Bridging is where small pieces of sediment and sand flow into the well path to restrict and ultimately stop flow.

According to the US Coast Guard, the fire has decreased to a small flame fuelled by residual gas at the top of the well.

The US Bureau of Safety and Environmental Enforcement and the US Coast Guard have conducted overflights to visually confirm this.

The fire began at 10.45pm US Central Daylight Time on July 23.

As the fire continued, the derrick and rig floor folded and collapsed over the rig structure.

Two fire-fighting vessels were in the area and relocated to a safe distance from the fire.

A third vessel with a fire-fighting capability and improved monitoring systems had been enroute and the Coast Guard cutter Pompano was standing by to assess the situation.

The Hercules 265 rig was working on the well, about 90km off the Louisiana coast for Walter Oil & Gas.

All 44 personnel aboard the rig when the "well control incident" occurred at about 8.45am on July 23 were evacuated.

The rig had been conducting completion work on a sidetrack to prepare the Well A-3 for production.