• Decommissioning Matrix

The Decommissioning Matrix

Over the coming years, an increasing number of offshore oil and gas installations will be approaching the end of their producing life. Abandoning a field not only involves removal of the platform itself but also hundreds of miles of pipeline, control lines and wellheads. These need to be covered over, trenched or entirely removed.

Stringent international legislation governs the process. Environmental impact assessments need to be conducted and only qualified companies utilising specialist vessels and subsea vehicles are allowed to undertake decommissioning work.

High Accuracy Positioning

All decommissioning operations require accurate knowledge of the 'as found' state in which they currently reside. Sonardyne's 6G® USBL techniques provide high accuracy independent positioning of sensors used to conduct bathymetric surveys of the structure and surrounding area.

Where accuracy requirements are higher such as after hurricane damage, 6G® Optimised USBL systems or seabed positioning systems such as 6G® LBL offer independent but integrated solutions.

The Wideband® 2 signals incorporated within these systems provide robust ranging and data telemetry amongst the hard reflective surfaces of structure jackets; ideally suited for pre-decommissioning activities.

Heavy Lift Barges used to recover debris and break apart structures into manageable sections require precise positioning. GPS technology provides accurate positioning but suffers from line of sight and multipath issues when alongside large platforms. Sonardyne's 6G® USBL and LUSBL systems provide high performance, survey grade acoustic positioning designed for Dynamic Positioning (DP) reference.

The Wideband® 2 signal architecture enables seamless multi-vessel capability, DP station keeping and simultaneous tracking of ROVs and crane wires. It is recognised as the optimum solution for both shallow and deepwater DP offering a proven and risk-free solution.

 

Inverted USBL

Sonardyne's 6G® Inverted USBL techniques can be operated outside the normal working cone of vessel deployed USBL systems providing bespoke solutions.

In situations whereby USBL systems cannot be used, 6G® sparse LBL aided INS increases system performance without the cost of large seabed equipment deployments and provide position information during acoustic signal outages. Subsea structure decommission involves tasks such as control line disconnection, rigid jumper/spool disconnection, structure recovery and the associated debris clearance. Often these tasks require basic positioning to aid diver and ROV positioning around the subsea structures.

 

Environmental Monitoring

Long term environmental monitoring of an abandoned site ensures the area remains hazard free. 6G® transponders can be programmed to operate autonomously without any control or commanding from an ROV or vessel. Acoustic ranges to other transponders and sensor data (SV, inclination, pressure, temperature, ADCP data) can be programmed to be acquired at specific intervals and logged internally. This can then be recovered via the integrated high speed acoustic telemetry when convenient.

High endurance versions are available where the housing is a glass sphere which can free fall to the seabed and remain there collecting data for five years.