Alpha Mahatvaraj of GMC Inc. discusses how their new mechanically connected risers could offer a potential solution for ultra-deepwater projects.
The contribution of ultra-deepwater developments to world oil production is expected to accelerate in the coming years provided that the escalating capital expenditures (capex) of these projects can be con- tained. A major component of the ultra- deepwater project capex is the SURF cost, particularly risers and flowlines. The current riser solutions for deepwa- ter fields including flexibles and steel reeled or J-lay welded risers have either limitations on service requirements or have significant cost impact.
GMC Ltd. developed a mechanical connector product line for risers and flowlines called intelligently connected pipe (ICP) to meet the emerging needs of the deepwater SURF market. The connection of risers and flowlines with pre-manufactured tubular eliminates the need for offshore welding and high-cost installation and lay vessels. The SURF installation market will be opened up to allow many potential new subsea contractors to bid for projects.
Flexibles manufacturers have yet to find a qualified solution for presalt risers, primarily due to the high CO2 content that attacks the carbon steel tensile layer. Additionally, deepwater and associated high pressures (internal and external) are at the limit or beyond the current capability of flexible pipe. Flexible risers currently do not offer a life of field solution and given that these wells can produce for over 20 years, the flexible route is a very costly option for the operator. Corrosion resistant alloy (CRA) clad steel pipe addresses these problems, however at greatly increased installation cost.
J-lay welded and reeled SCRs have their own inherent problems in that installation is very costly with the extremely high day rate of the specialized installation vessels.
|GMC's mechanical connectors. Photo by GMC Inc.|
Timing is a key issue
Recent presalt projects have been delayed by riser and subsea installation assets, a rare scenario as normally the FPSO was the critical path. Component time is therefore a critical issue and one of the big potential drivers for using connectors, which can be delivered much faster than flexible pipe or reeled steel spools. The ICP can be installed using a 120m DP MSV with a modular J-lay tower using a connector pipeline installation procedure (C-Lay) developed by GMC. Smaller installation vessels such as these are readily available unlike the conventional welded J-lay options. The large specialized installation vessels have a single line critical path and this has proved a problem for major operators with delays on other projects having cascade effects on installation schedules.
The ICP solution enables the operator to more quickly and cost effectively produce and manage well production. It allows local assets to be used in SURF rather than waiting for the large international contractors to plan the mobilization of assets from distant shores. Traditional welded lazy wave steel catenary riser (LWSCR), freestanding hybrid riser (FSHR), and flexible riser technologies are time consuming to manufacture as well as to install. Other opportunities for ICP exist in pipe-in-pipe, work-over risers, flow-lines and subsea jewelry applications to name just a few.
A key feature of ICP is the fabrication process, where the pipe joining happens off the critical path in a controlled onshore environment. This assures a high degree of consistency in the joining process and produces joints with high fatigue resistance. The coat- ing and CRA cladding of the joints for offshore installation can also be customized per project requirements. The ICP solution also enables operators to include more local content in the manufacture and installation of the risers and flowlines.
GMC’s mechanical connector is the enabling technology behind ICP. The connector is an axially made-up pin and box type connector designed to meet the requirements of ISO 13628-petroleum and natural gas industries, design and operation of subsea production systems-and API 2RD-dynamic risers for floating production systems, API standard 2RD, Second Edition, September 2013-and is fully qualified to the testing requirements per ISO 21329.
The connector has a redundant sealing mechanism with three separate seals. The figure (left) shows the three sealing locations and the metal to metal con- tact areas that comprise the connector sealing mechanism. It is also corrosive service compatible and fatigue resistant. The connectors are reusable, and the installed pipe can be recovered in reverse sequence, and can be cleaned, surveyed, and stored for reuse.
Assembly of the ICP pipe joints including the pipe to connector joints and the pipe-to-pipe joints is accomplished in a controlled manufacturing facility onshore, off the critical path of the installation project. Options for the joining process include friction joining which results in pipe joints that are 100% parent metal and exhibit fatigue and strength properties comparable to the parent pipe. This friction joining process can be fully automated to maximize efficiency and maintain the high quality of joints. GMC is currently conducting friction joining trials to qualify the process for high strength, high fatigue and corrosive service requirements.
Even for conventionally welded pipe joints, the ability to complete all welds in a controlled environment, including the ability to perform post-weld heat treatment and internal clean-up machining results in joints with superior strength and fatigue properties than can be accomplished by offshore welding. This removes the pipe joining process away from the critical path during offshore installation.
|Redundant seals. Photo by GMC.|
GMC analyzed a 12-riser field development installed at 2200m water depth and considered the riser scope only. When compared relative to reeled SCRs, J-lay welded SCRs and flexibles, the economic advantage was in excess of 25% of total costs for installation, riser procurement and engineering.
Installation is assumed to be completed by a local 120-130m MPV with a modular J-lay tower on board.
While this comparison alone provides compelling economic support for the ICP riser solution there is an additional consideration of a qualitative nature that should be taken into account when assessing the economics of ICP. This consideration is related to the risk profile of these large installation contracts and the schedule uncertainty associated with them. Installation contractors who have access to a very limited number of the highly specialized vessels required for either reeled SCR installation or welded J-lay are forced to price their projects based on a comparatively long block of time (so called “block booking”) in order to ensure that the vessel will be available when the project is ready for installation of the risers and flowlines. This results in project costs that can easily be double the cost calculated by simply multiplying day rates by the time required to install the risers. An ICP vessel however has a much lower day rate and can be easily assigned to other well intervention, IRM, or light construction tasks when not utilized for the riser installation. This allows project costs to be much closer to the actual duration, with weather being the one remaining risk for which to account.
Alpha Mahatvaraj is offshore products manager at GMC Inc., a subsidiary of GMC Ltd. He has over 15 years of experience in mechanical design and product development.
Recent projects include development of mechanical connectors for dynamic applications, design and delivery management of riser system components and TLP tendon connectors. GMC Ltd. is a deepwater product, engineering, and project management company that develops and produces enabling technologies.