TIMELINE-Events at Total's leaking Elgin platform

PARIS, April 3 Tue Apr 3, 2012 3:18pm BST

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PARIS, April 3 (Reuters) - Total plans to send eight experts to its leaking Elgin oil and gas platform on Wednesday afternoon or Thursday morning to assess the steps needed to stop the potentially explosive gas leak, a spokesman said on Tuesday.

Here is a timeline of events at the stricken platform:

--2001: The Elgin gas field starts production. The Elgin well head is connected to 8 production wells and 3 exploration wells. Six wells are still in production mode.

--January 2011: Total stops production at G4 well, the leaking well, after the group detects production problems. As a result, the French oil major plugs the well 5,500 metres below ground level to isolate it from its reservoir.

--February 25, 2012: While the well is no longer producing, Total detects pressure and temperature problems in the A, B and C annuli, the outer layers of the well's pipe casing.

--March 4: Total decides to "kill" the well, which involves injecting drilling mud into the well head to cap it indefinitely. In the following days, the group proceeds to carry out a risk assessment for the operation, mobilises the required equipment and brings it on site.

--March 25:

- Total proceeds to "kill" the well. The company uses the Rowan Vicking drilling rig to carry out the operation.

- Total detects a gas leak during the works and proceeds to evacuate the platform's all 238 staff in early afternoon.

- A flare on the Process, Utilities and Quarter (PUQ) platform, 100 metres away from the gas leak, is left alight to burn off excess gas in the platform, raising fears the gas cloud could ignite and cause a major explosion.

--March 29: Total says the source of the leak is a calcareous rock formation (hod) 4,000 metres below ground level.

--March 30: Total says the likely cause of the leak is high pressure that would have moved the ground and the pipe, creating some small cracks in the annuli A of the outer pipe casing.

--Total says it has decided to carry out two rescue operations in parallel: the first is the most risky one but is considered to be the fastest. It consists of sending experts by helicopter to land on the PUQ platform. The experts will then go to the production platform and plug a pump into the well from a nearby ship to inject drilling mud to shut the well.

The second option consists of drilling two relief wells to ease the pressure inside the G4 well. But this could take up to 6 months and be more costly.

-A senior union official says Total repeatedly assured workers on the Elgin platform that a leak was impossible until just hours before evacuating them.

--March 31: Total says the flare extinguished itself without human intervention on March 30, reducing the risk of a blast.

--April 2: Total says the leak is costing it $1.5 million per day in lost earnings and $1 million daily in response costs.

Source: Reuters News (Compiled by Muriel Boselli; editing by James Jukwey)