GB2475337A

GB2475337A - Subsea acoustic probe apparatus for monitoring oil risers

Info

Publication number: GB2475337A
Application number: GB0920105A
Authority: GB
Inventors: Shaun Dunn; Stefan Arndt; Graham Brown
Original assignee: Sonardyne International Ltd
Current assignee: Sonardyne International Ltd
Priority date: 2009-11-17
Filing date: 2009-11-17
Publication date: 2011-05-18
Also published as: GB0920105D0

Abstract

A subsea probe apparatus 100 comprises a subsea acoustic probe 102 for propagation of acoustic signals with respect to a riser wall 104. The subsea probe 102 is operably coupled to a propagation interface medium 108 for propagation of the acoustic signals therethrough and replacing an ambient medium, for example, the sea water. In just one example, the interface medium may be formed from a silicone based material which acoustically couples the acoustic probe 102 to the external surface 106 of the riser 104.

Description

SUBSEA PROBE APPARATUS, METHOD OF MANUFACTURE THEREOF,

SUBSEA PROBE SET APPARATUS AND SUBSEA STRUCTURE

MONITORING SYSTEM

[0001] The present invention relates to a subsea probe apparatus of the type that, for example, comprises a subsea acoustic probe disposed opposite a target structure to be monitored, for example a riser, such as a flexible riser. The present invention also relates to a subsea probe set of the type that, for example, comprises a subsea acoustic probe disposed opposite a target structure to be monitored, for example a riser, such as a flexible riser. The present invention further relates to a subsea structure monitoring system of the type that, for example, comprises a subsea acoustic probe disposed opposite a target structure to be monitored, for example a riser, such as a flexible riser. The present invention yet further relates to a method of manufacturing an acoustic probe for a subsea environment, the method being of the type that, for example, provides a subsea acoustic probe disposed opposite a target structure to be monitored, for example a riser, such as a flexible riser.

[0002] It is known to dispose structures below the surface of the sea in relation to marine projects. The marine environment is a relatively hostile environment, structures disposed beneath the sea surface being exposed to changing forces and corrosive seawater. It is therefore important to be able to monitor subsea structures in order to ensure that the structural integrity of the subsea structures is maintained and, if detected, repair or replace damaged parts of the subsea structure or even replace the subsea structure in its entirety.

[0003] One known type of subsea structure is a riser. The riser is a pipe through which liquid, for example a hydrocarbon, such as oil, travels. The riser has one end at, for example, the seabed and extends upwards to a drilling ship, an oil rig or a so-called Floating Production, Storage and Offloading (FPSO) vessel located on or above the surface of the sea.

[0004] The riser can comprise a multi-layer structure to provide strength and/or flexibility. In this regard, one type of so-called flexible riser comprises an outer armour layer and an inner armour layer. In order to ensure that the riser is able to perform a producing function of reliably carrying fluid, sometimes referred to as "product" from the seabed to a structure on or above the surface of the sea, or a non-producing function, for example the downwards transport of mud towards the seabed, it is necessary to detect whether the inner and/or outer armour layers are flooded in order to determine when remedial action is necessary to avoid leakage from the riser or indeed catastrophic failure of the riser.

[0005] One known technique for monitoring the structural status of the flexible riser is through use of an ultrasonic transducer. Other communications and processing equipment is, of course, coupled to the ultrasonic transducer. In order to deploy the ultrasonic transducer, the ultrasonic transducer is immersed in a marine environment and taken to a measurement location by, for example a diver or a Remotely Operated Vehicle (ROV). When in-situ, the ultrasonic transducer is operated to transmit a high frequency acoustic signal into the wall of the riser and to observe the time of arrival and magnitude of any acoustic reflections off the various annulus layers within the riser. The ultrasonic transducer is then moved to another location for measurement, but is ultimately removed from the seawater for reasons that will become apparent hereinbelow.

