Evaluation of potential helium source rocks and helium enrichment factors in coalbed methane in the eastern margin of Ordos basin

As a non-renewable noble gas with important industrial value, helium has significant implications for its resource exploration and development. The Ordos basin has become a core area for research on the generation, release, and enrichment laws of helium due to its unique geological structure, abundant stratigraphic lithology, and complex sources of helium in coalbed methane. We conducted analyses of gas compositions for coalbed methane samples and determined the U and Th contents for rock samples from the eastern margin of the Ordos basin. Based on these results, we calculated the helium generation potential of helium source rocks of different stratigraphic ages and lithologies in the same region. The results show that the helium content of 8 wells in the north of Sanjiao area is higher than 0.05%, and the helium content of 4 wells is greater than 0.1%, which meets the industrial helium extraction standard. The U and Th content and the volume of 4He released per gram of rock per year in different geological ages showed that the Carboniferous > Proterozoic > Permian > Archean > Ordovician > Cambrian, and the volume of 4He generated by radioactive decay per cubic meter of rock: Proterozoic > Archean > Carboniferous > Permian > Ordovician > Cambrian. In terms of different lithologies, the contents of U and Th and the volume of 4He released per gram of rock per year showed bauxite rock > coal > mudstone > basement rock> sandstone > carbonate rock, and the volume of 4He produced by the radioactive decay of each cubic meter of rock is: basement rock> bauxite rock > mudstone > coal > sandstone > carbonate rock. In summary, although the Carboniferous and bauxite rocks have high contents of U and Th and helium generation rates, the Archean-Proterozoic basement has the characteristics of ancient rock age and large development scale, and a large amount of 4He will accumulate during the radioactive decay of rocks. This fully indicates that the stratigraphic age, scale, and distribution, etc., play a key role in the helium generation process and will have a profound impact on the distribution pattern of regional helium resources, providing an important basis for in-depth exploration of the helium reservoir formation mechanism and subsequent resource exploration and development.