Espirito Santo Basin Research Articles

Modelo geológico evolutivo e deposicional do paleocânion de Regência, região onshore da Bacia do Espírito Santo, Cretáceo ao Eoceno

O paleocânion de Regência, reconhecido em subsuperfície na Bacia do Espírito Santo, foi originado no Cretáceo e preenchido até o Mesoeoceno. Dados de 31 seções sísmicas, 29 poços e marcadores bioestratigráficos substanciaram a elaboração de modelos geológicos que aprimoram o conhecimento sobre a evolução e a morfologia do paleocânion. Os resultados incluem correlações estratigráficas, interpretações de feições estruturais e das principais superfícies estratigráficas (topos das formações Mariricu, São Mateus, Regência e Urucutuca), mapas de contorno estrutural dos topos litoestratigráficos e seções esquemáticas. Desde seu início, o paleocânion foi estruturado por falhas no embasamento. Próximo ao topo da Formação Mariricu, de idade aptiana, já há indícios de geometria de extensa calha rasa. O paleocânion é dividido pela Zona de Charneira Cedro-Rio Doce (ZCCRD), sistema de falhas normais de direção N-S. A morfologia do paleocânion também foi controlada por diversas falhas normais nos blocos proximal e distal à ZCCRD, originadas no embasamento, ainda ativas quase até o final do preenchimento do paleocânion, com direção NE-SO. Falhas normais também tiveram papel determinante na origem de um canal secundário de grande porte a sudoeste, assim como outros menores ao longo da margem norte. Na porção proximal, depósitos neocretácicos foram preservados devido a abatimento e rotação de blocos por falhas normais. Pode-se inferir que o preenchimento eoeocênico proximal foi por sedimentos da mesma fonte que aqueles acumulados no depocentro do paleocânion. Refletores sísmicos sugerem a presença de abundantes canais escavados e preenchidos na porção inferior do cânion e transição cânion acima para canais dispersos. O conjunto de interpretações é sintetizado esquematicamente por meio de um modelo geológico evolutivo e deposicional.

On the taxonomy of the genus Cyclaspis Sars, 1865 (Crustacea: Cumacea: Bodotriidae) from the Brazilian coast, with three new records and descriptions of three new species

Cumaceans are an important component of the macrobenthic fauna and are preyed upon by several species of fishes. In the family Bodotriidae, Cyclaspis Sars, 1865 is the most speciose genus with more than 140 described species. Based on material from the Campos Basin and Espirito Santo Basin, southwestern Atlantic, we describe three new species of Cyclaspis: Cyclaspis goytacazes sp. nov., Cyclaspis lilianae sp. nov. and Cyclaspis tesauna sp. nov. We also report C. antipai Petrescu, 1995, C. roccatagliatai Petrescu, 1995 and C. unicornis Calman, 1907 as new records from the Brazilian coast. The first two species were known previously from Uruguay, and C. unicornis from the Caribbean Sea. Of the six species, only C. lilianae sp. nov. was found on the continental slope (415–1320 m) and the other five species were restricted to the continental shelf (18–139 m). A pictorial identification key for the 17 species of Cyclaspis known to occur in Brazil is provided.

CONTEXTO DEPOSICIONAL E EVOLUÇÃO ESTRATIGRÁFICA DE DEPÓSITOS ARENOSOS PLATAFORMAIS A PARTIR DA CARACTERIZAÇÃO SÍSMICA E DE ELETROFÁCIES, MAASTRICHTIANO DA BACIA DO ESPÍRITO SANTO, BRASIL

