Our second and third authors recognized in the late 1990s odd signatures in the oil geochemistry from wells southeast of the Merluza Graben (MG) trend in Brazil’s Santos Basin. We consider oil samples from seven wells which present a lesser question and a greater mystery. Our explanation first involves the lesser question of separating two structural influences in the early opening of the Austral South Atlantic and its penetration into the Santos Basin. We then address the genesis of oil samples that because of distinct geochemical markers avoid grouping into the dominant marine and sag families. Structural trends understood from answering the initial, ‘lesser question’ provide the means to explain the ‘oddball’ geochemistry. Mystery solved while opening a path for ongoing research into mixed-signature oils.

The work described here grew out of a need to compute a magnetic reduced to the pole grid over large areas of the world for purposes of geological interpretation. Formulas to do this are developed here and an example with results for real data is shown.

Is there a petroleum system here? How extensive and effective is it? How is it defined? Although we had presented a 2005 AAPG poster to address these questions, we now have performed an exploration look-back or case study demonstrating basin-wide presalt charge across Brazil's Santos Basin. Santos has been a disappointing gas province with meager results compared to the adjacent Campos Basin for the past two decades. We have reviewed and expanded presentations at AAPG and SEG conferences from 1998 to 2005, which were followed 17 months later by the supergiant Tupi discovery, now Lula Field. We document the progression of analyses and revision of interpretations as a case history for multidisciplinary work in a frontier region with, at the time, scant coverage of key data types. Despite our access to a broad range of material (oil and cuttings samples, piston core extracts, slicks analysis, regional seismic lines, potential field coverages, and published literature), only a handful of point samples directly fitted our hypothesis of a mature oil-prone presalt source, supported by our inference, from leakage at the basin margins, of basin-wide migration and charge. Although the volumes of data collected across the Santos Basin are orders of magnitude larger in 2019, with a concomitant improvement in understanding the petroleum system and overall basin evolution, we take pains to limit our focus to what was known as of mid-2005 (although perhaps published later), which still sufficed to point to the future success. Because the source presence and effectiveness are the first consideration in evaluating frontier basins, our methodology provides one template for understanding a key geologic risk We emphasize the importance of careful screening of inputs when information is scant and thus erroneous inferences are easily reached, with the need to take an exploration inference wherever data, once cross-validated, direct the explorer.

This paper discusses the geological and geophysical interpretation of rift structures in the region extending from the Rio Grande Rise, in the Southeastern Brazilian margin, towards the Cabo Frio High, which separates the Campos and Santos basins. We have analysed potential field data (gravity and magnetic) from the Argentine to the Brazilian oceanic basins and extending over the Pelotas, Santos and Campos basins. The Rio Grande Rise shows a relatively negative Bouguer anomaly in an area that corresponds to a major positive bathymetric feature between the Argentine and Brazil basins. North–south propagators related to the early spreading centres of the Atlantic Ocean are observed from Argentina towards the southern Santos Basin, which is characterized by an elevated basement topography relative to the Pelotas Basin. The region adjacent to the Florianopolis Fracture Zone between the Santos and Pelotas basins is also characterized by an elevated basement region aligned in an east–west direction, and locally it is marked by rift structures aligned along a NW–SE direction, forming a lineament or shear zone (Cruzeiro do Sul lineament) that extends from the Cabo Frio High towards the Rio Grande Rise, thus involving both continental and oceanic crusts. The Rio Grande Rise is associated with the east–west-trending fracture zones, which are characterized by several aligned magnetic anomalies in the southern Santos Basin. The Rio Grande Fracture Zone continues landward as the Sao Paulo Ridge, and extends towards the platform as the Florianopolis High. Oceanic propagators are identified from Argentina towards the Pelotas and Santos basins, and locally we observe rupturing of the salt layer by igneous intrusions or possibly by mantle exhumation. The Florianopolis (or Rio Grande) Fracture Zone is marked by an abrupt topographic offset separating the Pelotas Basin from the southern Santos Basin, and the associated volcanic belts limit the southernmost occurrence of the late Aptian evaporate sequence. The evaporite sequence in this segment of the continental margin shows remarkable layering of halite, anhydrite and carnalite. Conjugate to the Rio Grande Rise, the Walvis Ridge, offshore Namibia, is similarly a topographic high, but rift structures as observed in the Brazilian side are apparently unique in the South Atlantic. Alternative interpretations for the origin of the Rio Grande Rise include: a volcanic edifice or plateau rooted in the mantle; an intraplate shear zone affecting both continental and oceanic crust; an oceanic area of igneous over-productivity caused by a hotspot or a thermal anomaly in the mantle; a palaeo-spreading centre in the Cretaceous Atlantic Ocean; an area of excessive volcanic activity resulting from mantle differentiation due to adiabatic decompression; or perhaps an isolated remnant of continental crust left outboard of the Brazilian continental margin during the drifting process.

