The Experts below are selected from a list of 288 Experts worldwide ranked by ideXlab platform
Hiroaki Niitsuma - One of the best experts on this subject based on the ideXlab platform.
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shear wave splitting detected by using downhole triaxial seismic detector during dilation of artificial Subsurface Fracture
Geophysical Journal International, 2006Co-Authors: Hirokazu Moriya, Katsuro Tanaka, Hiroaki NiitsumaAbstract:SUMMARY A small change in traveltime and shear-wave splitting in elastic waves transmitted through a pressurized single Fracture has been detected through downhole triaxial cross-hole seismic measurements. A field experiment was carried out at Higashi‐Hachimantai Field of Tohoku University, Japan, where an artificial single Fracture had been created at 369 m by hydraulic fracturing in intact welded tuff. P and S waves transmitted through the pressurized single Fracture were measured by using a downhole three-component seismic detector installed in a borehole near the Fracture. In our previous studies, a small change in traveltime of about 0.1 ms was detected by using the cross-spectral moving window technique. In this recent study, the arrival times of split shear waves and the polarization directions were detected by using the wavelet transform of a three-component signal. The traveltime difference between the first and second shear waves was 0.05‐0.12 ms, when the wellhead pressure was increased up to 3.4 MPa and the incident angle of waves into the main Fracture was changed from 12 ◦ to 20 ◦ . A Fracture model of a single Fracture and a microcrack zone in the vicinity of the main Fracture was used to explain the shear-wave splitting phenomenon. The width of the reopening microcrack zone and the crack density were quantitatively evaluated by using the Fracture model and shear-wave splitting analysis. The best-fit theoretical curve to the observed data suggested that the width of the reopening zone was 0.8 m and the crack density was 0.39.
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study of microseismic doublet multiplet for evaluation of Subsurface Fracture system in soultz hdr field
2000Co-Authors: Hirokazu Moriya, Hiroaki Niitsuma, Katsuhiko Nakazato, Roy BariaAbstract:Reservoir structure of Soultz HDR field has been studied using doublet/multiplet. In this study, the reservoir structure characteristics are evaluated in detail using precise source location of induced microseismic doublet/multiplet, also the origin of multiplets is discussed. Microseismic events with similar waveforms have been corrected with the microseismic data set obtained during a hydraulic fracturing experiment in 1993, and the relative source locations have been determined by doublet analysis based on the cross spectrum analysis. The orientation of structural planes derived from hypocenter distributions of multiplets suggested that the dip angles of structural planes are changing with depth. The migration of seismic sources with time suggests that the doublet/multiplet tends to be located at the edge of the microseismic cloud.
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dispersion analysis of crack waves in an artificial Subsurface Fracture using two crack models
IEEE Transactions on Geoscience and Remote Sensing, 2000Co-Authors: K. Nagano, Hiroaki NiitsumaAbstract:The authors investigated crack-wave dispersions in an artificial Subsurface Fracture both experimentally and numerically using a wavelet analysis and two crack models. Crack-waves are seismic modes that propagate along a Fracture. The dispersion characteristics of crack-waves depend on the geometry and physical properties of a Fracture. The authors measured crack-waves at an artificial Subsurface Fracture in Higashi-Hachimantai Hot Dry Rock model field, Japan. This Subsurface Fracture is at a depth of about 370 m. During a measurement, they injected water into the Fracture and changed the interface conditions of the Fracture. A wavelet analysis provided the dispersion of the arrival times of crack-waves. The crack-waves showed positive velocity dispersion; i.e., low frequency components arrived later. As wellhead pressure increased due to water injection, the dispersion characteristics changed. A low-velocity-layer (LVL) model and a crack-stiffness model were examined to explain crack-wave dispersion. In the LVL model, rock layers with a low velocity surround a fluid layer. There is no contact between the LVLs. On the other hand, the crack-stiffness model considers crack stiffness due to contact between asperities on Fracture surfaces. The arrival-time curves calculated by the crack-stiffness model showed a good fit to the measured values. As wellhead pressure increased, crack stiffness decreased and thickness of a fluid layer increased. In contrast, the LVL model did not adequately duplicate the measured data.
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Crack-Wave Dispersion in an Opening Process of an Artificial Subsurface Fracture
61st EAGE Conference and Exhibition, 1999Co-Authors: K. Nagano, Hiroaki NiitsumaAbstract:We investigated crack-wave dispensions in an opening process of an artificial Subsurface Fracture.
