Audit of mooring system on Transocean Leader

Background for the audit

In December 2004, Eni experienced a serious accident involving the mooring system on the Ocean Vanguard during exploration drilling in the Norwegian Sea. Eni is about to commence exploration drilling in deep water on Cygnus (link).

Eni presented its plans concerning the mooring system on 28 September 2006. Spot checks revealed deficiencies in verification of the mooring system. Over the past year, Transocean has also experienced several incidents linked to the mooring systems. Based on an overall evaluation, the PSA decided to conduct audits of both Eni and Transocean.

Purpose of the audit

The purpose of the audit was to ensure that Eni performs site-specific evaluations in accordance with the regulations, as well as to verify the technical condition of the mooring system on the Transocean Leader.

Result of the audit

During the audit we found three nonconformities in relation to the petroleum regulations. These were linked to the test tension to ensure anchor holding power, vertical load on anchors and deficient calibration of line tension.

We also noted seven improvement items linked to verification, use of thrusters, basic data for the analyses, follow-up of suppliers, criteria for transitioning to survival mode*, internal follow-up and risk analyses.

*Survival mode
Condition on board a facility during extremely bad weather, in which preparations are made on board to secure the integrity of the facility and any wells. This typically includes changing the facility's draught, shutting down production, disconnecting from wells and other measures on board to reduce the risk of damage due to extreme weather. The criteria for transitioning to survival mode are defined in advance and are linked to specific environmental factors such as wave height, wind speed and strength of currents compared with the facility's design criteria and any analyses of mooring systems, etc.

Contact person i the Petroleum Safety Authority
Mike Theiss