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11th International Congress of the Brazilian Geophysical Society
- Conference date: 24 Aug 2009 - 28 Aug 2009
- Location: Salvador, Brazil
- Published: 24 August 2009
21 - 40 of 418 results
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Ss-Traveltime Parameters From Pp- And Ps-Reflections
Authors Bjørn Ursin, Martin Tygel and Einar IversenSS-wave traveltimes can be derived from PP- and PS-wave data with the previously derived “PP + PS=SS” method. We extend this method as follows: 1) The previous requirement that sources and receivers need to be located on a common acquisition surface is removed, which makes the method directly applicable to PS-waves recorded on the ocean bottom and PP-waves recorded at the ocean surface. 2) By using the concept and properties of surface-tosurface propagator matrices, the second-order traveltimes of the SS-waves are obtained. In the same way as for the original “PP+PS=SS” method, the proposed extension is valid for arbitrary anisotropic media. The propagator matrix and geometric spreading of an SS-wave reflected at a
given point on a target reflector are explicitly obtained from the propagators of the PP- and PS-waves reflected at the same point. These additional parameters provided by the extended ”PP+PS=SS” method can be used for a partial reconstruction of the SS-wave amplitude as well as for tomographic estimation of the elastic velocity model. A full simulation of the SS-wave, which includes reflection and transmission coefficients, cannot be directly obtained from the knowledge of PP- and PS-amplitudes.
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Multiple Attenuation With A Modified Parabolic Radon Transform
Authors B. Ursin, B. Abbad and M.J. PorsaniWe present a fast and efficient frequency-domain implementation of a modified parabolic Radon transform (modified PRT) based on a singular value decomposition with applications to multiple removal. With a change of variable, the problem is transformed into a complex linear system involving a single operator after merging the curvature-frequency parameters into a new variable. A complex singular value decomposition (SVD) can be applied to this operator and the forward modified parabolic Radon transform is computed for all frequency components within the signal bandwidth by means of complex back-substitution only.
The standard PRT can be obtained by interpolation in the modified transform domain. The method is also able to resolve the multiple energy from the primaries when they interfere in a small time interval and resists well to AVO effects in the data. The proposed modified PRT was successfully applied to a deep-water seismic line at the Gulf of Mexico to attenuate water-bottom multiples and subsequent peg-legs originating from multiple paths in the water column.
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Estimativa De Litofácies Através De Perfis De Poços Do Campo De Namorado (Bacia De Campos, Rj)
More LessThe recognition of several patterns has been used broadly in the interpretation of geophysical data. These data are specific physical answers of geological formations. The data, usually, it contains important physical information of the geology of the which those they result and reveals significant patterns of these geological structures. Among the methods of geophysical exploration, the well logging has great application in the location and evaluation of mineral resources, as the petroleum. A great challenge that it presents is the segmentation of these profiles in zones capable to identify some standards found in the reservoirs of petroleum. For the identification of some litologies, Gama Ray profiles were used (GR), Density (RHOB) and Neutron Porosity (NPHI). This work has for objective to identify the litologies patterns through the data of well log of Namorado Field in Campos Basin (RJ). The data were given up by Agência Nacional do Petróleo (ANP). For this work was utilized Interactive PetrophysicsTM software, which is commercialized by Schlumberger.
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Towards A Method For Ghost-Free Marine Acquisition
Authors Eivind Fromyr and Guillaume CamboisA dual sensor streamer effectively removes the receiver ghost from seismic data through dual sensor summation. The source ghost can be attenuated by spreading out the ghost contribution in time by towing the gun arrays in a multilevel arrangement. The combination of the two dramatically increases the bandwidth of marine seismic data. In particular, the low frequencies are significantly enhanced, which provides better penetration and improved Q estimation. The multi-level source will be biased towards low frequencies and have an anisotropic radiation pattern.
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Estudos Geofísicos Para Avaliação Ambiental De Uma Estação De Esgoto
Authors Eduardo Fernandes Henriques and Vagner Roberto ElisEstudos geofísicos para avaliação ambiental de uma estação de esgoto
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Título: Variações No Fluxo Geotermal Raso Em Locais Com Diferentes Graus De Proteção Vegetal Na Cidade De Humaitá (Am)
More LessA realização de monitoramento geotérmico na cidade de Humaitá-Am, no período de outubro/2007 a setembro/2008, às profundidades de 0,02 m, 0,5 m e 1,0 m, em locais com (c/c) e sem (s/c) cobertura vegetal, permitiu avaliações do fluxo geotérmico raso em escala local. Também foram utilizados os dados de condutividade térmica de amostras obtidas no local
estudado. Os resultados obtidos indicam variações do valor médio do fluxo geotermal raso de até 0,60 W/m2 , à profundidade de 0,5 m e de 0,15 W/m2, à profundidade de 1,0 m. Tais variações foram da ordem de 103 acima do valor do fluxo terrestre profundo na região. Constatouse a influência da proteção vegetal nos valores do fluxo geotermal raso, às profundidades estudadas. A existência de variações mensuráveis do fluxo a 1,0 m de profundidade indica que tais valores não podem ser negligenciáveis, nem associadas somente ao fluxo geotermal proveniente do interior da Terra, deve-se considerar também a intensidade da radiação solar incidente na superfície terrestre local.
