With an increasing number of developments in deeper water and more challenging environments, infrastructure and its associated installation has to be adaptable and capable of coping with unique conditions.
The Rochelle area lies approximately 185 km north east of Aberdeen, and is a combination of two gas condensate fields. The East Rochelle development -which was discovered in April 2000 – is located on Block 15/27, and the West Rochelle field, which encompasses blocks 15/26b and 15/26c, was discovered in October 2010. The Rochelle unit area is jointly owned by Endeavour International Corporation (44 per cent), Nexen Petroleum UK Ltd (41 per cent), and Premier (15 per cent).
In June 2011, Endeavour Energy UK, a wholly owned subsidiary of Endeavour International Corporation, awarded subsea specialist Technip an engineering, procurement, construction, and installation (EPCI) contract for the East Rochelle development.
The contract scope encompassed full project management and detailed design, procurement, fabrication, installation, and pre-commissioning of 30 km of production pipe-in-pipe, flexible riser, free-issue umbilicals, and subsea isolation valves and manifolds.
It also included construction and tie-in of spools to the wellhead structure, trenching, backfill, and rockdumping work. A further contract award for a 7 km extension to connect the West Rochelle well to the East well followed the initial agreement. Both wells are tied-back to the production facilities on the Scott platform through a subsea isolation valve umbilical (SSIV) and manifold.
Other work included platform flexible and umbilical pull-ins and commissioning, crossings’ installation, surveys, and pre-commissioning. The water depths along the pipeline route range from 137 m to 146 m.
Subsea engineering challenges
Field surveys carried out prior to work commencing on the Rochelle fields indicated soft clay seabed soil and multiple pockmarks (seabed depressions) throughout the field. This resulted in detailed engineering analysis to ensure adequate pipeline support at the trench transitions and crossings. Feedback from both the survey and the trenching vessels initially on the field enabled Technip to identify and correlate the information required to ensure an efficient offshore construction operation.
Technip used its extensive trenching database to predict the risks of trenching in very soft to soft clay. Shorter transition lengths at the transition-in and-out locations, as well as buoyancy and soft-soil skids, were implemented to prevent excessive sinkage. The soil-bearing capacity for the mid-span support to allow the 10 inch/14 inch pipe-in-pipe to cross two 30 inch pipelines was also assessed, and a stress analysis was carried out on the 30 inch pipeline (using ABAQUS finite-element analysis) to evaluate possible soil settlement in order to ensure the pipe was not at risk of buckling.
Breakthrough in pipelay technologies
The Rochelle project demonstrated a breakthrough in pipelay technologies. Technip’s recently upgraded Evanton spoolbase was used for both the fabrication and spooling of the 10 inch/14 inch pipe-in-pipe. The size and wall thickness of the pipe-in-pipe used for the project had very high stiffness levels, and the project team developed innovative engineering solutions in order to facilitate reeling the fabricated pipe-in-pipe on to Technip’s pipelay vessel, the Apache II. The detailed and comprehensive onshore activities contributed to an extremely successful offshore campaign.
Technip’s revised approach incorporated reelable and end bulkheads, a pawn head with split-head adaptor system to connect the pipe on to the vessel reel, and pipeline-fixed laydown lengths within the subsea target boxes. The development and introduction of the reelable bulkheads dramatically reduced the vessel’s offshore time, and also resulted in a reduced amount of welds and therefore non-destructive examination (NDE) being carried out offshore, decreasing the amount of time required to perform the connections onboard. The knock-on effect of these innovations was that the required weather window for pipelay offshore was also reduced.
As well as saving time offshore, the adoption of the pawn head and adaptor system minimised the amount of time the vessel spent in port while the pipe-in-pipe was reeled and loaded on to the vessel. Fixed laydown lengths subsequently saved time on vessel topsides’ work during the laydown of the pipe-in-pipe. The savings to the vessel in terms of operational time at the spoolbase were in the region of 15 per cent.
These innovations resulted in the installation of the pipe-in-pipe being carried out in record time. The Apache II was deployed to undertake the installation and took five trips – lasting a total of 25 days – to lay the required 37 km of pipe-in-pipe. This represents a reduction of approximately 32 per cent against the initial time estimate for this work.
The ability to reduce the in-field laydown times for each trip was particularly valuable, as some of the work took place during the winter months. Traditionally, operations carried out at this time of year are subject to fewer and smaller weather windows due to wind speeds and sea states that are incompatible with the necessary operations.
International resources and client relationships
Resources from across Technip were used to fulfill the contract. 37 km of Technip’s innovative rigid, reelable pipe-in-pipe were welded at Technip’s spoolbase in Evanton, while the flexible riser was manufactured at the company’s flexible manufacturing unit in Le Trait, France.
International mobility within Technip was key to the success of the project. The Rochelle project team was made up of staff from Australia, Canada, Malaysia, Nigeria, Norway, and the UK. Drawing from Technip’s global team ensured the right skillsets were available as and when they were required. In addition to ensuring the project was delivered safely with no lost time incidents, on time and within budget, this approach gives Technip the opportunity to “÷take it further’. It presents new challenges and exposes them to different environments in terms of geography as well as functional and segmental diversity.
