Mechanisms Controlling the Accumulation of Helium-Rich Coalbed Gas: Insights From the Haishiwan Mining Area, Minhe Basin, Northwest China

Summary Helium (He) is a strategic scarce resource. Despite the identification of numerous helium-bearing coalbed gas resources globally, their enrichment and accumulation mechanisms remain unclear. This study performed geological and geochemical analyses on coalbed gas and rock samples from Haishiwan mining area (HMA), Minhe Basin, China, focusing on helium-rich coalbed gas characteristics and formation mechanisms. Results show that the coalbed gas has low CH4 (avg. 36.54%) and abnormally high N2 (avg. 16.53%) and CO2 (avg. 26.66%), with He content 0.0339–0.2308% (avg. 0.104%)—meeting industrial grade (≥0.1%) and exceeding China’s major helium-bearing coalbed gas fields. 3He/4He (1.83 × 10−8 to 6.25 × 10−8), 40Ar/36Ar (506.7–1,107.1), and R/Ra (0.013–0.045) confirm crustal He origin. He is mainly sourced from basin basement metamorphic/ancient magmatic rocks, secondarily from Jurassic oil shales. Carrier gas (CO2+N2+CH4) significantly affects He content: crust-derived organic N2 shows weak positive correlation with He, while inorganic CO2 influx dilutes He. Tectonics and faults provide migration kinetic energy and channels; high formation temperature accelerates He release. Oil shales of layers A# and B# overlying the coal seams act as high-quality cap rocks, facilitating the preservation of coalbed gas and He. A high-helium coalbed gas accumulation model is proposed: high-geothermal ancient strata supply → deep fault transport → coal seam storage → overlying oil shale sealing.