May 15, 2008

Experts still looking for cause of Houston-area sinkhole

Houston

The saltwater disposal company nearly devoured by a giant sinkhole this week in the Houston area was injecting sometimes double the amount of saltwater into the ground that its state permit allowed.

But officials with the Texas Railroad Commission, which regulates such permits, stressed that the cause of the sinkhole in the small town of Daisetta has not been determined.

“We have no proven link between Deloach and the sinkhole,” commission spokeswoman Ramona Nye said.

Deloach Oil and Gas Wastewater Disposal Co. declined comment on the commission’s notice that the company had violated its permit by dumping 128,000 to 192,000 barrels a month down its disposal well. Its permit allowed 90,000.

The company injected about 800,000 barrels more than the 1 million barrels that the permit authorized in 2007, Nye said.

The company’s disposal well is 200 feet from the massive hole that stretches three football fields in diameter and 100 to 200 feet deep. It is just a block from the high school and town’s fire station.

Since the hole appeared as a crack on Wednesday morning and began to grow by as much as 20 feet at a time, it has gobbled up a tractor, 18-wheeler cab, trees, telephone poles and oil-field equipment.

Authorities believe the sinkhole may have stabilized as only a few clods of dirt were occasionally sloughing from its sides on last Friday.

Daisetta residents were given tours of the hole for the first time on Friday night. The public has been barred from the area as a safety precaution.

The giant hole has become something of a national curiosity, and residents were eager to see Daisetta’s little grand canyon.

“We want to let the children see that they won’t be sucked into the ground,” said Liberty County sheriff’s spokesman Hugh Bishop. “But after this, anybody who sneaks in there can be arrested.”

The town’s main street, which passes by the hole, remains closed to drivers.

Daisetta is an old oil field town and poised for potential sinkhole problems, geology experts say.

The town sits atop a large underground salt formation, known as a saltdome, which is a mile and a half in diameter and lies 650 feet to 1,900 feet below the surface, authorities say. A swampy area where oil has been pumped since the early 1900s surrounds the perimeter.

Sinkholes can form when rainfall, underground water or injected saltwater dissolves or washes out an underground cavity.

Fluids must penetrate a layer of topsoil and sandstone before reaching Daisetta’s caprock and salt where a cavity can be created, Nye said.

Some of the town’s old oil wells, which were never capped and don’t appear on any maps, might have piping that provides avenues for fluids to reach those areas, said Carl Norman, a geology consultant in Houston who is an expert on sinkholes.

Since 1968, Deloach has had a state permit to inject saltwater down a 1,181-foot-deep well by the northwest edge of the dome where the hole opened, Nye said.

The injection well, which is now shut down, is supposed to keep the saltwater safely contained within the sandstone layer.

Associated Press

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