PBS-SEPM 2023 August Luncheon - Mark Andreason

"Helium Exploration Workflow in the Four Corners area, Navajo Nation " - By Mark Andreason (Navajo Nation Oil and Gas Co.), Bill Cathey (Earthfield Technology LLC), Michael Cathey (Earthfield Technology LLC), and Gary Rice (Geofrontiers Corp.)
 
Abstract
Very high concentrations of helium (5-9%) have been historically discovered and produced within the Four Corners region of the Navajo Nation generally as a byproduct of oil and gas exploration.  The purposeful exploration for helium deposits requires an understanding of the helium system and what exploratory tools best take advantage of helium’s unique system.  From 2020-2021, NNOGC, funded by the US Dept. of Interior, conducted a detailed study over 1.7 million acres in the Four Corners area.  The study’s purpose was to better understand the mechanisms that result in the accumulation of high helium deposits and to identify new potential helium resources within the Navajo Lands.  Two aspects of the study will be discussed in this presentation: 1) a high-resolution aeromagnetic data (0.25 x 1 mile grid) over an area that contains the highest concentration of known helium deposits to better understand the source, migration, and possibly trapping aspects and 2) a high-density soil gas sampling survey (2232 samples, 0.125 mile grid) over several known and prospective helium deposits to see if there is a relationship between subsurface helium deposits and helium soil gas concentrations.  This presentation will show the results and benefits of high-resolution aeromagnetic and helium soil gas data in identifying potential helium prospects. These surveys also gave insights into the workings of the helium system.
 
The radioactive decay of uranium and thorium within the crust serves as the source for helium.  Radioactive decay is only a function of time, and thus very old and shallow (below the closure temperature) granitic rocks will have the highest concentrations of stored helium.  Release of helium from the granitic source can occur because of orogenic and/or magmatic events.  In the Four Corners study area, data suggests that magmatic events, particularly those related to the Oligocene to Miocene (28-19 Ma) Navajo Volcanic field, were the primary release and concentration mechanism for helium from the crustal source rocks.  Data also suggests that helium migration from rising intrusive bodies and basement lineaments is very short before encountering a trap.  Data from this study also suggests that the helium fields surrounding the Defiance uplift would have begun charging due to the Navajo Volcanic field magmatic activity or later.
 
The most helium prospective areas, as determined by this study, are basement highs intersected by basement lineaments and intermediate-depth intrusive bodies.  Over two hundred untested potential helium deposits were identified within the study area meeting these criteria.  Thirty-five (35) of these basement intersection-intrusive overlap areas had been previously tested resulting in a 45% success rate for finding significant high helium-rich deposits.  Helium soil gas sampling was also found to be indicative of identifying subsurface helium deposits and is a useful and cost-effective method to reduce the exploratory risks.