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Hydrologic Assessment of the San Juan Basin

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The San Juan Basin, an important source of oil and gas located in northwestern New Mexico, has recently experienced renewed production from the Cretaceous Mancos Shale through the use of horizontal drilling and hydrofracturing. The Bureau of Land Management commissioned this study of the possible impacts of new exploration and development of this resource on the land surface and on the groundwater supply.

Two reports, one summarizing the Reasonable Foreseeable Development (RFD) of oil and gas from the Mancos Shale and one assessing groundwater supply sustainability in the San Juan Basin, are included on this CD. In addition, the digital data and ArcGIS files used to calculate aquifer volumes and analyze water quality are available on the CD.

The RFD report concludes that the Mancos play can be effectively developed by drilling approximately 3650 wells, based on current production trends from horizontal wells drilled between 2010 and the autumn of 2014. About 2000 of those wells will be in the relatively untested, gas-prone northern part of the basin, and the remainder will be in the oil-prone southern part of the basin.

Important findings from the groundwater study are:

  1. The largest water right allocations in the San Juan Basin are assigned to mining (coal and uranium, 31.1 %), domestic users and municipalities (28.2%), and food production (24.7%). The petroleum industry owns 6.3% of the groundwater rights, totalling ca. 6674 acre-ft/year (afy).
  2. The water usage for horizontal wells in the San Juan Basin averages 3.13 af/well.
  3. At least 4.5 million acre-ft of groundwater was stored in the accessible parts (<2500 feet below ground surface) of the major sandstone aquifers prior to the development of groundwater resources in the San Juan Basin.
  4. Water chemistry data document the fact that fresh groundwater is located only 3 to 20 miles basinward of the outcrop belt for each sandstone aquifer. Brackish to saline waters are dominant in the center of the basin.

Funded by U. S. Bureau of Land Management through New Mexico Tech’s Department of Petroleum Engineering

For more information, please contact:
Dr. Shari Kelley, Senior Geophysicist


  1. Kelley, Shari; Engler, Thomas W.; Cather, Martha; Pokorny, Cathryn; Yang, Cheng-Heng; Mamer, Ethan; Hoffman, Gretchen; Wilch, Joe; Johnson, Peggy; Zeigler, Kate, 2014, Hydrologic assessment of oil and gas resource development of the Mancos Shale in the San Juan Basin, New Mexico, New Mexico Bureau Geology Mineral Resources, Open-file Report, v. 0566.

Selected References

  1. Engler, Thomas W.; Kelley, Shari; Cather, Martha, 2015, Reasonable foreseeable development (RFD) for northern New Mexico, New Mexico Bureau Geology Mineral Resources, Open-file Report, v. 0567, pp. 1-39.
  2. Newton, B. Talon; Mamer, Ethan; Timmons, Stacy, 2017, Hydrogeology and Geochemistry of the Animas River Alluvial Aquifer after the Gold King Mine Spill, San Juan County, New Mexico, New Mexico Bureau of Geology Mineral Resources, Open-file Report, v. 0592, pp. 65.

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