Interpretation of total wave‐field data over Lost Hills field, Kern County, California

Approximately 5 miles (8 km) of total wave‐field data were acquired by Production Geophysical Services (then Kim Tech., Inc.), using the OMNIPULSE® Multi‐mode Shear‐wave Generator source over the southern end of Lost Hills field, Kern County, California. The quality of the shear‐wave sections was excellent. They represent a significant improvement over conventional P‐wave sections from the area in that they provide better reflection continuity and imaging of the Lost Hills anticline. A multicomponent VSP, which was acquired close to the line, provided crucial P‐wave to S‐wave correlation, as well as fracture information. [Formula: see text] ratios computed from interval times ranged from 2.79 to 1.63. An anomalously low [Formula: see text] ratio of 1.65 in the zone of interest (Lower Reef Ridge to McDonald shale), confirmed by multicomponent VSP data, corresponds to the producing interval. Evidence of shear‐wave splitting due to azimuthal anisotropy was observed, so the SV‐wave and SH‐wave data sets were rotated into principal‐component axes of N45E for S1 and N45W for S2. The predominant fracture orientation changes from N45E at depth to N45W near the surface. This change in fracture orientation with depth was confirmed by multicomponent VSP data. Delay‐time ratios (used as a measure of fracture intensity) ranged from a maximum of 11.71 percent to a minimum of −5.48 percent across the structure. These ratios are interpreted to show changes in fracture intensity and orientation across the structure. Delay‐time ratios in the zone of interest were anomalously high (1.55–6.53 percent). Comparison of fracture intensity on the flanks of the structure with that on the crest indicates that the flanks have undergone greater deformation than the crest. The total wave‐field data set and associated analyses have provided significant structural and stratigraphic information on the Miocene Monterey formation over the Lost Hills field, highlighting the productive interval.

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Finite-difference modelling to evaluate seismic P-wave and shear-wave field data

Solid Earth ◽

10.5194/se-6-33-2015 ◽

2015 ◽

Vol 6 (1) ◽

pp. 33-47 ◽

Cited By ~ 3

Author(s):

T. Burschil ◽

T. Beilecke ◽

C. M. Krawczyk

Keyword(s):

Wave Field ◽

Shear Wave ◽

Field Data ◽

P Wave ◽

Sh Wave ◽

Surface Shear ◽

Near Surface ◽

Reflection Seismic ◽

Surface Shear Wave ◽

Seismic Measurements

Abstract. High-resolution reflection seismic methods are an established non-destructive tool for engineering tasks. In the near surface, shear-wave reflection seismic measurements usually offer a higher spatial resolution in the same effective signal frequency spectrum than P-wave data, but data quality varies more strongly. To discuss the causes of these differences, we investigated a P-wave and a SH-wave seismic reflection profile measured at the same location on the island of Föhr, Germany and applied seismic reflection processing to the field data as well as finite-difference modelling of the seismic wave field. The simulations calculated were adapted to the acquisition field geometry, comprising 2 m receiver distance (1 m for SH wave) and 4 m shot distance along the 1.5 km long P-wave and 800 m long SH-wave profiles. A Ricker wavelet and the use of absorbing frames were first-order model parameters. The petrophysical parameters to populate the structural models down to 400 m depth were taken from borehole data, VSP (vertical seismic profile) measurements and cross-plot relations. The simulation of the P-wave wave-field was based on interpretation of the P-wave depth section that included a priori information from boreholes and airborne electromagnetics. Velocities for 14 layers in the model were derived from the analysis of five nearby VSPs (vP =1600–2300 m s-1). Synthetic shot data were compared with the field data and seismic sections were created. Major features like direct wave and reflections are imaged. We reproduce the mayor reflectors in the depth section of the field data, e.g. a prominent till layer and several deep reflectors. The SH-wave model was adapted accordingly but only led to minor correlation with the field data and produced a higher signal-to-noise ratio. Therefore, we suggest to consider for future simulations additional features like intrinsic damping, thin layering, or a near-surface weathering layer. These may lead to a better understanding of key parameters determining the data quality of near-surface shear-wave seismic measurements.

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Interpretation of Total Wave Field Data Over Lost Hills Field, Kern County, California: ABSTRACT

AAPG Bulletin ◽

10.1306/703c8e66-1707-11d7-8645000102c1865d ◽

1988 ◽

Vol 72 ◽

Author(s):

Stewart G. Squires, Daniel Y. Kim

Keyword(s):

Wave Field ◽

Field Data ◽

Kern County ◽

Total Wave

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Interpretation of total wave field data over Lost Hills field, Kern County, California

10.1190/1.1892471 ◽

1988 ◽

Author(s):

Stewart G. Squires ◽

Christopher D. Y. Kim ◽

Daniel Y. Kim

Keyword(s):

Wave Field ◽

Field Data ◽

Kern County ◽

Total Wave

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Reflection seismology over azimuthally anisotropic media