Corpos arenosos de plataforma, como os cordões arenosos (sand ridges), constituem um significativo tipo de reservatório em bacia de margem continental, o que chama atenção para que esses corpos possam ser melhores estudados e caracterizados. Esse trabalho, localizado na região centro-oeste da bacia do Espírito Santo, visa caracterizar esse tipo de depósito, abordando seus atributos geométricos e anatômicos, e interpretar os principais fatores controladores associados à sua origem e evolução, através de uma abordagem baseada nos princípios da estratigrafia de sequências, culminando com a proposição de um modelo deposicional para os mesmos, a partir de dados sísmico 3D, 2D, além de dados de poços, como perfis litológicos, perfis geofísicos e dados cronoestratigráficos. Os sand ridges, do tipo lençol de areia de plataforma, interpretados na área de estudo são caracterizados por refletores positivos de alta amplitude, contínuos, e apresentam uma geometria em lençol. São intercalados por folhelhos caracterizados por refletores negativos de alta amplitude. Por meio dos elementos estratigráficos e deposicionais identificados, assume-se que esses corpos arenosos foram depositados devido a interações entre uma fonte de sedimentos que abastecia a região plataformal, provavelmente, o “paleocânion” de Fazenda Cedro, a dinâmica de avanço e recuo da linha de costa, além de correntes litorâneas e correntes de tempestade, as quais podem ter retrabalhado esses depósitos ao longo da plataforma.

Role of Brazil’s Continental Slopes in Being Provided with Hydrocarbon Resources

Abstract—Analysis more of 80 hydrocarbon fields, mainly oil-producing, in the deepwater part of the Santos, Campos and Espirito Santo basins reveal the tendency of these large fields to lie in a productive oil-pay belt extending in the sea depth from range from 400 to 2500 m (possibly 3000 m or more) in a system of external depressions stretching along the lower part of the continental slope. This belt may continued to the north. All the fields in this belt in reserves category are estimated as large and giant. In the last 10–15 years, exploration works have been conducted in this belt already in the presalt formation: in the Santos Basin, 29 fields; in the Campos Basin, 21; and in the Espirito Santo Basin 7. It is noteworthy that 48% of the total hydrocarbon production of the country formed in presalt carbonate deposits of the Aptian Formation on the continental slope, 44% postsalt rocks on the continental slope and shelf, and only 8% is attributed to the mainland. In the world, Brazil’s deepwater presalt Aptian Formation (Barremian–Aptian in the Santos Basin) is essentially unique. In recent decades, giant hydrocarbon accumulations have been discovered, thereby doubling the country’s oil and gas reserves to total reserves of more than 3 billion t and 4.7 trillion m3, respectively. The geology of the presalt formation is narrowly related to tectonic movements that took place during the breakup of the Gondwana supercontinent into the South American and African continents. This took place 150 Ma ago in the Early Cretaceous. The salt of the Aptian Formation is an excellent caprock, the presalt reservoirs are superior in their characteristics, the oil is light and sweet, and the source rocks are enriched in organic matter. The thickness of the Aptian salt is limited, varying from basin to basin; the main width of the salt is in the Santos Basin 400 km and the thickness is 2000 m; in the north, the thickness and width decrease; in the Sergipi Alagoas Basin, it already reaches 100 m.

Domínios Estruturais Relacionados à Tectônica do Sal na Região Sul da Bacia do Espírito Santo

The offshore portion of the drift section of the Espirito Santo basin is known for its stratigraphic and structural complexity related to the post-breakup salt tectonics. The movement of the salt deformed the sedimentary record of the drifte phase in the Domos de Sal Province, southern region of the basin, area of study of this work. In this research, structural domains related to salt tectonics were delineated according to the patterns and character of the structures present in the study area. The analyzes were performed using seismic data from 39 2D seismic sections and geophysical and geological data from wells drilled by the oil and gas industry. The stratigraphic-structural styles identified were: nucleated faults nucleated from the zones of detachment, carbonate rafts of albian age, turtle hull structures, domes, diapers, tongues and salt sheets. From the interpretation of structures related to salt tectonics, it was possible to delimit four structural domains. The first domain, present in the proximal region, is marked by the absence or small thickness of salt, structured with lithic faults and well defined zone of detachment; the second domain, in the intermediate portion, presents the association of small saline domes with the turbulent hull-like albian sedimentary section; the third domain displays well- -developed salt walls and walls; while the fourth domain, located in the most distal portion of the study area, presents the diameters with a subtle vergence to the east and salt tongues. With the seismic interpretation of the top of the salt, a structural contour map was generated in seismic time (TWT) that aided the delimitation of these four structural domains, as well as the observation of the alignment of the salt structures, with direction NNW-SSE. From the analysis of the structures present in the first three domains, it is suggested that they are under a distensive tectonic regime, whereas in the fourth domain it is inferred that they are resulting from compressive local conditions. The development of local tectonic regimes related to saline tectonics, which evolve from distensive to compressive in the WE direction, downdip, is explained by the salt displacement to the east caused by the slope geomorphological slope in the Espirito Santo basin and by the overload of subsequent on the platform from the Paleogene.