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Subsurface Fracture measurement with polarimetric borehole radar
IEEE Transactions on Geoscience and Remote Sensing, 1999Co-Authors: Takashi Miwa, Motoyuki Sato, Hiroaki NiitsumaAbstract:A full-polarimetric borehole radar system is presented with combinations of dipole antennas and axial slot antennas and is applied to Subsurface Fracture measurement. First, to determine a scattering matrix from measurements with antennas having different antenna transfer functions between orthogonal polarizations, the authors present an antenna compensation algorithm that is achieved by an inverse filtering method with the antenna transfer functions experimentally determined by crosshole measurements. The results of crosshole and single-hole measurements carried out in granite at the Kamaishi Mine are shown to verify the proposed method. In the crosshole measurement, the authors find that the used dipole and slot antennas have almost the same radiation pattern and frequency dependency from 50 to 120 MHz. The transmission matrices through the host rock are the unit matrix for most paths, while depolarization is observed in some sections. Reflections from Subsurface Fractures show significant depolarization in the polarimetric single-hole reflection measurements. Using the scattering matrix, it is evaluated that Subsurface Fractures have a randomly isotropic rough surface for wavelengths between 1 and 2 m on the rotation of polarization basis.
Douglas W Burbank - One of the best experts on this subject based on the ideXlab platform.
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quantifying bedrock Fracture patterns within the shallow Subsurface implications for rock mass strength bedrock landslides and erodibility
Journal of Geophysical Research, 2011Co-Authors: Brian A Clarke, Douglas W BurbankAbstract:[1] The role of bedrock Fractures and rock mass strength is often considered a primary influence on the efficiency of surface processes and the morphology of landscapes. Quantifying bedrock characteristics at hillslope scales, however, has proven difficult. Here, we present a new field-based method for quantifying the depth and apparent density of bedrock Fractures within the shallow Subsurface based on seismic refraction surveys. We examine variations in Subsurface Fracture patterns in both Fiordland and the Southern Alps of New Zealand to better constrain the influence of bedrock properties in governing rates and patterns of landslides, as well as the morphology of threshold landscapes. We argue that intense tectonic deformation produces uniform bedrock fracturing with depth, whereas geomorphic processes produce strong Fracture gradients focused within the shallow Subsurface. Additionally, we argue that hillslope strength and stability are functions of both the intact rock strength and the density of bedrock Fractures, such that for a given intact rock strength, a threshold Fracture-density exists that delineates between stable and unstable rock masses. In the Southern Alps, tectonic forces have pervasively Fractured intrinsically weak rock to the verge of instability, such that the entire rock mass is susceptible to failure and landslides can potentially extend to great depths. Conversely, in Fiordland, tectonic fracturing of the strong intact rock has produced Fracture densities less than the regional stability threshold. Therefore, bedrock failure in Fiordland generally occurs only after geomorphic fracturing has further reduced the rock mass strength. This dependence on geomorphic fracturing limits the depths of bedrock landslides to within this geomorphically weakened zone.
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Quantifying bedrock‐Fracture patterns within the shallow Subsurface: Implications for rock mass strength, bedrock landslides, and erodibility
Journal of Geophysical Research, 2011Co-Authors: Brian A Clarke, Douglas W BurbankAbstract:[1] The role of bedrock Fractures and rock mass strength is often considered a primary influence on the efficiency of surface processes and the morphology of landscapes. Quantifying bedrock characteristics at hillslope scales, however, has proven difficult. Here, we present a new field-based method for quantifying the depth and apparent density of bedrock Fractures within the shallow Subsurface based on seismic refraction surveys. We examine variations in Subsurface Fracture patterns in both Fiordland and the Southern Alps of New Zealand to better constrain the influence of bedrock properties in governing rates and patterns of landslides, as well as the morphology of threshold landscapes. We argue that intense tectonic deformation produces uniform bedrock fracturing with depth, whereas geomorphic processes produce strong Fracture gradients focused within the shallow Subsurface. Additionally, we argue that hillslope strength and stability are functions of both the intact rock strength and the density of bedrock Fractures, such that for a given intact rock strength, a threshold Fracture-density exists that delineates between stable and unstable rock masses. In the Southern Alps, tectonic forces have pervasively Fractured intrinsically weak rock to the verge of instability, such that the entire rock mass is susceptible to failure and landslides can potentially extend to great depths. Conversely, in Fiordland, tectonic fracturing of the strong intact rock has produced Fracture densities less than the regional stability threshold. Therefore, bedrock failure in Fiordland generally occurs only after geomorphic fracturing has further reduced the rock mass strength. This dependence on geomorphic fracturing limits the depths of bedrock landslides to within this geomorphically weakened zone.
