New technologies in groundwater exploration : surface Nuclear Magnetic Resonance

As groundwater becomes increasingly important for living and environment, techniques are asked for an improved exploration. The demand is not only to detect new groundwater resources but also to protect them. Geophysical techniques are the key to find groundwater. Combination of geophysical measurements with boreholes and borehole measurements help to describe groundwater systems and their dynamics. There are a number of geophysical techniques based on the principles of geoelectrics, electromagnetics, seismics, gravity and magnetics, which are used in exploration of geological structures in particular for the purpose of discovering georesources. The special geological setting of groundwater systems, i.e. structure and material, makes it necessary to adopt and modify existing geophysical techniques. A new discipline called hydrogeophysics has been formed and is growing fast. Efforts for direct detection of groundwater led recently to a new technique: Surface Nuclear Magnetic Resonance (SNMR). The principle of nuclear magnetic resonance, well known in physics, physical chemistry as well as in medicine, has successfully been adapted to assess the existence of groundwater and the aquifer parameters. This technique allows for the first time detecting and assessing water directly by only surface measurements allowing quantitative information about mobile water content as well as pore structure parameters leading to hydraulic conductivities. Function, results, interpretation, advantages and drawbacks of SNMR are reviewed in this paper showing the current state of art and developments. A comprehensive example of SNMR is presented with measurements conducted at the site of Nauen near Berlin. The site has Quaternary aquifers with differing layering of sand and till. The results are very satisfying as aquifers down to 50 m depth can be identified quite reliably. The water content is estimated with a high degree of accuracy and relaxation times allowed to derive hydraulic conductivities. Supplementary measurements with geoelectrics and radar made possible to complement and confirm the information achieved with SNMR as well as to apply a joint multimethod approach to aquifer assessment

Evaluation of surface nuclear magnetic resonance-estimated subsurface water content

The technique of nuclear magnetic resonance (NMR) has found widespread use in geophysical applications for determining rock properties (e.g. porosity and permeability) and state variables (e.g. water content) or to distinguish between oil and water. NMR measurements are most commonly made in the laboratory and in boreholes. The technique of surface NMR (or magnetic resonance sounding (MRS)) also takes advantage of the NMR phenomenon, but by measuring subsurface rock properties from the surface using large coils of some tens of meters and reaching depths as much as 150 m. We give here a brief review of the current state of the art of forward modeling and inversion techniques. In laboratory NMR a calibration is used to convert measured signal amplitudes into water content. Surface NMR-measured amplitudes cannot be converted by a simple calibration. The water content is derived by comparing a measured amplitude with an amplitude calculated for a given subsurface water content model as input for a forward modeling that must account for all relevant physics. A convenient option to check whether the measured signals are reliable or the forward modeling accounts for all effects is to make measurements in a well-defined environment. Therefore, measurements on top of a frozen lake were made with the latest-generation surface NMR instruments. We found the measured amplitudes to be in agreement with the calculated amplitudes for a model of 100 % water content. Assuming then both the forward modeling and the measurement to be correct, the uncertainty of the model is calculated with only a few per cent based on the measurement uncertainty

Groundwater resources assessment using integrated geophysical techniques in the southwestern region of Peninsular Malaysia.

Combined geophysical techniques such as multi-electrode resistivity, induced polarization, and borehole geophysical techniques were carried out on volcano-sedimentary rocks in the north of Gemas as part of the groundwater resource’s investigations. The result identifies four resistivity units: the tuffaceous mudstone, tuffaceous sandstone, the tuff bed, and the shale layer. Two types of aquifer systems in terms of storage were identified within the area: one within a fracture system (tuff), which is the leaky area through which vertical flow of groundwater occurs, and an intergranular property of the sandy material of the aquifer which includes sandstone and tuffaceous sandstone. The result also reveals that the aquifer occupies a surface area of about 3,250,555 m2 with a mean depth of 43.71 m and a net volume of 9.798 × 107 m3. From the approximate volume of the porous zone (28 %) and the total aquifer volume, a usable capacity of (274.339 ± 30.177) × 107 m3 of water in the study area can be deduced. This study provides useful information that can be used to develop a much broader understanding of the nature of groundwater potential in the area and their relationship with the local geology

Application of Surface wave methods for seismic site characterization

Surface-wave dispersion analysis is widely used in geophysics to infer a shear wave velocity model of the subsoil for a wide variety of applications. A shear-wave velocity model is obtained from the solution of an inverse problem based on the surface wave dispersive propagation in vertically heterogeneous media. The analysis can be based either on active source measurements or on seismic noise recordings. This paper discusses the most typical choices for collection and interpretation of experimental data, providing a state of the art on the different steps involved in surface wave surveys. In particular, the different strategies for processing experimental data and to solve the inverse problem are presented, along with their advantages and disadvantages. Also, some issues related to the characteristics of passive surface wave data and their use in H/V spectral ratio technique are discussed as additional information to be used independently or in conjunction with dispersion analysis. Finally, some recommendations for the use of surface wave methods are presented, while also outlining future trends in the research of this topic

