Development and anlysis of fast, approximate 3D Algorithms for interpretation of multi-component induction logging data

This report addresses the effects of electrical anisotropy on the 3D inversion of single-well induction logging data when anisotropy is not considered. Of concern are possible artifacts that may lead to an incorrect interpretation of the formation about the borehole. Comparison is made of 3D isotropic inversion on a suite of model data, with and without anisotropy, consisting of an infinite layer and layer terminated at the borehole. In both cases, the layer dip (or well deviation) is varied. Inversion of the anisotropic data result in an overestimate of the layer conductivity, and the lateral extent of the layer about the borehole

A resolution analysis of two geophysical imaging methods for characterizing and monitoring hydrologic conditions in the Vadose zone.

This research project analyzed the resolution of two geophysical imaging techniques, electrical resistivity tomography (ERT) and cross-borehole ground penetrating radar (XBGPR), for monitoring subsurface flow and transport processes within the vadose zone. The study was based on petrophysical conversion of moisture contents and solute distributions obtained from unsaturated flow forward modeling. This modeling incorporated boundary conditions from a potable water and a salt tracer infiltration experiment performed at the Sandia-Tech Vadose Zone (STVZ) facility, and high-resolution spatial grids (6.25-cm spacing over a 1700-m domain) and incorporated hydraulic properties measured on samples collected from the STVZ. The analysis process involved petrophysical conversion of moisture content and solute concentration fields to geophysical property fields, forward geophysical modeling using the geophysical property fields to obtain synthetic geophysical data, and finally, inversion of this synthetic data. These geophysical property models were then compared to those derived from the conversion of the hydrologic forward modeling to provide an understanding of the resolution and limitations of the geophysical techniques

Final report [The 15th Workshop on Electromagnetic Induction in the Earth, held 8/20-26/2000, and The 5th Magnetotelluric Data Interpretation Workshop, 8/17-19/2000]

This document reports on how the DOE helped to support travel of students and scientists to the conferences in Brazil. Attendee names, funding, and session titles are listed

A Resolution Analysis of Two Geophysical Imaging Methods for Characterizing and Monitoring Hydrologic Conditions in the Vadose Zone

This project has been designed to analyze the resolution of two different geophysical imaging techniques (electrical resistivity tomography and cross-borehole ground penetrating radar) for monitoring subsurface flow and transport processes within the vadose zone. This is to be accomplished through a coupled approach involving large scale unsaturated flow modeling, petrophysical conversion of the resulting 2 and 3 Dimensional water content and solute concentration fields to geophysical property models and generation of synthetic geophysical data, followed by the inversion of the synthetic geophysical data. The resolution, strengths, and limitations of the geophysical techniques will then be ascertained through an analysis involving comparisons between the original hydrologic modeling results and inverted geophysical images. Increasing levels of complexity will be added to the models as the project progresses through the addition of heterogeneity in the original hydrologic property model, and by adding uncertainty to the petrophysical relationship that couples the geophysical model to the hydrologic modeling results

A Hybrid Hydrologic-Geophysical Inverse Technique For The Assessment And Monitoring Of Leachates In The Vadose Zone

