Shear Wave Velocities Determined From Long-and Short-Spaced Borehole Acoustic Devices

1980 ◽  
Vol 20 (05) ◽  
pp. 317-326 ◽  
Author(s):  
E.A. Koerperich
Keyword(s):  
Shear Wave ◽  
Material Balance ◽  
Shear Velocity ◽  
High Amplitude ◽  
Compressional Wave ◽  
P Wave ◽  
Considerable Uncertainty ◽  
Seismic Amplitude ◽  
Wave Interference ◽  
Sand Control

Abstract Acoustic waveforms from long- and short-spacedsonic logs were investigated to determine ifshort-spaced tools give accurate measurements of shear wave velocity. Compressional wave interference canaffect shear velocities from both tools adversely.However, the short-spaced tool was useful over awider range of conditions. Introduction The areas where shear velocity data can be appliedtheoretically or empirically are diverse. Most of theseinvolve use of the dynamic elastic rock constants, which can be computed from shear (S) velocity[along with compressional (P) velocity and bulkdensity, which are obtained readily from existingwireline logging devices]. Some of these applicationareas are (1) seismic amplitude calibration andinterpretation, (2) sand control,(3) formationfracturing, reservoir material balance and subsidencestudies(through relationships between rock andpore-volume changes with stress),(4) lithologyand porosity, 14 and (5) geopressure prediction. While rich in possible application areas, shearvelocity is difficult to measure automatically withconventional acoustic devices and detection schemes.Except in limited lithology-logging conditions, manual examination of waveforms commonly isrequired to extract shear velocity. Even then there has been considerable uncertainty in shear arrivals onshort-spaced tools due to P-wave interference. Insofter rocks, conventional tools simply do nottransmit distinct shear arrivals. Current axial transmitter-receiver (T-R) toolsare designed primarily for detection of P waves.Downhole amplifiers adjusted to accentuate the firstP-wave arrival normally saturate through the shearand late P regions of the waveform. When downholegain is reduced to eliminate amplifier saturation, initial shear arrivals generally are superimposed onlate P arrivals. This interference makes automaticdetection difficult and leads to a concern about theconsistency and dependability of this arrival fordetermining shear velocity. The interference effect iscompounded in that the initial shear energycommonly is not extremely high relative to P-waveenergy. Rather shear amplitudes are generally lowinitially and increase with succeeding arrivals. Theshear breaking point, therefore, almost always isobscured by P-wave interference. In somelithologies, such as low-porosity carbonates, an earlyshear arrival (probably the second or third shearhalf-cycle)sometimes has relatively high amplitudecompared with superimposed P arrivals. This"high-amplitude" event is commonly used to determineshear velocity. SPEJ P. 317＾

scholarly journals Advantages of Shear Wave Seismic in Morrow Sandstone Detection

2011 ◽  
Vol 2011 ◽  
pp. 1-16 ◽  
Author(s):  
Paritosh Singh ◽  
Thomas Davis
Keyword(s):  
Shear Wave ◽  
Pure Shear ◽  
High Amplitude ◽  
Compressional Wave ◽  
Side Lobe ◽  
P Wave ◽  
S Wave ◽  
Converted Wave ◽  
P Waves ◽  
Wave Data

The Upper Morrow sandstones in the western Anadarko Basin have been prolific oil producers for more than five decades. Detection of Morrow sandstones is a major problem in the exploration of new fields and the characterization of existing fields because they are often very thin and laterally discontinuous. Until recently compressional wave data have been the primary resource for mapping the lateral extent of Morrow sandstones. The success with compressional wave datasets is limited because the acoustic impedance contrast between the reservoir sandstones and the encasing shales is small. Here, we have performed full waveform modeling study to understand the Morrow sandstone signatures on compressional wave (P-wave), converted-wave (PS-wave) and pure shear wave (S-wave) gathers. The contrast in rigidity between the Morrow sandstone and surrounding shale causes a strong seismic expression on the S-wave data. Morrow sandstone shows a distinct high amplitude event in pure S-wave modeled gathers as compared to the weaker P- and PS-wave events. Modeling also helps in understanding the adverse effect of interbed multiples (due to shallow high velocity anhydrite layers) and side lobe interference effects at the Morrow level. Modeling tied with the field data demonstrates that S-waves are more robust than P-waves in detecting the Morrow sandstone reservoirs.

