Douglas Miller - Academia.edu (original) (raw)

Papers by Douglas Miller

Research paper thumbnail of Imaging Structures under a Steel-Reinforced Concrete Floor

60th EAGE Conference and Exhibition, 1998

Research paper thumbnail of Backprojection versus backpropagation in multidimensional linearized inversion

GEOPHYSICS, 1989

Seismic migration can be viewed as either backprojection (diffraction‐stack) or backpropagation (... more Seismic migration can be viewed as either backprojection (diffraction‐stack) or backpropagation (wave‐field extrapolation) (e.g., Gazdag and Sguazzero, 1984). Migration by backprojection was the view supporting the first digital methods—the diffraction and common tangent stacks of what is now called classical or statistical migration (Lindsey and Hermann, 1970; Rockwell, 1971; Schneider, 1971; Johnson and French, 1982). In this approach, each data point is associated with an isochron surface passing through the scattering object. Data values are then interpreted as projections of reflectivity over the associated isochrons. Dually, each image point is associated with a reflection‐time surface passing through the data traces. The migrated image at that point is obtained as a weighted stack of data lying on the reflection‐time surface (Rockwell, 1971; Schneider, 1971). This amounts to a weighted backprojection in which each data point contributes to image points lying on its associated...

Research paper thumbnail of TWO‐PASS 3D MIGRATION AND LINEARIZED INVERSION IN THE (x, t)‐DOMAIN1

Geophysical Prospecting, 1989

3D Kirchhoff migration and acoustic Born inversion of zero‐offset seismic data in a constant‐velo... more 3D Kirchhoff migration and acoustic Born inversion of zero‐offset seismic data in a constant‐velocity medium can be uniformly factored as a cascade of two 2D diffraction integrals. The formal argument is based on a straightforward implementation of the original time‐domain approach of Gibson, Larner and Levin. The factorization differs from the factorization described by Jakubowicz and Levin in omitting all time‐dependent filters from the 2D operators in favour of ID filtrations performed as a preprocess and a postprocess.

Research paper thumbnail of Advanced Applications of Distributed Acoustic Sensing

Proceedings, 2017

A Distributed Acoustic Sensor (DAS) is capable of measuring the acoustic field at every point alo... more A Distributed Acoustic Sensor (DAS) is capable of measuring the acoustic field at every point along an optical fibre. Applications of this technology are becoming increasingly mature, with many companies making commercial decisions based on DAS data. In the geophysical field DAS is being used routinely to acquire VSP measurements either using wireline deployed or permanently installed fibre optic cables and active sources. The results in this paper show some comparisons with data from conventional sensors and highlight the benefits of these types of measurements.

Research paper thumbnail of Overview and Preliminary Results from the PoroTomo project at Brady Hot Springs, Nevada: Poroelastic Tomography by Adjoint Inverse Modeling of Data from Seismology, Geodesy, and Hydrology

In the geothermal field at Brady Hot Springs, Nevada, subsidence occurs over an elliptical area t... more In the geothermal field at Brady Hot Springs, Nevada, subsidence occurs over an elliptical area that is ~4 km by ~1.5 km. Highly permeable conduits along faults appear to channel fluids from shallow aquifers to the deep geothermal reservoir tapped by the production wells. Results from inverse modeling suggest that the deformation is a result of volumetric contraction in units with depth less than 600 m [Ali et al., 2016]. Characterizing such structures in terms of their rock-mechanical properties is essential to successful operations of Enhanced Geothermal Systems (EGS). The goal of the PoroTomo project is to assess an integrated technology for characterizing and monitoring changes in the rock-mechanical properties of an EGS reservoir in three dimensions with a spatial resolution better than 50 meters. In March 2016, we deployed the integrated technology in a 1500-by-500-by-400-meter volume at Brady Hot Springs. The data set includes: active seismic sources, fiber-optic cables for D...

Research paper thumbnail of Ground Probing Radar 1 Chapter 0 . 1 GROUND PROBING RADAR

Contents 0.1.1 Overview 1 0.1.2 Conceptual Description 2 0.1.3 Location and Imaging with GPR 6 0.... more Contents 0.1.1 Overview 1 0.1.2 Conceptual Description 2 0.1.3 Location and Imaging with GPR 6 0.1.4 Practical Description 13 0.1.5 Applications and examples 15 0.1.6 Acknowledgements 20

Research paper thumbnail of Distributed Acoustic Sensing (DAS) Based Vertical Seismic Profiling (VSP) for Monitoring CO2 Injected Into a Pinnacle-Reef Reservoir

SSRN Electronic Journal, 2019

Research paper thumbnail of Results of Field Testing of Simultaneous DAS and Geophone VSP

Proceedings 76th EAGE Conference and Exhibition Workshops, 2014

As part of a CO2 storage project at Citronelle, Alabama, VSP data was acquired with a short strin... more As part of a CO2 storage project at Citronelle, Alabama, VSP data was acquired with a short string of tubing-deployed, wall-locking, geophones (18 at 15 m spacing) and a long (3 km) fiber, also tubingdeployed. We will show data examples comparing geophone and DAS attributes such as spectral response, signal-to-noise ratio and ground motion sensitivity comparison.

