Methane leaking at depth from hydrocarbon wells poses an environmental and safety hazard. However, determining the occurrence and magnitude of gas migration at ground surface is challenging, as part of the leaking gas is retained during upward migration. We investigated migration through unconsolidated sedimentary aquifers using a two-phase, two-component (water and methane) flow and transport model constructed in DuMu^x. A sensitivity analysis for migration through a 60 m thick sandy aquifer showed that retention by dissolution can be significant even with low groundwater Darcy velocities of 1 m.yr⁻¹. Retention was negligible in the absence of groundwater flow. Besides groundwater velocity, both hydrogeological (permeability, entry pressure, pore-size distribution, and residual gas saturation) and leakage conditions (depth, magnitude and spatial dimensions) determined model outcomes. Additional simulations with interbedded finer grained sediments resulted in substantial lateral spreading of migrating gas. This delayed upward migration and enhanced retention in overlying sandy units where groundwater velocities are highest. Overall, the results of this study show that for unconsolidated aquifer systems and the most commonly observed leakage rates (0.1–10 m³.d⁻¹), significant amounts of migrating methane can be retained due to dissolution into laterally flowing groundwater. Consequently, resulting atmospheric methane emissions above such leaks may be delayed with decades after the onset of leakage, significantly reduced, or prevented entirely.

从碳氢化合物井深度泄漏的甲烷对环境和安全构成危害。然而，确定气体在地下的迁移的发生和程度是具有挑战性的，因为泄漏的气体的一部分在向上迁移期间被保留。我们使用在DuMu ^x中构建的两相，两成分（水和甲烷）流动和传输模型研究了通过非固结沉积含水层的迁移。对通过60 m厚砂质含水层的迁移的敏感性分析表明，即使在1 m.yr ^-1的地下水达西速度较低的情况下，通过溶出作用所保持的时间仍然很重要。。在没有地下水流的情况下，保留率可以忽略不计。除地下水速度外，水文地质条件（渗透率，入口压力，孔径分布和残余气体饱和度）和泄漏条件（深度，大小和空间尺寸）都决定了模型的结果。使用相互交错的细颗粒沉积物进行的其他模拟导致了迁移气体的大量横向扩散。这延迟了向上迁移，并增强了地下水流速最高的上砂质单元的滞留性。总的来说，这项研究的结果表明，对于非固结的含水层系统和最常见的渗漏率（0.1–10 m ³ .d ^-1），由于溶解到侧向流动的地下水中，可以保留大量的甲烷迁移。因此，在此类泄漏发生之后，所产生的大气甲烷排放量可能会在泄漏发生后的几十年后被延迟，明显减少或完全避免。