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Survey Design Considerations For Full Azimuth Acquisition Using A Single Recording Vessel
Authors David Hill, Gordon Brown, Rob Campbell and Ed HagerAzimuth-rich towed-streamer acquisition is established as a successful method for exploration in the Gulf of Mexico. The azimuth-rich data acquired to date has delivered better illumination and imaging, a higher signal-to-noise ratio, and improved seismic resolution. However, the azimuth-rich towed-streamer acquisition configurations used in the Gulf of Mexico are all multi-vessel. Moldoveanu (2008) introduced a method of acquiring azimuth-rich data with a single vessel. This paper describes a survey design and field test for a single-vessel azimuth-rich technique, which has the same acquisition effort as a 3-survey narrow-azimuth survey.
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Modelagem De Eletrofácies Em Minério De Ferro Por Classificador Knn
In this work are showed results for a logfacies procedure applied to a Brazilian iron ore deposit. The procedure has in its central core a KNN classifier, which is a multivariate statistical approach. Some auxiliary tools as step-by-step discriminant analysis, data standardization, and measurement of an n-dimensional Euclidian distance are also used. The well logs used for logfacies modeling are Gamma Ray (GR), Short Normal resistivity (SN), Self Potential (SP) and Sonic (DT). Five facies types are recognized. Due to the high number of available data, it
was possible to adopt K = 3, in a KNN procedure, providing a facies prediction with low error rate and without an excessive smoothed solution. Results show, at the majority of wells, a very good correspondence between lithofacies and logfacies columns, but in two wells the logfacies column show, in their upper part, a higher resolution than that of lithofacies column. The
general average index for correct prediction was 91.1%, thus indicating the applied procedure as suitable for iron ore facies recognition, at least for this ore deposit.
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Modelo Gravimétrico 2D Y Su Comparación Con Espesores Corticales Sísmicos En Una Sección A Los 30 ° De Latitud Sur
Authors Mario E. Gimenez, Myriam P. Martinez and Francisco RuizWe made a gravimetric model, on a section which crossed through the Andean Cordillera, Pampean Ranges and Precordillera in an west to east direction, at -30° latitude south and 71° at 65° longitude west. The response of gravimetric model of the crust, fixed to the curve of the Bouguer anomaly upward continuation at 40km in height, which would correspond to the moho ondulations. This result was compared with the crustal thickness obtained by means of: (1) the Moho depths given by the apparent phase velocities Pn (Fromm et al., 2004)and (2) receiver function of wave S (Heit et al., 2008). In This study evaluated the gravimetric effect of the three cortical models compared with the regional Bouguer anomaly. The conclusions reveal that the major discrepancy between the models is produced in the Cuyania terrane, principally in the Precordillera zone. This includes the "PACH" and "HEDI" seismological stations and on minor measurement to the "RINC" station, located in the Famatina terrane. In accordance with the existing geological information, the Precordillera is a thin-skin structure, whith a décollement horizon at 18km of depth.
From the isostatic viewpoint, based on the Airy concept, the region is an unbalanced, manifesting a scarcity of root. This evidence would be the contrast-position to the seismological models which indicate that below the Precordillera, the Moho excedes depths of 70 km, that being the deepest of the Andean Cordillera.
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Análise E Comparação Da Contaminação Por Hidrocarbonetos Em Postos De Combustíveis Utilizando O Método Gpr
Authors Fabíola Magalhães De Almeida and José Gouvêa LuizThe results of GPR profiling executed to investigate the subsurface under two gas stations are presented. The correlation of the GPR data to the local groundwater flux and to the gathered information about the gas stations history aloud to classify the subsurface of one of the stations as suspect of contamination and the other as probably contaminated. The GPR signature for the contamination was intense low reflection zones overlying zones of normal reflections.
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Features Of Lightning That Result On Fires In Some Regions Of Brazil
Authors Ana Paula Dos Santos Zepka and Osmar Pinto Jr.Fires caused by lightning are long studied worldwide. In Brazil, however, little is known about this issue and the characteristics of lightning that cause these fires. In order to study the characteristics of these natural fires a climatology of lightning that hit two important parks in Southeast and Center regions of Brazil, the National parks “Serra da Canastra” (PNSCa) in Minas Gerais and “Emas” (PNE) in Goiás, was made for the period from 2002 to 2007. The analysis was carried out using lightning data obtained from BrasilDat (Brazilian Lightning Detection Network) considering multiplicity, positive and negative peak current, number of flashes, percentage of positive flashes, complemented by temperature and relative humidity data. It was observed that the PNSCa has annually around 40% more lightning than PNE, although they are located in very close latitudes, but in the three months more critical for the occurrence of fires (August, September and October), the number of lightning is larger in the PNE.
