Conradi Mark S, Altobelli Stephen A, Sowko Nicholas J, Conradi Susan H, Fukushima Eiichi
ABQMR, Inc., 2301 Yale Blvd. SE, Suite C2, Albuquerque, NM 87106, USA; Washington University, Dept. of Physics, 1105, One Brookings Drive, Saint Louis, MO 63130, USA.
ABQMR, Inc., 2301 Yale Blvd. SE, Suite C2, Albuquerque, NM 87106, USA.
J Magn Reson. 2018 Mar;288:95-99. doi: 10.1016/j.jmr.2018.02.004. Epub 2018 Feb 7.
Earth's field NMR has been developed to detect oil trapped under or in Arctic sea-ice. A large challenge, addressed here, is the suppression of the water signal that dominates the oil signal. Selective suppression of water is based on relaxation time T because of the negligible chemical shifts in the weak earth's magnetic field, making all proton signals overlap spectroscopically. The first approach is inversion-null recovery, modified for use with pre-polarization. The requirements for efficient inversion over a wide range of B and subsequent adiabatic reorientation of the magnetization to align with the static field are stressed. The second method acquires FIDs at two durations of pre-polarization and cancels the water component of the signal after the data are acquired. While less elegant, this technique imposes no stringent requirements. Similar water suppression is found in simulations for the two methods. Oil detection in the presence of water is demonstrated experimentally with both techniques.
地球场核磁共振技术已被开发用于探测被困在北极海冰之下或之中的石油。本文所解决的一个重大挑战是抑制主导石油信号的水信号。由于在弱地磁场中化学位移可忽略不计，使得所有质子信号在光谱上重叠，因此对水的选择性抑制基于弛豫时间T。第一种方法是反演零恢复法，并针对预极化进行了改进。强调了在宽范围的B下进行有效反演以及随后使磁化绝热重新定向以与静磁场对齐的要求。第二种方法在两个预极化持续时间采集自由感应衰减信号，并在采集数据后消除信号中的水成分。虽然这种技术没那么精巧，但它没有严格的要求。两种方法的模拟结果显示出类似的水抑制效果。实验证明，这两种技术都能在有水存在的情况下检测石油。
