Department of Geophysics, Stanford University, 397 Panama Mall, Stanford, CA, 94305, USA.
U.S. Geological Survey, 11 Sherman Place, Unit 5015, Storrs, CT, 06269, USA.
Ground Water. 2021 Jan;59(1):31-48. doi: 10.1111/gwat.13014. Epub 2020 Jun 1.
Glacial aquifers are an important source of groundwater in the United States and require accurate characterization to make informed management decisions. One parameter that is crucial for understanding the movement of groundwater is hydraulic conductivity, K. Nuclear magnetic resonance (NMR) logging measures the NMR response associated with the water in geological materials. By utilizing an external magnetic field to manipulate the nuclear spins associated with H, the time-varying decay of the nuclear magnetization is measured. This logging method could provide an effective way to estimate K at submeter vertical resolution, but the models that relate NMR measurements to K require calibration. At two field sites in a glacial aquifer in central Wisconsin, we collected a total of four NMR logs and obtained measurements of K in their immediate vicinity with a direct-push permeameter (DPP). Using a bootstrap algorithm to calibrate the Schlumberger-Doll Research (SDR) NMR-K model, we estimated K to within a factor of 5 of the DPP measurements. The lowest levels of accuracy occurred in the lower-K (K < 10 m/s) intervals. We also evaluated the applicability of prior SDR model calibrations. We found the NMR calibration parameters varied with K, suggesting the SDR model does not incorporate all the properties of the pore space that control K. Thus, the expected range of K in an aquifer may need to be considered during calibration of NMR-K models. This study is the first step toward establishing NMR logging as an effective method for estimating K in glacial aquifers.
冰川含水层是美国地下水的重要来源，需要准确描述以做出明智的管理决策。了解地下水运动的一个关键参数是水力传导率 K。核磁共振 (NMR) 测井测量与地质材料中水分相关的 NMR 响应。通过利用外部磁场来操纵与 H 相关的核自旋，测量核磁化强度随时间的变化衰减。这种测井方法可以提供一种以亚米垂直分辨率估计 K 的有效方法，但将 NMR 测量值与 K 相关联的模型需要校准。在威斯康星州中部一个冰川含水层的两个野外站点，我们总共采集了 4 个 NMR 测井，并使用直接推压渗透率计 (DPP) 在其附近获得了 K 的测量值。我们使用自举算法校准 Schlumberger-Doll Research (SDR) NMR-K 模型，将 K 估计值与 DPP 测量值的误差控制在 5 倍以内。在 K 值较低（K < 10 m/s）的区间，精度最低。我们还评估了先前 SDR 模型校准的适用性。我们发现 NMR 校准参数随 K 而变化，这表明 SDR 模型并未包含控制 K 的孔隙空间的所有特性。因此，在对 NMR-K 模型进行校准时，可能需要考虑含水层中 K 的预期范围。本研究是将 NMR 测井确立为估计冰川含水层中 K 的有效方法的第一步。
