Valeria Cristina Ferreira Barbosa - Profile on Academia.edu (original) (raw)
Papers by Valeria Cristina Ferreira Barbosa
Pinga-Lab/Magnetic-Radial-Inversion
No description provided.
pinga-lab/magnetic-radial-inversion: Magnetic radial inversion
No description provided.
Correct structural index defined by base level estimates in Euler deconvolution
15th International Congress of the Brazilian Geophysical Society & EXPOGEF, Rio de Janeiro, Brazil, 31 July-3 August 2017
The main goal of Euler deconvolution is to define the source nature and its depth position. Besid... more The main goal of Euler deconvolution is to define the source nature and its depth position. Besides that, it estimates base level of the data and horizontal positions of the sources. To define the correct structural index most authors take advantage of the clustering in depth estimates. Some authors assume constant, linear or nonlinear base levels in their formulation, thus they estimate or eliminate this parameter from their analysis. With a tentative structural index, we take advantage of base level clustering when the correct structural index is used. We modeled three bodies with different structural indices and show that minimum variation of depth is sufficient to indicate the correct structural index when no interfering anomalies are present. In the presence of interfering anomalies, the minimum variation of base level estimates indicates the correct structural index. We simulated constant and nonlinear base levels in our tests. Application to a real data set shows that nonlinear base level is present possibly due to interfering anomalies. These results are valid independent of geomagnetic field incidence.
What to expect from Euler deconvolution estimates for isolated sources
15th International Congress of the Brazilian Geophysical Society & EXPOGEF, Rio de Janeiro, Brazil, 31 July-3 August 2017
Euler deconvolution is a technique based anomaly measurements, its derivatives and structural ind... more Euler deconvolution is a technique based anomaly measurements, its derivatives and structural index. The objective is to estimate the base level of the data, horizontal and vertical positions of the source, usually assuming a tentative structural index. Derivatives are calculated using different techniques and different methodologies exist to indicate the correct structural index. Most of the approaches define the correct depth estimates based on structural index estimated. We modeled anomalies magnetized by vertical and inclined directions, generated by an isolated magnetic monopole and calculated its analytical derivatives in order to show what expect from Euler deconvolution estimates for single sources. We then analyzed estimates over the sourceinfluence area and at the borders. These examples clearly show an outstanding pattern for depth and base level estimates when the correct structural index is used. The estimates at these cases, and only at these cases, are constant over the anomaly position. For these cases, this pattern can clearly identify the correct structural index, related to the nature of the source.
Base-level estimates to define the correct structural index in Euler deconvolution
SEG Technical Program Expanded Abstracts 2017
The main goal of Euler deconvolution is to define the nature of the source (i.e., the structural ... more The main goal of Euler deconvolution is to define the nature of the source (i.e., the structural index – SI) and its depth position. To define the correct structural index most authors take advantage of the clustering in depth estimates. With tentative structural indices, we take advantage of base level clustering when the correct SI is used. We modeled three bodies with different structural indices simulating interfering magnetic anomalies; even when we assume a null base level in the data the base level estimated by Euler deconvolution generate a nonlinear pattern. The minimum standard deviation of base level estimates over an area delineated by depth estimates can define the correct SI. Application to a real data set shows a nonlinear pattern of the estimated base level, possibly due to interfering anomalies. Our result may infer that the real body of the study is a plug intrusion.
