Most 3-D seismic vessels operating today are purpose-built for seismic operations, although until recently all were designed around an existing type of hull. Much of the design effort has been focused on the back decks, which must typically be capable of storing and deploying one or two arrays of airguns and at least eight—and in some cases up to 24—streamers, each 3 km to 8 km (1.9 miles to 5 miles) long. Within these constraints, seismic service companies have implemented a diverse range of vessel design strategies to give them technical and/or commercial competitive advantage.

Environmental performance

Polarcus is a pure-play marine geophysical company specializing in high-end 3-D towed streamer acquisition with a focus on environmental performance. Launched in 2008, it is led by a team of experienced maritime and seismic industry professionals. Unlike established players in the market, it was not encumbered with an aging fleet, and its funding provided the luxury to start from scratch with a tailored new vessel design. According to Peter Zickerman, the company’s executive vice president and head of strategic investments, Polarcus designed a “future-proof” vessel platform that integrated an array of optimization characteristics essential for delivering geophysical and operational excellence while simultaneously reducing operational risk in all environments, including environmentally sensitive sea areas and the Arctic.

The Polarcus fleet currently comprises eight vessels, each one of three distinct classes from Ulstein Design AS and each incorporating the Ulstein X-BOW hull. Zickerman said the X-BOW hull provides for a smoother and more fuel-efficient passage through water, reducing emissions and optimizing transit speed, especially in marginal weather. Reduced pitch, roll and heave acceleration dramatically reduces tugging of in-sea equipment, increasing the operational window and making for a safer workplace. Polarcus vessels have a range of audited qualifications for energy efficiency and other factors. It claims to be the only seismic contractor in the industry today with DNV-acknowledged arctic procedures. The fleet has high ice class (ICE-1A and 1A) designations and winterized capabilities.

Polarcus has no immediate plans for new vessels but intends to upgrade the propulsion system on two of its vessels to improve margins. Zickerman said that, in the current prevailing market conditions, the company is content to focus on cash generation from its existing asset base.

Consistent in-sea equipment

With the acquisition of Fugro's geoscience division, CGG claims the largest fleet of modern high-end 3-D vessels, with 20 of its vessels operating with between eight and 16 long-offset streamers and maximum capacities of 12 to 20 streamers. During the last three years, the company has invested around $1 billion to modernize its fleet, which includes two 20-streamer Ulstein SX120 X-BOWs. The X-BOWs and six other vessels have DNV CLEAN design class notation for the lowest environmental impact. The entire fleet can run on marine gas oil (MGO) that, although more expensive, produces lower emissions than standard heavy fuel oil (HFO).

The tight link between CGG and seismic manufacturer Sercel means that it has maintained a consistent platform of in-sea and related equipment. The entire CGG fleet is fitted with Sercel Sentinel solid streamers. Solid streamers are environmentally friendly and have been proven in sensitive frontier areas such as the Arctic. They have the highest resistance to physical damage and are recognized as being the quietest in the industry, with the best low-frequency signal-to-noise ratio.

All of CGG’s vessels have steerable streamers, most deploying Sercel Nautilus 3-in-1 streamer positioning, depth control and steering devices. All vessels are capable of acquiring BroadSeis broadband data, and the BroadSource broadband source—which complements BroadSeis—is currently available on some vessels and is being rolled out across the fleet.

Pulling power

Established as a marine geophysical company in 2010, Dolphin Geophysical has one of the most modern fleets in the industry. It has a long-term charter for eight seismic vessels, including three high-end 3-D vessels due for delivery in 2014 and 2015. The company has settled on a standard 3-D vessel design that provides a stable platform for seismic acquisition and fast transit between projects with efficient fuel usage. Its high-end 3-D vessels have bollard pull in excess of 200 tons that, in addition to fast transits, enables them to achieve the wide tows that several clients require. In 2012, working for Shell in the Orange Basin, South Africa, Polar Duchess created what the company believes to have been the world's largest floating object—eight streamers, each 8 km in length, separated by a distance of 200 m (656 ft), constituting a moving width of 1.4 km (0.9 miles) of equipment through the water. The drag from this tow is estimated to have been approximately 90 tons, which less powerful vessels could not have towed safely.

