Subsea Arrangements Optimization for Gas Export Systems

Abstract

Abstract When defining the subsea arrangement for a gas export system, a few options are available to connect a trunk gas pipeline to other pipelines or to FPUs, especially when there is uncertainty about future projects which may need to be connected to the export system. The objective of this paper is to present an assessment of different options based on a case study. A matrix will be generated pointing the pros and cons of different technical solutions regarding aspects such as: economicity for long and short distances, total length of pipelines, number of subsea structures, technology maturity, risks related to QHSE issues, risks to assets during installation, interruption of gas export during installation, construction duration and availability to deepwater. Considerations about the applicability and relative importance of each of the above mentioned parameters will also be included. Examples of subsea arrangements and strategies of acquisition for gas export systems projects include: using ILTs/ILYs for each connection; using ILTs/ILYs and PLEMs "offline", i.e., PLEMs with several hubs connected to in-line structures along the trunk pipeline; using PLEMs in-line, i.e., PLEMs connected directly to the trunk line, by means of rigid or flexible jumpers and PLETs; using diver assisted or diverless cut after hot tapping; using diver assisted or diverless cut in conjunction with smart plugs. Finally, nonconventional alternatives to export the gas like LNG, CNG, GTW or GTL will also be assessed. The results will present guidelines on how to select the most appropriate subsea arrangement for gas export systems, depending on the specificities of each project, such as: the extension of the field, the distance to shore, the maturity level of the present and future (interconnected) projects, the water depth, the distance between FPUs and others.