Abstract We describe an examination of two lines of evidence, tectono-structural evolution and hydrocarbon geochemistry, of asymmetric opening of the Atlantic Equatorial Margin. Our structural mapping used compilations of geophysical data and a review of both published literature and oil company public presentations. Geochemically, we accessed regional non-exclusive oil studies of the conjugate margins of Africa and South America, plus considerable published material. A group of non-exclusive oils was refined to 286, which clustered into five families, all represented along the NE Brazil margin but only one along the West African Transform (WAT) margin. Multiple lacustrine-sourced oils were seen around the South Atlantic, including NE Brazil, but a rich, oil-prone lacustrine source was not indicated offshore Ivory Coast and Ghana. Despite minor evidence of mixed source, possibly lacustrine stringers within an alluvial to marine setting, the predominant source is marine Cretaceous (Cenomanian–Turonian and possibly Albian). We find that opening asymmetry (a) biased the location of lacustrine (Early to mid-Cretaceous prerift to early synrift) source rocks to the NE Brazil margin and (b) locally narrowed the width of the optimal marine (Mid-Late Cretaceous postrift) WAT Margin source kitchens. Burial of the latter has aggravated the risk of late charge from light (condensate and gas) hydrocarbons.

Abstract The study focuses on the offshore Guyana–Suriname–French Guiana region. It draws from seismic, well, gravimetric and magnetic data. They indicate that the continental break-up along the western margin of the Demerara Plateau took place during the Callovian–Oxfordian, associated with the Central Atlantic opening, and accommodated by normal faults. The continental break-up in the SE offshore Guyana accommodated by strike-slip faults was coeval. The continental break-up along the NE and eastern margins of the Demerara Plateau took place during the late Aptian–Albian, associated with the opening of the Equatorial Atlantic, and accommodated by dextral strike-slip and normal faults, respectively. Different spreading vectors of the Central and Equatorial Atlantic required development of the Accommodation Block during the late Aptian/Albian–Paleocene in their contact region, and in the region between the Central Atlantic and its southernmost portion represented by the Offshore Guyana Block, which were separated from each other by the opening Equatorial Atlantic. Its role was to accommodate for about 20° mismatch between the Central and Equatorial Atlantic spreading vectors, which has decreased from the late Aptian/Albian to Paleocene down to 0°. Differential movements between the Central and Equatorial Atlantic oceans were also accommodated by strike-slip faults of the Guyana continental margin, some active until the Paleocene. Supplementary material: Extended methods and discussion chapters are available at http://www.geolsoc.org.uk/SUP18875

