UnB/IG - DISSERTAÇÕES E TESES DE
OUTROS CURSOS
DE PÓS-GRADUAÇÃO NO BRASIL
UNIVERSIDADE FEDERAL DE OURO PRETO
DEGEO -
Departamento de Geologia
Programa de Pós-Graduação
DISSERTAÇÕES DE MESTRADO
Petrologia e Características de Reservatório da Formação Sergi (Jurássico) no Campo de Sesmaria, Bacia do Recôncavo, Brasil. Dissertação de Mestrado, Departamento de Geologia, Universidade Federal de Ouro Preto, MG, 194 pp.
RESUMO
Petrology and characteristics of reservoir in Sergi formation (Jurassic) in Sesmaria Field, Recôncavo basin, Brasil. MSc Thesis; Department of Geology, University Federal of Ouro Preto, Minas Gerais, 194 pp
ABSTRACT
The Sesmaria Field is located on the eastern margin of the Recôncavo rift
basin, Brazil, and produces an average of 250 cubic meters of oil per day,
mostly from the Jurassic sandstones and conglomerates of the Sergi Formation.
This unit was deposited by a braided alluvial system that prograded from NW to
SE through a cratonic basin, previous to rift rupture, under an arid/semiarid
climate. These conditions produced sandy deposits of large original continuity
and compositional homogeneity.
The porosity and permeability of these essentially continuous and homogeneous
bodies were, subsequently, greatly changed by several intense diagenetic
processes, from shallow eodiagenetic to deep mesodiagenetic conditions. The
general sequence of diagenetic phases and processes is: 1) eodiagenetic
precipitates (caliches, silcretes and early dolomite); 2) mechanical clay
infiltration; 3) mechanical compaction; 4) chemical compaction; 5) secondary
quartz and feldspar overgrowths; 6) calcite cementation and replacement of
silicates; 7) secondary porosity generation by calcite dissolution; 8)
reactivation of mechanical compaction; 9) late authigenic precipitates (mainly
chlorite, quartz, albite, titanium minerals and pyrite).
The development of this general sequence was inhibited or even aborted where
early processes were particularly strong, such as in the top of Sergi Formation,
where clay infiltration was abundant.
The mesodiagenetic evolution history records the temperature-controlled
interaction between organic and inorganic materials, and subsurface fluid flow
regimes. These seemingly occurred in a 30 m.y. interval, between upper Jurassic
sedimentation and Aptian oil generation and migration. Reactions with carboxylic
organic acids and convective re-circulation of fluids seem to have been of major
importance in this evolution.
Controlled by this diagenetic evolution, reservoir pore geometry is very
inhomogeneous, from the scale of hundreds of meters to the microscopic, as
evidenced by pore casts and capillary pressure data from mercury
injection-withdrawal. This geometry results in low values of permeability and
poor non-wetting phase recovery efficiency. The presence of large amounts of
interstitial clays, the high complexity of pore geometry, and other reservoir
features require the adoption of specific drilling, evaluation, completion and
production procedures to minimize formation damage and to optimize oil recovery.
