Using an example from a failed hydrofracturing effort in a Texas oilfield, we show how frequency- and time-domain EM were used to delineate the lateral and vertical extent of salinization likely related to fluids and accompanying formation water migrating up the borehole and into the shallow subsurface. Ground, borehole, and airborne electromagnetic induction (EM) approaches have long been used to identify and assess near-surface impacts of oil and gas exploration and production activities, especially those associated with surface-water and groundwater salinization. These same approaches can be employed to address some of the near-surface issues related to hydrofracturing, such as the possible introduction of fluids and accompanying highly saline formation water into the shallow subsurface through improperly plugged boreholes, natural conduits (faults or fractures), and the borehole through which the fracture process occurs. EM approaches could find wider use in assessing pre-fracturing conditions in the upper 100 m or so, monitoring conditions during hydrofracturing operations, and quantifying change (or lack of it) after the process is complete.
