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Geophysics of the 21st Century - The Leap into the Future
- Conference date: 01 Sep 2003 - 04 Sep 2003
- Location: Moscow, Russia
- Published: 01 September 2003
41 - 60 of 322 results
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Interpretation and Visualization of drilling hazards in the South Caspian Basin: Zafar Mashal Prospect
Authors J.K. Mikkelsen and K. FowlerThe large offshore structures in the Azerbaijan sector of the South Caspian Basin are associated with
difficult drilling conditions due to a number of factors. 3D visualization and interpretation tools have been applied
to mitigate the numerous drilling hazards such as over pressured channels, shallow faults, shallow gas and mud
volcanoes. The same tools have been used to integrate interpretation results into the well plan and visualize the
associated drilling uncertainties.
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Performance of gravimagnetic anomaly algorithms for uniform polyhedra
Authors H. Holstein and E.M. SherrattFormulas for the gravity potential, eld, eld-gradient,
magnetic potential and eld of a polyhedral target
of spatially uniform density or magnetization su er
asymptotic rounding error that grows proportionally to a
power of the dimensionless target distance. The form of
the error growth can be speci ed by universal templates
that are applicable to a very wide class of targets and
arbitrary floating point precision, and hold for all the
standard gravimetric anomaly calculations.
A compact form of the anomaly formulas allows the theoretical
a priori templates to be be derived, depending
only on the presence or absence of foreshortening in the
observed anomaly, and class of anomaly formula used,
of which three kinds are found in the literature. Computational
results, con rming this claim, demonstrate
automatic method selection to accomplish maintenance
of rounding error to a speci ed level in magnetic eld
computations.
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Assessment of the subsidence and turfs in the internal Maliqi depression using geophysical methods
More LessAn area of about 120 km2 (from the Zvirina-Podgorie Line in North close to the Vashtemi-Shamolli
Line, which is the area of the former Maliqi Swamp) was covered by the geophysical methods. Geologically
this area consists of the Quaternary overburden formations (Q1-4) and the Upper Neogene, concretely not
differentiated Pliocene and Pliocene-Quaternary (N2-Q1) formations.
The main objectives of this study have been:
1. Investigation of the subsidence phenomenon, which may lead to the gradual formation of the Maliqi
Swamp.
2. Development of the monitoring network to observe the subsidence phenomenon.
3. Locating an eventual second turf layer under the known one and its control with integrated methods.
To achieve geological-geophysical (electrical) resulsts for the two first objectives there have been mostly
used geodesical methods.
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Investigation of ground water of karst origin using geophysical methods, Kastrat area, Albania
More LessGeophysical methods, especially electrical ones, are widely applied in solving urban problems and
ground water prospecting as well. Intensive works of ground water prospecting are closely related to the
emergent needs of the Albanian society as result of the rapid demographic changes because of population
migration during the transition period. This abstract provides the results of application of geophysical
methods in ground water prospecting and investigating of water-bearing potential of carstified limestones in
the Komuna Kastrat area, northwest Albania. These works are carried out within the framework of a project
for natural resources of northern Albania Prefectures.
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Examples of use of electric sounding and SP for finding and estimating the aquifers, Lezhe-Shkoder region, Albania.
More LessThe Lezhe-Shkoder-Hani Hotit region takes part in the governmental perspective plans for
developing the tourism and it is also one of main priorities for developing the agriculture. Therefore the
exploration and discovering the aquiferous basins and estimating their potential especially for potable water
is an immediate geologic task.
The aquifer exploration in this regionis related with alluvial deposits of Quaternary and with carstic zones of
carbonates.
The Quaternary formations are represented by deluvialand aluvial deposits composed of argillaceous
gravelsand partly by limestone and dolomite blocks. The thickness of this formations is up to 100-120m
The geophysical surveys carried out with electrical soundings have provided considerable information on
lithology of the formations in the area and water-bearing potential as well.
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Effective anisotropy due to thin VTI layers
By A. BakulinSeismic anisotropy observed in the field is a cumulative result of various mechanisms. Subsurface rocks often
possess intrinsic anisotropy approximated by a transversely isotropic solid with a vertical symmetry axis (VTI).