Gilberto Athayde Albertão (1993)
Abordagem interdisciplinar e epistemológica sobre as evidências do limite Cretáceo-Terciário, com base em leituras efetuadas no registro sedimentar das bacias da costa leste brasileira
Data da defesa: 19/1/1993
Área de concentração: Sedimentologia/Petrologia Sedimentar
Orientador: Prof. Paulo Pereira Martins Jr. (UFOP)
Co-orientador: Prof. Jorge Carlos Della Favera (UERJ)
Comissão Examinadora: Prof. Jannes Markus Mabesoone (UFPE); Eduardo Apostolos
Machado Koutsoukos (Petrobras); Antonio Manuel Ferreira De Figueiredo
(Petrobras)
Palavras-chave: Limite Cretáceo-Terciário (KT), Bacias Sedimentares Da Costa Leste Brasileira, Anomalia De Irídio, Impacto De Meteoros, Extinção Em Massa, Estratigrafia, Sedimentologia, Geoquímica, Tsunami, Epistemologia
RESUMO
Apesar da
inexistência de estudos com o detalhe requerido para se identificar uma seção
com a passagem Cretáceo-Terciário (K-T) completa nas bacias sedimentares
brasileiras, foram selecionadas para este trabalho diversas áreas, a partir dos
dados disponíveis no arquivo geral de poços da PETROBRÁS e de extensa pesquisa
bibliográfica. Também foram efetuadas descrições de campo bem como análises
petrográficas, micropaleontológicas, de difratometria de raios X, de isótopos
estáveis e de ativação neutrônica. A distinção do tipo de amostragem disponível
nas áreas estudadas (subsuperfície em poços da PETROBRÁS e afloramentos na Bacia
de Pernambuco/Paraíba) implicou um tratamento diferenciado:
(i) nos poços (dois na Bacia de Campos, dois na do Espírito Santo e um na de
Sergipe/Alagoas), amostras de calha (compostas a cada 3m) caracterizam
predominantemente folhelhos de talude. Os resultados das análises químicas foram
submetidos a um tratamento estatístico (estatística elementar e outras análises
mais sofisticadas, como a fatorial e a discriminante canônica), permitindo desse
modo verificar o predomínio de tendências locais, com ciclicidades
inter-regionais. O limite K-T marca também nítidas descontinuidades, dentre as
quais os baixos valores de cálcio são um exemplo;
(ii) os afloramentos estudados na Bacia de Pernambuco/Paraíba (PE/PB) permitiram
um detalhamento maior em nível de descrição petrográfica e paleoambiental: a
Formação Gramame (biomicritos margosos de ambiente nerítico externo) ocorre
sotoposta à Formação Maria Farinha (intercalações entre calcários - biomicritos,
biosparitos e calcilutitos - e folhelhos, depositados em ambiente nerítico
interno); as estruturas sedimentares (estratificações cruzadas hummocky,
granodecrescência ascendente e estratificação ondular, entre outras)
caracterizam uma plataforma (rampa) carbonática dominada por tempestades. A base
da Formação Maria Farinha (em particular a camada assinalada como D) constitui
um depósito sedimentar que indica a atuação de um processo de energia maior que
os demais. Em um nível contínuo de marga, acima do topo da camada D e presente
apenas na Pedreira Poty (município de Paulista, Estado de Pernambuco),
posiciona-se o limite K-T, de acordo com análises micropaleontológicas; nesse
mesmo nível, a análise geoquímica por ativação neutrônica revela uma anomalia
significativa de irídio, coincidente com um máximo no valor de carbono orgânico
total.
Com base nas características particulares da camada D, na "crise" da biota,
verificada através dos dados paleontológicos e nas anomalias geoquímicas,
testou-se uma hipótese explicativa para os processos sedimentares atuantes nas
proximidades do limite K-T, através de uma modelagem semiquantitativa; como
resultado, verificou-se a possibilidade da camada D representar um depósito
gerado por tsunami (maremoto).
Neste trabalho propõe-se que, dentre as áreas estudadas, a exposição da Pedreira
Poty represente a seqüência sedimentar mais completa da passagem K-T, com
evidências do evento (provavelmente impacto) do Cretáceo terminal: anomalia de
irídio (detectada pela primeira vez em baixas latitudes do Hemisfério Sul e, em
particular, na América do Sul) e um possível tsunamito, representado pela camada
D.
Interdisciplinary and epistemological approaching of the Cretaceous-Tertiary boundary evidences, based on reading the sedimentary record of the eastern marginal brazilian basins
Key-words: Cretaceous-Tertiary (KT) Boundary, Eastern Marginal Brazilian Basins, Iridium Anomaly, Meteor Impact, Mass Extinction, Stratigraphy, Sedimentology, Geochemistry, Tsunami, Epistemology
EXPANDED ABSTRACT
The work by Alvarez et al.
(1980), that rekindled the interest in the study of discontinuities of the
geological and biological records of the planet Earth, claims that the biotic
mass extinction taken place between the Cretaceous and Tertiary periods (K-T
boundary) was triggered by the impact of an asteroid of great dimensions on the
Earth. The evidences are anomalous enrichments of rare chemical elements (in
particular iridium) which usually present very low concentrations in the Earth
crust, right in the K-T boundary of sedimentary sequences in Italy, Denmark and
New Zealand.
