Evolution of sinkholes over Wink, Texas, observed by high-resolution optical, and SAR imagery

Two caprock and cover collapse sinkholes, Wink Sinks #1 and #2, in Winkler County, Texas, collapsed in 1980 and 2002, respectively. They are located in a region underlain by the Salado Formation on the eastern edge of the Delaware Basin. The sinkhole collapses were associated with intense hydrocarbon drilling and production activities in the Hendrick oilfield. Production records and prior investigations imply the sinkholes developed after salt dissolution due to freshwater intrusion, cavity formation, roof failure, and successive upward cavity migration. High-resolution (1 m) aerial photography shows the ensuing expansion of Wink Sink #2 from 2002 through 2010 and relative stability of the ground surface after 2010. Very high-resolution (25 cm) staring spotlight mode TerraSAR-X reveals the spatiotemporal details of Wink sinkhole deformations. The vicinities around the two existing sinkholes (Wink Sinks #1, #2) deformed at a rate of 5 cm/yr in line-of-sight (LOS) direction from October 2015 to March 2016, and the deformation was possibly caused by the gradual deposit of the debris from overlying unconsolidated Alluvium and Santa Rosa sandstones infilling the cavity after the sinkhole collapse. Specifically, the largest deformation of 53 cm/yr in LOS direction was found 1 km east of Wink Sink #2. Our study suggests that severe drought in 2011 widened and created fractures as well as ground fissures in the rocks overlying and underlying the salt formation due to the increased effective stress. Fractures, ground fissures, and the abandoned unplugged boreholes or improperly completed wells opened one or more vertical pathways of freshwater from groundwater flow and precipitation toward the salt bed, finally causing the rapid salt dissolution and the opening of new cavities. To explain the onset of a rapid subsidence near the Wink sinkholes, our study considers the combined effect of natural perturbation (i.e., drought, rock fractures, ground fissures, subsurface drainage, precipitation) and anthropogenic effects (i.e., improper well control). Our method to explore high-resolution imagery can be applied to characterize the sinkhole deformation and mitigate sinkhole-related geohazards.