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首页> 外文OA文献 >3-D characterization of high-permeability zones in a gravel aquifer using 2-D crosshole GPR full-waveform inversion and waveguide detection
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3-D characterization of high-permeability zones in a gravel aquifer using 2-D crosshole GPR full-waveform inversion and waveguide detection

机译：使用2-D井孔GPR全波形反演和波导检测对砾石含水层中高渗透性区域进行3-D表征

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Reliable high-resolution 3-D characterization of aquifers helps to improve our understanding of flow and transport processes when small-scale structures have a strong influence. Crosshole ground penetrating radar (GPR) is a powerful tool for characterizing aquifers due to the method's high-resolution and sensitivity to porosity and soil water content. Recently, a novel GPR full-waveform inversion algorithm was introduced, which is here applied and used for 3-D characterization by inverting six crosshole GPR cross-sections collected between four wells arranged in a square configuration close to the Thur River in Switzerland. The inversion results in the saturated part of this gravel aquifer reveals a significant improvement in resolution for the dielectric permittivity and electrical conductivity images compared to ray-based methods. Consistent structures where acquisition planes intersect indicate the robustness of the inversion process. A decimetre-scale layer with high dielectric permittivity was revealed at a depth of 5-6 m in all six cross-sections analysed here, and a less prominent zone with high dielectric permittivity was found at a depth of 7.5-9 m. These high-permittivity layers act as low-velocity waveguides and they are interpreted as high-porosity layers and possible zones of preferential flow. Porosity estimates from the permittivity models agree well with estimates from Neutron-Neutron logging data at the intersecting diagonal planes. Moreover, estimates of hydraulic permeability based on flowmeter logs confirm the presence of zones of preferential flow in these depth intervals. A detailed analysis of the measured data for transmitters located within the waveguides, revealed increased trace energy due to late-arrival elongated wave trains, which were observed for receiver positions straddling this zone. For the same receiver positions within the waveguide, a distinct minimum in the trace energy was visible when the transmitter was located outside the waveguide. A novel amplitude analysis was proposed to explore these maxima and minima of the trace energy. Laterally continuous low-velocity waveguides and their boundaries were identified in the measured data alone. In contrast to the full-waveform inversion, this method follows a simple workflow and needs no detailed and time consuming processing or inversion of the data. Comparison with the full-waveform inversion results confirmed the presence of the waveguides illustrating that full-waveform inversion return reliable results at the highest resolution currently possible at these scales. We envision that full-waveform inversion of GPR data will play an important role in a wide range of geological, hydrological, glacial and periglacial studies in the critical zone
机译：在小规模结构产生重大影响时，可靠的高分辨率3D含水层表征有助于增进我们对流动和输运过程的了解。井孔探地雷达（GPR）由于具有高分辨率和对孔隙度和土壤水分的敏感性，因此是表征含水层的有力工具。最近，引入了一种新颖的GPR全波形反演算法，该算法在此应用并通过反转在瑞士图尔河附近以正方形配置布置的四个井之间收集的六个交叉孔GPR横截面来进行3-D表征。与基于射线的方法相比，该砾石含水层饱和部分的反演结果揭示了介电常数和电导率图像分辨率的显着提高。采集平面相交的一致结构表明了反演过程的鲁棒性。在这里分析的所有六个横截面中，在5-6 m的深度处发现了一个具有高介电常数的十米尺度的层，在7.5-9 m的深度处发现了一个不太明显的具有高介电常数的区域。这些高介电常数层充当低速波导，并且被解释为高孔隙率层和优先流动的可能区域。介电常数模型的孔隙率估计值与相交对角线平面的中子-中子测井数据的估计值非常吻合。此外，基于流量计测井的水力渗透率估计值证实了在这些深度区间中存在优先流动区域。对位于波导内的发射器的测量数据的详细分析显示，由于迟到的细长波列导致了跟踪能量的增加，对于跨越该区域的接收器位置而言，观察到了这种现象。对于波导内相同的接收器位置，当发射器位于波导外部时，可以看到迹线能量的明显最小值。提出了一种新颖的幅度分析来探索痕量能量的这些最大值和最小值。仅在测量数据中即可确定横向连续的低速波导及其边界。与全波形反演相比，此方法遵循简单的工作流程，不需要详细且费时的数据处理或反演。与全波形反演结果的比较证实了波导的存在，说明了在这些规模下，目前可能以最高分辨率获得全波形反演的可靠结果。我们设想，GPR数据的全波形反演将在关键地区的广泛地质，水文，冰川和冰缘研究中发挥重要作用

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