The transport of helium from the crystalline continental basement and overlying Phanerozoic sedimentary formations to the near surface can be controlled by both diffusive and advective processes. The relative role of each is vital to helium resource prediction, and important in quantifying the residence times of fluids relevant to groundwater resources, hydrocarbon systems, geologic repositories for nuclear waste and carbon sequestration. The Williston Basin, North America, is a prominent sedimentary basin, providing an excellent natural laboratory to assess these processes. Here, we report noble gas isotopic and composition data for 28 gas samples from natural gas wells that sample different stratigraphic horizons down to the basement (Cretaceous to the Cambrian). Helium isotope ratios show a resolvable mantle ³He component (up to 4.7%) in most samples. Neon isotopic compositions of the Cambrian samples are consistent with a crystalline basement gas contribution. Both helium and neon isotopic observations provide evidence for the contribution of conservative noble gases from the crystalline basement or deeper into the overlying sedimentary basin. ⁴He groundwater concentrations in the sedimentary formations, calculated from ⁴He/²⁰Ne values in gas samples, are in excess of in situ U+Th ⁴He production in some shallow units and depleted in others, providing further evidence of cross formation gas contributions.

The highest ⁴He groundwater concentrations can be compared with the results obtained from a fully-coupled vertical scale transport model characterising diffusive-dominated transport through a static groundwater column. The model includes the ⁴He flux into the basin from the Precambrian basement and quantifies the apparent basement ⁴He flux to be between 0.8 - 1.6 × ${10}^{-6}$ mol ⁴He/m² yr, comparable to the steady-state flux estimated for the average continental crust (1.47 × ${10}^{-6}$ mol ⁴He/m² yr) (Torgersen, 2010). The lithologies in which ⁴He concentrations are significantly lower than the reference model predictions are consistent with a history of water flooding and produced water disposal in those formations over decades of hydrocarbon production. While an advective component cannot be ruled out, this work demonstrates the importance of both diffusion and the basin architecture development in controlling ⁴He flux into and out of different lithologies. The assumption of negligible ⁴He loss from the top surface of a lithology is often made when determining the ⁴He age of its groundwater. In the Williston Basin, this study shows that deeper lithologies may reach steady state at different stages of basin development, with shallower lithologies sometimes also showing significant ⁴He loss from their top surface. In the Williston Basin, ⁴He diffusive loss from the target lithology must be considered to accurately interpret ⁴He groundwater residence times and accumulation potential.

氦从晶体大陆基底和上覆显生宙沉积地层到近地表的传输可以通过扩散和平流过程控制。每一种的相对作用对于氦资源预测至关重要，并且对于量化与地下水资源、碳氢化合物系统、核废料地质储存库和碳封存相关的流体的停留时间也很重要。北美的威利斯顿盆地是一个著名的沉积盆地，为评估这些过程提供了一个极好的天然实验室。在这里，我们报告了来自天然气井的 28 个天然气样品的惰性气体同位素和成分数据，这些天然气井对地下（白垩纪至寒武纪）的不同地层层进行了采样。氦同位素比率显示可分辨的地幔³大多数样品中的 He 成分（高达 4.7%）。寒武纪样品的氖同位素组成与结晶基底气体的贡献一致。氦和氖同位素观测都为来自结晶基底或更深处上覆沉积盆地的保守惰性气体的贡献提供了证据。沉积地层中的⁴ He 地下水浓度，根据气体样品中的⁴ He/ ²⁰ Ne 值计算，在一些浅层单元中超过了原位U+Th ⁴ He 产量，而在其他单元中则枯竭，提供了跨地层气体贡献的进一步证据.

最高的⁴ He 地下水浓度可以与从完全耦合的垂直尺度传输模型获得的结果进行比较，该模型表征通过静态地下水柱的以扩散为主的传输。该模型包括从前寒武纪基底进入盆地的⁴ He 通量，并将表观基底⁴ He 通量量化为0.8 - 1.6 × ${10}^{-6}$mol ⁴ He/m ² yr，与估计的平均大陆地壳的稳态通量相当（1.47 × ${10}^{-6}$mol ⁴ He/m ² yr)（托格森，2010 年）。⁴ He 浓度显着低于参考模型预测的岩性与数十年油气生产中这些地层的注水和采出水处理历史一致。虽然不能排除平流成分，但这项工作证明了扩散和盆地结构发展在控制⁴ He 流入和流出不同岩性方面的重要性。可忽略不计的假设^4个从岩性的顶表面他损失确定时通常由⁴他的地下水年龄。在威利斯顿盆地，这项研究表明，在盆地发育的不同阶段，较深的岩性可能会达到稳定状态，较浅的岩性有时也会从其顶面显示出显着的⁴ He 损失。在威利斯顿盆地，必须考虑来自目标岩性的⁴ He 扩散损失，以准确解释⁴ He 地下水停留时间和聚集潜力。