UK Deepwater Drilling - Implications of the Gulf of Mexico Oil Spill - Energy and Climate Change Contents

Supplementary Memorandum submitted by Transocean

  I write in response to the letter I received from the Energy and Climate Change Committee on 7 December 2010 regarding a well control incident on the Shell UK-operated Sedco 711 drilling rig in the North Sea Bardolino Field on 23 December 2009. Transocean Drilling U.K. Limited. (Transocean) appreciates the opportunity to clarify several misstatements and inaccuracies reported in the Today Programme and other media outlets. As a threshold matter, Transocean notes that the 23 December 2009 incident on the Sedco 711 is a matter of public record, having been reported in several media outlets, including the New York Times and the European edition of the Wall Street Journal in August 2010, prior to the Committee's first inquiry on 7 September 2010.

  First, Transocean stresses that the safety programme onboard the rig functioned as designed, allowing one of the annulars on the blowout preventer to be closed and seal off the well, pursuant to the Transocean and Shell well control procedures for a "hard close in". Transocean took all appropriate actions to address the matter in the days and weeks following the incident. There were no casualties, no asset integrity loss, and a minimal amount of product—approximately three barrels of oil-based mud and the equivalent 0.9 tonnes of oil—lost to sea.

  Second, as required by the Health and Safety Executive (HSE) Regulation, the Operator, Shell UK, reported the incident to the HSE in an OIR9B filing on 24 December 2009, which under the Regulation must be submitted within ten days of the incident. This notice provided the agency with an explanation of what transpired on 23 December, and the agency had a full understanding of the incident. The HSE sent Shell UK Ltd a letter on 24 February 2010 acknowledging the incident and notifying Shell that "any release of hydrocarbons from a well could lead to enforcement action under the Regulation". The Department of Energy and Climate Change (DECC) was advised of the event by Transocean in a PON1 filing.

  As explained to the HSE in the OIR9B filing, the series of events that took place were as follows:

    The incident took place on 23 December 2009 at 17:15 onboard the Sedco 711 semi-submersible drilling rig during the upper completion clean up phase of the well.

    The lower completion had been installed and the isolation packer and formation isolation valve (FIV) were pressure tested. The FIV was then successfully inflow tested with a column of base oil confirming the integrity of the mechanical barrier to the reservoir. After the successful completion of the test, the clean up of the well to seawater began in preparation for final displacement to base oil.

    During the clean up and displacement, mud returns were routed to the reserve pits. As a result, volumes could not be monitored on the active pit system and thus, actual displacement could not be measured. There were indications of an increase in flow out in the rate of mud returns to the pit room during displacement, but this was expected due to the increased pump rate. After approximately ten minutes at a higher pump rate, the rate was reduced to allow the pit room to resolve the increasing flow issues.

    At this point the well began to flow, unloading mud onto the drill floor. The shaker alarms were triggered indicating an increase in gas levels. As soon as the mud was observed, the pumps were switched off and the blowout preventer was successfully activated with the lower annular. With the well shut in, the drill pipe was spaced out and the middle pipe rams of the blowout preventer were closed, securing the well.

    The general alarm was sounded by the control room. Emergency Response Procedures were initiated pursuant to the Operations Management Plan. The Emergency Response Team (ERT) provided a briefing informing that there were no casualties; full muster of 95 persons on board was achieved at 17:36. The ERT coordinator was contacted and continuously kept informed of the situation.

    The HSE was satisfied with the investigation led by Shell and the actions from the investigation report for Shell, Transocean and Schlumberger, and thus did not require a specific change in procedures as a result of the Sedco 711 incident on December 23. However, Transocean issued two operations advisories in response to the incident. A Well Operations Group Advisory, dated 5 April 2010 and issued to all Transocean installations, confirmed that the Well Control Handbook would be modified to clarify the requirements for monitoring and maintaining at least two barriers when displacing to an underbalanced fluid during completion operations. The second advisory was issued to the entire Transocean North Sea fleet and recommended specific follow-up actions related to well control preparedness during a completion phase, awareness of well control indicators, and adequate well programs.

    With regard to the "insufficient mud" referenced in the Today Programme, there was minimal reserve mud onboard the Sedco 711 as the mud in the hole was "kill mud weight" for pressures known in the well. The mud displaced from the hole after the blowout preventer was closed was contaminated with hydrocarbons and not suitable to pump back in the hole. As a result, good mud needed to be brought back onboard from a supply vessel.

    Finally, although the Bardolino well control incident and the Macondo blowout in the Gulf of Mexico appear to share certain elements in common—both involved an underbalanced column of drilling fluids in the well, for example—we believe that the two events, based on our current understanding of the events surrounding the 20 April Macondo incident, are distinct examples from which the industry as a whole can learn. While the Macondo blowout remains under investigation by Transocean and multiple U.S. governmental bodies, we know that the cementing of the final casing string and the use of an unusual spacer during negative pressure testing have been identified as potential contributing factors to the 20 April incident. By contrast, neither cement nor spacer material were identified by Shell or Transocean as underlying causes of the Bardolino incident. In addition, Bardolino involved the drilling of a deviated hole, rather than a vertical hole as with Macondo; Bardolino was drilled in the North Sea, not the U.S. Gulf of Mexico, which are starkly different drilling environments; and each incident involved a different operator. Transocean is not aware of any other incidents on its rigs in the North Sea in the last five years that are of a similar profile to the 23 December 2009 Bardolino incident.

  Transocean continues to operate its rigs on the UK Continental Shelf with the highest degree of safety and diligence. It is committed to ensuring a safe and reliable work place for its employees and stands willing to assist the Committee in its ongoing inquiry.

December 2010

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