Core-Derived Velocity Systematics, Mississippian Meramec Formation, Oklahoma

SPE Journal ◽  
2021 ◽  
pp. 1-10
Author(s):  
Jing Fu ◽  
Carl Sondergeld ◽  
Chandra Rai
Keyword(s):  
Shear Wave ◽  
Volume Fraction ◽  
Anisotropy Parameter ◽  
Clay Content ◽  
Weight Fraction ◽  
Shear Velocity ◽  
Compressional Wave ◽  
P Wave ◽  
S Wave ◽  
Trend Line

Summary Elastic wave velocities are commonly used to predict porosity, mineralogy, and lithology from formation properties. When only P-wave sonics are available in historical wells, systematics for predicting shear velocities are useful for developing elastic models. Although much research has been done on conventional reservoir velocity systematics, the equivalency for unconventional formations is still a work in progress. There has also been a limited number of research studies with laboratory measures published. Using laboratory pulse transmission ultrasonic data, we created a Vp-Vs systematic for the Meramec Formation in this study. The effects of porosity and mineralogy on velocities are explored, as well as a comparison of Meramec velocity systematics with well-established literature systematics. Vp and Vs measurements were taken on 385 dodecane-saturated core samples from seven Meramec wells (106 vertical and 279 horizontal plugs). S-wave and P-wave anisotropy in Meramec Formation samples used in this study are typically less than 10%. Each sample was also tested for porosity and mineralogy. We find that velocities are more sensitive to porosity than mineralogy by a factor of 10. Below are our equations for predicting Vp and Vs (in km/s), when only clay content and porosity are known. In these equations, φ is the volume fraction pores, and Clays is the weight fraction of clay. These equations are for those samples in which there is low P-wave and S-wave anisotropies:(1)Vp=6.4−1.2*Clays−15.4*φ(R2=0.5),(2)Vs=3.6−0.5*Clays−5.2*φ(R2=0.4). We suggest two methods for calculating Vs from Vp: Ignoring anisotropy, we combined both Vp and Vs measurements from all vertical plugs and low anisotropy horizontal plugs to create a single shear wave predictor; and considering anisotropy, Vp measurements from horizontal plugs were corrected using Thomsen’s compressional wave anisotropy parameter, after which a shear velocity predictor was generated. The shear wave predictors for dodecane-saturated measurements are as follows (all velocities are km/s):(3)Method 1: Vs= 0.90 + 0.42*Vp (R2=0.7),(4)Method 2: Vs= 0.80 + 0.45*Vp (R2=0.6). The residual and estimated error in Eq. 3 is slightly less than in Eq. 4. Even though there is a significant variance in measurement frequency, the Meramec velocity systematic shows good agreement with dipole wireline measurements using the first equation. The Meramec velocity systematics differ significantly from previously published systematics, such as the trend line by Greenberg and Castagna (1992) and the shale trend line by Vernik et al. (2018). Using the correlations by Greenberg and Castagna (1992) for limestone or dolomite, the shear velocities of the samples in this study cannot be predicted. These data have yielded shear wave systematics, which can be used in wireline and seismic investigations. The results suggest that the method of ignoring anisotropy yields a better Vs estimate than the one that takes anisotropy into account. Using well-established shear wave velocity systematics from the published literature can result in an estimated inaccuracy of greater than 16%. It is important to calibrate velocity systematics to the target formation.

Sonic logging of compressional‐wave velocities in a very slow formation

Geophysics ◽  
1995 ◽  
Vol 60 (6) ◽  
pp. 1627-1633 ◽  
Author(s):  
Bart W. Tichelaar ◽  
Klaas W. van Luik
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Compressional Wave ◽  
P Wave ◽  
Dipole Source ◽  
Frequency Spectra ◽  
Unconsolidated Sands ◽  
Wave Velocities ◽  
Shear Wave Velocities ◽  
Sonic Logging

