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Borehole Wall

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Chandong Chang – 1st expert 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 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.

Insun Song – 2nd expert 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 – 3rd expert on this subject based on the ideXlab platform

  • analysis on the transient heat transfer process inside and outside the Borehole for a vertical u tube ground heat exchanger under short term heat storage
    Renewable Energy, 2016
    Co-Authors: Yan Shang, Xiangli Li, Shaofeng Li

    Abstract:

    A three-dimensional unsteady model is established to study the heat transfer performance for a vertical U-tube ground heat exchanger (GHE). The transient heat transfer process between the inside and outside of the Borehole under short-term heat storage is analyzed. The results indicate that the soil temperature field in the depth direction at the center section is distributed in a “narrow belt shape”. The thermal interference distance of the ground heat exchanger under short-term heat storage is within a radius of 1 m, while the main heat transfer field is within a radius of 0.4 m. The inside Borehole temperature field is dominated by the inlet branch of the U-tube, and it gradually becomes uniform as the heat storage time increases. For the temperature difference between the inside and outside of the Borehole, the longer the heat storage time is, the greater the temperature difference between the Borehole Wall and the surrounding soil is and the lower the temperature difference between the fluid in the U-tube and the Borehole Wall is. At the same time, the change in temperature difference between the surrounding soil and the more distant boundary soil is not obvious.