Surface Nuclear Magnetic Resonance (SNMR) - A new method for exploration of ground water and aquifer properties

The Surface Nuclear Magnetic Resonance (SNMR) method is a fairly new technique in geophysics to assess ground water, i.e. existence, amount and productibility by measurements at the surface. The NMR technique used in medicine, physics and lately in borehole geophysics was adopted for surface measurements in the early eighties, and commercial equipment for measurements has been available since the mid nineties. The SNMR method has been tested at sites in Northern Germany with Quaternary sand and clay layers, to examine the suitability of this new method for groundwater exploration and environmental investigations. More information is obtained by SNMR, particularly with respect to aquifer parameters, than with other geophysical techniques. SNMR measurements were carried out at three borehole locations, together with 2D and 1D direct current geoelectrics and well logging (induction log, gamma-ray log and pulsed neutron-gamma log). Permeabilities were calculated from the grain-size distributions of core material determined in the laboratory. It is demonstrated that the SNMR method is able to detect groundwater and the results are in good agreement with other geophysical and hydrogeological data. Using the SNMR method, the water content of the unsaturated and saturated zones (i.e. porosity of an aquifer) can be reliably determined. This information and resistivity data permit in-situ determination of other aquifer parameters. Comparison of the SNMR results with borehole data clearly shows that the water content determined by SNMR is the free or mobile water in the pores. The permeabilities estimated from the SNMR decay times are similar to those derived from sieve analysis of core material. Thus, the combination of SNMR with geoelectric methods promises to be a powerful tool for studying aquifer properties

New technologies in groundwater exploration : surface Nuclear Magnetic Resonance

As groundwater becomes increasingly important for living and environment, techniques are asked for an improved exploration. The demand is not only to detect new groundwater resources but also to protect them. Geophysical techniques are the key to find groundwater. Combination of geophysical measurements with boreholes and borehole measurements help to describe groundwater systems and their dynamics. There are a number of geophysical techniques based on the principles of geoelectrics, electromagnetics, seismics, gravity and magnetics, which are used in exploration of geological structures in particular for the purpose of discovering georesources. The special geological setting of groundwater systems, i.e. structure and material, makes it necessary to adopt and modify existing geophysical techniques. A new discipline called hydrogeophysics has been formed and is growing fast. Efforts for direct detection of groundwater led recently to a new technique: Surface Nuclear Magnetic Resonance (SNMR). The principle of nuclear magnetic resonance, well known in physics, physical chemistry as well as in medicine, has successfully been adapted to assess the existence of groundwater and the aquifer parameters. This technique allows for the first time detecting and assessing water directly by only surface measurements allowing quantitative information about mobile water content as well as pore structure parameters leading to hydraulic conductivities. Function, results, interpretation, advantages and drawbacks of SNMR are reviewed in this paper showing the current state of art and developments. A comprehensive example of SNMR is presented with measurements conducted at the site of Nauen near Berlin. The site has Quaternary aquifers with differing layering of sand and till. The results are very satisfying as aquifers down to 50 m depth can be identified quite reliably. The water content is estimated with a high degree of accuracy and relaxation times allowed to derive hydraulic conductivities. Supplementary measurements with geoelectrics and radar made possible to complement and confirm the information achieved with SNMR as well as to apply a joint multimethod approach to aquifer assessment

Surface Nuclear Magnetic Resonance (SNMR) - A new method for exploration of ground water and aquifer properties

The Surface Nuclear Magnetic Resonance (SNMR) method is a fairly new technique in geophysics to assess ground water, i.e. existence, amount and productibility by measurements at the surface. The NMR technique used in medicine, physics and lately in borehole geophysics was adopted for surface measurements in the early eighties, and commercial equipment for measurements has been available since the mid nineties. The SNMR method has been tested at sites in Northern Germany with Quaternary sand and clay layers, to examine the suitability of this new method for groundwater exploration and environmental investigations. More information is obtained by SNMR, particularly with respect to aquifer parameters, than with other geophysical techniques. SNMR measurements were carried out at three borehole locations, together with 2D and 1D direct current geoelectrics and well logging (induction log, gamma-ray log and pulsed neutron-gamma log). Permeabilities were calculated from the grain-size distributions of core material determined in the laboratory. It is demonstrated that the SNMR method is able to detect groundwater and the results are in good agreement with other geophysical and hydrogeological data. Using the SNMR method, the water content of the unsaturated and saturated zones (i.e. porosity of an aquifer) can be reliably determined. This information and resistivity data permit in-situ determination of other aquifer parameters. Comparison of the SNMR results with borehole data clearly shows that the water content determined by SNMR is the free or mobile water in the pores. The permeabilities estimated from the SNMR decay times are similar to those derived from sieve analysis of core material. Thus, the combination of SNMR with geoelectric methods promises to be a powerful tool for studying aquifer properties