Borehole sonic waveforms are commonly acquired to produce logs of subsurface compressional and shear wave velocities. To this purpose, modern borehole sonic tools are usually equipped with various types of acoustic sources, i.e., monopole and dipole sources. While the dipole source has been specifically developed for measuring shear wave velocities, we found that the dipole source has an advantage over the monopole source when determining compressional wave velocities in a very slow formation consisting of unconsolidated sands with a porosity of about 35% and a shear wave velocity of about 465 m/s. In this formation, the recorded compressional refracted waves suffer from interference with another wavefield component identified as a leaky P‐wave, which hampers the determination of compressional wave velocities in the sands. For the dipole source, separation of the compressional refracted wave from the recorded waveforms is accomplished through bandpass filtering since the wavefield components appear as two distinctly separate contributions to the frequency spectrum: a compressional refracted wave centered at a frequency of 6.5 kHz and a leaky P‐wave centered at 1.3 kHz. For the monopole source, the frequency spectra of the various waveform components have considerable overlap. It is therefore not obvious what passband to choose to separate the compressional refracted wave from the monopole waveforms. The compressional wave velocity obtained for the sands from the dipole compressional refracted wave is about 2150 m/s. Phase velocities obtained for the dispersive leaky P‐wave excited by the dipole source range from 1800 m/s at 1.0 kHz to 1630 m/s at 1.6 kHz. It appears that the dipole source has an advantage over the monopole source for the data recorded in this very slow formation when separating the compressional refracted wave from the recorded waveforms to determine formation compressional wave velocities.

Seismic velocities of unconsolidated sands: Part 1 — Pressure trends from 0.1 to 20 MPa

Geophysics ◽  
2007 ◽  
Vol 72 (1) ◽  
pp. E1-E13 ◽  
Author(s):  
Michael A. Zimmer ◽  
Manika Prasad ◽  
Gary Mavko ◽  
Amos Nur
Keyword(s):  
Shear Wave ◽  
Pressure Dependence ◽  
Glass Bead ◽  
Theoretical Models ◽  
Compressional Wave ◽  
P Wave ◽  
Seismic Velocities ◽  
Unconsolidated Sands ◽  
Wave Velocities ◽  
Shear Wave Velocities

Knowledge of the pressure dependences of seismic velocities in unconsolidated sands is necessary for the remote prediction of effective pressures and for the projection of velocities to unsampled locations within shallow sand layers. We have measured the compressional- and shear-wave velocities and bulk, shear, and P-wave moduli at pressures from [Formula: see text] in a series of unconsolidated granular samples including dry and water-saturated natural sands and dry synthetic sand and glass-bead samples. The shear-wave velocities in these samples demonstrate an average pressure dependence approximately proportional to the fourth root of the effective pressure [Formula: see text], as commonly observed at lower pressures. For the compressional-wave velocities, theexponent in the pressure dependence of individual dry samples is consistently less than the exponent for the shear-wave velocity of the same sample, averaging 0.23 for the dry sands and 0.20 for the glass-bead samples. These pressure dependences are generally consistent over the entire pressure range measured. A comparison of the empirical results to theoretical predictions based on Hertz-Mindlin effective-medium models demonstrates that the theoretical models vastly overpredict the shear moduli of the dry granular frame unless the contacts are assumed to have no tangential stiffness. The models also predict a lower pressure exponent for the moduli and velocities [Formula: see text] than is generally observed in the data. We attribute this discrepancy in part to the inability of the models to account for decreases in the amount of slip or grain rotation occurring at grain-to-grain contacts with increasing pressure.

Nongeometrically converted shear waves in marine streamer data

Geophysics ◽  
2012 ◽  
Vol 77 (6) ◽  
pp. P45-P56 ◽  
Author(s):  
Guy Drijkoningen ◽  
Nihed el Allouche ◽  
Jan Thorbecke ◽  
Gábor Bada
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Body Wave ◽  
Shear Waves ◽  
Compressional Wave ◽  
Body Waves ◽  
P Wave ◽  
Streamer Data ◽  
Propagating Shear ◽  
Water Bottom

Under certain circumstances, marine streamer data contain nongeometrical shear body wave arrivals that can be used for imaging. These shear waves are generated via an evanescent compressional wave in the water and convert to propagating shear waves at the water bottom. They are called “nongeometrical” because the evanescent part in the water does not satisfy Snell’s law for real angles, but only for complex angles. The propagating shear waves then undergo reflection and refraction in the subsurface, and arrive at the receivers via an evanescent compressional wave. The required circumstances are that sources and receivers are near the water bottom, irrespective of the total water depth, and that the shear-wave velocity of the water bottom is smaller than the P-wave velocity in the water, most often the normal situation. This claim has been tested during a seismic experiment in the river Danube, south of Budapest, Hungary. To show that the shear-related arrivals are body rather than surface waves, a borehole was drilled and used for multicomponent recordings. The streamer data indeed show evidence of shear waves propagating as body waves, and the borehole data confirm that these arrivals are refracted shear waves. To illustrate the effect, finite-difference modeling has been performed and it confirmed the presence of such shear waves. The streamer data were subsequently processed to obtain a shear-wave refraction section; this was obtained by removing the Scholte wave arrival, separating the wavefield into different refracted arrivals, stacking and depth-converting each refracted arrival before adding the different depth sections together. The obtained section can be compared directly with the standard P-wave reflection section. The comparison shows that this approach can deliver refracted-shear-wave sections from streamer data in an efficient manner, because neither the source nor receivers need to be situated on the water bottom.