At many DOE facilities, the presence of radioactive wastes and other contaminants within the vadose zone poses a serious and ongoing threat to public health and safety. In many cases these contaminants have been introduced directly to the vadose zone through releases on the surface or in shallow pits, and through leaking storage facilities. To reduce the environmental risks these wastes pose, the DOE is currently considering two fundamentally different approaches. The first involves remediation by treating contaminants in-place while the second, and more economically feasible being examined by DOE, involves in-situ immobilization of the wastes. Immobilization would be achieved through both injection of subsurface grout barriers to block transport pathways and installation of surface caps to prevent additional water infiltration into contaminated formations. A necessary requirement of both remediation approaches is the need to obtain information on the spatial distributions of the hydraulic and transport properties, the amount of contamination in place, and flow and transport processes that are occurring. With this information in hand, informed decisions can be made in order to optimize the remediation process for each particular case. In particular, these capabilities could result in reduced remediation costs, as well as providing necessary data to illustrate regulatory compliance. To reach these goals, existing monitoring technologies need to be improved and innovative technologies need to be developed to measure the spatial distribution of, and the temporal changes in moisture contents and contaminant concentrations within the vadose zone. The primary objective of the funded research addressed these needs through the development and field-testing of a Hybrid Hydrologic-Geophysical Inverse Technique (HHGIT). The resulting technology provides the ability to both monitor the evolution of certain types of contaminant plumes, and to characterize hydrologic properties within the vadose zone at contaminated sites. The HHGIT combines geophysical measurements such as electrical resistivity tomography (ERT), cross borehole ground penetrating radar (XBGPR), neutron moisture logs, sparse hydrologic data, and geostatistical information on the geologic heterogeneity to provide 2- and 3-D of moisture and hydrologic property distributions. By linking these three types of information into a single inversion, much better estimates of spatially varying hydraulic properties can be obtained than could be from interpreting the data types individually. Because the method is a geostatistically based estimation technique, the estimates represent conditional mean hydraulic property fields. Thus, this method quantifies the uncertainty of the estimates as well as the estimates themselves

Numerical Analysis Of Three Component Induction Logging In Geothermal Reservoirs

This project is supporting the development of the ''Geo-Bilt'', geothermal electromagnetic-induction logging tool that is being built by ElectroManetic Instruments, Inc. The tool consists of three mutually orthogonal magnetic field antennas, and three-component magnetic field receivers located at different distances from the source. In its current configuration, the source that has a moment aligned along the borehole axis consists of a 1m long solenoid, while the two trans-axial sources consist of 1m by 8cm loops of wire. The receivers are located 2m and 5m away from the center of the sources, and five frequencies from 2 kHz to 40 kHz are being employed. This study is numerically investigating (1) the effect of the borehole on the measurements, and (2) the sensitivity of the tool to fracture zone-geometries that might be encountered in a geothermal field. The benefits of the results are that they will lead to a better understanding of the data that the tool produces during its testing phase and an idea of what the limitations of the tool are

A Numerical Analysis of 3D EM Imaging from a Single Borehole

In this study we analyze the feasibility of three dimensional (3D) electromagnetic (EM) imaging from a single borehole. The proposed logging tool consists of three mutually orthogonal magnetic dipole sources and multiple three component magnetic field receivers. A sensitivity analysis indicates that the most important sensor configuration for providing 3D geological information about the borehole consists of a transmitter with moment aligned parallel to the axis of the borehole, and receivers aligned perpendicular to the axis. The standard coaxial logging configuration provides the greatest depth of sensitivity compared to other configurations, but offers no information regarding 3D structure. Two other tool configurations in which both the source and receiver are aligned perpendicular to the borehole axis provide some directional information and therefore better image resolution, but not true 3D information. A 3D inversion algorithm has been employed to demonstrate the plausibility of 3D inversion using data collected with the proposed logging tool. This study demonstrates that an increase in image resolution results when three orthogonal sources are incorporated into the logging tool rather than a single axially aligned source

A RESOLUTION ANALYSIS OF TWO GEOPHYSICAL IMAGING METHODS FOR CHARACTERIZING AND MONITORING HYDROLOGIC CONDITIONS IN THE VADOSE ZONE

The objective of this study is to characterize and analyze in-situ flow and transport within the vadose zone during a mid-scale hydrologic infiltration experiment. This project has employed numerical and experimental tools developed under a previously funded EMSP proposal (project number 55332) to provide 3-D unsaturated hydrologic property distributions. In the present project, geophysical imaging techniques have been employed to track analogue contaminant plumes. The results are providing a better understanding of transport modes including the influence of natural heterogeneities and man-made structures within the vadose zone at DOE sites. In addition the data is providing checks against which numerical flow and transport simulations can be compare