Ormen Lange - Flow assurance challenges
Authors: Wilson Arild , Overaa Sverre J. , Holm Henning 
Published: October 2008

Ormen Lange is a gas field located 100 km off the Norwegian coast in water depths varying between 850 and 1,100 meters. The selected development scenario for Ormen Lange is a subsea tie-back to an onshore processing facility at Nyhamna.

The field is located in a prehistoric slide area with varying water depths, from 250 to 1,100 meters. The result of this subsea slide is an extremely uneven sea bottom with local summits 60 to 80 m high. The back wall of the slide is steep, up to 26 degrees. Environmental conditions are also challenging.

This paper describes the flow assurance challenges and technical solutions selected due to the harsh environmental conditions specific to the Ormen Lange development, including:Rough seabed combined with long tie-back distance.Sub-zero temperatures (-1° C). All together, this makes the Ormen Lange project one of the most challenging field developments worldwide with respect to flow assurance.

Introduction

The Ormen Lange field, discovered in 1997, is located offshore Norway approximately 130 km west-northwest of Kristiansund. The field covers an area approximately 10 km by 44 km. The reservoir is located at a depth ranging from 2,650 m to 2,915 m below mean sea level. Recoverable reserves are estimated to be approximately 375 billion Sm3 gas and 22 million m3 condensate. The intitial reservoir pressure is 290 bara, and the reservoir temperature ranges from 86 to 93 °C.

The field is located within a prehistoric slide area, the Storegga slide, with water depths varying from 850 to 1,100 m 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 consists of a subsea tie-back 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 to Sleipner and from there through a new 44" pipeline to receiving facilities in Easington, UK.

The annual gas export plateau will be approximately 21 billion Sm3 and the daily export capacity up to 70 million Sm3.

To maintain production when reservoir pressure declines, an offshore compression facility is planned for installation in the field with a planned start-up date in 2016. However, a subsea compression solution will be evaluated, in parallel, as a cost-effective alternative to a compression platform.

Field development and subsea system architecture

Due to the wide geographical extent of the Ormen Lange field, the risk of experiencing a segmented reservoir and, in addition, limitations with respect to long reach well/high deviated wells, the subsea architecture requires a high degree of flexibility. A phased development scheme has been selected for the field. The completion of subsea wells will be timed to maintain plateau production as the field depletes.