[0006] Whilst it would be preferable to deploy ultrasonic transducers in a subsea environment in a manner that engenders occasional retrieval of the transducers for maintenance as opposed to temporary immersion of the ultrasonic transducers for brief periods of time sufficient only to make measurements, the ultrasonic probes used are typically intended for short term immersion in a low corrosion medium, for example ultrasound gel, and in respect of medical applications. Consequently, when the same types of ultrasonic probes are used for marine applications, a number of practical impediments exist.

[0007] Firstly, aeration of seawater located between a face of the ultrasonic transducer and an external surface of the riser impedes acoustic propagation, resulting in poor propagation of acoustic waves between the ultrasonic transducer and the riser. Additionally, the immersion of the ultrasonic transducer in seawater can result in the formation of deposits on the face the ultrasonic transducer. In this respect, the seawater calcifies the surface of the ultrasonic transducer, but also hard and soft biofouling typically occurs on and/or between the face of the ultrasonic transducer and the outer surface of the riser when the ultrasonic transducer is immersed in seawater. Such deposits on the face of the ultrasonic transducer and/or between the face of the ultrasonic transducer and the external surface of the riser also contribute to poor propagation of acoustic waves between the ultrasonic transducer and the riser.

[0008] Additionally, the corrosive properties of seawater, which is salinated, are well-documented and so it will be readily appreciated that seawater can cause the face of the ultrasonic transducer to corrode, thereby degrading the performance of the ultrasonic transducer and possibly eventually rendering the ultrasonic transducer inoperable. In this regard, corrosion of the housing and potting materials of the ultrasonic probe due to the high oxygen content of seawater, particularly at shallower depths, is also possible, as well as water seepage into the front face of the ultrasonic probe.

[0009] Additionally, the ultrasonic probe is at risk from damage during abutment of the probe with the riser caused by poor handling or collision with the riser.

[0010] Another difficulty encountered when deploying the ultrasonic probes relates to alignment. Use of a single ultrasonic probe can result in misalignment of the ultrasonic probe with a relevant part of the riser, for example an outer annulus wire, and hence incorrect measurements are taken.

[0011] According to a first aspect of the present invention, there is provided a subsea probe apparatus comprising: a subsea acoustic probe for propagation of acoustic signals with respect to a target, the subsea probe being operably coupled to a propagation interface medium for propagation of the acoustic signals therethrough and replacing an ambient medium.

[0012] The propagation interface medium may provide a propagation path through the ambient medium for the acoustic signals to propagate with respect to the target.

[0013] The propagation medium interface may comprise a non-aquatic medium.

The non-aquatic medium may be a non-seawater medium.

[0014] The propagation medium interface may be a portion of solid material for supporting propagation of the acoustic signals therethrough. The portion of solid material may be formed from a polymer. The portion of solid material may be a silicone.

[0015] The propagation medium interface may comprise a housing comprising a liquid propagation material therein for supporting propagation of the acoustic signals therethrough. The housing may be a thin shell, for example an elastomeric shell, containing the liquid or gel propagation material.

[0016] The housing may define an open cavity for receiving the liquid propagation material therein; the housing may be substantially closed by a surface of the subsea acoustic probe.

[0017] The propagation medium interface may be compliant at least at one end thereof.

[0018] The propagation medium interface may comprise a coupling end for abutting a riser; the coupling end may be arranged so as to receive a side cylindrical surface for the riser.

[0019] The propagation medium interface may be arranged to taper outwards at one end thereof.

[0020] The propagation medium interface may be arranged to be flared.

[0021] The propagation medium interface may be arranged to be bell-shaped at one end thereof.

[0022] The propagation medium interface may be shaped at one end thereof to abut snugly a coupling surface.

[0023] The propagation medium interface may be arranged to encapsulate at least part of the subsea acoustic probe.

[0024] The propagation material interface may be arranged to envelop the subsea acoustic probe.

