Comparison of P‐ and S‐wave seismic data: A new method for detecting gas reservoirs

Geophysics ◽  
1984 ◽  
Vol 49 (9) ◽  
pp. 1420-1431 ◽  
Author(s):  
Ross Alan Ensley
Keyword(s):  
Shear Wave ◽  
Seismic Data ◽  
Quantitative Methods ◽  
Qualitative Evaluation ◽  
Compressional Wave ◽  
Bright Spot ◽  
S Wave ◽  
Gas Reservoirs ◽  
Compressional Waves

Compressional waves are sensitive to the type of pore fluid within rocks, but shear waves are only slightly affected by changes in fluid type. This suggests that a comparison of compressional‐ and shear‐wave seismic data recorded over a prospect may allow an interpreter to discriminate between gas‐related anomalies and those related to lithology. This case study documents that where a compressional‐wave “bright spot” or other direct hydrocarbon indicator is present, such a comparison can be used to verify the presence of gas. In practice, the technique can only be used for a qualitative evaluation. However, future improvement of shear‐wave data quality may enable the use of more quantitative methods as well.

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.

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.

On: “Comparison of P‐ and S‐wave seismic data: A new method for detecting gas reservoirs” by R. A. Ensley (GEOPHYSICS, 49, 1420‐1431, September, 1984).

Geophysics ◽  
1985 ◽  
Vol 50 (11) ◽  
pp. 1793-1793
Author(s):  
D. F. Winterstein
Keyword(s):  
Shear Wave ◽  
Seismic Data ◽  
New Method ◽  
Wave Group ◽  
S Wave ◽  
Gas Reservoirs ◽  
Wave Data

Ensley’s paper was based on data of the Conoco Shear Wave Group Shoot of 1977–1978; hence, many companies besides Exxon, including my own, have the Putah Sink data he showed. The stacked sections he showed look identical to the Conoco brute stacks furnished to group shoot participants. The brute stacks had no residual statics or stacking velocity corrections. Those of us who have processed S-wave data often have been pleasantly surprised at how much improvement can come from careful application of residual statics and stacking velocity corrections. Our experience shows that it is unwise to interpret stacked S-wave data that have not had benefit of such refinements.

A case study of stratigraphic interpretation using shear and compressional seismic data

Geophysics ◽  
1984 ◽  
Vol 49 (5) ◽  
pp. 509-520 ◽  
Author(s):  
M. D. McCormack ◽  
J. A. Dunbar ◽  
W. W. Sharp
Keyword(s):  
Physical Properties ◽  
Shear Wave ◽  
Transit Time ◽  
Seismic Data ◽  
Surface Profile ◽  
Compressional Wave ◽  
Horizontal Shear ◽  
Seismic Line ◽  
Transit Times

This paper describes the use of surface recorded compressional and horizontal shear wave seismic data to detect lateral changes in the physical properties of a clastic unit. Shear and compressional wave transit times were measured across a selected interval from CDP stacked sections derived from data collected along coincident shear and compressional seismic lines. At each surface position the ratio of the shear to compressional transit time across the target horizon is calculated. It is shown that lateral variations in this ratio, coupled with the behavior of the individual transit time curves, can be used to infer changes in the physical properties of a formation. The horizon selected for this case study was the lower Pennsylvanian Morrow formation which produces gas from channel sand bodies at the Empire Abo field, New Mexico. A detailed geologic section of the producing horizon was mapped along a seismic line oriented so that it crossed productive and nonproductive regions of the field. Shear and compressional Vibroseis® surveys were conducted along this surface profile using data acquisition parameters designed to produce comparable signal‐to‐noise ratios and resolution in both sets of field data. After processing, the shear and compressional interval transit times through the Morrow formation decreased in going from nonproductive to productive thicknesses of sand. Furthermore there is a proportionately greater decrease in the shear wave transit time than in the compressional transit time resulting in an overall decrease in the ratio of shear to compressional transit times. While several possible physical changes in the lateral properties of the reservoir could explain these observations, it is concluded that the primary mechanism causing these ratio changes is variation in the sand‐shale ratio within the Morrow formation.

