Fugro’s DeepData subsea instrument pods have been collecting motion data on subsea structures for a collective total of over 25,000 days, equating to over 70 years.
The first deployments were in the North Sea followed by other worldwide locations including the Gulf of Mexico, Canada, Australia, Mediterranean and the Caspian Sea, for a variety of applications.
DeepData pods monitor the integrity of subsea assets by measuring their motion. They use accelerometers and angular rate sensors to determine displacements and inclination. These measurements are necessary for assessing the response of a subsea structure to the effects of currents and wave loading. This is particularly useful in vibration monitoring of risers and pipelines, caused by vortex induced vibration (VIV), and tracking the fatigue of a wellhead through BOP stack motions.
The pods can interface with a variety of external sensors and communication equipment, and are deployed and recovered via a clamp onto the BOP stack or riser, using remotely operated vehicles (ROVs). This enables regular updates of actual subsea motions while the riser is deployed.
The recovered measurement data from the pods are enhanced by data processing techniques for display and interpretation. Spectral analysis helps identify the natural frequencies of the riser and vessel, which are critical for tailoring finite element models.
In harsher metocean environments or where predicted fatigue life of an asset is low, real-time monitoring of fatigue, VIV and other parameters can be a distinct advantage during operations. Having a real-time motion measurement system enables the fatigue life at critical welds and connectors to be calculated and monitored, and operations adjusted as necessary. To achieve real-time communication, hydroacoustic modems are deployed with the DeepData pods to facilitate communication to the surface.
“The success of DeepData is due to it being a robust system that has proven adaptable to a number of applications,” explains Gordon Hamilton, Fugro commercial manager. “These motion pods have been used extensively for monitoring the motions of risers and BOP stacks, but have also been used for other subsea applications such as motion monitoring of Christmas trees and decommissioned structures.”