Two methods for determining geophone orientations from VSP data

Geophysics ◽  
2006 ◽  
Vol 71 (4) ◽  
pp. V87-V97 ◽  
Author(s):  
Xiaoxian Zeng ◽  
George A. McMechan
Keyword(s):  
A Priori ◽  
Polarization Plane ◽  
Seismic Profile ◽  
P Wave ◽  
Earth Model ◽  
S Wave ◽  
Coherent Signals ◽  
Plane Method ◽  
Wave Separation ◽  
Vsp Data

Vertical seismic profile (VSP) data are usually acquired with three-component geophones of unknown azimuthal orientation. The geophone orientation must be estimated from the recorded data as a prerequisite to processing such as P- and S-wave separation, calculation of wave-incident directions, and 3D migration. We compare and combine two methods for estimating azimuthal orientation by least-squares fitting over a large number of shots. Combining the two methods can be done in an automated manner, which provides more accurate estimates of the geophone orientations than previous methods. In the polarization-plane method, we calculate the polarization plane of the first P-wave arrival. Then we subtract the source azimuth to determine the geophone orientation, independently for each geophone, with an angular uncertainty of [Formula: see text], and with no accumulated errors. In the relative-angle method, we obtain relative angles between adjacent geophone pairs using trace crosscorrelations, and operate on all coherent signals (even noise). Swapped geophone components can be detected automatically using the polarization-plane method. The main limitation of these (and all other known) methods is that uncertainties associated with path refraction are not estimated, unless some geophones have a priori known orientations, or we have a known earth model to correct for refraction.

P- and S-wave characterization of near‐surface reflectivity from glacial tills using vertical seismic profiles

Geophysics ◽  
1999 ◽  
Vol 64 (3) ◽  
pp. 970-980 ◽  
Author(s):  
Bradley J. Carr ◽  
Zoltan Hajnal
Keyword(s):  
Wave Energy ◽  
Acoustic Property ◽  
Seismic Profile ◽  
P Wave ◽  
S Wave ◽  
Glacial Deposits ◽  
Near Surface ◽  
Borehole Geophysics ◽  
Vsp Data

Fundamental reflectivity properties are established within the glacial deposits of central Saskatchewan, Canada. Multicomponent vertical seismic profile (VSP) data collected in three shallow boreholes are used to obtain detailed acoustic property information within the first 80 m of the near‐surface strata. The integration of both P- and S-wave VSP data, in conjunction with other borehole geophysics, provided a unique opportunity to obtain in‐situ seismic reflection response properties in layered clay and sand tills. P- and S-wave interval velocity profiles, in conjunction with P- and S-wave VSP reflectivities are analyzed to provide insight into seismic wavefield behavior within ∼80 m of the surface. In general, shear wave energy identifies more reflective intervals than the P-wave energy because of better vertical resolution for S-wave energy (0.75 m) compared to P-wave energy (2.3 m) based on quarter wavelength criterion. For these saturated, unconsolidated glacial deposits, more details about the lithologic constituents and in‐situ porosity are detectable from the S-wave reflectivity, but P-wave reflections provide a good technique for mapping the bulk changes. The principal cause of seismic reflectivity is the presence and/or amount of sand, and the degree of fluid‐filled porosity within the investigated formations.

Parameterization analysis and field validation of VTI-elastic full-waveform inversion in a walk-away vertical seismic profile configuration

Geophysics ◽  
2020 ◽  
Vol 85 (3) ◽  
pp. B87-B107 ◽  
Author(s):  
Wenyong Pan ◽  
Kristopher A. Innanen ◽  
Yanfei Wang
Keyword(s):  
Wave Velocity ◽  
Waveform Inversion ◽  
Seismic Profile ◽  
P Wave ◽  
Full Waveform Inversion ◽  
Walk Away ◽  
S Wave ◽  
Full Waveform ◽  
Trade Offs ◽  
Vsp Data

