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Magnetic Resonance in Fractured Granite Aquifer - Surface and Borehole Measurements in the Strengbach Catchment, France
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, 79th EAGE Conference and Exhibition 2017, Jun 2017, Volume 2017, p.1 - 5
Abstract
We performed Magnetic Resonance Sounding (MRS) and Nuclear Magnetic Resonance Logging (NML) methods at the Strengbach watershed, an environmental observatory in the Vosges (France), and we present here some preliminary results obtained in late April 2016. To our knowledge, very few NMR measurement in hard rock aquifers have been reported in the literature, and none combining surface and borehole NMR measurements to date.
Objectives of this survey were to estimate the water content in the weathering zone <20 m, and deeper in the fractured granite. After the feasibility of NML measurement in such low porosity ground was assessed, despite the EM noise level (anthropogenic noise mainly), we compare the obtained NML results with MRS inversion models, previous borehole logs and literature values.
NML was applied in 2 boreholes, down to 45 and 113 m depth. A high number of stacks appeared to be necessary due to the low signal and medium noise level, resulting in a measuring duration of 40 minutes for each depth. In comparison, a MRS sounding lasts around 10h with a maximum investigation around 60m. Finally, NML confirmed the conceptual model derived from MRS inversion results, which lack spatial resolution and accuracy at depth >40 m.