A long life acoustic monitoring system developed by Sonardyne to detect minute settlement changes in the seafloor has been successfully deployed for Brunei Shell Petroleum (BSP) in the South China Sea. The network of Autonomous Monitoring Transponders (AMTs) has been installed in 45 metres of water to record pressure and temperature at designated intervals.
Structure, pipeline and seabed settlement monitoring is regularly undertaken in life of field surveys to monitor the effects of oil and gas extraction.The challenge is to acquire the data to identify changes over time reliably and cost effectively. In 2013, BSP tasked Sonardyne with creating a custom engineered autonomous monitoring system to identify precise settlement figures for a field off the coast of Brunei. Site surveys revealed a seabed of undulating sand with rock and coral outcrops meaning that special consideration was needed for transponder deployment to prevent them sinking into the seabed and affecting data integrity.
Sonardyne has provided autonomous monitoring systems for many deepwater fields but shallow water operations pose additional challenges such as complex thermoclines and bio-fouling caused by organic materials in the water, both of which can affect equipment endurance and data accuracy.More practical challenges on this project were the likelihood of movement or damage to the transponders caused by trawler activities and commercial fishing.
AMTs precisely and repeatedly measure vertical movements; acquire and log sensor data from internal and external sensors; and wirelessly transmit data on demand at high speed to the surface for immediate analysis. The autonomous functionality of the transponder combined with low power electronics enables it to operate for several years without intervention, eliminating the cost for a vessel and ROV on location.
To protect against fishing and trawling activities, the AMTs were supplied in compact glass sphere housings shrouded within bespoke, low profile frames. Designed and manufactured by Sonardyne, the polypropylene frames provide resistance to snagging as well as corrosion and bio-fouling.The clam shell design features unique ballast points which are filled with concrete once the frames have arrived on location, minimising transport costs and manual handling risks. Prior to deployment, Sonardyne’s Monitor software configured each AMT to record precise seabed pressure, temperature and salinity hourly with noncritical data such as battery consumption, pitch and roll logged daily. As each transponder was deployed, it was tracked using the vessel’s USBL system and a minibeacon attached to the crane wire with an ROV used to inspect the as-laid position of the frame on the seabed. In total, four AMTs were deployed whilst a fifth was mounted on a nearby platform by divers. The system is now recording and logging data with a team from BSP periodically returning to the site to acoustically interrogate the AMTs and recover the data using a Sonardyne Dunker 6 transceiver deployed over the side of a vessel.The data is then transmitted to shore to analyse and identify any trends in seafloor deformation.
“Since 2007,AMTs have been deployed for long term settlement and deformation monitoring projects. This latest project has given us another chance to showcase our applications, knowledge and custom engineering capabilities to solve our clients’ subsea challenges.”