J. A. Rial - One of the best experts on this subject based on the ideXlab platform.
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an inversion scheme to model Subsurface Fracture systems using shear wave splitting polarization and delay time observations simultaneously
Geophysical Journal International, 2005Co-Authors: Ming Yang, Maya Elkibbi, J. A. RialAbstract:SUMMARY Shear wave splitting polarization (p) and delay time (Δt) observations are used to invert for Fracture orientation and intensity of fracturing, simultaneously. By addressing the different levels of uncertainty involved in measurements of these two parameters, as well as their dissimilar relationships to Fracture configuration, we have developed an inversion algorithm which reduces the primary double-response inversion to two connected single-response ones. We show that its inherent non-linearity complicates this problem, which therefore requires a more sophisticated attack than conventional inversion schemes. It will be shown that the construction of residue function contours in the model plane and the generation of surrogate data by simulation process are essential to this approach. We illustrate the capabilities of this technique by inverting shear wave splitting data from The Geysers geothermal reservoir in California. In principle the method should be useful for characterizing Fractured reservoirs, whether geothermal or hydrocarbon.
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Shear-wave splitting and reservoir crack characterization: the Coso geothermal field
Journal of Volcanology and Geothermal Research, 2002Co-Authors: Gordana Vlahovic, Maya Elkibbi, J. A. RialAbstract:Abstract This paper aims to improve current understanding of the Subsurface Fracture system in the Coso geothermal field, located in east-central California. The Coso reservoir is in active economic development, so that knowledge of the Subsurface Fracture system is of vital importance for an accurate evaluation of its geothermal potential and day-to-day production. To detect the geometry and density of Fracture systems we applied the shear-wave splitting technique to a large number of high-quality seismograms from local microearthquakes recorded by a permanent, 16-station, down-hole, 3-component seismic array running at 480 samples/s. The analysis of shear-wave splitting (seismic birefringence) provides parameters directly related to the strike of the Subsurface Fractures and their density (number of cracks per unit volume), and, consequently, is an important technique to outline zones of high permeability. Three major Fracture directions N10–30W, N0–20E, and N40–50E, of which the first and the second are the most prominent, were identified from the seismograms recorded by the 16-station down-hole array. All orientations are consistent with the known strike of local sets of faults and Fractures in local wells and at the surface, as well as with previous analyses of seismic anisotropy in the region. The high quality of the recordings has allowed us to launch an unprecedented investigation into the characteristics of the temporal variations in crack polarization and crack density in a producing geothermal environment. Preliminary results point to significant temporal changes in shear-wave time delays, probably influenced by temporal changes in crack density within a period of 5 years (1996–2000). They are tentatively interpreted as due to a local ∼3% increase in shear-wave velocity in the southwestern part of the field during 1999.
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Characterization of geothermal reservoir crack patterns using shear-wave splitting
GEOPHYSICS, 1997Co-Authors: Min Lou, J. A. RialAbstract:Microearthquakes recorded by a downhole, three-component seismic network deployed around the Coso, California, geothermal reservoir since 1992 display distinctive shear-wave splitting and clear polarization directions. From the polarizations we estimated three predominant Subsurface Fracture directions, and from the time delays of the split waves we determined tomographically the 3-D Fracture density distribution in the reservoir.
Motoyuki Sato - One of the best experts on this subject based on the ideXlab platform.
