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Title:
SENSOR MODULE FOR A MARINE BUOYANCY UNIT AND A SYSTEM AND METHOD FOR USING THE SAME
Document Type and Number:
WIPO Patent Application WO/2019/028500
Kind Code:
A1
Abstract:
A sensor module for a marine buoyancy unit is disclosed, the marine buoyancy unit configured to be releasably connected to a marine riser. The sensor module comprises a housing releasably connectable at least partially within the marine buoyancy unit, a sensor disposed within the housing and configured to measure a parameter associated with the riser, in particular a dynamic condition parameter, which can be logged and communicated to a base station.

Inventors:
JAYASINGHE KANISHKA MILINDA (AU)
MARCOLLO HAYDEN (AU)
POTTS ANDREW ELMHIRST (AU)
Application Number:
PCT/AU2018/050820
Publication Date:
February 14, 2019
Filing Date:
August 07, 2018
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
AMOG TECH PTY LTD (AU)
International Classes:
E21B17/01; B63B21/50; E21B7/12; E21B47/01; F16L1/24
Domestic Patent References:
WO2017000052A12017-01-05
WO2002088587A12002-11-07
Foreign References:
US9038730B22015-05-26
GB2430259A2007-03-21
GB2541722A2017-03-01
Attorney, Agent or Firm:
FPA PATENT ATTORNEYS PTY LTD (AU)
Download PDF:
Claims:
CLAIMS

1 . A sensor module for a marine buoyancy unit, the marine buoyancy unit configured to be releasably connected to a marine riser, the sensor module comprising: a housing releasably connectable at least partially within the marine buoyancy unit; a sensor disposed within the housing and configured to measure a parameter associated with the riser; and a communication unit operatively coupled to the sensor and configured to transmit the parameter. 2. The sensor module of claim 1 , wherein the housing is dimensioned so as to be releasably receivable at least partially within a complementarily dimensioned recess or cavity within the buoyancy unit.

3. The sensor module of claim 2, wherein the housing is fully receivable within the recess or cavity such that an outer surface of the housing is flush or substantially flush with an adjacent outer surface of the buoyancy unit exposed to water.

4. The sensor module of any preceding claim, wherein the housing includes a cover, to provide sealing closure of the housing and allowing access to the sensor and communication unit.

5. The sensor module of claim 4, wherein the sensor and communication unit are attached to the cover, such that removal of the cover from the housing enables removal of the sensor and communication unit from the housing.

6. The sensor module of claim 5, wherein the sensor and communication unit are mountable to a structural element fixedly attached to the inside of the cover.

7. The sensor module of any preceding claim, wherein the housing includes one or more first engagement features configured to respectively engage one or more second engagement features of the buoyancy unit so as to be releasably secured within the recess or cavity.

8. The sensor module of any preceding claim, including a mounting plate configured for releasable attachment to the housing and to the buoyancy unit.

9. The sensor module of claim 8, wherein said second engagement features of the buoyancy unit comprise anchors secured into the buoyancy unit, to which the mounting plate may be releasably secured.

10. The sensor module of claim 8 or claim 9, wherein said first engagement features of the housing are configured both to close the housing and to releasable secure the housing to said second engagement features of the buoyancy unit to the mounting plate.

1 1 . The sensor module of any preceding claim, configured for selective orientation of the housing when connecting with the marine buoyancy unit. 12. The sensor module of any preceding claim, wherein the sensor disposed within the housing is an inertial measurement unit, able to measure one or more of force, acceleration and angular rate of rotation in one or more axes perpendicular to a central longitudinal axis of the riser.

13. The sensor module of claim 12, including one or more of: a controller, a pressure sensor, a temperature sensor, a global positioning system (GPS), a further

communication unit, a memory unit, an RFID tag, a power source, and a means of replenishing the power source.

14. The sensor module of claim 13 including a pressure sensor and a controller, the controller configured to manage operation of the sensor module in accordance with detection of pressure indicating whether the housing is above or below sea level.

15. The sensor module of claim 13 or claim 14, including a memory unit arranged to store data measured by the sensor unit, the communication unit configured to transmit the parameter to the memory unit.

16. The sensor module of any one of claims 13 to 15, wherein the communication unit includes a transceiver configured to transmit the data from the sensor module to a remote base station.

17. A system comprising: one or more marine risers; and one or more buoyancy units releasably connected about a respective one of said one or more marine risers; wherein each of the one or more buoyancy units includes a sensor module configured to measure and transmit a parameter associated with a respective one of said one or more marine risers.

