- Home
- Conferences
- Conference Proceedings
- Conferences
6th International Congress of the Brazilian Geophysical Society
- Conference date: 15 Aug 1999 - 19 Aug 1999
- Location: Rio de Janeiro, Brazil
- Published: 15 August 1999
1 - 100 of 399 results
-
-
Survey Design For Vertical-Cable Seismic Acquisition
Authors Carlos Rodriguez-Suarez and Robert R. StewartThe vertical cable recording geometry has shown considerable promise as a seismic acquisition technique. It is
especially suitable for marine areas where any of the following are present: 1) obstacles (e.g. platforms or buoys) for a
vessel towing streamers, 2) deep to very deep water, 3) a complex subsurface geology, 4) pipelines on the sea bottom,
and 5) a hard (e.g., carbonate or basalt) sea floor. The last two situations may prohibit the use of ocean bottom cables
(OBC). On land, it can be seen as a 3D-VSP with one or more wells (cables).
If we are to acquire vertical cable data, we need to be able to design the surveys to best image the target geology in the
most economic way. Thus, we are interested in questions of source and receiver distribution and the resultant target
coverage.
Analysis of fold for regular grids of bins in vertical-cable acquisition was done for a straightforward, still realistic, 2.5-D
synthetic case. It describes a passive continental margin environment in a Mesozoic basin. Acquisition geometries with a
different numbers of vertical cables, hydrophones per cable, numbers of shot points and water depths were analyzed.
Three-dimensional ray tracing was used to obtain the reflection point from a target layer. Converted (P- to S-) waves, and
a land case were also analyzed.
The results show that good coverage can be obtained using only a single cable, a reasonable number of hydrophones
per cable and a fair shot point spacing. Deeper water acquisition shows better fold homogeneity than shallow water when
several cables are used on an optimized configuration.
-
-
-
Viabilidade Da Sísmica 4D Em Um Campo Terrestre Brasileiro: Enfoque De Rochas
We made a feasibility study for the application of the time lapse seismic technique on a shallow onshore Brazilian field, at
the Potiguar Basin, Rio Grande do Norte. This anonymous but real fluvial reservoir are now being subjected to vapor
injection, which is a good production technique for seismic monitoring. Seismic velocities measurements on core
samples and reservoir fluids, as well as fluid substitution on the available well log data, were used at the preliminary
stage of the feasibility study in order to quantify the velocities and impedance changes that the reservoir would
experience as a function of temperature, fluid saturation and pore pressure. Biot-Gassmann equations were combined
with the reservoir thermal simulation in order to construct a velocity and impedance model for the seismic modeling. It
was found that acoustic impedance changes as large as 40% would occur and that it should be resolved by the high
resolution 3D seismic. The initial and final seismic models and it’s updated versions shall help the reservoir geophysicists
on the interpretation of the real time lapse seismic data, which may provide insights on the fluid flow behavior and
reservoir heterogeneities.
-
-
-
High Precision/Fast Adaptive Step Size Ray-Tracing By Curvature Criteria
More LessHere I present one version of Hamilton based ray-tracing equations solution (Cerveny, 1987) (Popov,
1996) aiming at increasing precision as well as reducing and controling the computation’s effort. The
errors in numerical evaluating the differential ray-tracing equation can be classified in two kinds. First
the error in interpolating the velocity field and its derivatives. Second the error in evaluating the next
ray’s coordinates and slowness vector by the Runge-Kutta method. The first one has well-known solutions
like fourth order precision Bi-cubic spline interpolation (William et al., 1994). The second, the
fourth order precision Runge-Kutta method, needs the time step. If we apply a constant time step, it
requires the use of a high-density coordinate’s sampling when used for a non-homogeneous medium.
The reason is that the precision of ray-tracing is directly related to the curvature radio of the ray and the
last with the gradient of the square slowness. Then to obtain a high precision ray-tracing we need to decrease
the size of the time step in regions where there are large variations of the square slowness field
or on the other hand increase where there are no such variations. The result is an adaptive algorithm,
which automatically adapts the size of the ray coordinates interval to the necessity of the medium by
geophysical control. Despite the existence of the “adaptive control for Runge-Kutta method” (William
et al., 1994) it’s based in numerical considerations. Here I developed an alternative based on solid
physical arguments most properly useful for wave propagation purposes which can easily control the
accuracy of ray’s coordinates and in consequence the ray’s amplitudes (Lambaré, G. and Lucio, P.S.
and Hanyga A., 1996) and time of processing by just changing a parameter.
-
-
-
Um Algoritmo Prático De Modelagem 3-D Baseado Na Solução Da Equação Acústica Completa Da Onda
More LessEste trabalho apresenta a versão 3-D de um algoritmo para solução da equação acústica completa da onda,
baseado no método das diferenças finitas. Este algoritmo foi idealizado para requerer um mínimo de operações
extra para levar em conta as variações de densidade no meio. Também são exploradas técnicas de programação
capazes de reduzir sencivelmente os custos computacionais de tal aplicação. Com isto, a modelagempor solução
da equação da onda, que é uma poderosa ferramenta, pode se tornar mais prática para as aplições da indústria
do petróleo.
-
-
-
Contribuição Da Gravimetria Na Prospecção De Água Subterrânea No Litoral Norte Do Ceará, Brasil
More LessA gravity investigation is conducted in a coastal area in the northeastern Ceará State (Brazil). The objective of the survey is the detection of the regional geological structures which control the accumulation of underground water. This investigation consists of 1668 gravity stations, including previous surveys both in land and marine areas. The Bouguer gravity map is dominated by regional effect caused by the mantle uplift in the continental passive margin. To display more clearly the gravity anomalies caused by upper crustal heterogeneities, the local regional gravity field is removed by using a polynomial surface fitting. The resulting residual gravity anomaly map permits us to associate the gravity anomalies with known precambrian geologic units, granitic batholiths and surface structural features. The gravity lineaments are concordant with the NE-SW structural trends. In the northwestern of the studied area an elongated relative gravity low, visible in the residual map, indicates a NWSE secundary deformation trend, underlying of the sedimentary cover. These results will be prioritized and will be used to guide a more detailed geophysical survey.
-
-
-
Primeiros Resultados Do Sonar De Varredura Lateral Em Águas Profundas Rebocado Próximo Ao Fundo Marinho
More LessHigh resolution geophysical data has provided important results for petroleum industries facilities. Petrobras has been
acquiring deep towed sonar data since 1997 in all brazilian basins to obtain further detailed information of the sea floor to
support pipeline instalation. The seafloor imaging system (SIS-3000) described here uses the CHIRP technology to
provided high resolution sonar images and CHIRP subbottom data profiles. The SIS 3000 system is composed by two
subsystems as follow: tow vehicle and shipboard eletronics. This paper will present an overview of the deep towed
CHIRP sonar and some initial results in the Campos Basin.
-
-
-
A Rede De Detectores De Radiação Ultravioleta Solar Do Inpe
Nas duas últimas décadas verificou-se uma significativa redução do ozônio atmosférico global, criando uma
preocupação sobre o possível aumento da radiação UV-B na superfície terrestre. Entretanto, poucas medidas
de UV na superfície estavam disponíveis até meados de 1980, e a maioria destas concentrava-se no hemisfério
norte. Descreve-se neste trabalho a rede de detectores de UV do INPE e alguns resultados. O INPE vem
operando desde o início da década de noventa, vários detectores UV dos tipos radiômetros UV-Biometer, GUV e
Espectrofotômetros Brewer no Brasil, Bolívia, Chile e Antártica, constituindo uma base de dados com uma
significativa distribuição geográfica, de latitudes equatoriais, médias e polares. Esta distribuição espacial é
importante para o estudo do comportamento da radiação ultravioleta solar face ao quadro de mudanças
atmosféricas associado aos fenômenos da redução global do ozônio.
-
-
-
Medidas Da Radiação Uv-B Difusa Em Banda Larga E Estreita
Authors Abel A. Silva, Ezequiel Echer and Volker W.J.H. KirchhoffMesmo em dias de céu encoberto pode-se notar o bronzeamento da pele humana nas pessoas em atividade ao ar livre.
Esse fenômeno é devido a ação da componente difusa da radiação solar global UV-B. Estudos anteriores mostram que
essa radiação é importante para ângulos solares zenitais elevados, mais comuns nas latitudes altas. Neste trabalho é
feito um estudo da relação entre a radiação solar global UV e a sua componente difusa. As atividades foram conduzidas
em Cachoeira Paulista (23.1o S, 45.0o W) com radiômetros de banda larga e estreita em dias de céu limpo, tendo sido
verificado que a radiação difusa representa pelo menos 40% da global na faixa do UVB.
-
-
-
Topographic Effect Of Transient Electromagnetic Responses
Authors Wenbao Hu, Liangjun Yan and Xingong TangA three dimensional body is designed to simulate the valley shaped topography. Transient responses are
calculated for topography at source location and at receiver location respectively. Modeling results are shown
by relative anomalies in contours. The behavior of the topographic effect to transient eletromagnetic field
responses can be characterized by local anomaly for topography at receiver location, and by equivalently an
extra source with strong high frequency excitation for topography at source location. Learning from the
modeling results, it is emphasized that the ground wire source shall be set up at place as uniform as possible
for reliable deep sounding measurements.
-
-
-
Large Scale Multi-2D Prestack Depht Migration:A Gulf Of Mexico Deep Water Case Study
More LessThe attraction of the deep water Gulf has increased over recent years due to the advancement of several core
technologies. Foremost within these new applications is the use of pre-stack depth migration for illuminating
the sub-salt structure, at water depths in excess of 3300 meters. Large scale 2D depth migration projects (e.g. >
3000 miles) provide a cost effect way of ascertaining the regional sub-salt geology and highlighting areas for
prospect evaluation. The results from three large multi-2D, prestack depth migration projects are presented.
The unique problems associated with depth migrating in the deep water province are highlighted in terms of
acquisition, time processing and specifically the application of depth imaging technology for imaging of the
sub-salt. It is shown that a combination of long streamer acquisition with prestack depth imaging can provide
an adequate image of the sub-salt, suitable for prospect evaluation in a short period of time.
-
-
-
2D Seismic Data Images A Fold And Thrust Belt In Noerthwestern Venezuela
Authors R.C. Ahlborn and J.W. PowellOlder 2D seismic data in the Falc6n basin, Zulia and Falcon states, northwestern Venezuela, indicates the
probable existence of a fold and thrust belt in northwestern Venezuela. This belt is likely the result of the collision of
the Caribbean Plate with the South American Plate during the Paleogene. A second pulse during the Lower Miocene
is also recorded on 2D seismic profiles near the coast of Falcbn. Southwest vergent thrusts are evidenced in the
Cocuiza basin, on the Dabajuro high and the Coro platform. Younger south vergent thrusts with large fault
propagated folds are seen within the Urumaco trough. Although some of the low-angle thrusting is due to wrench
movements along the Oca fault system, much of the thrusting can be attributed to compression rather than
transpression during plate collision.
-
-
-
About Of The Digital Geomagnetic Records Processing With Noice
Authors Julio C. Gianibelli and Iris R. CabassiDigital records of the Total Intensity of the Earth Magnetic Field, realized by means of protonic precession
sensors per one minute, shows erratic pulses. The criterions of analysis and filtering of these pulses for
magnetically quiet days are studied. The more adequates methods had been the one of comparisson of
succesive samples, and the filtered method by means of a windows of the median determination.
In this paper, the results for records with ramdom spikes of the Trelew Magnetic Observatory (ϕ = 43°2683 S;
λ = 294°6183) are analyzed.
-
-
-
Different Styles Of Canyon Infill Related To Gravity And Bottom Current Processes : Examples From The Upper Slope Of The Se Brazilian Margin
Authors A.R. Viana, W. Almeida Jr. and L.C. MachadoA series of modern submarine canyons were examined in the south-eastern Brazilian margin in order to identify
the different styles of canyon filling and their relationship with sedimentary processes and sea-level changes.
Such study should be considered as a predictive tool in order to estimate the presence of reservoir-like
deposits. Four seismic facies related to intra-canyon depositional patterns were individualised in this study:
clinoform prograding lateral accretion (Cp), cahotic fill (Ch), parallel-to-divergent aggradation (Pd) and
horizontal strata (Pl). Relationship between these styles and sea-level changes was attempted and results
indicate a complex interaction between hydrodynamic conditions, position of sediment source and sediment
availability. Coriolis Effect seems to play a minor role in controlling the downcanyon flow/erosion processes.
Lateral accretion is mainly related to the southward flowing Brazil Current. Aggradation and horizontal strata are
related to a relative decrease in the Brazil Current action and to an increase in gravity flows activity.
-
-
-
Un Geoide De Precisión Para Uruguay Informe Del Proyecto Urugeoide 2000
More LessSe presenta el proyecto UruGeoide 2000, cuyo objetivo es la determinación de un modelo geoidal con precisión
centimétrica para Uruguay. La metodología propuesta, está basada en la combinación de un modelo geopotencial,
anomalias gravimétricas y un modelo numérico de terreno, a través de la técnica "remove-restore", usando
Transformada Rápida de Fourier. Los datos disponibles, así como las investigaciones realizadas en modelos
geopotenciales de alto grado y ultra alto grado, son presentados en este informe.
