We characterized horizontal hydraulic conductivity (K) of a fractured granitic aquifer using single- and cross-hole hydraulic tests to evaluate “scale effect.” For selected boreholes, K estimates were obtained using single-hole FLUTe liner and slug tests. Several cross-hole pumping tests were carried out at various durations. Drawdown responses were first interpreted using analytical well-test solutions to obtain an effective horizontal conductivity (K_eff) assuming a homogeneous and infinite aquifer. The same drawdowns were then numerically inverted using transient hydraulic tomography (THT) to delineate spatial distributions of K and storativity in the area encompassing the boreholes. Papadopulos (1965) and a nonlinear least squares minimization method produced a similar principal K_eff direction that is consistent with the dominant fracture strike observed from outcrop and borehole televiewer data. However, principal direction and magnitude of this K_eff depend on the pumping test duration and the number of monitoring boreholes used in the interpretation. As a group, K obtained from cross-hole tests is larger than that obtained from single-hole tests. However, because cross-hole tests stressed the aquifer at both interwell and larger scales, K_eff obtained from interpreting cross-hole data is observed to decrease with pumping time, likely due to the dominance of less permeable fractures at larger scale. This lateral reduction of mean K is also revealed by THT as low K zones surrounding the test boreholes. Overall, K is found to increase from single-hole to the interwell scale and then decrease at larger scale, exhibiting a non-monotonic scale effect.

中文翻译：

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破裂花岗岩含水层中的多尺度水力传导率表征：尺度效应评估

我们使用单孔和跨孔水力测试来表征破裂的花岗岩含水层的水平水力传导率 ( K )，以评估“规模效应”。对于选定的钻孔，使用单孔 FLUTe 衬管和段塞试验获得K估计值。在不同的持续时间进行了几次跨孔泵送测试。水位下降响应首先使用分析试井解决方案进行解释，以获得有效水平电导率 ( K _eff )，假设含水层为均质无限。然后使用瞬态水力断层扫描 (THT) 对相同的压降进行数值反演，以描绘K 的空间分布和井筒周围区域的蓄水能力。Papadopulos (1965) 和非线性最小二乘法最小化方法产生了类似的主要K _eff方向，该方向与从露头和钻孔电视数据观察到的主要裂缝走向一致。然而，这个K _{eff 的}主要方向和大小取决于抽水测试持续时间和解释中使用的监测钻孔的数量。作为一个整体，从跨孔测试获得的K大于从单孔测试获得的K。然而，由于跨孔测试在井间和更大尺度上对含水层施加压力，K _eff观察到从解释跨孔数据中获得的裂缝随着泵送时间而减少，这可能是由于在更大范围内渗透性较低的裂缝占主导地位。平均K 的这种横向减少也被 THT 揭示为测试钻孔周围的低K区。总体而言，发现K从单孔到井间尺度增加，然后在更大的尺度上减小，表现出非单调的尺度效应。