Andreas Weller

A new approach to fitting induced-polarization spectra

Best fitting of induced-polarization (IP) spectra by different models of Cole-Cole type evidences discrepancies in the resulting model parameters. The time constant determined from the same data could vary in magnitude over several decades. This effect, which makes an evaluation of the results of different models nearly impossible, is demonstrated by induced polarization measurements in the frequency range between 1.4 mHz and 12 kHz on thirteen mixtures of quartz sand and slag grains. The samples differ in size and the amount of the slag grains. Parameters describing the IP spectra are derived by fitting models of the Cole-Cole type to the measured data. The fitting quality of the generalized Cole-Cole model, the standard Cole-Cole model, and the Cole-Davidson model is investigated. The parameters derived from these models are compared and correlated with mass percentage and grain size of the slag particles. An alternative fittingapproach is introduced, using the decomposition of observed IP spectra into ...

On the estimation of specific surface per unit pore volume from induced polarization: A robust empirical relation fits multiple data sets

We analyze the relationship between induced polarization (IP) parameters and the specific surface area normalized to the pore volume ( Spor ) for an extensive sample database. We find that a single linear imaginary conductivity- Spor relation holds across a range of single-frequency IP data sets composed of sandstones and unconsolidated sediments that lack an appreciable metallic mineral content. We also apply a recent approach defined as Debye decomposition (DD) to determine normalized chargeability ( mn ) , a global estimate of polarization magnitude from available spectral IP (SIP) data sets. A strong linear relationship between mn and Spor is also found across multiple data sets. However, SIP model parameters determined for samples containing metallic minerals are approximately two orders of magnitude greater than for the model parameters estimated for the nonmetallic sample database. We propose a concept of “polarizability of the mineral-fluid interface per unit Spor ” to explain this difference, whi...

Estimating permeability of sandstone samples by nuclear magnetic resonance and spectral-induced polarization

Two techniques to estimate permeability are compared in this paper: nuclear magnetic resonance (NMR) and spectral-induced polarization (SIP). Both methods are based on relaxation processes. NMR records the relaxation of hydrogen nuclei after excitation in an external magnetic field. The phenomenon of induced polarization can be characterized by a relaxation of ions after excitation by an electric field. Hydrogen nuclei are concentrated in the pore water, the current flow is restricted to the pore space for most reservoir rocks, and permeability is related to the pore space geometry. Based on the similarity between fluid movement and current flow in the pore space, different relations have been published linking parameters derived from NMRand SIP data to predict permeability. NMR, SIP and permeability data have been acquired on 53 sandstone samples of the cretaceous Bahariya Formation (Western Desert, Egypt) including 27 samples showing a lamination that causes anisotropy. We compare the applicability of k...

Three-dimensional inversion of induced polarization data from simulated waste

The Idaho National Laboratory (INEL) Cold Test Pit (CTP) has been carefully constructed to simulate buried hazardous waste sites. An induced polarization (IP) survey of the CTP shows a very strong polarization and a modest resistivity response associated with the simulated waste. A three-dimensional (3-D) inversion algorithm based on the simultaneous iterative reconstruction technique (SIRT) and finite difference forward modelling has been applied to generate a subsurface model of complex resistivity. The lateral extents of the waste zone are well resolved. Limited depth extent is recognized, but the bottom of the waste appears too deep. With a modelling experiment, the intrinsic polarizability of the waste material is determined. Since IP is a technique for detection of diffuse occurrences of metallic material, this method holds promise as a method to distinguish buried waste from conductive soil material.

Evaluation of Geophysical Techniques for Dike Inspection

After some river embankment failures during recent floods in Germany, major investigation and improvement programs for river embankments have been implemented. Presently, the investigation mainly relies on existing documentation, visual inspection, and drilling and sampling. Geophysical techniques, which are applied non-destructively from the surface, have the potential to cover the gaps between sampling points and to enhance the reliability of subsurface information. This paper describes the evaluation results for resistivity, electromagnetic, seismic and GPR techniques acquired at a test site along the Mulde River in eastern Germany. The work was carried out under the government funded project DEISTRUKT. Each geophysical method has its own specific advantages and limitations. Keeping the requirements posed by current German guidelines for river embankments in mind, 2-D electrical resistivity tomography (ERT) is the method of first choice. However, all geophysical results have to be calibrated carefully using information, such as material properties and depth of structures, determined from boreholes. Although some recommendations are provided here, a set of detailed recommendations have been compiled in a handbook.