PreviousNext No Access14th International Congress of the Brazilian Geophysical Society & EXPOGEF, Rio de Janeiro, Brazil, 3-6 August 2015Advances in Depth to Basement Spectral Inversion of Gravity and Magnetic Data with Applications to Mexico and the Greater Gulf of MexicoAuthors: Mark E. OdegardMark E. OdegardGrizzly Geosciences, Ennis, Montana, and Insight Exploration, Aurora, Colorado, USASearch for more papers by this authorhttps://doi.org/10.1190/sbgf2015-146 SectionsAboutPDF/ePub ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InRedditEmail Abstract This paper presents the techniques and results of a depth to basement inversion effort over Mexico and the greater Gulf of Mexico and an analysis of the quality of the inversion. The spectral method was applied to magnetic and gravity data. New high resolution data sets for gravity and magnetic data have been merged and now cover all of these areas. The data used were derived from a variety of sources, and leveled and merged using techniques specially developed for large data sets. This paper presents a brief description of the development of a program to invert gravity and magnetic data using the spectral technique. The results of these developments are applied to determining the depth to basement and sediment thickness over These areas. To better understand the quality of the inversions three measures were used to try and quantify the possible errors in the inversions. The inversion utilize the Tau-P spectrum of the the radial spectrum in the inversion. Thus the Tau value, the semblance and an enhanced semblance were used in the error evaluation. Processed values of the parameters appear to indicate, but not give a quantative estimate of, the quality of the inversions. Examples from the inversion over Mexico and the greater Gulf of Mexico (MexGG) show the results of this investigation Results for South America and western Africa will be shown in the presentation. Keywords: inversion, Gulf of Mexico, spectral analysisPermalink: https://doi.org/10.1190/sbgf2015-146FiguresReferencesRelatedDetails 14th International Congress of the Brazilian Geophysical Society & EXPOGEF, Rio de Janeiro, Brazil, 3-6 August 2015ISSN (online):2159-6832Copyright: 2015 Pages: 1553 publication data© 2015 Published in electronic format with permission by the Brazilian Geophysical SocietyPublisher:Society of Exploration Geophysicists HistoryPublished Online: 06 Aug 2015 CITATION INFORMATION Mark E. Odegard, (2015), "Advances in Depth to Basement Spectral Inversion of Gravity and Magnetic Data with Applications to Mexico and the Greater Gulf of Mexico," SEG Global Meeting Abstracts : 745-748. https://doi.org/10.1190/sbgf2015-146 Plain-Language Summary KeywordsinversionGulf of Mexicospectral analysisPDF DownloadLoading ...

PreviousNext No Access13th International Congress of the Brazilian Geophysical Society & EXPOGEF, Rio de Janeiro, Brazil, 26–29 August 2013Defining Frontier Petroleum Systems: Examples from Plate Reconstructions of the Atlantic MarginsAuthors: Mark E. OdegardWilliam DicksonCraig F. SchiefelbeinJohn E. ZumbergeMark E. OdegardGrizzly Geosciences, Ennis, Montana, USA;Search for more papers by this author, William DicksonDIGs, Houston, TX, USA;Search for more papers by this author, Craig F. SchiefelbeinGeochemical Solutions International, Houston, TX, USA;Search for more papers by this author, and John E. ZumbergeGeomark, Houston, TX, USASearch for more papers by this authorhttps://doi.org/10.1190/sbgf2013-009 SectionsAboutPDF/ePub ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InRedditEmail Abstract Methods have been developed to reconstruct grids and images utilizing available plate reconstruction software. This has been applied to reconstructing the south Atlantic with the aim of understanding the paleo petroleum systems and geochemistry. Keywords: South America, case history, reconstruction, modeling, mappingPermalink: https://doi.org/10.1190/sbgf2013-009FiguresReferencesRelatedDetails 13th International Congress of the Brazilian Geophysical Society & EXPOGEF, Rio de Janeiro, Brazil, 26–29 August 2013ISSN (online):2159-6832Copyright: 2013 Pages: 2001 publication data© 2013 Published in electronic format with permission by the Brazilian Geophysical SocietyPublisher:Society of Exploration Geophysicists HistoryPublished: 09 Jan 2014 CITATION INFORMATION Mark E. Odegard, William Dickson, Craig F. Schiefelbein, and John E. Zumberge, (2013), "Defining Frontier Petroleum Systems: Examples from Plate Reconstructions of the Atlantic Margins," SEG Global Meeting Abstracts : 38-39. https://doi.org/10.1190/sbgf2013-009 Plain-Language Summary KeywordsSouth Americacase historyreconstructionmodelingmappingPDF DownloadLoading ...

