Northern Campos Basin Research Articles

Diagenetic products, settings and evolution of the pre-salt succession in the Northern Campos Basin, Brazil

Abstract Despite all the effort made towards an understanding of the sedimentary, tectonic and diagenetic evolution of the pre-salt sequence and the Pre-Salt reservoirs of the Northern Campos Basin (East Brazil), two knowledge gaps have yet to be filled: (1) a detailed study of diagenesis in the crystalline basement and rift phases; and (2) the timing of diagenetic events that affected the pre-salt succession. In this study, samples from these geologic units were analysed for mineral composition and paragenetic evolution, fluid temperature and salinity, stable isotope compositions and laser ablation inductively coupled plasma mass spectrometer derived U–Pb ages of carbonate phases. The U–Pb ages of replacive and vein-filling cements reveal three tectono-diagenetic events, named the Barremian–Aptian (BADE, 125–117 Ma), the Albo–Cenomanian (ACDE, 103–98 Ma) and the Campanian–Maastrichtian (CMDE, 83–70 Ma). Each phase is characterized by distinct minerals, precipitation temperatures and burial conditions. The hydrothermal qualifier, identified by the temperature contrast between fluid and host rock, was initially high during BADE, then diminished over time (through ACDE) until it achieved equilibrium with the host rocks during CMDE. Diagenetic events are not coeval with magmatism but do coincide with known regional tectonic events described in the literature and are interpreted to be the result of increasing intraplate stresses. Multidisciplinary studies that include diagenetic events constrained by geochronological data will certainly lead to more robust conceptual geologic models, and, therefore, to a more reliable management of resources and strategies such as enhanced oil recovery, carbon capture, utilization and storage, and drinking water.

Diagenetic Products, Settings and Evolution of the Presalt Succession in the Northern Campos Basin, Brazil

Abstract Despite all the effort made towards an understanding of the sedimentary, tectonic, and diagenetic evolution of the presalt sequence and the Pre-Salt reservoirs of the North Campos Basin (East Brazil), two knowledge gaps have yet to be filled: 1) a detailed study of diagenesis in the crystalline basement and rift phases, and 2) the timing of diagenetic events that affected the presalt succession. In this study, samples from these geologic units were analysed for mineral composition and paragenetic evolution, fluid temperature and salinity, stable isotope compositions, and LA-ICP-MS derived U-Pb ages of carbonate phases. The U-Pb ages of replacive and vein-filling cements reveal three tectono-diagenetic events, named Barremian-Aptian (BADE, 125-117 Ma), Albo-Cenomanian (ACDE, 103-98 Ma), and Campanian-Maastrichtian (CMDE, 83-70 Ma). Each phase is characterised by distinct minerals, precipitation temperatures, and burial conditions. The hydrothermal qualifier, identified by the temperature contrast between fluid and host rock, was initially high during BADE, then diminished over time (through ACDE) until it achieved equilibrium with the host rocks during CMDE. Diagenetic events are not coeval with magmatism but do coincide with known regional tectonic events described in the literature and are interpreted to be the result of increasing intraplate stresses. Multidisciplinary studies that include diagenetic events constrained by geochronological data will certainly lead to more robust conceptual geologic models, and therefore, to a more reliable management of resources and strategies such as Enhance Oil Recovery (EOR), Carbon Capture, Utilisation and Storage (CCUS), and drinking water. Supplementary material at https://doi.org/10.6084/m9.figshare.c.7103900

Oil Seep Detection Using Microwave Remote Sensing at Espírito Santo Basin, Eastern Brazil

Hydrocarbon seepage phenomena can be found in most petroleum provinces located in both coastal and ocean regions. The present work aims to identify, map and quantify oil seep candidates in the maritime portion of the Espírito Santo Sedimentary Basin using Synthetic Aperture Radar imagery from Radarsat-2 and Sentinel-1. The selection of the SAR images was made based on their basin coverage area. Meteorological and oceanographic data, when available, were used to assist interpretation. Later, the presence of structures that may enable fluids to escape (faults, fractures, salt domes, etc.) was verified in 101 seismic lines. After detailed analysis, the obtained data were gathered, aiming to classify the oil seep candidates found according to their probability of happening. There were 3 parameters, subdivided into criteria, used in the ranking score: SAR (distance of vessels, number nearby possible seeps and feature size), Geological (morphotectonic domains) and Seismic (distance from seismic lines, presence of structures and distance from structure). Each criterion received grades ranging from 0.1 to 1.0. The final score is given by the arithmetic mean of the parameters. This allowed the seep candidates to be organized in a ranking. The methodology was successful in identifying 54 promising features in the Espírito Santo basin and northern Campos basin. Half of the seep candidates found, 27 features, obtained a grade higher than 0.7, which strengthens the idea of being oil seeps. As an outcome a map was made in 1:3,500,000 scale with the location of all oil seep candidates mapped in this petroleum province.

