After a week of hearings at the federal inquiry into Australia’s third-largest oil spill, it is becoming clear the blow-out at the Montara well was caused by a chain of poor decisions and miscalculations.
Up to 2,000 barrels of oil and gas spewed from the Montara well into the Timor Sea every day for 10 weeks from August 21 last year.
But a picture is emerging that shows decisions made in the months leading up to the accident are to blame for the incident off Western Australia.
In February 2009, a West Atlas rig began drilling the well hundreds of kilometres off the Kimberley coast.
The Thai-based owner of the well, PTTEP Australasia, called for operations to be suspended in March so it could focus on other wells it owned in the Montara field.
This is where the project stopped going to plan.
PTTEP used pressure caps instead of a cement plug to temporarily stop the flow from the well.
That decision was approved by the Northern Territory Department of Resources in just 30 minutes, and the inquiry has raised questions about whether the agency acted diligently enough when regulating the oil company’s operations.
Two pressure caps were authorised to be used on the well as barriers, but only one was ever installed and, contrary to good oil field practice, it was never tested.
In his opening statement, counsel assisting the inquiry, Tom Howe, QC, said: “No one has been able to provide, to this point, a satisfactory explanation to the inquiry as to why the cap was not installed.”
A senior manager from Atlas Drilling, David Gouldin, has told the inquiry that the installation of the cap remained on a to-do list on a whiteboard in an office on the rig until the blow-out.
When the West Atlas drilling team returned to the well in August, workers removed the existing cap for cleaning. It was never reinstalled. Hours later, the well kicked and began releasing an uncontrolled flow of oil and gas that would not be blocked for months.
In addition to the missing pressure cap, further problems arose with the well’s cement casing.
Cement is used to set the drilling pipe in place and to ensure oil and gas does not leak into the surrounding ocean.
But while 199 barrels of cement should have been used to achieve the “top of cement” standard practice on the Montara well, only 133 barrels were used.
Even more mistakes appear to have occurred when that cement casing was tested.
Extra cement was pumped into the well in a test designed to check if the casing was full.
When the liquid flowed back as expected, it was thought to be pure cement. It has now emerged that the fluid was contaminated with seawater.
That mistake significantly weakened the strength of the casing as a barrier.
PTTEP supervisor Noel Treasure has told the inquiry that he “miscalculated” the volume of cement.
And while figures indicating the mistake were emailed to managers at both Atlas Drilling and PTTEP, it has been suggested there was not sufficient scrutiny of the information by on-shore personnel.
Atlas Drilling rig manager Donald Miller told the inquiry that he received the figures in a daily drilling report, but he did not focus enough on the report nor give it sufficient weight.
‘Nervous and upset’
During his evidence, Mr Treasure came under fire for failing to sign the first statement he made about the accident.
As the most senior representative from PTTEP working on the rig in the lead up to the spill, Mr Treasure made a draft witness statement in the week before the inquiry.
But instead of substantiating the statement, Mr Treasure chose instead to submit an amended statutory declaration.
When questioned about this, Mr Treasure told the inquiry he was frightened about civil liability.
“I was nervous and I was upset,” he said.
“I was worried about it, because I went through and checked some of my records afterwards … and some of the stuff I said in the statement was incorrect.”
Mr Treasure says he spoke to a senior PTTEP executive about his draft statement in the week before the inquiry began, but he says the executive did not ask him to change his statement.
As well as the cause of the spill, the inquiry will attempt to uncover why it took almost three months for the leak to be stopped.
It will also hear evidence about the environmental consequences of the accident and the current regulatory system for the offshore petroleum industry.
Commissioner David Borthwick is expected to submit a report on the inquiry’s findings by April 30.