Investigation of natural hydrogen and helium in the Bohai Bay Basin, China: insights from Earth's spheres interactions

Non-alkane gases such as H2, He, CO2, and H2S were often found in natural gas exploration in the lithospheric surface layer. Among them, H2 and He are widely distributed in deep and shallow geologic systems of the earth as green energy and scarce strategic resources, respectively. Undoubtedly, their resources are huge, and their exploration and development are getting more and more attention recently. However, natural H2 and He resources in the Earth's tectonically active regions are rarely mentioned. Considering the origin of H2 and He, the study of H2 and He resources in geological systems needs to explore the formation and distribution regularities from the perspective of the Earth's inner-spheres interactions, and to select favorable exploration areas. The Bohai Bay Basin is located at the subduction front of the Western Pacific Plate, with frequent interactions between the Earth's inner spheres, and shows H2 and He resources. It was found that the He-rich reservoirs in the Bohai Bay Basin are of crust-mantle complex genesis and have a sizeable contribution of mantle-sourced He (maximum 82.06%). The release of He from the deep mantle source into the shallow basin accumulation resulted in the highest He content (30,800 ppm) in the Huagou area. Natural H2 from the Bohai Bay Basin has a complex genesis and may be mainly produced by the serpentinization of mafic-ultramafic rocks from within the crust. Hydrogen isotope thermometer demonstrates that the temperature range of H2 formation is wide, ranging from 10 to 165°C, encompassing H2 from all over the world with a variety of genesis. Boxing Sag in the Bohai Bay Basin is a potential resource distribution area for H2 and He (especially 3He) due to the high frequency of deep magmatic volcanism, the development of deep faults, and superior preservation conditions. This work is important for the investigation of natural H2 and He resources in the tectonically active regions of the Earth, where there is frequent material-energy communication between the deep and the shallow.