18. A method of monitoring a marine riser comprising:

disposing a buoyancy unit on or about the marine riser, wherein the buoyancy unit includes a sensor module configured to measure and transmit a parameter associated with the riser; and

receiving the parameter associated with the riser and analysing the parameter to monitor the riser.

19. A method of monitoring a marine riser, comprising: providing a buoyancy unit having a recess or cavity; disposing a sensor module in the recess or cavity, the sensor module including equipment to measure dynamic conditions experienced by the sensor module; and disposing the buoyancy unit on or about the marine riser, such that the sensor module is mounted to the buoyancy unit in such a way that the dynamic conditions experienced by the sensor represent at least in part the dynamic conditions associated with the riser, the sensor module equipment logging the data representing said measured dynamic conditions while the riser is disposed under water.

20. The method of claim 19, the sensor module configured to transmit the data when in communication with an external receiver unit, the method including the step of analysing the data to monitor the structural health of the riser.

21 . The method of claim 19 or claim 20, wherein the buoyancy unit is provided with one or more engagement features at selected locations for securement of the sensor module to the buoyancy unit, the step of disposing the sensor module in the recess or cavity realised by way of an engagement ensuring a prescribed position and alignment of the sensor module measuring equipment relative to the marine riser once the buoyancy unit is in place around the riser.

22. The method of any one of claims 19 to 21 , wherein the sensor module comprises a housing with a hollow interior accessible from the exterior by removal of a portion of the housing when the riser is out of the water, and the method includes the step of disposing the sensor module equipment within the sensor module by structurally mounting the sensor module equipment to said portion of the housing, in such a way that accessing the interior of the sensor module results in removal of the equipment from the sensor module.

Description:
Sensor module for a marine buoyancy unit and a system and method for using the same

Field of the invention

The present invention relates to the monitoring of marine or subsea structures, such as risers, pipes, flow-lines, umbilicals, cables, and the like.

Background of the invention

In off-shore hydrocarbon production, drilling risers are utilised to deliver fluid from a subsea well to a drilling or production vessel at the surface and vice versa. Drilling risers are typically subject to bending, twisting, and longitudinal tension and

compression due to water currents and movements of the production vessel.

It is known for drilling risers to be cladded or 'dressed' with buoyancy units of typically low-density syntactic foam to offset or reduce the submerged weight and tensile stress experienced by a long riser string in the water. One or more buoyancy units may be releasably attached about a riser section during deployment of the riser string from the production vessel. Some buoyancy units, such as those described in WO 2016/205898, may be configured to reduce vibration and/or drag on the riser string.

So as to ensure correct and safe operation of the riser string, it is beneficial to monitor the mechanical stress experienced by individual riser sections that constitute the riser string. Examples of such 'structural health monitoring systems' are described in US 2012/0031620, US 7,721 ,61 1 , and AU 2013273664. These monitoring systems typically include one or more sensors disposed in or on a riser section that measure and record motions from which the mechanical stress and strain experienced by the riser section can be deduced. This data may be analysed upon retrieval of the riser section at the production vessel to determine, for example, the remaining operational life of the riser section before fatigue failure, or to update the remaining fatigue capacity of the wellhead on which the drilling riser is operating. Other methods of such monitoring involve underwater remotely operated vehicles (ROVs) obtaining data in close proximity to each sensor or wires that run along the drilling riser to the surface. However such approaches are generally not preferred due to the complexity in deployment and in retrieving data, with potential operational delays to the drilling schedule. The present invention is directed to addressing one or more deficiencies of the the abovementioned marine structural health monitoring systems, or at least to providing a useful alternative solution.

Reference to any prior art in the specification is not an acknowledgment or suggestion that this prior art forms part of the common general knowledge in any jurisdiction or that this prior art could reasonably be expected to be understood, regarded as relevant, and/or combined with other pieces of prior art by a skilled person in the art.

Summary of the invention In a first aspect, the present invention provides a sensor module for a marine buoyancy unit, the marine buoyancy unit configured to be releasably connected to a marine riser, the sensor module comprising: a housing releasably connectable at least partially within the marine buoyancy unit; a sensor disposed within the housing and configured to measure a parameter associated with the riser; and a communication unit operatively coupled to the sensor and configured to transmit the parameter.

