Abstract

A significant minority of sinkholes formed in gypsum bedrock in the Delaware Basin of west Texas and southeastern New Mexico are of human origin. These anthropogenic sinkholes are often associated with improperly cased abandoned oil wells, or with solution mining of salt beds in the shallow subsurface. In July, 2008 a sinkhole formed abruptly at the site of a brine well in Eddy Co., New Mexico. The well operator had been injecting fresh water into salt beds of the Permian Salado Formation and pumping out the resulting brine for use as oil field drilling fluid. Borehole problems had prevented the operator from conducting required downhole sonar surveys to assess the dimensions of subsurface void space. The resulting sinkhole formed in just a few hours by catastrophic collapse of overlying mudstone and gypsum, and in less than one month reached a diameter of 111 m and a depth of ∼64 m. The event has prompted the New Mexico Oil Conservation Division to review its regulations regarding brine well operations in the southeastern New Mexico oil fields. Fortuitously, a seismograph had been deployed ∼13 km southeast of the brine well a few months earlier, and precursor events were captured on the seismograph record a few hours before the subsurface cavity breached the surface. This may be the first documented seismologic record of catastrophic sinkhole formation.