Ormen Lange, North Sea Northern, Norway

Ormen Lange is located in the Norwegian Sea, approximately 140km west of Kristiansund. The discovery lies across blocks 6305/4, 6305/5, 6305/6 and 6305/8. Preliminary estimates show that Ormen Lange is the second-largest gas discovery on the Norwegian shelf. The discovery well 6305/5-1 was drilled in 1997 and production is most likely to start in 2006.

DISCOVERY

Hydro and Shell Norway signed an agreement for sharing responsibilities for the field. Norsk Hydro will be responsible for the development phase, while Shell will be responsible for developing the transport of the gas and all the commercial relationships.

• Norske Shell: 16% (production operator)
• Norsk Hydro Produksjon: 14.78% (drilling operator)
• Statoil: 8.87%
• State's Direct Financial Interest (SDFI): 45%
• BP Amoco Norge: 9.44%
• Esso Norge: 5.91%

The main gas reserves lie in a reservoir in the Vale formation. Drilling has confirmed the original estimated resources of 315 billion m³ of natural gas.

The difficulty in developing the field is due to the water depth and subsea topography. The field lies in a depth of 800-1200m, close to the steep back wall left by the Storegga submarine slide, which occurred 7,000-8,000 years ago. The Storegga slide was probably triggered by a major earthquake caused as the land masses rose at the end of the Ice Age, combined with weak sedimentary layers.

Norsk Hydro has carried out a programme of high-resolution seismic surveys, seabed mapping, shallow coring and deep geotechnical drilling.

This programme is also used to: evaluate large-scale margin stability, identify slide release mechanisms, evaluate the risk of new large and small slides, assess the consequences of possible reservoir subsidence as a result of production, evaluate possible measures to reduce risk in the event of a development, as well as map the seabed to identify good pipeline routes out of the slide area.

DEVELOPMENT SCENARIOS

There are four potential development solutions, and a range of transport alternatives:

SCENARIO 15A

Scenario 15a consists of a spar moored to the seabed. Ten wells feed into the platform and the hydrocarbons are exported through a pipeline running to a subsea sales gas tie-in point. The design specifies exporting gas at a rate of 49.36M m³/day and storing up to 30,270b/d of condensate. The facilities can also process 2,250b/d of water.

SCENARIO 15B

Scenario 15b is broadly similar to 15a, except that it will be developed using ten wells tied into a subsea template, then piped directly to the shore. The plateau production will be 15 years. The maximum gas- and water-production rates are the same as with 15a, but the storage specified is 36,130b/d.

SCENARIO 15C

This scenario produces Ormen Lange as a subsea completion, tied back to the shore. It would be developed using 16 wells and stay on plateau production for eight years. The gas export and water production would remain at 49.36M m³/day and 2,250b/d, respectively, but 26,750b/d of condensate would be sent for storage.

SCENARIO 15D

This envisages 12 wells being produced into a subsea template and piped to a concrete platform. Production would then be sent to the plant at Kollsnes. It would stay on plateau production for ten years. The gas export and water production would remain at 49.36M m³/day and 2,250b/d respectively, but 26,750b/d of condensate would be sent for storage.

In August 2000, the extension well 6305/8-1 confirmed gas volumes and a thin layer of oil, measuring a maximum of three metres. Norsk Hydro drilled the well into a chalk formation to a total depth of 3,175m, using the rig Scarabeo 5.

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