Sonardyne deploys new subsea sensors at Ormen Lange

Sonardyne is supporting Norske Shell’s ongoing long-term, large-scale seabed monitoring project at Ormen Lange, Norway’s second largest gas field.

The UK-based marine technology firm has for the first time deployed a new breed of underwater sensor that is able to self-calibrate, enabling precise, long-duration subsidence monitoring at all depths, at scale.

The 20-plus Fetch Ambient-Zero-Ambient (AZA) pressure monitoring transponders (PMTs), developed by underwater technology specialist Sonardyne, will support an ongoing long-term, large-scale seabed monitoring project at Ormen Lange – Norway’s second largest gas field – for A/S Norske Shell.

Unlike traditional pressure sensors, which suffer from drift over time, Sonardyne’s 20-plus Fetch Ambient-Zero-Ambient (AZA) pressure monitoring transponders (PMTs) autonomously re-calibrate in situ.

In-situ calibration unlocks the ability to be able to monitor seafloor subsidence with centimetric accuracy for up to 10 years, without a loss of precision or any need for retrieval and recalibration of the sensors, Sonardyne explains.

This is the latest deployment of Fetch PMTs at the Ormen Lange field, 120 kilometres offshore, in 800 – 1,100 metres water depth.

Each sensor collects pressure, temperature as well as inclination data at the seafloor, at pre-programmed intervals. The data is then periodically harvested, from an integrated high speed acoustic modem contained within each Fetch PMT or Fetch AZA PMT, using a choice of Sonardyne’s acoustic systems deployed from an unmanned surface vehicle (USV) or conventional ship. The data then helps calculate any vertical displacement of the seabed at the Ormen Lange field.

“Many years ago, geophysicists at Shell set Sonardyne the challenge of creating instruments that were sensitive enough to measure 1cm/year of vertical movement.

“With this latest generation of Fetch AZA, we have achieved that goal and unlocked the benefits of using this technology to detect extremely low levels of seafloor subsidence as part of proactive reservoir management programmes.”