Arquitetura estratigráfica dos depósitos fluviais albianos da base da Formação São Mateus no norte da Bacia do Espírito Santo

Os depósitos aluviais da Formação São Mateus (Albiano da Bacia do Espírito Santo, Brasil) consistem em importantes reservatórios. Entretanto, existem poucos trabalhos detalhando a estratigrafia deste intervalo estratigráfico. Em decorrência disso, este trabalho teve por objetivo estabelecer um fatiamento estratigráfico de alta resolução da seção basal desta unidade, a qual é constituída por depósitos fluviais. Diante das dificuldades apresentadas para a correlação estratigráfica desses depósitos, a estratégia de correlação utilizada foi a subdivisão da sucessão aluvial em ciclos estratigráficos. Este método se baseia na variação na razão entre as taxas de criação de acomodação e suprimento sedimentar (A:S) que diretamente controla o grau de amalgamação dos corpos arenosos de canais fluviais. Com isso, foram definidos seis ciclos compostos internamente por tratos de sistemas de alta e baixa acomodação. Esses ciclos refletem a estruturação do arranjo da amalgamação dos canais fluviais com os depósitos externos aos canais através da razão entre a taxa de acomodação (A) e a taxa de influxo sedimentar (S) formando ciclos.

Meteoric Water and Salt-Dome-Related Diagenesis in Tertiary Turbidite Reservoirs from the EspÍrito Santo Basin, Brazil

Abstract Quantitative petrography and stable-isotope and fluid-inclusion analysis revealed that the diagenetic evolution of two Tertiary turbidite sandstone reservoirs from the offshore part of the Espirito Santo Basin, eastern Brazil, was influenced by the flow of meteoric water and salt-dome-related fluids, which had different impacts on their quality. Influx of meteoric water during early burial, in response to relative sea-level fall, resulted in extensive kaolinization and dissolution of framework silicate grains. Mesogenetic compactional fluids were progressively modified by the proximity of salt domes, which led to ubiquitous feldspar albitization and localized quartz, calcite, and saddle-dolomite precipitation. Fluid inclusions in quartz overgrowths indicate that the precipitating fluids had salinities predominantly in the range 8–13 wt% NaCl equivalent and temperatures largely in the 100–155°C range (higher than present-day formation temperatures—105° up to 115°C). The distribution of feldspar albitization suggests that the fracture systems along the margins of the salt domes acted as preferential pathways for such hot brines. However, the influence of the salt domes on the diagenetic processes of the reservoirs was relatively mild, despite their proximity, because pore-filling neoformed illite is absent, and occurrence of quartz cement is limited in the sandstones, which may be related to the late burial of the reservoirs and the intermittent behavior of the salt-dome-associated fracture systems as effective conduits for reactive fluids. We expect that this paper may contribute to the understanding and prediction of diagenesis and reservoir properties of turbidite sandstones influenced by meteoric and salt-dome-related fluids in offshore Espirito Santo Basin and in other similar areas.

Differential compaction over Late Miocene submarine channels in SE Brazil: Implications for trap formation

