Numerical Model of Shale Compaction, Aquathermal Pressuring, and Hydraulic Fracturing: ABSTRACT (original) (raw)
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Journal of African Earth Sciences, 2006
Space-borne remote sensing imaging allows precise coverage of vast regions with basic data for geological exploration while significantly reducing exploration costs. These data provide valuable information for geological mapping and mineral exploration through highlighting geological structures such as lineaments, faults, and lithological contacts. The use of radar constitutes a very useful complement to optical remote sensing data, especially as regards to the surface but also the subsurface detection of structures. Specifically in arid desert areas, radar waves penetrate the dry surface sand sheet and highlight concealed geological structures or fossil river systems. We present a synthesis of two experiments designed to compare the contribution of radar and optical images to geological exploration using the Akjoujt region in Mauritania and the Bir Safsaf region in Egypt as study sites. Ground-Penetrating Radar (GPR) is used to evaluate volume scattering coming from subsurface dielectric heterogeneities in cases of radar penetration of the dry sand. This evaluation is based on correlating the reflectivity of the GPR section with backscattering coefficients extracted from radar images. Radar clearly demonstrates superior capability for precise detection of surface structures associated with dikes, lithological variation, or paleo-hydrogeological features. The effectiveness of radar for mapping in arid environments lies in the fact that geological features can be distinguished on the basis of their morphological expression and surface roughness. We also confirm that low frequency radar (L-band) can retrieve information about subsurface structures down to a few meters’ depth, where optical images cannot.
Geological mapping usually requires field visits, but the processing and interpretation of hyperspectral satellite images can also be very beneficial for this task. Microwave or radar remote sensing can obtain surface morphologies using synthetic aperture radar (SAR) images and reduce the duration of field visits dramatically by discriminating geological units based on lithology and texture. This requires the surface roughness to be modeled against microwave signal backscattering. The integral equation model (IEM) is the most well-known rough scattering model, in which surface roughness is calculated using the roughness height statistical parameter (rms-height); however, this study uses an improved IEM based on power-law geometry. The roughness map of the Anaran anticline (located between Dehloran and Ilam in Iran) using TerraSAR images is computed and classified to generate a morphological map. Calculating the roughness map requires training the IEM model and the formation of the look-up-table for pure lithological sites. In situ microtopography measurement was performed on seven different sites containing the main lithologies in the study area, using total station surveying, to train the mathematical model and compare and evaluate the results. Comparing this roughness map with ground-truth data at test sites indicates that computations using the new IEM model results in a misclassification of <10 % of the samples in the map. This error is acceptable, indicating that the new model could, in many cases, reduce the duration of field visits.
Evaluation of Landsat thematic mapper imagery for geologic applications
Proceedings of the IEEE, 2000
Landsat-4 Thematic Mapper (TM) imagery were enhanced and evaluated for geologic applications in both heavily and sparsely vegetated areas of the San Francisco Bay Region. False color corn posites of contrast-stretched spectral bands and principal compe nent combinations were found to provide the most lithologic and structural information for geologic interpretation. The 3@m spatial resolution and seven spectral bands of the TM sensor were successfully used to delineate regional geobotanical anomalies, faults, and fractures in the heavily vegetated New Almaden area of the Santa Cruz mountains and regional lithology and structure of the sparsely vegetated Diablo Range. A number of these features have not been previously recognized using conventional aerial and field mapping techniques. Data reduction techniques employed to reduce the effects of band correlation assisted the geologic interpretation in the heavily vegetated areas but were of little use in the sparsely vegetated areas. This work demonstrates the ability of TM imagery to assist in the interpretation of lithologic, structural, and g e e botanical features critical to deciphering a region's geology or mineral potential. lNTRODUCTlON Prior to the availability of satellite imagery, geologists relied on aerial photography to provide synoptic coverage of a project site. Color, black and white, and infrared aerial photography at various scales provides the geologist with an invaluable tool for mapping local surface structure and lithology. However, the use of aerial photography for geologic interpretation is limited by a number of factors, including: 1) Poor spectral resolution-the broad-band spectral range of aerial photographic film is generally insufficient to separate different lithologies. 2) The scale of aerial photography is commonly insufficient to recognize large surface features. Large features often require a cumbersome number of photographs to provide complete coverage.
In 1998-99, the U.S. Geological Survey conducted a crosshole radar tomographic experiment at the lateral-pile- load testsite on Treasure Island to nondestructively image the soil column for changes in void ratio before and after a liquefaction event that was caused by controlled blasting. A geotechnical borehole radar technique was used to acquire high-resolution two-dimensional radar velocity data. This method of nondestructive site characterization uses trans- illumination surveys through the soil column and tomo- graphic data-manipulation techniques to construct velocity tomograms, from which computed void ratios can be derived at 0.25- to 0.5-m-pixel footprints. Tomograms of void ratio are constructed by using a relation between soil void ratio and corresponding dielectric properties. The two-dimensional imagery is used to model changes in void ratio and to quantify void-ratio reduction in response to soil contraction during liquefaction. Predicted settlements based on planar-ra...
