Comparison of VSP and sonic-log data in nonvertical wells in a heterogeneous structure

Geophysics ◽  
2008 ◽  
Vol 73 (4) ◽  
pp. U19-U25 ◽  
Author(s):  
Petr Bulant ◽  
Luděk Klimeš
Keyword(s):  
Seismic Waves ◽  
Heterogeneous Structure ◽  
Geologic Structure ◽  
Log Data ◽  
Seismic Profiling ◽  
Vertical Seismic Profiling ◽  
Sonic Log ◽  
Vertical Propagation ◽  
Well Trajectory ◽  
The Difference

To compare the results of sonic-log measurements and of vertical seismic profiling (VSP), sonic-log velocities are used to estimate the corresponding traveltime in the geologic structure, which is then compared with the VSP traveltime. We show how to calculate the sonic-log traveltime in the geologic structure from the sonic-log velocities while taking into account the effects of the nonvertical propagation of seismic waves, resulting from the VSP-source offset and from heterogeneous velocity in the structure, together with the effects of the well trajectory deviating from strictly vertical. Errors caused by the commonly used assumption of vertical propagation may considerably exceed the difference of the measured VSP traveltimes from the sonic-log traveltimes.

Investigation of multiple reflections and wave conversion by means of a vertical wave test (vertical seismic profiling) in southern Mississippi

Geophysics ◽  
1982 ◽  
Vol 47 (7) ◽  
pp. 977-1000 ◽  
Author(s):  
C. C. Lash
Keyword(s):  
Wave Train ◽  
Low Frequency ◽  
P Wave ◽  
Multiple Reflections ◽  
Low Velocity ◽  
P Waves ◽  
S Waves ◽  
Seismic Profiling ◽  
Vertical Seismic Profiling ◽  
Sonic Log

A vertical wave test employing the vertical seismic profiling (VSP) technique in southern Mississippi confirmed suspicions that apparent multiple reflections might include converted waves as well as multiply reflected compressional waves. Both compressional (P) and shear (S) waves generated near the source were observed to travel to great depths, and P‐to‐S conversions were apparent in deep zones as well as shallow. P‐wave reflections were observed in agreement with predictions from synthetic records based on the sonic log. Up‐traveling P‐waves were reflected a short distance below the surface, at the base of the low‐velocity layer, and were followed as down‐traveling P‐waves to 200 ft depth by means of a vertical spread. Below 2000 ft and following the first P wave train, the predominate energy appeared to be down‐traveling P‐waves which could not be traced back to the reflection of up‐traveling P‐waves. The continuity of wavelets indicated instead that the strong down‐traveling S‐waves generated near the source produced P‐waves by S‐to‐P conversion somewhere in the zone between 800 and 1400 ft. The interference on the recordings made with an individual seismometer, or a small group of seismometers, using dynamite shots as the source was generally of a low‐frequency nature, so that the signal‐to‐noise (S/N) ratio was improved by the use of a high passband filter. The interference was greatly reduced without the need for a filter on recordings in which the source was a distributed charge of 100 ft length. The distributed charge produced much less shear‐wave energy in the P reflection band, demonstrating that the interference encountered when using a concentrated charge source was the consequence of the generation of S‐waves near the source. The distributed charges were previously chosen as a means for effectively eliminating secondary (ghost) reflections, an unwanted form of multiple reflections.

The O’Doherty‐Anstey formula and localization of seismic waves

Geophysics ◽  
1993 ◽  
Vol 58 (5) ◽  
pp. 736-740 ◽  
Author(s):  
Serguei A. Shapiro ◽  
Holger Zien
Keyword(s):  
Multiple Scattering ◽  
Seismic Waves ◽  
Seismic Attenuation ◽  
Adequate Description ◽  
Amplitude Variation ◽  
Amplitude Variation With Offset ◽  
Seismic Profiling ◽  
Seismic Amplitude ◽  
Vertical Seismic Profiling ◽  
Vsp Data

Angle (or offset) dependent effects of scattering in finely layered media can be observed and analyzed or must be compensated for in vertical seismic profiling data (VSP‐ data), crosshole observations, or seismic amplitude variation with offset (AVO) measurements. Moreover, the adequate description of multiple scattering is important for the study of seismic attenuation in sediments and for the design of inversion procedures.

Seismic versus sonic velocities: A vertical seismic profiling study

Geophysics ◽  
1984 ◽  
Vol 49 (8) ◽  
pp. 1153-1168 ◽  
Author(s):  
Robert R. Stewart ◽  
Phil D. Huddleston ◽  
Tze Kong Kan
Keyword(s):  
Wave Propagation ◽  
Layer Thickness ◽  
Seismic Wave ◽  
Short Path ◽  
Velocity Dispersion ◽  
Seismic Wave Propagation ◽  
Synthetic Seismograms ◽  
Seismic Profiling ◽  
Vertical Seismic Profiling ◽  
Sonic Log