Preferably, the housing is dimensioned so as to be releasably receivable at least partially within a complementarily dimensioned recess or cavity within the buoyancy unit. More preferably, the housing is fully receivable within the complementarily dimensioned recess or cavity such that an outer surface of the housing is flush or substantially flush with an adjacent outer surface of the buoyancy unit exposed to water.

The housing preferably includes a cover, to provide sealing closure of the housing and allowing access to the sensor and communication unit. The cover may be removable, or alternatively may be hingedly or otherwise connected with the rest of the housing.

The sensor and communication unit (and any other components of the sensor module, including a power source) may be attached to the cover, such that removal of the cover from the housing enables removal of those components from the housing. Preferably, the components are mountable to a structural element fixedly attached to the inside of the cover.

The housing may include one or more first engagement features configured to respectively engage one or more second engagement features of the buoyancy unit so as to be releasably secured within the recess or cavity. The one or more first and second engagement features may include a projection, detent, key, keyway, or recess.

In a preferred form, the sensor module includes a mounting plate configured for releasable attachment to the housing and to the buoyancy unit. In this way, the mounting plate affords firm, releasable securement of the housing within the recess or cavity.

The mounting plate may have a surface to be positioned substantially flush with an adjacent outer surface of the buoyancy unit exposed to water. Said second engagement features of the buoyancy unit preferably comprise anchors secured into the buoyancy unit, to which the housing or the mounting plate may be releasably secured (eg. by way of bolts). Said first engagement features of the housing (for example, one or more bolts) may be configured both to close the housing and to releasable secure the housing to said second engagement features of the buoyancy unit or to the mounting plate.

The parameter associated with the riser does not itself need be directly

measured; instead the sensor is able to measure a condition in the housing, which condition refers to said riser parameter.

The sensor disposed within the housing is preferably an inertial measurement unit (IMU). The IMU may include one or more accelerometers, gyroscopes, and magnetometers. Accordingly, the parameter measured by the IMU may be a specific force or acceleration of the housing and/or an angular rate of rotation of the housing. Advantageously, as the housing is releasably connectable within the buoyancy unit connected to the riser, the IMU may measure the specific force or acceleration and/or angular rate of rotation of the riser. Preferably, the IMU is configured to measure the acceleration and/or angular rate of rotation of the riser in at least two axes perpendicular to a central longitudinal axis of the riser. More preferably, the IMU is also configured to measure the acceleration and/or angular rate of rotation of the riser in an additional axis parallel to the central longitudinal axis of the riser.

Advantageously, the acceleration and/or angular rate of rotation of the riser (the 'IMU data') may be utilised to determine the amplitude and frequency of vibrations experienced by the riser due to any one or more of the following: water currents incident upon the riser, motion of a production vessel at the surface connected to the riser, and vibrations due to drilling/hydrocarbon production.

The housing may also include one or more of the following: a controller, a pressure sensor, a temperature sensor, a global positioning system (GPS), a further communication unit, a memory unit, a power source, and a means of replenishing the power source.

The controller may be configured to control any one or more of the IMU, the communication unit, the pressure sensor, the temperature sensor, the GPS, the memory unit, the power source, and the means of replenishing the power source. The IMU data is preferably stored in the memory unit, and the communication unit may be configured to transmit the parameter to the memory unit. Additionally or alternatively, the communication unit may include an RF transceiver and/or optical transceiver and/or an acoustic transceiver. In one embodiment, the communication unit may be located within the housing or may be located in or at the outer surface of the housing. Alternatively, in another embodiment, the communication unit may be located remote from the housing. In this embodiment, the communication unit may be

releasably mounted on or within the buoyancy unit to which the sensor module is releasably connected and the communication unit may be operatively connected to the sensor module by a wired connection. The RF transceiver and/or optical transceiver and/or the acoustic transceiver of the communication unit may be configured to transmit the IMU data from the sensor module to a remote base station located on the drilling or production vessel. The base station may include a data analysis system configured to analyse the IMU data and determine, for example, a remaining operational life of the riser before fatigue failure, and/or a remaining fatigue capacity of a wellhead on which the riser is operating. In one embodiment, the controller is configured to control the communication unit to transmit the IMU data upon retrieval of the connected buoyancy unit and riser at the production vessel, i.e. following drilling operations. In this embodiment, the

communication unit may be configured for connection to a suitable cable for uploading of data for external storage and analysis. Alternatively, it may be configured to transmit the IMU data upon the controller receiving a signal from the pressure sensor. The signal may correspond to a detection of at least mean sea level air pressure by the pressure sensor. Accordingly, in this embodiment, the sensor module would automatically, via the communication unit, transmit the IMU data to the base station upon retrieval of the riser at the production vessel. In this embodiment, the communication unit may also be configured, via the controller, to transmit the IMU data only when the power source is being replenished or charged.