Research paper thumbnail of Simultaneous Acquisition of Distributed Acoustic Seismic Surveys with Single-mode and Multi-mode Fiber Optic Cables at Aquistore CO2 Storage Site and a Comparison with 3C Geophones

Proceedings, 2015

A dynamite 3D VSP survey, a Vibrator 2D VSP survey and related calibration surveys at the Aquisto... more A dynamite 3D VSP survey, a Vibrator 2D VSP survey and related calibration surveys at the Aquistore CO 2 storage site in Saskatchewan served as a technology test for distributed acoustic sensing (DAS). DAS data was acquired as a vertical seismic profile (VSP) on two codeployed fibers, one single-mode (SM) and one multi-mode (MM), simultaneously with a 60-level 3-component wireline geophone array. A 2D grid of explosive shots, used for baseline 4D surface seismic, provided 3D-VSP data from all sensors, while vibrator sources were used for a single 2D VSP line. The DAS fibers were cemented in place on the outside of the well casing during the original well completion and extend to a depth of ~2.8 km. Good quality data was acquired by all systems with comparable SM and MM VSP results. DAS data converted to particle velocity and geophone data have comparable responses. Both explosive and vibroseis source types give good quality DAS data with expected improvement from two versus one vibroseis source. We observe variable coherent borehole noise attributed to variable cement quality. Good quality and comparable migrated images are obtained from DAS and geophone data. Following these tests, we conclude DAS 3D VSP is a viable candidate for time-lapse monitoring.

Research paper thumbnail of Field testing of fiber-optic distributed acoustic sensing (DAS) for subsurface seismic monitoring

The Leading Edge, 2013

Distributed acoustic sensing (DAS) is a relatively recent development in the use of fiber-optic c... more Distributed acoustic sensing (DAS) is a relatively recent development in the use of fiber-optic cable for measurement of ground motion. Discrete fiber-optic sensors, typically using a Bragg diffraction grating, have been in research and development and field testing for more than 15 years with geophysical applications at least 12 years old (Bostick, 2000, and summary in Keul et al., 2005). However, developments in recent years have sought to remove the need for point sensors by using the fiber cable itself as a sensor (Mestayer et al., 2011; Miller et al., 2012).

Research paper thumbnail of The promise of elastic anisotropy

International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, 1995

Research paper thumbnail of A new slant on seismic imaging: Migration and integral geometry

GEOPHYSICS, 1987

A new approach to seismic migration formalizes the classical diffraction (or common‐tangent) stac... more A new approach to seismic migration formalizes the classical diffraction (or common‐tangent) stack by relating it to linearized seismic inversion and the generalized Radon transform. This approach recasts migration as the problem of reconstructing the earth’s acoustic scattering potential from its integrals over isochron surfaces. The theory rests on a solution of the wave equation with the geometrical‐optics Green function and an approximate inversion formula for the generalized Radon transform. The method can handle both complex velocity models and (nearly) arbitrary configurations of sources and receivers. In this general case, the method can be implemented as a weighted diffraction stack, with the weights determined by tracing rays from image points to the experiment’s sources and receivers. When tested on a finite‐difference simulation of a deviated‐well vertical seismic profile (a hybrid experiment which is difficult to treat with conventional wave‐equation methods), the algor...

Research paper thumbnail of Multiparameter inversion, dip-moveout, and the generalized Radon transform

Geophysical inversion, 1992

In a recent paper, G. Beylkin and R. Burridge developed an algorithm, based on the inverse Genera... more In a recent paper, G. Beylkin and R. Burridge developed an algorithm, based on the inverse Generalized Radon Transform, for multiparameter inversion of surface seismic re°ection data. In their approach, elastic parameters (¹;¸; ½) of the object medium are represented as linear combinations of three scalar potentials. These potentials can be separately recovered from three prestack GRT migrations in which the obliquity factor is varied. The material parameters are then obtained by solving a small linear system of equations at each object point. This algorithm can be recast in terms of a GRT-based dip-movout operator. In this approach, zero-o®set data for each scalar potential are synthesized from positive-o®set data by application of a timedomain DMO operator with an appropriate obliquity dependence. Multiple copies of the synthesized zero-o®set data are then stacked and migrated as in ordinary DMO processing. This reconstructs the scalar potentials, which can in turn be solved for the material parameters. The GRT-DMO operator is obtained by applying a stationaryphase reduction of the cascaded operations of prestack GRT migration and forward zero-o®set modelling. The operator di®ers from previously described time-domain DMO operators in the modi¯cation of stacking amplitudes and in the presence of one-dimensional¯lters that are applied before and after stacking.

