There were no injuries reported when an explosion Saturday started the fire at a TransGas facility near Prud'homme, a village northeast of Saskatoon. TransGas is a subsidiary of Crown-owned SaskEnergy.
Company spokesman Dave Burdeniuk said there was a setback Wednesday morning, when a wellhead failed and caused a larger flame to burn.
The wellhead leads to one of seven underground caverns, which are used to store natural gas for the winter when demand for heating is greater.
"The pressure of the gas coming up the wellhead casing pipe ... pushed the wellhead out of the way," Burdeniuk said. "The wellhead was very heat damaged because it had endured the intensity of those flames.
"It was a situation that we had planned for. We had hoped to be able to use the existing wellhead to cap and seal off the cavern."
He said four families located within two kilometres of the site were to be out of their homes for the day.
"We will get them back into their homes as quickly as we can," he said.
The caverns are about 1.5 kilometres underground and as tall as a 12-storey office building.
The facility was unstaffed when the fire started, which is common on evenings and weekends when the demand for natural gas is low.
Automated equipment shut down the facility and a Calgary company specializing in oil and gas fires was called in to help extinguish the blaze, which generated flames up to 20 metres high.
Burdeniuk said the failure of the wellhead on Wednesday followed a 60-hour process to turn off the primary gas source feeding the flames.
The plan now is to install a new wellhead and seal off the cavern, he said.
Once the fire is under control, there will be an investigation to determine what happened with the wellhead, he said.