Alternatively, in the long-wavelength limit, ”layer-induced” VTI anisotropy may arise even in a stack of thin isotropic
constituent layers. In most practical cases these two effects occur simultaneously. We develop weak anisotropy and
weak contrast approximations to understand the contributions of intrinsic and layer-induced anisotropy. When the
contrast in elastic parameters between the constituents is small and their anisotropy is weak, then (to the first order)
layering-induced anisotropy is insignificant whereas intrinsic anisotropy produces effective Thomsen parameters equal
to the thickness-weighted average of the interval anisotropy parameters. This conclusion considerably simplifies
upscaling of finely-layered VTI media because to find the effective Thomsen parameter ² (or ± or °) one needs to
know only constituents ²’s (or ±’s or °’s correspondingly).
For larger variation in the elastic properties, each anisotropic parameter may be approximated as the sum of two
terms: one is the averaged intrinsic anisotropy and the other is a purely isotropic term related to fluctuations in
the vertical interval velocities. The isotropic term has been extensively investigated in literature, and all previous
conclusions may be directly applied to the more realistic VTI case considered in this study.
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Rock Property Determination Using Digital Rock Physics
Authors J. Dvorkin, A. Tutuncu, M. Tutuncu, A. Nur and A. MeseThe Digital Rock Physics (DRP) technology is based on a rigorous numerical simulation of physical experiments
in a realistic pore space, at the pore-scale level. The output is usually a macroscopic property conventionally
measured in the lab. For example, a single-phase viscous fluid flow simulation through a digitized pore space
provides absolute permeability. A simulation of electrical current provides conductivity, and a simulation of the
stress field provides the elastic moduli and strength. DRP complements lab measurements and, at the same time,
enormously enhances the geoscientist’s capabilities because digital experiments can be conducted in real time
and on small fragments of rock, such as drill cuttings. We report a feasibility study on DRP technology applied
to drill cutting samples to obtain porosity, permeability, and the P- and S-wave velocity.
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Enhanced signal-to-noise ratio and bandwidth through explosives design
Authors D. Bremner, G.A. Tite, P. Thompson and J. BrooksThe signal-to-noise ratio and bandwidth of explosive-sourced seismic data are the direct result of the
properties of the explosives used and the near-surface conditions. Conventional wisdom has dictated
that certain properties are desirable in seismic explosives. A series of experiments have shown that
some of these assumptions should be revisited.
Multivarient testing has confirmed that the efficacy of seismic explosives can be improved in many
environments. This reinforces the contention that the design of the explosive utilized is critical to the
ultimate quality of seismic data. These results suggest that a method of testing and customizing
explosives to take advantage of these variations can be established.
Current data suggest that 3 to 6 dB of signal enhancement may be achieved in the seismic bandwidth
through the use of metalized explosives. Examples of these improvements will be presented in the
paper. Based on these improvements, it should be possible to achieve better signal-to-noise ratio and
bandwidth.
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Borehole Integration Technologies for Seismic Reservoir Characterization: Application to Hassi Messaoud Field.
Authors S. Morice, M. Robinson, R. Lounis, S. Leaney, S. Tcherkashnev and M. WheelerNew technologies for integrating borehole information throughout the surface-seismic workflow have demonstrated superior seismic imaging and reservoir characterization, and reductions in project turn-around time. These technologies, and results from their application in Hassi Messaoud Field, Algeria are presented.
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Interval density mapping for thick layers
Authors I. Vasiljevic and J. MilovacA simple method for interval density determination in thick layers by joint analysis of surface and
subsurface gravity maps is presented in this paper. Method is designed for solving interval density
distribution problem in cases of significant lateral density variations above deep mines, where there is no
possibility to conduct gravity measurements along vertical shafts. Application of this method doesn't require
precise position and characteristics of anomalous masses. All that is necessary is a general idea of anomalous
zones distribution.
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The influence of near-seafloor low velocity layers on shallow marine seismic measurements
Authors H. Zöllner and P. SchikowskyDetailed investigations of the influence of low velocity layers, especially gassy-mud sediments were made,
based on industrial seismic data from the southern baltic sea. More than a half of the Greifswalder- Boddenbay
is covered by such sediments. In these regions absorption of more than 90 percent, strong high frequency
singing, low frequency waves and travel-time anomalies up to 50 ms were found.
Large Problems results from this travel-time anomalies because of potential misinterpretation as tectonic
structures. To distinguish between real tectonic structures and travel-time anomalies we investigated traces
of different offsets. At large offsets a local surface caused travel-time anomaly will be observed two times in
this seismogram. Two different reasons for travel-time anomalies was found: gassy mud sediment at the sea
bottom and pleistocene channels.
Static corrections of travel-time anomalies due to gassy mud sediments can be done by using variations of
first break travel-times as correction time values.
