Designed for seismic

WesternGeco christened the company’s latest seismic vessel, the Amazon Warrior. Paul Bidmead shares insights.

Efficient acquisition of high quality marine seismic data requires very large spreads of specialized in-sea equipment deployed by vessels with a unique set of operational characteristics. The vessels need to be efficient and cost-effective at their normal production speed of 5 knots, which on average represents approximately 80% of their time at sea. Seismic companies have identified various types of existing hull designs they considered suitable for their operations, and converted the top decks to accommo- date and deploy the specialized equipment. A feature common to all is that they were originally optimized for another purpose, which in most cases was to enable economic transit from one seaport to another at high cruising speeds. In November, WesternGeco christened Amazon Warrior – a newbuild vessel designed from the bottom up to deliver optimum performance while also providing fuel-efficiency during its estimated project-to-project transit speed of 17 knots.

Image Caption: The final decks being installed on Amazon Warrior after its naming ceremony on November 8, 2013.

Photo courtesy of  WesternGeco.

Vessel design trends

The marine seismic survey business saw rapid development in the 1980s, coinciding with over-capacity in many of the world’s fishing fleets. Several fishing trawlers were converted to tow multiple (typically 2-4) seismic streamers laterally separated behind the vessel by 50m (168ft) or more. Seismic service companies subsequently built new vessels capable of acquiring large 3D surveys. Meanwhile, developments in source and streamer technologies, combined with continuing improvements in 3D data processing and analysis techniques, have delivered increasingly accurate and reliable information for imaging the subsurface and mapping reservoir fluid movements. This knowledge supports optimized well placement and efficient field development strategies.

Image Caption: Tank testing of Amazon class hull design.

Photo courtesy of FORCE Technology, Denmark  

Most modern newbuild seismic ves- sels have highly-specialized back decks designed to store and deploy 1-2 arrays of airguns and at least 8 streamers, each up to 12km long, towed up to 200m (672ft) apart. Companies have implemented a range of strategies to provide suitable back and gun decks, but all have been combined with existing hull designs.

A new bottom-up approach

WesternGeco reviewed long-term forecasts for E&P activity and decided the future of the global seismic market was sufficiently buoyant to support an overall extension its seismic fleet. WesternGeco embarked on a project to design and build a new marine seismic platform capable of supporting all of its present and potential technologies and acquisition techniques for at least the next 10 years while also optimizing operational performance. The company decided to design the new vessel from scratch, having first defined its operational requirements. This approach is aligned with the Schlumberger philosophy of maintaining competitive advantage through technological differentiation; health, safety and environment (HSE) leadership; efficiency in different environments; and a “bottom-up” approach to design.

While the back and gun decks are designed to fit a hull, this project started with defining the seismic elements and operational criteria for the working areas through extensive research and analysis. Then, starting with clean sheet of paper and no preconceived ideas, engineers were tasked with designing a hull, propulsion system, and all the other vessel components required to optimally meet the seismic requirements while making sure that there were no compromises in HSE or operational efficiency.

People power A key feature of the design process, especially for the back and gun decks, was that it involved considerable input from experienced equipment users. The extensive WesternGeco HSE knowledge management database was used to evaluate and mitigate potential safety risks identified from a wide range of industry incidents and lessons learned. Workshops were organized that brought together designers, management, and numerous crew members with up-to-date and relevant experience of the various elements of marine seismic operations. HSE was a top design priority.

The first Amazon-class vessel is being built in Flensburg, Germany. The shipyard has been using 3D visualization technology in its design processes for more than 12 years. Initial designs were used to create virtual versions of specialist working environments, in which crews were able to provide realistic feedback on practicalities such as equipment handling, stepping, handling, and the safe movement of people and equipment.

The final vessel design addresses operational and HSE issues in all areas. Seismic and maritime workshops, stores, and supply handling are all on the same level and as close as possible to the equipment or machinery being supported. Passages and stairs are designed to reduce trips, slips and falls. The main deck is designed and positioned at a height designed to minimize potential for sea ingress. A new hands-free source deployment and recovery system is being designed within the Amazon project capable of being retrofitted into the existing fleet. In addition to a helicopter deck for offshore crew changes, a built-in offshore gangway is available for at-sea transfer of personnel, avoiding the need for small boats. Workboats designed for safe, efficient, replacement of streamer sections are located in both the port and starboard sides of the hull. The davit deployment design allows more than one small boat to be retrieved at any one time, ensuring that one or more can always be recovered on the lee side.

Unique design

The hull may appear conventional, but it was derived to meet detailed specifications for seismic operations. Flensburger Shipyard carried out seakeeping analyses and extensive tank testing, which was performed at the facilities of FORCE Technology in Denmark. WesternGeco maintained control and owns the vessel design. It also identified key suppliers with the best knowledge of the needs of the seismic industry, while the yard used its expertise to select suppliers and con- tractors required for building the vessel.

Image Caption: Computer rendering of  Amazon Warrior, in operation Q2 2014

Photo courtesy of   WesternGeco.

Specifications for the “Amazon-class” vessels include the ability to work world- wide in all operating arenas, including frontier areas. They will have a production endurance of 120 days, which is important in environmentally sensitive areas and where resupply may present challenges. Routine maintenance can be done during live operations and the docking interval is five years.

At 126m (413ft) long, 28-32m (92–105ft) wide, the vessel provides a large, powerful and stable platform for forward motion and maneuverability during operations in inclement weather conditions. The knife- shaped bow reduces slamming, helping to maintain streamer control and reduce noise in the seismic data. There is capacity for more than 200km of streamers and 18 streamer tow points. A “quad-deployment” design enables four steamers to be handled simultaneously. The vessels will be suitable for a variety of acquisition geometries including long offset, Coil Shooting, Dual Coil Shooting, and Continuous Line Acquisition. High streamer capacity and ample working space enable at-sea reconfiguration of streamers.

Environmental performance

The propulsion system, matching the hull, includes independent, ergonomically designed, port and starboard engine rooms. Full redundancy in the propulsion and steering systems means that normal production can be maintained in the event of a breakdown, which is important for production continuation and critical in mitigating safety risk within obstructed or environmentally sensitive areas. The propulsion pack is quiet, which benefits seismic data quality and will be welcomed by the crew. Cabins are designed to minimize external noise and the funnel is based on a cruise liner concept that avoids exhaust fumes on deck.

The newbuild uses only marine gas oil (MGO), which although more expensive, produces lower emissions than standard heavy oil. It has a low-loss electrical power distribution system, energy recovery air-conditioning systems, and energy efficient (variable speed) machinery. LED lighting systems provide power, safety and maintenance benefits. The vessels are designed to meet DNV CLEAN Class and CLEAN Design specifications and have ICE-1A class winterization for Arctic operations to Polar Class 7. Benefits include heated handrails, reduced risk of heavy ice buildup that could cause instability, and avoiding risk of anchors freezing to the deck. ICE Class does not necessarily mean that the vessel can work in icy waters, as the in-sea equipment could be vulnerable to damage; however, it does enable the vessel to safely enter a survey area earlier and leave later in a summer season.

A successful project The first Amazon-class vessel is scheduled to start operations in Q2 2014. The second is expected to be in service by Q4 2014. Construction is achieving all milestones on pre-planned dates, which will result in the new vessels going into production approximately 12 months after cutting first steel. OE

Paul Bidmead is WesternGeco’s marine marketing manager. He has 22 years’ experience in seismic operations and technical development.