Download or read book Cross borehole Fracture Mapping Using Electromagnetic Geotomography written by and published by . This book was released on 1982 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The Lawrence Livermore National Laboratory is evaluating high resolution geophysical techniques for characterization of nuclear waste repository sites. This report presents the results of the first phase of this project. We describe the evaluation of a new geophysical technique used to map fractures remotely between boreholes: electromagnetic geotomography used in conjunction with water tracers. Salt water is forced into the fractured rock mass, attenuating the high frequency electromagnetic waves used for probing. The locations in the rock where the salt water has induced signal losses are then mapped by geotomography. An experiment using this technique has been performed near Oracle, Arizona, in a granitic rock mass. The data obtained were reduced to gray level images, which show the calculated signal transmission properties of the rock mass. We analyzed these images and compared them with borehole geophysical data: neutron logs, acoustic velocity logs, caliper logs, and acoustic televiewer logs. Comparisons between the images and the borehole geophysical data suggest that geotomography has merit when used to map fracture in granite. Image anomalies, which can be indicative of fracturing along the borehole walls, usually coincide with geophysical log anomalies. Under the conditions of the Oracle experiment, available data indicate that clusters of fracture zones were detected. Single fractures were not detected. The thickness of the smallest recognizable fractured zone was 0.6 m (2 ft).
Download or read book Cross borehole Fracture Mapping Using Electromagnetic Geotomography written by A. L. Ramirez and published by . This book was released on 1982 with total page 58 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Use of Surface and Borehole Geophysical Surveys to Determine Fracture Orientation and Other Site Characteristics in Crystalline Bedrock Terrain Millville and Uxbridge Massachusetts written by Bruce P. Hansen and published by . This book was released on 1995 with total page 38 pages. Available in PDF, EPUB and Kindle. Book excerpt: ... Describes results of seismic and resistivity surface geophysical surveys that were conducted at 3 sites and borehole radar surveys conducted in 3 wells; directions of fracturing at each site are described; report also includes description of surface radar surveys, and geophysical surveys ...
Download or read book Application of Borehole Geophysics in the Characterization of Flow in Fractured Rocks written by F. L. Paillet and published by . This book was released on 1994 with total page 42 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book An Investigative Study of the Applicability of Generalized Linear Inverse Theory to Cross Borehole Geotomography written by Dion T. Fralick and published by . This book was released on 1986 with total page 88 pages. Available in PDF, EPUB and Kindle. Book excerpt: In geophysical exploration, reconstructing an image that maps the sub-surface characteristics of the earth is known as geotomography. This technique maps the region of interest in terms of some physical property such as signal attenuation or propagation velocity. Interpretation of these images or maps characterizes the geologic structures below the surface of the earth. Data for this type of imaging can be generated through the region of interest using either seismic or electromagnetic energy. In seismic geotomography, an accepted and widely used reconstruction technique is the inversion of travel-time residuals. The travel-time residuals (difference between the calculated and observed arrival times of particular signals) are expressed as a linear function and reduced in a least-squares sense using generalized linear inversion (GLI). The resulting solution provides information leading to the location of sub-surface anomalies. This investigation is concerned with mapping an underground region from data obtained by power measurements from boreholes on either side of the region of interest--a technique known as cross-borehole geotomography. The objective is to adapt and apply the reconstruction technique based on GLI used in seismic tomography to cross-borehole scanning data. To evaluate this technique the resulting image reconstructions is compared with those obtained from the algebraic reconstruction technique.
