- 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
381 - 399 of 399 results
-
-
Interpreting Avo Anomalies
By D.J. FosterWe investigated the effects of changes in rock properties on
AVO responses. In the slope-intercept domain, reflections
from wet sands and shales fall on a trend, the Fluid Line.
Reflections from the tops of sands containing gas or light
hydrocarbons fall on a trend below the Fluid Line;
reflections from the base of gas sands fall on a trend above
the Fluid Line. The distance of these trends from the Fluid
Line depends upon pore fluid compressibility; i.e., distance
increases with increasing compressibility. But, if all other
factors are equal, base of sand reflections are displaced
further from the Fluid Line than top of sand reflections.
Consequently, base of sand reflections, which identify
down-dip limits and fluid contacts, will be more prominent
than top of sand reflections. Porosity changes affect
acoustic impedance, but do not significantly impact the
Vp/Vs contrast. As a result, porosity changes move the
AVO responsea long trends parallel to the Fluid Line.
-
-
-
From Oblique Rifting To A Transform Margin: The Opening Of The Equatorial Atlantic
More LessFrom oblique rifting to a transform margin, what do we really know about that?
The integrated analysis of the Brazilian and African equatorial basins provided important insights regarding the process
of continental fragmentation through the activation of transform faults. A quite dynamic ruptural process produced an
unique segment among the Circum-Atlantic basins, which can not be adequately explained by conventional extensional
processes, such as passive or active rifting, or by mechanisms such as pure-shear or simple-shear, typical of divergent
margins. Even though shearing signatures and pull apart features are easily recognized throughout the margin, their
magnitude and rift architecture vary significantly accordingly with the distance from the main transform faults, generating
significant differences in the thermal evolution, basin architecture, tectonic subsidence, facies distribution and uplift history.
-
-
-
Defomartional Styls Of The West African Margin
Authors Bruce R. Rosendahl and Henrike Groschel-BeckerReprocessing of the PROBE Study seismic data set indicates that the continental margin between Cameroon
and Southern Gabon is separated into the North Douala and Gabon Basins by the Kribi Fracture Zone. This is
a 75 km-wide transform fault that trends NE-SW and intersects the coastline between 2-3’ N. Much of the
margin off Equatorial Guinea is influenced or controlled by fracture zone tectonics. North of the Kribi
Fracture Zone, oceanic crust extends to the coastline and floors a narrow shelf off Cameroon. Little rift
margin exists in the North Douala Basin. Reflection Moho beneath oceanic crust is relatively weak but
continuous throughout the North Douala Basin and oceanic crustal thickness is extremely uniform,
averaging about 1.75 s in two-way travel time. South of the Kribi Fracture Zone, oceanic crust is offset about
350 km to the southwest, creating a broad rift margin off Gabon. Rifting of the margin here seems to involve
brittle, upper continental crustal sheets overlying a series of ductile lenses that generally dip southeasterly.
The ductile lenses may unroof toward outer highs, which mark the boundary between oceanic and
continental lithosphere. Strong reflection events are often associated with the ductile shear zones that define
the lenses, but a single, continuous event representing reflection Moho cannot be mapped. The concept of a
regional reflection Moho beneath rifted continental crust may be flawed in this area. The tectonic and
rheological models presented here may be useful in framing hydrocarbon exploration tactics and strategies
along this passive margin.
-
-
-
Facies Recognition Using Wavelet Based Fractal Analysis On Compressed Seismic Data
Authors Juan R. Jiménez, Adrian Peinado and Reinaldo MichelenaWe present in this paper a method to analyze seismic data in the compressed domain which measures the changes in
the variance of the wavelet coefficients as a function of the scale of the transformation. After applying this method to
resistivity logs, acoustic impedance logs, and 3D seismic data around a Eocene, clastic reservoir, we show the wavelet
coefficients themselves contain relevant information about the subsurface that can be used for seismic based facies
classification without having to through the reconstruction process.
-
-
-
Estructura De La Cuenca De Antepaís En La Zona De Sutura De La Región Esmeralda - Minas, Provincia De Camagüey Según Datos Gravimétricos
More LessLa región de estudio se ubica al norte de Camagüey, extendéndose desde el poblado de Esmeralda hasta Minas
por todo el sur de la Sierra de Cubitas. En la misma se observa un amplio desarrollo de las ofiolitas
septentrionales en contacto tectónico con las rocas carbonatadas del paleomargen de Bahamas. Las ofiolitas
emplazadas tectónicamente sobre el margen, cubren los sedimentos de la cuenca de antepaís desarrollada en
el proceso de colisión oblicua entre las secuencias del Arco de Isla Volcánico del Cretácico y el Paleomargen
meridional pasivo de la Placa de Norteamérica.