Research paper thumbnail of The Correspondence Rule for Sonic Logging in Deviated Wells

For fast anisotropic formations, such as the North American gas shales, sonic logs measure group ... more For fast anisotropic formations, such as the North American gas shales, sonic logs measure group slowness for propagation with the group angle equal to the borehole inclination angle. For deviated wells, the distinction between group and phase angle is as important as the distinction between phase and group velocity. When inverting from sonic data to elastic parameters, the use of an incorrect correspondence rule can lead to inconsistent and unrealistic values, particularly for C13 or equivalently, Thomsen’s δ.

Research paper thumbnail of Reliability of velocity measurements made by monopole acoustic logging-while-drilling tools in fast formations

GEOPHYSICS, 2017

The accuracy of velocity measurements made using a monopole acoustic logging-while-drilling (ALWD... more The accuracy of velocity measurements made using a monopole acoustic logging-while-drilling (ALWD) measurement tool is influenced by the eccentering of the tool due to complex drill string movements. We have used the velocity of collar flexural mode (at the source frequency range) as a reference and classified the fast formations into (1) fast-fast (FF) formations with compressional velocity far larger than the collar flexural velocity and (2) slow-fast (SF) formations with compressional velocity approaching that of the collar flexural velocity. We use a 3D finite-difference method to simulate the response of an eccentered monopole ALWD tool with different eccentering magnitudes (offsets) for the two types of formations to facilitate better interpretation of velocity measurements made in an actual drilling environment. We find that the collar extensional mode, existing in the centralized and eccentered tool cases, only affects the formation P-wave measurement and can be eliminated b...

Research paper thumbnail of Incontrovertible evidence of anisotropy in crosswell data

SEG Technical Program Expanded Abstracts 1991, 1991

Crosswell seismic data collected at BP' s test site near Devine, Texas show clear evidence of P-w... more Crosswell seismic data collected at BP' s test site near Devine, Texas show clear evidence of P-wave anisotropy (v,/u, up to 1.3) confined to shale layers in a shale/carbonate sequence. Tomograms made assuming isotropy are severely degraded, but could be mistakenly interpreted as indicating (nonexistent) low velocity zones within the carbonates. The effects of the anisotropy are directly evident in the raw data once headwaves and internally reflected waves are correctly identified. Inversion for a layered, transversely isotropic, anisotropic medium yields a model that fits the data to the accuracy of the time picking. 1. Introduction. Crosswell data were collected using a piezoelectric pressure source with hydrophone receivers at BP' s test site near Devine, Texas. Source and receiver wells were vertical with a separation of 100m. The peak frequency

Research paper thumbnail of An in situ estimation of anisotropic elastic moduli for a submarine shale

Journal of Geophysical Research: Solid Earth, 1994

Direct arrival times and slownesses from wide-aperture walkaway vertical seismic profile data acq... more Direct arrival times and slownesses from wide-aperture walkaway vertical seismic profile data acquired in a layered anisotropic medium can be processed to give a direct estimate of the phase slowness surface associated with the medium at the depth of the receivers. This slowness surface can, in turn, be fit by an estimated transversely isotropic medium with a vertical symmetry axis (a "TIV" medium). While the method requires that the medium between the receivers and the surface be horizontally stratified, no further measurement or knowledge of that medium is required. When applied to data acquired in a compacting shale sequence (here termed the "Petronas shale") encountered by a well in the South China Sea, the method yields an estimated TIV medium that fits the data extremely well over 180 ø of propagation angles sampled by 201 source positions. The medium is strongly anisotropic. The anisotropy is significantly anelliptic and implies that the quasi-shear mode should be triplicated for off-axis propagation. Estimated density-normalized moduli (in units of km2/s 2) for the Petronas shale are All = 6.99-+ 0.21, A33 = 5.53 _ 0.17, A55 = 0.91 _+ 0.05, and A13-2.64 _+ 0.26. Densities in the logged zone just below the survey lie in the range between 2200 and 2400 kg/m 3 with an average value close to 2300 kg/m3.

