Background The Ordos Basin enjoys abundant natural gas resources, which generally bear helium, making this basin hold great helium resource potential. In this case, detailed exploration is essential for the future transition from natural gas-helium joint exploration to special helium exploration in the basin.

Objective and Method  To systematically investigate the distribution and potential of helium resources in the Ordos Basin, natural gas samples were taken from different areas of the basin for analysis and tests. To examine the primary factors controlling helium accumulation and enrichment, this study conducted a systematic analysis of the basement, sedimentary rock layers, fault systems, and tectonic evolutionary process of the basin.

Results and conclusions Two helium enrichment patterns are identified in the basin and can be further subdivided into three types. Specifically, two helium enrichment patterns are determined according to their carrier types: alkane and geothermal water as carriers. The alkane-carried gas can be further subdivided into two types based on the distance between gas reservoirs and the basement. The first type is represented by the Dongsheng gas field, characterized by the direct contact between gas reservoirs and the basement (vertical distance: less than 50 m) and an average helium volume fraction of 0.118%. The second type is exemplified by the Qingyang gas field, characterized by the near-distance contact between gas reservoirs and the basement (vertical distance: less than 1 500 m) and an average helium volume fraction of 0.105%. The geothermal water-carried gas refers to helium-rich water-soluble gas migrating via deep-seated faults. Such gas is represented by the Weihe graben, characterized by vertical distances of 1 500‒5 000 m from water-soluble gas above geothermal water to the basement and an average helium volume fraction of 2.5%. By analyzing the geological characteristics and helium enrichment factors of helium-rich areas, this study determined the primary factors controlling helium enrichment. Specifically, ancient U- and Th-rich granites in the shallowly buried basement are identified as important helium source rocks while also providing a material basis for helium enrichment. The deep-seated faults play a key role in connecting helium to shallow reservoirs. For instance, the basal strike-slip fault zone within the Qinyang gas field produces controlling effects on the Qingyang and Zhengning gas fields, also serving as a play fairway for helium enrichment. In the Qingyang gas field, areas with large-scale faults in the gas layers of the Taiyuan Formation exhibit high helium volume fractions (average: 0.105%). The formation of large-scale helium is inseparable from natural gas and water, with helium always emerging as an associated product. Therefore, effective reservoir-cap rock assemblages favor helium enrichment. Based on research on the magnetic anomalies and the distribution characteristics of deep-seated faults in the Ordos Basin, this study identified two optimal helium enrichment areas: shallow-buried areas of basal granites and areas with deep-seated faults. In combination with the current reservoir-cap rock configurations of gas fields, it determined nine play fairways with a total area of 40 000 km² in the basin: the Hetao Basin, the Yimeng paleocontinent, the northern Tianhuan sag, the Dingbian fault zone, the Zhidan-Jiaxian fault zone with a strong magnetic field, the Zijinshan volcanic rock invasion zone, the Qingyang paleo-uplift, the Yichuan-Huanglong fault zone, and the Weihe graben.