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Chandong Chang – One of the best experts on this subject based on the ideXlab platform.

  • present day stress states underneath the kumano basin to 2 km below seafloor based on Borehole Wall failures at iodp site c0002 nankai accretionary wedge
    Geochemistry Geophysics Geosystems, 2016
    Co-Authors: Chandong Chang, Insun Song
    Abstract:

    We constrain the state of stress to 2 km below seafloor in the Nankai accretionary prism at the Integrated Ocean Drilling Program (IODP) site C0002F, southwest Japan, based on Borehole Wall failures and rock strengths. The logging-while-drilling resistivity images from 872.5 to 2005.5 meters below seafloor show that drilling-mud control in riser drilling worked properly to minimize Borehole Wall failures. Available breakouts indicate a consistent maximum compression orientation subparallel to the subducting plate margin. Breakout analysis with drill logs suggests that breakouts occurred only when Borehole pressure was slightly lowered and time lag between hole cutting and image logging was several hours. This indicates that the observed breakouts are not immediate stress-induced failure, but brought up into shape gradually with time due to other mechanisms. Laboratory investigations on deformation and failure of the cores suggest that the time-delayed breakout might be a result of progressive rock spall-out in Borehole Wall damage zones that occur at a stress level close to failure condition. We constrain stress magnitudes assuming that the stress state is sufficient to bring about the damage zones at the Borehole Wall. An integrated method utilizing breakouts, drilling-induced tensile fractures, and a leak-off test suggests that the stress states are on the boundary between strike-slip faulting and normal faulting stress regimes, and somewhat variable depending on depth. The stress magnitudes in the accretionary wedge appear to be controlled by frictional strength of the rock, such that the differential stresses are constrained by the laboratory determined frictional coefficients. This article is protected by copyright. All rights reserved.

  • effect of anisotropic Borehole Wall failures when estimating in situ stresses a case study in the nankai accretionary wedge
    Marine and Petroleum Geology, 2013
    Co-Authors: Chandong Chang, Insun Song
    Abstract:

    Abstract Breakouts observed in a vertical Borehole (C0002A) drilled through two major tectonic sedimentary formations consisting of forearc basin (upper) and accretionary prism (lower) sediments in the Nankai accretionary wedge, Japan, exhibit distinctive geometric features in respective formations. Breakouts in the lower accretionary prism sediments are markedly wider than those in the forearc basin sediments, and breakout azimuths in the two units are horizontally rotated relative to one another. Breakout azimuths are widely used as a proxy for the determination of principal stress directions. However, strength anisotropies related to the presence of bedding planes may affect both breakout azimuths and widths, which can result in misleading in situ stress interpretations. While thinly bedded mudstones are the dominant lithology in both the forearc basin and accretionary prism sediments, bedding planes in the accretionary prism sediments are relatively steeper than those in the forearc basin sediments, with possible implications for breakout geometry and interpretations of principal stress directions. To investigate the effects of bedding planes on breakout geometry (azimuth and width), we conducted Borehole Wall failure analyses using a weak-plane failure model that incorporates material strength anisotropies. The model results show that breakout widths and orientations are strongly affected by steeply dipping (>40°) bedding planes in cases where dip directions are unaligned with the principal stress orientation. Our theoretical results suggest that variations in breakout azimuths in the C0002A site may be associated with bedding plane related strength anisotropy, and not associated with the rotation of stress field. That is, stress orientation is consistent throughout the Borehole (down to the bottom-hole depth of 1495 m below sea floor). In addition, disregarding the effects of bedding planes tends to yield an overestimation of in situ stress magnitude.