Research paper thumbnail of An exact inversion for anisotropic moduli from phase slowness data

Journal of Geophysical Research: Solid Earth, 1994

The problem of recovering density-normalized elastic moduli of a transversely isotropic anisotrop... more The problem of recovering density-normalized elastic moduli of a transversely isotropic anisotropic medium from data consisting of qP or qSV phase velocities measured in multiple directions is addressed. Previous studies have used linear fitting methods with approximate forms of the dispersion relation. Here, it is shown that with algebraic manipulation, and a prior estimate of the squared shear velocity along the symmetry axis (A55), it is possible to use simple linear methods with an exact alternative form of the anisotropic dispersion relation. The method is demonstrated with an application to data from a walkaway vertical seismic profile (VSP) experiment and then used as a tool to address several questions raised by that experiment. It is shown that given data with realistically achievable accuracy, the prior estimate of A 55 cannot be improved by optimizing the fit to qP data. It is shown that a near perfect fit by a transversely isotropic medium with a vertical symmetry axis (TIV) model to qP data collected in a single vertical plane does not rule out azimuthal anisotropy. Finally, it is shown that a variation of the method, combined with an algorithm suggested by Hood and Schoenberg, suggests a practical way to determine from walkaway VSP data, all the parameters of an orthorhombic medium formed by adding vertical fractures to a transversely isotropic medium. 1=(1' i=1, n) 21,651 21,652 MILLER AND SPENCER: EXACT ANISOTROPIC INVERSION

Research paper thumbnail of Velocity sensitivity in transversely isotropic media1

Geophysical Prospecting, 1996

Ve consider the problem of determining and predicting how the wave speeds in particular direction... more Ve consider the problem of determining and predicting how the wave speeds in particular directions for a transversely isotropic (TI) medium depend on particular combinations of the density-normalized moduli A;1. The expressions for the qP and qSZ velocities are known to depend on four moduli. Normally, we can only determine three independent parameters from qP data, or two from qSZ data, as the others have much lower sensitivity. The resolvable parameters are conveniently described by axial and off-axis parameters: for qP rays, Pe. : Art, Pgo. : Ay and Pcs": (An-l Arr)14-t(Arz+2455)12; and for qSV ruys, So.: Sso. : Ass and S+s.: (AtIAz)/4-Anl2. These parameters control the magnitude of the squared-velocities on the axes and at approximately 45". F'or an arbitrary TI medium, if the medium is perturbed in a way that preserves a particular parameter, then slowness points in the associated direction and mode witl be approximately preserved in the new medium. we refer to these parameters as 'push-pins', i.e. if a parameter is fixed, the associated part of the slowness surface is pinned in place. Because, these five push-pins only contain four independent moduli, we can only fix at most three push-pins. Perturbing one of the other parameters inevitably perturbs the other. Numerical results illustrating the linkage berween two push-pins, when three are fixed, are presented. So-called anomalous TI media occur when the roles of the qlt and qsv waves are reversed: in some directions the faster ray has transverse polarization. That, in turn, requires anomalous velocities at the push-pins, i.e. Ss.) 1r0,, S+s.) pa5,, and,lor Sso") Pee" (equivalent to the usual anomalous conditions Arr I Arr, AB + A55 < 0 and/or Azz I As). In the Appendix, we confirm that anomalous sensitivities of the velocities at the five push-pins only occur in such media, although the push-pins still apply if interpreted appropriately. Truly anomalous sensitivities, in which push-pins play no role, only occur in media near the boundary between normal and anomalous.

Research paper thumbnail of Compressive strength and elastic properties of a transversely isotropic calcareous mudstone

Geophysical Prospecting, 2013

This paper reports measurements of static and dynamic elastic properties plus compressive strengt... more This paper reports measurements of static and dynamic elastic properties plus compressive strength performed on a block of calcareous mudstone retrieved from an exploration well. Measurements of mechanical properties indicate that the mudstone is anisotropic with respect to all three properties. A detailed analysis of the elastic moduli computed using small unload reload cycles and simultaneous ultrasonic wave velocities shows both strong anisotropy and strong anelasticity. Surprisingly, the measurements are consistent with a mathematical description of a special type of anisotropic linear viscoelastic medium that is obtained by adding a set of compliant elements (e.g., contacts between clay particles, kerogen lenses, or micro-fractures) to an isotropic viscoelastic solid. This medium is fully characterized by density plus four parameters defining the viscoelastic solid and the excess normal compliance associated with the compliant elements. The mathematical model predicts a full set of parameters characterizing a transversely isotropic medium with a vertical axis of symmetry (a 'tiv' medium) for both low-and high-strain rate behaviour.

