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3D continuum and discontinuum modeling of coring and overcoring: impact of in situ stress magnitude and borehole orientation on micro-cracking
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DOI：10.1016/j.compgeo.2026.108500.png)
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Abstract
En 中文
Drilling changes the state of stress within the core. In high stress environments, this may cause micro-cracking within the core, which may, in turn, affect the properties of rock obtained from laboratory testing. This study examines the impact of in situ stress magnitude and borehole orientation on stress changes and associated micro-cracking during coring and overcoring. This research was conducted based on the well-documented case of the Underground Research Laboratory (URL) in Canada. For this purpose, continuum and discontinuum numerical methods were employed to simulate core damage in vertical and horizontal boreholes, and overcoring in horizontal boreholes at three stress domains at the URL. First, elastic stresses within the core during core drilling and overcoring were obtained using 3D continuum models. The induced stresses were compared to the crack initiation stress level and tensile strength of Lac du Bonnet (LdB) granite to assess the potential for damage. As expected, the induced stresses at the 240 and 420 Levels of the URL demonstrated potential for damage. Next, the Voronoi tessellation technique was used to generate a 3D grain structure in a discontinuum model to assess the impact of grain geometric heterogeneity on micro-cracking caused by coring and overcoring. The modeling results showed no damage at the 130 Level but increased damage, predominantly tensile micro-cracks, with increasing sampling depth. Fewer micro-cracks were found in cored and overcored samples drilled parallel to the major principal stress compared to other borehole orientations. It is concluded from modeling results that coring and overcoring should be conducted parallel to the major principal stress to reduce the impact of drilling-induced damage on laboratory properties of rock and in situ stress measurement results.
Keywords:
Core damage
Overcoring
Micro-cracks
Stress path
Underground Research Laboratory (URL)
Bonded Block Model (BBM)
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IF:
6.2
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7.0K
Citations:
2.9W
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