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Seismic reservoir description of the Barrosa Norte-El Triángulo fields, Argentina, using hybrid seismic inversion
Authors M. Benabentos, J. Perdomo, S. Mallick, E. Sanchez, L. Pianelli and C. SaavedraThe gas-bearing sands in the Barrosa Norte-El Triángulo field, Argentina are characterized by highamplitude
bright-spots on the stacked seismic data, and these anomalies have traditionally been used to
locate drilling sites. Drilling through these bright-spots has resulted in some pay and many dry wells.
Because the seismic reflection amplitudes are dependent on thickness, lithology, and porosity besides fluid
content, using bright-spots alone is ambiguous in detecting hydrocarbon sands from stacked seismic data.
To resolve the ambiguity, we use a 3D hybrid seismic inversion. This inversion provided a detailed and
accurate estimate of elastic earth properties, which were then used to calculate porosity and water
saturation maps for the reservoir.
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The Importance of Anisotropy for Prestack Imaging of Extensional Fault Systems
Authors B. ver West, P. Hilton and D. WilkinsonThe presence of anisotropy in the subsurface is a generally accepted but commonly overlooked
concept in processing. When it is addressed, usually only the effect on moveout is considered. This
paper shows the importance of including anisotropy in imaging, not only because it properly handles
the long offset moveout but also because it correctly handles the focusing and spatial positioning
which is subtler but may be even more important. The paper shows an imaging problem from the
coast of the Gulf of Mexico. It is a problem involving fault related rollover structures that are
common worldwide. The fundamental aspects of anisotropy in imaging are introduced. Then the
impact of anisotropic prestack time migration on this example is shown along with a practical strategy
for its implementation. The impact is demonstrated using sections and time slices from the 3D survey
comparing previous processing without anisotropy to new processing with anisotropy. The
anisotropic prestack time migration properly focuses and images the complex growth fault structures
and leads to significantly higher spatial resolution of the targets.
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Reservoir modeling of a thin carbonate reservoir using geostatistics and 4-D seismic attributes, Weyburn field, Saskatchewan, Canada
Authors T. Galikeev and T. DavisEnhanced oil recovery through CO2 injection is a commercially
proven technology and allows additional
recovery of typically 10-15% of the OOIP. Time-lapse
seismic data provide a valuable insight on dynamics of
a reservoir, which otherwise would not be possible by
analyzing conventional, one-time seismic data. Analysis
of seismic data acquired over the same area but at
different periods in time helps to monitor fluid front
movement, assists in detecting changes in rock properties
caused by CO2 injection, allows optimization of the field
production and, therefore, improve economical effect.
Weyburn field experiment was carried out by the Reservoir
Characterization Project of the Colorado School of
Mines with the cooperation from the field operator, En-
Cana corporation.
The seismic acquisition program at Weyburn includes
three 3-D 9-C surveys with the base survey acquired in
2000 just before the CO2 injection program began. Two
additional monitoring surveys were shot in 2001 and 2002,
exactly one and two years later.
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Enlarging of the «A» deposit within the Vx oil-gas field according to interpretation of 3D-seismic exploration
Authors F. Miroslav and B. MilovanOil-gas field VX is located at the NE part of Vojvodina, within Pannonian basin. The "A" deposit is
main reservoir of hydrocarbons within the VX oil-gas field. This deposit is known as one with the
highest oil production in Yugoslavia.
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3D Seismic Classification - An efficient approach for prospect identification in asset evaluation
Authors F. Xue, R. Broetz, D. Paddock and K. Hemsley3D seismic classification is a breakthrough technology to determine 3D distribution of pore fluid and lithology from multiple seismic attribute volumes. A supervised classification method was used to define classes of fluid and lithofacies based on knowledge of well production, lithology and seismic amplitude. Using cross-plot discriminant analysis, extra classes were defined based on their cluster distribution, separating classes based on their degree of risk. The generated class cubes provide the location of prospective targets and the associated probability cubes provide quantitative estimation of risk. 3D visualization techniques vividly display the distribution of fluid and lithofacies and also provide the volume-percentages of different classes, which is important for quality control. Multiple attribute 3D seismic classification analysis identifies top drilling targets in a matter of weeks instead of months.