Tectono‐stratigraphic evolution of the rift and post‐rift systems in the Northern Campos Basin, offshore Brazil

AbstractThe Campos and Santos Basins have been a focus of subsurface studies since the discovery in 2006 of large accumulations of hydrocarbons in the Early Cretaceous rift and post‐rift strata below Aptian evaporites. In this study, regional 2D seismic lines, a 3D seismic survey and well data were interpreted to reconstruct the tectono‐stratigraphic evolution of the rift and post‐rift stages in the northern sector of the Campos Basin. Detailed 3D seismic interpretation and geological modelling were used to subdivide the pre‐salt sedimentary record. This revealed a diachronous strain distribution along the Guriri Fault System (GFS), a roughly NE‐SW striking fault‐bounded horst that was a focus of rift‐related deformation. The syn‐rift succession is interpreted to be the product of two episodes of rifting (RP1 and RP2) with contrasting fault activity patterns and lithostratigraphy. Volcaniclastics and coarse siliciclastics of RP1 were deposited under WNW‐ESE transtension that formed discontinuous half‐grabens followed by extensive erosion and tectonic inversion. Structurally controlled bioclastic rudstones and hybrid deposits characterize RP2 and were deposited in elongated half‐grabens that delimit the GFS horst, which developed under an NW‐SE extension. Deposition under increasingly less tectonically active transitional and post‐rift stages dominated by thermal subsidence gradually led to the healing of the rift‐related structural relief. Selective reactivation of rift faults testifies active tectonic inversion through compression from immediate post‐rift throughout evaporite deposition. These interpretations are put into the context of recent geochronological data of onshore dyke emplacement and the new age constraints for the end of deposition of the pre‐salt sequence. Therefore, we propose an earlier onset on rifting in the Campos Basin, at the Berriasian.

Basement geology and its controls on the nucleation and growth of rift faults in the northern Campos Basin, offshore Brazil

AbstractThe rift phase of the Campos Basin developed during the Early Cretaceous on a heterogeneous crust comprising structures inherited from the Brasiliano‐Pan African tectonic events, mostly generated during the Neoproterozoic‐Cambrian amalgamation of western Gondwana blocks. The main rifting episode took place from the Hauterivian to the Barremian, then was succeeded by the transition and post‐rift (SAG) phases during the Aptian. Rift faults developed as a result of a progressive rotation of extension from E‐W to NW‐SE. The role of pre‐existing intra‐basement structures on the style and evolution of the rift faults was investigated using 3D high‐resolution seismic data, borehole logs and sidewall samples. Three seismic facies (SF1, SF2 and SF3) and three types of intra‐basement structures (Surfaces, Geobodies and Internal Reflections) were identified and mapped. They represent, respectively, contrasting levels of seismic anisotropy, interpreted as metamorphic foliation, and ductile shear zones that bound rock units with particular seismic facies signatures. Sidewall cores show that banded biotite‐gneiss is the predominant rock type in the eastern half of the study area, while more homogeneous granitoid is the dominant lithology on the west. Such a binary division of lithotypes is consistent with the distribution of mapped intra‐basement seismic facies and features. The contrasting basement heterogeneity across the study area is the major control in the strain distribution during rifting. Where the basement is highly heterogeneous, the pre‐existing fabric was selectively reactivated whenever its orientation was favourable, resulting in faults forming progressively as the extension direction rotates, whilst shallower low to very low angle basement fabric were cross‐cut by rift faults. Where the basement is homogeneous, only early formed faults remain active throughout the rifting.

Seismic record of a cyclic turbidite-contourite system in the Northern Campos Basin, SE Brazil