A partir de la digitalización del mapa gravimétrico de la región a escala 1:100 000 se realizaron diferentes
transformaciones del campo, tales como: cálculo de gradientes horizontales y verticales, Saxov\endash
Nygaard y Continuación Analítica Ascendente (CAA), aportando nuevos elementos que enriquecieron la
interpretación durante la correlación de la información geofísica y geológica, contenida esta última en el mapa
geológico 1:250 000.
El análisis conjugado de la información disponible permitió corroborar y profundizar en la ubicación, forma,
extensión y dirección de las principales estructuras disyuntivas presentes en la región (Camagüey, Cubitas), así
como la delimitación de la Cuenca Saramaguacán y los principales rasgos estructurales de la zona de la cuenca
antepaís sobrecorrida por las ofiolitas. Además se logró delimitar las áreas de desarrollo de los granitoides
tanto en superficie como en profundidad.
La modelación de varios perfiles que atraviesan el área aporta nuevos datos sobre la potencia y profundidad de
yacencia probable de la secuencia ofiolítica y su relación con los granitoides del arco volcánico y las
secuencias carbonatadas del Paleomargen de Bahamas.
-
-
-
Distribution Pattern And Sedimentation Of The Neogene Deep Water Section In The Campos Basin, Offshore Brazil
Authors Carlos E. Souza Cruz and Ciro Jorge AppiThe Campos Basin, offshore Rio de Janeiro State, was a deposition site of a thick deep-water sedimentary
section (maximum of 2500 meters) on the continental slope and basin during the Neogene (fig.1).
In Campos Basin the cycle boundaries are the key elements of sequence stratigraphy which can be identified in seismic
sections by conventional seismostratigraphy methods, well log correlation and biostratigraphy. Several third-order
unconformity events were identified in the studied interval (fig.2). Despite the good correspondence of cycle boundaries
with the global eustatic lowering, the sequence stratigraphy model does not explain the sequence pattern observed in
Campos Basin. This holds true especially with regard to the nature of deep-water wedges and some erosional
unconformities associated with them. These wedges consist entirely of deep-water facies with bathyal faunas, differently
from the conventional sequence stratigraphy model (fig.2).
-
-
-
Arco’S 2Nd Generation Large Screen Immersive Visualization Environment
Authors Tracy J. Stark, Geoffrey A. Dorn and Mary J. ColeIn 1996, ARCO began the construction of an Immersive Visualization Environment, which was
completed in 1997. This environment was designed to allow us to use commercially available software,
and to build proprietary immersive geoscience applications in order to reduce the cycle time and improve
the accuracy of making well location decisions. This environment consists of a 10x10x10 foot CAVE™
like structure. During more than two years of experience, we found the very immersive CAVE™ like
environment to be extremely valuable for working sessions of three to five people. We also found that
meetings had to be limited to 15 people due to the size of our environment. Therefore, we developed a
conceptual design of a second-generation system, which can be used for both high immersion work
sessions, like the system we currently have, and predominantly large group presentations. At the end of
1998, MechDyne was contracted to do an engineering design of such a reconfigurable visualization
environment. We budgeted for its construction in early 1999. The new system has flat screens, which are
superior to curved screens, and has open and closed configurations. The closed configuration is ideal
for a few people to work on their data in an immersive environment, while the open configuration is better
suited for displaying their results to a much larger audience. The system is designed to be reconfigured
from open to closed in about one hour.
-
-
-
Puesta A Punto Y Calibración De Medidores De Contaminantes Atmosféricos Gaseosos Y Variables Meteorologicas, Com Sistema De Trasmisión De Datos A Distancia
Authors B. Valenzuela B. and P. Pacheco H.El presente trabajo muestra la puesta a punto y calibración de un conjunto de medidores de contaminantes
atmosféricos (NOX, O3, NH3) y variables meteorológicas (dirección y velocidad del viento, temperatura, presión
atmosférica, radiación solar y humedad relativa), con la finalidad de testear la sensibilidad del instrumental. También se
somete a prueba el sistema de recepción y transmisión de datos a distancia. Finalmente, las mediciones se comparan
con instrumentos similares administrados por el SESMA de Santiago de Chile, normados según EPA.
