Advantages of Shear Wave Seismic in Morrow Sandstone Detection

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.

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Direct shear-wave seismic survey in Sanhu area, Qaidam Basin, west China

The Leading Edge ◽

10.1190/tle41010047.1 ◽

2022 ◽

Vol 41 (1) ◽

pp. 47-53

Author(s):

Zhiwen Deng ◽

Rui Zhang ◽

Liang Gou ◽

Shaohua Zhang ◽

Yuanyuan Yue ◽

...

Keyword(s):

Shear Wave ◽

Reservoir Characterization ◽

Qaidam Basin ◽

P Wave ◽

Data Sets ◽

Direct Shear ◽

Subsurface Structure ◽

S Wave ◽

West China ◽

Wave Data

The formation containing shallow gas clouds poses a major challenge for conventional P-wave seismic surveys in the Sanhu area, Qaidam Basin, west China, as it dramatically attenuates seismic P-waves, resulting in high uncertainty in the subsurface structure and complexity in reservoir characterization. To address this issue, we proposed a workflow of direct shear-wave seismic (S-S) surveys. This is because the shear wave is not significantly affected by the pore fluid. Our workflow includes acquisition, processing, and interpretation in calibration with conventional P-wave seismic data to obtain improved subsurface structure images and reservoir characterization. To procure a good S-wave seismic image, several key techniques were applied: (1) a newly developed S-wave vibrator, one of the most powerful such vibrators in the world, was used to send a strong S-wave into the subsurface; (2) the acquired 9C S-S data sets initially were rotated into SH-SH and SV-SV components and subsequently were rotated into fast and slow S-wave components; and (3) a surface-wave inversion technique was applied to obtain the near-surface shear-wave velocity, used for static correction. As expected, the S-wave data were not affected by the gas clouds. This allowed us to map the subsurface structures with stronger confidence than with the P-wave data. Such S-wave data materialize into similar frequency spectra as P-wave data with a better signal-to-noise ratio. Seismic attributes were also applied to the S-wave data sets. This resulted in clearly visible geologic features that were invisible in the P-wave data.

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

Society of Petroleum Engineers Journal ◽

10.2118/8237-pa ◽

1980 ◽

Vol 20 (05) ◽

pp. 317-326 ◽

Cited By ~ 3

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＾

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Circularly polarized shear waves used for VSP measurements

Geophysics ◽

10.1190/1.1443277 ◽

1992 ◽

Vol 57 (4) ◽

pp. 643-646

Author(s):

Hans A. K. Edelmann

Keyword(s):

Shear Wave ◽

Velocity Ratio ◽

Shear Waves ◽

Signal Amplitude ◽

P Wave ◽

Polarization Analysis ◽

S Wave ◽

P Waves ◽

Additional Processing ◽

Wave Recording

If shear waves are to be recorded, all other types of waves (including P waves) have to be regarded as noise. All data processing applied later is limited in its success, not so much by the character of the signal, but by the character of the noise superimposed on the signal. Therefore an optimum method for simultaneous P‐ and S‐wave recording does not exist per se. All efforts made in the field that help to enhance the relatively weak S‐wave signal enhance the possibility of a more detailed interpretation such as polarization analysis. In the course of shear‐wave investigations over a period of more than ten years, simultaneous P‐ and SV‐wave recording has yielded fairly good results for velocity ratio determination, but has never produced satisfying results for polarization analysis because of the interfering P‐wave events. When generating pure SH‐waves, however, P‐wave arrival amplitudes in a shot record can, under favorable conditions, be kept well below the SH‐wave amplitude (−40 dB). Through additional processing, a ratio of P‐ to SH‐signal amplitude of −60 dB can be reached. The improvement achieved by making separate shear‐wave recordings, obviously, must be weighed against the additional costs caused by these recordings.

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Estimating shear‐wave velocities from P-wave and converted‐wave data

Geophysics ◽

10.1190/1.1444556 ◽

1999 ◽

Vol 64 (2) ◽

pp. 504-507 ◽

Cited By ~ 1

Author(s):

Franklyn K. Levin

Keyword(s):

Wave Velocity ◽

Seismic Data ◽

P Wave ◽

S Wave ◽

Converted Wave ◽

Wave Data ◽

Wave Velocities ◽

Shear Wave Velocities ◽

P Wave Velocity ◽

Growing Body

Tessmer and Behle (1988) show that S-wave velocity can be estimated from surface seismic data if both normal P-wave data and converted‐wave data (P-SV) are available. The relation of Tessmer and Behle is [Formula: see text] (1) where [Formula: see text] is the S-wave velocity, [Formula: see text] is the P-wave velocity, and [Formula: see text] is the converted‐wave velocity. The growing body of converted‐wave data suggest a brief examination of the validity of equation (1) for velocities that vary with depth.