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Behavior Of The Atmospheric Sulphur Dioxide (So2) At Cachoeira Paulista – Sp, Through The Data Obtained By The Brewer Spectrophotometer
More LessFor a better comprehension of the atmospheric chemistry, it is necessary to understand the behavior of the trace gases and aerosols, since the atmospheric chemical and radiative properties depend upon them. But the behavior of some of these species is not well studied and characterized. An example is sulphur, that both in the gaseous as in the aerosol phase have great
environmental impact. With this purpose, a study to evaluate the behavior of the sulphur dioxide, an acid rain and sulfate aerosol precursor, and whose the main natural source are the volcanic eruptions will be shown. The ground-based observations presented in this study were made in the city of Cachoeira Paulista (22.6ºS, 45ºW), in the countryside of the State of São Paulo,
through the acquisition of the gas total column measured by the Brewer Spectrophotometer of the National Institute for Space Research – INPE, as part of a doctorate thesis that will focus the data along South America.
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Complex Imaging
Authors Jerry Kapoor, Denes Vigh, Nick Moldoveanu, Bill Dragoset, Hongyan Li and Pete WattersonThe past couple of years have seen a tremendous increase in the acquisition of wide azimuth (WAZ) surveys that provide improved subsalt imaging. We have seen a step change improvement in image quality compared to conventional narrow azimuth (NAZ) surveys, even when using minimal processing and existing, conventional-survey velocity models. The improvement in image quality is taken to the next level when the wide azimuth data are combined with other seismic and non-seismic measurements to build ever more highly constrained models, and then more accurately migrated with two-way wave-equation methods. In this presentation we will show examples of WAZ data processed with the latest technology such as true azimuth 3D multiple attenuation using the general surface multiple prediction (GSMP), wave equation based multiple attenuation (WEM MOD) and reverse time migration (RTM). We will also discuss development of our next generation of velocity model building tools and techniques such as full waveform inversion (FWI).
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Predição De Perfis Geofísicos De Poços Por Classificador Knn
More LessThere is a large diversity of well log curves but, in practice, its availability is always limited. Thus, sometimes a desired log curve is not available for a given application. However, well logs are in some level interdependent, so, it is possible to use some well logs to estimate another missing curve. In this work the multivariate statistical method KNN (K-nearest neighbors) is used to estimate a basic suite of well logs (GR, RHOB, NPHI, DT and ILD) from Namorado Field, offshore Brazil. KNN is adopted due to its simple implementation, low computer cost and
high resolution. A training data set was composed by random choice of 30% of standardized well log curves from 12 vertical wells. The remaining data was used for well log prediction. All wells have the complete suite of logs, but in order to check the performance of prediction, each time one log curve was removed from data base, a synthetic one was estimated and compared to the original curve, furnishing an average prediction error. KNN was a suitable method for synthetic curve estimation of the majority of well logs, with estimated curves well correlated
to real curves in terms of curve shape, well log values and resolution level. Nevertheless, the same prediction performance was not achieved for all log curves. For ILD curve the general prediction error was 186.9%, an unacceptable high value, meanwhile the prediction error was clearly satisfactory for GR (13.2%), NPHI (12.6%), DT (4.1%) and RHOB (1.5%).
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Comparison Of Measurements Of Diffusive Methane Fluxes And Stagnant Film Model Flux Estimate On The Manso Reservoir, Mato Grosso, Brazil
Authors Marcelo Gomes Da Silva, Luciano Marani and Plínio C. AlvaláThis work presents the methane fluxes and the used methodology in the reservoir hydroelectric power plant of Manso (Matogrosso, Brazil) were presented. Measurements of water dissolved methane (DM) in three different depths (subsuperficial, middle and near the sediments) were also made. These measurements show that the primary production of methane occurs mainly on
the sediments, and the consumption on water column is important to the emission balance. The diffusive methane flux was also estimated with the stagnant film model from the DM measured on the sub superficial water. The results were compared with the measured diffusive fluxes and shows that this model gives a good first estimative and that the water turbulence and wind have an important role on the methane emission from water bodies.
