SBM Offshore discusses some of the company’s developing technologies and how it is working toward unlocking reserves in the Gulf of Mexico.
Exploration for fields further offshore and in deeper waters is leading to the development of more complex reservoirs. It is also fueling technology innovation from service providers. Product development is driven by evolving market demand and relies on close collaboration with clients.
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A rendering of FPSO Turritella. Images from SBM Offshore. |
Dutch floating production and mooring system provider SBM Offshore was recognized at this year’s Offshore Technology Conference in Houston for its Very High Pressure (VHP) Fluid Swivel technology, which allows operators to use floating production storage and offloading (FPSO) units throughout the full development of ultra-high-pressure reservoirs. Previously, full development had not been possible where a weathervaning system was required in conjunction with fluid re-injection into the reservoir.
Back to work in the Gulf of Mexico
The VHP Fluid Swivel technology would be particularly relevant to the Paleogene reservoirs, or Lower Tertiary fields, in the US Gulf of Mexico. The US Bureau of Safety and Environmental Enforcement says that there are about 90 announced Gulf of Mexico deepwater prospects, “with operators setting and surpassing records in water depth and length.”
Currently, only two Lower Tertiary fields are in production today due to the extreme challenges of these reservoirs, which are characterized by extreme water depth and high-pressure/high-temperature (HP/HT). The Lower Tertiary formation in the Gulf of Mexico is situated approximately 280km offshore and runs 125km wide and 480km long.
Paleogene-aged sandstone reservoirs typically lay between 8000m and 10,000m below sea level. The extreme depths result in pressures in excess of 1400bar (20,000psi) and very high temperatures that test the limit of what the industry is capable of operating in today.
Until recently, no technology has existed to overcome the inherent difficulties that come with the ultra-deep fields, which range from 1500m to potentially as deep as 4300m.
New technology developed by SBM Offshore will enable FPSOs to be widely used for the extremely challenging Lower Tertiary fields. These solutions are applicable for both early production and full field developments.
The FPSO Turritella for Shell’s Stones development marks SBM Offshore’s first move into the region. Due to start operations in 2016, it will be the deepest production unit in the world at 2900m. For SBM Offshore, the list of industry firsts for Turritella also includes the first disconnectable turret with steel lazy-wave risers. As a consequence of the combination of water depth and steel risers, the buoy has the biggest displacement to date. Fitted with a very complex mooring system, it will have a processing capacity of 60,000bpd and 15MMscfd. For this turret, SBM Offshore developed and qualified several new components related to the buoy pull-in and latching systems, as well as a new design for the massive buoy.
The company is also attempting to address the remaining technology gaps in the industry with the development of its two new systems. Along with the previously mentioned VHP Fluid Swivel, the MoorSpar aims to make developments in the Gulf of Mexico become a more cost-effective reality by enabling larger disconnectable FPSOs for full field developments.
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Above: FPSO Turritella marks Dutch FPSO provider SBM Offshore’s introduction to the Gulf of Mexico. Images from SBM Offshore. |
Technical challenges
Some Lower Tertiary reservoirs appear to be poor quality, leading to low recovery factors. Oil players have launched a series of industry-wide initiatives to sponsor the oilfield service industry to fill the key technology gaps for subsea and well equipment.
Due to the characteristics of the Lower Tertiary reservoirs, SBM Offshore has found that the key challenges include:
Technical solutions for the Lower Tertiary Paleogene fields
SBM Offshore has developed and qualified a range of new technologies to meet these challenges. In addition, the company is mining existing its technologies to attempt to increase productivity, efficiency and safety. Here are some examples:
1. Disconnectable FPSO with steel risers for early production
SBM is building the FPSO Turritella for Shell’s Stones development. A Suezmax tanker is currently being converted in Keppel’s shipyard in Singapore. It will be the deepest production unit ever installed, and the first disconnectable system with steel risers.
Currently, only Petrobras has an FPSO operating in the Lower Tertiary area on the Cascade/Chinook fields, which is the first FPSO approved for use in the US sector of the Gulf of Mexico.
The FPSOs for Shell and Petrobras are both relatively simple processing units with no reservoir pressure maintenance in terms of water or gas injection. The primary purpose of the early production systems is to allow the operator to gain an understanding of the reservoir performance from a small number of wells, before deciding on the best full field development strategy. An FPSO minimizes the need to run a long export oil pipeline across difficult seabed terrain in ultra-deepwater.