[0025] According to a second aspect of the present invention, there is provided a subsea probe set apparatus comprising: a plurality of subsea probe apparatuses, each of the plurality of subsea probe apparatuses being a subsea probe apparatus as set forth above in relation to the first aspect of the invention; wherein the plurality of probe apparatuses is spatially configured so as to maximise coincidence with a plurality of spaced targets.

[0026] The propagation material interface may be common to the plurality of subsea probe apparatuses.

[0027] The propagation material interface may be arranged to encapsulate at least part of the respective subsea acoustic probes of the plurality of subsea probe apparatuses.

[0028] The propagation material interface may be arranged to envelop the respective subsea acoustic probes of the plurality of subsea probe apparatuses.

[0029] The plurality of subsea acoustic probes may be arranged as a cluster.

[0030] The plurality of subsea acoustic probes may be arranged as an array. The array may be a linear array.

[0031] According to a third aspect of the present invention, there is provided a subsea structure monitoring system comprising: a subsea probe apparatus as set forth above in relation to the first aspect of the invention; and a target structure, the propagation medium interface of the subsea probe apparatus abutting the target structure for monitoring.

[0032] The system may further comprise a clamp mechanism to maintain the propagation medium interface in abutment with the target structure.

[0033] The target structure may be a riser.

[0034] According to a fourth aspect of the present invention, there is provided a method of manufacturing an acoustic probe for a subsea environment, the method comprising: providing a subsea acoustic probe for propagation of acoustic signals with respect to the target structure; operably coupling the subsea probe to a propagation interface medium for propagation of the acoustic signals therethrough and replacing an ambient medium.

[0035] It is thus possible to provide an apparatus, system and method capable of facilitating long-term immersion of acoustic probes in a seawater environment, the front face of the acoustic probe being free of seawater and the contact surface of the propagation medium interface rninimising ingress of seawater between the contact surface and a structure to be measured. Consequently, bio-fouling, organic growth and calcification is mitigated, both on the surface of the acoustic probe and an abutting region of an external surface of the structure to be measured, thereby improving the performance of the acoustic probe. Furthermore, the shaping of the contact end of the propagation interface medium assists correct alignment of the acoustic probe with the surface of the structure to be measured, thereby improving quality of acoustic coupling due to the acoustic probe being correctly (orthogonal) directed at the surface of the structure to be measured. The compliant nature of the propagation interface medium provides a degree of shock absorption from external influences, for example movement and/or forces and/or temperature, thereby minimising damage to the acoustic probe, whilst also facilitating good mechanical coupling of the acoustic probe to the structure to be measured.

[0036] At least one embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram of a subsea probe apparatus constituting an embodiment of the invention; Figure 2 is a schematic diagram of another subsea probe apparatus constituting another embodiment of the invention; Figure 3 (a) and (b) are schematic diagrams of a subsea probe set apparatus comprising the subsea probe apparatus of Figure 1 and/or the subsea probe apparatus of Figure 2, and constituting further embodiment of the invention; and Figure 4 (a) and (b) are schematic diagrams of another subsea probe set apparatus comprising the subsea probe apparatus of Figure 1 and/or the subsea probe apparatus of Figure 2, and constituting yet another embodiment of the invention.

[0037] Throughout the following description identical reference numerals will be used to identify like parts.

[0038] Referring to Figure 1, a subsea probe apparatus 100 comprises an acoustic probe 102, for example an ultrasonic probe comprising an ultrasonic transducer (not shown) disposed opposite a structure to be measured, for example a riser 104. The acoustic probe 102 comprises an output surface 105 through which acoustic signals propagate. In this example, the riser 104 is a flexible riser, although the skilled person should appreciate that the riser can be a rigid riser.

The acoustic probe 102 is any suitable acoustic probe, for example one of the IM series of immersion transducers available from Imasonic SAS, France.

