Michael B. Rabinovich

Application of the integrated NMR-TDEM method in groundwater exploration in Israel

The Nuclear Magnetic Resonance (NMR) method is the only physical tool currently available which is able to detect directly the presence of fresh water in the subsurface. The Time Domain Electromagnetic (TDEM) method, in turn, has been proven highly efficient in detecting saline groundwater. The combined application of these two methods is the most promising way to delineate accurately groundwater-bearing aquifers and to evaluate the quality of the water. This idea was tested during the feasibility study carried out under different hydrogeological conditions throughout Israel during August-September 1992. The Russian Hydroscope and Geonics PROTEM-IV instruments were used for the NMR and TDEM measurements, respectively

On the influence of 3-D structures in the interpretation of transient electromagnetic sounding data

The limitations of a standard 1-D inversion applied to multidimensional (synthetic) data are investigated. Simple correction procedures for interpreting field data distorted by 3-D structures are suggested. Two different transmitter/receiver configurations of the transient electromagnetic (TEM) sounding method are examined: a central loop configuration for the near zone (sometimes called short offset) and a fixed transmitter/moving receiver configuration for the far zone (long offset). The 3-D models are structural depressions and highs in both resistive and conductive basements. The fixed transmitter (grounded dipole) in the long offset TEM configuration is located at a distance significantly greater than both the size and depth of the structure. In all cases, 1-D interpretation of the central loop soundings recovers geoelectric parameters of the section with good reliability, although fictitious layers may appear near vertical boundaries. The 1-D interpretation of long offset soundings does not, in most...

Detection of the water level in fractured phreatic aquifers using nuclear magnetic resonance (NMR) geophysical measurements

Abstract Correlation of geophysical data collected using the NMR method in the Negev Desert, Israel, with hydrogeological data from nearby observation wells is presented. The experiment was conducted near Kibbutz Revivim in the Besor drainage system (Fig. 1). The objective of the survey was to detect groundwater layers in the Quaternary cover filling and Eocene fractured aquifers down to a depth of 100 m. The experiment was performed using a combination of two different geophysical techniques, namely the NMR and time domain electromagnetic (TDEM) methods. The geophysical results were verified by measuring the water level in three observation wells, two of which were drilled several months after the geophysical survey was carried out. The water level measured in these follow-up observation wells shortly after drilling did not coincide with the geophysical data. However, it settled over a period of time and finally stabilized at a depth very similar to that obtained from the NMR measurements. This phenomenon is caused by the fractured nature of the phreatic aquifer. Since the flow of water in such aquifers is confined by the fractures, the appearance of water in the well during or shortly after drilling is determined solely by the intersection of the well and the fracture. Our experiments showed that geophysical measurements in fractured phreatic aquifers may have a distinct advantage over direct borehole measurements, since the former average the depth to the water table over large areas (several thousand square meters) while the latter are limited by the area of the borehole cross-section (several tens of square centimeters).

Detection of Tool Eccentricity Direction from Multi-Component Induction Responses

Summary Previous studies and field examples have indicated that most multi-component induction tool responses may be subject to strong tool eccentricity effect, particularly in a very conductive borehole environment. The MultiFrequency Focusing (MFF) technique has proven effective in reducing near zone effects including tool eccentricity. In this paper, we take a different approach to studying the eccentricity effect by detecting eccentricity direction based on single frequency responses. To precisely interpret the log data from multi-component induction tools that are sensitive to anisotropy, the paper presents a unique approach to determine eccentricity angle for deviated wells. The technique was validated with synthetic data for 3D decentralized tool for anisotropic formations. The model analysis provides the relationships between estimated eccentricity direction and tool responses at various single frequencies with different offsets. The results demonstrated that the proposed technique is well suited not only for thick layers with either conductive or resistive formation but also for layered formation with strong shoulder bed effect.