-
-
-
A Case Study: Using 3D Pre-Stack Depth Migration To Improve The Sub-Salt Image In Marbella, Mexico, Gulf Of Mexico
By Mark MorfordMarbella is an area with extensive salt domes and salt sheets combined with complex compressional features. The 3d time
migration performed on the dataset was insufficient to resolve the imaging problems in this complex area. In the time
migrated dataset there were problems defining the base of salt for most of the survey and the sub-salt faults and sub-salt
sediments were also not imaged. The purpose of this study was to build a geologically based velocity model and apply 3d
pre-stack depth migration in order to better image the base of salt and sub-salt sediments.
-
-
-
Major Types Of Deep-Water Reservoirs From The Eastern Brazilian Rift And Passive Margin Basins
More LessTurbidites and associated deep-water facies comprise the most important petroleum reservoirs in Brazil.
They contain original in place volumes of 57.2 billion bbl of oil, and 27.5 trillion cubic feet of gas, and total
reserves of 12.5 billion bbl of oil, and 8.3 trillion cubic feet of gas. Brazilian petroleum-bearing turbidites occur in
(1) CarboniferouslPermian, glaciomarine pre-rift (interior cratonic) successions, (2) Neocomian to Aptian,
lacustrine rift successions, and (3) Upper Albian to Lower Miocene, marine passive margin successions. Most of
the petroleum accumulations are distributed along the eastern Brazilian margin, which tectonic and sedimentary
evolution is linked to the Neocomian breakup of Gondwana and the subsequent opening of the South Atlantic
Ocean. Turbidites comprise 553 production zones from 171 oil and/or gas fields, mostly concentrated in the
Campos, Reconcavo, SergipelAlagoas, and Espirito Santo basins. This paper presents an overview of the
sedimentary facies, high-resolution stratigraphy, sandbody geometry, and reservoir heterogeneities of the major
types of Brazilian deep-water reservoirs, which include (1) gravel/sand-rich, turbidite channel complexes, (2)
trough-confined, gravel/sand-rich turbidite lobes, (3) unconfined, sand-rich turbidite lobes, (4) sand/mud-rich
turbidite lobes, (5) gravel/sand-rich turbidite and debrite aprons, (6) deposits of sand-rich, lacustrine density
underflows, (7) deposits of sand/mud-rich debris flows, and (8) deposits of sandy bottom currents.
-
-
-
The Alba Field Obc Seisnic Survey
Authors M.K. MacLeod, R.A. Hanson, M.J. Hadley, K.J. Reynolds, D. Lumley, S. McHugo and A. ProbertIn early 1998, Chevron acquired one of the world’s first full-field four-component ocean bottom cable surveys at the Alba
field in the central UK North Sea. The primary objective of the survey was to use converted shear waves to image the top
of the reservoir and internal shales within the reservoir interval. The secondary objective was to map water movement in
the reservoir after four years of production and water injection by comparing the P-wave OBC data with the original 1989
streamer data. Our initial interpretation shows that both objectives were achieved with dramatic results – the converted
shear wave images provide the clearest image of the Alba reservoir sands ever seen and production effects are obvious
on the new P-wave OBC data.
-
-
-
A Ten-Year Lightning Climatology For The United States (1989-1998)
More LessMore than two hundred million cloud-to-ground lightning flashes have been recorded in the last ten years in the
continental United States. We have the first decadal climate of lightning that reveals year-to-year variations, but also
persistent features that repeat every year. Maximum flash densities occur in Florida, but also in the upper Midwest and
over the Gulf Stream east of the Carolinas. Relative minimums in flash density are observed over the mountains in the
west and over the Appalachian Mountains in the east. The dominant polarity of the charge brought to ground, termed
negative and positive lightning, varies with the season and latitude. The positive flash density appears to be a function of
geographic altitude, but the negative flash density is apparently not a function of geographic elevation. Explanations for
these observations will be proposed.
-
-
-
Geophysical And Log Characterization Of Roncador Field, Campos Basin, Brazil
More LessRoncador oil field is a giant accumulation located in the northern area of Campos Basin, Brazil, in a bathymetric
contour varying from 1,500 to 1,900m. The reservoirs are maastrichtian turbidites and based upon their
distribution, the field may be divided in three areas (SE, SW na N). In the southeastern part five main zones are
identified; the sandstones are interbedded with shales and only the upper part may be associated to
conventonal sesmic amplitude anomaly. In the southwestern area of the field, the turbidites are amalgamated,
indicating incomplete depositional cycles except the highest part of the sequence where interbedding shales are
present. The northern area of Roncador acted as a bypassing zone during the lower sandstone deposition time
in the southern area of the field and only the the upper reservoirs were deposited. The sandstones are
characterized by textural and compositional immaturity. The rate of subsidence associated with halokinesis and
the preservation of sediments from erosion control the reservoir distribution differences along the field.
