Helium diffusion experiments in effective helium source rocks: A case study involving coal, shale, and granite

Helium diffusion in geological media is critical for assessing the feasibility of helium resources. However, the impact of effective stress and temperature on helium diffusion behavior for effective helium source rocks remains underexplored. In this study, we measured the helium diffusion coefficients in coal, shale, and granite by using the counter-diffusion method, combining advanced techniques such as, Field Emission Scanning Electron Microscopy, Energy Dispersive Spectroscopy, and Low-Field Nuclear Magnetic Resonance. The findings revealed variations in helium diffusion coefficients across different geological media in response to changes in temperature and effective stress, identifying critical thresholds that significantly affected helium migration. Moreover, a distinct correlation between porosity and diffusion behavior was observed, thereby, highlighting the importance of microstructural characteristics in controlling helium transport processes within geological media. These findings have not only added to the understanding of helium diffusion mechanisms but have also provided valuable insights to enhance the accuracy of helium resource exploration and evaluation.