MULTI-COMPONENT SEISMIC—THE TOOL FOR ALL REASONS

2002 ◽  
Vol 42 (1) ◽  
pp. 587
Author(s):  
F.L. Engelmark
Keyword(s):  
Fractured Reservoirs ◽  
Time Lapse ◽  
P Wave ◽  
Converted Wave ◽  
S Waves ◽  
The North ◽  
Impedance Contrast ◽  
Seismic Sensors ◽  
Wave Imaging ◽  
Wave Modes

Marine multi-component seismic, known as 4C, is an emerging seismic technology providing improved and sometimes unique solutions to many common problems. In the marine environment the seismic sensors have to be placed on the sea-floor to capture converted or shear wave modes that cannot propagate through liquid media. Although this means increased acquisition cost, the improved information content makes it money well spent to better image and characterise reservoirs.The 4C solutions fall into two major groups of five. First there are the imaging solutions:Improved standard P-wave imaging. Improved converted wave (P-S) resolution in the shallow sediments. Converted wave imaging through gas clouds. Converted wave imaging of low impedance contrast reservoirs. Improved sub-salt and sub-basalt imaging with converted waves. The second group consists of the five characterisation solutions:Improved fracture characterisation by means of P-S waves. Qualitative 4D or time-lapse characterisation of fractured reservoirs with low intrinsic permeability. Improved lithology and fluid characterisation by combining the information in the two wave modes. Improved quantitative time-lapse evaluation of pressure and saturation changes. Improved characterisation of drilling hazards by combined evaluation of the two wave modes. So far the most popular 4C solutions are imaging through gas and improved P-wave imaging of Jurassic reservoirs in the North Sea, for example the Statfjord, Brent and Beryl fields. However, as the technology is developing and maturing, the characterisation solutions will probably be the most common applications of 4C in the near future.

Analysis of conventional and converted mode reflections at Putah sink, California using three‐component data

Geophysics ◽  
1990 ◽  
Vol 55 (6) ◽  
pp. 646-659 ◽  
Author(s):  
C. Frasier ◽  
D. Winterstein
Keyword(s):  
Time Window ◽  
Structural Features ◽  
Low Noise ◽  
P Wave ◽  
Bright Spot ◽  
High Signal ◽  
Converted Wave ◽  
Gas Field ◽  
Seismic Line ◽  
S Waves

In 1980 Chevron recorded a three‐component seismic line using vertical (V) and transverse (T) motion vibrators over the Putah sink gas field near Davis, California. The purpose was to record the total vector motion of the various reflection types excited by the two sources, with emphasis on converted P‐S reflections. Analysis of the conventional reflection data agreed with results from the Conoco Shear Wave Group Shoot of 1977–1978. For example, the P‐P wave section had gas‐sand bright spots which were absent in the S‐S wave section. Shot profiles from the V vibrators showed strong P‐S converted wave events on the horizontal radial component (R) as expected. To our surprise, shot records from the T vibrators showed S‐P converted wave events on the V component, with low amplitudes but high signal‐to‐noise (S/N) ratios. These S‐P events were likely products of split S‐waves generated in anisotropic subsurface media. Components of these downgoing waves in the plane of incidence were converted to P‐waves on reflection and arrived at receivers in a low‐noise time window ahead of the S‐S waves. The two types of converted waves (P‐S and S‐P) were first stacked by common midpoint (CMP). The unexpected S‐P section was lower in true amplitude but much higher in S/N ratio than the P‐S section. The Winters gas‐sand bright spot was missing on the converted wave sections, mimicking the S‐S reflectivity as expected. CRP gathers were formed by rebinning data by a simple ray‐tracing formula based on the asymmetry of raypaths. CRP stacking improved P‐S and S‐P event resolution relative to CMP stacking and laterally aligned structural features with their counterparts on P and S sections. Thus, the unexpected S‐P data provided us with an extra check for our converted wave data processing.