[0039] The acoustic probe 102 is separated from an external surface 106 of the riser 104 by a propagation interface medium 108. The axial length of the propagation interface medium 108 from the output surface 105 of the acoustic probe to the external surface 106 of the riser 104 is between about 1 mm and about 25mm, for example between about 1mm and about 10 mm. In this example, the riser 104 has a multi-layer structure, the external surface 106 being of an external circumferential layer 110, the external layer 110 being adjacent an intermediate circumferential layer 112. The intermediate layer 112 is adjacent an inner circumferential layer 114. In order to provide the riser 104 with adequate strength and resistance to puncture, the external layer 110 of the riser 104 is formed from slanted armour wires. Similarly, the intermediate layer 112 is also formed from slanted armour wires.

[0040] When monitoring integrity of the riser 104, if the intermediate and external armour layers 112, 110 of the riser 104 are not flooded with seawater, a reflection of a signal emitted by the acoustic probe 102 is significantly attenuated. However, if the intermediate and external armour layers 112, 110 of the probe 104 are flooded, the structure of the reflected signal can be used to determine the thickness of the outer armour layer 110 to an accuracy of around 0.2mm.

[0041] In this example, the propagation interface medium 108 is formed from a silicone-based material and acoustically couples the acoustic probe 102 to the external surface 106 of the riser 104. However, the skilled person should appreciate that any suitable acoustic couplant can be employed to form the propagation interface medium, for example any suitable polymer, for example polyether block amide or polyethylene. Irrespective of the primary couplant used to bridge the space between the acoustic probe 102 and external surface 106 of the riser 104, the couplant has to be able to retain a shape and so, in this example is a compliant solid. The skilled person should appreciate that liquids can also be employed when retained within a housing that has a like shape to that of the propagation interface medium 108 formed from a compliant solid material as described above. In this respect, examples of suitable liquids, which include gels, are: propylene glycerol, glycerine, silicone gel or any other suitable gel-based material. In such embodiments, it is beneficial if the housing is formed from a compliant material. In some embodiments, the housing can be a thin shell, for example an elastomeric shell, containing the liquid or gel propagation material. It is, of course, beneficial to match the acoustic impedance of the material used to form the propagation interface medium 108 as much as possible with the acoustic impedance of the wall of the riser 104.

[0042] A useful feature of any material used is that it exhibits minimal degradation in the presence of seawater for long periods of time, for example one to 10 years.

[0043] The propagation interface medium 108 provides a medium through which acoustic signals can propagate with minimum attenuation, particularly but not exclusively ultrasonic signals, having frequencies of between about 3MHz and about 5MHz.

[0044] For completeness, it should be appreciated that the acoustic probe 102 is electrically coupled to electronic hardware by an electrical cable 118, for example a circuit board comprising a driver module (not shown), a signal processing module (not shown) and, optionally, communications module (not shown).

[0045] In this example, the acoustic probe 102 is part encapsulated in the propagation interface medium 108; although in another embodiment (Figure 2), the acoustic probe 102 can be completely enveloped in the propagation interface medium 108. Referring back to Figure 1, the propagation interface medium 108 tapers outwards or flares outwards with axial distance from the acoustic probe 102. The propagation interface medium 108 has a coupling end 116, which in this example is substantially bell-shaped in cross-section. The above-described shaping at the coupling end 116 of the propagation interface medium 108 results in a thinned region of deformable peripheral material that improves sealing when the propagation interface medium 108 abuts the external surface 106 of the riser 104.

[0046] Turning to Figure 2, in addition to or as an alternative to the tapered or flared shape formed at the coupling end 116 of the propagation interface medium 108, the coupling end 116 of the propagation interface medium 108 is shaped to define a substantially cylindrical surface having a vertical axis. In this regard, the coupling end 116 of the propagation interface medium 108 defines a concave surface 120 for abutment with the external surface 106 of the riser 104. The radius of the concave surface 120 is set according to the radius of the riser 104. Clearly, in some examples, where the axial length of the propagation interface medium 108 is towards a shorter end of the range of lengths set out above, the shapes formed at the coupling end 116 of the propagation interface medium 108 are not always possible.

