World-class welding technologies - Subsea 7

More documents

Recommendations

Info

06 Groundbreaking geotechnics In 2011, Subsea 7 commenced accelerated development in the field of Geotechnics in two areas of great significance for our clients’ deepwater operations, how seabed soils and pipelines interact, and how an enhanced appreciation of soil behaviour and failure mechanisms can optimise foundation design, particularly for very soft deepwater clays. Pipelines Subsea 7 actively participates in the Safebuck series of JIPs - currently in its third phase - but we have also internally funded work investigating the dynamic embedment (and hence friction and stability) of pipes laid on soft clays which are typically found at the deepwater sites where we work. Another key challenge being addressed is an improved understanding of the behaviour of carbonate sediments which are widespread in some developing oil and gas-rich regions such as Australia. Carbonate-rich soils exhibit different behaviour to their non-carbonate counterparts, so Subsea 7 undertook a study to investigate the response of carbonate soils to cyclic pipe loads by model testing in a geotechnical centrifuge. Model pipe set up for axial friction test The results of this study are counterintuitive to those predicted by classical soil mechanics, and the work represents a significant step forward in evolving a new constitutive model to describe the behaviour of carbonate soils. For further information contact paul.brunning@subsea7.com DEEP7 May 2012 Apparent friction derived from cyclic axial friction tests Foundations In our subsea construction business, there is constant pressure to optimise foundation design to be as efficient as possible in terms of installation without compromising functionality. Subsea 7 has produced recent research at the highly respected Centre for Offshore Foundation Systems at the University of Western Australia into an optimised design methodology that has led to the possibility of reducing the size of shallow foundations such as PLET mudmats by 20%, or alternatively able to withstand larger jumper loads. The geotechnical engineer is always interested in finding the most critical failure mechanism of a foundation. Subsea 7 has teamed up with the university to develop a new 3D analysis tool which could potentially halve the engineering hours spent designing foundations under complex loading. FE analysis for optimised foundation design Mudmats for PLET applications Looking to the future… Emerging challenges in the geotechnical industry are likely to include: • developing and improving the constitutive model for carbonate soils and applying it to foundation and pipeline design • how to quantify the degrading effects of solid hydrate and hydrate dissociation on soil properties • further optimisation of foundation designs as large and heavy processing facilities are moved subsea • developing design methods for ultra-deepwater soils where soil strength is more dominated by viscous behaviour than traditional shear strength • finding novel and effective ways to protect subsea infrastructure in the Arctic or ice-prone regions.
Cutting-edge simulation Subsea 7 has developed one of the most powerful installation simulation packages ever built, including unique finite element analysis (FEA) capabilities, and successfully installed the hardware on board construction vessel the Seven Seas for effective on-site operative training. The programme was developed over a two-year period for the Block 31 project offshore Angola. An unusual aspect of this deepwater project is the mid-water pull-in of the flexible risers that connect the vertical risers to the FPSO. These operations are carried out at an average depth of 200m, which presented uncommon problems. Unlike most pull-ins, the tasks are performed in a situation where everything in the scenario is mobile. The Upper Riser Assembly (URA), while weighing several hundred tonnes, can be easily moved and rotated should the ROV push it. When the flexible risers are attached to the subsea winch wires and the load transferred from the vessel crane to the winches, the URA, which in itself is dynamic, tends to follow the riser lay direction for many metres - which has the potential to compromise the minimum bending radius (MBR) of the flexible. The situation was risk-assessed, and it was decided that the risks could be mitigated by building the nine different scenarios (there are nine flexible risers) in a simulator. This would allow procedures to be checked, and also facilitate pilot training. The simulation predictions were shown to correlate well with measurements taken before and during the actual offshore operation. The development of the simulator though 2010 and 2011 pushed the pilottraining software and hardware well beyond their existing capacity, due to the large number of flexible and moving objects in each scenario. Most simulation training takes place at Subsea 7’s site in Aberdeen, but for this project it proved more effective to train the ROV pilots, superintendents, and Block 31 installation simulator in use on board the Seven Seas bridge supervisors on board the Seven Seas, in an environment with which they are already familiar. The simulations feature: • Variable sea conditions which can produce realistic motions of the Seven Seas (Subsea 7’s construction vessel on Block 31) • Sea currents that can be varied in both strength and direction at different depths to replicate the currents throughout the entire 2,100m water column • Two Hercules ROV systems, each with fully working manipulators and three selectable onboard cameras • Real-time FEA package calculating loads on, and MBR of, the flexibles • Two subsea winches complete with working line-out meters and load cells. The simulation FEA calculates the minimum bending radius of the flexible during ROV operations 07 The on-board simulator uses the existing Hercules 23 control console, with an additional six powerful PCs. A switch disconnects the topside control system from the ROV and changes operations from normal ROV control to simulation mode (this is only done when the vehicle is on deck!). For further information contact mike.bramley@subsea 7.com seabed-to-surface
Page 1 and 2: Technology news from Subsea 7 - May
Page 3 and 4: demonstrates how careful assessment
Page 5: Planning and precision combine on P
Page 9 and 10: Swaged end connection for reel-lay
Page 11 and 12: Seven Viking Due for launch in late

World-class welding technologies - Subsea 7

Create successful ePaper yourself

Delete template?

Save as template?