Hurricanes are prevalent in the Gulf of Mexico. To avoid exposure to this risk, FPSOs operating there need to be disconnectable, which is typically achieved by releasing a buoy to which the risers and mooring lines are attached. The buoy then sinks to a pre-determined depth. Once the storm passes, the FPSO returns and the buoy is reconnected so that production can recommence.
However, this type of development has limitations due to the maximum suspended weight that the disconnectable buoy can support; depending on water depth and riser design, a maximum of six to 10 risers and umbilicals can be accommodated. For Stones, SBM, in close collaboration with Shell, has developed the world’s largest disconnectable turret, complete with several new components needed to enable the buoy to be safely connected and disconnected.
Coupled analyses of steel risers and FPSOs enable SBM to optimize both the riser design and the vessel motions and excursions.
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SBM Offshore’s Very High Pressure Fluid Swivel, which was recognized at OTC 2014. |
2. Disconnectable FPSO with steel risers for full field development
Full field developments typically require a larger number of risers and umbilicals, which a disconnectable turret cannot accommodate. SBM developed the MoorSpar system, which is supported by a conventional, slender spar-type structure, with the capacity to support more risers and umbilicals. The concept is the result of more than seven years’ research, involving extensive model tests. It is ready to enter a major project FEED.
The concept makes use of a yoke on the FPSO, which is elevated on disconnection from the MoorSpar. This simplifies the riser design, as the spar remains floating when disconnected and the MoorSpar size can be adjusted to the riser loads. Moreover, when connected, the yoke decouples the FPSO motion from the risers, enabling the use of simple steel catenary risers instead of the more expensive lazy wave configurations.
The current industry pressure limit for an FPSO fluid swivel is 520bar, however, this is inadequate to allow water and/or gas reinjection into Lower Tertiary fields; pressures are needed well above this level. The solution from SBM is the VHP Fluid Swivel. The 830bar swivel design successfully passed a full qualification program. Long duration endurance runs equivalent to five years in North Sea conditions were undertaken. The swivel design can accommodate operating pressures up to 1,000bar (14,500psi). Further tests during 2014 will complete qualification at this pressure.
Launched in 2009, the development program has resulted in a patented technique to allow the swivel seals to accommodate much higher pressures. The resulting VHP fluid swivel is suitable for water injection, gas injection or WAG service. The high-pressure rating of the VHP Fluid Swivel has been achieved by limiting the pressure differential across individual seals in the swivel. An Oil Pressurization System (OPS) supplies two pressurized fluid barriers for this purpose: 860bar between the isolation and primary seals (first barrier), and 430bar between the primary and secondary seals (second barrier). There is ambient pressure between the secondary and tertiary barrier. The VHP OPS thus limits the pressure differential over any seal to 430bars, which is within the qualified capacity of the seals.
“The VHP Fluid Swivel demonstrates that our continued innovation is successfully bridging the technology gaps identified with our clients,” SBM Offshore Group Technology Director Michael Wyllie says.
3. Deep draft semisubmersible
For deepwater fields in harsh environments, SBM’s DeepDraft vessel holds the world record water depth for a floating production semisubmersible. Independence Hub semisubmersible FPU has been installed in the Gulf of Mexico, in 2415m water depth, since 2007. Its daily gas production capacity is 1 billion scf/d.
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An FPSO coupled with the MoorSpar technology, which allows it to support a large number of steel risers for a full-field development, where disconnection is required. |
The MoorSpar System
This technology permits an FPSO to take a higher riser load, and yet still allow disconnection to sail away from hurricanes. The MoorSpar system can be advantageous for high pressure and high temperature reservoirs as it avoids the need for flexible jumpers or risers.
The system device combines several proven technologies to provide a unique new solution for offshore field developments. It consists of a truss-like structure set above a long, slender buoy, which is moored to the seafloor.
FPSOs are connected to the facility through a standard articulated yoke system linked to a main roller bearing situated below a gimbal table at the top of the MoorSpar unit. This arrangement accommodates the yoke roll and pitch motions of the vessel while allowing the FPSO to weathervane. Steel risers are connected to the MoorSpar facility at riser porches located along the keel of the buoy. The riser is then linked to internal piping, which is routed up through the central column and then across hard piping and swivels to the FPSO.
By decoupling the FPSO motion from the risers, by means of the articulated yoke, the MoorSpar enables the use of simple steel catenary risers versus more expensive steel lazy wave risers.
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