Combination shear wave and compressional wave seismic energy vibrator

1982 ◽  
Vol 72 (4) ◽  
pp. 1347
Author(s):  
Kenneth H. Waters
Keyword(s):  
Shear Wave ◽  
Seismic Energy ◽  
Compressional Wave

Evaluation of direct hydrocarbon indicators through comparison of compressional‐ and shear‐wave seismic data: a case study of the Myrnam gas field, Alberta

Geophysics ◽  
1985 ◽  
Vol 50 (1) ◽  
pp. 37-48 ◽  
Author(s):  
Ross Alan Ensley
Keyword(s):  
Shear Wave ◽  
Seismic Data ◽  
Compressional Wave ◽  
Bright Spot ◽  
Low Velocity ◽  
Gas Reservoir ◽  
Gas Field ◽  
Compressional Waves ◽  
The Relationship

Shear waves differ from compressional waves in that their velocity is not significantly affected by changes in the fluid content of a rock. Because of this relationship, a gas‐related compressional‐wave “bright spot” or direct hydrocarbon indicator will have no comparable shear‐wave anomaly. In contrast, a lithology‐related compressional‐wave anomaly will have a corresponding shear‐wave anomaly. Thus, it is possible to use shear‐wave seismic data to evaluate compressional‐wave direct hydrocarbon indicators. This case study presents data from Myrnam, Alberta which exhibit the relationship between compressional‐ and shear‐wave seismic data over a gas reservoir and a low‐velocity coal.

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.

FLUID SATURATION EFFECTS ON DYNAMIC ELASTIC PROPERTIES OF SEDIMENTARY ROCKS

Geophysics ◽  
1976 ◽  
Vol 41 (5) ◽  
pp. 895-921 ◽  
Author(s):  
A. R. Gregory
Keyword(s):  
Shear Wave ◽  
Elastic Moduli ◽  
Sedimentary Rocks ◽  
Compressional Wave ◽  
Reflection Coefficients ◽  
High Porosity ◽  
Wave Velocities ◽  
Shear Wave Velocities ◽  
Fluid Saturation ◽  
Saturation Effects

The influence of saturation by water, oil, gas, and mixtures of these fluids on the densities, velocities, reflection coefficients, and elastic moduli of consolidated sedimentary rocks was determined in the laboratory by ultrasonic wave propagation methods. Twenty rock samples varying in age from Pliocene to early Devonian and in porosity from 4 to 41 percent were tested under uniform pressures equivalent to subsurface depths of 0 to 18,690 ft. Fluid saturation effects on compressional‐wave velocity are much larger in low‐porosity than in high‐porosity rocks; this correlation is strengthened by elevated pressures but is absent at atmospheric pressure. At a frequency of 1 MHz, the shear‐wave velocities do not always decrease when liquid pore saturants are added to rocks as theorized by Biot; agreement with theory is dependent upon pressure, porosity, fluid‐mineral chemical interactions, and the presence of microcracks in the cementing material. Experimental results support the belief that lower compressional‐wave velocities and higher reflection coefficients are obtained in sedimentary rocks that contain gas. Replacing pore liquids with gas markedly reduces the elastic moduli of rocks, and the effect is enhanced by decreasing pressure. As a rule, the moduli decrease as the porosity increases; Poisson’s ratio is an exception to the rule. Liquid and gas saturation in consolidated rocks can also be distinguished by the ratio of compressional and shear wave velocities [Formula: see text]. The potential diagnostic value of elastic moduli in seismic exploration may stimulate interest in the use of shear‐wave reflection methods in the field.

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 Modified Fixed Wall Oedometer When Considering Stress Dependence of Elastic Wave Velocities

Sensors ◽  
2020 ◽  
Vol 20 (21) ◽  
pp. 6291
Author(s):  
Jong-Sub Lee ◽  
Geunwoo Park ◽  
Yong-Hoon Byun ◽  
Changho Lee
Keyword(s):  
Elastic Wave ◽  
Shear Wave ◽  
Compressional Wave ◽  
Stress Dependence ◽  
Bender Elements ◽  
Wave Velocities ◽  
Shear Wave Velocities ◽  
Vertical Effective Stress ◽  
Side Friction ◽  
Applied Stresses

A modified oedometer cell for measuring the applied stresses and elastic waves at the top and bottom of the specimen is developed to evaluate the effect of the side friction on the stress dependence of the elastic wave velocities. In the modified cell, two load cells are installed at the top and bottom plates, respectively. To generate and detect the compressional and shear waves, a pair of piezo disk elements and a pair of bender elements are mounted at both the top and bottom plates. Experimental results show that the stresses measured at the bottom are smaller than those measured at the top during the loading and vice versa during unloading, regardless of the densities and heights of the specimens. Under nearly saturated conditions, the compressional wave velocities remain almost constant for the entire stress state. With plotting stresses measured at top, the shear wave velocities during unloading are greater than those during loading, whereas with plotting stresses measured at bottom, the shear wave velocities during unloading are smaller than those during loading owing to the side friction. The vertical effective stress may be simply determined from the average values of the stresses measured at the top and bottom of the specimens.

Direct estimation of shear‐wave interval velocities from seismic data

Geophysics ◽  
1985 ◽  
Vol 50 (4) ◽  
pp. 530-538 ◽  
Author(s):  
P. M. Carrion ◽  
S. Hassanzadeh
Keyword(s):  
Shear Wave ◽  
Small Angle ◽  
Seismic Data ◽  
Mode Conversion ◽  
Real Data ◽  
Compressional Wave ◽  
Compressional Waves ◽  
Common Depth Point ◽  
Interval Velocities ◽  
Wave Decomposition

Conventional velocity analysis of seismic data is based on normal moveout of common‐depth‐point (CDP) traveltime curves. Analysis is done in a hyperbolic framework and, therefore, is limited to using the small‐angle reflections only (muted data). Hence, it can estimate the interval velocities of compressional waves only, since mode conversion is negligible when small‐angle arrivals are concerned. We propose a new method which can estimate the interval velocities of compressional and mode‐converted waves separately. The method is based on slant stacking or plane‐wave decomposition (PWD) of the observed data (seismogram), which transforms the data from the conventional T-X domain into the intercept time‐ray parameter domain. Since PWD places most of the compressional energy into the precritical region of the slant‐stacked seismogram, the compressional‐wave interval velocities can be estimated using the “best ellipse” approximation on the assumption that the elliptic array velocity (stacking velocity) is approximately equal to the root‐mean‐square (rms) velocity. Similarly, shear‐wave interval velocities can be estimated by inverting the traveltime curves in the region of the PWD seismogram, where compressional waves decay exponentially (postcritical region). The method is illustrated by examples using synthetic and real data.

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