A new mixed turbidite-contourite system is described in the northern Campos Basin, southeastern Brazilian margin. This system is developed in a middle slope setting, and was formed through non-synchronous interaction between the turbidity current and a contour current in the same stratigraphic interval (Miocene). Depositional cycles were differentiated based on diagnostic seismic features. Seismic attributes, seismic facies, and isochron maps were used to identify alternating cycles of downslope and alongslope processes in the study area, along with the intermediate stage with features from both processes (mixed system). Seismic units were then associated with the dominant type of current. Alongslope current activity can be distinguished from the downslope current based on its acoustic characteristics (mainly low root-mean-square (RMS) amplitude values), internal architecture (clinoforms), and external geometry pattern (alongslope trend).On the other hand, downslope gravity currents develop deposits with high-amplitude or chaotic seismic facies, usually higher values of RMS amplitude, channel or channel-lobe features, erosive surfaces, and a basinward depositional trend. The first and oldest seismic unit (S1) was interpreted as a dominantly alongslope system, with vertical aggrading sigmoidal clinoforms and high-frequency, low-amplitude reflections commonly associated with fine-grained sedimentary deposits, typical of a plastered drift, along with a basinward mass transport deposit (MTD) from previous drift instability. Seismic unit S2 represents the intermediate stage where both gravity-driven and along-slope currents act asynchronously. Its is refered to as a mixed turbidite-contourite sequence that shows high-amplitude sediment waves migrating upslope and a moat feature that is carved in its upslope front. The interfingering between high- and low-amplitude reflectors, distal chaotic facies, together with sediment waves and a channel moat, points to a sand-rich deposit reworked by northward-flowing contour currents. Seismic units S3 and S4 show downslope features with chaotic facies (S3) and paleochannels with coarse basal lag deposits (high RMS amplitude values) (S4). In S4, a series of long-lived submarine channels formed. Last, seismic unit S5, referred to as the second plastered drift sequence, is marked by low-amplitude clinoforms that thin basinward. At the seafloor, submarine channel banks (formed at S4) covered by fine sediment deposits (from S5) show asymmetrical features with a slight northward depositional trend, indicating a northward-flowing bottom current, as the deposits are known to pile up in a downcurrent trend. Important information on the paleocurrents' direction was also made based on the final deposits display (e.g. terraces, sediment waves, paleochannels). Research on alternating dominant processes and transitional stages or mixed depositional systems, with both turbidites and contour currents, may provide a better understanding of deep-water depositional processes. Because these processes do not always fit previous depositional models that are mainly described for synchronous systems, new insights on cyclic non-synchronous mixed systems can improve our understanding of how mixed systems are organized through time and space. Being able to determine which were the dominant processes that controlled the sedimentation by indicating periods where the margin was mostly submitted to sediment transfer from continent to the basin and periods where the oceanic currents prevailed by redistributing sediments along the isobaths and replacing the axis of downslope transfer conduits. Setting new models on cyclic deposits and intermediate stages can have a future economic impact on potential hydrocarbon reservoir architecture.

Deep-burial hydrothermal alteration of the Pre-Salt carbonate reservoirs from northern Campos Basin, offshore Brazil: Evidence from petrography, fluid inclusions, Sr, C and O isotopes

Petrographic, mineralogical, elemental, isotopic and fluid inclusion analyses were integrated to unravel the diagenetic evolution of Brazilian Pre-Salt lacustrine carbonate reservoirs of northern Campos Basin, southeast Brazilian margin. Detailed thin section and cathodoluminescence petrography, scanning electron microscopy and electron microprobe analyses established a paragenetic evolution of diagenetic processes and products, comprising extensive dolomitization, silicification, and dissolution. A paragenesis including saddle dolomite, macrocrystalline calcite, mega-quartz, Sr-barite, celestine, fluorite, dickite, sphalerite, galena, and other metallic sulfides filling fractures and dissolution porosity, and aqueous fluid inclusions with homogenization temperatures of 92–152 °C and salinities between 13 and 26 wt % eq. NaCl characterized a hydrothermal system with some analogy to carbonate-hosted Pb–Zn Mississippi Valley (MVT) and Irish-type deposits. Petroleum inclusions and solid bitumen testify atypical oil generation and migration, associated with the hydrothermal flow. The host Pre-Salt spherulitic and fascicular carbonates present highly radiogenic 87 Sr/ 86 Sr ratios, indicating strong interaction with continental crust materials. Hydrothermal phases show δ 18 O values more negative than syngenetic and diagenetic carbonates. The δ 13 C values are interpreted as result of interaction between the hydrothermal fluids and the host rocks. The combined data set provides clear evidence of intense hydrothermal alteration of northern Campos Basin Pre-Salt reservoirs at deep-burial conditions (>2 km), possibly related to Late Cretaceous or more probably Paleogene magmatic activity. Mixed-sourced fluids bearing a basinal signature fed the hydrothermal system and promoted dissolution of the host rocks. The hydrothermal alterations had strong impact on the porosity, permeability, and heterogeneity, contributing, together with the associated fracturing, to the excellent production performance of the Pre-Salt reservoirs. • A deep-burial hydrothermal system is recognized in the Campos Basin Pre-Salt carbonates. • Hydrothermal phases show low δ 18 O values, and high Th and salinity fluid inclusions. • The geochemical and fluid inclusion signatures are similar to MVT deposits. • Hydrothermal fluids are the result of mixing between different sources. • Atypical oil generation and migration occurred associated with the hydrothermal action.

