REGIONAL HELIUM ACCUMULATION GEOCHEMISTRY, LA BARGE PLATFORM, WYOMING

Economic (>0.5%) accumulations of helium at the La Barge Platform in western Wyoming are the result of radiogenically-produced helium from sedimentary crust that was mobilized by deep basinal ground water flow or possibly hydrocarbons, and concentrated by diffusion into stable hydrocarbon traps. Helium production from the La Barge Platform is sourced from Paleozoic natural gas reservoirs; the resource is the largest in the nation representing approximately 55% of current helium production in the country. Though La Barge is the largest producer of helium and a target for new operators in the region, helium geochemistry at La Barge and the surrounding region is not well known.

Gas and water samples from six Mississippian producing gas wells and 17 gas-effusive springs were collected for chemical analysis from 2012 to 2016. Gas-effusive springs within a 200 km radius of La Barge were sampled during the same period. Water and gas samples from all locations were analyzed for composition, major and trace element concentrations, and stable and noble gas isotopes.

Helium and other noble gas isotope results from the samples indicate three distinct regional helium source groups that roughly match the three major geologic provinces in the region. The first is the tectonically stable sedimentary strata of the La Barge Platform region; results here suggest the helium has crustal origins and helium concentrations are relatively high. The helium of this group is not however purely crustal and appears to represent an unknown end member with R/R_A ratios of 0.05 to 0.07. The second group occurs to the west of La Barge in south eastern Idaho’s Basin and Range province. Here, there is more mantle-type helium with R/R_A values of 0.15-2.2 and at lower concentrations than the first region. The last group, the Yellowstone region to the north, is well documented in the literature with mantle type helium. This area was only tangentially sampled for this study. Overall, the higher concentrations of helium occur in the sedimentary La Barge Platform region samples and they are isotopically of more crustal origin than the samples from the other regions. High helium concentration gases at surface springs in this region suggest that additional, potentially economic reservoirs of the gas are present.