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| Titel |
Experimental Measurement of In Situ Stress |
| VerfasserIn |
Maria Tibbo, Bernd Milkereit, Farzine Nasseri, Douglas Schmitt, Paul Young |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250129486
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| Publikation (Nr.) |
 EGU/EGU2016-9609.pdf |
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| Zusammenfassung |
| The World Stress Map data is determined by stress indicators including earthquake focal
mechanisms, in situ measurement in mining, oil and gas boreholes as well as the
borehole cores, and geologic data. Unfortunately, these measurements are not only
infrequent but sometimes infeasible, and do not provide nearly enough data points
with high accuracy to correctly infer stress fields in deep mines around the world.
Improvements in stress measurements of Earth’s crust is fundamental to several industries
such as oil and gas, mining, nuclear waste management, and enhanced geothermal
systems.
Quantifying the state of stress and the geophysical properties of different rock types is a
major complication in geophysical monitoring of deep mines. Most stress measurement
techniques involve either the boreholes or their cores, however these measurements usually
only give stress along one axis, not the complete stress tensor. The goal of this project is to
investigate a new method of acquiring a complete stress tensor of the in situ stress in the
Earth’s crust.
This project is part of a comprehensive, exploration geophysical study in a deep, highly
stressed mine located in Sudbury, Ontario, Canada, and focuses on two boreholes located in
this mine. These boreholes are approximately 400 m long with NQ diameters and are located
at depths of about 1300 - 1600 m and 1700 - 2000 m. Two borehole logging surveys were
performed on both boreholes, October 2013 and July 2015, in order to perform a time-lapse
analysis of the geophysical changes in the mine. These multi-parameter surveys
include caliper, full waveform sonic, televiewer, chargeability (IP), and resistivity.
Laboratory experiments have been performed on borehole core samples of varying
geologies from each borehole. These experiments have measured the geophysical
properties including elastic modulus, bulk modulus, P- and S-wave velocities, and
density.
The apparatus’ used for this project are geophysical imaging cells capable of hydrostatic
stress (σ1 = σ2 = σ3), differential stress (σ1 > σ2 = σ3), and the unique true triaxial
stress (σ1 > σ2 > σ3). Velocity surveys can be acquired along all three axes, and
therefore the effects of σ1,σ2,σ3 on the velocity-stress curve can be obtained.
These geophysical cells are being used to reproduce the borehole P- and S-wave
velocities by altering the differential stress, allowing for the unique position of
determining the stress tensor. Currently, results have been obtained for differential stress
(σ1 > σ2 = σ3), and true triaxial experiments will determine if σ3 is the missing factor to
reproducing the borehole velocities. This project is the first to combine time - lapse
borehole logging data and experimental laboratory data to infer a complete stress
tensor. |
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