|Mumbai (Bombay) High North Platform|
|27 July 2005|
|Mumbai High, Indian Ocean|
|Oil and Natural Gas Corporation (ONGC)|
The Mumbai High Field was discovered in 1974 and is located in the Arabian Sea 160km west of the Mumbai coast. The field is divided into the north and south blocks, operated by the state-owned Oil & Natural Gas Corporation (ONGC). The field's installations comprise four platforms linked by bridges:
- NA small wellhead platform built 1976;
- MHF residential platform built 1978;
- MHN processing platform built 1981;
- MHW recent additional processing platform.
The complex imported fluids from 11 other satellite wellhead platforms and exported oil to shore via undersea pipelines, as well as processing gas for gas lift operations. The seven-storey high Mumbai High North (MHN) platform had five gas export risers and ten fluid import risers situated outside the platform jacket. In July 2005, a multi-purpose support vessel (MSV) collided with the MHN platform, severing at least one gas riser and causing a massive fire which destroyed the MHN platform within two hours.
At time of accident on 27 July 2005, the Noble Charlie Yester jack-up was undertaking drilling operations in the field and was positioned over the NA platform. The MSV Samudra Suraksha was working elsewhere in field supporting diving operations when a cook onboard the MSV cut off the tips of two fingers. Monsoon conditions onshore had grounded helicopters, so the injured person was to be transferred from the MSV to the MHN by crane lift for medical treatment. While approaching the MHN on the windward side, the MSV experienced problems with its computer-assisted azimuth thrusters so the MSV was brought in stern-first under manual control and the injured person was transfered off the MSV.
At around 1605 hours, strong swells pushed the MSV towards the MHN platform, causing the helideck at the rear of vessel to strike and sever one or more gas export risers on the MHN jacket. The resultant gas leak ignited within a short time. The close proximity of other risers and lack of fire protection caused further riser failure. The subsequent fire engulfed the platforms MHN and MHF, causing the complete destruction of the MHN. The fire also engulfed the MSV Samudra Suraksha, with heat radiation causing severe damage to the NA platform and the Noble Charlie Yester jack-up. Emergency shut-down valves (ESDVs) were in place at each end of the risers, but some risers were up to 12 km long and riser failure caused large amounts of gas to be uncontrollably released.
Six divers in saturation chambers on MSV were left behind when the vessel was abandoned. The were rescued 36 hours later. The MSV suffered extensive fire damage and was towed away from scene but later sank on 01 Aug 2005, about 18km off Mumbai coast.
Aftermath and Investigation
MHN collapsed after around two hours, leaving only the stump of its jacket above sea level. A total of 384 personnel were on board the MHN complex and NCY jack-up at the time of the accident. All installations were abandoned with 362 crew rescued and 22 reported dead (11 fatalities with 11 missing). The flow was shut down via sub-surface ESDVs. Significant problems were reported with the abandonment of all the installations involved: only two of eight lifeboats and one of ten liferafts at the complex were launched. A clean-up operation was also undertaken after a 10 nautical mile oil spill resulted from the fire.
Two areas were identified for investigation:
- the adequacy of and failures within the risk control systems;
- the adequacy of collision avoidance practices and procedures.
Points of interest under investigation include the location and vulnerability of the risers in the jacket relative to platform loading zones. Some riser protection guards were in place just above sea level, but these were only suitable for smaller offshore supply vessels and were not considered suitable for larger multi-purpose support vessels. Also under investigation is the quantity of riser contents likely to be discharged if a riser should fail below an emergency shutdown valve and the risk management process, including the vessel suitability, the crew competence, communications and collision avoidance measures.
The Bombay High field accounted for 40% of India's domestic production, of which the North platform accounted for one quarter. One month after the accident, production had been restored 60% of the pre-accident level.
HSE (UK): Mumbai High North Accident
HSE (UK): Riser Safety In UK Waters
Risk-i: Review 2005
Risk-i: Offshore Platform Fire, India
Rigzone: Mumbai High North Field has Restored Production
1. HSE (UK)
2. Canadian Wellsite
3. Canadian Wellsite
4. HSE (UK)
5. NOPSA Introduction