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Case Study

Wolfspar – Undersea Low-Frequency
Seismic Source

Scope

Wolfspar is a 25 ton towed underwater low frequency seismic source, intended to enhance seismic imaging beyond what is commonly achieved in surveys to explore hydrocarbons with air guns. The machine consists of pressure vessels, underwater rated electronics and power distribution, as well as hydraulic and pneumatic systems. After key engineering personnel of the company that designed this device migrated to Dynamic Structures, the company was tasked to maintain it, implement improvements and support offshore deployments. The original design scope of the project included the source device itself, as well as a deck control container for remote operation, associated tooling for deployment and spare part management. Since 2016 Dynamic Structures has worked through several design optimization and maintenance cycles between offshore deployments. During each deployment the technology was tested further, leading to lessons learned, which were then prioritized to improve reliability, maintainability and operability.

CLIENT

BP & Magseis Fairfield

LOCATION

Gulf of Mexico

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Challenge

The initial design challenge was to achieve design targets such as velocity, pressure and frequency accuracy with technology and components that were commercially readily available and which can be exposed to the harsh environment under water, offshore and significant vibrations. Although a scale model existed at the beginning of the project, it was clear that significant changes are required to scale the device to meet the geophysical requirements. Secondly, the device was initially designed as a proof of concept with the requirement to survive a limited amount of tests. During the course of the project this goal changed significantly, so that reliability and durability had to be improved wherever needed to minimize downtime and achieve the latest project goals. With any complex system, the project also had challenges in managing the interfaces between the major elements of the system. Several parties were involved to engineer the associated deck systems, the launch and recovery system, and the hydrodynamic aspects of.

Solution

Since the geophysical requirements pushed the envelope of what readily-available seals can withstand, an extensive component qualification test program was initiated early on in the project. Purpose build test rigs were devised to determine the suitability of seals and hydrostatic bearings. To verify system behavior including controls algorithms, hydraulics and pneumatics, a comprehensive MATLAB/Simulink simulation was generated. For mechanical and structural aspects, extensive FEA and analytical calculations were performed. Once the fabrication and assembly of the device was complete, an extensive test program followed. The unit underwent dry testing in a shop environment, followed by a static (not towed, not resonating) wet test in the port of Vancouver. Several lake tests followed in 2013 and 2014 to verify the resonance performance and if the geophysical requirements were met. A system integration test on a vessel with the associated deck equipment and in a towed arrangement followed in the Gulf of Mexico in December 2014. Dynamic Structures’ focus was the steady improvement of the device to meet reliability and durability targets and facilitate several surveys, where the unit was used in its intended environment under typical production parameters. After each major maintenance and improvement iteration, the system was thoroughly shop tested. Dynamic Structures supported several surveys with Engineering personnel offshore operating and maintaining the device.

Benefits

In spite of not being designed for the extended use, Dynamic Structures was able to maintain and improve the system to allow the repeated use through several offshore surveys. In several iterations the design has been refined and adapted to its actual use case, which was not completely clear in the early project phase. The engineers that carried the project from its design stage to the end were committed to making this project a success and proving the feasibility of this novel technology. It represents state of the art engineering in controls, electro-mechanical and fluid power engineering in the harshest environment. The skill set and experience of Dynamic Structures staff, as well as a track record with high-reliability systems were the main reasons that we were awarded this work.

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