-
-
-
Influência Transiente Da Temperatura Poço-Formação Em Perfis De Resistividade(Com Invasão)
More LessThe principal aim here is show a transient thermal-resistivity log dependence. The induction devices (ILM and
6ff40), common used in log interpretation, may have some errors and new corrections will be needed. This
features are presented when multilayer transient temperature is evaluated and applied to resistivity model. A
simple eight meters deep formation is simulated with 2d-thermal and resistivity model, composed by shale and
sandstone reservoir, where multiphase radial fluid flow was performed. Due mud circulation, temperature
dependence of apparent resistivity formation are evaluated and compared with the resistivity when wellformation
temperatures are the same (150oC). Errors into 1% to 12% are expected to medium and deep induction
log information with this model.
-
-
-
Using Seismic Data To Verify 3D Geometry - Some New Approaches To Field Qc
More LessIn today’s 3D surveys, the volume of data can be overwhelming. It is essential to have methods that quickly identify
errors and/or bad data. Modern field QC uses seismic trace attributes (energy levels within specified windows, energy
decay factors, first arrival times) in combination with survey information (shot and receiver positions) to create new
quality control measurements and displays, Such QC displays can quickly pinpoint location and other errors at both
shot and receiver positions. Examples of verifying 3D geometry, energy decay maps, and finding posrtron errors will
illustrate the latest QC methods.
-
-
-
Equatorial Spread-F And Plasma Bubbles: A Step Towards Prediction
Authors Inez S. Batista, M.A. Abdu, R.T. de Medeiros and J.H.A. SobralEquatorial spread F (ESF) and plasma bubbles are plasma irregularity phenomena that are known to occur in the
equatorial- and low-latitude ionospheric F region at evening and nighttime. Those irregularities cause
scintillation that disrupts trans ionospheric radio propagation, up to the GHz frequency range interfering on
communication systems including the Global Positioning System - GPS. Although the general characteristics of
spread F and bubbles, concerning their variation with season, solar cycle, and magnetic activity, are fairly well
understood, we do not know much about the cause of the day-to-day variability, a crucial point when prediction
is concerned. In this paper, we analyze ionospheric data from two low latitude stations in Brazil, in either
presence or absence of bubbles, in order to try to establish the conditions under which bubbles shall occur. We
conclude that the F layer critical frequency (foF2) in the afternoon-sunset hours (or equivalently the F layer
maximum density, NmF2) is a useful parameter to predict the occurrence of the bubble.
-
-
-
The Role Of The Stike-Slip Tectonics In The Evolution Of The Alboran Sea, Western Mediterranean
Authors José Rodriguez-Fernandez and Menchu ComasThe Alboran Basin is a Neogene extensional basin which originated and evolved since the early Miocene within a plate
tectonic setting of convergence between Iberia and Africa. The basin has been identified as formed by crustal stretching
and extensional tectonic from the early to the late Miocene. However, the current organization of the Alboran Sea basin
has resulted mainly from post-Miocene contractional tectonics superimposed on earlier extensional structures. The
present structural framework indicates that two sets of conjugate strike-slip systems (left-lateral faults with a NE-SW
trending, and right-lateral faults with a NW-SE trending; being 120• -130• the angle between the two strands) accounted
for a significant post-Messinian deformation of the Alboran Sea basin. The stress field evidenced by the wrench-tectonic
structures is consistent with the latest Neogene to Present Africa-Eurasie roughly N-S convergence plate kinematics in
the westernmost Mediterranean.
-
-
-
Efeito Da Profundidade Dos Eletrodos Em Levantamentos De Eletrorresistividade
Authors H.K. Sato and F.A.F. OliveiraThe influence of electrode depths in electroresistivity
survey is studied. Generally, the investigators don’t care
about this detail but it can introduce significant departures
on the apparent resistivity values obtained with
small electrode spacings. To check the influences, theoretical
analysis is performed using simulated vertical
electrical sounding with undergrounded Wenner array.
Field data using Schlumberger array are collected to
demonstrate the existence of such effects. Computed
apparent resistivity values obtained with the same field
array parameters, separations and depths, are successfully
fitted to the field data, and a horizontally layered
model is obtained. The studies with two layer models,
shown that the effects of undergrounded electrodes are
more expressivewhen the second layer is more conductive
than the first one. Ambiguities arise in the reversed situations.
-
-
-
Electromagnetic Waves Generation By The Hybrid Modulational Instability
More LessAn improved model of the fundamental plasma emission of type III solar radio bursts is presented. It is shown
that nonlinear conversion of a traveling Langmuir pump wave into an electromagnetic wave can occur via either
convective or absolute hybrid modulational instabilities, resulting from the coupling of two wave triplets, with
the Langmuir pump wave and ion-acoustic daughter wave common to both wave triplets. The properties of
these four-wave hybrid modulational instabilities are studied using the observed interplanetary parameters.
-
-
-
Atividade Solar Nos Anéis De Crescimento De Árvores Em Canela
Authors Nivaor Rodolfo Rigozo and Daniel Jean Roger NordemannTree ring studies are usually used to determine or verify climatic factors which prevail at a given place or region
and may cause tree ring width variations. Few studies are dedicated to the geophysical phenomena which may
underlie these tree ring width variations. Furthermore, it is known that some trrestrial phenomena suffer
influence from short and long time scale solar variability. So, a study on solar activity records in tree rings at
short time scales was developed. In order to determine a tree growth ring width mean chronology, an optical
and computational method was set up and applied to tree samples (araucaria and pine trees) from Canela-RS,
Brasil. Spectral analysis by maximum entropy method and iterative regression was applied to the search of
periodicities related to solar activity phenomena. The results obtained have shown periodicities related to 11 yr
and 22 yr solar cycle influence on tree growth rings.
-
-
-
Diurnal Variation Of Summertime Cloud-To-Ground Lightinig Activityactivityin The Southeastern Brazil
This paper reports the results of an analysis of 300,000 cloud-to-ground flashes recorded in the southeastern
Brazil in the summer season of 1993 in terms of the local time dependence of their characteristics. Whereas the
lightning activity of negative and positive cloud-to-ground flashes exhibit a diurnal cycle with a well-defined
time of maximum frequency in the afternoon, the flash multiplicity and peak current intensity do not exhibit such
a local time variation. The local time dependence and geographic distribution of the lightning activity are in
agreement with what is expected from isolated thunderstorms. In turn, the peak current intensity and the flash
multiplicity did not show any dependence on local time. The results are compared with similar data obtained in
the western and eastern U.S. in the period 1995-97.
-
-
-
Uma Análise Do Modelo De Madden&Marshall Para Descrever A Polarização Elétrica Observada Em Rochas Contendo Argila Disseminada
Authors Alexandre Nunes Barreto and Carlos Alberto DiasThe impedance function associated to the Madden & Marshall model proposed to describe membrane polarization,
was rewriten using five new parameters with clear petrophysicalmeaning. The behavior of this function was
analyzed together with its new parameters when varying the electrochemical parameters of the originalmodel and
some limitations were shown.
-
-
-
Long Term Variation Of The Lightning Flash Characteristics In The Southeastern Brazil:1988-1995
The long-term variation of the cloud-to-ground lightning flash density in terms of its geographical, monthly and
diurnal distribution is presented, based on the longest lightning data set ever obtained in the tropics. The
results are based on 12.8 millions cloud-to-ground lightning flashes recorded in the southeastern Brazil from
1988 to 1995 with a lightning network consisting of four LPATS sensors located in Minas Gerais. They should be
considered as reference for future studies in this region.
-
-
-
Estudo Geofísico Preliminar Com Os Métodos Tem/Fem Na Planície Costeira Norte Fluminense
More LessIn 1998, ON/CNPq and LENEP/UENF undertook a geophysical pilot study in the Northern Coastal Plain of Rio de Janeiro State, near Rio das Ostras town. The region is characterised by both the scarcity of drinking water for human consumption and the existence of saline intrusions; this last caused mainly by the presence of a complex quaternary geology and the excessive exploitation of the aquifers. The research was performed by employing the time (TEM) and frequency (FEM) domains electromagnetic methods to evaluate the effectiveness of both methods in these geological conditions in order to be able to formulate a more comprehensive hidrogeological research in the region in near future. The FEM profiles and the uni-dimensional interpretation of the TEM were able to depict the different geological formations, to locate the main aquifers and to reveal the salty water- fresh water contact. Our results evince a promising future for using eletromagnetic geophysical methods in the region as well as it confirmed that a regional survey is essential in the indication of most suitable places to locate productive fresh-water wells.
-
-
-
Mesospheric Reduction Of The Chemical Heating Rates By Nightglow Emissions At 23Os And 4Os
Authors P.R. Fagundes, D. Gobbi, H. Takahashi and Y. SahaiSimultaneous observations of several nightglow emissions have been carried out at Fortaleza (40S, 380W) and
Cachoeira Paulista (23oS, 45o W), Brazil, since 1987. Using the OH Meinel (9,4) and O2 atmospheric b(0,1) bands
observed at these two stations during the period from 1987 to 1994, we present and discuss the night-time
reduction in chemical heating rates by these mesospheric airglow emissions. The total emission rates of the OH
Meinel bands and O2 atmospheric b(0,0) and O2 infrared atmospheric (1Δg) bands were calculated using the
reported data for the relative band intensities I(ν/,ν//)/I(9,4), I(O2b(0,0))/I(O2 b(0,1)) and I(O2 (1Δg))/ I(O2b(0,1)). This
study showed that the reduction in chemical heating rates (RCH) by the OH Meinel bands, at both the locations,
has seasonal variations with monthly mean values varying from 0.4 K/day* to 0.9 K/day* (where day* means
averaged over the night). However, the RCH rates due to the radiation in the Meinel bands at Cachoeira Paulista
presented a weak ter-annual variations, whereas at Fortaleza semi-annual variations were observed. Also, the
RCH rates by O2* showed semi-annual variations at both locations, presenting values from 0.05 K/day* to 0.25
K/day*.
-
-
-
Comparison Between The Mesopause Temperature+D57 Profiles Measured With A Sodium Temperature Lidar And The Oh (6,2) And 02A (0,1) Rotational Temperatures 23Os
Authors P.P. Batista, B.R. Clemesha, D. Gobbi, M.P.P.M. Jorge, D.M. Simonich, H. Takahashi and I. VaselovskiiThe mesopause temperature profile has been measured at São José dos Campos (23.2o S, 45.9o W) for a total of 15
nights from July to October 1998. The technique used is the measurement of the Doppler temperature of the sodium
atoms present in the atmospheric sodium layer with a Lidar. During 7 of the 15 days of Lidar temperature data,
simultaneous measurements of the rotational temperature of the OH(6,2) band at 843.0 nm and the O2 (0,1)
Atmospheric band at 864.5 nm were obtained at a nearby station, Cachoeira Paulista (22.7o S , 45.2o W), with a tilting
filter photometer. There is a fair agreement between the OH temperature and the Gaussian weighted temperature
calculated using the Lidar temperatures centered on 84.7 km and with a half-width of 4.5 km, consistent with rocket
measurements for the OH emission profile, for most of the days. But no consistent combination of height and half-width
can reproduce the absolute value and variation of the O2 (0,1) temperature for most of the days, suggesting that the
transition probabilities used for determining the latter may need to be revised.
-
-
-
Study Of The Space Variations Of The Energetic He Ions At Low Altitudes In Brazilian And South Atlantic Magnetic Anomaly Region
Authors G. Pugacheva, A. Gusev, T. Kohno, I. Martin and W. SpjeldvikThe L distribution of 1 - 9 MeV/nuc helium ion flux observed with the low altitude Japanese OHZORA satellite
has a multipeak structure, different from one flux maximum of proton radiation belt and two flux maxima of
electron radiation belt. The peak fluxes of 1 - 3 MeV/nuc He ions are located at L=1.35-1.6, L ~ 1.8 - 2.3 (only in
1984), and L = 2.8 - 3.2. Recently, two low altitude satellite SAMPEX (1992 – up to now) and MIDORI (1996-97)
missions reported new observations of energetic He flux peaked at L ~ 2 and show the existence of stable (at
least with lifetime of several years) flux there at higher energies above 10 MeV/nuc in contrast to the lower
energies. To analyze the nature of the multipeak structure and the origin of the L=2 helium flux we studied
magnetic local time dependence of the peak helium fluxes observed by OHZORA. The 1 - 3 MeV/nuc helium ion
flux exhibits strong local-time variation at L ~ 3 having several times greater flux at the evening side at MLT =
17-21 hours than at the other MLT sides. The one of possible explanation of the flux variation with MLT is that ~
1 MeV/nuc helium ions do not drift around the Earth and are located at L about 3 due to the ion interactions
with the Earth's electric morning-evening field.