Sensing and Imaging An International Journal
The hydrological setting of a desert plain area located in Egypt, west of Aswan city, is still not well understood, and thus, its groundwater potential remains largely unknown. Images from the ALOS/PALSAR L-band sensor have been used to detect and delineate the subsurface structures in this area. Linear, elliptical and circular polarization transformations were applied to the ALOS/PALSAR full polarimetric data by changing the orientation angle (w°) and elliptical angle (v°). The circular polarization (w = 0°and v = 45°) proved to be the best transformation for revealing buried faults in various strike directions, which have not been reported in the last version of the official geologic map of this area. Such derived circular polarization images were further enhanced by applying the Optimal Polarization Contrast Enhancement method. The moisture content (O -S ) of the study sites was generally low, with an average of roughly 0.01%. The average Root Mean Square Height (h RMS ) of the surface roughness was also low with 0.01 cm across all sites. The relative dielectric constant (e r ) of the sand in the study area produced a very low value of 3.04. The effects of O -S , e r and h RMS on the radar backscattered signals turned out to be very low, thus providing, optimal conditions for L-band to penetrate relatively deeply. Moreover, 21 GPR profiles were acquired using 270 MHz shielded antennas to validate the radar remote sensing results. These GPR profiles reveal obvious offsets in the subsurface stratigraphy suggesting that such highly fractured zones are possibly favorable zones for groundwater accumulation.
Ground Penetrating Radar: Techniques in Geomorphology
Ground-penetrating radar (GPR) is an effective tool to visualise the structure of the shallow subsurface. The purpose of this article is to offer guidelines to non-specialist GPR users on the collection, processing and interpretation of GPR data in a range of environments. The discussion on survey design focuses on single fold, fixed-offset reflection profiling, the most common mode of GPR data collection, however the design factors can be applied to other survey types. Information on the visualisation of processed data, as well as the advantages and disadvantages of GPR, is provided. Possible applications of GPR in geomorphological research are presented, along with a case study outlining how GPR can be used to measure peat thickness.
Geocarto International, 2019
The present study investigates the potential of Synthetic Aperture Radar in demonstrating the relative percentage of sand, silt and clay content in the soil. The contribution of vegetation and topography in the backscattering coefficient has been significantly reduced by employing the Terrain Correction Model, Dual polarized SAR Vegetation Index, and Water Cloud Model. The target parameters namely 'Soil Roughness (h rms-soil)' and 'Dielectric Constant' (− ′) has arrived from crosspolarization ratio and modified Dubois model. The extracted target parameters are sufficiently correlated with in-situ Sand (R 2 =0.81) and Clay measurements (R 2 =0.78). The relative percentage of silt was mapped by the novel idea of performing the correlation analysis between h rms-soil and − ′ and thus represented the percentage of silt with reasonable accuracy (R 2 =0.77). From the soil triangle formed with three estimated target parameters, we found that the Clay category has shared around 35% of the total area followed by Sandy loam (23%).
Journal of Earth Science, 2014
This paper presents results from ground penetrating radar surveys using the SIR-10B GPR instrument (manufactured by Geophysical Survey System Inc., USA), with 400 MHz monostatic antenna (model 5 103). Survey was made over 3 excavation levels along the highway section at the Ras en Naqab escarpment area, Southwest Jordan. A total of 217 m along 4 profiles were covered in the winter of 2012. The objectives of the study are (i) to evaluate the resolution of the GPR technique in the field for detecting and locating anomalies caused by subsurface structures like cavities, fractures and faults, and (ii) to describe stratigraphic nomenclature of the subsurface rocks of the area. 2D interpretation of the obtained data and the geological information demonstrate a strong correlation between the GPR anomalies and the subsurface geology. Based upon the lateral and vertical velocity changes with depth, the thickness and orientation of the subsurface layers are outlined. Analysis of the exposed section shows good agreement between the estimated thicknesses of lithostratigraphic units and the quantitative assessment of the radar waves velocity inferred from GPR data.
Natural Hazards, 2014
Geological hazards and their effects are often geographically widespread. Consequently, their effective mapping and monitoring is best conducted using satellite and airborne imaging platforms to obtain broad scale, synoptic coverage. With a multitude of hazards and effects, potential data types, and processing techniques, it can be challenging to determine the best approach for mapping and monitoring. It is therefore critical to understand the spatial and temporal effects of any particular hazard on the environment before selecting the most appropriate data type/s and processing techniques to apply. This review is designed to assist the decision-making and selection process when embarking on a hazard mapping or monitoring exercise. It focuses on the application of optical, LiDAR, and synthetic aperture RADAR technologies for the assessment of pre-event risk and postevent damage. Geological hazards of global interest summarized here are landslides and erosion; seismic and tectonic hazards; ground subsidence; and flooding and tsunami.