Vp/Vs—A POTENTIAL HYDROCARBON INDICATOR

Geophysics ◽  
1976 ◽  
Vol 41 (5) ◽  
pp. 837-849 ◽  
Author(s):  
Robert H. Tatham ◽  
Paul L. Stoffa
Keyword(s):  
Shear Wave ◽  
Wave Velocity ◽  
Mode Conversion ◽  
High Water ◽  
Compressional Wave ◽  
P Wave ◽  
Angle Of Incidence ◽  
Seismic Velocities ◽  
Compressional Wave Velocity ◽  
Reflection Seismic

Theoretically and experimentally, the shear‐wave velocity of a porous rock has been shown to be less sensitive to fluid saturants than the compressional wave velocity. Thus, observation of the ratio of the seismic velocities for waves which traverse a changing or laterally varying zone of undersaturation or gas saturation could produce an observable anomaly which is independent of the regional variation in compressional wave velocity. One source of shear‐wave data in reflection seismic prospecting is mode conversion of P waves to shear waves in marine areas of high water bottom P-wave velocity. A relatively simple interpretative technique, based on amplitude variation as a function of the angle of incidence, is a possible discriminant between shear and multiple compressional arrivals, and data for a real case are shown. A normal moveout velocity analysis, carefully coupled with this offset discriminant, leads to the construction of a shear‐wave reflection section which can then be correlated with the usual compressional wave section. One such a section has been constructed, the variation in the ratio of the seismic velocities can be mapped, and potentially anomalous subsurface regions observed.

scholarly journals Subsonic near-surface P-velocity and low S-velocity observations using propagator inversion

Geophysics ◽  
2005 ◽  
Vol 70 (4) ◽  
pp. R15-R23 ◽  
Author(s):  
Robbert van Vossen ◽  
Andrew Curtis ◽  
Jeannot Trampert
Keyword(s):  
Shear Velocity ◽  
Confining Pressure ◽  
Compressional Wave ◽  
P Wave ◽  
Soil Conditions ◽  
Detailed Knowledge ◽  
S Wave ◽  
Near Surface ◽  
Unconsolidated Sands ◽  
Wave Velocities

Detailed knowledge of near-surface P- and S-wave velocities is important for processing and interpreting multicomponent land seismic data because (1) the entire wavefield passes through and is influenced by the near-surface soil conditions, (2) both source repeatability and receiver coupling also depend on these conditions, and (3) near-surface P- and S-wave velocities are required for wavefield decomposition and demultiple methods. However, it is often difficult to measure these velocities with conventional techniques because sensitivity to shallow-wave velocities is low and because of the presence of sharp velocity contrasts or gradients close to the earth's free surface. We demonstrate that these near-surface P- and S-wave velocities can be obtained using a propagator inversion. This approach requires data recorded by at least one multicomponent geophone at the surface and an additional multicomponent geophone at depth. The propagator between them then contains all information on the medium parameters governing wave propagation between the geophones at the surface and at depth. Hence, inverting the propagator gives local estimates for these parameters. This technique has been applied to data acquired in Zeist, the Netherlands. The near-surface sediments at this site are unconsolidated sands with a thin vegetation soil on top, and the sediments considered are located above the groundwater table. A buried geophone was positioned 1.05 m beneath receivers on the surface. Propagator inversion yielded low near-surface velocities, namely, 270 ± 15 m/s for the compressional-wave velocity, which is well below the sound velocity in air, and 150 ± 9 m/s for the shear velocity. Existing methods designed for imaging deeper structures cannot resolve these shallow material properties. Furthermore, velocities usually increase rapidly with depth close to the earth's surface because of increasing confining pressure. We suspect that for this reason, subsonic near-surface P-wave velocities are not commonly observed.

