Alagoas Basin Research Articles

Quantification and mapping of erosion in the Sergipe–Alagoas Basin using sonic logs and vitrinite reflectance data

Quantification and mapping of erosion in the Sergipe–Alagoas Basin using sonic logs and vitrinite reflectance data

Early Cretaceous marine microbiofacies from the South Atlantic Ocean (Sergipe–Alagoas Basin, Brazil): palaeobiogeographical and palaeoceanographical inferences

Early Cretaceous marine microbiofacies from the South Atlantic Ocean (Sergipe–Alagoas Basin, Brazil): palaeobiogeographical and palaeoceanographical inferences

The vertebrate fossil record from the Feliz Deserto Formation (Lower Cretaceous), Sergipe, NE Brazil: paleoecological, taphonomic, and paleobiogeographic implications

The Feliz Deserto Formation (Berriasian–Valanginian, Sergipe–Alagoas Basin, NE Brazil) preserved some of the earliest South American fossil records of the rifting stages which resulted in the Gondwana supercontinent break-up during the Early Cretaceous. Recently, the first spinosaurid theropod record of this formation was described, based on a tooth recovered from Canafístula 01 locality in Sergipe State. We add herein twenty-seven isolated specimens to the fossil record of the Lower Cretaceous Feliz Deserto Formation. The new material includes seven isolated spinosaurid theropod teeth of the spinosaurine clade, as well as an indeterminate theropod preungual pedal phalanx. In addition, we describe an isolated crocodyliform osteoderm, as well as eighteen isolated teeth, some of which were taxonomically identified in three distinct morphotypes of neosuchian crocodyliforms. These findings expand the Gondwanan fossil record of both spinosaurine theropods and neosuchian crocodyliforms. Despite the fragmented nature of the specimens, these new fossils allowed the characterization of their general taphonomic features with low fluvial transport of bioclast prior to the burial. The depositional paleoenvironment of the Canafístula 01 locality is compatible with the deltaic system unit, that characterizes part of the Feliz Deserto Formation during the Early Cretaceous. These fossil findings exemplify the co-occurrence of spinosaurid dinosaurs and more than one taxon of crocodyliforms in the deltaic-lacustrine paleoenvironment represented by the Feliz Deserto Formation. These new occurrences reinforce the fossiliferous potential of the Canafístula 01 locality, especially related to the paleovertebrates from the Lower Cretaceous of Brazil.

Parametric analysis by numerical simulation of an oil reservoir analogue from the Maceió formation (Alagoas basin)

In the northern part of the Maceió Formation, Alagoas Basin, there is the Barreiras do Boqueirão outcrop, located in Japaratinga (AL). In this outcrop a faciological, petrographic and diagenetic characterization of the sandstone outcrop was performed to build a simplified oil reservoir model. The response of the petrographic characterization provided porosity data along with the diagenetic processes. In this way, the geological study was able to provide input for further analysis regarding flow behavior. A simplified physical model representing the outcrop was first built, and two other physical models: one representing the petrophysical data used by Lira (2004), whose study was also carried out in the same outcrop, and an advanced recovery model through the steam injection method. Thus, it was possible to verify that the simplified model of the Maceió Formation presented low oil recovery and the continuous steam injection model had the best results in hydrocarbon production. Finally, a parametric analysis of the operational conditions of the injection wells was carried out in order to verify the influence of steam quality and injection flow rate on hydrocarbon recovery. The model with advanced recovery was the one that obtained the highest oil recovery, whereas the Lira (2004) model, even with the insertion of steam in the reservoir, did not present optimistic results. As for the oil production, it presented a discrepant recovery factor in relation to the value that was actually found in this study, and the simplified model of the Maceió formation indicated the lowest oil recovery.

