Rock Quality, Seismic Velocity, Attenuation and Anisotropy

Preface Introduction The multi-disciplinary scope of seismic and rock quality Revealing hidden rock conditions Some basic principles of P, S and Q Q and Q Limitations of refraction seismic bring tomographic solutions Nomenclature PART I1 Shallow seismic refraction, some basic theory, and the importance of rock type 1.1 The challenge of the near-surface in civil engineering 1.2 Some basic aspects concerning elastic body waves 1.2.1 Some sources of reduced elastic moduli 1.3 Relationships between Vp and Vs and their meaning in field work 1.4 Some advantages of shear waves 1.5 Basic estimation of rock-type and rock mass condition, from shallow seismic P-wave velocity 1.6 Some preliminary conversions from velocity to rock quality 1.7 Some limitations of the refraction seismic velocity interpretations 1.8 Assumed limitations may hide the strengths of the method 1.9 Seismic quality Q and apparent similarities to Q-rock 2 Environmental effects on velocity 2.1 Density and Vp 2.2 Porosity and Vp 2.3 Uniaxial compressive strength and Vp 2.4 Weathering and moisture content 2.5 Combined effects of moisture and pressure 2.6 Combined effects of moisture and low temperature 3 Effects of anisotropy on Vp 3.1 An introduction to velocity anisotropy caused by micro-cracks and jointing 3.2 Velocity anisotropy caused by fabric 3.3 Velocity anisotropy caused by rock joints 3.4 Velocity anisotropy caused by interbedding3.5 Velocity anisotropy caused by faults 4 Cross-hole velocity and cross-hole velocity tomography 4.1 Cross-hole seismic for extrapolation of properties 4.2 Cross-hole seismic tomography in tunnelling 4.3 Cross-hole tomography in mining 4.4 Using tomography to monitor blasting effects 4.5 Alternative tomograms 4.6 Cross-hole or cross-well reflection measurement and time-lapse tomography 5 Relationships between rock quality, depth and seismic velocity 5.1 Some preliminary relationships between RQD, F, and Vp 5.2 Relationship between rock quality Q and Vp for hard jointed, near-surface rock masses5.3 Effects of depth or stress on acoustic joint closure, velocities and amplitudes 5.3.1 Compression wave amplitude sensitivities to jointing 5.3.2 Stress and velocity coupling at the Gjøvik cavern site 5.4 Observations of effective stress effects on velocities 5.5 Integration of velocity, rock mass quality, porosity, stress, strength, deformability 6 Deformation moduli and seismic velocities 6.1 Correlating Vp with the ‘static’ moduli from deformation tests 6.2 Dynamic moduli and their relationship to static moduli 6.3 Some examples of the three dynamic moduli 6.4 Use of shear wave amplitude, frequency and petite-sismique 6.5 Correlation of deformation moduli with RMR and Q 7 Excavation disturbed zones and their seismic properties 7.1 Some effects of the free-surface on velocities and attenuation 7.2 EDZ phenomena around tunnels based on seismic monitoring 7.3 EDZ investigations in selected nuclear waste isolation studies 7.3.1 BWIP — EDZ studies 7.3.2 URL — EDZ studies 7.3.3 Äspö — EDZ studies 7.3.4 Stripa — effects of heating in the EDZ of a rock mass 7.4 Acoustic detection of stress effects around boreholes 8 Seismic measurements for tunnelling 8.1 Examples of seismic applications in tunnels 8.2 Examples of the use of seismic data in TBM excavations 8.3 Implications of inverse correlation between TBM advance rate and Vp 8.4 Use of probe drilling and seismic or sonic logging ahead of TBM tunnels 8.5 In-tunnel seismic measurements for looking ahead of the face 8.6 The possible consequences of insufficient seismic investigation due to depth limitations 9 Relationships between Vp, Lugeon value, permeability and grouting in jointed rock 9.1 Correlation between Vp and Lugeon value 9.2 Rock mass deformability and the Vp-L-Q correlation 9.3 Velocity and permeability measurements at in situ block tests 9.4 Detection of permeable zones using other geophysical methods 9.5 Monitoring the effects of grouting with seismic velocity 9.6 Interpreting grouting effects in relation to improved rock mass Q-parameters PART II10 Seismic quality Q and attenuation at many scales 10.1 Some basic aspects concerning attenuation and Qseismic 10.1.1 A preliminary discussion of the importance of strain