-
-
-
A 2D Simulation Of The Proton Radiaton Belt With Pellpack Code
Authors A. Gusev, I. Martin, G. Pugacheva, A. Christy and W. SpjeldvikThe numerical solution of diffusion equation for geomagnetically trapped protons taking into account
deceleration of protons by Coulomb interactions with free and bounded electrons, the charge exchange
process, the cosmic ray albedo neutron decay (CRAND) source and electric and magnetic radial diffusion was
obtained using the PELLPACK code based on the finite element method. The advantage of the method in
comparison with the traditional finite differences method is a several order greater speed of computation at the
same precision. When boundary conditions at L=7 are given with the distribution function extracted from
proton spectrum obtained on board of ATS 6 satellite, the PELLPACK code produces 2D unidirectional proton
flux at the top of geomagnetic lines from L=1 up to L=7 that satisfactory agrees with the AP8 model proton flux
for all proton energies more than ~ 300 - 500 keV. For less proton energies AP8 model predicts the trapped
proton fluxes on several orders of magnitude greater than PELLPACK code at L < 4 that possibly could be
explained by uncertainty of very low energy proton flux data at L=7. The detailed fitness of observational model
proton fluxes by numerical theoretical solution of transport equation is still not attained.
-
-
-
Fast 3-D Modeling And Inversion Of Surface Em Data
More LessThis work presents an algorithm for three-dimensional modeling and inversion of electromagnetic field data. In recent
years, there has been an increase in use of electromagnetic techniques for mineral, oil and geothermal exploration.
Since most of the targets are of three-dimensional nature, it is important to consider the full dimensionality of the problem
in the interpretation. The forward code is based on a finite difference approximation while the sensitivities needed in the
inversion are obtained from the forward problem based on the reciprocity principle. A parametric functional is constructed
using the data misfit and a model misfit to an a priori earth model, weighted by a regularization parameter. This functional
is then minimized using the conjugate gradient method. The most time consuming parts of an inversion algorithm are the
forward problem and calculation of the sensitivities. Also, in the 3-D problem, storage becomes another important issue.
First results will be presented, along with methods that will help improve both speed and storage on the way to make the
3-D problem tractable.
-
-
-
Sound Velocity Of Drilling Mud Saturated With Reservoir Gas
Authors José M. Carcione and Flávio PolettoDrillings muds are used to balance subsurface pressures, lubricate the drillstring, clean the
bottom of the hole, remove cuttings and aid formation evaluation. During drilling, the mud
is pumped down the drill pipe and returns via the annulus between the drill string and the
formations. If the pore-fluid formation pressure exceeds that of the mud column, reservoir gas
can enter the wellbore? creating a kick and causing severe damage. Knowledge of the in-situ
sound velocity of drilhng mud can be useful for evaluating the presence and amount of gas
invasion in the drilling fluid. Technologies such as mud pulse acoustic telemetry require this
information. In the following sections, we propose a model for calculating the in-situ density
and sound velocity of water-based and oil-based drilling muds containing formation gas.
-
-
-
A Study About The Occurrence Of Days With High Activity Of Cloud-To-Ground Lightning Flashes In The Southeastern Brazil In The Years 1992 To 1994
Authors Heloisa H. Faria, Osmar Pinto Junior, André M. Carvalho and Armando C. FilhoThe occurrence of days with high activity of cloud-to-ground lightning flashes in the southeastern Brazil in the
years 1992 to 1994 was investigated. The high activity days were arbitrarily defined as those with more than
20,000 cloud-to-ground flashes. The meteorological conditions and flash characteristics during these days were
determined. The lightning data were obtained through a lightning location system (LPATS), and the flash
characteristic studied were the polarity, the peak current intensity and the diurnal distribution.
-
-
-
Signal To Noise Ratio Enhancement By Adaptive Filtering
Authors Enrique D. Mercerat and Alberto H. CominguezAn adaptive filtering techniquewas implemented in order to remove random noise from seismic data. The operator
was calculated in the frequency-offset domain (FX), and it could enhance the lateral coherence of seismic events.
For each frequency an optimum Wiener filter was designed following the classical approach using the complete
seismic section. After that, an adaptive algorithm was implemented to actualize the filter coefficients in order to
reduce the output error. This automatic actualization avoided us the use of predetermined design windows. The
adaptive filter was based on a generalized expression of the least-mean square (LMS) filter dealing with complex
frequency input signal. The performance was evaluated on synthetic seismic data contaminated with additive
gaussian noise.
-
-
-
Seismic Imaging Of The Crust In The Aconquija And Adjacent Regions; Catamarca, Tucuman And Santiago Del Estero, Argentina
More LessDeep Seismic Study, in eastern and western foothills of Sierra de Aconquija, northwestern Sierras Pampeanas, Argentina, shows the deep structure of the range and the deep geometry of the Andean foreland basin. "Self-truncating" extended correlation algorithm was applied to compute cross-correlation between the sweep and the records of Vibroseis lines. Special procedures, such as finite difference migration, FX deconvolution, FMED processing and complex demodulation, were applied in order to improve the interpretation. On the eastern side of Sierra de Aconquija, the structure is characterized by reverse faulting with eastward vergence, with the Guasayán and El Rosario faults exhibiting the most deformation. To the south, the Guasayán fault produces the uplift of the Guasayán basement range over tertiary deposits, and can be identified in the seismic reflection record down to 40 km depth. On the western side of Sierra de Aconquija, the deep structure of Campo del Arenal is characterized by westward vergent structures controlled by the anisotropy of the Sierra de Aconquija basement. Further to the west, the deformation style changes to eastward vergence. Conspicuous sub-horizontal acoustic-reflectors at about 18, 30, 40 and 50 km depth, are interpreted as present or past brittle-ductile transitions.
-
-
-
Log-Derived Rock Strength Evaluation
Authors José Agnelo Soares and Lucia Duarte DillonSeveral oil industry operations, like borehole stability, pore collapse analysis and hydraulic fracturing, demand
rock mechanical knowledge that sometimes is unavailable or is only poorly known. Statistical relationships
defined through dynamic and static rock properties, simultaneously determined in lab tests, yield a novel
approach to continuously evaluate rock strength over whole depth well intervals.
-
-
-
Métodos Geoelétricos Aplicados No Estudo Do Lençol Freático Em Área De Disposição De Resíduos Industriais
Ensaios geofísicos pelo método da eletrorresistividade, utilizando as técnicas de campo da sondagem elétrica vertical –
SEV (arranjo Schlumberger) e caminhamento elétrico - CE (arranjo dipolo-dipolo), foram executados em áreas de
disposição de resíduos industriais no município de Iracemápolis-SP. Os estudos geofísicos visaram obter um
diagnóstico prévio dos materiais em subsuperfície frente à possível contaminação por resíduos industriais. Foram
executadas três SEV´s, as quais caracterizaram a litologia dos materiais em subsuperfície em solo superficial seco
(resistividade variando de 13 a 14.353 ohm.m), solo de alteração de diabásio (resistividade variando de 25 a 83 ohm.m)
e diabásio (resistividade de 617 ohm.m). A profundidade do nível d´água obtido apresentou uma variação de 9,3 (SEV-
01) a 13,5 (SEV-03) metros. Para o CE, foram levantadas cinco linhas, a partir das quais, pode-se delimitar a área de
disposição de resíduos, avaliar as condições da pluma de contaminação e determinar as direções preferenciais do fluxo
d´água subterrâneo. Mapas referentes a três níveis de investigação (profundidades teóricas de 10, 20 e 30 metros)
evidenciam que a pluma tende a diminuir sua faixa de contaminação em função da profundidade, restringindo-se a
locais isolados. Duas direções preferenciais do fluxo subterrâneo d´água foram identificadas, acompanhando, de um
modo geral, a topografia do local estudado.
-
-
-
Estudos Morfológicos Das Depleções Do Plasma Ionosférico Por Imagens Digitalizadas
Authors Daniela Cristina Santana, J.H.A. Sobral and H. TakahashiA ionosfera, ambiente natural de propagação dos sinais de comunicação, foi descoberta inicialmente devido a
observação de variações periódicas nas medições do campo geomagnético que combinadas com a alta condutividade
elétrica da ionosfera, podem alterar a trajetória desses sinais de comunicação. É uma região rica em fenômenos
naturais de importância direta para o homem e o para meio ambiente. É justamente um desses fenômenos, denominado
de depleções do plasma ionosférico, exclusivo das regiões equatoriais, que queremos enfatizar. Para o seu estudo, há
várias técnicas desenvolvidas, das quais podemos citar a luminescência atmosférica, ou o airglow. O acompanhamento
constante do airglow noturno permite realizar um estudo morfológico e dinâmico da ionosfera noturna. As imagens
digitalizadas do airglow noturno são obtidas pelo imageador all-sky 180º que é um equipamento recém desenvolvido
pelo grupo de pesquisa Luminescência Atmosférica - LUME, da área de Ciências Espaciais e Atmosféricas - CEA, do
Instituto Nacional de Pesquisas Espaciais – INPE e encontra-se em operação desde outubro de 1997 no laboratório do
LUME em Cachoeira Paulista(22.7ºS, 45.0ºW) – SP. O airglow noturno existe em vários comprimentos de onda sendo
que para o registro das depleções do plasma ionosférico é necessário a emissão do OI 6300 Å (λ = 630 nm), uma luz
vermelha de muita baixa intensidade, que está presente na termosfera. As depleções do plasma ionosférico variam a
intensidade da emissão do OI 630 nm de acordo com o cotidiano e a estação do ano. Os nossos estudos focalizam as
depleções do plasma ionosférico que ocorrem sobre a região de Cachoeira Paulista(22.7ºS, 45.0ºW) – SP,
principalmente as fortíssimas ocorrências nas noites de 30/01/1998 e 26/08/1998. As imagens digitalizadas das
depleções do plasma ionosférico via OI 630 nm obtidas pelo imageador all-sky 180º são analisadas e processadas por
aplicativos computacionais em desenvolvimento na linguagem computacional Interactive Data Language – IDL,
seguindo os padrões básicos para o desenvolvimento de um aplicativo computacional. Esses aplicativos computacionais
introduzem uma nova técnica fotométrica para o estudo das depleções do plasma ionosférico.
-
-
-
About The Seasonal Distribution Of Geomagnetic Activity
The annual distribution of geomagnetic activity is studied through the geomagnetic indices aa, Dst and AE,
according to different levels of intensity for each of the indices. For thresholds that correspond to moderate to
fairly intense storms, the distribution follows the well-known pattern of a seasonal variation, with maxima
around the equinoxes and minima near the solstices. However, the observed pattern deviates from this behavior
as the distribution refers to levels associated to the occurrence of more intense storms. For the latter type of
storms, the geomagnetic index aa shows the occurrence of a peak in July (but not in January, as a seasonal
symmetry would suggest). The contribution of very intense storms to the July peak seems to be evenly
distributed along the 11 solar cycles covered by this index. Furthermore, although the records for the indices
Dst and AE are restricted to shorter time intervals as compared to aa, they also show the possible existence of
this peak for July.
The present analysis gives also some indications for the existence of a peak in November in the distribution of
very intense storms. This peak shows up particularly for the indices Dst and AE, whose records go back only to
1957. Therefore, its real existence is more questionable than that of the peak for July.
-
-
-
Phase Relationship Between F-Region Electron Density And Electric Field Fluctuations-Some New Observations
Authors P. Muralikrishna, M.G.S. Aquino, S.M. Soares and M.C. De FariaIn-situ measurements of the height variation of the ionospheric electric field and electron density variations were made
with a rocket-borne electric field double probe and two different types of electron density probes. A Brazilian made
SONDA III rocket carrying these experiments in addition to other airglow experiments was launched on 18-th December,
1995 at 2117 hrs (LT) from the equatorial rocket launching station, Alcantara. The rocket reached an apogee altitude of
557km and covered a horizontal range of 589km. Several ground equipments were operated during the launch campaign
with the specific objective of knowing the ionospheric conditions at the time of launch and thereby to launch the rocket
into an F-region prone to the presence of large plasma bubbles. The rocket in fact passed through several medium scale
plasma bubbles and the electric field double probe and the electron density probes detected the presence of a wide
spectrum of electric field and electron density irregularities. In the base of the F-region the electric field double probe
measurements clearly indicated the presence of large amplitude fluctuations, closely associated with large amplitude
electron density irregularities But in the height region close to the rocket apogee though the electron density profile
showed the presence of large scale spatial structures, the electric field measurements did not show fluctuations of similar
amplitude. Being a nighttime launch one would expect the electron density irregularities, if generated by the well-known
cross-field instability mechanism, in height regions where the electron density gradient is downward, i.e in the same
direction as the ambient Hall electric field. An FFT algorithm was then used to estimate the spectral distribution of the
electric field and electron density fluctuations, thus estimating the height variation of the spectral variation. Some new
results on the phase relationship between the electric field and electron density fluctuations are presented here.
