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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