SOURCING AND CHARACTERIZING GEOCHEMICAL CHANGES FROM UNPERMITTED PRODUCED WATER DUMPING, PERMIAN BASIN, USA

Produced waters are the most voluminous waste stream of hydrocarbon production, with the Permian Basin of New Mexico and Texas producing more than 10⁷ barrels/day (1.7x10⁹ L/day). Despite calls for better produced water management in this semi-arid region, unpermitted produced water dumping remains a serious problem. This study focuses on the chemical and isotopic composition of 41 surface (0-5 cm) and core (0-30 cm) soil samples from 5 dump sites in the Mescalero sand dunes, southeast New Mexico. Surface samples identified as those impacted by produced water dumps (n=18) exhibit higher water content (p<0.01) and saturated electrical conductivity (up to 5.8% and 23.2 mS/cm) than control samples (n=15). Nearly all water extractable ions were enriched in dump surface samples relative to control samples, with major ions enriched by factors of 13 to 4,500 (averages). Isometric logratios of Br, Cl, and Na in water leachates from the dump samples overlap those of nearby produced waters from tight oil (e.g., Bone Spring) and conventional gas wells, which are of paleoseawater origin. ⁸⁷Sr/⁸⁶Sr composition of water leachates of surface control samples (0.70850–0.70894) correspond to that of local caliche, indicating Sr originated from local dust and precipitation. ⁸⁷Sr/⁸⁶Sr of surface dump samples are universally higher (0.70919–0.70942) than the control samples, and can be modeled by addition of ~1-200 ml of produced water from the Bone Spring, Strawn, or Morrow reservoirs to a kg of average control sample soil. Local production data from within the study area show that roughly 80% of produced water generated during the period of dumping came from horizontal Bone Spring wells. Data from core samples show that native Sr was completely flushed out to depths >30 cm at one site but not the other, suggesting site-specific controls on sub-surface flow of waste fluids. Surface dump samples also show a ~2-fold enrichment in ²²⁶Ra and ²²⁸Ra relative to control samples, but are well below activities from mass balance mixing calculations with produced waters suggesting Ra loss prior to or after dumping occurred. Results from this initial investigation demonstrate that unpermitted dumping of produced water degrades environmental quality and can be traced using isotopic tools.