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JOURNAL OF SEISMIC EXPLORATION
SEISMIC APPLICATIONS
book series
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Contents
& Abstracts Journal of Seismic Exploration
Volume
16, Number 1, July 2007
Volume 16, Number 2-4,
December 2007
Volume 17, Number 1, February 2008
Volume 17, Number 2-3,
April 2008
Volume 17, Number 4, September
2008
Volume 18, Number 1, January
2009
Volume 18, Number 2, April
2009
Volume 18, Number 3, July
2009
Volume 18, Number 4, October
2009
Volume 19, Number
1, January 2010
Volume 19, Number
2, April 2010
Volume 19, Number
3, July 2010
Volume 19, Number
4, October 2010
Volume 20, Number
1, February 2011
Volume 20, Number
2, May 2011
Volume 20, Number
3, September 2011
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| ABSTRACTS
Vol. 17, No. 1, February 2008 |
Droujinine, A., Buckner, S. and
Cameron, R., 2008. Sub-basalt converted-wave imaging - offshore
West Ireland.
High-velocity volcanic units that overlay lower velocity structures
hinder exploration in potential hydrocarbon producing areas
adjacent to the Corrib Field, offshore West Ireland. A recent
3D seismic reflection dataset acquired in the NW Corrib region
is used to map major volcanic units and a heavily faulted sub-volcanic
structure. The low frequency content of the seismic data is
taken into account in the acquisition design. A case study is
conducted to demonstrate how wave mode dependent data pre-processing,
velocity analysis and 3D prestack imaging techniques should
be integrated for the purpose of producing enhanced depth images
of the target zone when compared to conventional PP processing.
We show that the mode-converted waves of type PSPPSP provide
a better image of the sub-basalt structures than the PP waves.
Separation of wave modes in a pre-processing step is crucial
for imaging these different wave modes separately. For carrying
out the total velocity model building workflow, a priori knowledge
on the area in terms of the different geologic layers and their
geophysical parameters is very important. |
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Poot, H., Wapenaar, C.P.A. and
Fokkema, J.T., 2008. Slicing the earth: a layer-stripping method
employing a causality-based imaging condition.
We formulate the theory for a direct nonlinear seismic inversion
method in the acoustic approximation. It is a completely data-driven
method, aiming at the determination of subsurface properties
directly from the data. The theory is presented for the full
three-dimensional, laterally varying case. For this situation
we derive a layer replacement method based on the reciprocity
theorem and we derive an imaging condition based on causality.
Next we simplify the theory for the one-dimensional case and
give some synthetic results for this case. We explain how the
limited bandwidth of seismic data influences our method. We
propose a solution method to deal with the lack of low frequencies
in the data. This method uses the absolute value of the data.
Finally we present a synthetic inversion example for a laterally
varying earth model using common-midpoint techniques. |
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Keydar, S. and Mikenberg, M.,
2008. CMP traveltime approximation in 3D media as a function
of wavefront attributes.
We derive a new 3D traveltime moveout formula for common-midpoint
data (CMP), which depends on four parameters: the near-surface
velocity, two principal wavefront curvatures, and an azimuth
angle. The formula is derived using only elementary principles
of differential geometry and the eikonal equation. Being a function
of three wavefront parameters, the formula provides a better
approximation than the conventional CMP normal-moveout correction
formula. |
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Agersborg,
R., Johansen, T.A. and Ruud, B.O., 2008. Modelling reflection
signatures of pore fluids and dual porosity in carbonate reservoirs.
The motivation for this synthetic Amplitude Versus Angle (AVA)
study of an isotropic carbonate reservoir consisting of a dual
porosity on two scales is to identify possible seismic signatures
of carbonate rocks containing various fluids and pore connection
models. The reservoir is modelled for four scenarios on the
basis of a general theory for visco-elastic waves, where the
inclusion-based model operates with spheroidal cavities on two
scales. While the total porosity of the reservoir is considered
constant, the pores and cracks at the different scales are designed
to be either connected or isolated. The pore systems are saturated
with either gas, oil or water. Reflection coefficients are computed
for a 2-layer model consisting of a cap rock of shale above
the reservoir in order to analyze the effects of various pore
to pore connection and pore fluid models in the double porosity
systems.
The modelling shows how the AVA parameters change both due to
varying pore to pore connection and various pore fluid saturation
scenarios. If we assume estimated AVA parameters with some uncertainties,
the study indicates that it should be possible to obtain measurable
changes in the reflectivity due to changes of the pore connectivity
also when the introduced fluid has almost equal acoustic properties
as the displaced one. Such modelling studies should be of particular
relevance for studying diagenetic effects on seismic signatures,
as for instance, water and oil may have similar acoustic properties,
but different impact on the pore system over time. |
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Haase,
A.B. and Ursenbach, C.P., 2008. Spherical-wave AVO modeling
in elastic and anelastic two-layer media.
The AVO response of two-layer isotropic models for AVO Class
1 is investigated for P-waves and converted waves in elastic
and anelastic media. Zoeppritz reflection coefficients and the
Weyl/Sommerfeld-integral are utilized for the computations.
Spherical-wave results for RPP and RPS are compared with plane-wave
reflectivity. Depth dependence of spherical wave AVO is found
to be strongest near critical angles of Class 1. There is a
similar depth dependence between RPP and RPS for Class 1.
Anelastic effects are introduced via the constant-Q approximation.
Anelasticity modifies the AVO response of two-layer isotropic
models. However, when reflection amplitude losses due to attenuation
are compensated for by unit reflectivity scaling, AVO characteristics
similar to the elastic situation are found. Q-factor dependence
of spherical-wave AVO is found to be strongest near critical
angles of Class 1. This Q-dependence, to some degree, mimics
depth dependence of elastic comparisons. Wavelet stretch of
converted wave AVO reflection traces is observed in addition
to a phase rotation of all anelastic trace examples when compared
to the elastic situation. In summary, spherical-wave behaviour
affects amplitude versus offset, both for PP and PS reflections
in elastic and anelastic isotropic media. |
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