Spectral Induced Polarisation – a Geophysical Method for Archaeological Prospection in Peatlands

Abstract Compared to conventional electrical conductivity surveys the spectral induced polarisation (SIP) method measures the frequency dependence of conductivity amplitude and the phase shift between injected current and the resulting voltage signal. The phase shift is related to polarisation effects of materials. Laboratory investigations of peat, wood and soil samples show a considerable variation in the spectra of conductivity amplitude and phase shift. From the results of laboratory investigations it could be concluded that characteristic features of the phase spectra can be used to detect wooden relics of trackways or pile dwellings in the wetlands subsurface. Field surveys in the Federsee bog in southern Germany and the Campemoor bog in northern Germany prove that the method of spectral induced polarisation can be considered as a prospecting tool for archaeological surveying in wetlands. A shallow trackway in the Campemoor bog could be clearly verified by higher phase values measured at a frequency of 3Hz. The weak phase signal of a somewhat deeper plankway in the Federsee bog became only visible after data processing.

Permeability prediction of four Egyptian sandstone formations

Reliable formation evaluation for oil and gas reservoirs or the modeling of groundwater flow requires accurate information on petrophysical properties such as permeability or porosity of the reservoir rocks. Porosity can be easily determined both in the laboratory and from well logs. Accurate experimental permeability determination requires more expensive methods. As an alternative, physical models and/or empirical equations have been proposed to enable permeability prediction based on more easily measurable parameters. This paper evaluates five models and formulae for permeability estimation based on petrophysical parameters that are related to pore space geometry. The fundamental parameters that are related to pore size or specific internal surface were determined by nitrogen adsorption, nuclear magnetic resonance, and spectral induced polarisation measurements. Petrophysical parameters of 96 sandstone samples from four sandstone formations in Egypt were included in this study. The comparison of the predictive quality of the models provides more insight into the limitations of the individual models. The roughness of the internal surface, the clay content, the connectivity of the pore space and the distribution of iron minerals are identified as the most relevant properties affecting the predictive quality of the models.

Geotechnical and Geophysical Long-term Monitoring at a Levee of Red River in Vietnam

ABSTRACT The stability or safety of a levee during flooding depends on both the temporal development of the amplitude of the hydraulic loads in surface water and ground water and the change of soil parameters within the levee and subsoil. Therefore, a levee monitoring system should record the temporal development of the hydraulic loads of surface water and the resulting variations of water flow within the levee and subsoil. Long-term monitoring has been performed at a levee of Red River in Thai Binh province in Vietnam. The monitoring system consists of a permanent electrode array for resistivity imaging and geotechnical tools including tensiometers, frequency-domain reflectometry sensors and an observation well. The components were installed after a detailed inspection of the levee and foundation by drilling, sampling, and a geoelectrical survey. The levee monitoring system provided time series of the sensor data that were related to the variation of pore water pressure and water distribution. Additional...

Fractal dimension of pore space in carbonate samples from Tushka area (Egypt)

To investigate inhomogeneous and porous structures in nature, the concept of fractal dimension was established. This paper briefly introduces the definition and measurement methods of fractal dimension. Three different methods including mercury injection capillary pressure (MICP), nuclear magnetic resonance (NMR), and nitrogen adsorption (BET) were applied to determine the fractal dimensions of the pore space of eight carbonate rock samples taken from West Tushka area, Egypt. In the case of fractal behavior, the capillary pressure Pc and cumulative fraction Vc resulting from MICP are linearly related with a slope of D-3 in a double logarithmic plot with D being the value of fractal dimension. For NMR, the cumulative intensity fraction Vc and relaxation time T2 show a linear relation with a slope of 3-D in a double logarithmic plot. Fractal dimension can also be determined by the specific surface area Spor derived from nitrogen adsorption measurements and the effective hydraulic radius. The fractal dimension D shows a linear relation with the logarithm of Spor. The fractal dimension is also used in models of permeability prediction. To consider a more comprehensive data set, another 34 carbonate samples taken from the same study area were integrated in the discussion on BET method and permeability prediction. Most of the 42 rock samples show a good agreement between measured permeability and predicted permeability if the mean surface fractal dimension for each facies is used.

Petrographic and petrophysical investigation on carbonate samples (Upper Cretaceous) from the Tushka Area (Egypt) with special focus on the effective pore radius

Petrographic and petrophysical properties of 42 carbonate rock samples from the Tushka Area, Egypt have been investigated. The samples originate from the Upper Cretaceous taken from seven shallow wells and were subdivided into three microfacies. The petrographic characterization of the glauconite-rich, fossiliferous limestones was carried out over 17 thin sections and an additional measurement of the glauconite content by color differentiation. The facies were characterized as (1) oolithic, low-dolomitic, and low-glauconitic, fossil-rich packstone with a tendency towards floatstone or rudstone; (2) glauconite-rich, low-dolomitic floatstone with a tendency towards rudstone; and (3) glauconite and iron mineral-rich, sparry calcitic cemented, and low-dolomitic rudstone. The petrophysical investigation providing grain density, porosity, electrical conductivity, specific internal surface, permeability, magnetic susceptibility, and the pore throat geometry supports the classification into three facies. A strong relation between permeability and formation factor is observed. The median pore radius derived from mercury porosimetry proves to be a good estimate of the effective hydraulic radius. An increased content of iron oxides was identified in facies 3. The increased iron content is related to higher values of both magnetic susceptibility and specific internal surface.