Latest Ramform pushes the bounds in seismic vessel technology
Providing a major capacity boost and raising the stakes in the high-density segment of the rapidly growing market for marine seismic data acquisition, Norwegian-headquartered specialist Petroleum Geo-Services (PGS) is investing in a new generation of seismographic research ships, by David Tinsley.
Based on the unique, delta-shaped Ramform hull concept, the diesel-electric Titan-class vessels have been developed and equipped to extract the full potential of PGS’ flagship GeoStreamer technology. With the overarching purpose of collecting maximum amounts of data quickly, reliably and safely, the design heralds a new blend of efficiency, technical sophistication and capability, incorporating 24 streamer reels each able to hold and deploy 12,000m of recording cable.
Given first form in the recently commissioned Ramform Titan, the fifth-generation Ramform series embodies an extreme breadth aft of 70m on a length of 104.2m. The iconic and unusual hull shape enables a considerable amount of seismic equipment to be installed with no compromise to working space or safety, and confers enhanced stability, a vital factor in survey work performance and productivity. The volume attained in relation to length also allows for extreme fuel capacity, offering survey endurance of 150 days without refuelling.
The Titan class thereby introduces an accentuated breadth and denotes a step-up in size relative to the company’s preceding vessels, the 2008/2009-built Ramform Sovereign and Ramform Sterling, which have a maximum width of 40m and length overall of 102.2m.
From an industrial standpoint, the project has added significance in that the build programme has been entrusted to Japan whereas all four preceding generations of Ramform vessel were delivered from Norwegian yards. Ramform Titan was constructed at the Nagasaki complex of Mitsubishi Heavy Industries (MHI), whose original two-ship deal with PGS was augmented last year by orders for third and fourth vessels.
In recent years, MHI has implemented a new business strategy in which the emphasis has been placed on higher added-value construction, and the latest Ramform series is a graphic expression of this policy and the builder’s technical scope. Each of the first pair is costing approximately $250million, including construction supervision, commissioning, and the comprehensive seismic package.
Ramform Titan will spend her first season working on MultiClient projects in the North Sea. One of the company’s four business divisions, MultiClient manages seismic data PGS acquires, markets and sells on a non-exclusive basis. By contrast, the Marine Contract division provides seismic survey services to oil and gas exploration and production clients on exclusive terms.
Rising demand for high density surveys is driven by deepwater exploration and production in geologically-complex areas such as offshore Brazil and West Africa, and the Gulf of Mexico. In addition, the high fidelity data yielded by PGS’ proprietary, dual-sensor GeoStreamer technology is opening up new markets in mature basins, such as the North Sea. Key factors influencing success in the high density sphere are large spreads, long streamers and towing efficiency.
The Titan-class Ramforms are expected to strengthen PGS’ particular standing in areas affected by rough weather or harsh environmental conditions, or any sphere in which operational windows are short. The new vessels include a significantly upgraded GeoStreamer-based seismic package and are designed to apply the full benefits of GeoStreamer towing efficiency.
The unique seismic acquisition system uses particle motion as well as conventional pressure sensors (hydrophones) to yield superior seismic images. The GeoStreamer equipment records a far broader bandwidth of signals, including both lower and higher ends of the spectrum for clearer imaging of both deep and shallow targets. Access to lower frequencies, down to 2Hz, expands the usefulness of the data for exploration and reservoir analysis.
Through the successive generations, Ramform vessels are claimed to have been the first ships to tow eight, 10, 12, 14, 16 and 17 streamers, and units of the fleet routinely deploy 12 or more. Ramform Titan is equipped with 24 streamer reels, whereby 16 are placed abreast across the stern, with a further eight in a second row further forward. Six independent source array handling booms speed handling and reduce risk exposure.
The configuration and its extent affords PGS considerable survey flexibility, faster deployment and recovery of the recording gear, and enhanced overall efficiency, with the requisite operational safety. She will typically tow more than 12km² of equipment, encompassing several hundred thousand advanced recording sensors encased in 16 or more cables, each up to 10km in length, suspended 10m-20m below the surface. By installing a 24-reel outfit, the owner has ensured a very high level of operational redundancy as well as increased potential for the future.
The lateral offset of the streamers is achieved by deflectors. Ramform Titan applies the successful deflector handling arrangement used on the preceding S-class.
The sinusoidal waterline makes for stable motion behaviour across the beam, with the proportionally vast back deck ideally suited to the installation, deployment, retrieval and towing of the extensive seismic gear and related equipment, and affording substantial, interior instrument room capacity.
Diesel-electric main propulsion has been nominated in the interests of quiet running and operating flexibility. The plant in Ramform Titan is based on six 3,840kW engines in the main genset aggregates, making for a total power concentration of around 23MW, and feeding three 6MW electric propulsion motors driving three Wärtsilä controllable pitch propellers for a maximum propulsive effect of 18MW.
The six prime movers are Wärtsilä eight-cylinder, 32-series diesels. ABB supplied the electrical power and propulsion systems, including generators, transformers, frequency converters, medium voltage switchboards, electric propulsion motors, and power management system.
The ship is fully operational using just two of her three drivelines. This permits maintenance to be undertaken during production operations as well as conferring redundancy, which extends further to the dual, fully separated engine rooms, and to the power generation and auxiliary systems.
In-sea survey capabilities for monitoring and maintaining stern tubes and seals, combined with substantial onboard provision for spares storage, have permitted the drydocking interval to extended from five to seven and a half years, with resulting benefits for ship productivity.
The immense back deck and the relative protection it offers allows for safer handling of workboats at the waterline, using special launch cradles. Two stern-launched workboats are carried for in-sea maintenance of the streamer spread and other equipment. Ramform Titan is fitted with single cabins for 60 regular crew members, plus 10 twin-berth cabins for visitors and supernumeraries.
Two combined lifeboat/tenders, located on the sides of the ship at the turn into the parallel body section, can take the entire complement of 80 to safety in an emergency situation, or may be used in other operations. The craft are also equipped with Dacon scoop rescue systems for recovering personnel in a man-overboard situation. The forward-located helicopter deck and reception room provide for helicopter-based crew changes.
DNV is classing the new Ramform series. The society has employed advanced verification procedures including the hydrodynamics analysis necessitated by the design’s extreme main dimensions, and FMEA (failure modes and effects analysis) required for the RP (redundant propulsion) notation.
Second-of-class Ramform Atlas is due in the fourth quarter of 2013, while the second pair of newbuilds is scheduled to be delivered over the course of 2015.
The Ramform hull shape was originally based on that adopted for the Norwegian naval intelligence vessel Marjata. PGS acquired the rights to the vessel design and first employed this in the 1995-commissioned Ramform Explorer, carrying 10 streamer reels. Nine Ramform vessels are now in operation around the world, including the Shigen (formerly Ramform Victory), sold to Japan in 2008.
Principal Particulars--RAMFORM TITAN
Length oa 104.2m
Length bp 96.0m
Width at stern 70.0m
Gross tonnage 20,637gt
Streamer capacity 24 x 12km
Main propulsion system Diesel-electric
Main genset engines 6 x 3,840kW
Propulsion motors 3 x 6,000kW
Propellers 3 x controllable-pitch (CPP)
Bollard pull, acquisition mode 150t
Transit speed 16 knots
Fuel capacity 6,000m³
Endurance (production/transit) 150 days
Accommodation, berths 80
Class DNV +1A1, SPS, Ice C, E0, HELDK, RP, Clean Design, TMON, BIS, NAUT-AW, VIBR, COMF-C(3) V(3)
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