Life-of-field monitoring

To maintain the integrity of the FSHRs, the Subsea Technology Group from Petrobras’s R&D Centre in Brazil, prepared a specification for PAI of a comprehensive life-of-field subsea monitoring system and contracted BMT Scientific Marine Services as the systems integrator responsible for its delivery.  

BMT has experience in the development of offshore monitoring systems and, following the successful development of a similar system for the Petrobras P·52 platform in Brazil in 2007, BMT again chose to partner with Sonardyne for the positioning and telemetry component of the riser monitoring system. 

The primary requirement for the acoustic instrumentation is to monitor the position of each riser tower and of the turret buoy relative to the seabed. In addition, integrated sensors monitor depth, temperature, inclination and sound speed whilst the integrated modem transfers data from the load and attitude monitoring system on each riser tower to the turret buoy. The system uses Sonardyne Wideband acoustic telemetry to guarantee high speed and reliable data communications for all these tasks. 

Integrity – Measure, command and monitor

To ensure line-of-sight to each riser tower without obstruction by the flexible risers or mooring lines, the turret buoy was equipped with three of our transceivers. The transceivers perform the following multiple functions: 

• Measure ranges directly from themselves to the seabed transponder array in order to provide an accurate position for the turret buoy. 

• Send commands to transponders mounted near the top of each riser tower, instructing them to measure the ranges to the seabed array. The positions of the risers can then be accurately determined.  

• Acquire sensor data from the riser transponders and the seabed array. 

• Send commands to, and recover data from, BMT’s data logger on the risers, fitted with an acoustic modem.

The transponder on the risers and on the seabed are versions of our Autonomous Monitoring Transponders (AMTs) which operate an efficient Wideband command protocol. 

This allows much faster set up of transponder parameters and enables the sensors fitted to the riser transponders to be measured and reported at the same time as the acoustic measurements are made, greatly speeding up the acoustic monitoring cycle. 

In normal operation, data acquisition will be controlled by the topside monitoring system on the FPSO. In the event of a disconnection due to adverse weather or maintenance, the subsea system continues to record data on the turret buoy, which can later be downloaded by the FPSO or another vessel for processing by Petrobras proprietary software.  

The integrity monitoring system provides valuable data about the movement from either vortex-induced vibration or flow-induced vibration and loading on hybrid riser systems from currents and extreme weather events. 

The system demonstrated a growing demand for reliable subsea remote integrity monitoring that has been enabled by the high performance of Sonardyne monitoring and acoustic positioning, data communication systems and subsea strain and motion sensing systems.  

P-52 permanent subsea riser monitoring system

Sonardyne previously supplied the acoustic positioning and data recovery equipment for the single FSHR close to the Petrobras P-52 platform in the Brazilian Roncador field.  

Installed in the Autumn of 2007, a single acoustic transceiver on the platform communicates with the transponders and modem on the risers and with a seabed array of five Sonardyne Compatt 5 transponders.

Because of the large amount of data to recover from the data logger on the risers – over 90 Mbytes in the first six months – our High Data Rate Link (HDRL) was employed to transfer data from the loqqer to the platform. The monitoring system sends strain, motion and position information every four hours. 

This transfers data at the speed of 15,000 bps and is ideal for transferring the large data records to the surface error free and as efficiently as possible.  

Since its commissioning in 2007, the system has provided invaluable data for analysing the movement of the riser tower, allowing confidence in the development of more complex FSHR installations such as in the Cascade and Chinook field. 

(The original version of this article was first published in Sonardyne’s Baseline magazine in 2009. It has been lightly edited for present tense).  

https://www.sonardyne.com/wp-content/uploads/2021/06/baseline_issue_4.pdf