“We take a pragmatic, practical approach to our vessel specifications,” said Phil Suter, Dolphin’s vice president of marketing and sales. “For example, ICE-class B is a minimum specification on our recent and newbuild vessels. We question the value of rating vessels any higher when the in-sea equipment and lead-in sections have much lower resistance to ice damage.” The vessels are usually powered by low-sulfur HFO, but all have sufficient MGO reserves on board for use as a backup or, if required, for a project due to local environmental regulations or at the client’s request.

Dolphin’s newbuilds are similar to its current high-end vessels except they will be even bigger and more powerful. The Super Duke, scheduled for delivery in March 2015, will be able to tow up to 22 streamers at 100-m (328-ft) separation. “Our new vessels are based on selected standard hull designs but have otherwise been designed from scratch based on extensive operational experience,” Suter said. “Thanks to the size and power of the acquisition platform, our experts do not need to make any compromises when designing the back deck for the most efficient and safe operations.”

Radical hull design

Around 17 years ago Petroleum Geo-Services (PGS) embarked on a major project to plan its new generation of seismic platforms. It noted that, while various seismic companies had selected many different types of vessel hulls for conversion to 3-D operations, the original platforms were all purpose-designed for something else, namely to travel port-to-port at high economic cruising speeds. By contrast, during surveys, 3-D seismic vessels operate at a slow speed of around 5 knots, and to maintain large spreads of in-sea equipment they must deliver around 120 tons of forward thrust for extended periods of time. In addition, the large volumes of heavy in-sea equipment needed on a high-capacity 3-D vessel must be safely and efficiently carried, deployed and retrieved from above the water line. The company considered that squeezing this volume of equipment into a conventional hull generated stability challenges and required compromises in handling systems.

PGS selected the Ramform Class of vessels as its new seismic platform, based on the unusual hull design of Marjata, a purpose-built electronic intelligence collection vessel operated by the Norwegian Intelligence Service. PGS launched its first Ramform 3-D vessel in 1995, and the concept is now in its fifth generation, which it calls Titan-class. The company currently operates eight Ramform vessels, and three more Titan-class vessels will be delivered by the end of 2015. PGS says these vessels illustrate enhancements of many features that its designers and builders have incorporated for the single purpose of collecting the maximum amounts of seismic data as quickly, safely and reliably as possible.

Construction and equipping of Ramform Titan, the first of PGS’ new-generation vessels, was completed in April 2013. Its 104.2-m (342-ft) length is not unusual, but its 70-m (230-ft) width at the stern makes it one of the widest commercial vessels ever built. The hull shape provides enormous back-deck volume and a load-carrying capacity equivalent to conventional vessels many times its size. The Ramform Titan is equipped to tow up to 24 streamers, which PGS said is more than double the capacity of most conventional 3-D vessels and translates to higher productivity in operations. The vessel has fuel capacity of around 6 Mcm (212 Mcf), enabling it to operate for more than 150 days without refueling.

The seismic in-sea equipment weighs more than 600 tons and can be deployed over a 12-sq-km (4.7-sq-mile) area. The vessel has three engine rooms, each in isolated compartments, together providing up to 18 MW of power. Bollard pull in acquisition mode is 150 tons, and top speed for transit is 16 knots.

A buoyant market
Based on hydrocarbon supply and demand forecasts and projected E&P expenditure, seismic companies are confident their market will remain buoyant for the foreseeable future. Developments in source and streamer technologies combined with continuing improvements in 3-D data processing and analysis techniques are delivering 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. As the platform for marine operations, vessel design strategies remain key to the cost effectiveness of these companies’ seismic fleets.

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