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Attenuation of Residual Multiples and Coherent Noise in the Wavelet Transform Domain
Authors T. Pokrovskaia and R. WombellAlthough generally very powerful, noise and multiple attenuation techniques can often leave
remnants in seismic data. For example, noise from extraneous sources such as rigs and other
boats can be hard to model and fully remove using standard methods. Similarly, multiple
remnants are often present after multiple attenuation when multiples are generated by
relatively complex geology, such as rugose water bottoms or salt, and as such do not conform
to the assumptions of most multiple attenuation algorithms. These remnants can cause
problems in later processing, for example through the generation of migration noise and
contamination of AVO analysis etc. and therefore often need to be further attenuated in the
processing sequence. As these remnants are often localized and may have high amplitudes
compared to the underlying data, they can be relatively easy to identify and can be targeted in
a different number of domains. The application of a wavelet transform (wavelet
decomposition) on pre-stack data can be used to separate signal from coherent noise in both
frequency and time. The noise can then be removed from the data by a variety of noise
attenuation methods in the wavelet domain. We show two examples to illustrate the
effectiveness of this method: the attenuation of residual multiples and attenuation of boat
noise.
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In-line walkaway VSP processing and integration
Authors S. Leaney, S. Tcherkashnev, M. Wheeler and M. IdreesDuring July 2002 a large vertical aperture land walkaway data set (154 levels) was acquired simultaneously with
3D surface seismic operations. The objectives were to acquire data for 1) calibrated surface seismic processing, 2) high
resolution imaging near the borehole and 3) AVO measurements. This paper deals with the computations relevant to
integrated surface processing; with model calibration and in-line walkaway data processing for imaging and AVO.
Input to surface seismic processing came in several forms: an effective anisotropic velocity model derived from
direct times to guide velocity analysis, a calibrated model for ray-based spreading, transmission and Q compensation
applied prestack, modeling for optimum mute design and simulations and corridor stacks for borehole match-driven
optimized demultiple processing.
Walkaway processing includes surface-consistent vector wavefield processing, inverse Q filtering, elastic
wavefield separation and deconvolution done in the t-p domain. The Kirchhoff migration uses exact 1D VTI dynamic
ray-tracing and includes options for processing-consistent amplitude handling. Our processing sequence for AVO
analysis employs common shot separation and deconvolution to avoid mixing in offset.
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Evaluation of thrusting tectonics and reflection of flysch folds at top limestone level in Albania thrust belt (Western Balkan), based on geo-seismic study
Authors S. Dhima, E. Prenjasi, S. Nazaj and V. SiloOn earlier geo-seismic study for hydrocarbon exploration in Albania, every flysch fold “expressed” a
carbonate anticline structure in depth, accepting only a small asymmetry scale. But seismic survey and
drilled well data gained latter on proved that this interpretation concept isn’t always true.
A complex interpretation of geological and geophysical data concerning flysch folds, their asymetry and
reflection at top Eocene limestone level, as well as thrusting range have been in focus of many studies on the
Albanids Thrust Belt. (Fig.1)
Methodology analyses of seismic acqusition, as well as structural modelings before and after field survy
have implemented reading and interpretation of obtained seismic information.
Modelings based on certain structural and tectonic paterns, as well as on presettled parametres of lateral
spread of seismic waves velocities are made through several programs which operate upon certain values of
the x, h, v indicaters. (x-coordinate of a point on a reflection horizon in a profile, h-depth point from the
seismic datum, v-propagation velocity of the seismic wave from surface to the certain seismic horizon).
Realizing the modeling process the generation of a synthetic time section is make possible, where are given
only the reflections horizons drowing on the geological model. The utilization of modeling process in
seismic interpretation, helps identifying source and type of seismic horizons from all deposits thickness that
could be present on a time section. This conclusion is helpful in cases of flysch folds belonging to “flysch
thrust belts” in the Albania Thrust Belt.
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Integration of Time-Lapse Seismic and Production Logging Data: Jotun Field, Norway
Authors D.H. Johnston, W.P. Gouveia, A. Solberg and M. LauritzenTime-lapse (4D) seismic data acquired over the Norwegian North Sea Jotun Field is used to monitor water
sweep in the Paleocene-age Heimdal reservoir. Inversion of the seismic differences provides a direct
measure of the impedance increase associated with water displacing oil. This high-resolution image of water
sweep is consistent with production logging tool (PLT) data acquired in seven wells in the field. Combined
with integrated reservoir facies interpretations and with other production data, the 4D data successfully
derisked several proposed infill well locations and has identified new workover candidates and drilling
opportunities in the field. The results of this work demonstrate the strength of applying multidisciplinary
team efforts and partner cooperation to optimize asset value through tailored data acquisition programs and
drilling.
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