-
-
-
Petroleum System And Seismic Expression In The Campos Basin
The petroleum systems of the Campos Basin contains 60 billion barrels of discovered oil in place and
775 billion cubic meters of natural total gas in place, comprising one of the most prolific petroleum systems in
South America. It is located in southeast Brazil covering about 100,000 km2 with 44 oil fields, seven giants,
holding up to 90% of total Brazilian oil reserves and 50% of total natural gas reserves.
The Campos Basin produces mostly from turbiditic sandstones of the Carapebus formation
(Cretaceous-Tertiary), comprising the biggest part of the total production. Other important reservoirs are
calcarenites of the Macaé formation (Albian), bioclastic lacustrine limestones of the Lagoa Feia formation
(Barremian), and fractured basalts of the Cabiúnas formation (Neocomian).
The source rocks are saline-to-brackish lacustrine water shales of the Lagoa Feia formation (Barremian)
containing 5% TOC average, an average thickness about 100m with a maximum of 500m in depocenters,
covering approximately 50,000 km2.
Trapping style is chiefly structural for the Cabiúnas formation; structural-stratigraphic for the coquinas
(bioclastic limestones of the Lagoa Feia formation), where pinch-out of the coquinas is a common feature;
strongly structural for the calcarenites of the Macaé formation (rollovers related to salt tectonics), and finally
structural combined with sandstone pinch-out for Cretaceous and Tertiary turbidites of the Carapebus formation.
At the Corvina-Parati depocenter, thermal basin modeling suggests the onset of oil generation in late
Albian, reaching its maximum during the Miocene and it is still going on to present days. The top of oil window
is about 4,500m deep and transformation rate reaches up to 70%.
Seismically, the Campos Basin shows distinct response and characteristics according to lithologies
and ages. The lowermost sequence (Lagoa Feia and Cabiúnas formations) is poor in seismic attributes; the
geological model is more adequate for mapping reservoirs and defining best leads. From Middle Cretaceous up
to Miocene, the seismic attributes, such as amplitude anomalies, instantaneous phase, instantaneous
frequency, and AVO, have been used for defining reservoir geometry, and as good hydrocarbon indicators.
The events chart portrays the temporal relationship between elements and processes of the Lagoa Feia-
Carapebus (!) petroleum system in the central area of the basin, accountable for the Marlim oil field charging.
The success for oil exploration in the Campos Basin stems from the presence of excellent source rocks
and reservoirs, late migration, presence of internal structural highs, but mostly for the commitment to face deep
water exploration challenges.
-
-
-
An Outlook On The Petroleum Potential Of The Brazilian Deep Water
Authors C.F. Lucchesi and Lincoln R. GuardadoIn the middle 50’s, at the beginning of its exploratory history, Petrobras focused its efforts on the large paleozoic
basins and on the onshore portions of the Brazilian marginal basins. Large intracratonic basins spreaded from the
Equatorial Amazon jungle (Acre, Solimões and Amazon basins) and arid northeast (Parnaiba Basin) to the well
developed south-southeast region (Paraná Basin), and small onshore cretaceous marginal basins from the
northern coast (São Luiz and Barreirinhas basins) to the eastern coast (Recôncavo, Tucano, Sergipe-Alagoas,
Bahia–Sul and Espírito Santo basins) were explored. Field geology, gravity, and magnetics surveys, followed by
seismic and finally by wildcat wells, were the tools used on those early years. Despite some occurences in the
paleozoic basins, important commercial discoveries in onshore basins were restricted to the Reconcavo and
Sergipe-Alagoas marginal basins.
-
-
-
Late Tertiary-Quaternary Structural Styles: Serraria Del Interior Oriental Foothills, Northeastern Venezuela
More LessCompressive structures have been identified , along the Serranía del Interior Oriental Range foothills, using 2D
seismic reflexion profiles, recorded by PDVSA. Major tectonic elements, shown are: Urica fault, Tala - Pirital
thrusts and the Mud-diapir trend. Thrusts and associated ramps occurred during the Late Miocene - Pliocene.
Extensional features to the east, might have been triggered during the last 5 Ma. by remobilisation of lower
Miocene shale.