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Geophysical assessment of the hydraulic property of the Fracture systems around Lake Nasser-Egypt: In sight of polarimetric borehole radar
NRIAG Journal of Astronomy and Geophysics, 2014Co-Authors: Khamis Mansour, Alhussein A. Basheer, Taha Rabeh, Ahmed Khalil, A.a. Essam Eldin, Motoyuki SatoAbstract:Abstract Hydraulic property of the Subsurface structures is a complicated mission. In this work, the polarimetric analysis for the measured dataset applied by the polarimetric borehole radar system in order to delineate the characteristics of Subsurface Fractures. Two different locations in USA and Egypt were selected to perform our investigation. The first polarimetric dataset has been acquired at Mirror Lake, USA which is well known as a standard site for testing the hydraulic properties of Subsurface Fractures (Sato et al., 1999). The results show the presence of nine Fracture zones in one borehole FSE-1. The hydraulic properties were detected and the Subsurface Fractures were differentiated into four categories Fracture zones after deriving the radar polarimetric analysis of alpha, entropy and anisotropy parameters at 30 MHz frequency. The Fracture zones at 24.75, 47.8 and 55.2 m depths have the highest hydraulic transmissivity while the Fracture zones at 28.5, 36.15 m have the lowest hydraulic transmissivity. These results show a good consistency with the hydraulic permeability tracer test and the structures exist in the area. Similarly, we used the same technique to characterize the Subsurface Fracture systems detected by geoelectric and geomagnetic methods around Lake Nasser in Egypt using the previous results of Mirror Lake as a key guide. The results show a great correlation with detected structures prevailed in the sedimentary and basement rocks. These results illustrate an ideal explanation for the prevailed Subsurface structures and the recharging of the main Nubian sandstone aquifer from Lake Nasser. Also, these results also show that the northeast Fracture zone trends are most probably having the highest hydraulic transmissivity whereas the northwest Fracture zones have the lowest one. The integration of surface geophysical measurements with the polarimetric borehole radar and the polarimetric analysis of its datasets introduce better understanding of the recharging mechanism between surface water and the Subsurface aquifer and also can be used as clue for identifying the Subsurface structures for different areas.
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Subsurface Fracture characterisation using full polarimetric borehole radar data analysis with numerical simulation validation
Exploration Geophysics, 2012Co-Authors: Khamis Mansour, Motoyuki SatoAbstract:We report on the utilisation of a full polarimetric Subsurface borehole radar measuring system for efficient characterisation of Subsurface Fractures. This system can measure the full polarisation (HH, HV, VV and VH) of electromagnetic waves for one borehole, and thus enables us to obtain more information about Subsurface Fractures compared to that obtained from conventional borehole radar systems, which usually use only single polarisation. Polarimetric datasets have been acquired at several sites, particularly at Mirror Lake, USA, which is a well known site for testing Subsurface Fractures. Nine Fracture sets were observed in one borehole, FSE-1, in the Mirror Lake site. These were divided into four category Fracture sets depending on polarimetric analysis of alpha, entropy and anisotropy decomposition analysis of scattering behaviour from Fractures at frequency 30 MHz. We found that the characterised four Fractures sets have the highest hydraulic permeable zones at depths of 24.75 m, and 47.80 m. The lowest hydraulic permeable zones were found to be at 28.50 m, 36.15 m and 44.80 m. These results show a good consistency with the hydraulic Fractures permeability tracer test that was done by USGS. To validate these conclusions we implemented numerical simulation for a synthesised Fractures property using the Finite Difference Time Domain (FDTD) method. Here, we used a plane wave as an electromagnetic source with frequency ranging from 1 MHz to 200 MHz, and monitored the electromagnetic scattering for various Fractures. We found that distributions of alpha, entropy and anisotropy polarimetric parameters differ with the Fracture roughness property which validates the polarimetric analysis of the measured data.
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Consistency Analysis of Subsurface Fracture Characterization Using Different Polarimetry Techniques by a Borehole Radar
IEEE Geoscience and Remote Sensing Letters, 2007Co-Authors: Jian-guo Zhao, Motoyuki SatoAbstract:We present a fully polarimetric borehole radar in conjunction with radar polarimetry, Pauli decomposition, and H-alpha decomposition techniques to carry out physical characterization of Subsurface Fractures. Further tests are needed to validate the applicability of radar polarimetry analysis for physical characterization of Subsurface targets. Toward this goal, we present the implementation of two other decomposition techniques, namely: (1) the Durden-Freeman decomposition and (2) polarimetric anisotropy parameter methods, in the context of previous research and examine the consistency of results using various polarimetric decomposition techniques. While results from the radar polarimetry decomposition were found to depend greatly upon the kind of physical or mathematical models, these techniques seem to provide comparable performances in terms of Fracture characterization and classification.
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Subsurface water filled Fracture detection by borehole radar a case history
International Geoscience and Remote Sensing Symposium, 2005Co-Authors: Sixin Liu, Zhaofa Zeng, Motoyuki SatoAbstract:Borehole radar is a special mode of ground penetrating radar. It has several distinguished features from surface radar. For examples, by means of borehole access to deep regions below the surface, the radar sonde can be located relatively close to the anomalies or targets to be measured, this results in more precise targets response than surface measurement. The experimental site is located on the top of a granite hill west of Beijing, China. There are a group of boreholes intersected by many Fractures. The measured single-hole reflection data are processed and interpreted. The radial detecting range is more than 30 meters at this site. The Subsurface Fracture distribution can be imaged very clearly. Many Fractures can be "seen", and their distance from borehole and their dip angle can be determined. The azimuth determinations for these Fractures are possible in some situations. It is concluded that the borehole radar is an effective tool for Subsurface imaging.