What feeds shelf‐edge clinoforms over margins deprived of adjacent land sources? An example from southeastern Brazil

AbstractIn southeastern Brazil, the Serra do Mar coastal mountain range blocks the sediment influx from arriving at a ca. 1,500 km long continental margin comprising Santos and Pelotas basins. Despite this deprivation, the margin accumulated a ca. 1 km thick sedimentary succession since the Mid‐Miocene. Examination of seismic reflection and oceanographic data indicates that shelf‐margin clinoform formation exhibits a regional variability, with major sigmoidal clinoforms developed in the transitional area between both basins. Laterally, poorly developed oblique clinoforms constitute isolated depocenters along the shelf margin. The continuous clinoform development in the transitional area is attributed to the major influence on sediment transport patterns of several ocean bottom currents flowing along the margin, such as the Brazil Coastal Current, the Brazil Current and the Intermediate Water Brazil Current. These currents erode, transport and distribute sediments across the shelf break and upper slope from distant sediment sources located either north or south of the study area. The progressive southward strengthening of the Brazil Current could be responsible for a major southward sediment redistribution from the northern Campos Basin, and/or for sediment entrainment from northward‐induced transport by the Brazil Coastal Current, originally derived from the De la Plata Estuary. In the transition between Santos and Pelotas basins, the Intermediate Water Brazil Current splits forming the Santos Bifurcation, allowing for a continuous depositional process and clinoform generation. We suggest that ocean bottom currents may shape other shelf‐edge ‘contouritic clinoforms’ in continental margins mainly constructed by along‐strike sediment transport largely driven by long‐term geostrophic currents.

Depositional model of early Cretaceous lacustrine carbonate reservoirs of the Coqueiros formation - Northern Campos Basin, southeastern Brazil

Abstract Recent discoveries of giant hydrocarbon accumulations in coquinas and other lacustrine carbonate rocks of Rift and Post-rift (pre-salt) super-sequences of the Campos and Santos Basins have motivated a series of studies focused on understanding the genesis of these unique reservoirs. An integrated petrologic-sedimentologic-stratigraphic-seismic study of the Coqueiros Formation delineated the depositional model and evolution of reworked bioclastic rocks and other associated rocks deposited on the external high in the northern Campos Basin during the transition between late-rift and sag stages. Bioclastic rudstones and grainstones with moderate to high shell reworking represent 65% of the samples described. The following pieces of evidence point to a predominantly shallow lacustrine depositional environment, dominated by storm currents: (i) presence of high-angle (>14°) longshore cross-bedded rudstones; (ii) limited occurrence of muddy sediments interbedded with thick packages of amalgamated bioclastic rudstones; (iii) great lateral continuity of rudstone deposits devoid of matrix on the structural high, consistent with processes of storm action on large expanses of shallow lakes; (iv) deposits of massive rudstones, with disorganized shells, similar to the modern coastal bioclastic deposits of California and Shark Bay. Three sets of facies association are proposed: (i) high-energy facies, composed of bioclastic rudstones and grainstones devoid of matrix deposited above the fair weather wave base (FWB); (ii) low energy facies, composed of hybrid rocks with muddy or peloidal matrix and other fine grained rocks deposited below the FWB or in protected shallow environments; (iii) an alkaline set, composed of mainly magnesian clay ooids deposited in a more alkaline composition of lake water. The evolution of the facies associations over time demonstrates an overall fall of the relative lake level. High proportion of low energy facies associated with a deeper lacustrine environment occurs at the Coqueiros Fm. base, while at the top predominate high energy facies associated with a shallow lacustrine environment, in addition to magnesian clay-rich facies associated to restricted and alkaline water bodies. Paleocurrents suggest the activity of two main wind direction (northwest and southeast) over the external high that result in clean bioclastic facies with good reservoir potential on both flanks. The knowledge of wind directions during the late Barremian and early Aptian in the northern Campos Basin is extremely important for targeting the best depositional facies for hydrocarbon accumulation in the Coqueiros Formation.

Deposition, diagenetic and hydrothermal processes in the Aptian Pre-Salt lacustrine carbonate reservoirs of the northern Campos Basin, offshore Brazil

