A massive sinkhole near Artesia is prompting the state to re-evaluate rules governing brine wells used in oil and gas production.

The well, on County Road 217 about 17 miles southeast of Artesia, began collapsing last week. In a 24-hour period, it more than doubled in size until it was 300 to 400 feet in diameter, according to Oil Conservation Division engineers. It is 70 feet from the top of the hole to the waterline, and engineers had yet to determine the depth to the bottom Wednesday.

Brine wells are created by oil and gas companies that fill salt caverns with water, Jodi Porter, Oil Conservation Division spokeswoman, said Wednesday. The water is left until it is saturated with salt and the pumped back out to use in drilling processes.

The last such well that collapsed was in the 1990s, Porter said.

Oil and gas companies must obtain a permit from the division before drilling brine wells.

On Wednesday, Energy and Minerals Secretary Joanna Prukop directed the Oil Conservation Division to evaluate the rules and regulations governing brine wells, including an internal audit and inspection of all existing brine wells in New Mexico.

Scientists from the Oil Conservation Division, the Bureau of Land Management, the State Land Office, the New Mexico Bureau of Geology and Mineral Resources and the National Cave and Karst Research Institute are assessing horizontal and vertical movements of the ground to project future subsidence. A fence and "keep out" signs around the sinkhole will be completed by Friday.

The Oil Conservation Division also requested a brine well of similar age near Carlsbad to be shut down. The operator, I & W Inc., voluntarily stopped operation and will plug the well.

"There are several brine wells in New Mexico and we must ensure that they are all properly monitored to ensure safety and stability," Prukop said in a news statement. "We have now seen that these wells can collapse and the extensive damage such a collapse can generate."

Contact Staci Matlock at 470-9843 or smatlock@sfnewmexican.com.