonar beams.