Supplementary Memorandum submitted by
the Health and Safety Executive
WELL CONTROL
INCIDENT TRANSOCEAN
SEDCO 711 WELL
22/13A -8 (BARDOLINO)
Shell has informed us that HSE was informed of
the spill from the Sedco 711 platform and carried out its own
investigation of the series of events that led up to the spill.
How serious was the incident?
HSE answer:
Shell viewed this incident as high potential.
If the blowout preventer (BOP) had not shut the well in there
was the possibility for a blowout to occur with the resulting
potential for escalation of the incident. However, this can be
said for any "kick" (which is an early warning that
there has been an unexpected flow into the well and that action
must be taken) that are not detected and shut in promptly. In
this instance, the BOP did work effectively as planned and provided
the barrier to shut the well in, stop it flowing and allow it
to be brought back under control.
Did HSE require any changes to procedures as a
result of its investigations?
HSE answer:
As a result of the HSE investigation, and in
accordance with our Enforcement Management Model (which is a framework
which helps inspectors make enforcement decisions), a letter was
sent to Shell regarding their general well integrity responsibilities
under Regulation 13 Offshore Installations and Wells (Design and
Construction, etc) Regulations 1996. HSE assessed the corrective
actions implemented by Shell and Transocean and considered they
addressed the shortcomings that led to this incident and have
addressed the well control issues that occur when displacing drilling
mud out of the well.
How satisfactory was the response by the crew
to the incident?
HSE answer:
The crew's response to the incident in terms
of bringing the flow in the well under control (a "well kill")
was ultimately satisfactory. However the performance of the crew
prior to the incident was not satisfactory, as they did not detect
that the well was flowing sooner. The crew's risk awareness and
risk perception was blinkered by a previous positive test of the
operation of the Formation Isolation Valve and they did not fully
take into account that such a tested barrier can subsequently
fail. The crew should have also stopped the displacement of the
drilling mud from the well sooner to evaluate what was happening
in the well.
The crews well control preparedness was not
as their procedures called for as certain information was not
immediately available for use, and they had not had a well control
drill for 10 days. These issues were subsequently addressed in
the Shell/Transocean corrective actions.
Did the HSE consider whether the incident was
appropriately dealt with by the offshore management as events
developed?
HSE answer:
The comments above also apply to the offshore
management. Additionally the problems caused by not having sufficient
mud at the correct mud weight available should have been foreseeable,
planned for and dealt with better by the offshore and onshore
management. The changes that then took place to instigate an alternative
method of "well kill" were initially insufficiently
formalised. However, after further deliberation, the well kill
was stopped and reconsidered by onshore and offshore staff under
a formal and comprehensive management of change process, and the
revised method successfully circulated mud in the well under controlled
conditions.
Are such offshore drilling platforms required
to have mud of a sufficient density ready to kill the well? What
was the HSE's reaction to finding that the Sedco did not?
HSE answer:
There is no specific prescriptive requirement
to have mud of the required density that could kill the well onboard
a drilling installation at all times—there are fluid storage
limitations on some installations. It is therefore good industry
practice to have sufficient weighting agent onboard the installation
that can raise the mud's density to kill the well if required
(if excessive well bore pressure is experienced while preparing
the kill weight mud it can be managed in a controlled fashion).
In this incident, because the well had been
successfully inflow tested Shell considered that they could offload
the mud from the rig. HSE considers this could have been managed
better by the offshore management team, and ensured that this
was fed into the incident lessons learnt.
How may of the 56 oil spills in 2009 were as a
result if incidents which could have led to blowouts if evasive
action had not been taken?
HSE answer:
None of the 56 crude oil spills reported to
DECC in 2009 were related to drilling incidents which could have
led to a blowout.
The incident on 23 December did not give rise
to a spill of any crude oil to sea. The fluid released to sea
during the incident was a drilling mud that is classified as a
chemical under the provisions of DECC's Offshore Chemicals Regulations
2002. As such, the fluid release was reported to DECC as a chemical
release. The loss of the drilling mud did not result in any adverse
effect on the environment.
December 2010
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