Endeavour Energy UK’s CEO William L. Transier recognised this effect whilst working with Technip.
“Technip’s installation performance and attention to HSE at the Rochelle development has been excellent,” he said.
“Innovations in pipelay technologies introduced by the integrated Technip/ Endeavour teams established the ability to complete the work scope in record time and within budget.
“The successful installation performance, even during the winter months, demonstrates the value Endeavour sees in partnering with companies like Technip to create innovations that benefit the entire industry.”
Work on the Rochelle project to date has been completed in 750,000 man-hours with no recordable HSE incidents or accidents. Innovation combined with clear and effective communication between all involved in the project from Technip, Endeavor Energy UK, and third-party contractors ensured the smooth running of the project and the record-breaking delivery of the pipe-in-pipe installation.
Individual 12 m lengths of pipe are fabricated into pipe stalks at Technip’s custom-built Evanton spoolbase in the Cromarty Firth. Following numbering and a pre-weld inspection, the pipes are rolled on to an alignment welding station, where the ends are pre-heated. This is the start of a welding line and cycle that welds the sections in to 1 km long pipe stalks. At predetermined cycle times, a new section of pipe is added to the stalk, and each joint receives the required amount of weld passes at up to eight separate stations.
Welding is crucial to the entire process and the full range of mechanised and manual technologies are available. As the whole pipe-in-pipe fabrication process is onshore, the welding can be done in a controlled way to the highest technical standards and if there are any problems they can be dealt with quickly and effectively.
Weld inspection/non-destructive examination (NDE)
Following welding, the pipe moves through the visual weld inspection area to the non-destructive examination area. The primary examination techniques are traditional radiography, digital radiography, and automated ultrasonic examination, backed up by manual ultrasonic, magnetic particle, and/or dye-penetrant inspection as required.
The coating of the weld area is the next stage in the process. This is carried out in the field-joint coating area; generally mechanised three-layer polypropylene tape wrap, injection moulded polyurethane, or polypropylene are used.
1 km pipe stalks are fabricated for both the outer carrier pipe and the inner flowline in a pipe-in-pipe application. The completed pipe stalks are stored on the stalk racks or on the causeway waiting for pipe-in-pipe assembly.
The assembly of pipe-in-pipe stalks
Technip has designed and manufactured portable hydraulically operated pushframes to push the inner flowline pipe stalks into the outer carrier pipe stalks.
The carrier pipe stalk, fitted with a bell-mouth guide, is secured in a fixed clamp at one end of the pushframes, and the inner flowline pipe stalk is held in a sliding trolley clamp at the opposite end. There is a 4 m workspace between the two sets of clamps to allow the spacers and insulation to be fitted to the inner flowline. A hydraulic mechanism, capable of 100 tonnes of force, simply pushes one pipe stalk inside the other, 4 m at a time. It takes around 250 pushes to produce a 1 km long pipe-in-pipe stalk.
The completed pipe-in-pipe stalks are stored on the stalk racks or the causeway ready for spooling on to the reel lay vessel being used for the project.
The first pipe-in-pipe stalk is pulled through a tie-in station situated within the hydraulic pushframe. It is pulled along the spooling rollers and through a set of approach rollers onto the vessel’s reel. A pawn-head/split-head adaptor system is then used to connect the larger carrier pipe lead string to the vessel’s reel. The next pipe stalk is then ready to be connected to the first. This is done in the hydraulic pushframe and involves first welding the two inner flowline ends together. Once NDE of the weld has been carried out, the stick-out areas are then covered with insulation. A fire-retardant blanket is fitted over the insulation before the landward carrier-pipe stalk is pushed over the inner flowline weld area.
After completing the carrier tie-in weld, the trailing end of the inner flowline stalk is cut to the desired 500 mm stick-out, rebevelled, and cleared by NDE ready for the next tie-in. The whole process is repeated until the required pipe-in-pipe pipeline is onboard the relay vessel in one continuous length, ready for deployment in the field. Each vessel trip is dependent on reel capacity, which in turn dictates either total pipeline weight or volume.
Technip operates with some of the most advanced pipelay vessels in the offshore industry. The Apache II, which was used during the Endeavour Rochelle project, plays a major role in delivering subsea infrastructure around the globe. Once offshore, advanced technology on-board the vessel delivers all of the additional advantages of the reel-laying method. During the pipelay process, a pipe-straightener and -tensioner system are utilised prior to the pipe passing through a welding station situated on the ramp. Here anodes, valves, flanges, T-pieces, and miscellaneous equipment can be attached to the pipe as and when required. Thereafter, a monitoring system ensures lay-catenary parameters are maintained on deployment of the pipe. On multiple trip applications, subsequent tie-in welding, NDE, and field joint coating are carried out on the next trip as required.
With sophisticated dynamic-positioning systems and a range of offshore construction equipment, the reel-lay vessel can lay pipe with an unrivalled degree of accuracy in deep or shallow water and close to offshore installations.