  • in situ stress state in the nankai accretionary wedge estimated from Borehole Wall failures
    Geochemistry Geophysics Geosystems, 2010
    Co-Authors: Chandong Chang, Lisa C. Mcneill, Casey J Moore, Marianne Conin, Yasuhiro Yamada
    Abstract:

    We constrain the orientations and magnitudes of in situ strestress tenstensors using Borehole Wall failures (Borehole breakouts and drilling-induced tensile fractures) detected in four vertical Boreholes (C0002, C0001, C0004, and C0006 from NW to SE) drilled in the Nankai accretionary wedge. The directions of the maximum horizontal principal stress (SHmax), indicated by the azimuths of Borehole Wall failures, are consistent in individual holes, but those in C0002 (margin-parallel SHmax) are nearly perpendicular to those in all other holes (margin-normal SHmax). Constrained stress magnitudes in C0001 and C0002, using logged breakout widths combined with empirical rock strength derived from sonic velocity, as well as the presence of the drilling-induced tensile fractures, suggest that the stress state in the shallow portion of the wedge (fore-arc basin and slope sediment formations) is predominantly in favor of normal faulting and that the stress state in the deeper accretionary prism is in favor of probable strike-slip faulting or possible reverse faulting. Thus, the stress regime appears to be divided with depth by the major geological boundaries such as unconformities or thrust faults. The margin-perpendicular tectonic stress components in the two adjacent sites, C0001 and C0002, are different, suggesting that tectonic force driven by the plate pushing of the Philippine Sea plate does not uniformly propagate. Rather, the stress field is inferred to be influenced by additional factors such as local deformation caused by gravitation-driven extension in the fore arc and thrusting and bending within individual geologic domains.

Insun Song – One of the best experts on this subject based on the ideXlab platform.

  • present day stress states underneath the kumano basin to 2 km below seafloor based on Borehole Wall failures at iodp site c0002 nankai accretionary wedge
    Geochemistry Geophysics Geosystems, 2016
    Co-Authors: Chandong Chang, Insun Song
    Abstract:

    We constrain the state of stress to 2 km below seafloor in the Nankai accretionary prism at the Integrated Ocean Drilling Program (IODP) site C0002F, southwest Japan, based on Borehole Wall failures and rock strengths. The logging-while-drilling resistivity images from 872.5 to 2005.5 meters below seafloor show that drilling-mud control in riser drilling worked properly to minimize Borehole Wall failures. Available breakouts indicate a consistent maximum compression orientation subparallel to the subducting plate margin. Breakout analysis with drill logs suggests that breakouts occurred only when Borehole pressure was slightly lowered and time lag between hole cutting and image logging was several hours. This indicates that the observed breakouts are not immediate stress-induced failure, but brought up into shape gradually with time due to other mechanisms. Laboratory investigations on deformation and failure of the cores suggest that the time-delayed breakout might be a result of progressive rock spall-out in Borehole Wall damage zones that occur at a stress level close to failure condition. We constrain stress magnitudes assuming that the stress state is sufficient to bring about the damage zones at the Borehole Wall. An integrated method utilizing breakouts, drilling-induced tensile fractures, and a leak-off test suggests that the stress states are on the boundary between strike-slip faulting and normal faulting stress regimes, and somewhat variable depending on depth. The stress magnitudes in the accretionary wedge appear to be controlled by frictional strength of the rock, such that the differential stresses are constrained by the laboratory determined frictional coefficients. This article is protected by copyright. All rights reserved.

  • effect of anisotropic Borehole Wall failures when estimating in situ stresses a case study in the nankai accretionary wedge
    Marine and Petroleum Geology, 2013
    Co-Authors: Chandong Chang, Insun Song
    Abstract:

    Abstract Breakouts observed in a vertical Borehole (C0002A) drilled through two major tectonic sedimentary formations consisting of forearc basin (upper) and accretionary prism (lower) sediments in the Nankai accretionary wedge, Japan, exhibit distinctive geometric features in respective formations. Breakouts in the lower accretionary prism sediments are markedly wider than those in the forearc basin sediments, and breakout azimuths in the two units are horizontally rotated relative to one another. Breakout azimuths are widely used as a proxy for the determination of principal stress directions. However, strength anisotropies related to the presence of bedding planes may affect both breakout azimuths and widths, which can result in misleading in situ stress interpretations. While thinly bedded mudstones are the dominant lithology in both the forearc basin and accretionary prism sediments, bedding planes in the accretionary prism sediments are relatively steeper than those in the forearc basin sediments, with possible implications for breakout geometry and interpretations of principal stress directions. To investigate the effects of bedding planes on breakout geometry (azimuth and width), we conducted Borehole Wall failure analyses using a weak-plane failure model that incorporates material strength anisotropies. The model results show that breakout widths and orientations are strongly affected by steeply dipping (>40°) bedding planes in cases where dip directions are unaligned with the principal stress orientation. Our theoretical results suggest that variations in breakout azimuths in the C0002A site may be associated with bedding plane related strength anisotropy, and not associated with the rotation of stress field. That is, stress orientation is consistent throughout the Borehole (down to the bottom-hole depth of 1495 m below sea floor). In addition, disregarding the effects of bedding planes tends to yield an overestimation of in situ stress magnitude.

Shaofeng Li – One of the best experts on this subject based on the ideXlab platform.

Thomas Berlage – One of the best experts on this subject based on the ideXlab platform.

  • multi class supervised classification of electrical Borehole Wall images using texture features
    Computers & Geosciences, 2011
    Co-Authors: Matthias Jungmann, Christoph Clauser, Margarete Kopal, Thomas Berlage
    Abstract:

    Electrical Borehole Wall images represent micro-resistivity measurements at the Borehole Wall. The lithology reconstruction is often based on visual interpretation done by geologists. This analysis is very time-consuming and subjective. Different geologists may interpret the data differently. In this work, linear discdiscriminantlysis (LDA) in combination with texture features is used for an automated lithology reconstruction of ODP (Ocean Drilling Program) Borehole 1203A drilled during Leg 197. Six rock groups are identified by their textural properties in resistivity data obtained by a Formation MircoScanner (FMS). Although discriminant analysis can be used for multi-class classification, non-optimal decision criteria for certain groups could emerge. For this reason, we use a combination of 2-class (binary) classifiers to increase the overall classification accuracy. The generalization ability of the combined classifiers is evaluated and optimized on a testing dataset where a classification rate of more than 80% for each of the six rock groups is achieved. The combined, trained classifiers are then applied on the whole dataset obtaining a statistical reconstruction of the logged formation. Compared to a single multi-class classifier the combined binary classifiers show better classification results for certain rock groups and more stable results in larger intervals of equal rock type.

  • rock classification based on resistivity patterns in electrical Borehole Wall images
    Journal of Geophysics and Engineering, 2007
    Co-Authors: M. Linek, Matthias Jungmann, Renate Pechnig, Thomas Berlage, Christoph Clauser
    Abstract:

    Electrical Borehole Wall images represent grey-level-coded micro-resistivity measurements at the Borehole Wall. Different scientific methods have been implemented to transform image data into quantitative log curves. We introduce a pattern recognition technique applying texture analysis, which uses second-order statistics based on studying the occurrence of pixel pairs. We calculate so-called Haralick texture features such as contrast, energy, entropy and homogeneity. The supervised classification method is used for assigning characteristic texture features to different rock classes and assessing the discriminative power of these image features. We use classifiers obtained from training intervals to characterize the entire image data set recovered in ODP hole 1203A. This yields a synthetic lithology profile based on computed texture data. We show that Haralick features accurately classify 89.9% of the training intervals. We obtained misclassification for vesicular basaltic rocks. Hence, further image analysis tools are used to improve the classification reliability. We decompose the 2D image signal by the application of wavelet transformation in order to enhance image objects horizontally, diagonally and vertically. The resulting filtered images are used for further texture analysis. This combined classification based on Haralick features and wavelet transformation improved our classification up to a level of 98%. The application of wavelet transformation increases the consistency between standard logging profiles and texture-derived lithology. Texture analysis of Borehole Wall images offers the potential to facilitate objective analysis of multiple Boreholes with the same lithology.