Record of Brachyoxylon patagonicum, a Cheirolepidiaceae wood preserved by gelification in the Aptian Maceió Formation, Sergipe–Alagoas Basin, NE Brazil

A gelified wood from the late Aptian Maceió Formation (Sergipe–Alagoas Basin, northeastern Brazil) was studied under scanning electron microscopy and organic petrography allowing for the record of the fossil-species Brachyoxylon patagonicum, likely belonging to the Cheirolepidiaceae family. The anatomical structure of the secondary xylem is characterized by mixed type of radial tracheary pitting, composed exclusively by uniseriate bordered pits, in separated, contiguous and compressed arrangements. Cross-field pits are of the araucarioid type, xylem rays are uniseriate or rarely partially biseriate, and probable sporadic traumatic resin canals are present. The present record expands the paleobiogeographic distribution of the fossil-genus in South America and amplifies its climatic tolerance, since the parent plants lived in the Aptian Tropical Equatorial Hot arid belt. The presence of fungal remains within the wood tissue, and the absence of signs of plant defense against fungal decay suggest saprophytic fungus–wood interactions that likely occurred during a stage of aerobic exposure before burial.

Taphofacies and Petrofacies Theoretical Marine Models Applied to the Coquina of the Amaral Formation (Lusitanian Basin, Portugal)

The Amaral Formation has a wide geographic distribution within the Lusitanian Basin, at the western Iberian Margin (Portugal). The different depositional contexts for this unit enabled the distinction of three sectors: lagoon, lagoon-barrier, and marine-distal. The integration of the evolutionary taphonomic analysis of its fossil assemblages with the analysis of multiscale properties through the CAMURES methodology (Multiscale Reservoir Characterization) allowed the application of a methodology for the classification of coquina which was previously developed for the Morro do Chaves Formation (Sergipe–Alagoas Basin, Brazil). Here, it was adapted according to the complexity of the Amaral Formation deposits. The classification of ten taphofacies, in association with four lithofacies, allowed the definition of 84 petrofacies, based on the nature of the sedimentary and taphonomic processes. The relationship between the structural context, the systems tracts, the diversity of the fossil record, the classification of taphofacies and petrofacies, and the understanding of vertical and lateral variations of the sediments’ deposition within the unit support the construction of geological and theoretical models for coquina deposits. These models will allow for prediction of the spatial distribution of facies in other coquina analogous hydrocarbon reservoirs, as well as specifying the delimitation of reservoir zones for 3D geocellular modeling and flow simulation of hydrocarbon-producing reservoirs, thus improving predictive analyses.

Potential synergy between natural gas production and offshore wind power generation: a case study in northeast Brazil

Offshore wind energy production is non-existent in Brazil, although is currently considered in the country's expansion plans. New and promising oil and gas fields have recently been discovered in the Sergipe and Alagoas basin, corresponding to one third of current Brazilian production. This work analyzes the technical and economic viability of an Offshore Wind Farm to supply the energy demand of a Floating Liquified Natural Gas proposed to be used in those fields. The resulting estimated cost of capital and levelized cost of energy were in line with international values. However, the project proved to be unfeasible due to the high cost for its size and the low average price of energy generation. Nonetheless, the synergy between the oil and gas sector and offshore wind may include benefits such as the reduction of greenhouse gas emissions within the sector itself, making the non-renewable resource available for more noble use.

PETROGRAPHIC CHARACTERIZATION AND DIAGENESIS IN SANDSTONES OUTCROPS OF THE NORTHERN MACEIÓ FORMATION: IMPLICATIONS IN RESERVOIR QUALITY