-
-
-
3D Prestack Kirkhoff Beam Migration For Depth Imaging: Theory And Data Exemplos
Authors Yonghe Sun, Fuhao Qin, Steve Checkles and Jacques LeveilleWe present a beam implementation for 3D prestack Kirchho depth migration of seismic data. Unlike conven-
tional Kirchho migration in which the input seismic traces in time are migrated one at a time into the 3D image
volume for the Earth's subsurface, the beam migration processes a group of input traces at a time. The migration
of each group of traces, or supergather, consists of two major steps: slant stacking the traces into a
-
-
-
Depth Imaging In Deep Waters: A Case History
Authors Luigi Pizzaferri, Cesare Alberti, Giuseppe Bricchi, Fabio Luoni and Marco MarchesiniThe paper outlines the methodological approach followed to solve a complex problem of depth imaging in the
Nile Delta, offshore Egypt. The original time image was thought as being distorted not only by sea bottom
variations (from few hundred to a thousand meters) but also by the presence of large scale (thick Pleistocenic
sequence at high velocity) and smaller scale velocity anomalies (low velocity shales and high velocity
evaporites).
In the study area the possible target Miocene reservoirs lie below a thick sequence of Plio-Pleistocene
sediments and are sealed by an evaporitic sequence of varying thickness. Moreover the Miocene sequences
have low but almost uniform velocity, thus causing poor reflectivity and hence a poor signal-to-noise ratio.
An exploratory well (Well-1) did find an unexpected thick layer of relatively high velocity Pleistocene instead of
prognosed low velocity Pliocene. This caused a complete rethinking of the depth conversion approach followed
so far. It was decided to use the most up-to-date technologies, like Pre-Stack Depth Migration (PrSDM), to attack
the problem. Since there were constraints either in term of budget and time, it was decided to use 2D PrSDM
along 22 inlines to determine the velocity field and then perform a full 3D Post-Stack Depth Migration (PoSDM)
of the entire volume. This would have allowed a good compromise in terms of cost - benefit ratio. The final
depth volume showed quite clearly that a double culmination present in time turned out to be a single
culmination, yet to be drilled. A strict integration between depth imagers and the geologists and geophysicists
acquainted with the complex area proved to be one of the winning factor in the succesfull completion of the
study together with the use of PrSDM tools in the construction of the velocity volume.
-
-
-
Turbidite Slope Channels
Authors Mike Mayall and Ian StewartExtensive 3D seismic data from West Africa has started to show remarkable details of the geometry and facies of
Tertiary turbidite slope channels. The slope systems which have been studied are characterised by subtle to complex
topography created by salt or shale diapirism or faults. In the upper part of the slope the channels are often relatively
narrow (<1km) with fairly straight leveed margins which may or may not contain a moderate-high sinuosity channel axis.
Downslope the channels become broader (1-2km), highly sinuous (sinuosity >2) with erosional bases and local levee
and crevasse-splay development. In this part of the slope the channels typically show a vertical sequence which
comprises an erosional base, a coarse grained lag (by-pass phase), slumps and/or debris flows (locally derived or more
distant transport?), high N:G sandy fill of stacked channels which may be straight or sinuous and finally a lower N:G with
highly sinuous channels and levees. The relative proportion of each of these facies can vary significantly.
Moderate to high sinuosity is a characteristic of many of the channels however a range of sinuosity styles are present
these include i. Sinuosity controlled by local sea-floor topography ii. sinuous channels which show dominantly vertical
aggradation iii sinuous channels which show successive lateral shifts in the channel axis and iv. Channels, usually on a
smaller scale (10’s to 100m wide) which may show inclined reflectors dipping in the direction of channel migration. It is
this latter form of sinuosity which produces features very similar to fluvial systems. Facies seen in cores indicates that
turbidity current and debris flows process are dominant in all cases.
In our experience ponded systems i.e. basins in which the channel systems terminate on the slope as a result of slope
topography, are not common. The appearance of ‘ponding’ can be a function of the extent of the 3-D data set. In areas of
smaller data coverage it is often easy to interpret channel systems terminating in intra-slope basins. However with
increasing coverage of 3-D data the channels can usually be seen to have continuous but very convoluted courses which
takes them through and beyond complex slope topography. At sharp bends in channels it is common to observe sheetlike
seismic facies (although generally thin), extending away from the channels.
Topographic constraints within the slope topography may locally fix the course of the channel system for some time while
down-slope of the constriction the channels take different, usually compensatory off-setting courses through time.
Associated with the channels are more sheet-like seismic facies. The origin of these features is less clear and quite
possibly they have multiple origins. They may be parts of levees of the larger channels, minor splays which were
deposited laterally, splays which are an initial part of the channel avulsion process (similar to the HARPs of the Amazon
Fan), or by processes unrelated to the major channels.
These Tertiary channel systems have very similar geometries to those observed in many modern fans such as the
Amazon and the Zaire and pose many questions regarding the nature of the currents which transported and deposited
the sediments.
-