The US Bureau of Safety and Environmental Enforcement (BSEE) has laid the blame of the 2013 Hercules 265 blowout firmly at the door of the offshore drill crew.
Also sited by the investigation, were both companies involved, drilling company Hercules Offshore and operators Walter Oil & Gas.
The blowout occurred on 23rd July 2013, around 55 miles (89km) offshore Louisiana, in the South Timbalier Area Block 220.
The blowout resulted in a two day long fire that engulfed the jack-up drilling rig, leading to an abandonment by the crew and eventual collapse of the Texas deck and derrick.
A full investigation has since been undertaken jointly by both the US BSEE and the US Coast Guard, who have just released their report.
BSEE Investigation Report
According to the report, the initial cause of the incited was the miscalculation of drilling fluid density by the drill crew.
The repot said that by mixing the zinc bromide completion fluid incorrectly, the crew had not made a fluid capable of handling the full range of different pressures that were encountered in the reservoir.
This created a negative imbalance in the column, causing an influx of gas into the well known as a kick.
However, the report went on to describe how the drill crew had not noticed the kick had occurred and continued.
The resulting situation allowed natural gas to pushup though the well eventually escaping at the rig floor.
The report stated that drill crew had only realised there was a problem when completion fluid began to ‘shoot’ out from the open annuals and drill pipe.
The blowout forced drillipipe into the top drive, causing damage, and stopped any hopes the drill crew had of installing a safety valve in the top if the drill string to close in the well.
The investigation also found that the Blowout Preventer (BOP), was inadequate to handle the pressures encountered in the well.
The report said that the decision by the drill crew to activate the BOP and close in the well came far too late. It said that the BOP was eventually activate remotely from the OIM’s office, however, by this time the pressure was far to high, stopping the BOP shear rams from working.
The investigation also found that the BOP was not capable of handling the sand brought up from the reservoir, even if it had of activated.
The report showed images of the resulting damage to the BOP caused by sand, in effect sandblasting its way right through the steel of the BOP.
After 13 hours of natural gas flowing uncontrollably form the well, it ignited, resulting in a fire which continued to burn for two days, before eventually extinguished itself after sediment built-up within the well stopping the flow of gas.
The report said the evacuation of all crew took place only ten minuets after the initial kick from the well. Only minor injuries were sustained by the drill crew on the drill floor, mainly due to burs from completion fluid.
A Video Showing The Blow Out Prior To Igniting
BSEE Director,, Brian Salerno said: “This incident bares similarities to other blowouts on the Outer Continental Shelf. “Given these equipment and human failures noted in the report, this incident could have easily resulted in a more tragic outcome, and must be viewed as very serious,”
Offshore operators Walter Oil & Gas are also yet to respond to the report.