Recent researches have revealed new information in the study and
characterization of the K-T boundary. They point to peculiarities present in the
boundary layer of different places all through the globe, besides the anomalies
of iridium: shocked quartz, microspherules, microtektites, soot and
identification of tsunamiites and impact craters, both related to the K-T
boundary, have brought new life into the impact hypothesis.
Despite the non-existence of studies on details for an identification of a
complete section with a K-T transition in the brazilian sedimentary basins, some
areas (outcrop data) and drilling wells (subsurface data) have been selected on
a PETROBRÁS data basis. The drilling wells are RJ-1 and RJ-2 (Campos Basin),
ES-1 and ES-2 (Espírito Santo Basin) and SE-1 (Sergipe/Alagoas Basin); some
outcrops from the Pernambuco/Paraíba Basin (Olinda Sub-Basin) were also
selected.
Besides the field descriptions, different samples were collected from drilling
wells and outcrops, and analyzed through the following methods:
(i) petrographic analysis (with magnifying glass, petrographic microscope and
scanning electronic microscope - SEM);
(ii) micropaleontological analysis: planktonic foraminifers and palynological
elements (mainly pollens, spores, algae and dynoflagellates);
(iii) diffractometric analysis (XRD) - bulk rocks and clay minerals;
(iv) stable isotopes analysis (carbon and oxygen) and insoluble residue (IR) and
total organic carbon (TOC) analyses;
(v) special geochemical analysis ("microchemical" and through the solid-state
energy dispersive X-ray analyser - EDS - attached to the SEM);
(vi) instrumental neutronic activation analysis (INAA), which provided
concentrations for 46 chemical elements, including iridium (it was performed by
the Los Alamos National Laboratory team, USA).
Two different kinds of sampling (subsurface and outcrop data) called for two
different treatments.
It is visible through petrographic analyses of the cutting samples (subsurface
data) that lithologies in the drilling wells comprise mainly slope shales.
Besides, the same data were submitted to mathematic treatment: simple
statistical analyses (means, variances, T and F tests etc.), factor analysis and
discriminant canonical analysis. The result of the factor analysis led to the
definition of a group of chemical elements representative of various profiles to
the selected drilling wells; it also attested to the predominance of specific
behaviours with local tendencies and conspicuous cyclicities of inter-regional
character; the discriminant analysis showed not only a very clear discontinuity
of the chemical data but also of the mineralogical data between the Cretaceous
and Tertiary periods.
Outcrops studied in the Pernambuco/Paraíba Basin (in special the ones in the
Poty Quarry, near Recife, and Ponta do Funil area, near Goiana, both in the
State of Pernambuco) led to a bigger detailing on a petrographic and
paleoenvironmental basis; these outcrop samples were also submitted to greater
number of analysis. The Gramame Formation (marly biomicrites of deep
neritic-upper bathyal environments) is found underneath the Maria Farinha
Formation (intercalations between limestones - biomicrites, biosparites and
calcilutites - and shales deposited in middle-deep neritic environment) with an
erosive lithologic contact. The sedimentary structures (hummocky cross
stratification, fining upwards and wavy bedding) characterize a carbonate
platform (ramp) controlled by storms in a process of progressive marine
regression (interpretation buttressed up by the ichnofossil, geochemical,
paleontological and mineralogical data). The base of the Maria Farinha
Formation, particularly the layer D, is a sedimentary deposit formed through a
process of higher energy than the other layers.
The K-T boundary is situated in a continuous layer of marlstones which is found
only in the Poty Quarry (layer I); the boundary is defined through
micropaleontological analysis where it occurs the major biotic extinctions. At
this very same level, the geochemical analysis shows relevant iridium and TOC
anomalies. Although carbon and oxygen isotopic data reveal some trends, they
seem to be partially influenced by diagenesis.
The special characteristics of the layer D (grain-size, combination and
fragmentation of fossils, abundant and coarse phosphatized fragments, and
sedimentary structures) and the occurrence of geochemical anomalies, right above
its top, on the same layer that sets the K-T boundary biostratigraphically
(layer I), led to the carrying out of a test concerning the hypothesis of the
active processes in this boundary, through a semi-quantitative modelling. The
result obtained showed that it is likely that a tsunami process is responsible
for the settling of the layer D.