The acquisition of geological data is of fundamental importance for the study of areas potentially relevant to the occurrence of petroleum systems. In this context, the development of research in outcropping rock formations has proven to be a potential method to investigate the geology of the geological unit studied in subsurface. One of several examples found in Brazil are the outcrops Barreiras do Boqueirão and Praia de Japaratinga, belonging to the Maceió Formation, located in the northern coast of Alagoas State. The Maceió Formation has the lowest cretaceous sedimentation record within the Alagoas Basin. This sedimentation, present almost in the entire basin, is located mainly in its subsurface. This geological unit is composed of several lithologies, including a turbiditic sequence predominantly formed by shales, sandstones and conglomerates. This environment makes it possible the occurrence of a petroleum system. Our research group chose to investigate this environment because turbiditic sandstones are excellent petroleum reservoirs, and they have a great economic relevance in the Brazilian petroleum scenario. To develop this research, a petrographic characterization of the Maceió Formation sandstones was conducted to help determine the compositional and diagenetic aspects of these rocks and infer the influence of diagenetic processes on the quality of these sandstones as reservoirs. The petrographic analysis showed that the studied sandstones can be classified as arkose and quartzenite, present moderate porosity and good permeability, observed through the predominant presence of floating contacts between the grains. The porosity is predominantly primary intergranular, averaging 15%, but secondary porosity by fracture and dissolution of primary grains also occurs. The sandstones of the Maceió Formation are poorly and moderately selected, with angular, sub-angular and sub-rounded grains, showing low to medium textural maturity, which may also influence the quality of the reservoir, impairing the primary porosity in the samples. The three diagenetic stages were identified as: eodiagenesis, mesodiagenesis, and telodiagenesis. The diagenetic processes found were: mechanical compaction, beginning of chemical compaction, clay infiltration, pyrite cementation, grain dissolution, chlorite cementation, quartz sintaxial growth, and mineral alteration and replacement. Mineral replacement was a phenomenon observed quite expressively in the samples analyzed. This event was evidenced, particularly, by the substitution of muscovite and feldspar for kaolinite, the alteration of biotite was also identified in the samples. Therefore, one can infer that the diagenetic processes had little influence on the reduction of the original porosity in the samples studied. In general, considering all the analyses performed in this research, one can see that the sandstones of the Maceió Formation (northern portion) present a good reservoir quality.

Gravity data as a faulting assessment tool for unconventional reservoirs regional exploration: The Sergipe–Alagoas Basin example

This paper introduces a gravity regional interpretation workflow for mapping the natural fracture system, a challenge in unconventional reservoir exploration. The workflow comprises coupling two gravity data attributes, the tilt angle and the multiscale edge detection (worming), to build a high-resolution image structural framework of a given basin’s basement. That includes a description of the fault directions and fault density, consolidated in a fault distribution map. The proposed workflow was applied to available gravity data of a representative passive-margin basin, the Sergipe-Alagoas Basin, Brazil. The source rocks of Sergipe-Alagoas are organic-rich shale deposited in the principal depocenters during the rift phase of the basin’s evolution. These shaly units are the unconventional reservoirs in the basin. These organic-rich shales are acknowledged as syn-rift unconventional reservoir analogs of all Brazilian continental margin basins and many other passive-margin basins worldwide. The workflow recognized two fault trends in the studied area. A principal NE–SW and a minor NW–SE. 3D seismic interpretation validated the proposed workflow by successfully associating the gravity faults with traditional fault attributes. One advantage of this workflow is that it can be implemented over broad regions at a minimum expense. The proposed method can be used to rank opportunities in unconventional exploration.

Drilling the Aptian–Albian of the Sergipe–Alagoas Basin, Brazil: paleobiogeographic and paleoceanographic studies in the South Atlantic

Abstract. The Aptian–Albian interval is characterized by significant paleoclimatic, paleoceanographic, and paleogeographic changes, which in turn affected the distribution and evolution of marine ecosystems. Despite the importance of such studies, there have been few correlations between Aptian–Albian sections of the Tethys Sea and those of the South Atlantic Ocean. This interval, including the Aptian–Albian transition, is preserved in the deposits of the Riachuelo Formation (Sergipe–Alagoas Basin, Brazil) located in the South Atlantic Ocean; therefore, this location was chosen for drilling four new cores. The goals of this paper are as follows: (1) to explain the drilling operation carried out in the deposits of the Riachuelo Formation and the methods used; (2) to present a brief lithostratigraphic characterization of the holes and the paleomagnetic data of core SER-03; and (3) to describe the high potential of the cores recovered for additional investigation in the future. The lithostratigraphic units of the SER-01 core consist mainly of coarse- to fine-grained sandstone, shales, marls, and mudstones; the SER-02 core was excluded due to low recovery; the SER-03 core is mainly composed of fine-grained sediments (shale, marls, and packstone) and bears some ammonite shells; the lithology of core SER-04 is mainly sandstones. Magnetic susceptibility values (χlf and χhf) and frequency-dependent susceptibility (χfd) data suggest that the section is located within the Cretaceous Normal Superchron. Future studies on these cores integrating micropaleontological, paleoichnological, geochemical, stratigraphic, and paleomagnetic (e.g., relative intensity) data will allow for a better understanding of paleoceanographic and paleogeographic events related to the early evolution of the South Atlantic Ocean and how these events correlate to similar events in Tethyan sections.