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SHEAR‐WAVE RECORDING USING CONTINUOUS SIGNAL METHODS PART II—LATER EXPERIMENTATION

Geophysics ◽

10.1190/1.1439925 ◽

1968 ◽

Vol 33 (2) ◽

pp. 240-254 ◽

Cited By ~ 8

Author(s):

E. L. Erickson ◽

D. E. Miller ◽

K. H. Waters

Keyword(s):

Shear Wave ◽

P Wave ◽

Quality Of Data ◽

Low Velocity ◽

Depth Of Penetration ◽

Borehole Data ◽

P Waves ◽

Wave Data ◽

Wave Research ◽

Absolute Correlation

The emphasis in this shear‐wave research was placed on determining the general quality of data which could be obtained in different areas and whether such quality was consistent with the main objective of getting information from the shear‐wave data which could not be obtained from the corresponding P‐wave data. Borehole data are presented to show that the SH source of vibrations generates a downward‐propagating, horizontally polarized shear wave. Shear velocities were determined for depth intervals of two to three hundred feet, but no absolute correlation between [Formula: see text] and lithology could be established. In the deeper sedimentary section, [Formula: see text] averages about one‐half; but in the low velocity, or weathering layer, the ratio may be as small as one sixth. All the reflection record problems which arise from wave propagation phenomena in the LVL are generally much worse for SH waves than for P waves because of the very small SH velocities in the LVL. Nevertheless, by using large source and receiver patterns and various processing techniques, interpretable SH reflection records were obtained in almost every test area. It has been possible to obtain a depth of penetration about equal to that of the corresponding P‐wave records, with some reservations. The relative quality to be obtained has proved unpredictable. Several examples of SH reflection sections are presented with the corresponding P reflection sections. Some of these field examples show definite differences between the corresponding P and SH reflection sections. Such differences represent new information which potentially can be useful to the exploration geophysicist.

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Core-Derived Velocity Systematics, Mississippian Meramec Formation, Oklahoma

SPE Journal ◽

10.2118/206753-pa ◽

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.

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Some comments on common-asymptotic-conversion-point (CACP) sorting of converted-wave data in isotropic, laterally inhomogeneous media

Geophysics ◽

10.1190/1.1925750 ◽

2005 ◽

Vol 70 (3) ◽

pp. U29-U36 ◽

Cited By ~ 2

Author(s):

Mirko van der Baan

Keyword(s):

Wave Velocity ◽

Velocity Ratio ◽

P Wave ◽

Pure Mode ◽

S Wave ◽

Converted Wave ◽

Wave Data ◽

Conversion Point ◽

Isotropic Media ◽

Zero Offset

Common-midpoint (CMP) sorting of pure-mode data in arbitrarily complex isotropic or anisotropic media leads to moveout curves that are symmetric around zero offset. This greatly simplifies velocity determination of pure-mode data. Common-asymptotic-conversion-point (CACP) sorting of converted-wave data, on the other hand, only centers the apexes of all traveltimes around zero offset in arbitrarily complex but isotropic media with a constant P-wave/S-wave velocity ratio everywhere. A depth-varying CACP sorting may therefore be required to position all traveltimes properly around zero offset in structurally complex areas. Moreover, converted-wave moveout is nearly always asymmetric and nonhyperbolic. Thus, positive and negative offsets need to be processed independently in a 2D line, and 3D data volumes are to be divided in common azimuth gathers. All of these factors tend to complicate converted-wave velocity analysis significantly.

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Ultrasonic and seismic constraints on crystallographic preferred orientations of the Priestley Glacier shear margin, Antarctica

10.5194/tc-2021-382 ◽

2022 ◽

Author(s):

Franz Lutz ◽

David J. Prior ◽

Holly Still ◽

M. Hamish Bowman ◽

Bia Boucinhas ◽

...

