Subsea Facilities
Authors: Bernt Thomas 
Published: October 2008

This paper presents the system design and concept solutions selected for the Ormen Lange subsea facilities.

The field is located in a remote area off the coast of Norway and system availability has been a key driver in the subsea system selection and design. This paper focuses on the following elements:Ormen Lange key technical challenges and concept development.Subsea system architecture.Design premises and essential functional requirements that have driven the subsea design.Selected subsea system hardware solutions with emphasis on availability of the key functions.Technology qualification programs that will be executed in order to provide confidence in the selected solutions.

Introduction

The Ormen Lange field, discovered by Norsk Hydro in 1997, is located in the Norwegian Sea, approximately 100 km off the northwest coast of Norway. The field is located within a prehistoric slide area, the Storegga Slide, with water depths ranging from 850 to 1,100 meters in the planned development area. The seabed in the Storegga Slide is extremely irregular with soil conditions varying from very stiff clay with boulders to soft clay.

The selected development concept for Ormen Lange comprises a subsea tieback to a shore terminal as shown in Fig. 1. The shore terminal will be located at Nyhamna, close to the city of Molde. The gas will be produced from up to 24 subsea wells. The well fluid will be transported to the land terminal through two 30" multiphase lines. After processing, the dry gas will be transported from the land terminal through a new 42" pipeline via the Sleipner riser platform and further through a new 44" pipeline to the gas reception terminal in Easington, England.

Technical challenges

The key technical challenges for the Ormen Lange subsea development are:Deepwater and metocean conditions.Hydrate prevention.Long offset control.High well flow rates. It has been an overall goal to develop a cost effective and technically robust subsea system consisting of well-proven building blocks and to minimize the amount of technology development/qualification. This is considered important in order to reduce the risks and uncertainties related to the project execution.

Concept development

The subsea system selected for Ormen Lange has been developed over a period of 3-4 years as a joint effort between Hydro, Shell and numerous equipment manufacturers and suppliers. The supplier industry has played an active and important role in the concept development.

A FEED study was undertaken with FMC Kongsberg Subsea during the first half of 2003. The results of this study formed the basis for establishing the functional requirements for the Ormen Lange subsea production system. An overall aim of the FEED study was to develop a concept consisting of units that could be delivered by all the major international subsea system suppliers.

In mid-2003, supplementary studies were undertaken with all the three potential subsea engineering, procurement and construction (EPC) contractors; ABB, Aker Kvaerner and FMC Kongsberg Subsea. The aim of these studies was to familiarize the potential EPC contractors with the Ormen Lange system layout, functional and specific technical requirements, field development program and schedule requirements and finally to ensure a consistent basis prior to the tendering phase.