Legchenko Anatoly, Descloitres Marc, Bost Adelphe, Ruiz Laurent, Reddy Mohan, Girard Jean-François, Sekhar Muddu, Mohan Kumar M S, Braun Jean-Jacques
Institut de Recherche pour le Developpement (IRD), Grenoble, France.
Ground Water. 2006 Jul-Aug;44(4):547-54. doi: 10.1111/j.1745-6584.2006.00198.x.
The performance of the Magnetic Resonance Sounding (MRS) method applied to the investigation of heterogeneous hard-rock aquifers was studied. It was shown using both numerical modeling and field measurements that MRS could be applied to the investigation of the weathered part of hard-rock aquifers when the product of the free water content multiplied by the thickness of the aquifer is >0.2 (for example, 10-m-thick layer with a 2% water content). Using a currently available one-dimensional MRS system, the method allows the characterization of two-dimensional subsurface structures with acceptable accuracy when the size of the subsurface anomaly is equal to or greater than the MRS loop. However, the fractured part of hard-rock aquifers characterized by low effective porosity (<0.5%) cannot be resolved using currently available MRS equipment. It was found that shallow water in the weathered part of the aquifer may screen MRS signals from deeper water-saturated layers, thus further reducing the possibility of investigating deeper fractured aquifers. A field study using the NUMIS(plus) MRS system developed by IRIS Instruments was carried out on an experimental watershed in southern India. A heterogeneous unconfined aquifer in a gneissic formation was successfully localized, and MRS results were confirmed by drilling shortly after the geophysical study. The top of the aquifer revealed by MRS was found to be in a good agreement with observed static water level measurements in boreholes.
研究了应用于非均质硬岩含水层调查的磁共振测深（MRS）方法的性能。通过数值模拟和现场测量表明，当自由水含量与含水层厚度的乘积大于0.2时（例如，厚度为10米、含水量为2%的层），MRS可应用于硬岩含水层风化部分的调查。使用目前可用的一维MRS系统，当地下异常的尺寸等于或大于MRS回线时，该方法能够以可接受的精度表征二维地下结构。然而，目前可用的MRS设备无法分辨有效孔隙率低（<0.5%）的硬岩含水层的裂隙部分。研究发现，含水层风化部分的浅层水可能会屏蔽来自更深层饱水层的MRS信号，从而进一步降低调查更深层裂隙含水层的可能性。在印度南部的一个实验流域进行了一项使用IRIS Instruments公司开发的NUMIS(plus) MRS系统的现场研究。成功定位了片麻岩地层中的一个非均质无压含水层，并且在地球物理研究后不久通过钻探证实了MRS结果。发现MRS揭示的含水层顶部与钻孔中观测到的静水位测量结果高度吻合。
