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EAGE Vibroseis Workshop - Vibroseis acquisition and processing half century later, new developments in data quality and productivity
- Conference date: 13 Oct 2008 - 15 Oct 2008
- Location: Prague, Czech Republic
- ISBN: 978-94-6282-067-8
- Published: 13 October 2008
1 - 20 of 34 results
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Looking Back on 40 Years of Vibro-Seismic
By R. GarottaFrom the beginning of its industrial use, the problem of the vibrator was to turn a weak and
long near field signature into a spike strong and sharp enough to provide penetration and
resolution comparable to those of the uncontested shot hole reference.
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How do Hydraulic Vibrators Work? A Look Inside the Black Box
By J. SallasRoughly half of today’s land seismic data surveys use P-wave hydraulic vibrators for sources.
The use of measured source signals and ability to control source spectral output in both
amplitude and phase has led to many innovative ways to dramatically increase acquisition
productivity. A working knowledge of how the vibrator system works and its limitations can
provide insight into how best to effectively radiate compression waves, extend bandwidth and
avoid pitfalls. This presentation offers a basic overview to help provide that insight.
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Developments in Vibrator Control
Authors G. Ollivrin and D. BoucardThe type of output used to control a vibrator was a subject of controversy some 25 to 30 years
ago. The field data collected by the acquisition systems must be correlated by a “pilot” signal
for the results to be comparable with impulsive data. But which vibrator signal corresponds to
the going down signal? A great discussion started. Baseplate velocity had been used as the
feedback control, as well as reaction mass acceleration. Over the years, the use of ground
force, measured as the weighted sum of baseplate and reaction mass accelerations, has found
wide acceptance.
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Modeling And Modal Analysis Of Vibrator Mechanical System
By Z. WeiModern seismic vibrators are essentially hydro-mechanical systems driven by a servo-valve
that is electronically controlled. A schematic cross-section of the reaction mass, the baseplate
assembly and a hydraulic power supply system are shown in Figure 1. The piston, which is a
part of the baseplate driven structure, is rigidly connected to the baseplate pad. The piston
moves in a cylindrical bore inside the reaction mass and divides the cylinder into an upper
chamber and a lower chamber. High-pressure hydraulic oil fed alternately into the upper and
lower chambers drives the reaction mass up-and-down. The force acting on the reaction mass
is equally and oppositely applied to the piston. Through the baseplate structure the force is
transmitted into the ground.
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Development of a Super-Heavy Vibrator
Authors G. Caradec and P. ButtinThe Nomand 90 project (Fig 1.) was to develop a super-heavy vibrator able to produce at full drive low frequencies (5Hz) as well as high frequencies (250Hz, depending on ground properties) and to lower the distortion. To achieve these goals, different solutions in mass and base plate design as well as for accumulators have been evaluated and tested.
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Vibroseis Processing for Truer Amplitudes: Do We Dare to Replace Cross-correlation by Deconvolution?
More LessThe goal of vibroseis data acquisition and processing is to produce seismic reflection data
with a known spatially-invariant w avelet, preferably zero-phase, such that any variations in
the data can be attributed to variations in geology. It is impossible to achieve this goal unless
the data are deconvolved for the true ground force. Determination of the true ground force
using current methods is at best approximate. A combination of approaches may lead to a
more satisfactory approximation.
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Seismic Vibrator Impedance And Near-Surface Properties
More LessSince the early days of Vibroseis, it has been observed that the vibrator behavior differs for
different near-surface conditions. In its simplest form, the earth can be regarded as a spring,
resulting in a baseplate motion that decreases with increasing earth stiffness (increasing spring
constant). It was also observed that this simple spring model was accurate for low frequencies
but inadequate to explain the baseplate motion for higher frequencies, where several
resonance phenomena were observed in the vibrator response.
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Seismic Source Comparison
Authors J. Meunier and R. Daures3 seismic source types, vibrators, explosives and weight drop are compared. A seismic
wavelet is estimated for each source. The wavelets are normalized using specific source
parameters: mass for the explosives, mass and heights for the weight drop, Peak force and
sweep rate for the vibrators. The observed amplitude levels are compared to the input energy.
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Calibrated Vibroseis Sweep Design
Authors J. Quigley and C. BagainiAdvances in seismic recording instrumentation have made it possible to contemplate practical
acquisition scenarios with tens of thousands of active recording channels and many thousands
of Vibroseis source positions per day. The seismic survey designer is faced with the question
of how best to exploit this new operational capability to achieve ‘fit-for-purpose’ processed
seismic data, within project economics. Among the factors to be considered are the source
point density (# VP/km2), source point geometry (shot line and points intervals), and the level
and spectral content of source energy to be delivered at each source point. The latter point
and its relationship to the Signal-to-Environmental-Noise-Ratio (SENR) of the acquired data
is the subject of discussion proposed in this abstract.
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Benefits of Correcting for Vibrator-Earth Coupling Variation
By R. GhoseAlong a seismic line the coupling of the vibrator to the ground is generally variable.