Elastic full-waveform inversion (FWI) in transversely isotropic media with a vertical symmetry axis (VTI) is applied to field walk-away vertical seismic profile (W-VSP) data acquired in Western Canada. The performance of VTI-elastic FWI is significantly influenced by the model parameterization choice. Synthetic analysis based on specific field survey configuration is carried out to evaluate three different VTI-elastic model parameterizations. Interparameter trade-offs are quantified using the recently introduced interparameter contamination sensitivity kernel approach. Synthetic results suggest that neglecting anisotropy leads to inaccurate velocity estimations. For the conventional vertical velocity-Thomsen’s parameter parameterization (i.e., vertical P-wave velocity, vertical S-wave velocity, Thomsen’s parameters [Formula: see text] and [Formula: see text]), a sequential inversion strategy is designed to reduce strong natural interparameter trade-offs. The model parameterizations of elastic-constant ([Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text]) and velocity-based (vertical, horizontal, and normal move-out P-wave velocities and vertical S-wave velocity) models appear to suffer from fewer interparameter trade-offs, providing more reliable velocity and anisotropy models. Results derived from application of VTI-elastic FWI to the field W-VSP data set tend to support the synthetic conclusions. Multiparameter point spread functions are calculated to quantify the local interparameter trade-offs of the inverted models. The output inversion results are interpreted to provide valuable references regarding the target hydrocarbon reservoir.

Nonlinear two‐dimensional elastic inversion of multioffset seismic data

Geophysics ◽  
1987 ◽  
Vol 52 (9) ◽  
pp. 1211-1228 ◽  
Author(s):  
Peter Mora
Keyword(s):  
Wave Equation ◽  
Wave Velocity ◽  
A Priori ◽  
Gaussian Model ◽  
Wave Impedance ◽  
P Wave ◽  
S Wave ◽  
Elastic Wave Equation ◽  
Gradient Direction ◽  
P Wave Velocity

The treatment of multioffset seismic data as an acoustic wave field is becoming increasingly disturbing to many geophysicists who see a multitude of wave phenomena, such as amplitude‐offset variations and shearwave events, which can only be explained by using the more correct elastic wave equation. Not only are such phenomena ignored by acoustic theory, but they are also treated as undesirable noise when they should be used to provide extra information, such as S‐wave velocity, about the subsurface. The problems of using the conventional acoustic wave equation approach can be eliminated via an elastic approach. In this paper, equations have been derived to perform an inversion for P‐wave velocity, S‐wave velocity, and density as well as the P‐wave impedance, S‐wave impedance, and density. These are better resolved than the Lamé parameters. The inversion is based on nonlinear least squares and proceeds by iteratively updating the earth parameters until a good fit is achieved between the observed data and the modeled data corresponding to these earth parameters. The iterations are based on the preconditioned conjugate gradient algorithm. The fundamental requirement of such a least‐squares algorithm is the gradient direction which tells how to update the model parameters. The gradient direction can be derived directly from the wave equation and it may be computed by several wave propagations. Although in principle any scheme could be chosen to perform the wave propagations, the elastic finite‐ difference method is used because it directly simulates the elastic wave equation and can handle complex, and thus realistic, distributions of elastic parameters. This method of inversion is costly since it is similar to an iterative prestack shot‐profile migration. However, it has greater power than any migration since it solves for the P‐wave velocity, S‐wave velocity, and density and can handle very general situations including transmission problems. Three main weaknesses of this technique are that it requires fairly accurate a priori knowledge of the low‐ wavenumber velocity model, it assumes Gaussian model statistics, and it is very computer‐intensive. All these problems seem surmountable. The low‐wavenumber information can be obtained either by a prior tomographic step, by the conventional normal‐moveout method, by a priori knowledge and empirical relationships, or by adding an additional inversion step for low wavenumbers to each iteration. The Gaussian statistics can be altered by preconditioning the gradient direction, perhaps to make the solution blocky in appearance like well logs, or by using large model variances in the inversion to reduce the effect of the Gaussian model constraints. Moreover, with some improvements to the algorithm and more parallel computers, it is hoped the technique will soon become routinely feasible.

