The NSW Mine Safety Investigation Unit has published an investigation update on a drilling incident which left a 26 year old man a quadriplegic.
The man was struck by a blooie line which had violently lifted under high pressure. The incident occurred in August 2012 at the Ashton Coal project, approximately 14km north west of Singleton in the Hunter Valley of New South Wales.
During drilling operations on alluvial plains, the drill head became bogged at a depth of around 120 m. It could rotate, but could not be raised or lowered. Compressed air was applied by the drill string to the drill head in an effort to force a discharge of material from the borehole.
Witnesses reported a loud noise, like an explosion.
The blooie line was seen to rise into the air and to cause the driller’s floor and the deck floor to also rise. The drill rig operator was thrown up into the air and fell onto the driller’s console with the blooie line falling on him.
The cause and circumstances of the incident are being investigated, but through observation of the drill rig and subsequent inquiries it has become apparent that;
drilling technique (rotary air hammer), water make, air pressure and stuffing box/surface casing/blooie line design are significant factors.
In investigation update suggests the primary surface casing was not installed to the correct depth and as a result the borehole wall lost integrity below the casing. This caused alluvial material and water to enter the borehole and jam the drill pipe in the hole.
The driller, in his efforts to free the stuck drill pipe, pressurised the hole behind the blockage and began back reaming. As the blockage broke free a catastrophic release of water and cuttings has ejected from the borehole annulus creating the explosion observed by the drilling supervisor.
Investigation of the incident by the NSW Mine Safety Investigation Unit is continuing.
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