The interpretation of a tracer experiment conducted in a single fracture under conditions of natural groundwater flow
The interpretation of a tracer experiment conducted in a single fracture under conditions of natural groundwater flow
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DOI：
10.1029/1999wr900143
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发表时间：
1999-08
影响因子：
5.4
通讯作者：
P. Lapcevic;K. Novakowski;E. Sudicky
中科院分区：
文献类型：
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作者：
P. Lapcevic;K. Novakowski;E. Sudicky
开发描述稀疏裂缝介质水文地质的概念模型需要在现场尺度上表征离散裂缝的特性。在这项研究中，解释了在页岩和石灰岩互层序列的离散裂缝中自然地下水流条件下进行的示踪实验。该实验通过向裂缝面注入少量示踪剂开始，使用 35×40 m 区域内的 27 个钻孔监测示踪剂运动。测试数据显示示踪羽流沿平均地下水流方向纵向和横向传播。使用二维有限元输运模型解释现场突破曲线，该模型结合了纵向和横向色散、向岩石基质的扩散以及恒定的裂缝孔径。通过改变孔径场的空间相关性和方差，以蒙特卡罗格式进行了包含孔径变化影响的附加模拟。恒定孔径分析发现，示踪剂实验确定的平均孔径比水力方法测量的平均孔径大约20%。模拟数据需要基质孔隙度值在 1% 到 3% 之间、恒定的纵向色散率 0.1 m 以及横向色散率的大范围从 0.01 到 0.22 m。观察到孔径和基质孔隙率随距离增加的趋势，表明示踪剂运输遵循越来越曲折的路径。尽管可变孔径模拟不适合现场数据，但具有 0.5 m 各向同性空间相关长度和 10,000 μm2 方差的孔径场提供了与现场羽流的形状和浓度最相似的模拟羽流。孔径分布的水力测量证据表明，这是对自然孔径场的合理估计。
The development of conceptual models to describe the hydrogeology of sparsely fractured media requires the characterization of the properties of discrete fractures at the field scale. In this study, a tracer experiment conducted under conditions of natural groundwater flow in a discrete fracture in an interbedded shale and limestone sequence is interpreted. This experiment, which was initiated by injecting a small quantity of tracer into the fracture plane, involved monitoring tracer movement using 27 boreholes within a 35×40 m area. Test data revealed a tracer plume which spread both longitudinally and transversely in the direction of mean groundwater flow. The field breakthrough curves were interpreted using a two‐dimensional finite element transport model that incorporated longitudinal and transverse dispersion, diffusion into the rock matrix, and constant fracture aperture. Additional simulations which incorporated the effects of aperture variability were conducted in a Monte Carlo format by varying the spatial correlation and variance of the aperture field. The constant aperture analysis found that the mean aperture determined from the tracer experiment was approximately 20% greater than the mean aperture measured by hydraulic methods. Values of matrix porosity ranging between 1 and 3%, a constant longitudinal dispersivity of 0.1 m, and a large range in transverse dispersivity from 0.01 to 0.22 m were required to simulate the data. Trends of increasing aperture and matrix porosity with distance were observed, suggesting that tracer transport followed increasingly tortuous pathways. Although the variable aperture simulations were not fitted to the field data, the aperture field having an isotropic spatial correlation length of 0.5 m and variance of 10,000 μm2 provided simulated plumes that appeared to be most similar to the shape and concentration of the field plume. Evidence from the hydraulic measurement of the aperture distribution suggests that this is a reasonable estimate of the natural aperture field.