Keyword(s):

Ice Core ◽

Seismic Profile ◽

P Wave ◽

Quality Data ◽

S Wave ◽

P Waves ◽

Velocity Anisotropy ◽

Wave Data ◽

Axis Alignment ◽

Safety Considerations

Abstract. Crystallographic preferred orientations (CPOs) are particularly important in controlling the mechanical properties of glacial shear margins. Logistical and safety considerations often make direct sampling of shear margins difficult and geophysical measurements are commonly used to constrain the CPOs. We present here the first direct comparison of seismic and ultrasonic data with measured CPOs in a polar shear margin. The measured CPO from ice samples from a 58 m deep borehole in the left lateral shear margin of the Priestley Glacier, Antarctica, is dominated by horizontal c-axes aligned sub-perpendicular to flow. A vertical seismic profile experiment with hammer shots up to 50 m away from the borehole, in four different azimuthal directions, shows velocity anisotropy of both P-waves and S-waves. Matching P-wave data to the anisotropy corresponding to CPO models defined by horizontally aligned c-axes gives two possible solutions for c-axis azimuth, one of which matches the c-axis measurements. If both P-wave and S-wave data are used, there is one best fit for azimuth and intensity of c-axis alignment that matches well the measurements. Azimuthal P-wave and S-wave ultrasonic data recorded in the laboratory on the ice core show clear anisotropy that matches that predicted from the CPO of the samples. With good quality data, azimuthal increments of 30° or less will constrain well the orientation and intensity of c-axis alignment. Our experiments provide a good framework for planning seismic surveys aimed at constraining the anisotropy of shear margins.

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Study of Converted-Wave Modeling: AVO Application for Shallow Gas Models

Jurnal Geofisika ◽

10.36435/jgf.v16i2.362 ◽

2018 ◽

Vol 16 (2) ◽

pp. 19 ◽

Cited By ~ 1

Author(s):

Natashia Christy Viony ◽

Wahyu Triyoso

Keyword(s):

Data Processing ◽

Vertical Component ◽

Hydrocarbon Exploration ◽

P Wave ◽

Diffraction Effect ◽

S Wave ◽

Converted Wave ◽

Gas Reservoir ◽

Shallow Gas ◽

Wave Data

The application of converted-wave seismic method in hydrocarbon exploration has increased significantly. Since the conventional seismic ceases to provide an adequate result in complex geology area and it provides an ambiguous brightspot response. The main principle is that an incident P-wave produces reflected and converted P and SV wave when the downgoing P-wave impinges on an interface. Converted-wave seismic uses the multicomponent receiver that records both of vertical component and horizontal component. The vertical component is assumed to correspond to the compressional PP wave and the horizontal correspond to the PS converted-wave. In this research, a synthetic model with the shallow gas and the salt dome below are constructed. The purpose of this study is to analyze the brightspot due to the presence of shallow gas and its effect to the quality of PP and PS wave reflection below the gas zone. To achieve the goal, both vertical and horizontal seismic data processing are performed. In horizontal data processing, the best gamma function (Vp/Vs) value is estimated to produce the better and reliable image. The result shows that the brightspot response in conventional data doesn’t exist in converted-wave data and the imaging below the gas zone in converted-wave data is better than the conventional due to the attenuation and diffraction effect that caused by gas column. Processing is followed by AVO analysis to compare the AVO response of PP and PS data in characterizing gas reservoir. Both PP and PS AVO curve shows the consistency with synthetic AVO from well data. Gas reservoir is a class 1 AVO anomaly with positive intercept and negative gradient on PP data. However, PS AVO curve does not refer any anomaly. It is because S-wave is not sensitive to the existence of rock saturant.

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A simple method for resolving large converted‐wave (P-SV) statics

Geophysics ◽

10.1190/1.1443426 ◽

1993 ◽

Vol 58 (3) ◽

pp. 429-433 ◽

Cited By ~ 27

Author(s):

Peter W. Cary ◽

David W. S. Eaton

Keyword(s):

P Wave ◽

S Wave ◽

Converted Wave ◽

P Waves ◽

Simple Method ◽

Near Surface ◽

S Waves ◽

Static Solutions ◽

Surface Fluctuations

The processing of converted‐wave (P-SV) seismic data requires certain special considerations, such as commonconversion‐point (CCP) binning techniques (Tessmer and Behle, 1988) and a modified normal moveout formula (Slotboom, 1990), that makes it different for processing conventional P-P data. However, from the processor’s perspective, the most problematic step is often the determination of residual S‐wave statics, which are commonly two to ten times greater than the P‐wave statics for the same location (Tatham and McCormack, 1991). Conventional residualstatics algorithms often produce numerous cycle skips when attempting to resolve very large statics. Unlike P‐waves, the velocity of S‐waves is virtually unaffected by near‐surface fluctuations in the water table (Figure 1). Hence, the P‐wave and S‐wave static solutions are largely unrelated to each other, so it is generally not feasible to approximate the S‐wave statics by simply scaling the known P‐wave static values (Anno, 1986).

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