Fault zones in the Upper Jurassic aquifer of the North Alpine Foreland Basin are generally regions with possibly increased hydraulic properties. They are consequently often part of the geothermal exploration concepts in this area and a primary target for the drilling operation. Data from this aquifer, gathered in pump tests, however, show that only four out of 41 successful wells exhibit hydraulic proof for the presence of such a fault zone in terms of a bi-/linear flow regime. Besides technical effects, also the contrast in hydraulic properties itself, between fault zone and surrounding host rock, can prevent the detection of a fault zone in pump test data. This means a certain threshold has to be surpassed until its effects become clearly visible. A simplified realistic numerical model was constructed and calibrated with pressure data from an exploration site in the south of Munich. This model was then used to observe the presence of linear and bilinear flows in dependence on the Malm aquifers parameter space. Sampling the possible hydraulic property combinations with the help of an HPC (high-performance computing) cluster and automating the detection of the corresponding main flow type allowed to quantify the areas in parameter space where the fault zone-related flow regimes of interest are present. Through the investigation of more than 30,000 combinations between fault zone permeability, matrix permeability, fault zone storage, matrix storage and fault zone thickness, it was found that, in the parameter space of the Malm aquifer, a bilinear flow can be observed for the first time only if the matrix permeability is lower than 2.0 × 10−13 m2, and a linear flow for matrix permeability values below 6.0 × 10−14 m2. Additionally, it was shown that fault zones, which have better hydraulic properties than the surrounding matrix, can indeed be hidden in pumping tests due to the parameter setting.

中文翻译：

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地热井抽水试验中断层带的水力行为：北高山前陆盆地上侏罗统含水层的数值模拟参数分析

北高山前陆盆地上侏罗统含水层的断层带通常是水力特性可能增加的区域。因此，它们通常是该地区地热勘探概念的一部分，并且是钻井作业的主要目标。但是，在泵测试中收集到的来自该含水层的数据表明，在双向/线性流态方面，在41口成功的井中，只有四口井显示出存在此类断层带的水力证明。除了技术效果外，断层带与周围岩体之间的水力特性本身的差异还可以防止在泵测试数据中检测到断层带。这意味着必须超过某个阈值，直到其效果变得清晰可见。构建了一个简化的现实数值模型，并使用慕尼黑南部某勘探地点的压力数据进行了校准。然后使用该模型来观察依赖于Malm含水层参数空间的线性和双线性流的存在。借助HPC（高性能计算）群集对可能的水力特性组合进行采样，并自动检测相应的主流类型，从而可以量化参数空间中存在感兴趣的断层相关流态的区域。通过对断层带渗透率，基质渗透率，断层带存储，基质存储和断层带厚度之间的30,000多种组合的研究，发现在Malm含水层的参数空间中，仅当基质渗透率低于2.0×10-13 m2时才首次观察到双线性流，而当基质渗透率值低于6.0×10-14 m2时才观察到线性流。此外，结果表明，由于参数设置的缘故，在水力测试中确实可以隐藏水力特性优于周围基质的断层带。