The effect of sample disturbance on laboratory properties of Lac du Bonnet granite

1994 ◽  
Vol 31 (5) ◽  
pp. 692-702 ◽  
Author(s):  
C. Derek Martin ◽  
Brian Stimpson
Keyword(s):  
In Situ Stress ◽  
P Wave ◽  
Confining Stress ◽  
Near Surface ◽  
Brittle Rocks ◽  
Frictional Properties ◽  
Stress Dependent ◽  
Sample Disturbance ◽  
Core Discing

Laboratory properties of Lac du Bonnet granite samples collected at depths ranging from near-surface to 1000 m were established. The laboratory properties indicated that either the in situ properties were changing with depth or the samples were changing with depth. Comparison of P-wave velocities in the samples and in situ confirmed the latter, i.e., sample disturbance was affecting the laboratory properties. The strength of the damaged samples indicated that sample disturbance affected the cohesion of the material, not the frictional properties, and that the cohesion loss cannot be accounted for, by applying a confining stress. Sample disturbance started to affect the laboratory properties of Lac du Bonnet granite when the maximum far-field in situ stress exceeded about 10% of the unconfined compression strength. Key words : sample disturbance, core discing, cohesion, brittle rocks, damage, microcracks, stress-dependent Young's modulus.

Effects of sample disturbance on the stress-induced microfracturing characteristics of brittle rock

1999 ◽  
Vol 36 (2) ◽  
pp. 239-250 ◽  
Author(s):  
E Eberhardt ◽  
D Stead ◽  
B Stimpson
Keyword(s):  
Crack Initiation ◽  
Elastic Stiffness ◽  
In Situ Stress ◽  
Brittle Rock ◽  
Stress Threshold ◽  
Fracture Crack ◽  
Sample Disturbance ◽  
Underground Research Laboratory ◽  
Stress Domains

The effects of sampling disturbance on the laboratory-derived mechanical properties of brittle rock were measured on cored samples of Lac du Bonnet granite taken from three different in situ stress domains at the Underground Research Laboratory of Atomic Energy of Canada Limited. A variety of independent measurements and scanning electron microscope observations demonstrate that stress-induced sampling disturbance increased with increasing in situ stresses. The degree of damage was reflected in laboratory measurements of acoustic velocity and elastic stiffness. Examination of the stress-induced microfracturing characteristics during uniaxial compression of the samples revealed that the degree of sampling disturbance had only minor effects on the stress levels at which new cracks were generated (i.e., the crack initiation stress threshold). Crack-coalescence and crack-damage thresholds, on the other hand, significantly decreased with increased sampling disturbance. The presence of numerous stress-relief cracks in the samples retrieved from the highest in situ stress domains was seen to weaken the rock by providing an increased number of planes of weakness for active cracks to propagate along. A 36% strength decrease was seen in samples retrieved from the highest in situ stress domain (sigma1 - sigma3 approximate 40 MPa) as compared with those taken from the lowest in situ stress domain (sigma1 - sigma3 approximate 10 MPa).Key words: sample disturbance, brittle fracture, crack initiation, crack propagation, material properties, rock failure.

scholarly journals The Role of In Situ Stress in Organizing Flow Pathways in Natural Fracture Networks at the Percolation Threshold

Geofluids ◽  
2019 ◽  
Vol 2019 ◽  
pp. 1-14 ◽  
Author(s):  
Chuanyin Jiang ◽  
Xiaoguang Wang ◽  
Zhixue Sun ◽  
Qinghua Lei
Keyword(s):  
Fluid Flow ◽  
Percolation Threshold ◽  
Fractured Reservoirs ◽  
Fracture Network ◽  
In Situ Stress ◽  
Natural Fracture ◽  
Fracture Aperture ◽  
Dilation Effect ◽  
Stress Dependent

We investigated the effect of in situ stresses on fluid flow in a natural fracture network. The fracture network model is based on an actual critically connected (i.e., close to the percolation threshold) fracture pattern mapped from a field outcrop. We derive stress-dependent fracture aperture fields using a hybrid finite-discrete element method. We analyze the changes of aperture distribution and fluid flow field with variations of in situ stress orientation and magnitude. Our simulations show that an isotropic stress loading tends to reduce fracture apertures and suppress fluid flow, resulting in a decrease of equivalent permeability of the fractured rock. Anisotropic stresses may cause a significant amount of sliding of fracture walls accompanied with shear-induced dilation along some preferentially oriented fractures, resulting in enhanced flow heterogeneity and channelization. When the differential stress is further elevated, fracture propagation becomes prevailing and creates some new flow paths via linking preexisting natural fractures, which attempts to increase the bulk permeability but attenuates the flow channelization. Comparing to the shear-induced dilation effect, it appears that the propagation of new cracks leads to a more prominent permeability enhancement for the natural fracture system. The results have particularly important implications for predicting the hydraulic responses of fractured rocks to in situ stress fields and may provide useful guidance for the strategy design of geofluid production from naturally fractured reservoirs.

Near-surface in situ stress: Introduction

1984 ◽  
Vol 89 (B11) ◽  
pp. 9321 ◽  
Author(s):  
Terry Engelder ◽  
Marc L. Sbar
Keyword(s):  
In Situ Stress ◽  
Near Surface

Determination of three-dimensional directions of in situ stress from core discing

Rock Stress ◽  
2020 ◽  
pp. 237-243
Author(s):  
K. Matsuki ◽  
N. Kaga ◽  
T. Yokoyama ◽  
N. Tsuda
Keyword(s):  
Three Dimensional ◽  
In Situ Stress ◽  
Core Discing
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