The rupture was discovered when no pressure rise could be observed in the injection well. A colorant was added, and the coloured water was observed on the sea surface.
Draugen had two water injectors, positioned at the southern and northern fringes of the reservoir respectively so that water pumped down would drive oil towards the production wells.
After the flowline rupture, only the northern water injector was in use. It was uncertain how this temporary disruption to injection would affect the reservoir.[REMOVE]Fotnote: Tidens Krav, “Brudd i vannrør ved plattformen”, 17 July 1995.
An investigation team, including French flowline manufacturer Coflexip, was established to identify the causes of the failure.
Produced and installed in 1992-94, the flowline was built up of five main layers – an innermost plastic liner, a tension ring, double tensile reinforcement and an outer sheath.
A friction coating was also incorporated between the reinforcement layers, but no outer layer able to resist collapse from external pressure had been provided.
The team concluded that the rupture was caused by a manufacturing fault in the inner plastic liner which had allowed water under high pressure to penetrate the reinforcement layers.
Since the latter were not designed to withstand direct water pressure, they became deformed when powerful forces arose locally in the flowline.[REMOVE]Fotnote: Draugen technical committee, section for marine technology, division for safety and the working environment, Norwegian Petroleum Directorate, 1 February 2000.
Repairs were carried out which allowed water injection through the SWIT to resume at full capacity from the beginning of September. This work cost some NOK 53 million.[REMOVE]Fotnote: Norwegian Petroleum Directorate. Management committee meeting, PL 093, Draugen, 3 July 1995.
Kristiansund daily Tidens Krav asked whether any risk existed of something similar occurring with the oil flowlines on Draugen, but Shell said this was very unlikely.
The flowlines used had been approved and cleared for oil production, it noted, and safety requirements for such clearance were strict.[REMOVE]Fotnote: Tidens Krav, 17 July 1995, “Brudd i vannrør ved plattformen”.
Nevertheless, a similar but more dramatic incident occurred with a Coflexip flowline in 2000. See the separate article on “2000 – second injection flowline failure”.