SHEAR‐WAVE RECORDING USING CONTINUOUS SIGNAL METHODS PART I—EARLY DEVELOPMENT

Geophysics ◽  
1968 ◽  
Vol 33 (2) ◽  
pp. 229-239 ◽  
Author(s):  
J. T. Cherry ◽  
K. H. Waters
Keyword(s):  
Shear Wave ◽  
Early Development ◽  
Wave Velocity ◽  
Field Work ◽  
Compressional Wave ◽  
P Wave ◽  
Wave Reflections ◽  
Continuous Signal ◽  
Equipment Development ◽  
Wave Recording

In recent years, it has been found possible to record shear‐wave reflections and horizontally traveling shear waves using continuous signal methods. Thus paper traces the equipment development and field work performed during this research. The earliest work with a version of a swinging‐weight vibrator showed that shear‐wave reflections could be recorded. This fact provided the impetus to make modifications to equipment to meet difficulties caused by lack of energy and lack of frequency bandwidth. Examples are given which show the flexibility of the system in providing comparison between the horizontally traveling surface waves induced and recorded by the various combinations of vibrator sources and geophone types and their relative orientations. Frequency selection by the different modes is well illustrated. For most of the reflection examples, the average ratio of shear‐wave velocity to compressional‐wave velocity in the first few thousands of feet is near 0.5. Finally, to complete the early development, the version of the shear‐wave vibrator and recording system which was used for most of the additional work is described. In order to make comparison of P‐wave and SH‐wave reflection records easier, this system provided for a 2:1 compression of the shear‐wave time scale as well as a 2:1 ratio of frequency output between the P‐ and SH‐vibrator systems. A few examples of SH reflection profiles achieved with this system are presented.

Relationships between compressional‐wave and shear‐wave velocities in clastic silicate rocks

Geophysics ◽  
1985 ◽  
Vol 50 (4) ◽  
pp. 571-581 ◽  
Author(s):  
J. P. Castagna ◽  
M. L. Batzle ◽  
R. L. Eastwood
Keyword(s):  
Bulk Modulus ◽  
Shear Wave ◽  
Wave Velocity ◽  
Velocity Ratio ◽  
Shear Velocity ◽  
Compressional Wave ◽  
Wave Velocities ◽  
Shear Wave Velocities ◽  
Water Saturated ◽  
Silicate Rocks

New velocity data in addition to literature data derived from sonic log, seismic, and laboratory measurements are analyzed for clastic silicate rocks. These data demonstrate simple systematic relationships between compressional and shear wave velocities. For water‐saturated clastic silicate rocks, shear wave velocity is approximately linearly related to compressional wave velocity and the compressional‐to‐shear velocity ratio decreases with increasing compressional velocity. Laboratory data for dry sandstones indicate a nearly constant compressional‐to‐shear velocity ratio with rigidity approximately equal to bulk modulus. Ideal models for regular packings of spheres and cracked solids exhibit behavior similar to the observed water‐saturated and dry trends. For dry rigidity equal to dry bulk modulus, Gassmann’s equations predict velocities in close agreement with data from the water‐saturated rock.

Anisotropic correction of sonic logs in wells with large relative dip

Geophysics ◽  
2008 ◽  
Vol 73 (1) ◽  
pp. E1-E5 ◽  
Author(s):  
Lev Vernik
Keyword(s):  
Reservoir Characterization ◽  
Low Frequency ◽  
P Wave ◽  
Amplitude Variation With Offset ◽  
Seismic Amplitude ◽  
Avo Inversion ◽  
Pore Pressure Prediction ◽  
Siliciclastic Rocks ◽  
Dip Angle ◽  
Sonic Logs

Seismic reservoir characterization and pore-pressure prediction projects rely heavily on the accuracy and consistency of sonic logs. Sonic data acquisition in wells with large relative dip is known to suffer from anisotropic effects related to microanisotropy of shales and thin-bed laminations of sand, silt, and shale. Nonetheless, if anisotropy parameters can be related to shale content [Formula: see text] in siliciclastic rocks, then I show that it is straightforward to compute the anisotropy correction to both compressional and shear logs using [Formula: see text] and the formation relative dip angle. The resulting rotated P-wave sonic logs can be used to enhance time-depth ties, velocity to effective stress transforms, and low-frequency models necessary for prestack seismic amplitude variation with offset (AVO) inversion.

Sign in / Sign up

Export Citation Format

Share Document