levels 10.1.2 A preliminary look at the attenuating effect of cracks of larger scale 10.2 Attenuation and seismic Q from laboratory measurement 10.2.1 A more detailed discussion of friction as an attenuation mechanism 10.2.2 Effects of partial saturation on seismic Q 10.3 Effect of confining pressure on seismic Q 10.3.1 The four components of elastic attenuation 10.3.2 Effect on Qp and Qs of loading rock samples towards failure 10.4 The effects of single rock joints on seismic Q 10.5 Attenuation and seismic Q from near-surface measurements 10.5.1 Potential links to rock mass quality parameters in jointed rock 10.5.2 Effects of unconsolidated sediments on seismic Q 10.5.3 Influence of frequency variations on attenuation in jointed and bedded rock 10.6 Attenuation in the crust as interpreted from earthquake coda 10.6.1 Coda Qc from earthquake sources and its relation to rock quality Qc 10.6.2 Frequency dependence of coda Qc due to depth effects 10.6.3 Temporal changes of coda Qc prior to earthquakes 10.6.4 Possible separation of attenuation into scattering and intrinsic mechanisms 10.6.5 Changed coda Q during seismic events 10.6.6 Attenuation of damage due to acceleration 10.6.7 Do microcracks or tectonic structure cause attenuation 10.6.8 Down-the-well seismometers to minimise site effects 10.6.9 Rock mass quality parallels 10.7 Attenuation across continents 10.7.1 Plate tectonics, sub-duction zones and seismic Q 10.7.2 Young and old oceanic lithosphere 10.7.3 Lateral and depth variation of seismic Q and seismic velocity 10.7.4 Cross-continent Lg coda Q variations and their explanation 10.7.5 Effect of thick sediments on continental Lg coda 10.8 Some recent attenuation measurements in petroleum reservoir environments 10.8.1 Anomalous values of seismic Q in reservoirs due to major structures 10.8.2 Evidence for fracturing effects in reservoirs on seismic Q 10.8.3 Different methods of analysis give different seismic Q 11 Velocity structure of the earth’s crust 11.1 An introduction to crustal velocity structures 11.2 The continental velocity structures 11.3 The continental margin velocity structures 11.3.1 Explaining a velocity anomaly 11.4 The mid-Atlantic ridge velocity structures 11.4.1 A possible effective stress discrepancy in early testing 11.4.2 Smoother depth velocity models 11.4.3 Recognition of lower effective stress levels beneath the oceans 11.4.4 Direct observation of sub-ocean floor velocities 11.4.5 Sub-ocean floor attenuation measurements 11.4.6 A question of porosities, aspect ratios and sealing 11.4.7 A velocity-depth discussion 11.4.8 Fracture zones 11.5 The East Pacific Rise velocity structures11.5.1 More porosity and fracture aspect ratio theories 11.5.2 First sub-Pacific ocean core with sonic logs and permeability tests11.5.3 Attenuation and seismic Q due to fracturing and alteration 11.5.4 Seismic attenuation tomography across the East Pacific Rise 11.5.5 Continuous sub-ocean floor seismic profiles 11.6 Age effects summary for Atlantic Ridge and Pacific Rise 11.6.1 Decline of hydrothermal circulation with age and sediment cover 11.6.2 The analogy of pre-grouting as a form of mineralization 12 Rock stress, pore pressure, borehole stability and sonic logging 12.1 Pore pressure, over-pressure, and minimum stress 12.1.1 Pore pressure and over-pressure and cross-discipline terms 12.1.2 Minimum stress and mud-weight 12.2 Stress anisotropy and its intolerance by weak rock 12.2.1 Reversal of Ko trends nearer the surface 12.3 Relevance to logging of borehole disturbed zone 12.4 Borehole in continuum becomes borehole in local discontinuum 12.5 The EDZ caused by joints, fractures and bedding-planes 12.6 Loss of porosity due to extreme depth 12.7 Dipole shear-wave logging of boreholes 12.7.1 Some further development of logging tools 12.8 Mud filtrate invasion 12.9 Challenges from ultra HPHT 13 Rock physics at laboratory scale 13.1 Compressional velocity and porosity13.2 Density, Vs and Vp 13.3 Velocity, aspect ratio, pressure, brine and gas 13.4 Velocity, temperature and influence of fluid 13.5 Velocity, clay content and permeability 13.6 Stratigraphy based velocity to permeability estimation 13.6.1 Correlation to field processes 13.7 Velocity with patchy saturation effects in mixed units 13.8 Dynamic Poisson’s