The safe installation of the first tension-leg wellhead platform offshore Brazil could pave the way for future similar developments, says DNV GL’s Mike Roberts and David Ryan.
Chevron’s Papa Terra facility offshore Brazil. Photo from DNV GL.
First production from Papa Terra this March signaled the successful completion of a landmark development: the first tension leg wellhead platform (TLWP), P-61, for South America and inaugural application of dry tree technology off Brazil.
DNV GL’s global teams played an important role in identifying, mitigating and eliminating risk during what was a particularly high-profile and complex project – P-61’s safe construction, transportation, installation and operation 110km off the South American coast.
The project may mean TLPs are increasingly considered as viable future development options to tap the region’s significant deepwater reserves.
The Petrobras-operated Papa Terra heavy oilfield is in Campos Basin block BC-20, at 1190m water depth. The field is estimated to contain from 700 million to 1 billion boe. P-61 was installed in April 2014 connected to a tender assist drilling rig moored nearby, transferring hydrocarbons through flexible lines to the P-63 FPSO, about 350m away.
The TLWP has dry trees connected to top tensioned risers, with the tender assist drilling rig supporting all the well drilling and workover activities.
A total 13 production wells are being connected to P-61, with the first well, PPT-16, having started production in March.
As with many TLPs, construction took place in multiple locations.
The topsides were constructed at the Keppel FELS’ yard in Singapore; the tendons and piles in the US, and the hull by Keppel FELS Brazil, at its BrasFELS yard. The topsides were transported to Brazil in late 2012, for mating with the hull using floatover methodology. The TLWP installation was completed in March 2014.
Global scope and expertise
The Papa Terra facility. Photo from Programa de Aceleração do Crescimento, from Flickr under creative commons license.
FloaTEC, the US-based joint venture between McDermott and Keppel FELS, responsible for engineering, procurement, construction and installation of the TLWP, called on DNV GL’s marine assurance and technical advisory team in 2010 to provide marine warranty services (MWS).
As an MWS provider, DNV GL has supported the safe construction, transportation and installation of approximately 80% of the world’s TLPs, starting in the 1980s when the-then Noble Denton was involved in the installation of the first platform of this kind: Hutton, in the North Sea.
For P-61, DNV GL worked closely with FloaTEC, acting as third party verifier on behalf of the underwriters to identify, minimize and, where possible, eliminate project risk during specific activities in line with its own internationally-recognized guidelines.
The project involved reviewing hundreds of design and installation documents and drawings for the various components, including heavy lift procedures for site fabrication and procedures for the transportation of tendons and tendon buoyancy modules from the Gulf of Mexico to Brazil.
The team also reviewed the procedures for the floatover of the topsides onto the hull, as well as the asset’s subsequent tow and installation offshore, including the installation of the piles and tendons.
Benefits and challenges
Generally, TLPs are a widely adopted and trusted solution for deepwater developments, particularly where there is an infrastructure already in place. They have a smaller footprint on the seabed and are particularly stable as they are not subject to swell and roll motions.
Yet, TLPs do present specific challenges that need to be addressed in advance through the creation and agreement of appropriate procedures, which require independent MWS verification.
For P-61, like many TLPs, the real complexity is below the surface, particularly considering the intricate infrastructure that comprises tendon systems, subsea risers and umbilicals.
In this case, the design of the various mooring systems, specifically between the FPSO, the TLP and the tender assist rig needed to be carefully planned using 3D assessments to avoid infrastructure clashes such as the crossing of mooring lines throughout the entire installation process, not just the final integration.
The Campos Basin is an exposed deepwater environment. Specific issues included swell conditions, affecting the installation vessel and the TLP’s hull, which could have caused considerable project delays.
Vertical motion caused by swell, or vertical surge, becomes an issue during the integration phase, when the tendons are being connected to the hull. Here, maximum environmental criteria were developed, to ensure the optimum environmental conditions and required weather window was established using historical environmental data for the location.
Meteorological and oceanographic information is a key requirement for location approvals, transportation and structure design, and weather-limited operations. Procedures were also put in place to mitigate the impact of adverse weather and, though installation was halted at times because of extreme conditions, this was an orderly procedure with only minor delays in order to maintain the safety of the operation and personnel.
Logistical and design approach
Various elements of a TLP are typically constructed in multiple locations and need to be transported safely to the final destination for assembly and installation. P-61 was no exception.
At Keppel FELS yard in Singapore, the designers took the innovative approach of constructing the topsides on a purpose-built barge, specifically to suit the floatover operation. The barge and topsides were floated on to a heavy lift vessel for transport to Brazil with the transportation route round Cape of Good Hope, which is notorious for extreme weather conditions.
Hull construction was also unusual. Normally, the hull portion is built as one unit with four columns; however, the Brasfels dry dock in Brazil was not wide enough to support this method and, as such, the lower part of the hull and starter columns were built as two C-shaped sections. Both were floated out jointly before being welded together. The fabrication was continued with the completion of the four columns.
This floatout was subject to incredibly tight parameters, with small clearances between the keel of the hull, the temporary supports in the dry dock and the dry dock sill. Everything had been considered to ensure the operation’s feasibility: the floatout not only had to be timed with high tide in order to have the maximum depth at the exit point, but there had to be careful weight management of the hull to ensure it was not sitting too low in the water.
Despite current oil and gas price challenges, there remains huge potential offshore Brazil, a region home to more than 7.5 million sq km of on- and offshore reserves. International investment is increasingly likely due to the ongoing 13th licensing round, covering some 266 blocks across 10 geological basins, together with current proposals to reform the pre-salt production-sharing regime.
The design of the various spread mooring systems required for the FPSO and the tender assist rig meant that if a spread mooring system was used for P-61, the offshore location would have had a very complex system of mooring lines, subsea risers and umbilicals. This would have been difficult to install and maintain adequate clearances between any mooring lines, subsea risers and umbilicals. By using a TLP, the number of mooring lines was significantly reduced thus alleviating this problem.
Added to that, now the industry in Brazil has seen its first TLP installation, it is possible the technology will be increasingly considered as a viable and effective development option to exploit these reserves.
Mike Roberts has more than 31 years’ engineering and management experience, including 25 years in the design and installation of offshore structures. Roberts is also the Global Technical Authority for three of the Noble Denton Marine Assurance and Advisory Guidelines and is presently re-writing these guidelines following the merger of DNV and GL Noble Denton.
Captain David Ryan is a master Mariner with more than 35 years’ experience at sea and onshore in the marine industry, with the last 14 years specializing in marine warranty, marine casualty investigation, and marine risk management. Ryan is the Marine Manager in the Houston hub and a member of Noble Denton Marine Assurance and Advisory Technical Standards Committee on the subjects of Marine Warranty/Marine Assurance and Marine Transportations.