We contend that the Poty Quarry outcrops represent, among other areas surveyed
in this work, the most complete sedimentary sequence of the K-T boundary
(sitting around 60cm above the base of the Maria Farinha Formation). There are
evidences of a terminal Cretaceous event (probable meteoritic impact): anomalies
of iridium detected for the first time in low latitudes of the Southern
Hemisphere (in particular in South America) and of TOC, and a possible impact
-generated tsunamiite which is represented by layer D.
Antonio Admilson Peraro (1998)
Gênese de estruturas antiformais observadas em linhas sísmicas no rifte Tucano-Jatobá
RESUMO:
As estruturas antiformais observadas em linhas sísmicas no rifte
Tucano-Jatobá, situado no nordeste brasileiro, foram causadas, essencialmente,
por seis mecanismos diferentes: rollovers, falhas do embasamento, compactação
diferencial, variação de rejeito ao longo de grandes falhamentos, compressões
localizadas associadas a movimentos transtrativos, e dobras forçadas.
Dobras associadas a rollovers são predominantes e podem ser subdivididas em
rollovers simples (único), duplos (falhas sintética e antitética conjugadas) e
com geometria rampa-patamar-rampa.
Dobras associadas à variação de rejeito ao longo de falhamentos e à compactação
diferencial são mais comuns junto à falha de borda do Tucano Sul (Falha de
Inhambupe). As dobras forçadas aparecem próximas à Falha de Adustina (falha de
borda do Tucano Central). Movimentos transtrativos importantes ocorreram no
Domínio Norte do rifte (Tucano Norte e Jatobá), e, portanto, é lá que se
concentram os dobramentos associados à movimentação transtrativa. As dobras
originadas por falhamentos do embasamento aparecem dispersas por todo o rifte,
e, maioritariamente, afetam toda a seção estratigráfica, rifte e pré-rifte.
Todas essas interpretações foram confirmadas por modelagens sísmicas.
Diversas estruturas foram reproduzidas com sucesso em modelagens físicas. A
geometria do falhamento, condição de contorno da modelagem, foi obtida através
da interpretação da seção sísmica e da construção e balanceamento da seção
geológica correspondente. Dados relativos ao balanceamento das seções geológicas
sugerem que a movimentação transtrativa se iniciou tardiamente no Tucano Norte.
A partir de modelagens físicas concluiu-se que as fraquezas preexistentes no
embasamento tiveram papel fundamental na geração e geometria das estruturas
resultantes, por vezes, exercendo maior influência que a orientação dos esforços
que as formaram.
Genesis of antiforms observed on seismic profiles of the Tucano-Jatoba Rift (Northeastern Brazil)
ABSTRACT:
Antiforms observed on seismic profiles of the Tucano-Jatoba Rift located
in northeastern Brazil were formed essentially by six distinct mechanisms:
rollovers, faults related to the basement, compaction, variations in fault
displacement along major faults, local compression associated to transtension
and forced folds.
Folds associated to rollovers are predominant and may be divided into the
following categories: simple rollovers (a single folded structure), double
rollovers (where sinthetic and antithetic conjugate faults are present); and
ramp-flat-ramp rollovers.
Folds originated by variations on both fault displacement and differential
compaction are the most common feature observed next to the Inhambupe Fault
(South Tucano border fault). Forced folds appear close to the Adustina Fault
(Central Tucano border fault). Transtension played na important role in the rift
Northern Domain (North Tucano and Jatobá).
As a result, there is a concentration of folded structures in that region. Folds
caused by basement-related faults widespread along the Tucano-Jatoba Rift,
affecting both the pre-rift and synrift sections. All these interpretations were
constrained by seismic modeling.
Analogue models were successful in generating the structures as interpreted in
the seismic profiles. Fault geometry, the main contour constrain for the
analogues, was provided by an interpreted seismic profile and its correspondent
balanced geological section. The interpretation show evidence that transtension
was late in North Tucano. From the experiments was possible to conclude that
preexistent weak zones in the basement played a fundamental role in the
generation and the geometry of the structures. Their influence on those
strucutres are apparently more important than the stress orientation.