-
-
-
Ionospheric Experiments On Board The Brazilian Scientific Applications Satellites Saci-1 And Saci-2
Authors P. Muralikrishna, M.A. Abdu, S. Domingos, J.A.C.F. Neri and L.P. VieiraA set of three plasma diagnostic experiments, known as PLASMEX, are developed for launch on board the
Brazilian Scientific Applications Satellites SACI-1 and SACI-2. The main objective of the experiments is to
investigate the phenomenon of ionospheric plasma bubbles, known to exist in the ionospheric region over a
wide range of latitudes. It is intended to make measurements of the density, temperature and spectral
distribution of the irregularities in the ionospheric plasma using (1) a High Frequency Capacitance Probe for
measuring the plasma density, (2) a fixed-bias Langmuir Probe for measuring the electron density profile and
the spectral distribution of plasma irregularities, and (3) an Electron Temperature Probe for measuring the
kinetic temperature of the ionospheric electrons. While the satellite SACI-1, is to be launched this year from
China on board a LONG MARCH rocket SACI-2 is also expected to be launched this year on board a Brazilian
satellite launch vehicle VLS from Alcantara-MA. In the High Frequency Capacitance Probe a metallic sensor in
the form of a sphere of about 60mm diameter is used as a capacitance element in the tank circuit of a "Clapp"
type oscillator. In the fixed bias Langmuir Probe a metallic sensor, similar to that used in the HFC experiment, is
used to collect the elctron or ion currents from the ambient plasma. The sensor potential is selected using
telecommands, from four predetermined values namely -1V, 0V, +1V and +2V. In the Electron Temperature Probe
two semicircular metallic sensors in the form of a circular disc, is used to determine the kinetic temperature of
the ionospheric electrons. On board SACI-1 the HFC, LP and ETP sensors are mounted at the extremities of
three of the four solar panels, while on board SACI-2 they are mounted at the extremities of three deployable
booms about 1m long. The PLASMEX experiments will be operated by commands from an onboard Microcontroller.
While SACI-1 has a near polar sun synchronous orbit, SACI-2 has a low inclination orbit. Thus SACI-1
can give a complete global coverage for the measurement of plasma parameters, while SACI-2 can give detailed
information on the behaviour of these parameters in the low latitude and equatorial regions. A brief summary of
the experiments PLASMEX along with details of the data acquisition system, on board processing of the LP ac
data etc. is presented here.
-
-
-
Equatorial Spread-F Irregularities As Observed By Three Different Rocket-Borne Plasma Density Probes
Authors P. Muralikrishna, M.A. Abdu, M.G.S. Aquino and M.C. De FariaSome new results obtained from in-situ measurements of the height variation of the ionospheric electron density made
with rocket-borne electron density probes during a campaign conducted from Alcantara (2.31oS; 35.2oW) in Brazil are
presented here. The campaign designated Guará was conducted in collaboration with NASA. In addition to several
plasma diagnostic instruments provided by other participating institutes the Aeronomy Division in the Instiuto Nacional de
Pesquisas Espaciais in Brazil provided a High Frequency Capacitance probe that measured the height profile of the
electron density. During the Guara campaign, a Black Brant X sounding rocket was launched on 14-th October 1994 at
1955hrs (LT) to investigate into the phenomenon of high-altitude equatorial spread-F events. The rocket, as expected
passed through an active topside spread-F event, monitored simultaneously by several ground-based instruments. The
electron density height profile and the amplitude of the electron density fluctuations were measured simultaneously by
three different plasma density probes; a High Frequency Capacitance (HFC) probe, a conventional Langmuir Probe (LP)
and a Plasma Frequency Probe (PFP). While the PFP provided the absolute electron density, the LP gave the relative
variation in the electron density. The electron density profile obtained from the HFC probe measurements is practically
absolute except for a plasma sheath factor. But this technique does not provide the small scale electron density
fluctuation amplitude. The three experiments provided data, which could be used not only to obtain reliable electron
density data, but also to arrive at some of the inherent difficulties associated with each of these techniques. For example
the elctron density profiles estimated from the HFC and PFP experiments are almost identical except for a small factor
varying with altitude. The amplitude of large scale fluctuations provided by the LP measurements is considerably less
than that provided by HFC and PFP. The k-spectra of the plasma irregularities were obtained by the spectral analysis of
the electron density fluctuation data. The electron density irregularites associated with the plasma bubbles were seen to
have rather sharp lines in their k-spectra extending over a wide range of altitude. What one would expect from the
existing theories on the generation of small scale irregularities by the cascading process is a flat k-spectrum. Present
results may be indicative of the presence of preferred wave modes in developing plasma bubbles.
-
-
-
Obtencion De Parametros Fisicos Y Elasticos Mediante Tomografia De Transmision "Cross-Hole
More LessEn este trabajo presentamos los resultados de emplear una técnica tomográfica de inversión sísmica para la
reconstrucción de imágenes del subsuelo, en términos de las velocidades de las ondas P y S, así como una
técnica para la representación de parámetros sísmicos, tal como la relación de velocidades de la onda P y onda
S, la densidad, las constantes elásticas, y la porosidad, a partir de observaciones del tiempo de tránsito.
La metodología se aplicó a datos reales obtenidos de un experimento realizado en un campo petrolero ubicado
en el Estado de Texas, E.U.A., del cual se tenían algunos datos geológicos. Se obtuvieron los tomogramas de
los parámetros sísmicos, los cuales permitieron corroborar los datos litológicos, y así mismo inferir otros
detalles de la estructura interna del subsuelo.
Finalmente, hacemos énfasis de la importancia de aplicar la Tecnología descrita, en los campos petroleros de
México, ya que nos permitirá conocer las características físicas y elásticas de los yacimientos y analizar su
comportamiento lateral, etapas importantes que se realizan durante la caracterización de yacimientos.
-
-
-
Disturbances On Magnetotelluric Data Due To Electrified Railway
More LessMagnetotelluric (MT) soundings were made on two transverse profiles to the Campos do Jordão Railway (CJR) in the
period range of 4 to 3000s. The profiles are located in two adjacent regions of the São Paulo State with contrasting
conductivity: the conductive sedimentary region of Taubaté Basin and the resistive crystalline region of Serra da
Mantiqueira. The data were collected during diurnal and nocturnal periods, when the CJR operates with DC current and
when it is turned off, respectively. The objective of this study is to attempt to eliminate the electromagnetic noise
produced by the CJR in the diurnal data. To achieve this goal we plan to use some techniques based on the MT
response function estimation and then to estimate the resistivity profile of the region. This profile will be compared with
the results obtained from nocturnal data, not contaminated with the noise of the CJR, to verify the relative efficacy of the
methods employed to filter out the electromagnetic noise. The preliminary results indicate that the Serra da Mantiqueira
region is 177.8 times more resistive than the Basin and that the skin depth in the Basin is of 2.7 km.
-
-
-
On The Role Of Cosmic Rays In The Atmospheric Processes
Authors Yuri I. Stozhkov, V.I. Ermankov, I.M. Martin, P.E. Pokrevsky and M.G.S. MelloThe role of charged particles in processes in the atmosphere is considered. It is shown that these particles play the
important role in the global electric circuit provided the conductivity of air. The steady state equation describing ion
production rate and their recombination is analyzed on the base of experimental data on cosmic ray fluxes and ions
concentrations. These data were obtained at polar, middle and equatorial latitudes in the atmosphere from the ground
level up to 30-35 km. The influence of charged particle fluxes on rainfall values during Forbush decrease and powerful
solar proton events is demonstrated. Also, the mechanism of thunderstorm electricity production, separation of opposite
sign charges, and lightning production is discussed.
-
-
-
Participação Da Unicamp Com Experimentos Na Estação Espacial Internacional
A collaborative project to study Solar-Earth relationship using International Space Station (ISS), prepared by Institute of
Space Research (IKI) of Rusian Academy of Science and State University of Campinas (Unicamp) will be described. The
main objective will be identify phenomena relating solar influences in climatology variations on Earth, mainly intensity of
rains in Brazil. Infrared, visible and X-ray detectors will be installed on board of ISS russian segment to realize monitoring
on Brazilian territory.
-
-
-
Structure And Development Of The Powell Basin (Ne Antarctic Peninsula)
More LessPowell Basin is one of the few present-day examples of a small ocean basin largely surrounded by blocks of
continental crust. The western and eastern margins are conjugate passive margins having a transitional crust in the
continent-ocean boundary. The distinct characteristics of these two margins suggest a degree of asymmetry in their
development. A possible origin of asymmetrical extension during the initial rifting stage may be the occurrence of a
shear zone with an eastwards dipping component. A spreading ridge, located in the central part of the basin, split
into two crests that may be interpreted as two segments of an overlapping spreading centre (OSC). The rifting
episode could have begun about 35-40 Ma. A maximum age of Early Oligocene (29 Ma latest Early Oligocene) is
proposed for the ocean basin spreading, that appears to have ceased during the Early Miocene (23 Ma). The
eastward motion of the South Orkney Microcontinent relative to the Antarctic Peninsula created this basin. A pullapart
origin, related to a dextral fault system, has been proposed for the basin development. However, a possible
alternative is to consider that the transcurrent fault bounding the basin has opposite kinematics (sinistral the
northern one and dextral the southern one). In this model, the continental crust at the north of the Powell Basin
remains fixed in relation to the Antarctic Peninsula.
-
-
-
Resultados Preliminares De La Campaña De Ozonosondeo En Una Localidad De Altura (La Paz, Bolivia)
Authors Francesco Zaratti, Marcos Andrade and Ricardo FornoSe analizan los datos de once lanzamientos de sondas de ozono realizados en la región de La Paz ( 3400 m
snm) en el mes de Junio de 1998. Se estudia el comportamiento de variables como la temperatura, la altura de la
tropopausa, el contenido troposférico de ozono, la distribución estratosférica del ozono y el valor integral del
mismo. Se comparan los resultados obtenidos en esa campaña con los datos de un trabajo similar realizado en
1963 en la misma localidad con el fin de poner en evidencia eventuales modificaciones en la atmósfera local. Se
discute también un posible origen de la disminución del ozono total sobre las tierras altas tropicales.
-
-
-
Impactos Sócio-Ambientais Provocados Por Emanações Radiogênicas De Rochas “Graníticas” Utilizadas Em Ambientes Internos
More LessSão avaliados fatos referentes ao estudo das emanações radiogênicas produzidas por rochas “graníticas”
utilizadas em ambientes internos, relativos aos impactos sociais, ambientais, de segurança no trabalho,na
indústria e na comercialização desses materiais, observados durante o desenvolvimento das medições.
-
-
-
Applicability Of Eudo-Rotation Technique For Land Vsp With Difference In Surface Conditions At The Source Locations In Anisotropy Study
Authors Sergei Gorshkalev and Wladimir KarstenPseudo-rotation technique may be applied in marine VSP study of azìmuthal anisotropy of horizontally layered
media. lt uses multicomponent downhole registration of downgoing converted PS-waves from two symmetrical
sources with small offsets because directed sources of S-waves can not be used on sea. Land symmetrícal
sources are more widely used than directed sources, so we would like to estimate efficiency of this technique
for land VSP. The land survey conditions involve variations of near-surface properties and altitudes, which
cause the travel times of identical waves to differ. The technique of equalization of these travel times before the
pseudo-rotation was suggested. lt was tested on synthetical data of full wavefield. The model used was based
on the VSP surveys in the Yurubchen-Tokhomo oilfield zone in Eastern Siberia.
-
-
-
Estudo Das Estruturas Coerentes Na Cla Clara Por Radar Doppler
More LessThe evaluation of the respective role played by the coherent structures and the turbulence in the vertical transport within
the atmospheric boundary layer was the scientific objective of the TRAC experiment, the experimental framework of this
study, that made use in June 1993 of coordinated aircraft-radar measurements. The analyzed cases of ABL showed that
the radar was able to provide a coherent and continuous representation of the meteorological fields over a horizontal
range of several tens of kilometers and vertically up to 2.5 km, i.e., well beyond the top of ABL. Coherent structures
appeared as a common feature of the ABL under study and not as an exception. From radar measurements we found in
particular that turbulent scales of the inertial sub-range were modulated by the coherent structures. The capability of the
detection of weather cumulis located at the top of the ABL show that the radar is able to provide a description of the
entire ABL including the processes in the entrainement zone.
-
-
-
High Resolution Aeromagnetics As And Aid To Geologic Mapping Of Rio Das Velhas Greenstone Belt, Quadrilátero Ferrívero, Minas Gerais, Brasil
Authors Adelene M. Silva, Anne McCafferty, Augusto C.B.Pires, Hengrem Xia and Issamu EndoA high resolution geophysical survey was acquired in 1992 as a part of Rio das Velhas Project and was used to investigate the regional structural setting of the area and better define lithological boundaries. High resolution geophysical surveying is fundamental to modern geoscientific mapping, providing cost-effective definition of structure and lithology in a diverse range of geological terrains. The airborne magnetic data are particularly valuable for defining northsouth Archean structures and the continuity inside the study area. This paper illustrates the usefulness of the aeromagnetic data in the support of geological mapping in the Rio das Velhas Greenstone Belt.