On the prediction of settlement from high-resolution shear-wave reflection seismic data: The Trondheim harbour case study, mid Norway

2013 ◽  
Vol 167 ◽  
pp. 72-83 ◽  
Author(s):  
J.S. L'Heureux ◽  
M. Long ◽  
M. Vanneste ◽  
G. Sauvin ◽  
L. Hansen ◽  
...  
Keyword(s):  
High Resolution ◽  
Shear Wave ◽  
Seismic Data ◽  
Wave Reflection ◽  
Reflection Seismic

3D Alford rotation analysis for the Diamond M Field, Midland Basin, Texas

2014 ◽  
Vol 2 (2) ◽  
pp. SE63-SE75 ◽  
Author(s):  
Oswaldo E. Davogustto Cataldo ◽  
Timothy J. Kwiatkowski ◽  
Kurt J. Marfurt ◽  
Steven L. Roche ◽  
James W. Thomas
Keyword(s):  
Vertical Component ◽  
Horizontal Stress ◽  
Compressional Wave ◽  
Carbonate Reservoir ◽  
S Wave ◽  
Stress Regime ◽  
Compressional Waves ◽  
Principal Axes ◽  
Wave Splitting ◽  
Processing Effort

The 2C by 2C S-wave survey generated significant excitement in the mid-1980s, but then it fell out of favor when S-wave splitting initially attributed to fractures was also found to be associated with an anisotropic stress regime. In general, 2C by 2C data require more expensive acquisition and more processing effort to obtain images comparable to 1C “compressional wave” data acquired with vertical component sources and receivers. Because S-waves are insensitive to fluids, and hence the water table, the effective S-wave weathering zone is greater than that for compressional waves, making statics more difficult. S-wave splitting due to anisotropy complicates residual statics and velocity analysis as well as the final image. S-wave frequencies and S-wave moveout are closer to those of contaminating ground roll than compressional waves. Since Alford’s introduction of S-wave rotation from survey coordinates to the principal axes in 1986, geoscientist and engineers retain their interest in fractures but are also keenly interested in the direction and magnitude of maximum horizontal stress. Simultaneous sweep and improved recording technology have reduced the acquisition cost to approximate that of 1C data. Alford’s work was applied to 2C by 2C poststack data. We extended the Alford rotation to prestack data using a modern high-fold 2C by 2C survey acquired over a fractured carbonate reservoir in the Diamond M Field, Texas. Through careful processing, the resulting images were comparable and in many places superior to that of the contemporaneously acquired 1C data. More importantly, we found a good correlation between our derived fracture azimuth map and the fracture azimuth log data from wells present in the field.

Relationships among compressional wave attenuation, porosity, clay content, and permeability in sandstones

Geophysics ◽  
1990 ◽  
Vol 55 (8) ◽  
pp. 998-1014 ◽  
Author(s):  
T. Klimentos ◽  
C. McCann
Keyword(s):  
Seismic Data ◽  
Wave Attenuation ◽  
Clay Content ◽  
Spectral Ratio ◽  
Confining Pressure ◽  
Compressional Wave ◽  
Biot Theory ◽  
Attenuation Coefficients ◽  
Compressional Waves ◽  
High Attenuation

Anelastic attenuation is the process by which rocks convert compressional waves into heat and thereby modify the amplitude and phase of the waves. Understanding the causes of compressional wave attenuation is important in the acquisition, processing, and interpretation of high‐resolution seismic data, and in deducing the physical properties of rocks from seismic data. We have measured the attenuation coefficients of compressional waves in 42 sandstones at a confining pressure of 40 MPa (equivalent to a depth of burial of about 1.5 km) in a frequency range from 0.5 to 1.5 MHz. The compressional wave measurements were made using a pulse‐echo method in which the sample (5 cm diameter, 1.8 cm to 3.5 cm long) was sandwiched between perspex (lucite) buffer rods inside the high‐pressure rig. The attenuation of the sample was estimated from the logarithmic spectral ratio of the signals (corrected for beam spreading) reflected from the top and base of the sample. The results show that for these samples, compressional wave attenuation (α, dB/cm) at 1 MHz and 40 MPa is related to clay content (C, percent) and porosity (ϕ, percent) by α=0.0315ϕ+0.241C−0.132 with a correlation coefficient of 0.88. The relationship between attenuation and permeability is less well defined: Those samples with permeabilities less than 50 md have high attenuation coefficients (generally greater than 1 dB/cm) while those with permeabilities greater than 50 md have low attenuation coefficients (generally less than 1 dB/cm) at 1 MHz at 40 MPa. These experimental data can be accounted for by modifications of the Biot theory and by consideration of the Sewell/Urick theory of compressional wave attenuation in porous, fluid‐saturated media.