We used high-quality three-dimensional (3-D) seismic data to quantify the timing and magnitude of differential compaction over a Late Miocene submarine channel complex in SE Brazil (Espirito Santo Basin). A thickness-relief method was applied to quantify the thickness variations in strata deposited over the channel complex. We found that differential compaction started after the channel complex was buried by ∼200 m of strata, as revealed by thinning horizons observed over a compaction-related anticline. The size of the anticline is greatest in the south of the study area, reaching heights of 41 ms (∼50 m). Fluid expelled through faults on the margins of the channel complex formed large depressions. These depressions increased in size after deep-water currents removed the fluid-rich sediment filling them. Differential compaction also occurred over deposits downslope of knickpoints, reaching maximum heights of 29 ms (∼35 m). Seismic reflections onlap the knickpoint face and are believed to comprise slumped strata and debrites. Two-way traveltime isochron and amplitude maps indicate that there are limited connectivity and lateral continuity of the coarse-grained units. Differential compaction over these deposits created anticlines with four-way dip closure. As a consequence, isolated reservoirs were closed vertically by the compaction anticlines and laterally by strata onlapping the knickpoint face. These unique reservoirs could have been charged by migration of hydrocarbons along sands at the base of the channel complex. A fill-to-spill model is hypothesized using the above mechanism: Once an isolated anticlinal trap reached spill point, hydrocarbons migrated upslope into the next trap. Traps like these could form above submarine channels in similar basins around the world (e.g., Gulf of Mexico, west coast of Africa) after early burial.

The Role of Mass Wasting In the Progressive Development Of Submarine Channels (Espírito Santo Basin, Se Brazil)

A Pliocene–Quaternary submarine channel system, influenced by localized mass wasting, is investigated using high-resolution 3D seismic data from offshore Espirito Santo Basin, SE Brazil. Three abandoned channels, a channel belt, and a mass-transport deposit (MTD) are recognized in the channel system in a confluence region confined by salt diapirs. In this confluence region, the cross-sectional area (CSA) of the channel system can be up to 1.2 km2, i.e., 4 to 10 times larger than other parts of the study area. These significant changes in the architecture and morphology of the channel system resulted from the interaction between mass-wasting processes and turbidity flows. We postulate that a basal erosional scar created by mass-wasting processes was later filled with an MTD. This basal scar was then used as a preferential pathway for turbidity flows, which were captured by its headwall and lateral margins. The interpreted data show that the captured turbidity flows greatly widened the basal scar but caused only small modifications in scar height. This predominance of widening processes over channel incision occurred because part of the MTD in the basal scar was removed downslope by turbidity flows and replaced by channel-fill deposits. This paper shows that important flow-capture processes can predominate in channel-confluence regions of continental slopes. Basal scars can capture turbidity flows and facilitate flow channelization, which are key processes for submarine-channel initiation. Importantly, the replacement of MTDs by channel-fill deposits has profound implications for reservoir volumes and net-to-gross ratios in channel systems and partly depends on the properties of the turbidity flows, such as their erosive ability and frequency. The more erosive and frequent flows are captured by the basal scar, the larger is the accommodation space created for subsequent sand-prone turbidites.

The role of gravitational collapse in controlling the evolution of crestal fault systems (Espirito Santo Basin, SE Brazil) – Discussion

The role of gravitational collapse in controlling the evolution of crestal fault systems (Espirito Santo Basin, SE Brazil) – Discussion

The role of gravitational collapse in controlling the evolution of crestal fault systems (Espírito Santo Basin, SE Brazil) – Reply

A high-quality 3D seismic volume from offshore Espirito Santo Basin (SE Brazil) is used to assess the importance of gravitational collapse to the formation of crestal faults above salt structures. A crestal fault system is imaged in detail using seismic attributes such as curvature and variance, which are later complemented by analyses of throw vs. distance (T-D) and throw vs. depth (T-Z). In the study area, crestal faults comprise closely spaced arrays and are bounded by large listric faults, herein called border faults. Two episodes of growth are identified in two opposite-dipping fault families separated by a transverse accommodation zone. Statistical analyses for eighty-four (84) faults show that fault spacing is < 250 m, with border faults showing the larger throw values. Fault throw varies between 8 ms and 80 ms two-way time for crestal faults, and 60–80 ms two-way time for border faults. Fault length varies between ∼410 m and 1750 m, with border faults ranging from 1250 m to 1750 m. This work shows that border faults accommodated most of the strain associated with salt growth and collapse. The growth history of crestal faults favours an isolated fault propagation model with fault segment linkage being associated with the lateral propagation of discrete fault segments. Importantly, two episodes of fault growth are identified as synchronous to two phases of seafloor erosion, rendering local unconformities as competent markers of fault reactivation at a local scale. This paper has crucial implications for the understanding of fault growth as a means to assess drilling risk and oil and gas migration on continental margins. As a corollary, this work demonstrates that: 1) a certain degree of spatial organisation occurs in crestal fault systems; 2) transverse accommodation zones can form regions in which fault propagation is enhanced and regional dips of faults change in 4D.

