ABSTRACT Electrical resistivity tomography is a technique widely used for the investigation of the structure and fluid dynamics of the shallow subsurface, particularly for hydro‐geophysical purposes, sometimes using cross‐borehole configurations. The results of electrical resistivity tomography inversion and their usefulness in solving hydrogeophysical problems, even though invariably limited by resolution issues, depend strongly on the accuracy of inversion, which in turn depends on a proper estimation and handling of data and model errors. Among model errors, one approximation often applied in cross‐hole electrical resistivity tomography is that of neglecting the effects of boreholes and the fluids therein. Such effects inevitably impact the current and potential patterns as measured by electrodes in the boreholes themselves. In the presence of very saline fluids, in particular, this model approximation may prove inadequate and the tomographic inversion may yield images strongly contaminated by artefacts. In this paper, we present a case study where highly saline water was used for hydraulic fracturing to improve permeability of a shallow formation impacted by hydrocarbon contamination, with the final aim of improving the effectiveness of in situ contaminant oxidation. The hydraulic fracturing was monitored via time‐lapse cross‐hole electrical resistivity tomography. Arrival of the saline water in the monitoring borehole likely caused a strong borehole effect that significantly affected the quality and usefulness of electrical resistivity tomography inversions. In this paper, we analyse the experimental dataset and produce, via three‐dimensional electrical resistivity tomography forward modelling, a viable explanation for the observed, paradoxical field results.

中文翻译：

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钻孔效应导致交叉钻孔电阻率层析成像中的伪影：水力压裂案例研究

摘要 电阻率层析成像是一种广泛用于研究浅层地下结构和流体动力学的技术，特别是用于水文地球物理目的，有时使用交叉钻孔配置。电阻率层析成像反演的结果及其在解决水文地球物理问题中的有用性，尽管总是受到分辨率问题的限制，但在很大程度上取决于反演的准确性，而反演的准确性又取决于对数据和模型错误的正确估计和处理。在模型误差中，常用于跨孔电阻率层析成像的一种近似方法是忽略钻孔和其中流体的影响。这种效应不可避免地会影响由钻孔本身中的电极测量的电流和电位模式。特别是在非常咸的流体存在的情况下，这种模型近似可能证明是不够的，并且断层摄影反演可能会产生被人工制品严重污染的图像。在本文中，我们提出了一个案例研究，其中使用高盐水进行水力压裂以提高受碳氢化合物污染影响的浅层地层的渗透率，最终目的是提高原位污染物氧化的有效性。通过延时跨孔电阻率层析成像监测水力压裂。监测钻孔中盐水的到达可能会引起强烈的钻孔效应，从而显着影响电阻率层析成像反演的质量和有效性。在本文中，我们分析实验数据集并产生，