ABSTRACT Downhole nuclear magnetic resonance technology was applied in four boreholes intersecting glaciomarine sediments of the Ottawa Valley, Ontario. The study evaluated the ability of slim‐hole nuclear magnetic resonance tools to measure in situ volumetric water contents (porosities in saturated sediments) for geohazard and hydrogeological applications. The sediments are composed of clay‐ and silt‐sized grains of glacially eroded rock flour derived from the Precambrian Shield containing trace amounts of magnetic minerals, and porosities ranging from 40 to 74 porosity units (PU, 1% porosity = 1 PU). Two nuclear magnetic resonance instruments were deployed with echo times of 0.5 and 1.0 ms, and diameters of investigation ranging from 14.0 to 30.5 cm. Quantitative nuclear magnetic resonance porosities in the sediments were typically within ±5 PU (95% within ±10 PU) of core calibration data sets in the silty clays where threshold bulk magnetic susceptibility values were <30 × 10−4 SI. This was found to deviate, however, where the concentration and mineralogy of magnetic particles changed, interpreted to be shortening relaxation times which led to underestimation of true water contents. This effect is correlated with a change in depth from magnetite to superparamagnetic nanoparticles of greigite (low‐temperature iron monosulphide) magnetism, interpreted to occur at the sulphate‐methane interface. Clay mineralogy and pore water chemistry were also examined as contributing factors, but were not found to significantly shorten nuclear magnetic resonance relaxation responses. Very short T2 times (<2 ms) are typical in these particular silty clays, requiring a tool with an echo spacing of <1.0 ms. Due to increased potential for sediment disturbance around a well caused by the geotechnical sensitivity of the sediments, a nuclear magnetic resonance instrument with multiple frequencies provided signal penetration out to various diameters around the tool, giving needed information about the size of the disturbed zone surrounding the casing.

中文翻译：

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加拿大安大略省渥太华附近冰川沉积物中的井下核磁共振测井

摘要 井下核磁共振技术被应用于与安大略省渥太华谷冰川沉积物相交的四个钻孔。该研究评估了小孔核磁共振工具在地质灾害和水文地质应用中测量原位体积含水量（饱和沉积物中的孔隙率）的能力。沉积物由粘土和粉砂大小的冰川侵蚀岩粉颗粒组成，这些颗粒来自前寒武纪地盾，含有微量磁性矿物，孔隙度范围为 40 到 74 个孔隙度单位（PU，1% 孔隙度 = 1 PU）。部署了两台核磁共振仪器，回波时间分别为 0.5 和 1.0 毫秒，调查直径范围为 14.0 至 30.5 厘米。沉积物中的定量核磁共振孔隙度通常在粉质粘土岩心校准数据集的 ±5 PU（±10 PU 内的 95%）内，其中阈值体积磁化率值 <30 × 10-4 SI。然而，在磁性粒子的浓度和矿物学发生变化的情况下，发现这会发生偏差，解释为缩短了弛豫时间，从而导致对真实水含量的低估。这种效应与从磁铁矿到超顺磁性纳米颗粒（低温单硫化铁）磁性的深度变化相关，解释为发生在硫酸盐-甲烷界面。粘土矿物学和孔隙水化学也被视为影响因素，但未发现显着缩短核磁共振弛豫响应。非常短的 T2 时间 (<2 ms) 在这些特定粉质粘土中是典型的，需要回波间隔 <1.0 ms 的工具。由于沉积物的岩土工程敏感性导致井周围沉积物扰动的可能性增加，具有多个频率的核磁共振仪器将信号穿透到工具周围的不同直径，提供有关井周围扰动区大小的所需信息套管。