The discovery of large oil accumulations in the rift and sag Pre-Salt sections of the Campos and Santos Basins has revived interest in the exploration of the lacustrine carbonate reservoirs in the Brazilian and African marginal basins. More than half of Brazilian oil production originates from the Pre-Salt reservoirs of these offshore basins. A study integrating systematic petrography, cathodoluminescence, scanning electron microscopy, microprobe and X-ray diffraction was performed on seven wells in the northern Campos Basin. This study highlights the major primary, diagenetic and hydrothermal features of the Pre-Salt succession, with the aim to improve our understanding of the factors that influence the porosity and permeability distribution in these important lacustrine carbonate reservoirs. The Pre-Salt deposits correspond to bioclastic grainstones and rudstones, syngenetic crusts of fascicular calcite, and intraclastic grainstones and rudstones of reworked crust fragments and calcite spherulites. Magnesian silicates are frequently associated with carbonate deposits. In the sag phase, stevensitic laminations constitute the substrate for the precipitation of calcite crusts and spherulites, which displace and replace the syngenetic magnesian clay deposits. In the rift section, stevensitic ooids are mixed with bioclasts or form ooidal arenites. Pre-Salt carbonate reservoirs have undergone a complex and heterogeneous diagenetic evolution. Eodiagenetic processes include the dissolution, neomorphism and cementation of bivalve bioclasts in the rift, as well as the dissolution of magnesian silicates and their replacement by calcite spherulites, silica and dolomite in the sag section. Burial alterations are commonly associated with hydrothermal fluids carried through faults and fracture systems. These fluids promote dolomitization, silicification, and dissolution at varying degrees and intensities. Eodiagenetic precipitation and dissolution owing to variations in the lake water chemistry and the episodic flow of hydrothermal fluids under burial conditions control the creation, redistribution, and obliteration of porosity in the Pre-Salt reservoirs.

Ascidian spicules of Quaternary sediments from the lower slope of the Campos Basin (Brazil)

Piston core GL-77 was collected in the lower slope of the northern Campos Basin, Brazil, and consists essentially of muds that have been deposited in turbiditic currents over the last 130 ka, at least, which corresponds to the Upper Pleistocene-Holocene interval. The identified ascidian spicules belong to the Didemnidae Family and are represented by species Micrascidites vulgaris, Bonetia brevis, Rigaudia multiradiata and Monniotia fasciculata. These species have irregular abundance and distribution, with Micrascidites vulgaris being the most common. Their occurrence is interpreted as resulting from transport to the depositional site in response to climate fluctuations (glacial and interglacial periods). The transport of ascidian spicules from a shallow-water sea is supported by the presence of terrestrial organic matter, mainly phytoclasts, sporomorphs and microphytoplankton, which were transported to the slope by the river systems. The results found in this study show that the relative frequency distribution pattern of didemnid spicules is a useful tool for monitoring sediment transport in the slope.

Architecture and Tectono-magmatic evolution of the Campos Rifted Margin: Control of OCT structure by basement inheritance

Abstract The formation of rifted margins involves the deformation of pre-existing lithosphere whose rheological and mechanical behavior during extension is complex since it is the product of numerous earlier tectonic events. In this work we investigate the Campos Rifted Margin (CRM) architecture, with the aim of exploring the role of basement inheritance and early magmatism on margin evolution. We present a new compilation of high resolution aeromagnetic data, integrated with seismic interpretation and crustal thickness from 3D gravity inversion, to resolve margin architecture, ocean-continent transition (OCT) structure and the oceanward extent of continental basement. We examine the lateral variation of crustal rheology, necking geometry and rift segmentation, revealing striking spatial heterogeneities that separate three distinct sectors along the Campos margin. The basement of the Campos Rifted Margin consists of Precambrian/Eo-Paleozoic Ribeira Belt (RB) and the easternmost Cabo Frio Tectonic Domain (CFTD) whose Neoproterozoic-Cambrian nappes and thrusts are well preserved offshore and give a rheologically layered crust. This pre-rift basement configuration, along with the Mesozoic magmatism, has resulted in different crustal responses to extension which vary from north to south. It influenced the temporal and spatial distribution of deformation, and as a consequence, the necking geometry, subsidence and sedimentary evolution of the margin. We show that the Campos basin evolution was controlled by crustal inheritance corresponding to that observed in onshore basement terranes. The more massive basement of the northern Campos basin can be correlated with the post-collisional Cambro-Ordovician magmatic province of the Aracuai belt that partially obliterated the earlier orogenic structures. The lack of a structured crust localized the strain generating the observed narrow necking zone. In addition, its more mafic composition resulted in a competent crust which also influenced the rifting processes. In contrast the basement of the central and southern Campos margin, represented by the Cabo Frio Tectonic Domain, is structurally and petrologically distinct from the Aracuai Belt and has layered orogenic crust which responded differently to rifting stresses forming the observed wide necking zone. We propose that the Campos Rifted Margin evolved from a pre-rift complex inherited rheology which dominated the first stages of rifting. However once the crust was highly extended, the deformation was nearly synchronous regionally, leading to giant salt basin formation and breakup.