Broadband marine controlled-source electromagnetic for subsalt and around salt exploration

Salt basins, mainly Tertiary basins with mobilized salt, are notoriously difficult places to explore because of the traditionally poor seismic images typically obtained around and below salt bodies. In areas where the salt structures are extremely complex, the seismic signal-to-noise ratio may still be limited and, therefore, complicate the estimation of the velocity field variations that could be used to migrate the seismic data correctly and recover a good image suitable for prospect generation. We have evaluated the results of an integrated seismic-electromagnetic (EM) two-step interpretation workflow that we applied to a broadband marine controlled-source EM (mCSEM) research survey acquired over a selected ultra-deepwater area of Espirito Santo Basin, Brazil. The presence of shallow allochthonous salt structures makes around salt and subsalt seismic depth imaging remarkably challenging. To illustrate the proposed workflow, we have concentrated on a subdomain of the mCSEM data set, in which a shallow allochthonous salt body has been interpreted before. In the first step, we applied a 3D pixel-based inversion to the mCSEM data intending to recover the first guess of the geometry and resistivity of the salt body, but also the background resistivity. As a starting model, we used a resistivity mesh given by seismic interpretation and resistivity information provided by available nearby wells. Then, we applied a structure-based inversion to the mCSEM data, in which the retrieved model in step one was used as an input. The goal of that second inversion was to recover the base of the salt interface. The top of the salt and the background resistivities remained fixed throughout the process. As a result, we were able to define better the base of the allochthonous salt body. That was reinterpreted approximately 300–700 m shallower than interpreted from narrow azimuth seismic.

High-resolution facies modeling of presalt lacustrine carbonates reservoir analog: Morro do Chaves Formation example, Sergipe-Alagoas Basin, Brazil

Barremian lacustrine carbonates, mainly coquinas, are the reservoir rocks of the large presalt petroleum discoveries in deep to ultradeepwaters, at the southeast Brazilian margin, namely, the Santos, Campos, and Espirito Santo Basins. The complex geologic setting of those discoveries, with massive overburden of salt bodies, makes the seismic imaging of the carbonate reservoirs an expensive and challenging issue. In this setting, accurate facies models are a requirement to the predictability of the carbonate reservoir intervals. We have developed an analog high-resolution coquinas facies model based on an interpretation of a pseudo-3D ground penetrating radar survey. We relied not only on the trace amplitude analysis, but also on trace attributes to reduce the ambiguity of the interpretation due to possible visual biases, which may relate electromagnetic reflection amplitude to geologic relevance. We have used the dip and texture attributes to help us better understand the subsurface and to focus on the main stratigraphic features of the reservoir analog. We have applied the dip attribute to discriminate among distinct facies and to provide a dip-steered horizon-tracking tool, honoring the stratigraphic layering. We have also used a texture attribute to downgrade high-frequency noise in the amplitude cube and emphasize the main stratigraphic horizons separating reflections with a similar and consistent pattern. Then, we produced a joint interpretation, based on three trace attributes, that is, amplitude, dip, and texture, to highlight the main radar facies. That resulted in a facies model in which three southwest–northeast-striking coquina bars (reservoir facies), associated with transgressive systems tract interbedded with shales (nonreservoir facies) of highstand systems tract, are clearly marked.

