Saturday, January 27, 2007

Exploration drilling may be responsible for mud volcano eruption

Gas drilling on the Indonesian island of Java has triggered a "mud volcano" that has killed 13 people and may render four square miles (ten square kilometers) of countryside uninhabitable for years.

In a report released on January 23, a team of British researchers says the deadly upwelling began when an exploratory gas well punched through a layer of rock 9,300 feet (2,800 meters) below the surface, allowing hot, high-pressure water to escape.

The water carried mud to the surface, where it has spread across a region 2.5 miles (4 kilometers) in diameter in the eight months since the eruption began.

The mud volcano is similar to a gusher or blowout, which occur in oil drilling when oil or gas squirt to the surface, the team says. This upwelling, however, spews out a volume of mud equivalent to a dozen Olympic swimming pools each day.

Although the eruption isn't as violent as a conventional volcano, more than a dozen people died when a natural gas pipeline ruptured.

The research team, who published their findings in the February issue of GSA Today, also estimate that the volcano, called Lusi, will leave more than 11,000 people permanently displaced.

Human Causes

Mud volcanoes occur when pressures deep within the Earth cause mud to squirt to the surface, said Richard Davies, lead author of the study.

"It's simply an eruption of mud and liquids," added Davies, who directs the Center for Research into Earth Energy Systems at Durham University. "There are probably a couple of thousand on planet Earth."

Typically, the eruptions are caused by tectonic forces or by the compaction of sediments at the deltas of large rivers, such as the Mississippi. "They're very common features," Davies said.

But even though an earthquake had occurred in the Java region only two days prior to the eruption, the delayed mud release almost certainly confirms a human cause, the new research points out.

If an earthquake was the cause, the eruption should have begun immediately, the scientists say.
Another unusual feature of the Indonesian eruption is that it involves a very thin, liquid mud, says Davies' colleague, Richard Swarbrick of Geopressure Technology Ltd.

That's unfortunate, because the thin mud could flow for long distances, increasing the devastation.
Also of concern is the fact that the mud is apparently being eroded out from deep underground, creating a cavern.

That means that the land around the volcano might collapse to form a crater, Swarbrick said.
The duration of the volcano's activity is also of concern.

Normally, mud volcanoes erupt quickly, then peter out to a slow ooze intermingled with the occasional major upwelling. But in Java the flow rate appears to have doubled since the eruption began, Swarbrick said.

At its center, the pancake-like deposit is already about 33 feet (10 meters) thick, Durham University's Davies added.

"It's carried on for a long time at a high rate, which suggests it's not going to stop tomorrow," he said.

Ultimately, the scientists say, they hope to learn more how to prevent such incidents from occurring in future oil and gas exploration.

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