Download or read book Topical Report on Subsurface Fracture Mapping from Geothermal Wellbores Phase I Pulsed Radar Techniques Phase II Conventional Logging Methods Phase III Magnetic Borehole Ranging written by and published by . This book was released on 1980 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: To advance the state-of-the-art in Hot Dry Rock technology, an evaluation is made of (i) the use of radar to map far-field fractures, (ii) the use of more than twenty different conventional well logging tools to map borehole-fracture intercepts, and (iii) the use of magnetic dipole ranging to determine the relative positions of the injection well and the production well within the fractured zone. It is found that according to calculations, VHF backscatter radar has the potential for mapping fractures within a distance of 50 +- 20 meters from the wellbore. A new technique for improving fracture identification is presented. Analyses of extant data indicate that when used synergistically the (1) caliper, (2) resistivity dipmeter, (3) televiewer, (4) television, (5) impression packer, and (6) acoustic transmission are useful for mapping borehole-fracture intercepts. Improvements in both data interpretation techniques and high temperature operation are required. The surveying of one borehole from another appears feasible at ranges of up to 200 to 500 meters by using a low frequency magnetic field generated by a moderately strong dipole source (a solenoid) located in one borehole, a sensitive B field detector that traverses part of the second borehole, narrow band filtering, and special data inversion techniques.
Download or read book Subsurface Fracture Mapping from Geothermal Wellbores Final Report written by and published by . This book was released on 1983 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: To advance the state-of-the-art in Hot Dry Rock technology, and evaluation is made of (1) the use of both electromagnetic and acoustic radar to map far-field fractures, (2) the use of more than twenty different conventional well logging tools to map borehole-fracture intercepts, (3) the use of magnetic dipole ranging to determine the relative positions of the injection well and the production well within the fractured zone, (4) the use of passive microseismic methods to determine the orientation and extent of hydraulic fractures, and (5) the application of signal processing techniques to fracture mapping including tomography, holography, synthetic aperture, image reconstruction, and the relative importance of phase and amplitude information. It is found that according to calculations, VHF backscatter radar has the potential for mapping fractures within a distance of 50 +- 20 meters from the wellbore. A new technique for improving fracture identification is presented. The range of acoustic radar is five to seven times greater than that of VHF radar when compared on the basis of equal resolution, i.e., equal wavelengths. Analyses of extant data indicate that when used synergistically the (1) caliper, (2) resistivity dipmeter, (3) televiewer, (4) television, (5) impression packer, and (6) acoustic transmission are useful for mapping borehole-fracture intercepts. A new model of hydraulic fracturing is presented which indicates that a hydraulic fracture is dynamically unstable; consequently, improvements in locating the crack tip may be possible. The importance of phase in signal processing is stressed and those techniques which employ phase data are emphasized for field use.
Download or read book Improving Characterization of Fractured Rock Using 3D Cross borehole Electrical Resistivity Tomography ERT written by Judith L. Robinson and published by . This book was released on 2015 with total page 146 pages. Available in PDF, EPUB and Kindle. Book excerpt: There is a growing need to understand the hydraulic properties of fractured rock for the development and extraction of natural resources and also to engineer remediation strategies at contaminated sites. The characterization of fractured rock is inherently complex due to the multifaceted interrelationships between stress, temperature, roughness and fracture geometry that affect hydraulic conductivity and flow paths that have hydraulic properties varying over orders of magnitude. Often, sparse data points are interpolated from borehole locations to infer the spatial distribution of flow and transport within fractures. However, these fracture distributions are often poorly resolved due to the heterogeneity of these networks between the borehole locations. Electrical resistivity tomography (ERT) is a viable technology to characterize fractured rock as the electrical pathways mimic hydraulic pathways in fractured rock, assuming surface conduction is small. Previous work using ERT in fractured rock gave limited hydrogeological information due to finite element modeling techniques which were not physically appropriate for fractured rock and lack of instrumentation to permit imaging of isolated fracture zones. Synthetic and field datasets were used to incorporate field information to yield an improved hydrogeological interpretation. Specifically, model constraints were incorporated in the inversion modeling and borehole deviations defining these boundaries were explicitly defined in the discretization. Where this information was incorporated, ERT time-lapse changes in conductivity were more focused surrounding fracture locations and borehole effects were minimized. A rigorous examination of localized effects of de-regularization was undertaken and it was found that uncertainty in these boundaries can lead to spurious inversion artifacts. Electrode arrays within seven boreholes were designed, which included isolation bladders and a water sample/injection line. This design facilitated multiple tracer tests in a fractured mudstone to be conducted. The spatial scale of this experiment was such that the primary hydrogeological heterogeneity controlling flow and transport was captured, providing unique information relative to that acquired from borehole logging methods alone. The modeling techniques and instrumentation advancements detailed in this dissertation demonstrates the potential of ERT at fractured rock sites to work towards creating comprehensive flow and transport models.