In an alternative embodiment, the controller may be configured to control the communication unit to transmit the IMU data continuously to the base station during deployment of the riser, i.e. at any time the riser is within the water. In one embodiment, the communication unit may transmit the IMU data directly to the base station, for example, via the RF transceiver. In an alternative embodiment, the communication unit may transmit the IMU data to a receiver unit located on a tether extending from the base station to the sensor module. In a further alternative embodiment, the controller may be configured to control the communication unit to transmit the IMU data from a first sensor module about a first riser section to a second sensor module about a second riser section, the second sensor module preferably being relatively closer to the base station than the first sensor module. The second sensor module is preferably configured to transmit its own IMU data and the IMU data from the first sensor module to the base station, or to an additional one or more adjacent sensor modules preferably relatively closer to the base station than the second sensor module. In this embodiment, a first communication unit associated with the first sensor module may be operatively connected to a second communication unit associated with the second sensor module by a wired or wireless connection. Alternatively, a third communication unit intermediate the first and second sensor modules may be utilised to: receive the IMU data from the first sensor module via the first communication unit by a wired or wireless connection; and transmit the received IMU data to the second sensor module by a wired or wireless connection. In this embodiment, the first sensor module is preferably located at one end of the buoyancy unit, and the third communication unit is preferably located at an opposite end of the buoyancy unit, the opposite end being relatively closer to the second sensor module about the second riser section. In these embodiments, the wired connection may comprise a cable extending along and/or within the buoyancy unit, and the wireless connection may comprise one or more of an RF transceiver, an optical transceiver, and an acoustic transceiver.

The sensor module may also be configured, via the controller, to begin

measuring and recording the IMU data upon the pressure sensor receiving a signal corresponding to submergence of the housing in the water and/or cease measuring and recording the IMU data upon the pressure sensor receiving a signal corresponding to mean sea level air pressure (i.e. air pressure at the production vessel).

The housing is preferably sealed or sealable in a closed configuration to prevent water ingress. In other words, the housing is preferably waterproof in the closed configuration. The housing may also be configured in an open configuration to enable servicing of its various components, such as the memory unit and the power source.

At least a portion of the pressure sensor is located in or at the outer surface of the housing exposed to water to thereby obtain ambient pressure sensor data, i.e. depth readings. The pressure sensor data may be stored in the memory unit and/or transmitted by the communication unit to the base station in the manner described above in relation to the IMU data. Additionally, data measured by the temperature sensor and the GPS may also be stored in the memory unit and/or transmitted by the communication unit to the base station in the manner described above. The pressure sensor is preferably configured to measure pressures from about 0.1 MPa to 31 MPa. The temperature sensor is preferably configured to measure temperatures between -10° C and 50°C.

The housing preferably comprises a composite material or any other suitable material transparent to RF. The composite or other material must be configured to withstand the low temperatures and high pressures associated with subsea

hydrocarbon production, and must be substantially resistant to corrosion. The power source may include a Lithium-Polymer battery. The Lithium-Polymer battery is preferably configured to energise any one or more of the IMU, the

communication unit, the controller, the pressure sensor, the temperature sensor, the GPS, and the memory unit. The means of replenishing the battery may include an inductive charging unit. The inductive charging unit may charge the battery by receiving energy via induction. The energy may be from a power source external to the housing and preferably located on the production vessel.

The housing may also include an RFID tag configured to associate the sensor module with a particular buoyancy unit and/or riser. Advantageously, as is described above, the sensor module is a replaceable unit releasably connected within the buoyancy unit. Therefore, upon retrieval of the riser and buoyancy unit at the production vessel, the sensor module may be readily replaced with a similar sensor module to reduce riser downtime and manual handling.

In a further aspect, the present invention provides a system comprising: one or more marine risers; and one or more buoyancy units releasably connected about a respective one of the one or more risers; wherein each of the one or more buoyancy units includes a sensor module configured to measure and transmit a parameter associated with a respective one of the one or more risers.

This aspect of the invention therefore provides a marine structural health monitoring solution for a riser system. The sensor module may be a sensor module according to the first aspect of the invention.