Influence of Diagenesis On the Quality of Lower Cretaceous Pre-salt Lacustrine Carbonate Reservoirs from Northern Campos Basin, Offshore Brazil

Influence of Diagenesis On the Quality of Lower Cretaceous Pre-salt Lacustrine Carbonate Reservoirs from Northern Campos Basin, Offshore Brazil

Bioestratigrafia e inferências paleobatimétricas, com base em foraminíferos, do intervalo Paleógeno–Neógeno no norte da Bacia de Campos (poço Campos-01)

The micropaleontological analysis of a section of 1020 m (1760 m–2780 m) from the Campos-01 exploratory well, located at the Northern Campos Basin under 1338 m of water depth, provided a great diversity of foraminifera species recovered mostly from strata of Cenozoic age. The objective of this study is to recognize a biostratigraphic framework for the Paleogene–Neogene section crossed by the Campos-01 well, to identify unconformities in the sedimentary record, and to know paleoenvironmental characteristics of the interval in terms of paleobathymetry. For this study, 53 cutting samples were selected and the calcareous microfossils (planktic and benthic foraminifera) were analyzed both qualitatively and quantitatively. As a result of the observed stratigraphic distribution of planktic foraminifera species, the biozones P16 (uppermost Eocene), N4, N5?–N6?, N7, (lower Miocene), N8, N9, N10?–N13?, N14–N15 (middle–upper Miocene), N16 and N17 (upper Miocene), of Blow (1969), were recognized. The presence of two unconformities is suggested, representing biostratigraphical record breaks between the depth 2720 m and 2740 m (Paleocene–upper Eocene, middle part), and between the samples 2640 m and 2670 m (Oligocene). To the upper Eocene, the paleobathymetry was interpreted to have been outer neritic, which is supported by the reduction of the total abundance of foraminifera and the presence of a benthic foraminifera association typical of this environment. In the Miocene section, from the base to the top, it was noted that the percentage of planktic foraminifera corresponds to a trend of increasing paleodepth, indicating an increment of distance from the coast, with presence of genera and some species of benthic foraminifera that suggest the predominance of the upper bathyal paleobathymetry to this interval.

Paleogene-Neogene calcareous nannofossil biostratigraphy and paleoecological inferences from northern Campos Basin, Brazil (well Campos-01)

Quantitative analyses of calcareous nannofossils were performed on 50 ditch-cuttings samples from a well drilled in the northern Campos Basin, Brazil. Nine zones and two subzones were recognised in the Paleogene-Neogene section. The absence of zones NN9-NN7 (earliest late-latest middle Miocene), NP25-NP21 (Oligocene) and NP18-NP1 (earliest late Eocene-Paleocene) implies the occurrence of three stratigraphic breaks/unconformities within the studied interval. Nannofossil assemblages present suggest an open-ocean depositional environment under oligotrophic-surface water conditions for the Miocene section of the well. Hughesius spp. and Umbilicosphaera spp., here named the “small dark” group, were recognised as an index of high nutrient concentration. We suggest that small coccolith/nannolith size is a better indicator of eutrophic condition than taxonomic affinity. Morphometric analysis of specimens of Sphenolithus belemnos and Sphenolithus disbelemnos showed that size tends to decrease within the highstand system tract. The influx of nutrients associated with the highstand could explain this size reduction and may also support our hypothesis that small specimens are indicative of high nutrient concentrations in the surface water.

Caracterização Faciológica dos Reservatórios e Depósitos Associados do Campo de Frade, Bacia de Campos, Rio de Janeiro

The Frade Field, located in the northern Campos Basin, corresponds to Oligo-Miocene deep-water reservoirs bracketed between the Azul and Cinza regional markers. Such depositional systems are of great economic significance, representing a large percentage of Brazilian hydrocarbon reserves and production. This paper presents the characterization of the facies that comprise the Frade Field reservoirs and associated deposits. The study included the analysis of 154 m of core from three wells, which are representative of four main field reservoirs. Twelve facies are recognized, of which two are conglomeratic, four are sandy, one is of mixed sand-mud composition and three are heterolithic. The interpretation of these facies indicates a depositional system dominated by the interaction of processes as diverse as debris flows, turbulent flows, bottom currents and slides. The reservoir facies are predominantly bipartite and turbiditic flow sands, whereas the non reservoir facies include mass-transport aprons and cemented debris flow rhodolithic conglomerates, both being very common in the described sequences. Overestimation of hydrocarbon volumes may occur should such facies be inadequately represented. However, when present as interbedded units within the reservoir facies, they generally do not have enough lateral continuity to significantly impair hydraulic connectivity of the reservoir.

