Numerical simulations explore for the first time the role of mega columns and aperture variability on particle transport through mature volumetric contraction networks as informed by a unique synthesis of network propagation and maturity. Columnar fracture patterns are generated by updating a series of Voronoi centers to the midpoint of a generated polygon over many iterations, creating 250 network realizations. A DFN simulator solves for fluid flow and tracks conservative particle trajectories within each network. Dominant fracture attributes impacting fluid flow and solute transport in volumetric contraction networks are fracture orientation, density, and aperture/transmissivity. Ensemble plume snapshots generated by networks with equal fracture transmissivity define a baseline-level of dispersion that is solely attributed to network structure and connectivity. Longitudinal and transverse dispersion increase and the center of plume mass becomes delayed relative to the baseline case when fracture transmissivity is varied according to a lognormal distribution. The incorporation of highly-transmissive, large-aperture mega column fractures leads to plume snapshots with a more pronounced leading edge and an order of magnitude faster average breakthrough times. The breakthrough curves contain three peaks reflecting contrasting transport pathways in which particles are: (i) initially placed in mega column fractures and remain in these features until exiting the model domain, (ii) initially placed into small column fractures, incur additional time to migrate and enter a mega column fracture, and remain within those mega columns, and (iii) initially placed in small column fractures and remain in these fractures. Incorporating variability in fracture transmissivity for both small column and mega column fractures disrupts the binary distinction between small column and mega column fracture velocities and leads to dispersed breakthroughs over long time scales with a single peak. These results demonstrate that preferential flow paths emerge in volumetric contraction networks due to contracts in fracture transmissivity, not fracture connectivity as observed in tectonic networks.

中文翻译：

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具有巨型柱结构和孔径变化的柱状体积收缩网络的溶质输运特性


数值模拟首次探索了巨型柱和孔径变化对通过成熟体积收缩网络的颗粒传输的作用，这是通过网络传播和成熟度的独特综合得出的。通过多次迭代将一系列 Voronoi 中心更新到生成的多边形的中点来生成柱状断裂模式，从而创建 250 个网络实现。 DFN 模拟器求解流体流动并跟踪每个网络内的保守粒子轨迹。影响体积收缩网络中流体流动和溶质传输的主要裂缝属性是裂缝方向、密度和孔径/透射率。由具有相等断裂透射率的网络生成的系综羽流快照定义了仅归因于网络结构和连接性的基线色散水平。当裂缝透射率根据对数正态分布变化时，纵向和横向色散增加，并且羽流质量中心相对于基线情况延迟。高透射性、大孔径巨型柱状裂缝的结合导致羽流快照具有更明显的前缘和更快的平均突破时间一个数量级。突破曲线包含反映对比传输路径的三个峰，其中颗粒：(i) 最初放置在巨型柱状裂缝中，并保留在这些特征中，直到退出模型域，(ii) 最初放置在小型柱状裂缝中，导致额外的迁移时间并进入巨型柱裂缝，并保留在这些巨型柱内，以及(iii)最初放置在小柱裂缝中并保留在这些裂缝中。 将小柱状裂缝和巨型柱状裂缝的裂缝透射率的变化结合起来，破坏了小柱状裂缝和巨型柱状裂缝速度之间的二元区别，并导致在长时间尺度上具有单峰的分散突破。这些结果表明，由于裂缝透射率的收缩，而不是构造网络中观察到的裂缝连通性，体积收缩网络中出现了优先流动路径。