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2015 represents an important milestone for Statoil as both the Gullfaks and Åsgard subsea compression projects achieved production start-up. The Gullfaks subsea wet gas compression system is projected to increase recovery from the Gullfaks South Brent reservoir by 22 million barrels of oil equivalent. The solution involves two 5 megawatt wet gas compressors that handle a production rate of 10 million standard cubic metres of gas per day. The compressor system is connected to existing subsea templates and piping 15 kilometres from Gullfaks C. The Åsgard subsea compression system is projected to provide 306 million barrels of oil equivalent in increased recovery from the Mikkel and Midgard fields. The solution involves two 11.5 megawatt centrifugal compressors that handle a production rate of 21 million standard cubic metres of gas per day. The compressor system is connected to existing subsea templates and piping 40 kilometres from Åsgard B. The difference in scale and boosting requirements helps to explain why two quite different technical solutions have been selected. This presentation will provide an overview of the two projects including: Why subsea compression The business cases and technology selection The technology assessment and qualification. The execution program for the projects including engineering, procurement, construction, testing and installation. Commissioning and start up Future subsea compression opportunities
The paper reviews the way leading up to the Subsea Factory Compressor Stations with focus on important technology step-stones and breakthroughs. A dedicated and long term focus on technology development through R&D has been carried out within a series of disciplines supporting the subsea production application. The development has been along two important axis; multiphase flow and subsea systems. A comprehensive R&D effort was initiated in the beginning of the eighties resulting in a highly successful and profitable development and implementation on the Norwegian continental shelf, namely the subsea industry. Through a series of successful tie-backs and long distance multiphase flow lines, the ultimate concept was achieved for gas-condensate systems represented by the unprocessed transportation of well stream directly to shore. The first multiphase pumps were installed in the late -90 and in 2000 the first subsea separation station was started up. Today subsea boosting and separation is proven technology. In 2011, building the first subsea gas compression station was initiated, taken the last step to a full subsea factory installation. To realise subsea compression, the main components have been subject to a systematic technology qualification process. The paper describes how Statoil's large scale laboratory facilities has been mandatory for full scale qualification testing as well as focus on quality to achieve the necessary level of confidence. The Subsea Compression projects solely, have carried out nearly 60 qualification activities, further detailed in the paper. The paper also looks forward and point out that the subsea processing solutions that have been qualified and implemented can be utilized to achieve cost efficient solutions with low environmental footprint.
It had become clear that the Norwegian serpent, veterans of the North Sea development call Ormen Lange the Ormen Lange, would be a heavyweight in all respects. In cooperation with internationally takes its name from the ship of Viking King Olav Tryggvasson. The safety along with future natural conditions, including potential giant serpent, stretching across four North Sea blocks, is destined tsunamis, and conditions resulting from project activities. The U.K. gas market is the largest in undertaken by the industry. Gas will be transported more than 1200 Europe, with annual consumption of 3.9 Tcf. Total investment cost is estimated at U.S. $10.2 billion, be subjected not only to mountainous terrain created in the scar including $7.2 billion for development and $3 billion for the transport area of the Storegga avalanche slide, but also to cold polar currents system.
Shear forces between cable elements inherently increase fatigue damage of dynamic cables and umbilicals. In particular at deep waters, this effect may be the dominant factor when estimating the cable’s fatigue life. However, due to complex cable geometries and complex material properties, it is challenging to identify and to model the shear forces accurately. This paper presents the results of eight small-scale experiments run on the prototype of a novel test rig. In each experiment, a bitumen-coated armor wire is pulled out of a cable stub at constant pulling speed. The associated pulling force is measured and logged. The experiment results provide new insights which are discussed in the paper. The paper also develops a novel, dynamic model which expresses the pulling force as function of the pulling displacement. The model resembles the main characteristics of the physical system well.
Manufacturers of subsea power cables, umbilicals, and power umbilicals are constantly being challenged to deliver products for deeper waters and for lower-temperature areas, while being highly cost-effective. This combination of technological challenges and cost optimization no longer allows large margins of safety to be added to compensate for uncertainties in analyses and physical testing. Hence, improving analysis tools and test methods is essential to meet the challenges that are facing the cable and umbilical industry.
Among the cable properties that are most important to identify correctly are the cable’s fatigue life and capacity (allowed combinations of axial cable tension and cable bending curvature). These properties are essential for the cable to operate successfully throughout its expected lifetime. Both properties are inherently highly sensitive to shear forces between the cable elements. Due to different pitch lengths and alternating lay directions of the helical layers, shear forces are set up between the cable elements whenever the cable is bent. Fig. 1 shows a photography of an umbilical. In the photography the alternating lay directions can easily be seen.
Konradsen, Bjorn (Technological Analyses Centre) | Slora, Roger (Technological Analyses Centre) | Woll, Frank (Technological Analyses Centre) | Basler, Remy (Technological Analyses Centre) | Håvik, Eivind (Umbilical Department)
Umbilicals supply subsea oil and gas wells, subsea manifolds and any subsea system requiring remote control with energy (electric and hydraulic) and chemicals. An umbilical typically consists of steel tubes, signal cables, fiber optic elements and an outer protective sheath. More recently, it has also been common to include power phases in the umbilical. The umbilical is then named power umbilical.
The task/process that moves the umbilical from a place to another is often referred to as spooling and handling. It is common to guide the umbilical via rollers during this process. Axial tension necessary to move the umbilical forward at desired spooling speed is normally applied by use of tensioners/caterpillars. Change in direction is managed by arranging the rollers in a curvature (bending diameter) with an adequate deflection angle.
Higher umbilical bending stiffness requires higher bending moment in order to bend the umbilical to a given bending diameter. At the same time the contact forces toward the rollers increases.
Nexans Norway AS has identified deformation of thin wall steel tubes as a critical failure mode in umbilicals with high bending stiffness. Nexans Norway AS has therefore completed a project with an objective to incorporate a calculation tool in the standard detail engineering process in order to prevent this type of failure. This paper focuses on the developed calculation tool.
The outputs from the calculation tool are maximum allowable roller distance and minimum allowable bending diameter. Required input data are applied axial tension, the umbilical bending stiffness, dimensions and mechanical properties of the steel tube. Acceptable level for ovalization of the tube has to be specified as well.
The calculations are based on two models, one local ovality model for steel tubes and one global model for bending of the umbilical. The tube model consists of tabulated data for ovality versus applied contact force for a variety of tube dimensions. The data is developed by use of finite element analyses in ANSYS and verified by testing. The physical testing has been done by local ovalization of different tube sizes. The global model is based on analytical formulas that have been verified by use finite element analysis in ANSYS and OrcaFlex. The outputs described above are found by combining both models.