Ostracods from the late Albian–early Cenomanian of the Sergipe–Alagoas Basin, Brazil: New taxonomic and biostratigraphic inferences

This paper presents new taxonomic reports and biostratigraphic inferences based on ostracods in the basal section of the cored well UFRJ-2-LRJ-01-SE, perforated in the Votorantim quarry, Sergipe-Alagoas Basin, Brazil. The studied material comprised 44 samples in the range 438.65 to 315.30 m, identifying 52 species of ostracods distributed in 31 genera and 16 families. Five new species are proposed: Aracajuia separatta sp. nov.; Cytheropteron laranjeirensis sp. nov.; Microxestoleberis riachuelensis sp. nov.; Parahemingwayela fauthi sp. nov. and Quasihermanites? punctata sp. nov. The age of the studied interval was established by the occurrence of Aracajuia antiqua (MSA–1) between 434.00 and 347.25 m indicating the upper Albian. The first occurrence of Bythoceratina tamarae marks the upper Albian–lower Cenomanian boundary at 315.30 m. The biozones proposed with ostracodes coincides with the biozones of calcareous nannofossils made found at cored well.

Permian mixed carbonate–siliciclastic lagoon coastal system in West-Central Gondwana

Although in recent years mixed carbonate–siliciclastic platforms have been increasingly recognized in the Permian of Western Gondwana, there is no detailed description of these mixed systems in West-Central Gondwana. This study focuses on the Permian of the Sergipe–Alagoas Basin (NE Brazil), with the aim of filling this knowledge gap. Based on sedimentological data and microfacies analysis, six facies associations (FA) were identified: FA1 is an eolian–fluvial system, composed of stratified sandstones, FA2 and FA3 represent a mixed tidal flat–lagoon system composed of microbialites, pelitic/micritic sediments and intraclastic packstones, FA4 represents shoreface wave deposits composed of laminated sandstones and silicified grainstones, and FA5 and FA6 are interpreted as a barrier–tidal inlet system, composed of oolitic/intraclastic grainstones, subtidal microbialites, and mixed rudstones. Facies associations reflect the paleoenvironmental conditions of a coastal environment, with dunes and small rivers adjacent to a mixed carbonate–siliciclastic ramp. This is defined as a lagoon system associated with tidal flats protected from the high-energy region by carbonate shoals and microbial constructions. These deposits represent the eastern portion of a shallow epicontinental sea that covered lowlands in West-Central Gondwana within the arid–semiarid belt, whose climate characteristics are reflected in eolian deposits, desiccation structures, mixed carbonate–siliciclastic facies, and fossil records. The main diagenetic feature observed in petrographic analyses was an early diagenetic silicification. Although the absence of spiculites and shelf configuration did not allow a correlation with the Permian glass ramp model, similarities were observed with Eocene glass ramps of Australia, and a relationship with the Permian Chert Event is suggested.

Relationship between biofabric and petrophysics in coquinas, insights on Brazilian Barremian–Aptian carbonates of the Santos and Sergipe–Alagoas Basins

Coquinas are a sedimentary rock composed mainly of shells and their fragments with a carbonate or siliciclastic matrix. These rocks exhibit a high range of porosity and permeability values that are related to depositional and diagenetic processes. A series of coquina reservoirs were discovered in the Campos and Santos Basins in the eastern margin of Brazil and the understanding of the petrophysical properties of these rocks is essential for reservoir production. In this work, samples from the Morro do Chaves Formation (Sergipe–Alagoas Basin) and the Itapema Formation (Santos Basin) were selected to identify the porosity vs permeability relationship according to the biofabric characteristics and porosity control. The biofabric textures where classified into four groups according to taphonomic patterns and diagenetic modification: (i) well-sorted and preserved biofabric, (ii) well-sorted and altered biofabric, (iii) unsorted and preserved biofabric, and (iv) unsorted and altered biofabric. The porosity control varies in all groups from depositional to diagenetic with distinct pore types, pore sizes, and pore connectivity that are located in different global hydraulic elements. The analysis of the pore space was carried out through laboratorial measurements (gas injection) and by images from high-resolution computed tomography from plug samples, resulting in a pore network model where values of pore radius, pore throat radius, and coordination number were obtained. The best values of porosity and permeability are related to well-sorted altered biofabrics, whereas the lowest values, either with unsorted biofabrics, with low pore connectivity, or biofabrics that had the porosity reduced by compaction and cementation.

