Drilling caused Indonesian mud volcano

Posted 2008/06/09 at 9:34 pm EDT

WASHINGTON, June 9, 2008 (Reuters) — Drilling of a gas exploration well, and not an earthquake, set off a volcano that has been spewing boiling mud for two years and has displaced more than 50,000 people on the Indonesian island of Java, experts said on Monday.

An aerial view of the gas emission from the crater of a mud volcano in Porong, East Java province May 29, 2008. REUTERS/Sigit Pamungkas

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Records kept by oil and gas company Lapindo Brantas during the drilling of a gas exploration well called Banjar-Panji-1 show specific incidents that could have triggered the disaster, the international team of experts said.

"We are more certain than ever that the Lusi mud volcano is an unnatural disaster and was triggered by drilling the Banjar-Panji-1 well," said Richard Davies, a professor of earth sciences at Britain's Durham University.

"We show that the day before the mud volcano started, there was a huge 'kick' in the well, which is an influx of fluid and gas into the wellbore," Davies said in a statement.

"We show that after the kick, the pressure in the well went beyond a critical level. This resulted in the leakage of the fluid from the well and the rock formations to the surface -- a so-called underground blowout. This fluid picked up mud during its ascent, and Lusi was born."

The team of British, American, Indonesian and Australian scientists, writing in the journal Earth and Planetary Science Letters, said this pressurized fluid fractured the surrounding rock. Mud spurted out of cracks instead of the wellhead.

"There is not a hope on Earth they are going to stop it now," said the University of California Berkeley's Michael Manga, who worked on the study.

"You can plug up a hole, but if you try to plug a crack, stuff just flows around the plug, or the crack gets bigger. The well now has no effect on the erupting mud, it was just the trigger that initiated it."

MILLIONS IN DAMAGE

In addition to the evacuations, Lusi has caused millions of dollars in damage since it erupted in May 2006. It now covers more than 2.5 square miles and the mud is flowing at a rate of 100,000 cubic meters (3.53 million cu ft) a day.

The mining company and some experts had argued that the cause was the 6.3 magnitude Yogyakarta earthquake and its aftershocks that shook the island two days before the eruption.

That quake, centered 160 miles from the mud volcano, killed 6,000 people and left 1.5 million homeless.

Manga and Berkeley graduate student Maria Brumm tested this idea but found the change in pressure underground due to the earthquake would have been far too small to cause the mud volcano.

"We have known for hundreds of years that earthquakes can trigger eruptions. In this case, the earthquake was simply too small and too far away," Manga said.

A mud volcano is usually a naturally occurring phenomenon created when a mix of mud, water and gas forms underground and is forced to the surface. There are a few thousand on earth.

PT Energi Mega Persada indirectly controls Lapindo, which holds a 50 percent stake in the Brantas block where the mud originated. PT Medco Energi International Tbk holds a 32 percent stake and Australia-based Santos Ltd the rest.

Indonesia's government has ordered Lapindo to pay 3.8 trillion rupiah ($406 million) in compensation to the victims and to cover the damage.

($1 = 9,355 rupiah (Reporting by Maggie Fox; Editing by Eric Walsh)