Research paper thumbnail of Imaging Structures under a Steel-Reinforced Concrete Floor

60th EAGE Conference and Exhibition, 1998

Research paper thumbnail of Backprojection versus backpropagation in multidimensional linearized inversion

GEOPHYSICS, 1989

Seismic migration can be viewed as either backprojection (diffraction‐stack) or backpropagation (... more Seismic migration can be viewed as either backprojection (diffraction‐stack) or backpropagation (wave‐field extrapolation) (e.g., Gazdag and Sguazzero, 1984). Migration by backprojection was the view supporting the first digital methods—the diffraction and common tangent stacks of what is now called classical or statistical migration (Lindsey and Hermann, 1970; Rockwell, 1971; Schneider, 1971; Johnson and French, 1982). In this approach, each data point is associated with an isochron surface passing through the scattering object. Data values are then interpreted as projections of reflectivity over the associated isochrons. Dually, each image point is associated with a reflection‐time surface passing through the data traces. The migrated image at that point is obtained as a weighted stack of data lying on the reflection‐time surface (Rockwell, 1971; Schneider, 1971). This amounts to a weighted backprojection in which each data point contributes to image points lying on its associated...

Research paper thumbnail of TWO‐PASS 3D MIGRATION AND LINEARIZED INVERSION IN THE (x, t)‐DOMAIN1

Geophysical Prospecting, 1989

3D Kirchhoff migration and acoustic Born inversion of zero‐offset seismic data in a constant‐velo... more 3D Kirchhoff migration and acoustic Born inversion of zero‐offset seismic data in a constant‐velocity medium can be uniformly factored as a cascade of two 2D diffraction integrals. The formal argument is based on a straightforward implementation of the original time‐domain approach of Gibson, Larner and Levin. The factorization differs from the factorization described by Jakubowicz and Levin in omitting all time‐dependent filters from the 2D operators in favour of ID filtrations performed as a preprocess and a postprocess.

Research paper thumbnail of Advanced Applications of Distributed Acoustic Sensing

Proceedings, 2017

A Distributed Acoustic Sensor (DAS) is capable of measuring the acoustic field at every point alo... more A Distributed Acoustic Sensor (DAS) is capable of measuring the acoustic field at every point along an optical fibre. Applications of this technology are becoming increasingly mature, with many companies making commercial decisions based on DAS data. In the geophysical field DAS is being used routinely to acquire VSP measurements either using wireline deployed or permanently installed fibre optic cables and active sources. The results in this paper show some comparisons with data from conventional sensors and highlight the benefits of these types of measurements.

Research paper thumbnail of Overview and Preliminary Results from the PoroTomo project at Brady Hot Springs, Nevada: Poroelastic Tomography by Adjoint Inverse Modeling of Data from Seismology, Geodesy, and Hydrology

In the geothermal field at Brady Hot Springs, Nevada, subsidence occurs over an elliptical area t... more In the geothermal field at Brady Hot Springs, Nevada, subsidence occurs over an elliptical area that is ~4 km by ~1.5 km. Highly permeable conduits along faults appear to channel fluids from shallow aquifers to the deep geothermal reservoir tapped by the production wells. Results from inverse modeling suggest that the deformation is a result of volumetric contraction in units with depth less than 600 m [Ali et al., 2016]. Characterizing such structures in terms of their rock-mechanical properties is essential to successful operations of Enhanced Geothermal Systems (EGS). The goal of the PoroTomo project is to assess an integrated technology for characterizing and monitoring changes in the rock-mechanical properties of an EGS reservoir in three dimensions with a spatial resolution better than 50 meters. In March 2016, we deployed the integrated technology in a 1500-by-500-by-400-meter volume at Brady Hot Springs. The data set includes: active seismic sources, fiber-optic cables for D...

Research paper thumbnail of Ground Probing Radar 1 Chapter 0 . 1 GROUND PROBING RADAR

Contents 0.1.1 Overview 1 0.1.2 Conceptual Description 2 0.1.3 Location and Imaging with GPR 6 0.... more Contents 0.1.1 Overview 1 0.1.2 Conceptual Description 2 0.1.3 Location and Imaging with GPR 6 0.1.4 Practical Description 13 0.1.5 Applications and examples 15 0.1.6 Acknowledgements 20

Research paper thumbnail of Distributed Acoustic Sensing (DAS) Based Vertical Seismic Profiling (VSP) for Monitoring CO2 Injected Into a Pinnacle-Reef Reservoir

SSRN Electronic Journal, 2019

Research paper thumbnail of Results of Field Testing of Simultaneous DAS and Geophone VSP

Proceedings 76th EAGE Conference and Exhibition Workshops, 2014

As part of a CO2 storage project at Citronelle, Alabama, VSP data was acquired with a short strin... more As part of a CO2 storage project at Citronelle, Alabama, VSP data was acquired with a short string of tubing-deployed, wall-locking, geophones (18 at 15 m spacing) and a long (3 km) fiber, also tubingdeployed. We will show data examples comparing geophone and DAS attributes such as spectral response, signal-to-noise ratio and ground motion sensitivity comparison.

