Helium: Exploration Methodology for a Strategic Resource

Abstract

Helium exploration is still in its infancy. Noble gas and stable isotopic analyses have proven to be effective tools in the past for determining the correlation between 4He and associated N2 and the role of groundwater in the transport and focusing of these gases alongside unrelated natural gases such as CH4 and CO2 into traps (Ballentine and Sherwood-Lollar, 2002). In this thesis these tracers are used to further understand aspects of the helium system such as source(s), gas migration pathways and trapping mechanisms and from this to ultimately present a framework for a helium exploration method.
Geochemical studies were conducted on CH4-rich helium gas reservoirs in the Mid-Continent US and, for the first time, on N2-rich helium gas reservoirs in Utah, Montana and Saskatchewan, Canada. Both types of 4He-rich system showed consistent 4He-associated N2 endmembers with δ15N values between -3.00‰ and +2.45‰; a range associated with low grade metamorphic crustal sources indicating that the source of the economic 4He and associated N2 in shallow reservoirs is likely derived from variable isotopic mixing between the basement and overlying sediments.
From these studies it was also ascertained that in all fields the mechanism for 4He and associated N2 degassing into reservoirs appears to be related in some degree to groundwater and to the saturation threshold of 4He-associated N2 thereby defining possible secondary migration pathways for the helium system.
New noble gas data from thermal springs in the West and East branches of the Tanzanian section of the EARS show 4He concentrations of up to 10.5% indicating the active release or primary migration of high helium and high N2 gases in the region. This coupled with potential traps in the nearby Rukwa Basin could provide a high helium reservoir in the future. First estimates for the basin, derived from 4He analyses (< 4% 4He) combined with seismic and soil gas surveys for the basin translate to a P50 estimate of probable reserves of 98 Bcf which would be enough to supply the current global helium demand for ~14 years if current demand remains steady.