In a further aspect, the present invention provides a method of monitoring a marine riser, comprising: disposing a buoyancy unit on or about the marine riser, wherein the buoyancy unit includes a sensor module configured to measure and transmit a parameter associated with the riser; and receiving the parameter associated with the riser and analysing the parameter to monitor the riser. The sensor module may be a sensor module according to the first aspect of the invention.

In a further aspect, the present invention provides a method of monitoring a marine riser, comprising: providing a buoyancy unit having a recess or cavity; disposing a sensor module in the recess or cavity, the sensor module including equipment to measure dynamic conditions experienced by the sensor module; and disposing the buoyancy unit on or about the marine riser, such that the sensor module is mounted to the buoyancy unit in such a way that the dynamic conditions experienced by the sensor represent at least in part the dynamic conditions associated with the riser, the sensor module equipment logging the data representing said measured dynamic conditions while the riser is disposed under water. The sensor module is preferably configured to transmit the data when in communication with an external receiver unit, the method including the step of analysing the data to monitor the structural health of the riser.

The buoyancy unit may be provided with one or more engagement features at selected locations for securement of the sensor module to the buoyancy unit, the step of disposing the sensor module in the recess or cavity realised by way of an engagement ensuring a prescribed position and alignment of the sensor module measuring equipment relative to the marine riser once the buoyancy unit is in place around the riser.

In a preferred form, the sensor module comprises a housing with a hollow interior accessible from the exterior by removal of a portion of the housing when the riser if out of the water, the method including disposing the sensor module equipment within the sensor module by structurally mounting the sensor module equipment to said portion of the housing, in such a way that accessing the interior of the sensor module results in removal of the equipment from the sensor module. The sensor module may be a sensor module according to the first aspect of the invention.

Although the sensor module of the invention is described herein in relation to its use with marine or subsea risers, the invention is not intended to be limited to this use. The invention may be utilised with any other marine or subsea structure to which a buoyancy unit is releasably connected, such as pipes, flow-lines, umbilicals, cables, and the like.

Further aspects of the present invention and further embodiments of the aspects described in the preceding paragraphs will become apparent from the following description, given by way of example and with reference to the accompanying drawings.

Brief description of the drawings

Figure 1 is a view of an off-shore hydrocarbon production vessel including a riser string having a plurality of buoyancy units disposed therabout;

Figure 2 is a schematic representation of a buoyancy unit including a sensor module according to an embodiment of the invention;

Figure 3 is partial side cross-sectional view of a sensor module according to an embodiment of the invention, releasably connected within a buoyancy unit disposed about a riser;

Figure 4 shows a part of the sensor module of Figure 3; and Figure 5 is a partial side cross-sectional view of the sensor module of Figure 3 secured in position in a buoyancy unit attached to a riser string.

Detailed description of the embodiments

Referring to Figure 1 , there is shown an offshore hydrocarbon production facility or vessel 10. Extending below a surface of the water 12 and fluidly connected to the drilling or production vessel 10 is a drilling riser string 14 comprising a plurality of fluidly connected riser sections 16. The riser string 14 extends below the production facility 10 to a subsea oil well (not shown) below the seabed. Releasably connected about each riser section 16 is a buoyancy unit 18. The buoyancy units 18 typically comprise a low- density syntactic foam configured to reduce the submerged weight and tensile stress experienced by each riser section 16. Tensile stress on a particular riser section may arise from, for example, its connection to an adjacent and relatively lower riser section (i.e. a riser closer to the seabed). The buoyancy units 18 are typically releasably installed about the riser sections 16 whilst on the production vessel 10 prior to their deployment.

According to the invention, each of the buoyancy units 18 include a sensor module 20 (Figure 2) configured to measure and transmit a parameter associated with the riser section 16 about which the buoyancy unit 18 is releasably connected.

Referring to the schematic illustration in Figure 2, the sensor module 20 comprises a housing 22 releasably connected at least partially within the buoyancy unit 18. An instrumentation package or unit 24 is disposed within the housing 22 and includes a sensor 26 configured to measure the parameter associated with the riser section 16 (the riser section 16 is not illustrated in Figure 2). The instrumentation unit 24 also includes a communication unit 27 having an RF transceiver 28 operatively coupled to the sensor 26 via a controller 30 and configured to transmit the parameter. The parameter may be transmitted to a base station (not shown) on the production vessel 10 for analysis. As described below, analysing the parameter associated with the riser section 16 allows assessment (eg. by a trained operator and/or machine analysis) of the structural health of the riser section 16. This information can be used in determining ofa remaining operational life of the riser section 16 before fatigue failure.

