Sanford William E, Cook Peter G, Robinson Neville I, Weatherill Douglas
Department of Geosciences, Colorado State University, Fort Collins, 80523-1482, USA.
Ground Water. 2006 Jul-Aug;44(4):564-73. doi: 10.1111/j.1745-6584.2006.00161.x.
Forced-gradient tracer tests in fractured aquifers often report low mass recoveries. In fractured aquifers, fractures intersected by one borehole may not be intersected by another. As a result (1) injected tracer can follow pathways away from the withdrawal well causing low mass recovery and (2) recovered water can follow pathways not connected to the injection well causing significant tracer dilution. These two effects occur along with other forms of apparent mass loss. If the strength of the connection between wells and the amount of dilution can be predicted ahead of time, tracer tests can be designed to optimize mass recovery and dilution. A technique is developed to use hydraulic tests in fractured aquifers to calculate the conductance (strength of connection) between well pairs and to predict mass recovery and amount of dilution during forced gradient tracer tests. Flow is considered to take place through conduits, which connect the wells to each other and to distant sources or sinks. Mass recovery is related to the proportion of flow leaving the injection well and arriving at the withdrawal well, and dilution is related to the proportion of the flow from the withdrawal well that is derived from the injection well. The technique can be used to choose well pairs for tracer tests, what injection and withdrawal rates to use, and which direction to establish the hydraulic gradient to maximize mass recovery and/or minimize dilution. The method is applied to several tracer tests in fractured aquifers in the Clare Valley, South Australia.
在裂隙含水层中进行的强制梯度示踪剂试验常常显示出较低的质量回收率。在裂隙含水层中，一个钻孔相交的裂隙可能不会被另一个钻孔相交。因此，（1）注入的示踪剂可能会沿着远离抽水井的路径流动，导致质量回收率较低；（2）回采水可能会沿着与注入井不相连的路径流动，导致示踪剂显著稀释。这两种效应与其他形式的表观质量损失同时发生。如果能提前预测井之间连接的强度和稀释量，就可以设计示踪剂试验来优化质量回收率和稀释情况。开发了一种技术，利用裂隙含水层中的水力试验来计算井对之间的传导率（连接强度），并预测强制梯度示踪剂试验期间的质量回收率和稀释量。水流被认为是通过将井彼此连接以及与远处的源或汇相连的管道发生的。质量回收率与离开注入井并到达抽水井的水流比例有关，稀释与来自抽水井且源自注入井的水流比例有关。该技术可用于选择示踪剂试验的井对、使用的注入和回采速率，以及确定水力梯度的方向，以最大限度地提高质量回收率和/或最小化稀释。该方法应用于南澳大利亚克莱尔谷裂隙含水层中的几次示踪剂试验。