Application of instantaneous rotations to S‐wave vertical seismic profiling

Geophysics ◽  
1997 ◽  
Vol 62 (5) ◽  
pp. 1365-1368
Author(s):  
M. Boulfoul ◽  
Doyle R. Watts
Keyword(s):  
High Amplitude ◽  
Seismic Profile ◽  
P Wave ◽  
Petroleum Exploration ◽  
S Wave ◽  
Amplitude Variation With Offset ◽  
Seismic Profiling ◽  
Vertical Seismic Profiling ◽  
Seismic Models ◽  
Low Amplitude

The petroleum exploration industry uses S‐wave vertical seismic profiling (VSP) to determine S‐wave velocities from downgoing direct arrivals, and S‐wave reflectivities from upgoing waves. Seismic models for quantitative calibration of amplitude variation with offset (AVO) data require S‐wave velocity profiles (Castagna et al., 1993). Vertical summations (Hardage, 1983) of the upgoing waves produce S‐wave composite traces and enable interpretation of S‐wave seismic profile sections. In the simplest application of amplitude anomalies, the coincidence of high amplitude P‐wave reflectivity and low amplitude S‐wave reflectivity is potentially a direct indicator of the presence of natural gas.

The interrelationship between electrical resistivity and VP/VS ratio: A novel approach to constrain the subsurface resistivity structure in data gap areas in a seismogenic zone

Geophysics ◽  
2021 ◽  
pp. 1-44
Author(s):  
Ujjal K. Borah ◽  
Prasanta K. Patro
Keyword(s):  
Electrical Resistivity ◽  
A Priori ◽  
Fault Zones ◽  
Middle Part ◽  
Seismogenic Zone ◽  
Earth Model ◽  
Seismic Zone ◽  
S Wave ◽  
Data Gap ◽  
Earthquake Zone

Large man-made water-reservoirs promote fluid diffusion and cause critically stressed fault zones underneath to trigger earthquakes. Electrical resistivity is a crucial property to investigate such fluid-filled fault zones. We, therefore, carry out magnetotelluric (MT) investigation to explore an intra-plate earthquake zone, which is related to artificial reservoir triggered seismicity. However, due to surface access restrictions, our dataset has a gap in coverage in the middle part of the study area. This data gap region coincides with the earthquake hypocenter distribution in that intra-plate earthquake zone. Therefore, it is vital to fill the data gap to get the electrical signature of the active seismic zone. To compensate for the data gap, we develop a relation that connects resistivity with the ratio of seismic P- to S-wave velocity ( VP/ VS). Utilizing this relation, we estimate a priori resistivity distribution in the data gap region from known vp/vs values during inversion to compensate for the data gap. A comparison study of the root mean square (RMS) misfits of inversion outputs (with and without data gap filled) proves the effectiveness of the established relation. The inversion outputs obtained using the established relation brings out fault signatures in the data gap region. To examine the reliability and accuracy of these fault signatures, we occupy a portion of the data gap with new MT sites. We compare the inversion output from this new setup with the inversion output obtained from the established relation and observe that the electrical signatures in both outputs are spatially correlated. Further, a synthetic test on a similar earth model establishes the credibility and robustness of the derived relation.

Amplitude-based misfit functions in viscoelastic full-waveform inversion applied to walk-away vertical seismic profile data

Geophysics ◽  
2019 ◽  
Vol 84 (5) ◽  
pp. B335-B351 ◽  
Author(s):  
Wenyong Pan ◽  
Kristopher A. Innanen
Keyword(s):  
Amplitude Ratio ◽  
Waveform Inversion ◽  
Seismic Profile ◽  
P Wave ◽  
Western Canada ◽  
Full Waveform Inversion ◽  
Walk Away ◽  
Profile Data ◽  
S Wave ◽  
Full Waveform