Bathymetric and regional changes in benthic macrofaunal assemblages on the deep Eastern Brazilian margin, SW Atlantic

Deep-sea continental slopes have valuable mineral and biological resources in close proximity to diverse, undersampled and fragile marine benthic ecosystems. The eastern Brazilian Continental Margin (19.01°S to 21.06°S, 37.88°W to 40.22°W) is an important economic region for both fishing and oil industries, but is poorly understood with respect to the structure of the soft-sediment benthic fauna, their regional distribution and their bathymetric patterns. To identify spatial and temporal patterns of benthic macrofaunal assemblages on the slope (400 to 3000m), the Espirito Santo Basin Assessment Project (AMBES, coordinated by Cenpes-Petrobras) sampled 42 stations across the Brazilian Eastern Slope during both Summer 2012 and Winter 2013. We found a significant decrease in macrofaunal abundance at the 400m isobath along the slope near the northern region of the Espirito Santo Basin, suggesting benthic responses to upwelling events towards the south in Campos Basin and southern Espirito Santo Basin. The taxonomic diversity and assemblage composition also changed significantly across depth zones with mid-slope peaks of diversity at 1000–1300m. In general, macrofaunal assemblages were strongly related to slope depth, suggesting a strong influence of productivity gradients and water mass distribution on this oligotrophic margin. Sediment grain size was marginally important to macrofaunal composition on the upper slope. In general, macrofaunal assemblages on the slope of Espirito Santo Basin are similar to other areas of the SE Brazilian margin, but regional changes in response to productivity and depth need to be considered for management strategies in the face of increasing economic activities off-shore.

Ultralightweight Proppants for Long Horizontal Gravel Packs

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 150581, ’Ultralightweight Proppants: Best Practices for Long Horizontal Gravel Packs Offshore Brazil,’ by A.T. Jardim Neto, F.G.M. Prata, and J.R. Gomez, Baker Hughes, and C.A. Pedroso, SPE, M.O. Martins, and D.N. Silva, SPE, Petrobras, prepared for the 2012 North Africa Technical Conference and Exhibition, Cairo, 20-22 February. The paper has not been peer reviewed. Operators developing and producing reservoirs with deepwater and ultradeepwater wells are pushing technical limits with horizontal extension. Deepwater wells completed in unconsolidated formations usually have low fracture gradients, severe-leakoff zones, or significant washouts. Long horizontal open holes may become technically difficult or economically unfeasible to gravel pack by use of conventional fluids and gravels. Use of ultralightweight proppants (ULWPs) has enabled gravel packing in these longer horizontal open holes. The reduced gravel density allows a significant reduction in pumping rate to avoid fracturing the formation, minimize fluid losses, and eliminate the risk of premature screenout because of excessive gravel settling. Introduction Horizontal openhole gravel-pack (HOHGP) completions are preferred by many operators, especially in permeable unconsolidated formations. Offshore Brazil, especially in the Campos and Espirito Santo basins, HOHGP completions are used to develop post-salt reservoirs. The most common gravels used in the early wells were natural gravels and conventional ceramics. The particle densities (2.65 to 2.73 g/cm3) caused much difficulty with proppant transport, hence an increased dune height that could lead to premature screenout at low pumping rates. A lower-density proppant would be easier to transport with unviscosified fluids such as completion brines, thus allowing the use of reduced pumping rates to circulate proppant at the bottom of the screen and pack the entire horizontal open hole successfully. Two types of ULWPs have been used for this purpose, one with a specific gravity of 1.25 and one with specific gravity ranging from 1.75 to 1.90 (ULWP-1.25 and ULWP-1.75, respectively). Well Configuration and Completion Most fields in the Campos and Espirito Santo basins are developed with a minimum number of wells, some being extended-reach wells. To reduce the number of casing strings, a slender-well design often is used. The horizontal open hole is drilled at 90° to final depth with an 8½- or 9½-in. bit and drill-in fluid. After the final horizontal extension is reached, the drill-in fluid is replaced with completion brine. Then, the completion assembly is run into the well. The completion equipment comprises an isolation packer and 13 Cr premium screens. The gravel-pack operation is performed with a special horizontal tool system that allows gravel packing and stimulation of the horizontal well in a single trip.