-
-
-
Anisotropy In A Vicinity Of A Borehole From The Qp Wave Slowness And Polarization
Authors Ivan Psencik and Xuyao ZhengWe propose an algorithm for evaluating weak anisotropy parameters at receivers in a borehole in a multi-
azimuthal multiple-source o set VSP experiment. The parameters can be determined from measurements of
slowness vectors and/or deviations of measured qP wave particle motions from the slowness vectors at indi-
vidual receivers. The formulae presented are applicable under assumption of arbitrary but weak anisotropy
and vertical inhomogeneity of the medium. The formulae represent, in several respects, generalization of an
algorithm proposed by Gaiser (1990) and an alternative to the algorithm proposed by Horne et al. (1998).
Basic formulae and a synthetic example of their application are presented.
-
-
-
Prestack Depht Migration In The Presence Of Low Relief,High Velocity Layers
Authors R. Gareth Williams, Peter Whiting and Jerry YoungDepth migration is more accurate than time migration in that it images seismic data correctly in the presence of
lateral velocity changes. However, for mild lateral velocity gradients we often use time migration for reasons of
cost and stability; the time spent deriving an accurate velocity field and the increased sensitivity of depth
migration to the velocity field make depth migration more difficult to apply. For these reasons, depth migration
has often only been used when time migration is perceived to fail to image the data properly. Very often, this
means that depth migration is only used in particularly difficult and complex geological environments such as
overthrust belts and beneath salt diapirs. Unfortunately, in these environments, depth migration often does not
provide a clear image where none existed without depth migration because either the ray paths diverge causing
the subsurface not to be illuminated by the recording, or current model building techniques are inadequate for
such complicated cases. For example, many model updating techniques assume the starting model is either
close to the correct answer, slowly varying or that flat horizons exist.
Experience of imaging beneath the basalts of the Shetland-Faroes basin, the tabular salt of the Gulf of
Mexico, the shallow carbonates of N. W Australia and the chalk layer of the North Sea has shown that prestack
depth migration can be used to improve imaging substantially beneath these low relief but high velocity layers.
In the Shetland-Faroes basin, volcanic flows form a barrier to imaging of deeper sedimentary rocks. PSDM has
improved imaging both within and below the multiple lava flows. In the Gulf of Mexico, tabular salt causes
significant ray path bending and subsequent distortion of the images of the underlying geology. In the Browse
Basin, rugged seabed topography can cause imaging problems that can be addressed with prestack depth
migration. In many parts of the North Sea a chalk layer with gentle dips lies above the oil and gas bearing
targets. All of these geological environments are characterised by fast velocity layers (for example, the chalk is
typically twice the velocity of the overburden) and even low dips at the top and base of these layers cause
problems for imaging deeper targets. The ray path bending can either prevent an image being formed at all,
distortion of any image that is obtained or loss of resolution. PSDM has been found to be beneficial in all these
cases. Prestack depth migration should not be viewed as just a tool for extreme geological cases.
Post stack depth migration may provide better positioning and imaging than post stack time migration.
Therefore, in low relief areas, it is tempting to use post stack depth migration instead of prestack. However, the
ray path distortion caused by the low relief, fast velocity layers we are considering is significantly offset
dependent. This causes image distortion and loss of resolution that cannot be recovered stack. Also, model
building via post stack depth migration is subjective – the only test is whether the final image agrees with the
interpreter’s expectation. Prestack depth migration affords the qualitative test that if the velocity model is
correct then the primary events within depth migrated image gathers are flattened and will stack coherently.
-
-
-
Co-Location Of Surveys In Space And Time For Improved Accuracy And Sensitivity In 4D Marine Surveys
Authors R. Gareth Williams, Richard Leggot, Mark Skinner and Steve JesticoTime lapse, or 4D, seismic surveys are designed to monitor changes in the seismic response of hydrocarbon
reservoirs caused by production. In many reservoirs, the acoustic impedance changes induced by production
are small and therefore we are looking for weak 4D signals. This means that 4D surveying requires a high
degree of accuracy in order to detect a reliable 4D signal. In marine 4D surveys, variations in geometry caused
by currents, variations in wave height and variations within the water column all combine to reduce the
repeatability of the recording. Successful 4D processing must take account of these factors
Interpretation of 4D results has often been done on difference sections obtained by simply taking the difference
between two vintages of data previously processed for 3D purposes. Variations in the individual survey results
will be caused by variations in recording equipment and geometry, variations in feathering and infill, variations
within the water column and variations in processing. In order to compensate for these differences, matching
filters are applied to the datasets. In this method, it is assumed that matching the overburden will compensate
for all of the above factors in a single filter (perhaps a single filter per trace) and thus reveal the true change at
the reservoir level. Although this approach implies that the biggest difference between the two surveys will be
outside the matching design window, it does not mean that these changes are only caused by reservoir
production. Indeed, the difference between the datasets is often found to increase everywhere outside the
design window. For example, data shot over the Oseberg field in 1989 and 1991 were normalised by applying
scalars derived in a 150ms window around the water bottom for each trace. Equalising the amplitudes around
the water bottom INCREASED the difference energy over a larger window from 0s to 3s, illustrating the dangers
inherent in simply matching different datasets to optimise the 4D signal.
Since the differences between two datasets are caused by a number of factors, it is likely to be better to address
each problem separately rather than attempting to do so with a single matching filter. The first, obvious step is
to process both datasets simultaneously for 4D purposes. This eliminates differences in processing methods
and algorithms and also testing of whether or not particular processing steps improve the 4D difference. Within
this processing, variations in positioning (in space and time) should be addressed separately from, say, wavelet
changes. Finally, matching filters may still be appropriate, but now they are addressing only residual differences
in the seismic system.
To examine how sensitive taking the difference between two datasets can be, consider two 40 Hz Ricker
wavelets separated by a 1ms static shift. Figure 1 shows the two wavelets and the difference between them. The
peak difference is about 25% of the peak value of each wavelet. Increasing the static shift to 4ms causes the
peak value and the RMS of the difference to approximately equal the equivalent values for the individual
wavelets. Static shifts greater than this cause the difference to have peak and RMS values up to twice that of the
individual wavelets. This demonstrates that we will have to account for small timing and positioning shifts
between vintages if we are to reduce the background difference ‘noise’ and detect true changes caused by
hydrocarbon production. Moreover, many reservoirs require sensitivities of less than 25% in order for the
production induced seismic changes to be detectable i.e accuracy to better than 1ms for the above synthetic
wavelets.
-
-
-
Deep Crustal Structure Of The Area Of Intersection Between The Shackleton Fracture Zone And The West Scotia Ridge (Drake Passage, Antarctica)
The Shackleton Fracture Zone represents the present-day boundary between the Antarctic and Scotia plates in the
Drake Passage. The West Scotia Ridge is an extinct spreading center, which formed the oceanic crust of the Scotia
Plate in this region and that intersects with the Shackleton Fracture Zone. New multichannel seismic, gravimetric,
magnetometric and multibeam swath bathymetry data were acquired during the ANTPAC 97/98 cruise with the Spanish
vessel B/O HESPERIDES in the area and reveal that these structures are asymmetric and developed as a consequence
of the overprinting of extensional and contractional deformation events. Thrusting of these young oceanic crusts
produces crustal thickening and shallow oceanic reliefs and ridges.
-
-
-
Contaminação Do Subsolo Monitorada Por Resistividade Elétrica
Authors Carlos T.C. Nascimento, Sérgio Koide and Augusto C.B. PiresO método geofísico de perfilagem elétrica horizontal é uma técnica que pode ser utilizada para a detecção de
contaminantes no subsolo. Neste trabalho, este método foi empregado para visualizar a migração de efluentes
de fossa séptica dispostos no subsolo, através de valas de infiltração. O contraste de resistividade elétrica
entre o solo seco e o solo com presença de efluente permitiu delimitar as áreas contaminadas. Os resultados
obtidos possibilitaram identificar um padrão de movimentação tanto horizontal, como vertical do contaminante.
Dados complementares, obtidos através de coleta de amostras da água do subsolo, mostram que a
contaminação já atingiu um aqüífero freático que situa-se a cerca de 8 metros abaixo das valas de infiltração.
-
-
-
Coplanar Coils Response In A Borehole
Authors Paulo Roberto de Carvalho and Om Prakash VermaNone of the traditional resistivity borehole devices possesses azimuthal investigation properties whereas the
unconventional coplanar coil array has, by design, this attribute. Theoretical electromagnetic radial and vertical
responses have been obtained for the conventional two coil coaxial system and the unconventional coplanar array.
From the comparative studies of the responses of these two coil system we can conclude:
1) The skin effects for the coplanar coil array are stronger than coaxial, this disadvantage almost disappear after skin
effects correction; 2) Polarization “horns” occur in coplanar profiles against the bed boundaries indicating their presence;
and 3) The azimuthal attributes of the coplanar system can be explored in the investigations of the axially asymmetrical
geological situations such as vugular or fracture zones, inclinded beds and invasion zones in horizontal wells.
-
-
-
Redução E Aplicação Da Bte À Geofísica De Poços
More LessA eficiência na modelagem numérica de perfis nucleares de poços esbarra na obtenção de uma equação ideal aos objetivos propostos. A equação de difusão mais simples empregada origina-se da aplicação da Lei de Fick na redução da equação de transporte de Boltzmann (BTE).
-
-
-
Parâmetros Físicos Em Perfilagem Nuclear De Poços -Raios Gama
More LessNeste trabalho os parâmetros físicos das formçõaes, tais como o coeficiente de difusão e as seções de
choque total e de espalhamento, são determinados através da distribuição de Kleín-Nishina e de regressão
linear múltipla de dados experimentais. A adequação destes parâmetros à modelagem numérica de sistemas
de multigrupos de energia são pressupostos básicos para a compreensão das medidas das diversas sondas
de poço que utilizam como fontes, raios gama artificiais e/ou naturais.
-
-
-
Inversão Gravimétrica Do Relevo Descontínuo De Uma Bacia Sedimentar
More LessWe present a new stable gravity inversion method applied to the mapping of an interface separating two homogeneous media. In contrast with previous similar methods, it does not impose an overall smoothness on the estimated interface to stabilize the solution. The density contrast between the media is assumed to be known. The interpretation model for the upper medium consists of rectangular juxtaposed prisms whose thicknesses represent the depths to the interface and are the parameters to be estimated. The true interface is assumed to be flat everywhere except at faults. To incorporate this attribute into the estimated relief, we developed an iterative process where three kinds of constraints are imposed on parameters: (a) proximity between values of adjacent parameters, (b) lower and upper bounds to parameters, and (c) proximity between the values of parameters and fixed numerical values. Starting with an initial solution which presents an overall smooth relief, the method enhances initially estimated geometric features of the interface; that is, flat areas will tend to become flatter and steep areas will tend to become steeper. This is accomplished by weighting the constraints, which requires proximity between adjacent parameters. The weights are initialized with values equal to unity and are automatically updated to enhance any discrepancy between adjacent depths that have been detected at the initial solution. Constraints (b) and (c) are used both to compensate for the decrease in solution stability due to the introduction of small weights, and to reinforce flatness at the basin bottom. Constraint (b) imposes that any depth be nonnegative and smaller than an a priori known maximum depth value whereas constraint (c) imposes that all depths be closest to a value greater than the maximum depth. The tradeoff between these conflicting constraints is attained with a final relief presenting flat bottom and steep borders. The method was tested with synthetic data produced by a simulated sedimentary cratonic extensional basin having a smooth floor, steep edges and known depth to the bottom. The results showed an improvement in the resolution of the relief, leading to a reliable mapping both of the sharp discontinuities at the borders and of the lateral extent of the base of the basin. The method was also applied to the Bouguer anomaly from the northern portion of Steptoe Valley, Nevada, delineating an isolated basin with a wider, flat base and more straight borders as compared with the estimate imposing overall smoothness on the relief.
-
-
-
Inversão Gravimétrica Do Relevo Não Suave De Uma Bacia Sedimentar Com Variação Do Contraste De Densidade
More LessWe present a new stable method for interpreting the basement relief of a sedimentary basin which delineates
sharp discontinuities in the basement relief and incorporates any law known a priori for the spatial variation of
the density contrast. The subsurface region containing the basin is discretized into a grid of juxtaposed
elementary prisms whose density contrasts are the parameters to be estimated. It is imposed that any vertical
line intersect the basement relief only once and that the mass deficiency be concentrated near the Earth's
surface, subject to the observed gravity anomaly being fitted within the experimental errors. In addition, upper
and lower bounds on the density contrast of each prism are introduced a priori (one of the bounds being zero)
and the method assigns to each elementary prism a density contrast which is close to either bound. The
basement relief is, therefore, delineated by the contact between the prisms with null and nonnull estimated
density contrasts, the latter occupying the upper part of the discretized region. Thus, the method is stabilized by
introducing constraints favoring solutions having the attributes (shared by most sedimentary basins) of being
an isolated compact source with lateral borders dipping either vertically or toward the basin center and having
horizontal dimensions much greater than its largest vertical dimension. Arbitrary laws of spatial variations of
the density contrast, if known a priori, may be incorporated to the problem by assigning suitable values to the
nonnull bound of each prism. The proposed method differs from previous stable methods by using no
smoothness constraint on the interface to be estimated. As a result, it may be applied not only to intracratonic
sag basins where the basement relief is essentially smooth, but also to rift basins whose basements present
discontinuities caused by faults. The method's utility in mapping such basements were demonstrated in tests
using synthetic data produced by simulated rift basins. The method mapped with good precision a sequence
of step faults which are close to each other and present small vertical slips, a feature particularly difficult to
detect from gravity data only. The method was also able to map isolated discontinuities with large vertical
throw. The method was applied to the gravity data from Recôncavo Basin, Brazil. The results showed close
agreement with known geological structures of the basin. It also demonstrated the method's ability to map a
sequence of alternating terraces and structural lows, which could not be detected just from the inspection of
the gravity anomaly.