This is particularly true in case of loose, weathered ground condition. If this variation
is not accounted for during raw vibrogram compression, the effective source wavelet
in the seismic data becomes variable. This has a negative implication on both imaging
and characterization results. To correct for the vibrator-earth coupling variations at
different source locations, one needs to be able to measure the source motion for the
entire (or at least for a large part of the) frequency bandwidth of the sweep. For large
vibrators, a reliable measurement is not a simple task because of the large force, the
limited rigidity of the vibrator baseplate, and the nonlinear near-field deformation.
However, in the recent years, new developments that try to address these issues have
been reported.
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Effect of seismic attenuation and velocity dispersion on processing and interpretation of broadband Vibroseis data
Authors L. F. Sun and B. MilkereitBecause of the controllability of both the amplitude and phase spectra, broadband uncorrelated
Vibroseis data are ideally suited to study the effect of attenuation and velocity dispersion on the
Vibroseis correlation process. They are also suited to study the linkage between reservoir
petrophysics and seismic properties, such as velocity dispersion and frequency- dependent
attenuation coefficient.
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10 Years and 60 Slip-Sweep 3Ds for Productivity and Seismic Data Quality
Authors S. Mahrooqi, P. Matheny, S. Abri and N. PeckThe un-patented “Slip-Sweep” technique of vibroseis data acquisition was developed by
Petroleum Development Oman LLC (PDO), in cooperation with the instrument manufacturer
Sercel and several seismic contractors working with PDO in the mid to late 1990’s.
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Practical Issues in Achieving High-Quality HFVS Data
Authors S. Chiu, J. Brewer and P. M. EickThe increase of productivity using simultaneous multiple sources also adds more complexity
in field acquisition and data processing. There are a number of key issues associated only
with High Fidelity Vibratory Seismic (HFVS1) technology. Understanding its pitfalls, one can
fully realize the potential benefits of this technology. We will demonstrate some of the pitfalls
by focusing on three main areas: the uniqueness of the phase-encoding scheme; the
importance of quality control of vibratory phases in the field; and pitfalls of inverting HFVS
data. We apply our best practice to a large 3D data set and illustrate the integration of field
acquisition and data processing, leading to high-resolution images of geological structures.
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Simultaneous Sourcing Without Compromise
Authors C. E. Krohn and R. NeelamaniThe use of high-efficiency simultaneous sourcing methods results in a signal-to-noise
compromise. Noise arises because multiple seismograms need to be recovered or separated
from a smaller number of vibroseis field records compared to methods, such as HFVS (High
Fidelity Vibratory Seismic), in which there are as many sweeps as there are vibrators. We
show that iterative methods can improve the separation and remove noise for seismograms
recorded with multiple vibrators operating simultaneously with a single sweep. The iterative
methods start with an initial separation. Then, updated seismograms are produced by
adjusting them to match the survey data and to satisfy characteristics of noise-free
seismograms. The match to survey data involves reconvolving parts of the initial
seismograms with an estimate of the vibrator signatures and stacking. The method is
especially effective at removing the noise at the bottom of records for Continuous-HFVS SM
(Krohn and Johnson, 2005). With these iterative methods, the full efficiency of simultaneous
sourcing can be obtained without a noise compromise.
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Distance Separated Simultaneous Sweeping: the World’s Fastest Vibroseis Technique
By J. BouskaBP has recently developed a new simultaneous-source technology, which has been used to
efficiently acquire a large (2700km2) wide-offset, wide-azimuth, high-density (1500 fold) 3D
survey, in the interior of Oman. The BP-DS3 productivity enhancing technique allowed the
acquisition crew to acquire as much seismic in a single day, as formerly required a full week.
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A history of seismic acquisition design in Saudi Arabia - lessons learned
More LessIn Saudi Arabia, the vibroseis signal is commonly low and both ambient and source-generated
noise is high. Acquisition methods along with processing must be used to enhance the signal
and suppress the noise. Over time with advances in the number of available recording
channels and in high efficiency surface sources, particularly vibroseis, we have moved from
large mega-arrays to smaller arrays and toward point source and point receiver acquisition. At
the same time, less array summing of individual sources and receivers is done in the field, and
more noise mitigation is done in processing. The balance between improved signal-to-noise
data quality, productivity and cost is a recurring theme and continues even today. In the
1990s, we introduced universal fine sampling or “uncommitted” acquisition for 2D data. But
even today, unsummed point source and receiver survey designs cannot affordably be
acquired in 3D, with sufficient density to adequately handle both the signal and noise
challenges.
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Challenging Data Quality but Superb Reservoir Property Estimation
Authors C. E. Krohn and T. ClarkeWe have obtained a superb 3D image of reservoir porosity from seismic data recorded in a
very challenging data quality area. To mitigate the strong ground roll, vibroseis data was
acquired with 10-m source intervals using HFVS (High Fidelity Vibratory Seismic), saving
$3 million over conventional methods. As part of the HFVS method, the ground-force signal
was recorded for every shot and used for source separation and deterministic deconvolution.
This minimizes coupling variations and increases wavelet stability and phase control. After
processing, the potential for bandlimited reservoir property inversion was evaluated. The
rock physics analyses were particularly favorable with clear separation of sands and shales. A
wavelet derived from the vibrator wavelet gave excellent well ties for the angle stacks and
was used for spectral balancing. After band-limited inversion, the resulting seismic porosity
and shale predictions are an excellent match to well logs, and the resulting porosity image of
the reservoir clearly portrays the fluvial deposition (Figure 1).
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