Research paper thumbnail of Simultaneous Acquisition of Distributed Acoustic Seismic Surveys with Single-mode and Multi-mode Fiber Optic Cables at Aquistore CO2 Storage Site and a Comparison with 3C Geophones

Proceedings, 2015

A dynamite 3D VSP survey, a Vibrator 2D VSP survey and related calibration surveys at the Aquisto... more A dynamite 3D VSP survey, a Vibrator 2D VSP survey and related calibration surveys at the Aquistore CO 2 storage site in Saskatchewan served as a technology test for distributed acoustic sensing (DAS). DAS data was acquired as a vertical seismic profile (VSP) on two codeployed fibers, one single-mode (SM) and one multi-mode (MM), simultaneously with a 60-level 3-component wireline geophone array. A 2D grid of explosive shots, used for baseline 4D surface seismic, provided 3D-VSP data from all sensors, while vibrator sources were used for a single 2D VSP line. The DAS fibers were cemented in place on the outside of the well casing during the original well completion and extend to a depth of ~2.8 km. Good quality data was acquired by all systems with comparable SM and MM VSP results. DAS data converted to particle velocity and geophone data have comparable responses. Both explosive and vibroseis source types give good quality DAS data with expected improvement from two versus one vibroseis source. We observe variable coherent borehole noise attributed to variable cement quality. Good quality and comparable migrated images are obtained from DAS and geophone data. Following these tests, we conclude DAS 3D VSP is a viable candidate for time-lapse monitoring.

Research paper thumbnail of Field testing of fiber-optic distributed acoustic sensing (DAS) for subsurface seismic monitoring

The Leading Edge, 2013

Distributed acoustic sensing (DAS) is a relatively recent development in the use of fiber-optic c... more Distributed acoustic sensing (DAS) is a relatively recent development in the use of fiber-optic cable for measurement of ground motion. Discrete fiber-optic sensors, typically using a Bragg diffraction grating, have been in research and development and field testing for more than 15 years with geophysical applications at least 12 years old (Bostick, 2000, and summary in Keul et al., 2005). However, developments in recent years have sought to remove the need for point sensors by using the fiber cable itself as a sensor (Mestayer et al., 2011; Miller et al., 2012).

Research paper thumbnail of The promise of elastic anisotropy

International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, 1995

Research paper thumbnail of A new slant on seismic imaging: Migration and integral geometry

GEOPHYSICS, 1987

A new approach to seismic migration formalizes the classical diffraction (or common‐tangent) stac... more A new approach to seismic migration formalizes the classical diffraction (or common‐tangent) stack by relating it to linearized seismic inversion and the generalized Radon transform. This approach recasts migration as the problem of reconstructing the earth’s acoustic scattering potential from its integrals over isochron surfaces. The theory rests on a solution of the wave equation with the geometrical‐optics Green function and an approximate inversion formula for the generalized Radon transform. The method can handle both complex velocity models and (nearly) arbitrary configurations of sources and receivers. In this general case, the method can be implemented as a weighted diffraction stack, with the weights determined by tracing rays from image points to the experiment’s sources and receivers. When tested on a finite‐difference simulation of a deviated‐well vertical seismic profile (a hybrid experiment which is difficult to treat with conventional wave‐equation methods), the algor...

Research paper thumbnail of Multiparameter inversion, dip-moveout, and the generalized Radon transform

Geophysical inversion, 1992

In a recent paper, G. Beylkin and R. Burridge developed an algorithm, based on the inverse Genera... more In a recent paper, G. Beylkin and R. Burridge developed an algorithm, based on the inverse Generalized Radon Transform, for multiparameter inversion of surface seismic re°ection data. In their approach, elastic parameters (¹;¸; ½) of the object medium are represented as linear combinations of three scalar potentials. These potentials can be separately recovered from three prestack GRT migrations in which the obliquity factor is varied. The material parameters are then obtained by solving a small linear system of equations at each object point. This algorithm can be recast in terms of a GRT-based dip-movout operator. In this approach, zero-o®set data for each scalar potential are synthesized from positive-o®set data by application of a timedomain DMO operator with an appropriate obliquity dependence. Multiple copies of the synthesized zero-o®set data are then stacked and migrated as in ordinary DMO processing. This reconstructs the scalar potentials, which can in turn be solved for the material parameters. The GRT-DMO operator is obtained by applying a stationaryphase reduction of the cascaded operations of prestack GRT migration and forward zero-o®set modelling. The operator di®ers from previously described time-domain DMO operators in the modi¯cation of stacking amplitudes and in the presence of one-dimensional¯lters that are applied before and after stacking.

