Borehole nuclear magnetic resonance as a promising 3D mapping tool in peatland studies

Abstract

The potential and limitations of the Borehole Nuclear Magnetic Resonance (BNMR) technique as an in situ measurement for peatland soil characterization was tested in 163 boreholes at four selected peatlands in Denmark. The BNMR data effectively differentiated various geological units in peatland environments due to their distinct NMR responses. Moreover, field-scale variations of the porosity and pore size distribution (e.g., porosity variations within a single geological unit) were mapped to reveal possible trends reflecting geological or hydrogeological conditions in a peatland. Additionally, some of the NMR parameters were found to be correlated with peat decomposition or the degree of humification. The estimation of hydraulic conductivity (K) based on NMR data was also examined for various geological units and compared with slug test measurements. While NMR-based hydraulic conductivity estimations for sand and gyttja (fine-grained sediment with high organic matter) geological units fall within an acceptable range of error, we encountered challenges in achieving reliable estimations for peat. This study showed the potential of BNMR as a robust, rapid, and reliable in situ tool for soil characterization in peatland research.

Keywords

• NMR logging
• Peat
• Pore size distribution
• Porosity
• Degree of decomposition