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.

Bioclastic accumulation in a lake rift basin: The Early Cretaceous coquinas of the Sergipe–Alagoas Basin, Brazil

ABSTRACTCoquinas constitute widespread deposits in lacustrine, estuarine, and shallow marine settings, where they are a valuable source of information on environmental conditions. Thick coquina successions were deposited in a series of lacustrine rift basins that formed along the Brazilian Continental Margin during the early stages of the opening of the South Atlantic Ocean, in the Early Cretaceous. In the Sergipe–Alagoas Basin, the coquina sequence, equivalent to the Morro do Chaves Formation, crops out in the Atol Quarry, and is considered a relevant analog for the economically important hydrocarbon reservoirs in the Pre-salt strata (Barremian to Aptian) of the Campos Basin (Pampo, Badejo, and Linguado oil fields), which occur only in the subsurface. The aim of this study is to generate a depositional and stratigraphic model through facies and stratigraphic analyses of a well core. These analyses allowed the geological characterization of the Morro do Chaves Formation and of its transition to the adjacent stratigraphic units, the Coqueiro Seco Formation above and the Penedo Formation below, contributing to the growing knowledge of sedimentation in rift basins and exploratory models in hydrocarbon-producing reservoirs. Facies analysis consists of sedimentological, taphonomic, and stratigraphic features of the rocks. Fourteen depositional facies were recognized, stacked into low-frequency and high-frequency, deepening-upward and shallowing-upward cycles driven by the interaction between climate and tectonism. A depositional model is presented, based on the correlation between well-core and outcrop data described in previous studies, providing insights into the spatial distribution of facies. The detailed analysis of facies and stacking patterns sheds light on depositional processes, paleoenvironmental conditions, and the evolution of the system through time, so we may better understand analogous deposits in the geological record.

High-resolution sequence stratigraphy of a cretaceous mixed siliciclastic-carbonate platform succession of the Sergipe–Alagoas Basin, NE Brazil

The Sergipe–Alagoas Basin, in northeastern Brazil, has extensive exposures of carbonate rocks that may be studied as analogues to hydrocarbon reservoirs. The outcrops are equivalent to the pre-salt and post-salt reservoirs of the Campos and Santos basins, the most important hydrocarbon exploration targets nowadays in Brazil. Outcrops and well logs of the Riachuelo Formation, the most important for analogue studies of Cretaceous marine carbonate reservoirs of the Campos Basin due to the great variability of facies, are described and interpreted to identify the depositional cycles and stratigraphic sequences. Three unconformities formed during the initial drift phase of the basin are recognized. The depositional setting of the studied section changes from a siliciclastic-dominated continental to shallow-marine mixed siliciclastic-carbonate at the base to a shallow-marine carbonate platform in the upper part. The transgressive–regressive (T–R) sequence model was used for the stratigraphic analysis, leading to a stratigraphic framework of three third-order T–R sequences, with an estimated duration of approximately 2.0, 4.5 and 1.5 Ma, respectively. Consequently, the higher frequency cycles identified in the well logs represent a timing of circa 140,000 years, and are interpreted as fourth-order depositional cycles.

