The fate of the 33 men trapped 688 m underground in the San José mine in Chile captivated the world in a way that few events have.
Their 68-day ordeal finally came to an end on the 13 October, when they were all safely winched to the surface under the gaze of an estimated one billion television viewers around the world.
However, that the miners are safe is due in no small part to the specialist expertise of an Australian drilling consultant.
Kelvin Brown, the Perth-based global products manager of Imdex’s Reflex Instruments, was heavily involved in the ultimately successful efforts to locate the men.
The incident began on the 5th of August when the mine’s roof collapsed, leaving the workers stranded in a refuge chamber measuring around 50 square metres.
Drill rigs raced to the scene and immediately began boring into the earth to find them, using a technique known as directional drilling, which essentially means the hole is at an angle between horizontal and vertical.
According to Brown, the initial efforts to find the men, while done with the best intentions, were carried out with too much haste and not enough care.
“When the Mining Ministry put the call out for the neighbouring resource companies to free up their drill rigs, there were suddenly nine rigs on site and everybody was just rushing,” he told Australian Mining.
“They had poor historical data of the ground, they drilled too hard and too fast and they did not make their own data as they went along.
“When I got there on there on the 16th of August, there was probably about ten holes that had already been drilled and none of them were going anywhere near the chamber.”
Brown said the efforts had also been hampered by significant underground deviation, thanks to the mine’s geology.
“In all forms of drilling, even when you drill a hole in your wall, the drill bit will follow the path of least resistance,” he said.
“This principle will govern how much the drill bit deviates from its original direction and it is especially prevalent in directional drilling.
“The ground at San José consisted of mainly hard rock, but it also had layers of softer rock between.
“The drill bits tend to deviate quite a lot when you have these combinations of hard and soft rock.”
At the request of the Chilean Government, Reflex agreed to provide equipment and expertise to help with the search efforts.
Brown travelled to mine, which is located some 45 km north of the city of Copiapó, with a supply of down hole motors, which are designed to correct and control the deviation of the drill bit so it can be used to help the boring.
“The equipment was used there in the same way it would be used in most applications,” he said.
“The only difference was that I was drilling to hit a rescue chamber for some miners, rather than an orebody.
“The chamber was 50 square metres and while I have certainly drilled for targets zones of that size before, they have never been full of people.”
Brown also brought digital surveying equipment with him, which he said was crucial in ensuring the drilling was heading in the right direction.
“You can use this equipment to triangulate the exact position of the drill bit and therefore plot the borehole,” he said.
“But as I said, the problem was that the historical data of the mine was really poor.
“In one case, I was halfway through a drill and then they told me the target may actually be six metres above those co-ordinates.
“So I would shoot for the upper target and then make an attempt at the bottom target.”
Brown said the politics of the situation had a direct impact on how effectively he could drill.
“My equipment is best used to plot a path using the natural deviations to steer the drill to the target rather than to actually correct a deviation after the event,” he said.
“I did some calculations when I first got there and recommended to the Mining Minister [Laurence Golborne] that instead of correcting a badly broken drill hole, we should actually create a new one based on the survey data that I now had.
“He did not want to do that, because politically, the Government needed to be seen doing everything possible, which meant flying over an Australian expert with the latest in technology.
“So we had to go along with that show, which was disappointing, but that was the way it had to play out.”
Despite this, one of the bore holes finally intersected the chamber on 22 August and the miners attached notes to the drill bit to let everyone know they were alive.
Camera probes were then sent down the hole to relay pictures back to the miner’s families, who had been keeping a vigil on the surface.
The images revealed the men were in reasonable physical condition, considering they had endured 18 days trapped in high temperatures and humidity and with little food.
They had been surviving on only tiny morsels of tuna, biscuits and milk every 48 hours.
Brown’s team had to switch to reverse-circulation drilling to complete two other breakthrough holes, because the water used to remove the drill cuttings was flooding the chamber.
“You cannot control reverse-circulation drilling with a down hole motor, so my role changed and I became more involved with the bore design and planning,” he said.
“Overall, if the same thing happened tomorrow, I would do it all the same way again.
“But, I would probably push a little bit harder to have everyone work with the ground instead off against it.”
The rescue
The three breakthrough holes were used to ferry the blue plastic containers, called ‘palomas’ (doves in English), which carried food, clothing and equipment.
Meanwhile three large exploration rigs moved onsite to begin constructing the bore that would be used to free the miners.
The rig that ultimately succeeded in reaching the chamber first on the 9 October, a Schramm T130XD Telemast air drill, used the third breakthrough hole as a pilot and expanded it.
The rescues began at around midnight on 12 October, with 31-year-old Florencio Ávalos the first to reach the surface.
One by one, the miners were carried to their freedom in a 54 cm diameter capsules designed especially for the rescue.
The miners’ shift supervisor, 54-year-old Luis Urzúa, was the last man rescued at nearly 10PM the next day.