Integrating New Seismic Technology and Regional Basin Geology Now a Must

Management Since the discovery of the giant Tupi-Lula pre-salt complex in the Santos Basin of Brazil, explorers have been integrating new seismic technology advances with the fundamentals of regional basin geology to extend the pre-salt play across the Atlantic margin into deep waters and below the salt off the west coast of Africa. In 2005, Petrobras drilled a wildcat well on the Parati prospect in the deep waters of the Santos Basin, and encountered condensate gas below a thick layer of salt. The following year, Petrobras and its partners, BG Group and Galp Energia, announced that the Tupi wildcat, drilled to 16,060 ft in almost 7,000 ft of water, flowed at 4,900 B/D of sweet 30°API crude oil, 0.7 sulphur content, and 6.6 MMcf/D gas on a ⅝-in choke. This confirmed that a new geologic play had been discovered below the salt. Over the next few years, exploration efforts continued in this new pre-salt play, resulting in additional discoveries in the Santos and to the north in the Campos and Espirito Santo basins. Agencia Nacional do Petroleo (ANP) studies suggested that the charge and accumulation models for this new pre-salt cluster area of the Santos Basin contained reserves exceeding 30 billion bbl and possibly as large as 60 billion bbl of oil reserves. Though the thick layers of salt above the oil accumulations create challenges in seismic imaging and exploratory drilling, the salt has also served, through geologic time, as a superb seal that allows thick columns of oil to accumulate and be preserved. Many exploration companies have already constructed regional geologic and plate tectonic models that recognize that these world-class pre-salt hydrocarbon accumulations off the east coast of Brazil may have counterparts on the conjugate margin of the Atlantic Basin in the deep waters offshore Congo, Gabon, Angola, and Namibia. A geologic model from Cobalt International shows a cross section of the Atlantic rift system that predicts similar geology between the two margins (Fig. 1).

Distribution and characterization of failed (mega)blocks along salt ridges, southeast Brazil: Implications for vertical fluid flow on continental margins

Three-dimensional seismic data are used to assess the control of halokinetic structures on the distribution of blocks in a mass transport deposit in the Espirito Santo Basin, southeast Brazil. In contrast to what is commonly observed over growing salt structures, the thickness of the MTD-A1 is larger on top of a northwest trending salt ridge. Emphasis was given to the statistical analysis of 172 remnant and rafted blocks identified within Eocene mass transport deposits (MTD-A1). Three styles of block deformation are identified and scale relationships between the geometry of blocks and their relative position on the salt ridge are presented. Average block height reaches 130 m. Average block area reaches 0.43 km2, while 11.3% of the total area (A) investigated is covered by blocks (5% < A < 17%). On the basis of variations in block geometry (height, area, width/length ratio, orientation) and their relative distribution, we interpret that most failed strata have been remobilized by adjacent topography created during growth of the investigated salt ridge. We show that the origin of the blocks is linked to densely spaced sets of halokinetic-related faults that deformed the prefailure strata. The presence of underlying faults and blocks of remnant and rafted strata potentially induces sharp variations in the internal permeability of MTD-A1. Thus, the interpreted data shows that megablocks in MTDs can constitute viable fluid pathways on otherwise low-permeability units. This character can significantly decrease seal competence above and on the flanks of halokinetic structures.

Sand-Control Aspects for Long-Horizontal-Section Wells in Unconsolidated Heavy-Oil Reservoirs