Pressure-Transient and Production-Data Analysis of an Unconsolidated Formation

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 147506, ’Pressure-Transient and Production-Data Analysis of a Horizontal Well in an Unconsolidated Formation in Frade, Brazil,’ by Yan Pan, SPE, Russ Ewy, SPE, Don Ringe, SPE, Medhat M. Kamal, SPE, Ralph Affinito, SPE, and Oluwole Sotunde, SPE, Chevron, prepared for the 2011 SPE Annual Technical Conference and Exhibition, Denver, 30 October-2 November. The paper has not been peer reviewed. Frade Asset is a medium-heavy-oil field in the northern Campos basin, approximately 75 miles offshore Rio de Janeiro in 3,500-ft water depth. The structure is a low-relief anticline with two main fault blocks consisting of four stacked unconsolidated reservoirs. The field produces from nine horizontal oil wells with three vertical water-injection wells to maintain reservoir pressure. Continuous well monitoring and reservoir characterization are key to cost-efficient development in this deepwater subsea field. Introduction The development strategy for the field includes horizontal production wells and deviated injection wells to maintain reservoir pressure. The asset-management team realized the challenges of this particular field and made the decision to install permanent downhole gauges in every production and injection well drilled, with a reservoir-surveillance plan in place to monitor well and reservoir performance. Active reservoir surveillance enabled engineers to make sound and quick operating decisions, such as shutting in wells, changing chokes, or planning well interventions on the basis of dynamic data collected continuously at wells. It also provided real-time information for improved reservoir characterization, model forecasts, and optimized development plans. Because data stream in continuously, the cycle from data collection to updating reservoir models to forecasting field performance to optimizing development could be shortened. Example Well: Producer 2 Well Producer 2 is in the upthrown fault block, as shown in Fig. 1, and had an original reservoir pressure of 3,079 psia and a reservoir temperature of 110°F. The net pay thickness is approximately 42 m, and the horizontal well was drilled 30 m above the sealing bottom of the reservoir. The well trajectory was parallel to the fault to the southwest and to the axial fairway edge to the northeast. The well was completed with an openhole gravel pack, and the total completion length was 507 m. The permanent downhole gauge was installed above the top of the gravel-pack completion.

An Ultradeepwater Heavy-Oil Development Offshore Brazil

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper OTC 20537, ’Parque das Conchas BC-10 - An Ultra- Deepwater Heavy Oil Development Offshore Brazil,’ by K.H. Stingl, Shell International E&P, and A. Paardekam, SPE Shell Brazil E&P, originally prepared for the 2010 Offshore Technology Conference, Houston, 3-6 May. The paper has not been peer reviewed. Parque das Conchas is an ultradeep-water heavy-oil development in the northern Campos basin offshore Brazil. The project is a joint venture between Shell, Petrobras, and Oil and Natural Gas Corporation of India. The first phase of the project is the development of three independent subsea fields tied back to the centrally located turret-moored floating production, storage, and offloading (FPSO) host facility, the FPSO Espirito Santo. Introduction The Parque das Conchas development grew out of a substantial exploration and appraisal program beginning in 2000 in which 13 wells were drilled and six discoveries were made. The Declaration of Commerciality was signed with the Brazilian National Petroleum Agency in December 2005, and the project was sanctioned in November 2006. The four main reservoirs—Ostra, Abalone, Argonauta B west, and Argonauta O north—were named after shellfish indigenous to the area. Together, they form “Parque das Conchas,” or “Shell Park,” in Portuguese. This is the first project in Brazil taken by Shell from exploration discovery to production. First oil from Phase 1 was achieved on 12 July 2009, just 9 years after discovery. Development Abalone, Ostra, and Argonauta B west are small-to-medium in size and stratigraphically complex, with highly faulted, compartmentalized, unconsolidated sand packages. The reservoir pressures are low, and the oils range from heavy to light, ranging in gravity from 17 to 42°API. A fourth heavy-oil field, Argonauta O north, will be tied back as part of Phase 2 and is planned to be ready for production in 2013. The Argonauta O north field contains 16°API oil and will require waterflood for reservoir-pressure support. The Phase 1 subsea infrastructure consists of 10 producing wells and one gas-injection well connected by 100 km of insulated and uninsulated flowlines ranging in size from 6 to 12 in., 15 flow-line sleds, two production manifolds, two artificial-lift manifolds housing a total of six vertical subsea-separation caissons with 1,500-hp electrical submersible pumps (ESPs), and 25 rigid jumpers, all of which are serviced by approximately 30 km of multicircuit high-voltage electrohydraulic (HVEH) umbilicals connected to the FPSO. The gas is processed on the FPSO, and to avoid flaring and to reduce CO2 emissions, it currently is being injected into a gas-injection well. A dedicated 40-km-long 6-in. uninsulated Parque das Conchas trunkline has been installed from the FPSO and will be tied into the Petrobras Caipixaba gas-export pipeline at the Petrobras BC-60 location scheduled to be operational in 2010. The oil is stored on the FPSO and offloaded to shuttle tankers as required.