Geophysics ◽

10.1190/1.1442464 ◽

1988 ◽

Vol 53 (3) ◽

pp. 304-313 ◽

Cited By ~ 132

Author(s):

Leon Thomsen

Keyword(s):

Field Data ◽

Shear Waves ◽

Azimuthal Anisotropy ◽

Reflection Seismology ◽

Reflection Amplitude ◽

Seismic Shear ◽

Fracture Intensity ◽

Survey Line ◽

Vsp Data ◽

High Vertical Resolution

Recent surveys have shown that azimuthal anisotropy (due most plausibly to aligned fractures) has an important effect on seismic shear waves. Previous work had discussed these effects on VSP data; the same effects are seen in surface recording of reflections at small to moderate angles of incidence. The anisotropic effects on different polarization components of vertically traveling shear waves permit the recognition and estimation of very small degrees of azimuthal anisotropy (of order ⩾1 percent), as in an interferometer. Anisotropic effects on traveltime yield estimates of anisotropy which are averages over large depth intervals. Often, raw field data must be corrected for these effects before the reflectors may be imaged; two variations of a rotational algorithm to determine the “principal time series” are derived. Anisotropic effects on moveout lead to abnormal moveout unless the survey line is parallel to the fractures. Anisotropic effects on reflection amplitude permit the recognition and estimation of anisotropy (hence fracture intensity) differences at the reflecting horizon, i.e., with high vertical resolution.

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Finite difference modelling to evaluate seismic <i>P</i> wave and shear wave field data

Solid Earth Discussions ◽

10.5194/sed-6-2169-2014 ◽

2014 ◽

Vol 6 (2) ◽

pp. 2169-2213

Author(s):

T. Burschil ◽

T. Beilecke ◽

C. M. Krawczyk

Keyword(s):

Finite Difference ◽

Data Quality ◽

Shear Wave ◽

Field Data ◽

Wave Reflection ◽

P Wave ◽

Sh Wave ◽

Near Surface ◽

Reflection Seismic ◽

Seismic Measurements

Abstract. High-resolution reflection seismic methods are an established non-destructive tool for engineering tasks. In the near surface, shear wave reflection seismic measurements usually offer a higher spatial resolution in the same effective signal frequency spectrum than P wave data, but data quality varies more strongly. To discuss the causes of these differences, we investigated a P wave and a SH wave reflection seismic profile measured at the same location on Föhr island, and applied reflection seismic processing to the field data as well as finite difference modelling of the seismic wavefield (SOFI FD-code). The simulations calculated were adapted to the acquisition field geometry, comprising 2 m receiver distance and 4 m shot distance along the 1.5 km long P wave and 800 m long SH wave profiles. A Ricker-Wavelet and the use of absorbing frames were first order model parameters. The petrophysical parameters to populate the structural models down to 400 m depth are taken from borehole data, VSP measurements and cross-plot relations. The first simulation of the P wave wavefield was based on a simplified hydrogeological model of the survey location containing six lithostratigraphic units. Single shot data were compared and seismic sections created. Major features like direct wave, refracted waves and reflections are imaged, but the reflectors describing a prominent till layer at ca. 80 m depth was missing. Therefore, the P wave input model was refined and 16 units assigned. These define a laterally more variable velocity model (vP = 1600–2300 m s−1) leading to a much better reproduction of the field data. The SH wave model was adapted accordingly but only led to minor correlation with the field data and produced a higher signal-to-noise ratio. Therefore, we suggest to consider for future simulations additional features like intrinsic damping, thin layering, or a near surface weathering layer. These may lead to a better understanding of key parameters determining the data quality of near-surface seismic measurements.

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Shear‐wave studies in glacial till

Geophysics ◽

10.1190/1.1444429 ◽

1998 ◽

Vol 63 (4) ◽

pp. 1273-1284 ◽

Cited By ~ 20

Author(s):

Bradley J. Carr ◽

Zoltan Hajnal ◽

Arnfinn Prugger

Keyword(s):

Shear Wave ◽

P Wave ◽

Vertical Resolution ◽

S Wave ◽

Glacial Deposits ◽

Seismic Line ◽

S Waves ◽

Additional Information ◽

Vsp Data ◽

Clay Percentage

Within a high‐resolution shallow reflection survey program in Saskatchewan, Canada, S-waves were produced using a single seismo‐electric blasting cap and were found to be distinguishable from surface wave phases. The local glacial deposits have average velocities of 450 m/s. [Formula: see text] ratios average 3.6 in these sequences, but they vary laterally, according to the velocity analyses done in two boreholes drilled along the seismic line. Vertical resolution for S-wave reflections are 0.75 m [in the vertical seismic profiling (VSP) data] and 1.5 m (in the CDP data). Yet, the S-wave CDP results are still better than corresponding P-wave data, which had a vertical resolution of 2.6 m. S-wave anisotropy is inferred in the glacial deposits on the basis of particle motion analysis and interpretations of S-wave splitting. However, the amount of observed splitting is small (∼2–6 ms over 5–10 m) and could go undetected for seismic surveys with larger sampling intervals. VSPs indicate that S-wave reflectivity is caused by both distinct and subtle lithologic changes (e.g., clay/sand contacts or changes in clay percentage within a particular till unit) and changes in bulk porosity. Migrated S-wave sections from line 1 and line 2 image reflections from sand layers within the tills as well as the first “bedrock” sequence (known as the Judith River Formation). Shear wave images are not only feasible in unconsolidated materials, but provide additional information about structural relationships within these till units.