Housing 22 of sensor module 20 is designed to provide a sealed pressure vessel for containment of instrumentation unit 24 in a subsea environment. In one embodiment, housing 22 comprises a composite material transparent to RF transmission and is advantageously dimensioned so as to be releasably receiveable within a

complementarily dimensioned recess or cavity 32 within the buoyancy unit 18. By utilising a suitable composite material, the housing 22 is configured to withstand the low temperatures and high pressures of environments associated with subsea hydrocarbon production, and is designed to be substantially resistant to corrosion. In an alternative embodiment, housing 22 is fabricated from stainless steel. As discussed further below with reference to Figure 5, housing 22 is configured to be received in the recess 32 of the buoyancy unit 18 such that an upper outer or external surface 34 of the housing 22 is substantially flush with an adjacent outer surface 36 of the buoyancy unit 18 exposed to water. The housing 22 is mounted within the recess 32 and releasably secured thereto by a suitable mounting bracket.

The sensor 26 of instrumentation unit 24 is an inertial measurement unit (IMU) 40. The IMU 40 includes one or more accelerometers, gyroscopes, and magnetometers each configured to measure a specific force or accelerations of the housing 22 and/or an angular rate of rotation of the housing 22. Advantageously, as the housing 22 is releasably connected within the buoyancy unit 18, which is connected about the riser section 16, the IMU 40 measures the specific forces, accelerations and/or angular rates of rotation of the riser section 16 (as the movement of the housing 22 exactly

corresponds to the movement of the riser section 16). The IMU 40 is configured to measure the acceleration of the riser section 16 in a range of about

-0.34 g to 0.34 g in two axes perpendicular to a central longitudinal axis of the riser section 16. Additionally, the IMU 40 is configured to measure the angular rate of rotation of the riser section 16 in the two axes in a range of about -3.07s to 3.07s. Together, the acceleration of the riser section 16 and the angular rate of rotation of the riser section 16 constitute IMU data.

Advantageously, the IMU data is utilised to determine the amplitude and frequency of vibrations experienced by the riser section 16. The IMU data from a plurality of sensor modules 20 associated with a respective plurality of riser sections 16 may be utilised to determine a combined amplitude and frequency of vibration of the riser string 14, and for example, an excitation frequency of the riser string 14.

A particular riser section 16 may vibrate due to any one or more of the following: water currents incident upon the riser section 16, motion of the production vessel 10 at the surface which is fluidly connected to the riser string 14, and vibrations due to production and/or return fluid moving through the riser string 14. Advantageously, the IMU 40 is configured to measure riser section 16 vibration frequencies within the range of 0 Hz to 0.3 Hz. The IMU 40 is also configured to sample riser section vibration frequencies at a minimum sampling frequency of 10.0 Hz. The IMU is further configured to measure vibration amplitudes up to one riser diameter in the abovementioned two axes with a minimum resolution of approximately 1 mm. As is mentioned above, the frequency and amplitude of vibration of the riser section 16 may be utilised to assess the structural health of the riser section 16 and/or riser string 14, and for example, may be utilised to determine a remaining operational life of a particular riser section 16 before fatigue failure. Alternatively or additionally, the IMU data may be utilised to assess the structural health of a subsea wellhead (not shown) to which the riser is connected. The housing 22 of the sensor module 20 is sealed in a closed configuration to prevent water ingress when releasably received within the buoyancy unit 18. As will be understood, and as discussed further below, the housing 22 can be opened to enable servicing of the instrumentation unit 24 and any one or more of the other components within the housing 22.

The instrumentation unit 24 also includes a pressure sensor 44, a memory unit 46, and a power source in the form of Lithium-Polymer batteries 48. The controller 30 is configured to control the IMU 40, the communication unit 27, the pressure sensor 44, the memory unit 46, and the power source 48. The power source 48 is configured to energise any one or more of the IMU 40, the communication unit 27, the controller 30, the pressure sensor 44, and the memory unit 46. The housing 22 also includes an inductive charging unit (not shown) configured to charge the batteries 48 by receiving energy via induction. The received energy may be from a power source external to the housing. The batteries 48 may be recharged whilst the housing 22 is located within the buoyancy unit 18 whilst on the production vessel 10, or alternatively, once the housing 22 has been removed from the buoyancy unit 18. The batteries 48 may also be of the disposable non-rechargeable type.

