Scarab/Saffon Subsea System: Design and Installation Aspects

Abstract

Abstract The Scarab/Saffron field development is the first deepwater field in the Mediterranean. To present day standards the water depth at the field location is not extreme and the pipeline system can be installed by "conventional" methods. The total system comprises a large number of components, such as two large diameter export lines, a large PLEM, two manifolds, eight 10" in-field flow lines, umbilicals and their termination units, flying leads etc. However, the design and installation presented some other challenges to the project team and the Contractors. The system is installed in an area that is seismically active and has a number of highly unusual seabed features. Seismic aspects played an important role in the layout of the system and in the design of some of the foundations of the equipment. Up to now few fields have been designed in seismically active areas and novel techniques were used to the design of some of the components. The challenges are in the variations in water-depth, (0 to 650 meters), in pipeline diameter (4 inch to 36 inch) and the different types of umbilicals. No single marine vessel can perform all the installation activities for such a wide range of pipeline sizes and sub sea system components. Flat bottom derrick / lay barges, a semi-submersible installation vessel, a small diameter pipeline installation vessel and other marine construction installation vessels were employed to perform the installation activities of the Scarab / Saffron field development. The planning of the fabrication, delivery, testing, installation and commissioning in a relatively short time presented a major challenge to everybody working on the project. This paper presents details of the pipeline system and the considerations that led to the field layout. Methods of installation and vessels used are described as well as captured lessons learnt. Introduction The design, procurement and installation of the Scarab/Saffron field development was divided into four packages:The design and manufacture of the sub sea equipment;The design, procurement and installation of the offshore pipelines and the installation of the sub sea equipment and umbilicals;The design and manufacture of the hydraulic and electrical umbilicals;The drilling and completion of the wells. This paper is concerned with the design and installation of the pipeline system and its structural elements. The installation work was awarded to Stolt Offshore AS with a major subcontract to Petrojet Marine Services for the installation of the landfall, the large diameter export pipelines in the shallow water sections and the fabrication of a large number of structural elements to Petrojet. Details of the sub sea equipment, the umbilicals and the drilling aspects can be found in other papers on the Scarab/Saffron development. Field Layout The layout of the field was defined during the FEED stage prior to the performance of the pre-engineering survey campaign. The general location is shown in Figure 1. Starting in the deepwater area, the Scarab and Saffron fields comprise 5 and 3 wells respectively. Each well is separately drilled and completed. All wells are connected to a 10" flow line by means of a rigid steel jumper, connecting a CVC on the wellhead to a CVC on the PLET of the 10"line. The 10" lines connect the wells to a manifold in the manifold area in a water depth of some 410 m. The wells are controlled and provided with glycol and methanol by in-field umbilicals. These run from the wells to the Subsea Distribution Assembly (SDA) in the manifold area.