Fundamental understanding of solute transport behaviors in rock fractures is of great importance to many hydrogeological processes. The fate of fluid-borne solutes is inherently linked to fluid flow process in rock fractures, which is usually theoretically and numerically analyzed under the assumption of classic no-slip boundary condition. However, fluid slippage at rock surfaces is possibly present in some geological environments, such as hydrophilicity change in rock surfaces exposed to organic substances, or the immobile wetting film covering rock surfaces. These situations would induce a non-zero velocity at the boundary walls for flowing fluid, i.e., fluid slippage, which leads to a violation of the no-slip assumption. Nonetheless, the effect of slippery boundary on fluid-borne solute transport is poorly understood for rock fractures. This study systematically investigated the slippery boundary effect on solute transport in rough-walled rock fractures under different flow regimes. A series of pore-scale simulation results showed that the slippery boundary has a profound influence on both microscale and macroscale solute transport behaviors in rock fractures. Such an influence became more significant with increasing hydraulic gradient, accompanied by the flow regime transitioning from Darcy to non-Darcian. For Darcy flow regime, the slippery boundary exerted its influence on solute transport by altering velocity distribution pattern in rock fracture; while for non-Darcian flow regime, the enlarged eddy volume and promoted mass transfer process by the slippery boundary profoundly affected solute transport behaviors. Further discussion indicated that the predictive models with parameters estimated from the conventional no-slip boundary condition cannot directly apply to the slip one. Moreover, the effect of slippery boundary would possibly have an impact on larger-scale fractured rock aquifers which requires further verification. The results and findings enrich the understanding of solute transport in fractured rocks where the slippery boundary is prevalently present, and contribute to developing predictive models for complex geological environments.

对岩石裂缝中溶质运移行为的基本了解对于许多水文地质过程至关重要。流体溶质的命运与岩石裂缝中的流体流动过程有着内在的联系，通常在经典的无滑移边界条件的假设下，从理论和数值上进行分析。但是，在某些地质环境中，岩石表面可能会出现流体滑移，例如暴露于有机物质的岩石表面的亲水性发生变化，或覆盖岩石表面的固定式润湿膜。这些情况将在边界壁上引起流动流体的非零速度，即流体滑移，这导致违反无滑假设。但是，对于岩石裂缝，人们对滑动边界对流体溶质运移的影响知之甚少。这项研究系统地研究了在不同流动状态下，滑边界边界对溶质在粗糙壁岩石裂缝中的运移的影响。一系列孔隙尺度模拟结果表明，滑移边界对岩石裂缝中的微观尺度和宏观尺度的溶质运移行为都具有深远的影响。随着水力梯度的增加，伴随着从达西流向非达西流的过渡，这种影响变得更加显着。对于达西（Darcy）流态，滑移边界通过改变岩石裂缝中的速度分布模式而对溶质运移产生影响。而对于非达西流态，湿滑边界扩大的涡流和促进的传质过程深刻地影响了溶质的运移行为。进一步的讨论表明，具有从常规的非滑移边界条件估计的参数的预测模型不能直接应用于滑移模型。此外，光滑边界的影响可能会对较大规模的裂隙岩性含水层产生影响，这需要进一步验证。结果和发现丰富了对普遍存在滑边界的裂隙岩石中溶质运移的理解，并有助于开发复杂地质环境的预测模型。