[0047] In order to form the propagation interface medium 108, a mould having any of the shapes described above is provided and a curable or settable liquid or gel is poured into the mould until solid. Thereafter, the formed propagation interface medium 108 is removed from the mould. As will be appreciated by the skilled person, the acoustic probe 102 can be immersed in the propagation interface medium 108 while in a liquid or gel state so that the liquid or gel sets in a manner such that the propagation interface medium 108 is coupled to the acoustic probe 102.

[0048] In operation, the subsea probe apparatus 100 is brought into abutment with the external surface 106 of the riser 104. The subsea probe apparatus 100 is then urged against the external surface 106 of the riser 104 in order to expel seawater from between the external surface 106 of the riser 104 and the coupling end 116 of the propagation interface medium 108 and to minimise ingress of seawater between the concave surface 120 of the coupling end 116 of the propagation interface medium 108 and the external surface 106 of the riser 104. In this regard, the shape of the coupling end 116 is such that a sufficiently large surface area, for example between about 25cm2 and about 250cm2, is defined to achieve the expulsion of seawater and minimisation of ingress of seawater described above. After abutment with the riser 104, the subsea probe apparatus is then clamped to the riser 104 in the position achieved using any suitable clamping arrangement.

[0049] In another embodiment, more than one subsea probe apparatuses 100 can be grouped together to improve reliability of measurement. When monitoring the integrity of the riser 104 in order to detect flooding of the riser 104, it is desirable to measure the thickness of the external layer 110 of the riser 104, because as described above, measurement of the thickness of the external layer can be achieved to a particularly good degree of accuracy when the riser 104 is flooded. However, it is necessary to measure the thickness of the armour wires 122 and so misalignment of the acoustic probe 102 with a gap between wires as opposed to alignment with one of the wires will result in erroneous measurements.

Consequently, it is desirable for acoustic signals 124 emitted by the acoustic probe to be directed to the armour wires as opposed to the gaps therebetween.

[0050] In this regard, the exact location of an armour wire 122 as opposed to a gap separating armour wires is not evident from the exterior of the riser 104 when the subsea probe apparatus 100 is being fitted to the external surface 106 of the riser 104. Consequently, more than one subsea probe apparatuses 100, for example four subsea probe apparatuses 100, are deployed in a configuration, for example an array, such as a linear array, which ensures that at least one acoustic probe of the plurality of acoustic probes of the more than one subsea probe apparatuses 100, directs acoustic energy 124 towards one of the armour wires.

This can be seen in Figure 3 by the uppermost and lowermost acoustic probes being aligned with the central two armour wires 122.

[0051] Of course, an array is only one example of a configuration of the subsea probe apparatuses 100 and other configurations are conceivable, for example a cluster (Figure 4), such as a staggered cluster. As can be seen in Figure 4, the inner two acoustic probes are aligned with the central two armour wires 122.

[0052] In either of the above two embodiments relating to use of more than one subsea probe apparatuses 100, the propagation interface medium 108 can be common to all or some of the acoustic probes 102 in order to ensure a predetermined separation between acoustic probes 102, i.e. some or all of the acoustic probes 102 share the propagation interface medium 108. Furthermore, if desired, some or all of the acoustic probes 102 can be part-enveloped by the propagation interface medium 108 or completely encapsulated in the propagation interface medium 108.

