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

Supplementary Memorandum submitted by the Health and Safety Executive


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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