Vertical seismic profiling (VSP) techniques provide a method to measure accurately the seismic velocity and lithologic structure near the borehole. The analysis of a VSP survey can also provide insight into seismic‐wave propagation especially when related to sonic measurements. But VSP and sonic log velocities (or traveltimes) are often found to disagree. Recent field evidence of these differences suggests that the VSP traveltimes are delayed with respect to the integrated sonic times, especially in the deep section (>3000 ft), by about 2.0 ms/1000 ft on the average. The VSP has numerous applications in exploration geophysics, such as calibrating the sonic log. It is thus important to understand why the two measurements differ. Differences in the geometries, source frequencies, and instrumental errors of the two surveys are reviewed. More detailed analysis of seismic wave propagation in the VSP shows that short‐path multiples and velocity dispersion can have a significant delaying effect on the seismic traveltimes. One‐dimensional, wide‐band VSP synthetic seismograms are generated in the frequency domain to study these effects. Different parameters (bandwidth, signal‐to‐noise, layer thickness, multiples, attenuation, dispersion) are varied in the synthetic seismograms. A comparative display of synthetic VSP traveltime minus the integrated sonic time is used to view the effects of these parameters on the synthetic traces. Reasonable variation in noise, layer thickness, bandwidth, and picking method have a small effect on traveltimes. Field data from the Anadarko Basin (4 wells) and an East Texas well are examined with the same technique. From the modeling and field examples, it is found that short‐path multiples can cause a seismic pulse delay of up to 2.0 ms/1000 ft with respect to the integrated sonic log in highly cyclically stratified sections. Velocity dispersion associated with attenuation can have a larger effect, causing up to 7.0 ms/1000 ft delay of the VSP traveltimes with respect to the integrated sonic. These wave propagation effects can explain the observed discrepancy between VSP and integrated sonic times in the deep section.

VSP detection of interbed multiples using inside‐outside corridor stacking

Geophysics ◽  
1997 ◽  
Vol 62 (5) ◽  
pp. 1628-1635 ◽  
Author(s):  
Andrew Burton ◽  
Larry Lines
Keyword(s):  
Well Log ◽  
Multiple Reflections ◽  
Log Data ◽  
Seismic Profiling ◽  
Vertical Seismic Profiling ◽  
Long Period ◽  
Multiple Attenuation ◽  
Predictive Deconvolution ◽  
Short Period ◽  
And Inversion

One of the most difficult problems in the exploration of Devonian reefs is the separation of primaries and short period interbed multiples. This is especially true in cases where weak primary reflections from porous reefal carbonates can be easily masked by interbed multiples generated from stronger shale/carbonate reflections above the reef. This problem of primary‐multiple separation is difficult since there are small normal moveout differences between the primary and short‐period multiple reflections, thus stacking might not be as effective at suppressing multiples as one would hope. Also, predictive deconvolution may be ineffective if it is difficult to design an accurate prediction distance for the deconvolution filter. The ineffectiveness of stacking and deconvolution in some cases has caused us to look for other alternatives. A recent paper by Lines (1996) advocates the use of shaping deconvolution and inversion methods that use well log information. Since reliable well log data are not always available, we examine a vertical seismic profiling (VSP) corridor stacking method for multiple identification proposed in Hardage (1983, 154–155) which obviates some of the conventional problems and which does not require well log data. A variation of this concept was applied to long‐period multiple attenuation by Hampson and Mewhort (1983).

Separation of frequency-dependent scattering and inelastic absorption by waveform inversion of VSP data constrained by well logs

2019 ◽  
pp. 94-97
Author(s):  
A. S. Pirogova
Keyword(s):  
Seismic Waves ◽  
Waveform Inversion ◽  
Seismic Attenuation ◽  
Well Log ◽  
Frequency Dependent ◽  
Seismic Profiling ◽  
Vertical Seismic Profiling ◽  
The Earth ◽  
Two Factors ◽  
Vsp Data

The paper presents an approach to estimation of frequency-dependent attenuation of seismic waves propagating in the earth subsurface. The approach is based on the waveform inversion of vertical seismic profiling data acquired in a borehole. Incorporation of well log data (in particular, sonic and density logs) in the forward modelling routine allows for separation of two factors that cause frequency-dependent seismic attenuation. In particular, the inversion facilitates separation of 1D scattering versus inelastic absorption in the horizontally layered subsurface.

Estimation of fracture compliance based on group delays inferred from full-waveform sonic log data

2021 ◽  
Author(s):  
Zhenya Zhou ◽  
Eva Caspari ◽  
Nicolás D. Barbosa ◽  
Andrew Greenwood ◽  
Klaus Holliger
Keyword(s):  
Time Delay ◽  
Travel Time ◽  
Seismic Waves ◽  
Test Site ◽  
P Wave ◽  
Log Data ◽  
Full Waveform ◽  
Sonic Log ◽  
Wide Range ◽  
First Arrival Travel Times

<p>Fractures, which are ubiquitous in the Earth’s upper crust, have significant impacts on a wide range of human activities, and, hence, their adequate characterization is of wide interest and importance. Seismic methods have significant potential for effectively addressing this objective. When a seismic wave propagates across a fluid-filled fracture, its amplitude is diminished and its travel time is increased. Based on the linear slip theory, the associated amplitude decays and phase delays<strong> </strong>can be used to estimate the mechanical compliance of fractures.<strong> </strong>Full-waveform sonic (FWS) log data are particularly well-suited for this purpose. While the amplitudes of FWS data acquired during standard continuous logging runs (tool being moved uphole at a constant logging speed) can be somewhat unstable, the associated first-arrival travel times are generally quite robust. In this work, we exploit the relation between the time delay that seismic waves experience across fractures and relate them to the associated compliances. Specifically, we estimate fracture compliance from the differences in group time delay of the refracted P-wave between fractured and non-fractured sections along a borehole. Numerical simulations indicate that the proposed method provides reliable compliance estimates not only for individual fractures, but also for sets of multiple discrete fractures. This finding is corroborated by applying our approach to FWS log data acquired in the course of standard logging runs in the Bedretto Underground Laboratory (www.bedrettolab.ethz.ch). Our estimates are comparable to previously inferred compliance values in a closely comparable geological environment (Grimsel test site, www.grimsel.com). The latter were inferred under rather ideal conditions, involving the quasi-static acquisition of the FWS data as well as the combination of amplitude and travel time information for their interpretation. An interesting and important open question, which we plan to address in the following, concerns the influence of the heterogeneity of the host rock embedding the fractures on compliance estimation in general and on the proposed method in particular.</p>

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