Stratigraphic evolution of a Brazilian carbonate platform during the Cretaceous: the late Albian–early Turonian of the Sergipe–Alagoas Basin

The Cretaceous of Brazil is widely known for vast carbonate platforms that developed along the Brazilian east coast. An onshore well drilled and logged in Sergipe State on a structural low allowed the recovery and study of a continuous 439-m core section that records an interval aged from the late Albian to the early Turonian. The section is characterized by calcilutites, marls, and shales, with occasional carbonate breccias. Ten sedimentary microfacies were recognized that indicate deposition in a deep-marine paleoenvironment constantly affected by gravitational flows. These deposits were influenced by climatic variation, as suggested by the alternation of micritic and clayey layers. The analysis of the vertical microfacies pattern, supported by well logs and geochemistry analyses, led to the subdivision of the core into three third-order depositional sequences. A long-term sea-level rise trend in the studied interval, which records the evolution of a partially protected carbonate-siliciclastic mixed platform to a distally steepened carbonate ramp, is proposed herein. The conclusion obtained by this study is important to the understanding of carbonate platform evolution, with the integrated approach of microfacies, geochemistry, and well logs proving to be essential in obtaining precise information when working with deep-marine deposits.

Lithospheric structuration onshore-offshore of the Sergipe-Alagoas passive margin, NE Brazil, based on wide-angle seismic data

The structure and nature of the crust underlying the Camamu-Almada-Jequitinhonha-Sergipe-Alagoas basins System, in the NE Brazilian margin, were investigated based on the interpretation of 12 wide-angle seismic profiles acquired during the SALSA (Sergipe ALagoas Seismic Acquisition) experiment in 2014. In this work, we present two 220-km-long NW-SE combined wide-angle and reflection seismic profiles, SL 01 and SL 02, that have been acquired using 15 ocean-bottom-seismometers along each profile, offshore the southern part of the Sergipe Alagoas Basin (SAB), north of the Vaza-Barris Transfer zone. The SL 02 has a 150-km long inland continuation with 20 land-seismic-stations until the Sergipano Fold Belt (SFB). Wide-angle seismic forward modeling allows us to precisely divide the crust in three domains: beneath the continental shelf, a ∼100 km wide necking zone is imaged where the continental crust thins from ∼35 km on the Unthinned Continental Domain, which displays a three-layered crust structure, to less than 8 km on the Oceanic Crust Domain. In the necking zone, the upper and the middle layers thin dramatically and almost disappear, while the Moho discontinuity shows clear PmPs. The Continental-Oceanic Crust Boundary (COB) is located at ∼80 km from the coastline and is marked by intracrustal seismic reflectors and changes in the seismic velocity, showing a sharp transition. On profile SL02, the oceanic crust is perturbed by a volcanic edifice together with an anomalous velocity zone underneath the area.

Palynology of the Morro do Chaves Formation (Lower Cretaceous), Sergipe Alagoas Basin, NE Brazil: Paleoenvironmental implications for the early history of the South Atlantic

The break-up of Gondwana and the origin of related source rocks and reservoir intervals of the Brazilian coastal basins are being increasingly studied in the last decades. In this context the Sergipe-Alagoas Basin, which lies to the north of the Campos Basin hydrocarbon province, becomes relevant for the completeness of its depositional sequences. This paper presents, for the first time, the detailed palynological record from the Morro do Chaves Formation, located at the InterCement Quarry, near São Miguel dos Campos, Alagoas. The analysis of samples from the mudstone intervals of the unit mainly composed by coquinas has enabled new biostratigraphic, paleoenvironmental and paleogeographic interpretations of the evolution of the South Atlantic. The occurrence of the species Dicheiropollis etruscus, with a vertical distribution ranging from the Berriasian to the Barremian, supports the late Barremian age for the lowermost part of the Morro do Chaves Formation, traditionally interpreted as having been deposited in a lacustrine environment, close to herbaceous plants, surrounded by remote mountainous areas with arboreal vegetation. The occurrence of algae phycomata of the Class Prasinophyceae, associated with Scenedesmus and Botryoccocus, organisms that tolerate some salinity in its uppermost part, together with other biotic and abiotic data, corroborate the possibility of relating the Morro do Chaves Formation to a marine and/or brackish depositional environment, which may have resulted from a marine flooding in the northern sector of the Sergipe-Alagoas Basin during Early Cretaceous times. The results of this work support a paleogeographic model characterized by an episodic input of Tethyan waters towards the north of the South American continent.

