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Geologic, Geographic, and Temporal Variations in Saltwater Disposal Practices Within the Permian Region, Texas and New Mexico, U.S.A.


Subsurface disposal of saltwater co-produced with oil and gas has become a critical issue in the United States because of linkages to induced seismicity, as seen in Oklahoma and North-Central Texas. The objective of this study is to assess the geologic, geographic, and temporal variations in saltwater disposal activity (SWD) within the Permian Region of Texas and New Mexico, the largest oil and gas region of the USA.

Data was compiled and analyzed for all SWD wells in the Permian. SWD permits, well architecture, and volumes were gathered, quality-checked, interpreted for disposal intervals and geologic targets, and summarized at formation, subregion, 100-sq. mi., and monthly scales. Geologic targets were interpreted by intersecting depth intervals with 56 gridded structural horizons. A stratigraphic correlation chart was developed and colored in a heated color scale to show subsurface distribution of SWD volumes. SWD volumes were mapped in 100-sq. mi. grid blocks and colored using the same scale to display geographic variation. Monthly volumes, active well counts, and cumulative volume were represented in a time-series chart overlain with earthquake occurrences.From 1978 to 2016, 30 billion barrels of saltwater were disposed into 72 geologic units via 8,201 active wells within 6 subregions. For the first 35 years, the Midland Basin and Central Basin Platform (CBP) were the most active subregions. Over the last five years (2011-2016), SWD shifted away from the CBP and into the Delaware Basin. The 72 geologic targets range in age from Cretaceous to Cambrian, which encompasses most of the Permian subsurface. Approximately half of the saltwater is disposed into shallow, young Guadalupian-aged formations with increasing volume over time, despite concerns of overpressuring, interference with production, and induced seismicity. The San Andres in the Midland Basin is experiencing interference in production due to locally exceeded disposal capacity; operators are exploring alternative targets. The Ellenburger is a potentially underutilized target but poses seismicity concern from its adjacency to crystalline basement and deep-seated faults.This research presents SWD activity across the Permian Region; it does not indicate causation of seismicity. Analytic results of SWD locations, depths, rates, and targets are used as critical input into integrated assessments of induced seismicity within the TexNet Center for Integrated Seismicity Research.