Tensor Euler deconvolution has been developed to help interpret gravity tensor gradient data in terms of 3-D subsurface geological structure. Two forms of Euler deconvolution have been used in this study: conventional Euler deconvolution using three gradients of the vertical component of the gravity vector and tensor Euler deconvolution using all tensor gradients. These methods have been tested on point, prism, and cylindrical mass models using line and gridded data forms. The methods were then applied to measured gravity tensor gradient data for the Eugene Island area of the Gulf of Mexico using gridded and ungridded data forms. The results from the model and measured data show significantly improved performance of the tensor Euler deconvolution method, which exploits all measured tensor gradients and hence provides additional constraints on the Euler solutions.

ABSTRACT This paper discusses the geological and geophysical interpretation of rift structures in the region extending from the Rio Grande Rise, in the Southeastern Brazilian margin, towards the Cabo Frio High, which separates the Campos and Santos basins. We have analysed potential field data (gravity and magnetic) from the Argentine to the Brazilian oceanic basins and extending over the Pelotas, Santos and Campos basins. The Rio Grande Rise shows a relatively negative Bouguer anomaly in an area that corresponds to a major positive bathymetric feature between the Argentine and Brazil basins. North–south propagators related to the early spreading centres of the Atlantic Ocean are observed from Argentina towards the southern Santos Basin, which is characterized by an elevated basement topography relative to the Pelotas Basin. The region adjacent to the Florianópolis Fracture Zone between the Santos and Pelotas basins is also characterized by an elevated basement region aligned in an east–west direction, and locally it is marked by rift structures aligned along a NW–SE direction, forming a lineament or shear zone (Cruzeiro do Sul lineament) that extends from the Cabo Frio High towards the Rio Grande Rise, thus involving both continental and oceanic crusts. The Rio Grande Rise is associated with the east–west-trending fracture zones, which are characterized by several aligned magnetic anomalies in the southern Santos Basin. The Rio Grande Fracture Zone continues landward as the São Paulo Ridge, and extends towards the platform as the Florianópolis High. Oceanic propagators are identified from Argentina towards the Pelotas and Santos basins, and locally we observe rupturing of the salt layer by igneous intrusions or possibly by mantle exhumation. The Florianópolis (or Rio Grande) Fracture Zone is marked by an abrupt topographic offset separating the Pelotas Basin from the southern Santos Basin, and the associated volcanic belts limit the southernmost occurrence of the late Aptian evaporite sequence. The evaporite sequence in this segment of the continental margin shows remarkable layering of halite, anhydrite and carnalite. Conjugate to the Rio Grande Rise, the Walvis Ridge, offshore Namibia, is similarly a topographic high, but rift structures as observed in the Brazilian side are apparently unique in the South Atlantic. Alternative interpretations for the origin of the Rio Grande Rise include: a volcanic edifice or plateau rooted in the mantle; an intraplate shear zone affecting both continental and oceanic crust; an oceanic area of igneous over-productivity caused by a hotspot or a thermal anomaly in the mantle; a palaeo-spreading centre in the Cretaceous Atlantic Ocean; an area of excessive volcanic activity resulting from mantle differentiation due to adiabatic decompression; or perhaps an isolated remnant of continental crust left outboard of the Brazilian continental margin during the drifting process.

The Sub-Andean basins of South America are among the most prolific oil-producing areas of the world. From western Venezuela to southern Argentina there are no fewer than sixteen separate oil productive basins which lie directly east of the Andes. Production is from formations ranging in age from Devonian to Tertiary and recoverable oil to date exceeds 80 billion barrels, of which approximately 50 billion barrels have already been produced. The sedimentary basins of South America that occur around the PreCambrian Guyana and Brazilian shield areas, along the Andean mountain chain, and offshore on the continental margins contain sedimentary rocks ranging from Paleozoic to Cenozoic age. These basins are described by their relationship to the Mesozoic Andean volcanic arc as forearc Coastal basins and backarc Sub-Andean and Intermontane basins.

This paper presents the techniques and results of a depth to basement inversion effort over the South China Sea area of Southeast Asia. Integrating the results of the inversions with geoseismic, well and geological data results in an accurate and informative description of the tectonics and structure of the area. Results show that significant packages of sediments of exploration interest exist that have not been exploited. Basin geometry and structure can be derived from the inversion of gravity and magnetic data. Using some newly developed techniques these inversions can also discriminate between different lithologies. Magnetic data can be inverted for magnetic basement and for intermediate layers of volcanic material. Gravity data can be inverted for structures which produce density contrasts in basins. Combining these results, basin structure can be explored to determine depth to basement, to high density structures such as carbonates, and to high susceptibility structures such as volcanics. New high resolution data sets for gravity and magnetic data have been merged and now cover all of greater Southeast Asia. These data allow us to extend our interpretation to all offshore basins and some onshore as well. We use the structural interpretations described above along with enhancements of gravity, magnetic and digital elevation model data. Combining these interpretations and enhancements with published data in a GIS environment allows us to constrain additional interpretations of tectonic development, and sedimentary facies and structures in basins. Examples are shown for basins around the South China Sea. Early results from offshore South America will also be presented.

PreviousNext No AccessSEG Technical Program Expanded Abstracts 2005Sediment thickness, basement structure and tectonics from inversion and modeling over northeastern South AmericaAuthors: Mark E. OdegardAllan E. KeanW. Robert WeberKirsten FletcherMohammed KidwaiMark E. OdegardGrizzly GeosciencesSearch for more papers by this author, Allan E. KeanRepsol YPFSearch for more papers by this author, W. Robert WeberHouston Gravity ImagesSearch for more papers by this author, Kirsten FletcherGETECH, Ltd.Search for more papers by this author, and Mohammed KidwaiGETECH, Inc.Search for more papers by this authorhttps://doi.org/10.1190/1.2148281 SectionsAboutPDF/ePub ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InRedditEmail Abstract This paper presents the techniques and results of a depth to basement inversion and modeling effort over the Guyana, Suriname, and French Guiana area of northeastern South America. A new development in the application of spectral inversion of both gravity and magnetic data has allowed us to extend the inversion over the entire study. Integrating the results of the spectral inversions with Euler deconvolution and 2‐D modeling results in an accurate and informative description of the tectonics and structure of the area. Results show that significant packages of sediments of exploration interest have been deposited over most of the offshore area. This indicates that the USGS (2000) estimate of over fifteen BBOE for the area is highly possible.Permalink: https://doi.org/10.1190/1.2148281FiguresReferencesRelatedDetailsCited ByDefining a supergiant petroleum system in Brazil’s Santos Basin with multidisciplinary methods: One template for exploration successWilliam Dickson, Craig Schiefelbein, and Mark Odegard21 October 2019 | Interpretation, Vol. 7, No. 4A Sediment Thickness Map of South America Using Automated Inversion of Magnetic and Gravity Data for Depth to BasementMark E. Odegard13 March 2014Structural And Lithological Inversion Using Gravity And Magnetic Data Integrated With Geological InformationMark E. Odegard, William G. Dickson, Janice M. Christ, and James Ganath23 November 2007 SEG Technical Program Expanded Abstracts 2005ISSN (print):1052-3812 ISSN (online):1949-4645Copyright: 2005 Pages: 2668 publication data© 2005 Copyright © 2005 Society of Exploration GeophysicistsPublisher:Society of Exploration Geophysicists HistoryPublished: 07 Dec 2005 CITATION INFORMATION Mark E. Odegard, Allan E. Kean, W. Robert Weber, Kirsten Fletcher, and Mohammed Kidwai, (2005), "Sediment thickness, basement structure and tectonics from inversion and modeling over northeastern South America," SEG Technical Program Expanded Abstracts : 806-808. https://doi.org/10.1190/1.2148281 Plain-Language Summary PDF DownloadLoading ...