Diagenetic Preservation and Modification of Porosity in Aptian Lithic Reservoirs from the Sergipe–alagoas Basin, Ne Brazil

Research Article| November 14, 2017 Diagenetic Preservation and Modification of Porosity in Aptian Lithic Reservoirs from the Sergipe–alagoas Basin, Ne Brazil Argos B.S. Schrank; Argos B.S. Schrank Geosciences Institute, Federal University of Rio Grande do Sul, Avenida Bento Gonçalves, 9500 Porto Alegre, Brazil Search for other works by this author on: GSW Google Scholar Sabrina D. Altenhofen; Sabrina D. Altenhofen Geosciences Institute, Federal University of Rio Grande do Sul, Avenida Bento Gonçalves, 9500 Porto Alegre, Brazil Search for other works by this author on: GSW Google Scholar Luiz F. De Ros Luiz F. De Ros Geosciences Institute, Federal University of Rio Grande do Sul, Avenida Bento Gonçalves, 9500 Porto Alegre, Brazil Search for other works by this author on: GSW Google Scholar Author and Article Information Argos B.S. Schrank Geosciences Institute, Federal University of Rio Grande do Sul, Avenida Bento Gonçalves, 9500 Porto Alegre, Brazil Sabrina D. Altenhofen Geosciences Institute, Federal University of Rio Grande do Sul, Avenida Bento Gonçalves, 9500 Porto Alegre, Brazil Luiz F. De Ros Geosciences Institute, Federal University of Rio Grande do Sul, Avenida Bento Gonçalves, 9500 Porto Alegre, Brazil e-mail: argosssb@hotmail.com Publisher: SEPM Society for Sedimentary Geology First Online: 14 Nov 2017 Online Issn: 1938-3681 Print Issn: 1527-1404 Copyright © 2017, SEPM (Society for Sedimentary Geology) Journal of Sedimentary Research (2017) 87 (11): 1156–1175. https://doi.org/10.2110/jsr.2017.64 Article history First Online: 14 Nov 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Argos B.S. Schrank, Sabrina D. Altenhofen, Luiz F. De Ros; Diagenetic Preservation and Modification of Porosity in Aptian Lithic Reservoirs from the Sergipe–alagoas Basin, Ne Brazil. Journal of Sedimentary Research 2017;; 87 (11): 1156–1175. doi: https://doi.org/10.2110/jsr.2017.64 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyJournal of Sedimentary Research Search Advanced Search Abstract Litharenites composed of sedimentary and low-grade metamorphic rock fragments are rarely good hydrocarbon reservoirs. Most of their primary porosity is lost by ductile grain deformation during mechanical compaction. However, the lithic Carmópolis Member of the Muribeca Formation from the Sergipe–Alagoas Basin, NE Brazil, is one of the most important oil reservoirs of the country. The high reservoir quality of the Carmópolis Member, despite its unusual composition rich in low-grade metamorphic fragments, indicates the occurrence of effective porosity preservation processes. The understanding of the occurrence and distribution of these porosity preservation processes are of paramount importance to optimize the recovery from producing oilfields, for the further development of these reservoirs, and for the exploration for similar reservoirs. The Carmópolis Member consists of alluvial conglomerates and sandstones intercalated with fine-grained lacustrine and alluvial-plain sediments deposited during the Aptian, in an arid environment. Detailed petrographic analyses were performed on 135 thin sections taken from cores of six wells, with support from SEM and EDS analyses. The reservoirs correspond mainly to conglomerates and to medium- to coarse-grained conglomeratic sandstones, classified as litharenite phyllarenites, subordinately feldspathic litharenites, and lithic arkoses. Dolomite is the most abundant cement. Other volumetrically significant processes are K-feldspar and calcite precipitation, feldspar dissolution, and deformation of ductile grains due to compaction. Twenty reservoir petrofacies were defined, based on the main aspects of primary composition and texture and diagenesis that control the porosity. Although partial dolomite cementation was previously considered as the main process of porosity preservation in the Carmópolis reservoirs, the present study suggests that other mechanisms such as early oil saturation may have been important for preserving their quality. Variations in depositional texture and composition, and in the distribution of these processes, resulted in the various defined reservoir petrofacies. Oil and the fluids that precipitated dolomite migrated up along major faults from deeply buried fine sediments to the shallow reservoirs. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.