-
-
-
Hidrologia Subterranea Da Area De Um Aterro Sanitario Utilizando Geofisica Eletrica
More LessElectrical sounding measurements of resistivity and induced polarization parameters combined with a selfpotencial surveywere used for mapping the sub-surface geology and hidrology around the new Salvador sanitary landfill. This landfill is located within the Rio Joanes basin, close to a surface reservoir used for water supply in the Salvador Metropolitan Area. The main aquifer
zone is represented by sandstones of Barreiras Formation and the wheathered basement. The geophysical results are presented as structural sections and maps showing the geometry and the lithologic variability of this aquifer. They may serve as a geophysical reference for monitoring the eventual groundwater changes caused by the landfill operation.
-
-
-
Detecção De Refletores Sísmicos Por Rede Neural Discreta
Authors Alexandre Beltrão Ferreira and André AndradeThe artificial neural networks have proven to be a powerful tool to solving a wide variety of optimization
problems. In this work we develop a recurrent network with no self-feedback loops and no hidden neurons for
seismic signal processing where this neural network gives us reflectivity location and reflectivity magnitude
estimation. The most important advantage of this neural network is the use a type of activation function which
permits three possible states of neuron to estimate the position of the seismic reflectors in such way to
reproduce its true polarities. The operational evaluation of this neural network architecture is accomplished in
synthetic data obtained through the ray theory.
-
-
-
Automatic Lithologies Identification From Well Log
Authors André Andrade and Anna Ilcéa FischettiThe complex mineralogical constitution of reservoir rocks and the need of correct lithology identification in a borehole
from well log data, makes lithologic identification of a rock possible, not by means of a complete mineralogical
description, but through the identification of its main mineral constituents or essential mineral.
For identification of essential mineral, through the well log data, several numeric methods were developed, like the
compositional analysis and graphical methods, such as the M-N plot (BURKE et al,1969).
We show here, the mineral essential determination method from well log data, by means of a simulation of interpretation
performed by log analyst utilization of the M-N plot, through an artificial neural network architecture with competitive
layer, intending to simulate the decision problem of log analyst, when the M-N plot is used.
In the enviroment of artificial neural network computations, the log analyst decision problem simulation, when
M-N plot is used, can be understood as a decision problem with an alternative finite number or as non-linear
classification of stimulus group in the patterns set.
The perfomance of this approach is shown over real data from PETROBRAS obtained at Amazon Basin.
-
-
-
Wireline Logs Restoration Through Self-Adjustable F
Authors Carlos Eduardo Guerra and André AndradeThe lack of a good vertical resolution of deep investigation wireline tools is the main cause of difficulties in the
log interpretation, mainly in the cases where the layers reservoirs have thickness less than the vertical
resolution of the tool. The combined measurement of shallow and deep resistivities, for instant, enable the
parameters determination like Rt( true resistivity), Rxo (resistivity of invaded zone) and di (diameter of invasion).
But in complex reservoirs we have difficulty in obtaining a confident reading of Rt due the low vertical resolution
of deep reading tools. In this work, we present a methodology that outlines this problem, using image
processing techniques, which allow to incorporate information from high-resolution log into the low-resolution
log. This information is generated by the shallow investigation tool, whose measurements do not relate directly
with the reservoir parameters. The final result is an improvement in the vertical resolution of logs got from
deep investigation tools.
-
-
-
Automatic First Break Picking In Seismic Traces By Neural Network
Authors Anna Ilcéa Fischetti and André AndradeThe first break picking is a manual task of seismic interpreters performed before many computational
seismic processing, based in their geological and geophysical experience and interpretative criterions.
In this paper we propose an automatic approaches to this task, based in the apresentation of an artificial neural
network architecture, that quest simulate the human visual system behavior in a decision problem form. The
applicability, efficiency and limitations of this approach will be appraised in synthetic data obtained starting out
from the ray theory.
-
-
-
South Central Andes Gravity,New Data Base
Authors M. Araneda, M.S. Avendaño, S. Schmidt, H.J. Götze, J. Muñoz and M. SchmitzFrom 1993 to 1998 approximately 3.927 gravity stations were taken in the Central Southen Andes, comprising the
southern central zone of Chile and the central western part of Argentina, between latitudes 37.50ºS to 42.5ºS and
69ºW as far as the coast of the Pacific Ocean. To this information, 9.123 old stations were included, which were
reprocessed and when in some doubt, were remeasured. Now the the database contains 13.050 gravity stations
available which can be used along with other geophysical and geological information for an interdisciplinary
interpretation to be able to understand some structural aspects and evolution of the Southern Central Andes. In
this paper, we present the new data base by means of maps of Bouguer anomaly and isistatic anomaly, together
with a very preliminary interpretation.
-
-
-
Efeitos Das Tempestades Magnéticas Na Ionosfera De Baixa Latitude
Authors Cristina Sayuri Yamashita, J.H.A. Sobral and M.A. AbduAs tempestades magnéticas e os seus efeitos na ionosfera terrestre constituem atualmente um dos temas de
maior interesse da comunidade científica especializada no campo de estudos da climatologia espacial cujo
conteúdo versa sobre o estudo integrado do sistema ionosfera/termosfera/magnetosfera/meio interplanetário.
As tempestades magnéticas são caracterizadas basicamente por fortes depleções na variação temporal do
parâmetro geomagnético Dst e também por valores elevados do índice Kp. Durante a ocorrência delas, a
ionosfera sofre perturbações em nível global. O objetivo deste estudo é analisar em detalhe os efeitos de uma
grande tempestade magnética na ionosfera sobre a região de Fortaleza. Os principais efeitos ionosféricos a
serem aqui investigados são os seguintes: 1) Penetração de campos elétricos zonais (direção leste-oeste) na
região de baixa e média latitude; 2) Efeitos dos ventos termosféricos perturbados (Disturbance Dynamo). A
metodologia a ser empregada para o estudo dos efeitos ionosféricos das tempestades magnéticas consiste
basicamente na comparação dos parâmetros ionosféricos dos dias magneticamente perturbados com o valor
médio dos mesmos parâmetros dos dias magneticamente quietos.
-
-
-
Mt Studies At Sedimentary Basin Of Sierras Pampeanas, Argentina
Authors Cristina Pomposiello, Ana Osella, Alicia Favetto and Claudia SainatoMT data from profiles located over intermontane sedimentary basins of Sierras Pampeanas in North-West of
Argentina are analyzed through 2D inversion methods.
These basins are very deep and have an important deposit of Tertiary sediments. Sediments contain Miocene to
recent sequences of volcanic or continental detrial origin. Lithological variations occur from one intermontane
basin to another and they lie on a basement peneplain surface formed after the middle Paleozoic and frequently
exhumed on the range.
The resulting electrical models show sedimentary sequences with variable thickness (between 3 to 9 km). In all
cases, a very conductive layer beneath the basement are detected.
-
-
-
Condicionamento Estrutural Sobre O Aqüífero Barreiras E Sistema Lacustre Do Bonfim-Nísia Floresta-Rn
Authors Leandson R.F. Lucena, Sebastião K. Oliveira and Walter E. MedeirosA cenozoic sedimentar region, localized near the eastern coastline of Rio Grande do Norte state, Brazil, was studied. This region contains the Bonfim lake that is an importante source of potable water to supply the cities in the region, including Natal (capital of the state). A joint study of morphotectonic, geologic, gravimetric and resistivity data revealed that the shallow structural trends are aproximately paralel to the deep structural trends. Based on this concordance, it is suggested that the shallow structures were formed, at least in part, activating the older and deeper structures. The Bonfim lake is localized on the crossing of two regional trends; these structures define a graben, which is resposible for the local increase in the saturated thickness of the Barreiras aquifer. The refered graben conditionates the groundwater flow from the Barreiras aquifer to the Bonfim lake.
-
-
-
Estudio Geofísico De La Cuenca De Grenada
Authors Nuris Orihuela Guevara and Daniel LoureiroThe results of a combined gravimetric-magnetic study of the Grenada Basin are presented. Two domains migth
be recognized based on the map patterns of the anomalies in the area. South of parallel 15.5° regional gravity
shows a steep and steady gradient, presumably associated to the development of a relatively thick sedimentary
basin. Modeling of a gravimetric profile suggests that the thickness of the crust varies from a maximun of
about 25 km under the Aves Ridge, to less than 8km beneath the Grenada Basin, where it might be covered by
as much as 7 km od sediments. This architecture is interpreted as a result of the development of the Grenada
Basin in an extensional back-arc setting. Furthermore, the high frequency magnetic anomalies along the profile
have been successfully matched using a madel where the uppermost oceanic crust was divided into alternately
normally and reversely magnetized blocks. The fact that no major uplift or ridge trace is actually present in the
basin is regarded as a result of thermal subsidence enhanced by sediment loading postdating the sea floor
spreading event.
The second domain, north of parallel 15,5°, is characterized by high frequency residuals probably indicating a
shallow and strongly faulted basement.
-
-
-
First Mesopause Temperature Profiles From A Fixed Lidar Station At 23º S
Authors B.R. Clemesha, P.P. Batista, P.P.M. Jorge, D.M. Simonich, H. Takahashi and I. VeselovskiiThe INPE sodium lidar, which has been in operation since 1972, was recently modified so as to enable
measurements to be made of the Doppler temperature of the Na atoms in the atmospheric sodium layer. A
relatively simple modification to the dye laser transmitter causes it to produce a multi-line output with 1.98 pm
spacing between individual lines, each of which has a bandwidth of less than 0.05 pm. By changing the gas
pressure in the Fabry-Perot interferometer which produces this line structure, it is possible to switch between a
laser output where the lines exactly coincide in wavelength with the Na D2 hyperfine lines, and one where the
central laser line is exactly equidistant from the D2 lines. Doppler temperature is measured by determining the
change in the effective backscattering cross-section of atmospheric Na atoms when the laser is switched
between these two positions. Measurements were made on a total of 15 nights from July to October, 1998,
providing temperature profiles between heights of about 83 and 105 km. Almost all measurements showed a
mesopause temperature structure strongly perturbed by tides and gravity waves, with peaks in sodium density
occurring at almost the same height as the temperature maxima on the bottom side of the sodium layer. The
lowest temperatures, between 170 and 200 K, typically occur above 100 km, and the average profile for all our
measurements is similar to the winter profile seen at mid-latitudes, with a mesopause temperature of 190 K at
103 km.
-
-
-
Migración De Solutos En Formaciones Porosas Saturadas
Authors Jacqueline Köhn, Eduardo E. Kruse and Juan E. SantosEste trabajo se refiere al modelado del flujo subterráneo y la simulación del transporte de contaminantes en
formaciones porosas saturadas. La elaboración de un modelo matemático que describa esta situación no sólo
es útil para representar el estado actual de contaminación sino para realizar un pronóstico hacia el futuro. La
metodología utilizada se basa en la observación, teorización y simulación que se puede obtener en geofísica
vinculando las distintas posibilidades que brinda la interrelación de respuestas reales del comportamiento
hidrológico y la matemática aplicada que proporciona la estructura lógica para descifrar los efectos individuales
de los fenómenos físicos generales. La técnica numérica TVD y el método iterativo mixto de características
fueron empleados para la simulación de transporte bidimensional de contaminantes. Con el objetivo de
comparar ambos métodos se planteó un caso sintético de migración de contaminante conservativo (cloruro) a
partir de una fuente continua y puntual ubicada en la zona saturada.
-
-
-
Rooted Structuring As Key For Southern Apennine Oil Exploration
Authors Anna Del Ben and Icilio FinettiIt is Authors’ opinion that a key point for the evaluation of the prospect in Southern Apennine, having as target
the top of the Apulian Platform, is constituted by the type of the structure involved. That is, if the explored
feature is formed by a block rooted with its own basement and practically not or not much displaced, in that
case the preservation of the integrity of the reservoir and its oil trapping is possible. But when the explored
structure consists of thrust-blocks, disrooted from their basement and prominently displaced, than the resulting
reservoir/cover conditions don not allow oil trapping or preservation of oil accumulation. Examples of both
types of features are examined.