Download or read book Cross borehole Electromagnetic Tomography Using a Stepped Frequency Source written by Albert Keng Howe Thong and published by . This book was released on 1995 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book In situ Fracture Mapping Using Geotomography and Brine Tracers written by F. J. Deadrick and published by . This book was released on 1982 with total page 8 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Using Borehole Geophysics and Cross borehole Flow Testing to Define Hydraulic Connections Between Fracture Zones in Bedrock Aquifers written by and published by . This book was released on 1993 with total page 19 pages. Available in PDF, EPUB and Kindle. Book excerpt: Nearly a decade of intensive geophysical logging at fractured rock hydrology research sites indicates that geophysical logs can be used to identify and characterize fractures intersecting boreholes. However, borehole-to-borehole flow tests indicate that only a few of the apparently open fractures found to intersect boreholes conduct flow under test conditions. This paper presents a systematic approach to fracture characterization designed to define the distribution of fractures along boreholes, relate the measured fracture distribution to structure and lithology of the rock mass, and define the nature of fracture flow paths across borehole arrays. Conventional electrical resistivity, gamma, and caliper logs are used to define lithology and large-scale structure. Borehole wall image logs obtained with the borehole televiewer are used to give the depth, orientation, and relative size of fractures in situ. High-resolution flowmeter measurements are used to identify fractures conducting flow in the rock mass adjacent to the boreholes. Changes in the flow field over time are used to characterize the hydraulic properties of fracture intersections between boreholes. Application of this approach to an array of 13 boreholes at the Mirror Lake, New Hamsphire site demonstrates that the transient flow analysis can be used to distinguish between fractures communicating with each other between observation boreholes, and those that are hydraulically isolated from each other in the surrounding rock mass. The Mirror Lake results also demonstrate that the method is sensitive to the effects of boreholes on the hydraulic properties of the fractured-rock aquifer. Experiments conducted before and after the drilling of additional boreholes in the array and before and after installation of packers in existing boreholes demonstrate that the presence of new boreholes or the inflation of packers in existing boreholes has a large effect on the measured hydraulic properties of the rock mass surrounding the borehole array.
Download or read book Low Frequency Electromagnetic Cross borehole Imaging written by M. Pihlman and published by . This book was released on 1988 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Geotomography Applied at the Stripa Mine in Sweden written by Justin Taro Okada and published by . This book was released on 1980 with total page 32 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Conductive Fracture Mapping written by and published by . This book was released on 2001 with total page 75 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Identification of Groundwater producing Fractures by Using an Electromagnetic Borehole Flowmeter in Monitoring Wells on the Oak Ridge Reservation Oak Ridge Tennessee written by and published by . This book was released on 1992 with total page 54 pages. Available in PDF, EPUB and Kindle. Book excerpt: This report describes the results of electromagnetic borehole flowmeter surveys taken on the Oak Ridge Reservation (ORR) with an instrument developed by the Engineering Laboratory of Tennessee Valley Authority (TVA). The borehole flowmeter can be used during water injection or pumping to determine the depth, vertical extent, and relative permeability of fractures that are intercepted by the wells. The flowmeter can also be used to measure any natural water flows, up or down an openhole interval, from one permeable fracture to another. These and other data have been used to select screen intervals or sampling ports in newly constructed wells on the ORR, to evaluate the potential for cross-contamination (the flow dissolved pollutants from one level to another in a well or corehole), and to characterize permeable fractures and permeable intervals in wells.
Download or read book Velocity Reconstruction in Cross borehole Computerized Geotomography Using First Breaks for Explosion generated Waves written by Bernard Kui T. Chin and published by . This book was released on 1991 with total page 188 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Evaluation of Borehole Electromagnetic and Seismic Detection of Fractures written by Hsi-Tien Chang and published by . This book was released on 1984 with total page 75 pages. Available in PDF, EPUB and Kindle. Book excerpt:
