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Vladimir Grechka

Vladimir Grechka
Borehole Seismic, LLC

Ph.D.

About

208
Publications
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4,698
Citations

Publications

Publications (208)
Conference Paper
Full-text available
An order-of-magnitude higher frequencies in down-hole microseismic data than those in conventional surface seismic data offer an exciting possibility to image shale reservoirs at unprecedentedly high resolution , useful for geologic interpretation of reservoir structures on the scale of a few meters and for the understanding of intricacies of inter...
Conference Paper
Full-text available
Moment tensors of kinematically double-couple mic-roseismic events triggered in anisotropic formations are known to exhibit non-double-couple focal mechanisms. Their weak anisotropy approximation reveals the combinations of anisotropy coefficients of vertically transversely isotropic focal regions responsible for the deviations of moment tensors fr...
Conference Paper
Full-text available
Gyration tensors, originally devised to quantify shapes of static populations of points distributed in 3D space, are extended to dynamically varying populations, providing the theoretical foundation for analyzing their spatiotemporal evolution. Computation of gyration tensors for hypocenters of microseismic events triggered during hydraulic stimula...
Article
Full-text available
To study the topology of polarization fields in homogeneous anisotropic media, we formulate the classic Christoffel equation in the polarization variables and solve it for the slowness vectors of plane waves corresponding to a given polarization. This task might emerge in passive seismology when neither ray nor wavefront-normal direction of a body...
Article
Full-text available
Moment tensors of kinematically double-couple microseismic events triggered in anisotropic formations are known to exhibit non-double-couple focal mechanisms. The weak anisotropy approximation of these mechanisms reveals the combinations of anisotropy coefficients of vertically transversely isotropic and orthorhombic focal regions responsible for t...
Preprint
Full-text available
We formulate the classic Christoffel equation in the polarization variables and solve it for the slowness vectors of plane waves corresponding to a given unit polarization vector. Our analysis shows that, unless the equation degenerates and yields an infinite number of different slowness vectors, the finite nonzero number of its legitimate solution...
Preprint
Full-text available
A typical singularity of elastic wave propagation, often termed a shear-wave singularity, takes place when the Christoffel equation has a double root or, equivalently, two out of three slowness or phase-velocity sheets share a common point. We examine triple singularities, corresponding to triple degeneracies of the Christoffel equation, and establ...
Article
In this article, the Editor of Geophysics provides an overview of all technical articles in this issue of the journal.
Preprint
Full-text available
Reflection moveout of pure modes recorded on conventional-length spreads is described by a normal-moveout (NMO) velocity that depends on the orientation of the common-midpoint (CMP) line. Here, we introduce the concept of NMO-velocity surfaces, obtained by plotting the NMO velocity as the radius-vector along all possible directions in 3-D space, an...
Preprint
Full-text available
Conventional fracture-characterization methods assume the presence of a single set of aligned, vertical cracks in the subsurface. We relax this assumption and demonstrate the feasibility of seismic characterization of multiple fracture sets. Our technique relies on recent numerical findings, indicating that multiple, differently oriented, possibly...
Preprint
Full-text available
Multi-azimuth walkaway vertical seismic profiling (VSP) is an established technique for the estimation of in situ slowness surfaces and inferring anisotropy parameters. Normally, this the technique requires the assumption of lateral homogeneity, which makes the horizontal slowness components at depths of downhole receivers equal to those measured a...
Preprint
Multi-azimuth walkaway vertical seismic profiling (VSP) is an established technique for the estimation of in situ slowness surfaces and inferring anisotropy parameters. Normally, this technique requires the assumption of lateral homogeneity, which makes the horizontal slowness components at depths of downhole receivers equal to those measured at th...
Preprint
Full-text available
Multiple vertical fracture sets, possibly combined with horizontal fine layering, produce an equivalent medium of monoclinic symmetry with a horizontal symmetry plane. Here, we show that multi component wide azimuth reflection data (combined with known vertical velocity or reflector depth) or multi-azimuth walkaway $VSP$ surveys provide enough info...
Article
Full-text available
The recent downturn in the oil industry hit geophysicists especially hard. As entire geophysics departments were shut down, U.S. service companies reported losing 38% of their workforce by March 2016 ¹ . Layoffs across the U.S. oil industry as a whole have been much milder though, registering only a relatively modest decline of 12% from the peak em...
Article
Full-text available
We examine the feasibility of high-resolution microseismic imaging of unconventional reservoirs. Given frequencies in typical downhole microseismic data that are almost an order of magnitude higher than in seismic reflection data, a comparable increase in image resolution might be expected, bringing potential resolution of downhole microseismic ima...
Conference Paper
Full-text available
Article
Full-text available
Three algebraic surfaces – the slowness surface, the phase-velocity surface, and the group-velocity surface – play a fundamental role in the theory of seismic wave propagation in anisotropic elastic media. While the slowness (sometimes called phase-slowness) and phase-velocity surfaces are fairly simple and their main algebraic properties are well...
Article
Full-text available
Microseismic data acquired in a single observation well parallel to the axis of rotational symmetry of surrounding rocks - typically, in a vertical well drilled through a horizontally layered isotropic or vertically transversely isotropic formation - cannot be uniquely inverted for six independent components comprising the full seismic moment tenso...
Conference Paper
A recently proposed paraxial ray-based technique for relative location of microseismicity is extended to accommodate several master events with respect to which other events, termed the slaves, are located. The multi-master extension addresses two issues inherent for the existing single-master algorithm: a gradual decrease of its accuracy with the...
Article
Full-text available
A recently proposed paraxial ray-based technique for relative location of microseismicity is extended to accommodate several master events with respect to which other events, termed the slaves, are located. The multi-master extension addresses two issues inherent for the existing single-master algorithm: a gradual decrease of its accuracy with the...
Article
Full-text available
Most papers the readers find in this special section were presented at the First International Workshop on Microseismic Technology held in Asheville, North Carolina, USA, on 17–22 August 2014. The workshop’s organizing and technical program committee consisted of Werner Heigl (Apache Corporation), Vladimir Grechka (Marathon Oil), Leo Eisner (IRSM A...
Conference Paper
Full-text available
Applying the two-point paraxial ray tracing, we develop a technique for relative location of microseismic events. Our technique assumes the availability of a perforation shot or an already located microseismic event, termed the master, for which the paraxial ray tracing has been performed. The ray-tracing output for the master makes it possible to...
Conference Paper
Full-text available
A recently published analytic technique for computing locations of microseismic events jointly with velocities of homogeneous isotropic models is extended to surface microseismic monitoring and transverse isotropy with a tilted symmetry axis (TTI). The analysis of traveltimes of the direct P-, SV-, and SH-waves, conducted under the assumptions of h...
Article
Full-text available
The existing paradigm, widely accepted in the microseismic community, asserts the impossibility of unambiguous estimation of full seismic moment tensor from three-component data recorded in a single straight borehole. The statement of inversion nonuniqueness, related to the lack of illumination of the off-plane moment component in the zero solid-an...
Article
Full-text available
Applying the two-point paraxial ray tracing, we develop a technique for relative location of microseismic events. Our technique assumes the availability of a perforation shot or an already located microseismic event, termed the master, for which the paraxial ray tracing has been performed. The ray-tracing output for the master makes it possible to...
Article
Full-text available
A recently published analytic technique for computing locations of microseismic events jointly with velocities of homogeneous isotropic media was extended to surface microseismic monitoring and transversely isotropic models with tilted symmetry axes (TTI). The analysis of traveltimes of the direct P-, SV-, and SH-waves, conducted under the assumpti...
Article
Full-text available
Using the model information and in situ data on hydrofracturing in an oil and gas reservoir of the Bakken Formation (USA), potential of locating hypocenters of microseismic events concurrently with determining parameters of velocity anisotropy of seismic waves in rock mass is analyzed. It is shown that inclusion of anisotropy in the analysis improv...
Conference Paper
Full-text available
Shear waves excited by natural sources constitute a significant part of useful energy recorded in downhole microseismic surveys. In rocks, such as fractured shales, exhibiting symmetries lower than transverse isotropy (TI), the shear wavefronts are always multivalued in certain directions, potentially complicating the data processing and analysis....
Article
Modern downhole microseismic surveys often employ geometries in which ray trajectories generated by a collection of locatable events provide full polar and azimuthal coverage, making it possible to estimate the in situ seismic anisotropy. We show that traveltimes and particle motions of the direct P‐ and shear‐waves acquired in such geometries can...
Conference Paper
Full-text available
Hydraulic fracturing, routinely applied for enhancing the permeability of unconventional oil and gas reservoirs, is one of the possible causes for azimuthal anisotropy of the treated formations. Accounting for both naturally occurring and completion induced azimuthal anisotropy leads to marked improvements in the results of microseismic data proces...
Conference Paper
Full-text available
The past decade witnessed rapid development of the theory of seismic interferometry followed by numerous applications of interferometric approaches in seismic exploration and exploitation. This body of work, partially collected in the "Seismic Interferometry" supplement of Geophysics (2006), SEG's 2008 reprint volume edited by Wapenaar et al., and...
Conference Paper
Full-text available
Modern downhole microseismic surveys employ geometries in which ray trajectories generated by locatable events provide full azimuthal and polar coverage, making it possible to estimate in-situ seismic anisotropy. Traveltimes and particle motions of the direct P- and shear-waves acquired in such geometries can constrain stiffness tensors of triclini...
Article
Full-text available
Locating microseismic events is a basic task in mining, geothermal, and hydraulic-fracturing applications of induced seismicity. Our paper derives analytic solutions to the joint event-location/velocity-estimation problem for downhole data-acquisition geometries in homogeneous isotropic media. We show that traveltimes and polarizations of the direc...
Article
Full-text available
Obtaining hypocenters of microseismic events, a primary task in mining, geothermal, and hydraulic-fracturing applications of induced seismicity, requires a velocity model for computing those hypocenters. In our paper, relying on a notion that information provided by microseismic events themselves enables one to construct a velocity model and calcul...
Article
Full-text available
Two-point ray tracing in anisotropic media requires the group and phase velocities to be calculated along ray directions available at each step of a ray bending algorithm. This computation, usually done iteratively or through velocity tables, becomes exceedingly involved for shear-waves that have multivalued group-velocity surfaces, such as in the...
Article
Full-text available
It is usually believed that angular aperture of seismic data should be at least 20 degrees to allow estimation of the subsurface anisotropy. Although this is certainly true for reflection data, for which anisotropy parameters are inverted from the stacking velocities or the nonhyperbolic moveout, traveltimes of direct P- and S-waves recorded in typ...
Article
Full-text available
Passive seismic tomography, in which the event locations and the velocity model are inferred simultaneously, is seldom used to process microseismic surveys acquired in the oil and gas industry. We discuss advantages of applying tomographic ideas to typical microseismic data recorded in a single, nearly vertical well to monitor hydraulic stimulation...
Article
Full-text available
In this article, the Editor of Geophysics provides an overview of all technical articles in this issue of the journal.
Article
In this article the Editor of Geophysics provides an overview of all technical articles in this issue of the journal.
Conference Paper
Full-text available
Velocity models for locating microseismic events recorded in the oil-industry applications are usually derived from sonic logs and perforation shots. Instead of fixing these models, as is conventionally done, we update them when locating the events. This added flexibility not only improves the accuracy of predicting traveltimes of the recorded P- a...
Article
In this article, the Editor of Geophysics provides an overview of all technical articles in this issue of the journal.
Article
In this article, the Editor of Geophysics provides an overview of all technical articles in this issue of the journal.
Conference Paper
Full-text available
Microseismic events are usually located in the oil-industry applications using velocity models derived from sonic logs and perforation shots. Instead of fixing these models, as is normally done, we update them when locating the events. This added flexibility not only improves the accuracy of predicting travel-times of the recorded P- and S-waves bu...
Article
Geophysics invariably relies on expert reviewers to maintain the high quality of the journal. I am pleased to recognize several dedicated individuals whose efforts helped improve the technical content of papers published in the last year. In addition to honoring our outstanding reviewers, I would like to sincerely thank Bill Harlan who decided to s...
Article
In this article, the Editor of Geophysics provides an overview of all technical articles in this issue of the journal.
Article
Full-text available
Recent advances in parameter estimation and seismic pro-cessing have allowed incorporation of anisotropic models into a wide range of seismic methods. In particular, vertical and tilted transverse isotropy are currently treated as an inte-gral part of velocity fields employed in prestack depth migra-tion algorithms, especially those based on the wa...
Article
In this article, the Editor of Geophysics provides an overview of all technical articles in this issue of the journal.
Article
In this article, the Editor of Geophysics provides an overview of all technical articles in this issue of the journal.
Article
As they say, none of us is as knowledgeable and experienced as all of us. Peer-reviewed journals fully understand this truth and rely on reviewers to help authors produce quality papers. In addition to honoring outstanding Geophysics reviewers below, I would like to express my deep appreciation to associate editors Robert Ferguson, Sergey Fomel, Kl...
Article
Full-text available
You might be reading this column in the new “digital edition” of The Leading Edge. The digital edition is a new format in which SEG members can read TLE. It is a cover-to-cover digital replication of the entire printed edition, including all ads and links from URLs and e-mail addresses. It includes intuitive and robust navigation, the ability to pr...