Viscoelastic full-waveform inversion is applied to walk-away vertical seismic profile data acquired at a producing heavy-oil field in Western Canada for the determination of subsurface velocity models (P-wave velocity [Formula: see text] and S-wave velocity [Formula: see text]) and attenuation models (P-wave quality factor [Formula: see text] and S-wave quality factor [Formula: see text]). To mitigate strong velocity-attenuation trade-offs, a two-stage approach is adopted. In Stage I, [Formula: see text] and [Formula: see text] models are first inverted using a standard waveform-difference (WD) misfit function. Following this, in Stage II, different amplitude-based misfit functions are used to estimate the [Formula: see text] and [Formula: see text] models. Compared to the traditional WD misfit function, the amplitude-based misfit functions exhibit stronger sensitivity to attenuation anomalies and appear to be able to invert [Formula: see text] and [Formula: see text] models more reliably in the presence of velocity errors. Overall, the root-mean-square amplitude-ratio and spectral amplitude-ratio misfit functions outperform other misfit function choices. In the final outputs of our inversion, significant drops in the [Formula: see text] to [Formula: see text] ratio (~1.6) and Poisson’s ratio (~0.23) are apparent within the Clearwater Formation (depth ~0.45–0.50 km) of the Mannville Group in the Western Canada Sedimentary Basin. Strong [Formula: see text] (~20) and [Formula: see text] (~15) anomalies are also evident in this zone. These observations provide information to help identify the target attenuative reservoir saturated with heavy-oil resources.

Velocity anisotropy in shale determined from crosshole seismic and vertical seismic profile data

Geophysics ◽  
1990 ◽  
Vol 55 (4) ◽  
pp. 470-479 ◽  
Author(s):  
D. F. Winterstein ◽  
B. N. P. Paulsson
Keyword(s):  
Seismic Profile ◽  
P Wave ◽  
Isotropic Model ◽  
S Wave ◽  
Vertical Seismic Profile ◽  
Near Surface ◽  
S Waves ◽  
Velocity Anisotropy ◽  
Wave Velocities ◽  
Late Tertiary

Crosshole and vertical seismic profile (VST) data made possible accurate characterization of the elastic properties, including noticeable velocity anisotropy, of a near‐surface late Tertiary shale formation. Shear‐wave splitting was obvious in both crosshole and VSP data. In crosshole data, two orthologonally polarrized shear (S) waves arrived 19 ms in the uppermost 246 ft (75 m). Vertically traveling S waves of the VSP separated about 10 ms in the uppermost 300 ft (90 m) but remained at nearly constant separation below that level. A transversely isotropic model, which incorporates a rapid increase in S-wave velocities with depth but slow increase in P-wave velocities, closely fits the data over most of the measured interval. Elastic constants of the transvesely isotropic model show spherical P- and [Formula: see text]wave velocity surfaces but an ellipsoidal [Formula: see text]wave surface with a ratio of major to minor axes of 1.15. The magnitude of this S-wave anisotropy is consistent with and lends credence to S-wave anisotropy magnitudes deduced less directly from data of many sedimentary basins.

Quantifying hydraulically induced fracture height and density from rapid time-lapse DAS VSP

Geophysics ◽  
2020 ◽  
pp. 1-26
Author(s):  
Xiaomin Zhao ◽  
Mark E. Willis ◽  
Tanya Inks ◽  
Glenn A. Wilson
Keyword(s):  
Rock Physics ◽  
Horizontal Wells ◽  
Time Lapse ◽  
Seismic Profile ◽  
P Wave ◽  
Fracture Properties ◽  
Vsp Data ◽  
Rock Physics Modeling ◽  
Physics Modeling ◽  
Fracture Height

Several recent studies have advanced the use of time-lapse distributed acoustic sensing (DAS) vertical seismic profile (VSP) data in horizontal wells for determining hydraulically stimulated fracture properties. Hydraulic fracturing in a horizontal well typically generates vertical fractures in the rock medium around each stage. We model the hydraulically stimulated formation with vertical fracture sets about the lateral wellbore as a horizontally transverse isotropic (HTI) medium. Rock physics modeling is used to relate the anisotropy parameters to fracture properties. This modeling was used to develop an inversion for P-wave time delay to fracture height and density of each stage. Field data from two horizontal wells were analyzed, and fracture height evaluated using this technique agreed with microseismic analysis.

scholarly journals Downhole distributed acoustic seismic profiling at Skytrain Ice Rise, West Antarctica

2021 ◽  
Author(s):  
Alex Brisbourne ◽  
Mike Kendall ◽  
Sofia Kufner ◽  
Thomas Hudson ◽  
Andrew Smith
Keyword(s):  
Wave Energy ◽  
Drilling Fluid ◽  
Ice Sheet ◽  
Seismic Profile ◽  
Seismic Attenuation ◽  
Weddell Sea ◽  
P Wave ◽  
West Antarctica ◽  
S Wave ◽  
Ice Flow