Fracture detection using azimuthal variation of P-wave moveout from orthogonal seismic survey lines

Geophysics ◽  
1999 ◽  
Vol 64 (4) ◽  
pp. 1193-1201 ◽  
Author(s):  
Xiang‐Yang Li
Keyword(s):  
P Wave ◽  
Seismic Survey ◽  
Fracture Detection ◽  
Data Set ◽  
The North ◽  
High Impedance ◽  
Impedance Contrast ◽  
The North Sea ◽  
Marine Exploration ◽  
Orthogonal Pairs

An algorithm is proposed for determining the fracture orientation based on the azimuthal variations in the P-wave reflection moveout for a target interval. The differential moveout between orthogonal survey lines from the bottom of a given target shows cos 2ϕ variations with the line azimuth ϕ measured from the fracture strike for a fixed offset. A configuration of four intersecting survey lines may be used to quantify the fracture strike. The four lines form two orthogonal pairs, and the fracture strike can be obtained by analyzing the crossplot of the two corresponding pairs of the differential moveouts. An offset‐depth ratio (x/z) of 1.0 or greater (up to 1.5) is often required to quantify the moveout difference reliably. The sensitivity of the method is further enhanced by low/high impedance contrast at the top target interface but is greatly reduced by high/low impedance contrast. The method may be particularly useful in marine exploration with repeated surveys of various vintages where continuous azimuthal coverage is often not available. A data set from the North Sea is used to illustrate the technique.

Imaging beneath a high‐velocity layer using converted waves

Geophysics ◽  
1992 ◽  
Vol 57 (11) ◽  
pp. 1444-1452 ◽  
Author(s):  
Guy W. Purnell
Keyword(s):  
High Velocity ◽  
Energy Partitioning ◽  
P Wave ◽  
Converted Wave ◽  
P Waves ◽  
Lower Velocity ◽  
S Waves ◽  
High Velocity Layer ◽  
The Waves ◽  
Velocity Layer

High‐velocity layers (HVLs) often hinder seismic imaging of deeper reflectors using conventional techniques. A major factor is often the unusual energy partitioning of waves incident at an HVL boundary from lower‐velocity material. Using elastic physical modeling, I demonstrate that one effect of this factor is to limit the range of dips beneath an HVL that can be imaged using unconverted P‐wave arrivals. At the same time, however, partitioning may also result in P‐waves outside the HVL coupling efficiently with S‐waves inside. By exploiting some of the waves that convert upon transmission into and/or out of the physical‐model HVL, I am able to image a much broader range of underlying dips. This is accomplished by acoustic migration tailored (via the migration velocities used) for selected families of converted‐wave arrivals.

Dipping structure under Dourbes, Belgium, determined by receiver function modeling and inversion

1995 ◽  
Vol 85 (1) ◽  
pp. 254-268 ◽  
Author(s):  
Jie Zhang ◽  
Charles A. Langston
Keyword(s):  
Receiver Function ◽  
Receiver Functions ◽  
P Wave ◽  
P Waves ◽  
S Waves ◽  
The North ◽  
Shear Wave Velocities ◽  
Geophysical Surveys ◽  
Vector Rotation ◽  
Anomalous Particle