Article
Full-text available
Microseismic monitoring of hydraulic well treatments is one of the most useful seismic techniques that can aid the development of tight-gas and shale-gas fields. The main challenge in these fields is an extremely low formation permeability, which lies in the microdarcy or even nanodarcy range and requires thousands of closely spaced wells to drain...
Article
Full-text available
In this article, the Editor of Geophysics provides an overview of all technical articles in this issue of the journal.
Article
Full-text available
The main objective of hydraulic well stimulation is creating fractures in a tight rock that enhance its natural permeability and make hydrocarbon production economic. Because the geometry of fractures and the permeability of treated formation influence the subsequent production, their assessment is important for the development of tight-gas fields....
Article
In this article, the Editor of Geophysics provides an overview of all technical articles in this issue of the journal.
Article
Seismic investigations using shear-wave and converted wave techniques show that very often reflected PS- and SS-waves have anomalous polarizations (accessory components). This phenomenon cannot be explained in terms of isotropic models with dipping boundaries. Computations of synthetic seismograms of reflected PS- and SS-waves were made for differe...
Article
Full-text available
It is usually believed that Gassmann fluid substitution can be performed only for a fully interconnected portion of the pore space. While this is certainly true, the presence of disconnected porosity does not necessarily invalidate Gassmann's predictions. This unconventional view is supported with an analytic proof of the equivalence of Gassmann th...
Article
Full-text available
Most papers in this special issue were presented at the 13th International Workshop on Seismic Anisotropy (13IWSA) held in Winter Park, Colorado, U.S.A. on 10–15 August 2008. The organizing committee included Ilya Tsvankin and Ken Larner of the Center for Wave Phenomena at Colorado School of Mines and James Gaiser and Edward Jenner of ION/GXT Imagi...
Article
Full-text available
Shear waves from microearthquakes induced by hydraulic fracturing are observed on three-component (3C) accelerometers along a 2 km surface profile. The S-wave waveforms exhibit at least two distinct phases suggesting shear-wave splitting. This observation implies the existence of shear anisotropy between the stimulated reservoir and the surface arr...
Article
Between 2003 and 2007, three scientific meetings were held under the “Rainbow in the Earth” banner in Oklahoma, U.S.A., California, U.S.A., and Scotland, U. K. The aim of the meetings was to bring together scientists from a diverse range of disciplines for a discussion around a common theme of scale and frequency dependence of geophysical propertie...
Conference Paper
Full-text available
Elliptical velocity dependence on the direction of wave propagation is the simplest type of anisotropy that might be encountered in the subsurface. When the symmetry axis is vertical, describing elliptical anisotropy (EA) requires only one parameter - the ellipticity coefficient - in addition to the conventional isotropic velocity. It is tempting,...
Conference Paper
Full-text available
The main objective of hydraulic well stimulation is creating fractures in a tight rock that enhance its natural permeability and make hydrocarbon production economic. As both the geometry of fractures and the permeability of treated formation influence the subsequent production, their assessment is important for development of tight-gas fields. Whi...
Article
Full-text available
It is usually believed that Gassmann fluid substitution can be performed only for a fully interconnected portion of the pore space. While this is certainly true, the presence of dis-connected porosity does not necessarily invalidate Gas-smann's predictions. This unconventional view is supported with an analytic proof of the equivalence of Gassmann...
Article
Full-text available
We establish an exact equivalence of the non-interaction approximation (NIA) and Gassmann theory in describing the changes in effective elasticity due to variations in the bulk modulus of fluid infill of isolated inclusions that have identical shapes and orientations. If the sizes of inclusions (pores or fractures) are equal, the fluid pressures in...
Article
Full-text available
The existing fracture-characterization techniques are based on assuming the unfractured host rock either to be isotropic or the magnitudes of both the background and crack-induced anisotropies to be small. I relax both assumptions and examine the effective media caused by fractures with realistic (not small) crack densities in a strongly anisotropi...
Article
Full-text available
The non-interaction approximation (NIA) formulated in compliances and the differential effective media (DEM) schemes are believed to be the most accurate theories for predicting the effective elasticity of fractured solids. While their predictions are always plausible, the DEM yields consistently softer effective properties than does the NIA. Here...
Article
Full-text available
We discuss, improve, and apply the slowness-polarization method for estimating local anisotropy from VSP data. Although the idea of fitting a given anisotropic model to the apparent slownesses measured along a well and polarization vectors recorded by three-component downhole geophones is hardly new, we extend the area of applicability of the techn...