Claims

Claims: 1. A subsea probe apparatus comprising: a subsea acoustic probe for propagation of acoustic signals with respect to a target, the subsea probe being operably coupled to a propagation interface medium for propagation of the acoustic signals therethrough and replacing an ambient medium.
2. An apparatus as claimed in Claim 1, wherein the propagation interface medium provides a propagation path through the ambient medium for the acoustic signals to propagate with respect to the target.
3. An apparatus as claimed in Claim 1 or Claim 2, wherein the propagation medium interface comprises a non-aquatic medium.
4. An apparatus as claimed in any one of the preceding claims, wherein the propagation medium interface is a portion of solid material for supporting propagation of the acoustic signals therethrough.
5. An apparatus as claimed in Claim 4, wherein the portion of solid material is formed from a polymer.
6. An apparatus as claimed in Claim 5, wherein the portion of solid material is a silicone.
7. An apparatus as claimed in any one of Claims 1 to 3, wherein the propagation medium interface comprises a housing comprising a liquid propagation material therein for supporting propagation of the acoustic signals thereth rough.
8. An apparatus as claimed in Claim 7, wherein the housing defines an open cavity for receiving the liquid propagation material therein, the housing being closed by a surface of the subsea acoustic probe.
9. An apparatus as claimed in any one of the preceding claims, wherein the propagation medium interface is compliant at least at one end thereof.
10. An apparatus as claimed in any one of the preceding claims, wherein the propagation medium interface comprises a coupling end for abutting a riser, the coupling end being arranged so as to receive a side cylindrical surface for the riser.
11. An apparatus as claimed in any one of the preceding claims, wherein the propagation medium interface is arranged to taper outwards at one end thereof.
12. An apparatus as claimed in any one of the preceding claims, wherein the propagation medium interface is arranged to be flared.
13. An apparatus as claimed in any one of the preceding claims, wherein the propagation medium interface is arranged to be bell-shaped at one end thereof.
14. An apparatus as claimed in any one of the preceding claims, wherein the propagation medium interface is shaped at one end thereof to abut snugly a coupling surface.
15. An apparatus as claimed in any one of the preceding claims, wherein the propagation medium interface is arranged to encapsulate at least part of the subsea acoustic probe.
16. An apparatus as claimed in any one of the preceding claims, wherein the propagation material interface is arranged to envelop the subsea acoustic probe.
17. A subsea probe set apparatus comprising: a plurality of subsea probe apparatuses, each of the plurality of subsea probe apparatuses being a subsea probe apparatus as claimed in any one of the preceding claims; wherein the plurality of probe apparatuses is spatially configured so as to maximise coincidence with a plurality of spaced targets.
18. An apparatus as claimed in Claim 17, wherein the propagation material interface is common to the plurality of subsea probe apparatuses.
19. An apparatus as claimed in Claim 17 or Claim 18, wherein the propagation material interface is arranged to encapsulate at least part of the respective subsea acoustic probes of the plurality of subsea probe apparatuses.
20. An apparatus as claimed in Claim 17 or Claim 18 or Claim 19, wherein the propagation material interface is arranged to envelop the respective subsea acoustic probes of the plurality of subsea probe apparatuses.
21. An apparatus as claimed in any one of claims 17 to 20, wherein the plurality of subsea acoustic probes are arranged as a cluster.
22. An apparatus as claimed in any one of claims 17 to 20, wherein the plurality of subsea acoustic probes is arranged as an array.
23. An apparatus as claimed in Claim 22, wherein the array is a linear array.
24. A subsea structure monitoring system comprising: a subsea probe apparatus as claimed in any one of Claims 1 to 16; and a target structure, the propagation medium interface of the subsea probe apparatus abutting the target structure for monitoring.
25. A system as claimed in Claim 24, further comprising: a clamp mechanism to maintain the propagation medium interface in abutment with the target structure.
26. A system as claimed in Claim 24 or Claim 25, wherein the target structure is a riser.
27. A method of manufacturing an acoustic probe for a subsea environment, the method comprising: providing a subsea acoustic probe for propagation of acoustic signals with respect to the target structure; operably coupling the subsea probe to a propagation interface medium for propagation of the acoustic signals therethrough and replacing an ambient medium.
28. A subsea probe apparatus substantially as hereinbefore described with reference to the accompanying drawings.
29. A subsea probe set apparatus substantially as hereinbefore described with reference to the accompanying drawings.
30. A subsea structure monitoring system substantially as hereinbefore described with reference to the accompanying drawings.
31. A method of manufacturing an acoustic probe substantially as hereinbefore described with reference to the accompanying drawings.