Research paper thumbnail of The Correspondence Rule for Sonic Logging in Deviated Wells

For fast anisotropic formations, such as the North American gas shales, sonic logs measure group ... more For fast anisotropic formations, such as the North American gas shales, sonic logs measure group slowness for propagation with the group angle equal to the borehole inclination angle. For deviated wells, the distinction between group and phase angle is as important as the distinction between phase and group velocity. When inverting from sonic data to elastic parameters, the use of an incorrect correspondence rule can lead to inconsistent and unrealistic values, particularly for C13 or equivalently, Thomsen’s δ.

Research paper thumbnail of Reliability of velocity measurements made by monopole acoustic logging-while-drilling tools in fast formations

GEOPHYSICS, 2017

The accuracy of velocity measurements made using a monopole acoustic logging-while-drilling (ALWD... more The accuracy of velocity measurements made using a monopole acoustic logging-while-drilling (ALWD) measurement tool is influenced by the eccentering of the tool due to complex drill string movements. We have used the velocity of collar flexural mode (at the source frequency range) as a reference and classified the fast formations into (1) fast-fast (FF) formations with compressional velocity far larger than the collar flexural velocity and (2) slow-fast (SF) formations with compressional velocity approaching that of the collar flexural velocity. We use a 3D finite-difference method to simulate the response of an eccentered monopole ALWD tool with different eccentering magnitudes (offsets) for the two types of formations to facilitate better interpretation of velocity measurements made in an actual drilling environment. We find that the collar extensional mode, existing in the centralized and eccentered tool cases, only affects the formation P-wave measurement and can be eliminated b...

Research paper thumbnail of Incontrovertible evidence of anisotropy in crosswell data

SEG Technical Program Expanded Abstracts 1991, 1991

Crosswell seismic data collected at BP' s test site near Devine, Texas show clear evidence of P-w... more Crosswell seismic data collected at BP' s test site near Devine, Texas show clear evidence of P-wave anisotropy (v,/u, up to 1.3) confined to shale layers in a shale/carbonate sequence. Tomograms made assuming isotropy are severely degraded, but could be mistakenly interpreted as indicating (nonexistent) low velocity zones within the carbonates. The effects of the anisotropy are directly evident in the raw data once headwaves and internally reflected waves are correctly identified. Inversion for a layered, transversely isotropic, anisotropic medium yields a model that fits the data to the accuracy of the time picking. 1. Introduction. Crosswell data were collected using a piezoelectric pressure source with hydrophone receivers at BP' s test site near Devine, Texas. Source and receiver wells were vertical with a separation of 100m. The peak frequency

Research paper thumbnail of An in situ estimation of anisotropic elastic moduli for a submarine shale

Journal of Geophysical Research: Solid Earth, 1994

Direct arrival times and slownesses from wide-aperture walkaway vertical seismic profile data acq... more Direct arrival times and slownesses from wide-aperture walkaway vertical seismic profile data acquired in a layered anisotropic medium can be processed to give a direct estimate of the phase slowness surface associated with the medium at the depth of the receivers. This slowness surface can, in turn, be fit by an estimated transversely isotropic medium with a vertical symmetry axis (a "TIV" medium). While the method requires that the medium between the receivers and the surface be horizontally stratified, no further measurement or knowledge of that medium is required. When applied to data acquired in a compacting shale sequence (here termed the "Petronas shale") encountered by a well in the South China Sea, the method yields an estimated TIV medium that fits the data extremely well over 180 ø of propagation angles sampled by 201 source positions. The medium is strongly anisotropic. The anisotropy is significantly anelliptic and implies that the quasi-shear mode should be triplicated for off-axis propagation. Estimated density-normalized moduli (in units of km2/s 2) for the Petronas shale are All = 6.99-+ 0.21, A33 = 5.53 _ 0.17, A55 = 0.91 _+ 0.05, and A13-2.64 _+ 0.26. Densities in the logged zone just below the survey lie in the range between 2200 and 2400 kg/m 3 with an average value close to 2300 kg/m3.