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Inverse Crs
Authors Hervé Perroud, Martin Tygel and Lucas FreitasThe CRS method is a powerful tool to produce highquality stacked images of multi-coverage seismic data. As a result of the application of CRS, not only a stacked section, but also a number of attributes defined at each point of that section, is produced. In this way, one can think of the CRS application as a transformation from data space to attribute space. However, as the CRS method is purely kinematic, it should be completed by amplitude information, that we propose to obtain from the zero-offset (ZO) section and common midpoint (CMP) gather. In this
paper, we propose an algorithm for an (approximate) inverse CRS transformation, namely one that (approximately) transforms the CRS attributes back to data space. The CRS transform pair established in this way may find a number of applications in seismic imaging and data processing, in the same way as other wellknown transformations, e.g., Fourier, Radon, tau-p, etc.
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Tectonic Framework Of The Rio Do Peixe Basin (Northeast Brazil)
The “Interior Basins” of Northeast Brazil represent
erosional remnants of a series of basins located south of
the Potiguar Basin, overlying the pre-Cambrian crystalline
basement of the Borborema Province. These basins were
originated during the early Cretaceous rifting that shaped
the present continental margin of northeastern Brazil.
Besides their own hydrocarbon exploration potential, the
Interior Basins provide terrain analogues for better
understanding the continental margin basins, this being
one of the objectives of the Interior Basins Project
(agreement PETROBRAS / UFRN / PPGG), which
supported the seismic survey in the Rio do Peixe Basin,
subject of this paper. Combined with gravity and field
data, the seismic sections allowed an improved view of
the three-dimensional architecture of the Rio do Peixe
Basin. In this basin, the combination of the current
erosion level with the geometry of the main faults
highlights the existence of different half-grabens (Pombal,
Sousa, Brejo das Freiras), whose sedimentary filling
(apart from Cenozoic deposits) defines the Rio do Peixe
Group, comprising the Antenor Navarro (alluvial fans /
braided channels), Sousa (shallow lacustrine / floodplain)
and Rio Piranhas (alluvial fans / braided channels)
formations. Structural data integration characterizes a
NW-extension kinematics for the rifting event, responsible
for fault nucleation controlled by basement structures,
particularly the location and foliation dip of the late
Neoproterozoic, Brasiliano strike-slip shear zones. Based
on the structural style and petrographic-diagenetic
features, one can infer larger original dimensions for this
basin and similar counterparts in the region, which were
reduced (with exposure of the crystalline highs) by the
significant erosion that occurred in late to post-rift and
subsequent evolutionary stages of this region.
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Extração De Atributos De Atenuação De Ondas Elásticas Em Rochas Sedimentares
Authors Zigma M. Moreira, José Agnelo Soares and Luiz LandauThis work presents practical results for extraction of Pand
S-wave attenuation attributes in samples of badly
selected sandstone and mature and immature shales.
Laboratorial measurements in dry rock samples, under
several levels of confining pressure, were done through
ultrasonic transmission of pulses. The attenuation
attributes had been extracted by the spectral ratio
method. Results indicate that the procedure adopted for
extraction of attenuation attributes was efficient in
supplying compatible values with those presented in
literature. For all samples, the factor Q, both for P and S
waves, grows with the increase of the confining pressure.
Samples of immature shale present low speeds and high
values of factor Q. While QP is greater than QS for
samples of immature shale, inverse relationship is
observed for mature shales, suggesting a potential new
method for distinction between oil generating and sealing
shales.
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Seismic Modeling As A Tool For Designing 3D Seismic Surveys
It is well known to the geophysical community that
the use of seismic modeling is an important tool for
survey design. However, operational restrictions and
cost together with a tight time schedule for the
design of 3D projects restricts the amount of different
parameters and geometries that can be tested for a
particular area. Ray tracing over 3D geologic models
has been applied by the oil industry for some time to
decide what parameters should be applied to a given
survey. These parameters include, for example, sail
line direction, streamer separation and length. These
studies are also important for the development of
new techniques, in which is possible to evaluate the
contribution of long offsets and azimuths. In this
work, the area under study is characterized by the
presence of a thick allochthonous salt body, and our
aim was to assess different survey parameters and
geometries so the subsalt layers of interest can be
well illuminated. Two software’s running in different
platforms were used to assess the appropriate survey
design and it will be shown that they could effectively
contribute for parameter evaluation.
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Requirements For Resolution
Authors Mark S. Egan, Antoun Salama, George El-Kaseeh and Joe SeissigerEvery seismic survey has resolution objectives for the final 3D migrated image. Temporal resolution cannot be considered separately from spatial resolution. This would be true even for the case of continuous functions. But in the world of sampled data, the interrelationship is even stronger. A result is that in order to achieve a desired temporal resolution, the most key parameter can sometimes be the spatial sampling interval. If that interval does indeed need to be small, one immediate implication is that very accurate coordinate information is needed for the source and receiver positions. Theoretically this is not a problem in onshore surveys, but it is a little more challenging offshore. Another immediate implication is that a dramatic increase in the number of shots and/or the use of high channel-count systems can be required for the data acquisition. Assessing the resolution obtainable from such candidate survey designs can be accomplished by modeling. Examples are provided.
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