  • Automatic Rock Classification Based on Texture Analysis in Electrical Borehole Wall Images
    68th EAGE Conference and Exhibition incorporating SPE EUROPEC 2006, 2006
    Co-Authors: M. Linek, Matthias Jungmann, Renate Pechnig, Thomas Berlage, Christoph Clauser
    Abstract:

    Electrical Borehole Wall images are widely used for Borehole inspection and reservoir characterization. So far, this data is mostly qualitatively used to investigate structure and lithology mapping. We present a method for image characterization which is based on the application of texture analysis in order to transform image data into quantitative log curves. We derive so-called Haralick texture features from Borehole Wall images. Based on a supervised classification technique, we train texture features within assigned rock classes, determine their classifiers, and apply classification function on the entire data set. This enable automatic rock determination based on quantitative image data.

Yasuhiro Yamada – One of the best experts on this subject based on the ideXlab platform.

  • Small-scale stress fluctuations in Borehole breakouts and their implication in identifying potential active faults around the seismogenic megasplay fault, Nankai Trough, SW Japan
    Earth Planets and Space, 2015
    Co-Authors: Yasuhiro Yamada, Jun Shibanuma
    Abstract:

    Borehole breakouts are enlargements and elongation of a Borehole in a particular direction, caused by failure of the Borehole Wall rock due to concentration of stresses around the Borehole, and thus, have been widely used to determine the in situ stress orientation. We used electrical Borehole Wall images obtained during offshore scientific drilling (IODP) that penetrated through a seismogenic megasplay fault in the Nankai Trough, off SW Japan, and extracted a number of Borehole breakouts. Most of the breakouts show directions that can be explained by the regional convergence, but some are obviously rotated by faults and fractures in the megasplay fault zone and in its hanging Wall. Stress magnitudes estimated from the width of the breakouts also show some decrease in the horizontal stresses, suggesting that slip along the faults and fractures release shear stress affecting these surfaces. Since such surfaces may have the capability to reactivate where the stresses affecting the surface are geometrically appropriate, the method presented in this paper may contribute to identifying active fault surfaces. This knowledge allows us to identify which surfaces need to be examined in detail to assess their potential for future activity.

  • in situ stress state in the nankai accretionary wedge estimated from Borehole Wall failures
    Geochemistry Geophysics Geosystems, 2010
    Co-Authors: Chandong Chang, Lisa C. Mcneill, Casey J Moore, Marianne Conin, Yasuhiro Yamada
    Abstract:

    We constrain the orientations and magnitudes of in situ stress tensors using Borehole Wall failures (Borehole breakouts and drilling-induced tensile fractures) detected in four vertical Boreholes (C0002, C0001, C0004, and C0006 from NW to SE) drilled in the Nankai accretionary wedge. The directions of the maximum horizontal principal stress (SHmax), indicated by the azimuths of Borehole Wall failures, are consistent in individual holes, but those in C0002 (margin-parallel SHmax) are nearly perpendicular to those in all other holes (margin-normal SHmax). Constrained stress magnitudes in C0001 and C0002, using logged breakout widths combined with empirical rock strength derived from sonic velocity, as well as the presence of the drilling-induced tensile fractures, suggest that the stress state in the shallow portion of the wedge (fore-arc basin and slope sediment formations) is predominantly in favor of normal faulting and that the stress state in the deeper accretionary prism is in favor of probable strike-slip faulting or possible reverse faulting. Thus, the stress regime appears to be divided with depth by the major geological boundaries such as unconformities or thrust faults. The margin-perpendicular tectonic stress components in the two adjacent sites, C0001 and C0002, are different, suggesting that tectonic force driven by the plate pushing of the Philippine Sea plate does not uniformly propagate. Rather, the stress field is inferred to be influenced by additional factors such as local deformation caused by gravitation-driven extension in the fore arc and thrusting and bending within individual geologic domains.