Distinguished Author Series articles are general, descriptive representations that summarize the state of the art in an area of technology by describing recent developments for readers who are not specialists in the topics discussed. Written by individuals recognized as experts in the area, these articles provide key references to more definitive work and present specific details only to illustrate the technology. Purpose: to inform the general readership of recent advances in various areas of petroleum engineering. Abstract Gravel Packing is the most frequently applied sand-control technique for horizontal wells in the Campos and Espirito Santo basins, offshore Brazil. Because of critical conditions, such as the deep and ultradeep water and low fracture gradients, much precision is required to ensure openhole-gravelpacking (OHGP) success. An important scenario for offshore development in Brazil includes heavy-oil fields in deep water possibly requiring 2000 m of openhole horizontal sections. Gravel packing is a strong candidate for sand-control because of the wide experience acquired and the high reliability level of such applications (if pressure-loss issues can be overcome). Among the operational issues related to hydraulics, the following are critical: equivalent-circulating-density restrictions, fluid displacement while running the screens, and gravel-pack placement (if this is the adopted sand-control technique). This paper focuses on the following aspects: Petrobras experience in more than 270 OHGP completions in offshore environments, techniques for extending hydraulic limits (e.g., rathole zero, rathole bypass, multiple alpha waves, flow-divergence tools, and lightweight proppants), and a multidisciplinary approach to face challenging well designs for heavy-oil reservoirs, including research and development (R&amp;D), tool development, and field implementation. Introduction Horizontal wells have become the main wellbore architecture for offshore development in unconsolidated oil reservoirs along the Brazilian coast. Most drilling challenges, especially concerning wellbore stability and cuttings transport, were overcome with experience. The major completion issue deals with sand control: OHGP techniques have been developed especially for Campos basin applications. More than 250 horizontal wells have been gravel packed successfully in Brazilian offshore fields (Marques et al. 2007). By 2000, Petrobras was discovering significant amounts of heavy oil in offshore turbidites. Marlim Sul, Roncador, Marlim Leste, Albacora Leste, Jubarte, and Oliva fields are examples of heavy-oil accumulations in Campos, Espirito Santo, and Santos basins. Fig. 1 highlights some of the most important heavy-oil provinces along the Brazilian coast.

Faulting of salt-withdrawal basins during early halokinesis: Effects on the Paleogene Rio Doce Canyon system (Espírito Santo Basin, Brazil)

Three-dimensional seismic-reflection data are used in the analysis of submarine channel systems in the Espirito Santo Basin, Brazil. The exceptional quality of the studied data set allows the detailed documentation of the geometry, regional distribution, and statistical parameters of salt-related normal faults, and their effect on the Rio Doce Canyon system (RDCS). On the Espirito Santo continental slope, normal faulting was triggered during early halokinesis (stage A) but barely controlled the initial evolution of the RDCS, which incised the continental slope axially within a salt-withdrawal basin. However, in a second stage (stage B), crestal or radial faults controlled erosion over growing salt structures, whereas synclinal and channel-margin fault sets dissected overbank strata to the RDCS. In the later part of stage B, channel sinuosity decreased sharply in response to fault activity and associated sea-floor destabilization. Vertical propagation of blind faults was triggered in a third stage (stage C), in association with crestal collapse of buried salt anticlines and regional diapirism, but synclinal and channel-margin faults did not propagate vertically above a regional unconformity marking the base of stage C strata. Statistical analyses of observed fault sets demonstrate that synclinal faults are in average 2.3 times longer than the crestal or radial types but record 60% of the throw (average 83 m [272 ft]) experienced by the latter. In addition, the fault sets are shown to have contributed to local cannibalization of the sea floor, vertical stacking of channel-fill strata, and structural and depositional compartmentalization of potential reservoir successions. As a result, channel systems show marked differences in mean values for sinuosity, height, and width in relation to five main phases of channel development. The structural setting in the study area differs from productive areas offshore Espirito Santo (e.g., Golfinho field), west Africa, and Gulf of Mexico, revealing in distal parts of the Brazilian margin the existence of local controls on submarine channel architecture and structural compartmentalization prior to the main stages of diapirism.

Trails of depressions and sediment waves along submarine channels on the continental margin of Espirito Santo Basin, Brazil

Trails of depressions and associated sediment waves that follow the courses of underlying erosional submarine channels in Neogene strata in the Espirito Santo Basin on the Brazilian continental margin are described here. The features were imaged using three-dimensional seismic data, and they have a wavelength of several hundred meters and heights of tens of meters. Individual depressions are also found above knickpoints, scarps, and irregular top surfaces of mass-transport complexes. We propose that the depressions form initially as flute-shaped troughs of channel-confined sediment waves and develop into more circular depressions as a result of deposition on the shallow, upslope-facing stoss flanks and erosion or nondeposition in the lee flanks and the troughs. Depressions above topographical irregularities are interpreted to form when downslope-flowing currents encounter a break in slope, leading to excavation of a depression at the break and deposition of sediment downslope. This mechanism may be analogous to the formation of plunge pools and base-of-slope depressions. Similar features have been observed previously in several bathymetric data sets as well as created in numerical models and are thus considered ubiquitous in submarine settings.