-
-
-
Multiple Attenuation In The Plane Wave Domain By Matching Filter
Authors Reynam Pestana, Paul L. Stoffa and Mrinal SenIn this paper we present a method of multiple attenuation
in the plane wave domain that uses a filter estimation
procedure to match the angle dependent primaries
to predict the observed multiples. The filter is obtained
through the solution of an optimization problem. Instead
of using a source function estimate we use the primaries
from the shallow part of the data (reflectivity) to estimate
the multiples associated with these events that are correct
in traveltime, but not necessarily in amplitude. Using
this filter the amplitude and phase of the multiples
are estimated and the predictedmultiples are subtracted
from the data to obtain multiple free data. The application
of this method is illustrated on synthetic and real
data and the results demonstrate its effectiveness in attenuating
multiples. The proposed method is computationally
very efficient.
-
-
-
Seismic Sedimentology Of Mioceno Deposits In The Mioceno Norte Area,Lake Maracaibo,Venezuela
Authors Hongliu Zeng, William A. Ambrose, Edgar Villalta, Roger Tyler and Noel TylerThis study provides a case history in which the reservoir-level facies interpretation in a densely drilled, but spatially
restricted, area containing 240 wells is extended to a ‘bigger, 3-D-survey area’ by means of seismic sedimentology. In
turn, seismic facies images verify and improve upon the existing facies interpretation by adding control between and
beyond wells.
-
-
-
Application Of Rms Amplitude Anomaly Mapping In Inferring Controls On Fluid Saturation And Fault-Bound Reservoir Compartments In The C4 Member (Lower Misoa Formation), Phase Iii Area, Bloque I Area , Lake Maracaibo, Venezuela
Three-dimensional seismic data are increasingly being used in reservoir characterization studies as an aid in
detecting and delineating structural and lithologic features as well as changes in fluid distribution that may not
be resolvable with log data at wide well spacings. Amplitude maps, in addition to displaying distribution of
lithology, can also be effective in inferring subtle faults associated with changes in reservoir fluid content.
In a IZmonth reservoir characterization study of tide-dominated deltaic and shelf reservoirs of the Lower
Eocene Misoa Formation in a 4-mi*(10.4-km*) rectangular area (Phase III Area) in the Bloque I Area,
3-D seismic data were used in conjunction with logs from approximately 50 wells to detect and delineate faults
and to infer interwell sand-body distribution. The goal of this reservoir analysis was to construct an improved
geological model of oil- and gas-productive reservoirs in the Lower Eocene to better understand controls on
reservoir compartmentalization and to identify areas of unswept hydrocarbons. This paper provides examples
from the C4 Member and demonstrates how 3-D seismic data were used to infer the presence of faults not
previously detected in earlier studies of these reservoirs with conventional log data and to illustrate their control
on fluid distribution.
-
-
-
3D Seismic Stratal-Surface Concepts Applied To The Interpretation Of A Fluvial Chanell System Deposited In A High-Accommodation Environment
Authors Bob A. Hardage and Randy L. RemingtonA fundamental thesis of seismic stratigraphy is that seismic reflections follow impedance contrasts that coincide with
strata1 surfaces. which are surfaces where depositional processes occur at a fixed moment in geologic time. This stratalsurface
concept IS used herein to image a narrow (width -300 ft). thin, fluvial channel system that is embedded within a
seismic reflection peak. The peak reflects from a large (about 2. X 2.mi) area of nonchannel facies that dominate its waveshape.
The targeted channel facies are confined to an interval that vertically spans less than 30 ft According to principles of
seismic stratigraphy, four conformable seismic strata1 surfaces that pass through the interior of this channel sequence
were constructed across the 3-D seismic-data volume. The channel images portrayed on these seismic horizons, which
were spaced at vertical increments of 2 ms. illustrate the principle that seismic altributes viewed on seismic strata1
surfaces provide valuable images offacies distributions within thin-bed sequences and help seismic interpreters segregate
channel facies from nonchannel facie? Acomparison is made between channel images on seismic strata1 surfaces that
are conformable to two different reference surfaces, one reference surface being positioned below the targeled fluvial
system and the second reference surface being above the thin-bed channels This comparison supports the premise
that seismic interpreters should extrapolate strata1 surfaces both upward and downward across a thin-bed target to
optimize the image of that target.
-
-
-
Emprego Do Gpr Para Estudos Geológicos Na Mineração Jundu, Descalvado-Sp
Authors Jorge Luís Porsani and Walter Malaqutti FilhoThe GPR method was used in the Jundu mines, located in Descalvado-SP, to subsided geological detail studies.
For such, it was carried out several profiles with the antennas of 50 and 100 MHz, being used the Ramac-Mala
equipment. The obtained data were processed and presented in the form of profiles. The interpretation of the
results allowed to detail the stratigraphy, and determine the depth of the water table. It was determined the
influence area provoked by the collapse of the top of the cave. The results present na excelent concordance
with the information given by drilling holes and geological outcrop studies.
-
-
-
A New Approach To Map Host Rock For Gold Exploration In The Rio Das Velhas Greenstone Belt, Quadrilátero Ferrível, Minas Gerais, Brazil
Authors Adelene M. da Silva, Anne E. McCarfertt and Augusto C.B. PiresAn empirical modeling approach was used to locate zones that are favorable for gold mineralization in Rio das Velhas Greenstone Belt, Quadrilátero Ferrífero (QF). A known spatial coincidence exists between banded iron formation (BIF) host lithology, structures and mineralogy type that are indicative of gold. Quantitative relationships between airborne geophysical and geological data sets with known gold occurrences were determined using probability ratio analysis. Spatial associations between geophysical data and host lithology were combined to produce predictive models to explore for Archean oxide-BIF-hosted deposits. This approach has shown great capability for linking geological and geophysical interpretation. The results of this modeling map areas of exposed and subsurface geologic units that are important to gold exploration in the area.
-
-
-
South Shetland Block - Antarctic Plate Boundary: A Present-Day Example Of Progressive Transition From Extensional To Transcurrent Boudary
Authors Luiz Gamboa, Jesús Galindo-Zaldivar, Andrés Maldonado, Saizo Nakao and Yao BochuThe South Shetland Block is a fragment of continental crust that extends between the South Shetland Trench
and the Bransfield Basin. Its southern boundary shows present-day tectonic activity and its nature changes
along strike from a spreading center in the area between the South Shetland Islands and the Antarctic Peninsula
to a transtensional boundary at the northern part of the block. Eastwards, along the South Scotia Ridge, the fault
system finally intersects the transcurrent boundary between the Antarctic and Scotia Plate. The variability in the
features of the southern boundary of the block is probably a consequence of the variable orientation of active
faults in a nearly constant stress field. The study of several transects of the boundary indicates that extensional
structures are generally asymmetrical. The Bransfield Strait has been formed by an asymmetrical extension,
probably related to a low-angle normal fault dipping towards the NW.
-
-
-
4D Seismics - Principles And Application
More LessThe aspect of monitoring reservoirs clearly comprises all aspects of data acquisition, processing and
interpretation. Certain rules apply in order to keep the monitoring process stable, where the most important
ones are:
- to maintain the same 3D-acquisition geometry: the same geometry then guarantees that the same S/N-ratio in
terms of noise-suppression is achieved, one example being here e.g. the aspect of multiple-suppression for the
entire data-volume.
- to maintain the same processing flow: nevertheless of course e.g. residual statics have to be computed based
on the individual volumes of data. Another example here is the process of deconvolution.
- to use the first 3D-volume (usually called the base-line survey) to establish the basic processing flow as well
as to establish the underlying macromodel (velocities V(x,y,z) and velocity interfaces) and (if needed), by
sequence stratigraphic interpretation the 3D-litho model of the reservoir unit.
- to decide upon the monitoring quantity, i.e. which quantity to use for 4D-evaluation. The default here is to use
Acoustic Impedance (AI) (which means that after proper imaging the data is subject to a suitable inversion
algorithm, usually at post-migration stage).
Clearly the type of reservoir to be monitored has impact on the acquisition effort, since we have to distinguish
between two basic types of reservoirs:
- High-impedance reservoirs, i.e. carbonates. As a „rule of thumb“ the maximum changes here are up to 5% (in
acoustic impedance) and
- Low-impedance reservoirs, i.e. sandstones. The „rule of thumb“-Figure here is up to 10% of AI-change.
In any case for the actual reservoir under consideration its sensitivity to fluid substitution has to be evaluated,
usually based on the Biot-Gassmann-formalism for the Zero-Offset case. This part of a 4D-evaluation is called
the calibration part. If done properly, the outcome is a reliable estimate of the dynamic range of the changes in
acoustic impedance due to ongoing production. In addition one needs to estimate the lateral „area of change“ to
be expected by producing the reservoir
during the timespan in between the two seismic surveys.
-
-
-
Thermobaric Dependences Of Physical Properties Of Rocks Discavered By The Krivoy Rog Ultradeep Borehole
By T.S. LebedevInformation about results of studies of thermobaric changes of physical properties of rocks discovered in
drilling the Krivoy Rog ultradeep borehole (Ukraine) are summarized. Pethrophysical models of the Earth’s crust
of the area of its location are set up.
The main tasks of drilling this borehole located in an iron province which is one of the largest in the world were
to elucidate the formation conditions, composition, properties and evolution of the Earth’s crust of continental
type within the area of the development of precambrian iron-silicon and granite-greenstone formations of the
Central Ukrainian Shield. Also specified was the interpretation of anomalies of the observed geophysical fields
and the nature of seismic boundaries in crust.
For this purpose and to set up a regional petrophysical model of the interior we have obtained a new unique
information on PT-changes of physical characteristics of rocks discovered by the borehole. The drifted part of
the section is mainly represented by metaconglomerates, various schists, quartzites, amphibolites,
plagiogranites and some other lower-proterozoic and upper-archean mineral formations of different
composition. Almost all rocks encountered in drilling show differently expressed banding, schistosity and linear
arrangement of minerals.
The method worked out earlier in which specialized chambers are used was applied in a set of laboratory
petrophysical PT-experiments on samples of a representative collection of cores. We carefully studied elastic,
thermal, electrical and magnetic parameters of rocks in characteristic strictly oriented structural and textural
with simulating respective deep thermobaric conditions in PT-experiments. We are founding the nature of the
anisotropy of the distribution of the studied petrophysical parameters found within the section and which is
most probably preserved even at greater depth (below the hole bottom).
The features of thermobaric changes of specific electrical resistance and dielectrical constant of the rocks
studied are due to their saturation with fluids, mineralization of the latter, dissociation and dehydration of
carbonates, micas and other minerals. With increasing pressure the thermal conductivity and thermal diffusivity
coefficients of rocks are increased by almost one third. They evently decrease with increasing temperature. We
have established a relatively early stage of metamorphism of mineral formations. At the simultaneous
programmed PT-effect the remanent magnetization of the most samples containing ferromagnetics is featured
by anomalous changes in respective directions. Based on experimental PT data obtained by the method
proposed, changes of elastic anisotropy of core samples were studied and criteria-precursors of the destruction
of the near-shaft space during borehole drifting were found. They are mainly due to violation of the elastic
lithostatic balance of the geologic medium.
An analysis of the results of the whole set of petrophysical PT-experiments and the geologic-geophysical
information enabled us to assume possible changes of properties, composition and state of rocks at depth so
far not reached by drilling. We have also set up prognosed deep petrovelocity, geoelectrical and lithological
models of the Earth’s crust of the area of the Krivoy Rog over- and underthrust structure.
I sincerely thank all my researchers that participated in the investigations.
-
-
-
Migration And Modeling Of Pick Data With Traveltimes
Authors Cole C. Harris and Michael O. MarcouxKirchhoff migration and modeling algorithms are integral methods in which the dominant contribution to the
integral is from the stationary phase regions of the operator-mapped input data. We have developed an analogy
to such Kirchhoff methods for application to event picks derived from seismic data. In contrast to the Kirchhoff
algorithm, our method explicitly detects the stationary phase regions in the operator-mapped input pick dataset
and associates with each an output pick. Unlike map-migration type algorithms, this method does not require
horizon dip information, or even that the picks be assembled into distinct horizons. Thus, relatively simple
automated seismic data picking algorithms may be employed to generate the input pick dataset.
Two applications of these algorithms are depth model verification using reflection time pick migration and the
generation of reflection time picks from time-migrated data for use in traveltime tomography.
Both migration and modeling algorithms have been verified on a pick dataset derived from a relatively complex
model incorporating steep dips and non-smooth reflectors.
-
-
-
Estudos De Cavidades Em Arenito Utilizando Gravimetria E Caminhamento Elétrico
Authors J.C. Dourado, W.M. Filho, A.C. de O. Braga, V.R. Elis and N. NavaEste trabalho mostra o resultado dos ensaios geofísicos realizados na Mineração Jundu, com o objetivo de
detectar cavidades no interior do arenito. Os levantamentos de campo foram realizados em uma bancada onde,
devido ao desmoronamento do teto, uma cavidade foi encontrada. No total foram levantadas 269 pontos
gravimétricos em uma malha aproximada de 5 por 5 metros e aproximadamente 1400 metros lineares de perfis
de resitividade elétrica utilizando-se da técnica de caminhamento elétrico com arranjo dipolo-dipolo, sendo que
o espaçamento entre os dipolos foi de 5metros.