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Radar polarimetry for Subsurface imaging
Multispectral and Hyperspectral Image Acquisition and Processing, 2001Co-Authors: Motoyuki SatoAbstract:The use of radar polarimetry for Subsurface sensing is introduced in this paper. We developed a polarimetric borehole radar, which can acquire the full-polarimetric radar profile in a borehole. The measured profile showed that Subsurface Fracture characteristics can be obtained from the polarimetric analysis. This information is closely related to Subsurface Fracture characteristics, which cannot directly be imaged by conventional radar.
Brian A Clarke - One of the best experts on this subject based on the ideXlab platform.
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quantifying bedrock Fracture patterns within the shallow Subsurface implications for rock mass strength bedrock landslides and erodibility
Journal of Geophysical Research, 2011Co-Authors: Brian A Clarke, Douglas W BurbankAbstract:[1] The role of bedrock Fractures and rock mass strength is often considered a primary influence on the efficiency of surface processes and the morphology of landscapes. Quantifying bedrock characteristics at hillslope scales, however, has proven difficult. Here, we present a new field-based method for quantifying the depth and apparent density of bedrock Fractures within the shallow Subsurface based on seismic refraction surveys. We examine variations in Subsurface Fracture patterns in both Fiordland and the Southern Alps of New Zealand to better constrain the influence of bedrock properties in governing rates and patterns of landslides, as well as the morphology of threshold landscapes. We argue that intense tectonic deformation produces uniform bedrock fracturing with depth, whereas geomorphic processes produce strong Fracture gradients focused within the shallow Subsurface. Additionally, we argue that hillslope strength and stability are functions of both the intact rock strength and the density of bedrock Fractures, such that for a given intact rock strength, a threshold Fracture-density exists that delineates between stable and unstable rock masses. In the Southern Alps, tectonic forces have pervasively Fractured intrinsically weak rock to the verge of instability, such that the entire rock mass is susceptible to failure and landslides can potentially extend to great depths. Conversely, in Fiordland, tectonic fracturing of the strong intact rock has produced Fracture densities less than the regional stability threshold. Therefore, bedrock failure in Fiordland generally occurs only after geomorphic fracturing has further reduced the rock mass strength. This dependence on geomorphic fracturing limits the depths of bedrock landslides to within this geomorphically weakened zone.
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Quantifying bedrock‐Fracture patterns within the shallow Subsurface: Implications for rock mass strength, bedrock landslides, and erodibility
Journal of Geophysical Research, 2011Co-Authors: Brian A Clarke, Douglas W BurbankAbstract:[1] The role of bedrock Fractures and rock mass strength is often considered a primary influence on the efficiency of surface processes and the morphology of landscapes. Quantifying bedrock characteristics at hillslope scales, however, has proven difficult. Here, we present a new field-based method for quantifying the depth and apparent density of bedrock Fractures within the shallow Subsurface based on seismic refraction surveys. We examine variations in Subsurface Fracture patterns in both Fiordland and the Southern Alps of New Zealand to better constrain the influence of bedrock properties in governing rates and patterns of landslides, as well as the morphology of threshold landscapes. We argue that intense tectonic deformation produces uniform bedrock fracturing with depth, whereas geomorphic processes produce strong Fracture gradients focused within the shallow Subsurface. Additionally, we argue that hillslope strength and stability are functions of both the intact rock strength and the density of bedrock Fractures, such that for a given intact rock strength, a threshold Fracture-density exists that delineates between stable and unstable rock masses. In the Southern Alps, tectonic forces have pervasively Fractured intrinsically weak rock to the verge of instability, such that the entire rock mass is susceptible to failure and landslides can potentially extend to great depths. Conversely, in Fiordland, tectonic fracturing of the strong intact rock has produced Fracture densities less than the regional stability threshold. Therefore, bedrock failure in Fiordland generally occurs only after geomorphic fracturing has further reduced the rock mass strength. This dependence on geomorphic fracturing limits the depths of bedrock landslides to within this geomorphically weakened zone.