<p>Antarctic ice sheet history is imprinted in the structure and fabric of the ice column. At ice rises, the signature of ice flow history is preserved due to the low strain rates inherent at these independent ice flow centres. We present results from a distributed acoustic sensing (DAS) experiment at Skytrain Ice Rise in the Weddell Sea Sector of West Antarctica, aimed at delineating the englacial fabric to improve our understanding of ice sheet history in the region. This pilot experiment demonstrates the feasibility of an innovative technique to delineate ice rise structure. Both direct and reflected P- and S-wave energy, as well as surface wave energy, are observed using a range of source offsets, i.e., a walkaway vertical seismic profile (VSP), recorded using fibre optic cable. Significant noise, which results from the cable hanging untethered in the borehole, is modelled and suppressed at the processing stage. At greater depth, where the cable is suspended in drilling fluid, seismic interval velocities and attenuation are measured. Vertical P-wave velocities are high (V<sub>INT</sub> = 4029 ± 244 m s<sup>-1</sup>) and consistent with a strong vertical cluster fabric. Seismic attenuation is high (Q<sub>INT </sub>= 75 ± 12) and contrary to observations in ice sheets over this temperature range. The signal level is too low, and the noise level too high, to undertake analysis of englacial fabric variability. However, modelling of P- and S-wave traveltimes and amplitudes with a range of fabric geometries, combined with these measurements, demonstrates the capacity of the DAS method to discriminate englacial fabric distribution. From this pilot study we make a number of recommendations for future experiments aimed at quantifying englacial fabric to improve our understanding of recent ice sheet history.</p><p> </p>

Practical concept of traveltime inversion of simulated P-wave vertical seismic profile data in weak to moderate arbitrary anisotropy

Geophysics ◽  
2020 ◽  
Vol 85 (4) ◽  
pp. C107-C123
Author(s):  
Ivan Pšenčík ◽  
Bohuslav Růžek ◽  
Petr Jílek
Keyword(s):  
Waveform Inversion ◽  
Anisotropic Media ◽  
Compressional Wave ◽  
Seismic Profile ◽  
P Wave ◽  
Source Distribution ◽  
S Wave ◽  
Vertical Seismic Profile ◽  
Weak Anisotropy ◽  
Traveltime Inversion

We have developed a practical concept of compressional wave (P-wave) traveltime inversion in weakly to moderately anisotropic media of arbitrary symmetry and orientation. The concept provides sufficient freedom to explain and reproduce observed anisotropic seismic signatures to a high degree of accuracy. The key to this concept is the proposed P-wave anisotropy parameterization (A-parameters) that, together with the use of the weak-anisotropy approximation, leads to a significantly simplified theory. Here, as an example, we use a simple and transparent formula relating P-wave traveltimes to 15 P-wave A-parameters describing anisotropy of arbitrary symmetry. The formula is used in the inversion scheme, which does not require any a priori information about anisotropy symmetry and its orientation, and it is applicable to weak and moderate anisotropy. As the first step, we test applicability of the proposed scheme on a blind inversion of synthetic P-wave traveltimes generated in vertical seismic profile experiments in homogeneous models. Three models of varying anisotropy are used: tilted orthorhombic and triclinic models of moderate anisotropy (approximately 10%) and an orthorhombic model of strong anisotropy (>25%) with a horizontal plane of symmetry. In all cases, the inversion yields the complete set of 15 P-wave A-parameters, which make reconstruction of corresponding phase-velocity surfaces possible with high accuracy. The inversion scheme is robust with respect to noise and the source distribution pattern. Its quality depends on the angular illumination of the medium; we determine how the absence of nearly horizontal propagation directions affects inversion accuracy. The results of the inversion are applicable, for example, in migration or as a starting model for inversion methods, such as full-waveform inversion, if a model refinement is desired. A similar procedure could be designed for the inversion of S-wave traveltimes in anisotropic media of arbitrary symmetry.

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