No local onde se encontrava a cavidade os ensaios responderam coerentemente, isto é, o levantamento
gravimétrico mostrou um baixo na anomalia Bouguer, enquanto que a resistividade elétrica mostrava um
aumento de valores. Outra anomalia foi confirmada posteriormente onde anomalias geofísicas foram
detectadas.
-
-
-
Factorial Kriging Analysis - A Geostatistical Approach To Improve Reservoir Characterization With Seismic Data
More LessIn this work the Factorial Kriging analysis for the filtering of seismic attributes applied to reservoir
characterization is considered. Factorial Kriging works in the spatial domain in a similar way to the Spectral
Analysis in the frequency domain. The incorporation of filtered attributes as a secondary variable in kriging
system is discussed. Results prove that Factorial Kriging is an efficient technique for the filtering of seismic
attributes images, of which geologic features are enhanced. The attribute filtering improves the correlation
between the attributes and the well data and the estimates of the reservoir properties. The differences between
the estimates obtained by External Drift Kriging and Collocated Cokriging are also reduced.
-
-
-
Estudio Geofisico De Los Depositos De Grafito, Area Osumita, Estado Cojedes, Venezuela
Authors Nuris Orihuela Guevara and Laura PiñeroEn el contenido de este trabajo se presentan los resultados de la evaluación geofísica preliminar desarrollada en la zona del Cerro Osumita, Estado Cojedes. A partir del objetivo de la evaluación: Mineralización de Grafito Cristalizado, se selecciona la técnica electromagnética (EM) descrita como VLF, esperando respuestas EM suficientemente significativa como para distinguir en profundidad la mineralización de su roca caja descrita esencialmente como rocas metamórficas. Para cumplir con este objetivo fueron levantados dos perfiles de orientación NW-SE en los cuales se midió la componente en fase (%F) y la componente en cuadratura (%Q) del campo resultante. A partir de esta información se genera la interpretación cualitativa y cuantitativa de resultados de la cual destaca la presencia de 2 cuerpos de grafito distribuidos en 1250 m a lo largo del perfil I, de estos se considera de interés comercial sólo uno de ellos. Adicionalmente se debe indicar que existen dificultades en la interpretación de resultados en la franja norte del perfil antes indicado motivado en la presencia de cambios en las propiedades electromagnéticas de la roca caja.
-
-
-
Salt-Tectonics Provinces Across The Continental-Oceanic Boundary In The Brazilian And West African Margins
Authors W.U. Mohriak, M.P.A. Jackson and C. CramezRecently acquired seismic data extends from the platform toward the continental-oceanic crustal boundary in
ultradeep water along the South Atlantic conjugate margins. Preliminary interpretation, particularly along a
regional transect in the Eastern Brazilian margin, reveals four main salt tectonics provinces that correspond to
tectonic domains: the proximal (shelf to upper slope); the intermediate (mid to lower slope), the salt diapir
province (lower slope to deep basin), and the deep basin to oceanic crust domain. Extensional tectonics
predominate in the proximal and intermediate domains, whereas the deep-water domain is characterized by
compressional features. The transition from rifted continental to oceanic crust is characterized by volcanic
features, igneous intrusions and wedges of seaward-dipping reflecto.
-
-
-
Method Of Transformation Between Reflector Dip Angle And Stratigraphic Dip Angle
By Niantian LinThe calibration of stratigraphic horizon usually depends on outcrop data when interpreting seismic data in frontier area
where there is lack of well. The outcrop data is often expressed as the stratigraphic dip angle, how can we directly and
easily transform the stratigraphic dip angle from depth domain to time domain. The paper derives a depth-time
transformation equation of the stratigraphic dip angle with various scale parameters of seismic section and outcrop data
by analytic geometry, which may be suitable for the depth-time transformation under any geological structural feature
and other field.
Keywords: Stratigraphic dip angle, Reflector dip angle, Depth-time transformation.
-
-
-
The Magnetotail During Geomagnetic Perturbed Periods
More LessBy studying geomagnetic indices and interplanetary magnetic field records, two geomagnetic storm characterized by
Dst peak less than -100 nT are researched. Both intervals are characterized by substorm events with important
maximum amplitude values (AE index greater than 800 nT) which don't contribute in the same manner, to build the ring current.
The lack of the satellite data during both geomagnetic disturbances do not allow to estimate the plasmoid energy. Some
hours without data could indicate the disappearance of plasma and magnetic field into the plasmasheet.
-
-
-
Utilização De Dados Gamaespectrométricos No Auxílio Ao Mapeamento Geológico Da Região De Barra Bonita, Cerro Azul-Pr
Authors M. Liki, B. Trzaskos and F.F. VeselyThe present paper discuss a geological–geophysical study at Cerro Azul district, State of Paraná, Brazil, in an
area of 42 Km2. The district is part of the Proterozoic Ribeira fold belt, and it contains metamorphic rocks, two
syncollisional granitic intrusions (Três Córregos and Morro Grande) as well as Mesozoic mafic dykes.
Comparing geological map and gamaespectrometrical data (K, U, Th) aerial and terrestrial, it was observed that:
1) the thorium values and profiles seem to reflect the distinct litologies of the area; 2) potassium maps and
profiles show the contacts between granites and host rocks, as well as, the different facies at the Três Córregos
granite; 3) comparing the U, K and Th values of the two granite bodies, Morro Grande is more radioactive.
-
-
-
Caracterización Sísmica Del Corte Geológico En El Cinturón Sobrecorrido Cubano. Nuevas Estructuras Para La Búsqueda De Hidrocarburos
Authors Sofia López, Rafael Socorro, P. Vedado and C. HabanaEl archipiélago cubano es un cinturón plegado y sobrecorrido desde el Cretácico Superior
hasta el Reciente, derivado de la colisión del arco volcánico cretácico con el margen
continental de América del Norte, por 10 que presenta una geología muy compleja dentro
del área del Caribe.
Desde 1972 hasta nuestros días se han adquirido más de 10 000 Km. de líneas sísmicas 2D
y 2 levantamientos 3D, se han perforado más de 1500 pozos a más de 1500m y existen
levantamientos gravimagnetométricos en varias escalas. Todos estos datos muestran la
complejidad y variabilidad de las condiciones sismogeológicas, particularmente acentuadas
en la Provincia Gasopetrolífera Norte Cubana, donde se localizan los dos yacimientos más
importantes de Cuba “Varadero” y “Puerto Escondido”, asociados a las rocas carbonatadas
del margen continental.
-
-
-
Upper Mantle Seismic Velocity Structure Beneath Se Brazil From P- And S-Wave Travel Time Inversions
Authors Martin Schimmel, Marcelo Assumpção and John VanDecarWe present preliminary results from teleseismic travel time inversions for P- and S-wave data mainly recorded at portable broadband stations in SE Brazil. The stations have been employed at more than 27 sites within an area of 500 km x 1000 km during the years 1992 - 1998. More than 3800 relative P- and 3900 relative S-wave arrival times, including core phases, have been obtained from the waveforms simultaneously recorded at 4 or more stations. The model is parameterized by splines under tensions and the P and S relative phase times are independently inverted for slowness perturbations, earthquake relocations, and station corrections. The final models represent the least amount of structure required to explain the residuals within a defined standard error. The results confirm the existence of a fossil plume conduit, permit a more detailed separation of geological structures and velocity perturbations down to about 1000 km depth.
-
-
-
Ray Tracing By Simulated Annealing In Complicated 3-D Models
Authors Danilo R. Velis and Tadeusz J. UlrychWe present a novel ray-tracing method for obtaining the minimum traveltime raypath connecting any two fixed points in complicated 3-D geological models.
-
-
-
Determinação Da Velocidade De Sedimentação Da Baia De Todos Os Santos Usando Pb-210
More LessCinco testemunhos de sedimento da parte norte da baía de Todos os Santos foram analisados para Pb210. Os
testemunhos eram compostos majoritariamente por areia fina, seguida de areia muito fina e lama. No testemunho BTS2,
a atividade do excesso de Pb210 em fatias de 1 cm esteve entre 0,475 e 0,073 dpm g-1, com uma atividade do Pb210
suportado de 0,379 dpm g-1, os quais estão dentro dos valores esperados para sedimentos marinhos ricos em areia.
Para este testemunho, o fluxo anual de massa foi de 545 ± 61 mg cm–2 a–1, ao qual corresponde uma taxa de
sedimentação de 0,218 ± 0,024 cm a-1. Nos testemunhos BTS1, BTS3, BTS4 e BTS5, a atividade do Pb210 foi
praticamente constante com a profundidade sugerindo que o material foi remexido recentemente.
-
-
-
Construção De Um Espectro-Fotômetro Para Monitoramento Da Temperatura Da Mesopausa Na Região Polar Antártica
Authors Cristiano Max Wrasse, Hisao Takahashi and Geancarlos Guedes RettoriUm espectro-fotômetro, para observar a emissão de luminescência da hidroxila está sendo construido
no laboratório LUME do INPE. O fotômetro mede o espectro do ramo P da banda OH(8,3), determinando a
temperatura rotacional da molécula. Esta temperatura rotacional indica a temperatura cinética da atmosfera
ambiente. Portanto a emissão do OH pode ser utilizada para monitorar a temperatura da atmosfera na região da
mesopausa. O presente trabalho apresenta o objetivo, metodologia e o diagrama de blocos do fotômetro em
construção.
-
-
-
Imageamento Do Airglow Em Cachoeira Paulista (23 S, 45 W)
More LessUm sistema de imageamento Instalado em Cachoeira Paulista (22.70 S, 45.00) usando uma câmera CCD com
quatro filtros de interferência realiza medidas rotineiramente durante 15 dias de cada mês. São imageados o OI
557,7 nm, o OI 630,0 nm, a banda de Meinel OH(6,2) na região do infravermelho próximo (<930 nm) e o
background contínuo em 578 nm. Foram observadas estruturas de ondas na emissão do OH e em alguns
períodos bolhas de plasma no OI 557,7 nm e OI 630.0 nm. Apresentaremos e discutiremos algumas destas
imagens.
-
-
-
Interpretación Del Levantamiento Aerogeofísico Complejo 1:50000 Del Nordeste De La Provincia De Hlguín (Cuba)
More LessEl área de estudio está ocupada en más de un 85 % por rocas típicas de corteza oceánica pertenecientes al complejo ofiolítico Moa \endash Baracoa. Los datos aeroespectrométrico y magnéticos que cubren dicha área pertenecen al levantamiento aerogeofísico complejo 1:50 000 del extremo oriental de Cuba. Su interpretación compleja enriqueció el conocimiento geológico del área aportando nuevos elementos litoestructurales. Inicialmente a los datos aeromagnéticos se le realizaron varias ransformaciones del campo: reducción al polo, cálculo de gradientes, mapas de relieve sombreados y Continuación Analítica Ascendente (CAA), a partir de las cuales se generaron mapas que fueron analizados de manera conjunta durante la interpretación.
Los datos aeroespectrométrico de contenidos de eU (ppm), eTh (ppm), K (%) y sus radios (U/Th, U/K y Th/K) fueron representados en forma de imágenes en las cuales se analizaron sus distribuciones espaciales y correlación con las litologías presentes en el área. El análisis combinado de la información geológica y geofísica permitió: definir las áreas de predominio de las principales litologías, zonas de mayores y menores espesores de las serpentinitas, delimitar áreas de alteraciones hidrotermales, definir la forma, extensión y el carácter supuesto y comprobado de las principales estructuras disyuntivas, ubicar posibles frentes de escamas decabalgamientos, corroborar el carácter alóctono del complejo ofiolítico en esta región, delimitar las áreas de desarrollo de las cortezas lateríticas ferroniquelíferas y valorar el grado de meteorización de las ofiolitas serpentinizadas, así como las zonas de mayor enriquecimientos de Vanadio dentro de los yacimientos de lateritas ferroniquelíferas.
-
-
-
Two-Pass 3D Prestack Time Migration
Authors Andre R. Rosa, Carlos Cunha, Ivan Pedrosa, Jairo Panetta, Silvio Sinedino and Vera BragaWe describe a method to perform two-pass 3-D Kirchho prestack time migration whose com-
putation time is nearly the square-root of that required for the one-pass algorithm. To better
understand the conditions and restrictions associated with the application of the method we
discuss the kinematical approximations involved in its derivation. A real data example shows
that this approach can be applied with success in areas with moderate structural complexity.
-
-
-
A Wave-Equation Modeling And Migration Algorithm For Anisotropics Media
Authors Ricardo A.R. Fernandes and Irshad Raman MuftiThe interpretation of seismic data acquired in areas characterized by velocity anisotropy is of particular
interest in reservoir geophysics. Foward modeling and adequate seismic migration algorithms can
enhance the dependability of interpretation. We attack this problem by exploiting the most fundamental
property of the anisotropic media which makes them different from the isotropic media, viz., the variation
of velocity with direction. This is accomplished by splitting the wave equation and replacing it by
two or more simpler equations which involve only one spatial derivative but a different velocity in each
case. The evaluation of the wavefield is carried out by setting up a finite-difference model in which a set
of difference relations derived from the simpler equations is used in an alternate fashion. We present
two examples of application, one in 2D and another in 3D.
-