Generation and processing of pseudo‐shear‐wave data: Theory and case study

Geophysics ◽  
2003 ◽  
Vol 68 (6) ◽  
pp. 1807-1816 ◽  
Author(s):  
Vladimir Grechka ◽  
Pawan Dewangan
Keyword(s):  
Shear Wave ◽  
Pure Shear ◽  
Transversely Isotropic ◽  
Velocity Model ◽  
Velocity Analysis ◽  
Ocean Bottom ◽  
S Wave ◽  
Velocity Models ◽  
Conversion Point

Processing of converted (PS) waves currently adopted by the exploration industry is essentially based on resorting the PS data into common‐conversion‐point gathers and using them for velocity analysis. Here, we explore an alternative procedure. Our key idea is to generate the so‐called pseudo‐shear (ΨS) seismograms from the recorded PP and PS traces and run conventional velocity analysis on the reconstructed ΨS data. This results in an effective S‐wave velocity model because our method creates data that possess kinematics of pure shear‐wave primaries. We never deal with such complexities of converted waves as moveout asymmetry, reflection point dispersal, and polarity reversal; therefore, these generally troublesome features become irrelevant. We describe the details of our methodology and examine its behavior both analytically and numerically. We apply the developed processing flow to a four‐component ocean‐bottom cable line acquired in the Gulf of Mexico. Since the obtained stacking velocities of P‐ and ΨS‐waves indicate the presence of effective anisotropy, we proceed with estimating a family of kinematically equivalent vertical transversely isotropic (VTI) velocity models of the subsurface.

scholarly journals Seismic Short-Refraction Studies on the Ross Ice Shelf, Antarctica

1979 ◽  
Vol 24 (90) ◽  
pp. 313-319
Author(s):  
Joseph F. Kirchner ◽  
Charles R. Bentley
Keyword(s):  
Shear Wave ◽  
Transverse Isotropy ◽  
Compressional Wave ◽  
Least Squares Regression ◽  
Horizontal Shear ◽  
Ice Shelf ◽  
Compressional Waves ◽  
Ross Ice Shelf ◽  
Wave Velocities ◽  
Shear Wave Velocities

AbstractSeismic short-refraction studies were carried out at five stations on the Ross Ice Shelf during the 1976–77 summer season as part of the comprehensive Ross Ice Shelf Geophysical and Glaciological Survey. Measurements of the velocities of compressional waves were made at each location. Compressional wave velocities were measured along more than one azimuth at three sites, and shear wave velocities (both components) at two. Travel-time curves were fitted to an exponential expression by means of a non-linear least-squares regression technique. The errors in the apparent velocities are estimated to be about ±50 m s–1 at short distances, diminishing to about ±10 m s–1 near the ends of the profiles. Compressional-wave velocities show only slight variations with azimuth and only over certain depth intervals, showing that constant-velocity surfaces are essentially horizontal. Shear-wave velocities, however, exhibit large variations according to azimuth and polarization, indicating that transverse isotropy is violated at least in the upper 30–40 m of the ice shelf. It is believed that the anisotropy is caused by structural details in the firn perhaps modified by preferred crystal orientation and that it may arise at least partly from anisotropic stresses in the ice shelf.

UNDERSTANDING AND USING QUALITATIVE METHODS IN PERFORMANCE MEASUREMENT

2016 ◽  
pp. 46-57
Author(s):  
H.M Kasinath
Keyword(s):  
Qualitative Methods ◽  
Performance Measurement ◽  
Quantitative Methods ◽  
Qualitative Evaluation ◽  
Psychological Research ◽  
Practical Reasons ◽  
Qualitative And Quantitative Methods ◽  
Quasi Experimental ◽  
Constructivist Approaches

Qualitative methods are used in research that is designed to provide an in-depth description of a specific programme, practice, or setting. Three of the possible reasons for choosing qualitative methods are explored in this article: (a) the researcher's view of the world, (b) the nature of the research questions, and (c) practical reasons associated with the nature of qualitative methods. Different types of qualitative research methods are practiced in educational and psychological research out of which, the paper showcases seven strategies Ethnographic research, Case study, Phenomenological research, Grounded theory, Participative inquiry, Clinical research and Focus groups. Qualitative evaluation methods are an essential part of the range of tools that evaluators call upon in their practice. Since the 1970s, when qualitative evaluation methodswerefirstintroducedas alternativetotheexperimental/quasi-experimental paradigms, the philosophical underpinnings and methodological requirements for sound qualitative evaluation have transformed the evaluation profession. Debates continue about the relative merits of positivistic and constructivist approaches to evaluation, but many evaluators have come to the view that pragmatically, it is desirable to mix qualitative and quantitative methods. More specifically the present paper examines the need for understanding and using qualitative methods in performance measurement.

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