Advantageously, the instrumentation unit 24 and the batteries 48 are removably mounted within the housing 22 through connection to a mounting arm 100, as discussed further below with reference to Figure 4. As illustrated in Figure 2, at least an upper portion or face 50 of the pressure sensor 44 is located on the external surface 34 of the housing 22 and is exposed to water to thereby obtain ambient pressure sensor data or depth readings. The pressure sensor data may also be stored in the memory unit and/or transmitted by the RF transceiver 28 to the base station in the manner described below. The IMU data is stored in the memory unit 46 for either immediate or delayed retrieval by the controller 30 and transmission by the RF transceiver 28 to the base station located upon the production vessel 10. In the illustrated embodiment, the controller 30 is configured to control the RF transceiver 28 to transmit the IMU data to the base station upon retrieval of the riser section 16 and its associated buoyancy unit 18 at the production vessel 10. Specifically, the RF transceiver 28 is configured to transmit the IMU data stored with the memory unit 46 upon the controller 30 receiving a pressure signal from the pressure sensor 44 corresponding to a detection of sustained sea level air pressure. Accordingly, the sensor module 20 is therefore configured to automatically, via the controller 30, transmit the IMU data to the base station upon retrieval of the riser section 16 at the surface, i.e. at the production vessel 10. In this embodiment, the RF transciever 28 may also be configured, via the controller 30, to transmit the IMU data only when the lithium-ion batteries 48 are being recharged.

As will be understood, the controller 30 can be configured to only measure and store the IMU data on determinination from the signal received from pressure sensor 44 that the sensor module is below water level, and to power down the module on determinination that the sensor module is at or close to sea level. This allows

conservation of battery life, ensuring that the IMU data is only logged when the relevant part of rise 16 is submerged. In some forms, instrumentation unit 24 may include a GPS unit, in which case it may be configured to remain powered up when sensor module 20 is out of the water, to assist in retrieval or location. Accordingly, as each riser section 16 is retrieved after a drilling operation, the sensor module 20 associated with each buoyancy unit 18 about the riser section 16 will transmit its stored IMU data to the base station for analysis.

In an alternative form, the stored IMU data is transmitted by downloading to the base station or to an intermediate storage unit over a hardwire connection once the sensor module has been opened and memory unit 46 accessed.

As shown in the embodiment illustrated in Figure 3, the housing 22 of sensor module 20 comprises a cylindrical body 222 (fabricated from a steel pipe section) connected at its lower end to a dished base cap 224 by weld 226. Top end of cylindrical body 222 is connected to the depending collar 230 of an annular flange 228 by weld 232. As shown in the figure, annular flange 228 has a central bore to provide a mouth of the sensor module 20, having a stepped shaping to provide a close fit around the outer face and upper edge of cylindrical body 222, the mouth of flange 228 having the same diameter as the inner diameter of cylindrical body 222. In its outer part, annular flange 228 has a plurality of bolt-receiving bores 234, eg. four angularly spaced bores.

The cover 60 of sensor module 20 is a disk form plate of the same outer diameter as annular flange 228, with an eyebolt 62 centrally positioned on and welded to its upper surface. Near its outer circumference cover 60 has a plurality of bolt-receiving bores 64, arranged in a complementary arrangement to bores 234 in annular flange 228. In addition, cover 60 is provided with a first threaded bore 66 to accommodate a threaded bleed plug 80 and a second threaded bore 68 to accommodate a cable plug (not shown). As shown in Figure 3, annular flange 228 on its upper surface and cover 60 on its lower surface are provided with complementary circular grooves, shaped and dimensioned to receive O-ring 70. When the two are urged together by way of bolts introduced through the bolt-receiving bores 64 and 234 a sealed closure of sensor module 20 results.

In this embodiment, cover 60 is removable from housing 22, its removal and attachment realising opening and closing of the sensor module to access the internal components. It will be understood that in other forms the cover may be hingedly attached to the housing, or attached in another way to remain connected with the rest of the housing on opening.

