Helium: Uses, Formation, Exploration & Production
With uses in advanced healthcare and science, helium is an increasingly valuable commodity. Recent helium supply shortages have led to a renewed interest in exploration and drilling for the rare inert gas.
Helium in economically-viable concentrations has been found in Cambrian- to Devonian-age formations that are common in Western Canada, resulting from predictable processes of generation and migration.
What is Helium and What is it Used For?
Helium is an inert gas, with unique properties because of its low atomic weight. Although it is the second-most abundant element in the universe, helium is relatively rare on Earth because it is lighter than air and escapes the atmosphere upon release.
Liquid helium is extremely cold, which makes it an excellent cooling medium for state-of-the-art science and technology. For example, liquid helium is used to cool the Large Hadron Collider (LHC), satellite instruments, and the superconducting magnets in MRI scanners and NMR spectrometers.
In manufacturing, helium is used to make fibre-optics, semiconductors, and barcode scanners. Helium-ion microscopes and certain types of arc welding also require helium.
How is Helium Formed? — Generation Processes
A small fraction of helium found on Earth in economic accumulations is primordial (present when the earth formed).
Most terrestrial, economically-viable helium (He) is formed by the alpha decay of radioactive uranium (U) and thorium (Th) into lead (Pb).
What is alpha decay and how does it generate helium?
Alpha decay is one of the pathways by which radioactive elements eventually decay into non-radioactive elements. For example, uranium-238 decays to thorium-234 via alpha decay.
The product of alpha decay is an alpha particle, which consists of two protons and two neutrons — identical to the nucleus of a helium-4 atom.
Isotopes that decay to generate helium
There are three key isotopes that lead to the generation of helium: uranium-238, uranium-235, and thorium-232. Each of these is a primordial radioactive isotope.
They were present when the Earth formed, and their half-lives are sufficiently long so that a good fraction of that original content has not yet decayed.
How much helium does each isotope generate?
Uranium-238 eventually decays to lead-206 via the uranium decay series (aka radium series), ultimately producing eight alpha particles.
Uranium-235 eventually decays to lead-207 via the actinium decay series, ultimately producing seven alpha particles.
Thorium-232 eventually decays to lead-208 via the thorium decay series, ultimately producing six alpha particles.
Generation potential
Helium generation in typical (average) rocks are a function of time of generation. Hot shales have by far the greatest generation potential, with a generation rate about 8 times higher than average shale.
Typical sandstones and carbonates have less generation potential than average shales (Brown A.A. (2010) Formation of High Helium Gases: A Guide for Explorationists).
Where is Helium Found? — Migration Processes
Helium-rich gas follows similar distribution processes to conventional oil and gas accumulations. However, helium’s interaction with gas and water has a much greater influence on accumulations.
Pore water accumulation
Helium generated by the alpha decay of uranium and thorium isotopes diffuses into the surrounding pore water.
Typically, the concentration of helium in the pore water increases along with uranium and thorium concentration and age. It also tends to increase with decreasing porosity. (Brown A.A. (2010) Formation of High Helium Gases: A Guide for Explorationists).
Helium transfers from solid grains into pore water, where it accumulates. Old, stagnate water collects more helium than young, hydrodynamic water.
Gaseous helium
When another gas comes into contact with helium-rich water, the helium partitions into the gas phase.
Gaseous helium migrates with other gas to traps — like conventional oil and gas accumulations.
Typically, high-helium gases are more likely to form at shallow depth rather than deeper in the earth — meaning cool thermal gradients favour higher helium in gases.
Helium Exploration & Production in North America
As a general rule, helium of economic values is typically found along the periphery of Prolific petroleum systems, between 0.5 and 2.5km depth.
Most exploration of helium has been focused on Cambrian formations. Typically these are offering the most economic percentages of helium and provide the necessary trapping systems. However, sedimentary rocks with high uranium and thorium have a good helium source potential.
Monadnocks
Most companies are acquiring seismic data over areas that have tested for helium. They are pursuing monadnocks. A monadnock (by definition) is an upstanding rock, hill or mountain on an otherwise flat plain. Some Precambrian monadnocks have sedimentary rocks of Cambrian age draped overtop. This is what provides the needed trapping mechanism. Monadnocks are easily identified in seismic data.
Western Canada as a helium resource
Canada has the 5th or 6th largest Helium Resource in the world behind the U.S, Qatar, Algeria, Russia and possibly Tanzania (Yurkowski, M.M. (2016): Helium in south-western Saskatchewan: accumulation and geological setting; Saskatchewan Ministry of the Economy, Saskatchewan Geological Survey, Open File report 2016-1, 20.p and Microsoft Excel file).
Geographically, helium exploration and production is taking place in Alberta, Saskatchewan, and Montana. Southwest Manitoba also shows potential for helium production.
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