Abstract Teleseismic broadband P and S waves recorded at the NARS station NE06 (Dourbes, Belgium) are shown to exhibit strong anomalous particle motion not attributable to instrument miscalibration or malfunction. Azimuthally varying radial and tangential components have been observed on 38 recordings after vector rotation of horizontal P waves into the ray direction. The tangenital P waves attain amplitudes comparable to the radial components from the east with negative polarity and west with positive polarity, but tend to be zero in the north and south, suggesting major discontinuities in the crust dipping southward. The SH wave from the east contains a large SPmP phase, an S-to-P conversion at the free surface and then reflected back to the surface from the Moho. The polarity of this SPmP phase presents further evidence for a southward-dipping Moho. We employ ray theory for three-dimensionally dipping interfaces to compute the P-wave response. Linear inverse theory with smoothness constraints is applied to the simultaneous inversions of P-wave receiver functions for four different backazimuths. Through the progressive change of interface strike and dip and the inversion of layer shear-wave velocities, a dipping crustal model that is consistent with both the observed waveforms and results of previous local geophysical surveys has been determined. The results suggest a large velocity contrast in the shallow structure near the surface, another major interface at a depth of 12 km with dip of 10°, and a seismically transparent unit below the interface. The interface at a depth of 12 km reportedly emerges at the Midi fault 50 km north of the station NE06.

Identifying, removing, and imaging P‐S conversions at salt‐sediment interfaces

Geophysics ◽  
2003 ◽  
Vol 68 (3) ◽  
pp. 1052-1059 ◽  
Author(s):  
Richard S. Lu ◽  
Dennis E. Willen ◽  
Ian A. Watson
Keyword(s):  
P Wave ◽  
Time Interval ◽  
S Wave ◽  
Converted Wave ◽  
Prestack Depth Migration ◽  
Depth Migration ◽  
Time Migration ◽  
Wave Imaging ◽  
Wave Image ◽  
Converted Waves

The large velocity contrast between salt and the surrounding sediments generates strong conversions between P‐ and S‐wave energy. The resulting converted events can be noise on P‐wave migrated images and should be identified and removed to facilitate interpretation. On the other hand, they can also be used to image a salt body and its adjacent sediments when the P‐wave image is inadequate. The converted waves with smaller reflection and transmission angles and much larger critical angles generate substantially different illumination than does the P‐wave. In areas where time migration is valid, the ratio between salt thickness in time and the time interval between the P‐wave and the converted‐wave salt base on a time‐migrated image is about 2.6 or 1.3, depending upon whether the seismic wave propagates along one or both of the downgoing and upcoming raypaths in salt as the S‐wave, respectively. These ratios can be used together with forward seismic modeling and 2D prestack depth migration to identify the converted‐wave base‐of‐salt (BOS) events in time and depth and to correctly interpret the subsalt sediments. It is possible to mute converted‐wave events from prestack traces according to their computed arrival times. Prestack depth migration of the muted data extends the updip continuation of subsalt sedimentary beds, and improves the salt–sediment terminations in the P‐wave image. Prestack and poststack depth‐migrated examples illustrate that the P‐wave and the three modes of converted waves preferentially image different parts of the base of salt. In some areas, the P‐wave BOS can be very weak, obscured by noise, or completely absent. Converted‐wave imaging complements P‐wave imaging in delineating the BOS for velocity model building.

Multicomponent prestack depth migration using the elastic screen method

Geophysics ◽  
2005 ◽  
Vol 70 (1) ◽  
pp. S30-S37 ◽  
Author(s):  
Xiao-Bi Xie ◽  
Ru-Shan Wu
Keyword(s):  
Synthetic Data ◽  
Data Sets ◽  
Converted Wave ◽  
Prestack Depth Migration ◽  
Depth Migration ◽  
S Waves ◽  
Angle Correction ◽  
Scattering Effects ◽  
Wave Imaging ◽  
Migration Method

A 3D multicomponent prestack depth-migration method is presented. An elastic-screen propagator based on one-way wave propagation with a wide-angle correction is used to extrapolate both source and receiver wavefields. The elastic-screen propagator neglects backscattered waves but can handle forward multiple-scattering effects, such as focusing/defocusing, diffraction, interference, and conversions between P- and S-waves. Vector-imaging conditions are used to generate a P-P image and a P-S converted-wave image. The application of the multicomponent elastic propagator and vector-imaging condition preserves more information carried by the elastic waves. It also solves the polarization problem of converted-wave imaging. Partial images from different sources with correct polarizations can be stacked to generate a final image. Numerical examples using 2D synthetic data sets are presented to show the feasibility of this method.