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Multicomponent VSP imaging of tight-gas sands

Geophysics ◽

10.1190/1.2335646 ◽

2006 ◽

Vol 71 (6) ◽

pp. E83-E90 ◽

Cited By ~ 2

Author(s):

John O’Brien ◽

Ron Harris

Keyword(s):

Shear Wave ◽

Negative Impact ◽

Mode Conversion ◽

Strong Support ◽

Seismic Profile ◽

Limited Range ◽

P Wave ◽

Wave Source ◽

Cotton Valley ◽

Vsp Data

Low-porosity Bossier and Cotton Valley sands of the East Texas Basin, U. S., have only a small acoustic impedance contrast with the encasing shales but a greater relative contrast in shear-wave impedance. Vertical seismic profile (VSP) data acquired with both a near-offset and far-offset P-wave source clearly demonstrate the P-P reflectivity and P-S mode conversions within the Bossier section. We designate conventional P-wave reflectivity as P-P, shear-wave reflectivity as S-S, and P-wave/shear-wave mode conversion data as P-S. While Bossier P-P reflectivity is low, it appears to be adequate for mapping thick sandbodies such as the York Sandstone, the main exploration target in this area. However, P-P reflectivity is even lower and is inadequate for imaging the overlying Cotton Valley Sands. In contrast, the far-offset VSP data acquired with a P-wave source demonstrate a high level of P-S-mode conversion, which is used to image this interval with definition that is not provided by P-P reflectivity. This provides strong support for the use of P-S-mode conversion imaging for seismic characterization of tight sand reservoirs. Near-offset shear-wave VSP data acquired with a shearwave source show low S/N ratio and limited bandwidth for the downgoing waveform because of the depth of the target; shear-wave energy appears to have a more limited range of propagation than P-waves. Such effects may also have a strong negative impact on multicomponent imaging of these sands using surface seismic techniques. Multicomponent 3D VSP imaging provides a superior solution by placing the geophones closer to the subsurface zone of interest.

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IDENTIFIKASI ORIENTASI REKAHAN MIKRO AREA PANAS BUMI MONTE AMIATA BERDASARKAN ANALISIS STUDI SHEAR WAVE SPLITTING

Indonesian Physical Review ◽

10.29303/ipr.v3i2.56 ◽

2020 ◽

Vol 3 (2) ◽

pp. 72

Author(s):

Irfan - Hanif ◽

Ahmad Zaenudin ◽

Nandi Haerudin ◽

Rahmat C Wibowo

Keyword(s):

Wave Propagation ◽

Shear Wave ◽

Shear Wave Splitting ◽

Earthquake Source ◽

Polarization Direction ◽

Fracture Orientation ◽

High Anisotropy ◽

Wave Splitting ◽

Fracture Intensity ◽

Fracture Distribution

Shear Wave Splitting is an application of seismic wave to analyse the anisotropy level of a certain medium. Generally, shear wave propagation through a rock formation will be polarized (φ) into two parts especially when the medium structures are different, such as fracture. The polarized shear wave which is perpendicular to fracture will propagate slower than the wave that propagates parallel to the fracture. The delay time (δt) of both wave is proportional with the fracture intensity along the wave propagation from the source to the station. The description regarding fracture orientation can be obtained by analysing both Shear Wave Splitting parameters (φ and δt), and this information is adequately important in geothermal exploration or exploitation phase at Mt. Amiata. Based on the result of this research, the micro earthquake source is focused on the east to the south area and spread along 3 earthquake stations. The existence of micro earthquake source is mainly focused at the depth of 1 to 4 km. In addition, the polarization direction of each earthquake station at the geological map shows a dominant fracture orientation consistently at NW-SE. All of the three stations also show that the polarization direction is integrated to the local fault existence in the subsurface. Furthermore, the research shows that the high intensity fracture distribution occurred at MCIV station area in the southern part of research location. Meanwhile, the low intensity fracture distribution occurred at ARCI and SACS station area in the western and the eastern part of research location. The high value of fracture intensity accompanied by the high amount of structure intensity, strengthen the prediction of the high anisotropy existence which potentially tends to the high permeability presence at the area.Keywords: shear wave splitting, anisotropy, fracture, geothermal, polarization direction, fracture intensity.

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