Bleed plug 80 provides a pressure relief means for sensor module 20, and includes a hex nut cap 82 with a depending sealing flange, a threaded body 84, a neck 86 connecting body 84 to cap 82, and an internal bleed channel 88 providing a fluid connection between the lower face of body 84 and the outer surface of neck 86. When bleed plug 80 is introduced to first threaded bore 66 and tightened, cap 82 sealingly closes the bore against any fluid passage. In use, it is possible that a pressure differential can develop between the inside and the outside of the sensor module, in particular through gas build-up due to chemical activity of batteries 48 after a prolonged time. Before sensor module 20 is opened, bleed plug 80 is loosened, which allows pressures to readily equalise by gas/air transfer between the interior of module 20 and the neck outlet of passage 80. A threaded cable plug can be introduced into threaded bore 68 in a sealing manner, to allow passage of a lead or tube to the sensing element of pressure sensor 50, to afford monitoring of the pressure at the upper surface of cover 60. Figure 4 illustrates how the internal components of sensor module 20 are supported by cover 60 to form a single unit for simple one-step disassembly. To this end, an elongated stem 100 is connected by weld 101 to the lower face of cover 60, to project downwardly therefrom. Near the upper end of stem 100 are connected two transverse mounting arms 102, with apertures 104 for location-specified mounting of the various electronic components of module 20 (as discussed in detail above). Further towards the distal end of stem 100 are provided two tiers of battery holder plates 106, with apertures 108 for mounting of batteries 48. In this embodiment, each tier includes three equispaced battery holder plates 106, each connected to stem 100 by a support web 1 10 (see section A-A of Figure 4). As will be understood, this structure provides a simple, robust and compact way of providing the internal components of sensor module 20 in a unitary form such that, when the module is accessed, removal of the cover affords removal of all the internal components.

The mounting of sensor module 20 to buoyancy unit 18 is illustrated in Figure 5. Cylindrical recess 32 is provided at a selected position in the upper surface of buoyancy unit 18, having a stepped shaping as shown to accommodate the flanged form of the body of housing 22. An outer concentric annular recess is provided around this recess to accommodate an annular mounting plate 90, which has a central aperture providing access to the top of cover 60. Around this central aperture are a plurality of bolt- receiving bores in an arrangement complementary to that of bolt-receiving bores 64 and 234.

The recess is formed in the fabrication of the buoyancy unit, to be compatible with the shape and alignment features of sensor module 20 and associated components discussed herein. A plurality of anchor bolts 95 are provided in buoyancy unit 18, to provide a secure anchoring of mounting plate 90 and thus sensor module 20. Anchor bolts 95 are angularly regularly spaced around recess 32, radially equidistant from the centreline thereof. As the syntactic foam used for buoyancy components of this sort is generally not of particularly high strength, anchor bolts 95 are provided as cast-in spread anchors (as shown in Figure 5), or an alternative means of providing suitable pullout resistance is used. Mounting plate 90 is provided with a plurality of bolt-receiving bores in an arrangement complementary to that of anchor bolts 95, so that mounting plate 90 can be securely mounted to buoyancy unit 18 by way of nuts 96. In this way, the external face of the mounting of the sensor unit is flush with the upper surface of buoyancy unit 18, to minimise any impact the unit may have on the hydraulic behaviour of the buoyancy unit (and thus on the riser string generally). As seen in Figure 5, stud bolts 92 are passed through the bolt-receiving bores

234 and 64 in annular flange 228 and cover 60 respectively, as well as the bolt- receiving bores around the central bore of mounting plate 90, and nuts 93 are tightened thereto to seal the closure of the sensor module 20 and to secure the whole unit to mounting plate 90. The lower ends of stud bolts 92 are accommodated in receiving recesses 33 formed as outer portions of recess 32.

It is important that the IMU 40 is mounted in a selected design position and orientation relative to riser 60, and to this end the assembly is provided with means to ensure that sensor module 20 must be introduced into recess 32 in a fixed orientation. This can be done by way of visual indicators on the top surfaces of the various components. In addition, one of the stud bolts 92 may be longer than the others, and one of the receiving recesses may of increased depth, to aid in achieving the desired angular orientation.

As will be understood, there is great benefit in the monitoring system not being provided on the riser itself, to minimise manual handling on the rig or production vessel. Previous solutions involving attaching instrumentation to the riser as it is deployed involved significant handling delays and introduced undesirable additional operational risk.

Advantageously, as each sensor module 20 is releasably receivable within a buoyancy unit 18, each sensor module 20 constitutes a separate replaceable unit that may be readily retrieved and then replaced with another similar sensor module.

Practically, this reduces the amount of time a particular buoyancy unit and riser section remain unused on the production vessel 10. Further still, the high-precision IMU data from each sensor module enables a trained operator to assess the structural health of particular a riser section and, for example, determine a remaining operational life of the riser section before fatigue failure. It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention. It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.

As used herein, except where the context requires otherwise, the term 'comprise' and variations of the term, such as 'comprising', 'comprises' and 'comprised', are not intended to exclude further additives, components, integers or steps.