A torrent of hot mud erupted 200m from the Banjar Panji-1 exploration well during deep drilling on May 29 last year, spewing up to 150,000 cubic meters of sludge per day. The well is part-owned by Santos and operated by Indonesian company Lapindo Brantas.

Despite efforts to stop the deluge, the mud has swallowed massive tracts of agricultural land and heavily populated villages, forcing some 12,000 villagers to flee their homes.

The British study, Birth of a Mud Volcano, published in the US Geological Society of America journal, GSA Today, said drilling probably caused the mud eruption.

“The mud eruption appears to have been triggered by drilling of overpressured porous and permeable limestones at depths of 2830m below the surface,” the article said.

The finding contradicts claims from Lapindo, which said the flow was triggered by a natural disaster, possibly an earthquake some 300km away. Santos has maintained silence on the possible cause, but the third joint venture Indonesian partner, PT Medco Energi, said “gross negligence” was to blame and alleges the 3km-deep well was not properly cased.

But the UK study found the earthquake was coincidental, saying it happened two days before the mud volcano erupted and no other similar volcanoes occurred in the region after the tremor.

It also warned the flow could continue “for many months and possibly years to come.”

“A region several kilometres wide should undergo sag-like subsidence over the coming months with more dramatic collapse surrounding the main vent,” the article said.

Lapindo has put the cost of the clean-up of the mud at about $A229 million, but analysts have estimated the true cost could run up to $1.4 billion. That would leave Santos, which has an 18% stake in the project, exposed to the tune of more than $254 million.

The Adelaide-based company initially made a provision of $24 million for the cost of fixing the site, but that figure has since blown out to $43 million. It has already paid $US15 million ($A19 million) into the JV’s fund to support social, technical and environmental responses to the disaster.

Indonesian police have been investigating the case for months and have now named 13 suspects.

Santos has said it would not comment on the likely cause of the mud volcano while a police investigation was underway.