Examining the processing differences between P and P-S waves in a Rocky Mountain Foothills model

2014 ◽  
Vol 54 (2) ◽  
pp. 504
Author(s):  
Sanjeev Rajput ◽  
Michael Ring
Keyword(s):  
Rocky Mountain ◽  
P Wave ◽  
S Wave ◽  
Converted Wave ◽  
Wave Source ◽  
Depth Migration ◽  
S Waves ◽  
Full Waveform ◽  
Fluid Saturation ◽  
Converted Waves

For the past two decades, most of the shear-wave (S-wave) or converted wave (P-S) acquisitions were performed with P-wave source by making the use of downgoing P-waves converting to upgoing S-waves at the mode conversion boundaries. The processing of converted waves requires studying asymmetric reflection at the conversion point, difference in geometries and conditions of source and receiver, and the partitioning of energy into orthogonally polarised components. Interpretation of P-S sections incorporates the identification of P-S waves, full waveform modeling, correlation with P-wave sections and depth migration. The main applications of P-S wave imaging are to obtain a measure of subsurface S-wave properties relating to rock type and fluid saturation (in addition to the P-wave values), imaging through gas clouds and shale diapers, and imaging interfaces with low P-wave contrast but significant S-wave changes. This study examines the major differences in processing of P and P-S wave surveys and the feasibility of identifying converted mode reflections by P-wave sources in anisotropic media. Two-dimensional synthetic seismograms for a realistic rocky mountain foothills model were studied. A Kirchhoff-based technique that includes anisotropic velocities is used for depth migration of converted waves. The results from depth imaging show that P-S section help in distinguishing amplitude associated with hydrocarbons from those caused by localised stratigraphic changes. In addition, the full waveform elastic modeling is useful in finding an appropriate balance between capturing high-quality P-wave data and P-S data challenges in a survey.

Examining the processing differences between P and P-S waves in a Rocky Mountain Foothills model

2014 ◽  
Vol 54 (2) ◽  
pp. 536
Author(s):  
Sanjeev Rajput ◽  
Michael Ring
Keyword(s):  
Rocky Mountain ◽  
P Wave ◽  
S Wave ◽  
Converted Wave ◽  
Wave Source ◽  
Depth Migration ◽  
S Waves ◽  
Full Waveform ◽  
Fluid Saturation ◽  
Converted Waves

For the past two decades, most of the shear-wave (S-wave) or converted wave (P-S) acquisitions were performed with P-wave source by making the use of downgoing P-waves converting to upgoing S-waves at the mode conversion boundaries. The processing of converted waves requires studying asymmetric reflection at the conversion point, difference in geometries and conditions of source and receiver, and the partitioning of energy into orthogonally polarised components. Interpretation of P-S sections incorporates the identification of P-S waves, full waveform modeling, correlation with P-wave sections and depth migration. The main applications of P-S wave imaging are to obtain a measure of subsurface S-wave properties relating to rock type and fluid saturation (in addition to the P-wave values), imaging through gas clouds and shale diapers, and imaging interfaces with low P-wave contrast but significant S-wave changes. This study examines the major differences in processing of P and P-S wave surveys and the feasibility of identifying converted mode reflections by P-wave sources in anisotropic media. Two-dimensional synthetic seismograms for a realistic rocky mountain foothills model were studied. A Kirchhoff-based technique that includes anisotropic velocities is used for depth migration of converted waves. The results from depth imaging show that P-S section help in distinguishing amplitude associated with hydrocarbons from those caused by localised stratigraphic changes. In addition, the full waveform elastic modeling is useful in finding an appropriate balance between capturing high-quality P-wave data and P-S data challenges in a survey.

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

Geophysics ◽  
1993 ◽  
Vol 58 (3) ◽  
pp. 429-433 ◽  
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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