Reconstituição do clima de ondas no sul-sudeste brasileiro entre 1997 e 2005

Uma reconstituição dos campos de onda pretéritos no oceano Atlântico Sul foi realizada pelo modelo de ondas WAVEWATCH III onde testes foram feitos para determinar as configurações das grades numéricas mais adequadas para o estudo e para a verificação e calibração da qualidade dos ventos e forçantes selecionadas para a elaboração do hindcast dos campos de onda. Em relação aos campos de vento do modelo observou-se valores subestimados abaixo de 7, 5 m/s e superestimados acima de 7, 5 m/s, quando comparados aos dados de vento medidos das Bacias de Campos e Santos. Portanto foi realizada uma correção nas forçantes de vento para essa região. A avaliação da reconstituição dos campos de onda em eventos severos fez-se a luz de medições do radar de ondas MIROS na plataforma P-25 da PETROBRAS, na Bacia de Campos. A comparação dos dados mostrou que as simulações realizadas com o modelo usando forçantes atmosféricas ajustadas, em geral, reproduzem os estados de mar mais severos medidos de ondas, tanto em termos de altura significativa de onda (Hs), quanto de período de pico (Tp). As simulações, no entanto, podem subestimar detalhes como a intensidade do mar local nos primeiros momentos da tempestade, no caso de estado de mar bimodal e ignorar a presença de campos de onda gerados em sistemas atmosféricos mais compactos, devido à baixa resolução das forçantes atmosféricas empregadas. De uma forma geral, os resultados foram bons e o modelo caracteriza o clima de ondas desta região oeste do oceano Atlântico Sul.

Espirito Santo: The New Deepwater Frontier in Brazil

This article, written by Technology Editor Dennis Denney, contains highlights of paper OTC 19082, "Espirito Santo: The New Deepwater Frontier in Brazil," by Marcio Felix Carvalho Bezerra, SPE, and Nery Vicente Milani De Rossi, SPE, Petrobras, prepared for the 2007 Offshore Technology Conference, Houston, 30 April–3 May. Petrobras has been active in five simultaneous exploration and production frontiers in the Espirito Santo basin, namely gas in shallow water, light and heavy oil in deepwater, and light oil in ultradeep water and onshore. Petrobras has invested in new infrastructure projects including pipelines, processing plants, and a new port to support offshore operations. The company also has participated in research projects in partnership with the Federal University of Espirito Santo. Introduction Petrobras' activities in the state of Espirito Santo, in southeastern Brazil, encompass the Espirito Santo basin (onshore and offshore) and the northern portion of the Campos basin (offshore). Activities began in 1957 with an onshore focus. In 1968, Brazil's first offshore well was drilled in the Espirito Santo basin. In 1978, the Cacao field was the first offshore commercial discovery in the Espirito Santo basin, in a water depth of 19 m. Onshore production began in 1973, reaching maximum production of 25,000 BOPD in 1984, declining to 9,000 BOPD in 1998, when new fields were discovered by use of new technologies (e.g., 3D seismic). In early 2001, the first commercial deepwater discovery was the Jubarte field in the northern Campos basin, followed in 2003 by the discovery of light oil in deep waters in the Espirito Santo basin (Golfinho field). Projects Jubarte. Production began with a 2-month extended well test (EWT). This field produced approximately 20,000 BOPD through the Seillean floating production, storage, and offloading (FPSO) vessel. Phase-1 field development began December 2006 through FPSO P-34 with a production capacity of 60,000 BOPD. Phase 2 is planned for 2010 through FPSO P-57, with a capacity of 180,000 BOPD. Heavy-oil-production technologies include use of long horizontal wells to increase the production, use of electrical submersible pumps (ESPs) installed on the seabed as the main artificial-lift method with gas lift as backup, and the conversion of the FPSO P-34 to process heavy oil. Neighboring the Jubarte field, Cachalote, Baleia Franca, and Baleia Ana fields were discovered in 1500-m water depth. Production is scheduled to begin in 2012. The Baleia Azul field (1300 m water depth), south of Jubarte, may begin operation in 2014. The Caxareu, Pirambu, and Manganga fields were discovered in 2006 and are in the study phase to define the production systems. The Nautilus, Abalone, Ostra, and Argonauta fields are being developed in two phases, with the first phase in 2009, through an FPSO with capacity for 100,000 BOPD. Catua. The Catua field (in water depth of 1800 m), is 50 km southeast of Jubarte and contains 42°API oil in a carbonate reservoir. Discovered in 2005, an EWT is planned for 2008 to define the technical and commercial feasibility.