ratio, effective stress and pore fluid 13.9 Dynamic moduli for estimating static deformation moduli 13.10 Attenuation due to fluid type, frequency, clay, over-pressure, compliant minerals, dual porosity 13.10.1 Comparison of velocity and attenuation in the presence of gas or brine 13.10.2 Attenuation when dry or gas or brine saturated 13.10.3 Effect of frequency on velocity and attenuation, dry or with brine 13.10.4 Attenuation for distinguishing gas condensate from oil and water 13.10.5 Attenuation in the presence of clay content 13.10.6 Attenuation due to compliant minerals and microcracks 13.10.7 Attenuation with dual porosity samples of limestones 13.10.8 Attenuation in the presence of over-pressure 13.11 Attenuation in the presence of anisotropy 13.11.1 Attenuation for fluid front monitoring 13.12 Anisotropic velocity and attenuation in shales 13.12.1 Attenuation anisotropy expressions e , g and d 13.13 Permeability and velocity anisotropy due to fabric, joints and fractures 13.13.1 Seismic monitoring of fracture development and permeability 13.14 Rock mass quality, attenuation and modulus 14 P-waves for characterising fractured reservoirs 14.1 Some classic relationships between age, depth and velocity 14.2 Anisotropy and heterogeneity caused by inter-bedded strata and jointing 14.2.1 Some basic anisotropy theory 14.3 Shallow cross-well seismic tomography 14.3.1 Shallow cross-well seismic in fractured rock 14.3.2 Cross-well seismic tomography with permeability measurement 14.3.3 Cross-well seismic in deeper reservoir characterization 14.4 Detecting finely inter-layered sequences 14.4.1 Larger scale differentiation of facies 14.5 Detecting anisotropy caused by fractures with multi-azimuth VSP 14.5.1 Fracture azimuth and stress azimuth from P-wave surveys 14.5.2 Sonic log and VSP dispersion effects and erratic seismic Q 14.6 Dispersion as an alternative method of characterization 14.7 AVO and AVOA using P-waves for fracture detection 14.7.1 Model dependence of AVOA fracture orientation 14.7.2 Conjugate joint or fracture sets also cause anisotropy 14.7.3 Vp anisotropy caused by faulting 14.7.4 Poisson’s ratio anisotropy caused by fracturing 14.8 4C four-component acquisition of seismic including C-waves 14.9 4D seismic monitoring of reservoirs 14.9.1 Possible limitations of some rock physics data 14.9.2 Oil saturation mapping with 4D seismic 14.10 4D monitoring of compaction and porosity at Ekofisk 14.10.1 Seismic detection of subsidence in the overburden 14.10.2 The periodically neglected joint behaviour at Ekofisk 14.11 Water flood causes joint opening and potential shearing 14.12 Low frequencies for sub-basalt imaging 14.13 Recent reservoir anisotropy investigations involving P-waves and attenuation 15 Shear wave splitting in fractured reservoirs and resulting from earthquakes 15.1 Introduction 15.2 Shear wave splitting and its many implications 15.2.1 Some sources of shear-wave splitting 15.3 Crack density and EDA 15.3.1 A discussion of ‘criticality’ due to microcracks 15.3.2 Temporal changes in polarization in Cornwall HDR 15.3.3 A critique of Crampin’s microcrack model 15.3.4 90°-flips in polarization 15.4 Theory relating joint compliances with shear wave splitting 15.4.1 An unrealistic rock simulant suggests equality between ZN and ZT 15.4.2 Subsequent inequality of ZN and ZT 15.4.3 Off-vertical fracture dip or incidence angle, and normal compliance 15.4.4 Discussion of scale effects and stiffness 15.5 Dynamic and static stiffness tests on joints by Pyrak-Nolte 15.5.1 Discussion of stiffness data gaps and discipline bridging needs 15.5.2 Fracture stiffness and permeability 15.6 Normal and shear compliance theories for resolving fluid type 15.6.1 In situ compliances in a fault zone inferred from seismic Q 15.7 Shear wave splitting from earthquakes 15.7.1 Shear-wave splitting in the New Madrid seismic zone 15.7.2 Shear-wave splitting at Parkfield seismic monitoring array 15.7.3 Shear-wave splitting recorded at depth in Cajon Pass borehole 15.7.4 Stress-monitoring site (SMS) anomalies from Iceland 15.7.5 SW-Iceland, Station BJA shear wave anomalies 15.7.6 Effects of shearing on stiffness and shear wave amplitude 15.7.7 Shear-wave splitting at a geothermal field 15.7.8 Shear wave splitting during after-shocks of the