Research paper thumbnail of An exact inversion for anisotropic moduli from phase slowness data

Journal of Geophysical Research: Solid Earth, 1994

The problem of recovering density-normalized elastic moduli of a transversely isotropic anisotrop... more The problem of recovering density-normalized elastic moduli of a transversely isotropic anisotropic medium from data consisting of qP or qSV phase velocities measured in multiple directions is addressed. Previous studies have used linear fitting methods with approximate forms of the dispersion relation. Here, it is shown that with algebraic manipulation, and a prior estimate of the squared shear velocity along the symmetry axis (A55), it is possible to use simple linear methods with an exact alternative form of the anisotropic dispersion relation. The method is demonstrated with an application to data from a walkaway vertical seismic profile (VSP) experiment and then used as a tool to address several questions raised by that experiment. It is shown that given data with realistically achievable accuracy, the prior estimate of A 55 cannot be improved by optimizing the fit to qP data. It is shown that a near perfect fit by a transversely isotropic medium with a vertical symmetry axis (TIV) model to qP data collected in a single vertical plane does not rule out azimuthal anisotropy. Finally, it is shown that a variation of the method, combined with an algorithm suggested by Hood and Schoenberg, suggests a practical way to determine from walkaway VSP data, all the parameters of an orthorhombic medium formed by adding vertical fractures to a transversely isotropic medium. 1=(1' i=1, n) 21,651 21,652 MILLER AND SPENCER: EXACT ANISOTROPIC INVERSION

Research paper thumbnail of Velocity sensitivity in transversely isotropic media1

Geophysical Prospecting, 1996

Ve consider the problem of determining and predicting how the wave speeds in particular direction... more Ve consider the problem of determining and predicting how the wave speeds in particular directions for a transversely isotropic (TI) medium depend on particular combinations of the density-normalized moduli A;1. The expressions for the qP and qSZ velocities are known to depend on four moduli. Normally, we can only determine three independent parameters from qP data, or two from qSZ data, as the others have much lower sensitivity. The resolvable parameters are conveniently described by axial and off-axis parameters: for qP rays, Pe. : Art, Pgo. : Ay and Pcs": (An-l Arr)14-t(Arz+2455)12; and for qSV ruys, So.: Sso. : Ass and S+s.: (AtIAz)/4-Anl2. These parameters control the magnitude of the squared-velocities on the axes and at approximately 45". F'or an arbitrary TI medium, if the medium is perturbed in a way that preserves a particular parameter, then slowness points in the associated direction and mode witl be approximately preserved in the new medium. we refer to these parameters as 'push-pins', i.e. if a parameter is fixed, the associated part of the slowness surface is pinned in place. Because, these five push-pins only contain four independent moduli, we can only fix at most three push-pins. Perturbing one of the other parameters inevitably perturbs the other. Numerical results illustrating the linkage berween two push-pins, when three are fixed, are presented. So-called anomalous TI media occur when the roles of the qlt and qsv waves are reversed: in some directions the faster ray has transverse polarization. That, in turn, requires anomalous velocities at the push-pins, i.e. Ss.) 1r0,, S+s.) pa5,, and,lor Sso") Pee" (equivalent to the usual anomalous conditions Arr I Arr, AB + A55 < 0 and/or Azz I As). In the Appendix, we confirm that anomalous sensitivities of the velocities at the five push-pins only occur in such media, although the push-pins still apply if interpreted appropriately. Truly anomalous sensitivities, in which push-pins play no role, only occur in media near the boundary between normal and anomalous.

Research paper thumbnail of Compressive strength and elastic properties of a transversely isotropic calcareous mudstone

Geophysical Prospecting, 2013

This paper reports measurements of static and dynamic elastic properties plus compressive strengt... more This paper reports measurements of static and dynamic elastic properties plus compressive strength performed on a block of calcareous mudstone retrieved from an exploration well. Measurements of mechanical properties indicate that the mudstone is anisotropic with respect to all three properties. A detailed analysis of the elastic moduli computed using small unload reload cycles and simultaneous ultrasonic wave velocities shows both strong anisotropy and strong anelasticity. Surprisingly, the measurements are consistent with a mathematical description of a special type of anisotropic linear viscoelastic medium that is obtained by adding a set of compliant elements (e.g., contacts between clay particles, kerogen lenses, or micro-fractures) to an isotropic viscoelastic solid. This medium is fully characterized by density plus four parameters defining the viscoelastic solid and the excess normal compliance associated with the compliant elements. The mathematical model predicts a full set of parameters characterizing a transversely isotropic medium with a vertical axis of symmetry (a 'tiv' medium) for both low-and high-strain rate behaviour.