Geologic processes that control sourcing and migration of subsurface helium

Thesis

There is an ever-pressing need to find more helium (He) because 1) it is an essential resource for modern life, 2) reserves are dwindling faster than He accumulations are discovered, and 3) new He projects are delayed. The motivation for this work is to provide updated frameworks on the geologic processes and migration mechanisms of He in the mid-continent USA, using noble gas geochemistry, structural geology and geophysics. The Colorado Plateau field area (Four Corners area), USA was chosen to represent a moderate tectonic activity environment, and Yellowstone (and its environs), USA, were chosen to represent a very tectonically active region and to investigate the impact of heat on gas release. In the Four Corners area, utilizing bulk gas and isotopes of hydrocarbons, non-hydrocarbons, and noble gases (n=31), we construct mass balance and noble gas fractionation models that provide evidence for advective fault-controlled systems responsible for basement sourced He accumulations. Regarding Yellowstone, utilizing heat flow data, bulk gas, and isotopes of non-hydrocarbons and noble gases (n=43), we quantify gas origin, fluid flow, and heat influence in a regional context using noble gas heat and fractionation models. We show a poor relationship regarding He and heat flow on a regional scale for Yellowstone, and we propose that localized heat sources are important in releasing He trapped in minerals. Our prediction of fault-controlled He-systems in the Four Corners area is corroborated with high-resolution geophysical data that shows a strong non-random relationship with He-rich occurrences and structural features (faults/intrusions) and historical He-well data (n=94). Based on the distributions of these relationships, we create a regional probabilistic predictive He map to reduce exploration risk. Additional work utilizing soil gas data (n=1974), was used to construct a higher-resolution localized predictive model calibrated with real-world data illustrating areas that are higher-likelihood of containing He-rich gas.

Authors: Halford, DT

• DOI: 10.5287/ora-00zdnvm4m
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: helium exploration; helium sources and migration; statistical models; noble gas and stable isotope geochemistry; crustal-fluid interactions; structural geology; helium systems
• Subjects: Geology; Geophysics; Geochemistry