ELECTRICAL RESISTIVITY SURVEYS OF ANTHROPOGENIC KARST PHENOMENA ASSOCIATED WITH BRINE WELL OPERATIONS: SOUTHEASTERN NEW MEXICO, USA

A significant minority of sinkholes and other karst phenomena in southeastern New Mexico are of human origin, and are often associated with solution mining of salt beds in the shallow subsurface. In 2008 two brine wells in a sparsely populated area of northern Eddy Co., New Mexico abruptly collapsed as a result of solution mining operations. The well operators had been injecting fresh water into underlying salt beds and pumping out brine for use as oil field drilling fluid. A third brine well within the city limits of Carlsbad, NM has been shut down to forestall possible sinkhole development in this more densely populated area. Electrical resistivity surveys conducted over the site of the brine well confirm the presence of a large, brine-filled cavity beneath the wellhead. Laterally extensive zones of low resistivity beneath the wellsite represent either open cavities and conduits caused by solution mining, or highly fractured and/or brecciated, brine-saturated intervals that may have formed by sagging and collapse into underlying cavities. The data also indicate that significant upward stoping has occurred into overlying strata.