Chi-Chi earthquake in Taiwan 15.7.9 Shear-wave splitting under the Mid-Atlantic Ridge 15.8 Recent cases of shear wave splitting in petroleum reservoirs 15.8.1 Some examples of S-wave and PS-wave acquisition methods 15.8.2 Classification of fractured reservoirs 15.8.3 Crack density and shearing of conjugate sets at Ekofisk might enhance splitting 15.8.4 Links between shear wave anisotropy and permeability15.8.5 Polarization-stress alignment from shallow shear-wave splitting 15.8.6 Shear-wave splitting in argillaceous rocks 15.8.7 Time-lapse application of shear-wave splitting over reservoirs 15.8.8 Temporal shear-wave splitting using AE from the Valhall cap-rock 15.8.9 Shear-wave splitting and fluid identification at the Natih field 15.9 Dual-porosity poro-elastic modelling of dispersion and fracture size effects 15.9.1 A brief survey of rock mechanics pseudo-static models of jointed rock 15.9.2 A very brief review of slip-interface, fracture network and poro-elastic crack models 15.9.3 Applications of Chapman model to Bluebell Altamont fractured gas reservoir 15.9.4 The SeisRox model 15.9.5 Numerical modelling of dynamic joint stiffness effects 15.9.6 A ‘sugar cube’ model representation 15.10 A porous and fractured physical model as a numerical model validation 16 Joint stiffness and compliance and the joint shearing mechanism 16.1 Some important non-linear joint and fracture behaviour modes 16.2 Aspects of fluid flow in deforming rock joints 16.2.1 Coupled stress-flow behaviour under normal closure 16.2.2 Coupled stress-flow behaviour under shear deformation 16.3 Some important details concerning rock joint stiffnesses Kn and Ks 16.3.1 Initial normal stiffness measured at low stress 16.3.2 Normal stiffness at elevated normal stress levels16.4 Ratios of Kn over Ks under static and dynamic conditions 16.4.1 Frequency dependence of fracture normal stiffness 16.4.2 Ratios of static Kn to static Ks for different block sizes 16.4.3 Field measurements of compliance ZN 16.4.4 Investigation of normal and shear compliances on artificial surfaces in limestones 16.4.5 The Worthington-Lubbe-Hudson range of compliances 16.4.6 Pseudo-static stiffness data for clay filled discontinuities and major shear zones 16.4.7 Shear stress application may apparently affect compliance 16.5 Effect of dry or saturated conditions on shear and normal stiffnesses 16.5.1 Joint roughness coefficient (JRC) 16.5.2 Joint wall compression strength (JCS) 16.5.3 Basic friction angle f b and residual friction angle f r 16.5.4 Empirical equations for the shear behaviour of rock joints 16.6 Mechanical over-closure, thermal-closure, and joint stiffness modification 16.6.1 Normal stiffness estimation 16.6.2 Thermal over-closure of joints and some implications 16.6.3 Mechanical over-closure 16.7 Consequences of shear stress on polarization and permeability 16.7.1 Stress distribution caused by shearing joints, and possible consequences for shear wave splitting 16.7.2 The strength-deformation components of jointed rock masses 16.7.3 Permeability linked to joint shearing 16.7.4 Reservoir seismic case records with possible shearing 16.7.5 The apertures expected of highly stressed ‘open’ joints 16.7.6 Modelling apertures with the BB model 16.7.7 Open joints caused by anisotropic stress, low shear strength, dilation 16.8 Non-linear shear strength and the critical shearing crust 16.8.1 Non-linear strength envelopes and scale effects 16.9 Critically stressed open fractures that indicate conductivity 16.9.1 The JRC contribution at different scales and deformations 16.9.2 Does pre-peak or post-peak strength resist the assumed crustal shear stress? 16.10 Rotation of joint attributes and unequal conjugate jointing may explain azimuthal deviation of S-wave polarization 16.11 Classic stress transformation equations ignore the non-coaxiality of stress and displacement 16.12 Estimating shallow crustal permeability from a modified rock quality Q-water 16.12.1 The problem of clay-sealed discontinuities 17 Conclusions Appendix A — The Qrock parameter ratings The six parameters defined Combination in pairs Definitions of characterization and classification as used in rock engineering Notes on Q-method of rock mass classification Appendix B — A worked example ReferencesIndex Colour Plates