Geophysical Journal International, 2016
The Python code that produces the results presented here is available under a BSD 3-clause open-s... more The Python code that produces the results presented here is available under a BSD 3-clause open-source license at github.com/pinga-lab/paper-moho-inversion-tesseroids Moho model and data: The Moho depth model for South America and the data used to generate it are available under a Creative Commons Attribution 4.0
Synthetic total-field magnetic anomaly data and code to perform Euler deconvolution on it
Presentation: Deep-pass — An aeromagnetic data filter to enhance deep features in marginal basins
How two gravity-gradient inversion methods can be used to reveal different geologic features of ore deposit — A case study from the Quadrilátero Ferrífero (Brazil)
Journal of Applied Geophysics, 2016
Abstract Airborne gravity gradiometry data have been recently used in mining surveys to map the 3... more Abstract Airborne gravity gradiometry data have been recently used in mining surveys to map the 3D geometry of ore deposits. This task can be achieved by different gravity-gradient inversion methods, many of which use a voxel-based discretization of the Earth's subsurface. To produce a unique and stable solution, an inversion method introduces particular constraints. One constraining inversion introduces a depth-weighting function in the first-order Tikhonov regularization imposing a smoothing on the density-contrast distributions that are not restricted to near-surface regions. Another gravity-gradient inversion, the method of planting anomalous densities, imposes compactness and sharp boundaries on the density-contrast distributions. We used these two inversion methods to invert the airborne gravity-gradient data over the iron-ore deposit at the southern flank of the Gandarela syncline in Quadrilatero Ferrifero (Brazil). Because these methods differ from each other in the particular constraint used, the estimated 3D density-contrast distributions reveal different geologic features of ore deposit. The depth-weighting smoothing inversion reveals variable dip directions along the strike of the retrieved iron-ore body. The planting anomalous density inversion estimates a compact iron-ore mass with a single density contrast, which reveals a variable volume of the iron ore along its strike increasing towards the hinge zone of the Gandarela syncline which is the zone of maximum compression. The combination of the geologic features inferred from each estimate leads to a synergistic effect, revealing that the iron-ore deposit is strongly controlled by the Gandarela syncline.
3D gravity Gradient Inversion by Planting Density Anomalies
73rd EAGE Conference and Exhibition incorporating SPE EUROPEC 2011, 2011
ABSTRACT We present a new gravity gradient tensor inversion for estimating a 3D density-contrast ... more ABSTRACT We present a new gravity gradient tensor inversion for estimating a 3D density-contrast distribution defined on a user-specified grid of prisms. Our method consists of an iterative algorithm that does not require the solution of large equation system. Instead, the solution grows systematically around user-specified prismatic elements called “seeds”. Each seed can have a different density contrast, allowing the interpretation of multiples bodies with different density contrasts. The compactness of the solution is imposed by means of a regularizing function that favors compact bodies closest to the priorly specified seeds. The solution grows by accreting neighboring prisms of the current solution. The prisms for the accretion are chosen by systematically searching the set of current neighboring prisms. Therefore, this approach allows that the columns of the Jacobian matrix be calculated on demand. This is a known technique from computer science called “lazy evaluation”, which greatly reduces the demand of computer memory and processing time. Test on synthetic data from multiple buried sources at different depths and on real data collected over iron deposits located in the Quadrilátero Ferr'ifero, southeastern region of Brazil, confirmed the ability of our method in detecting sharp and compact bodies.
Presentation: Source geometry estimation using the mass excess criterion to constrain 3-D radial inversion of gravity data
Deconvolu��o de Euler: passado, presente e futuro - um tutorial
Presentation: Polynomial Equivalent Layer
Presentation: 3D depth-to-basement and density contrast estimates using gravity and borehole data
Reconstitui��o gravim�trica compacta
9th International Congress of the Brazilian Geophysical Society & EXPOGEF, Salvador, Bahia, Brazil, 11-14 September 2005, 2005
We present a new gravity inversion method, which produces an apparent density contrast mapping on... more We present a new gravity inversion method, which produces an apparent density contrast mapping on the horizontal plane, based on the combination of the minimization of the first-order entropy with the maximization of the zeroth-order entropy. The interpretation model consists of a horizontal grid of 3D vertical prisms, and the parameters to be estimated are the prisms density contrasts. The maximization of the zeroth-order entropy is equivalent to the global smoothness constraint whereas the minimization of the first-order entropy favors solutions presenting abrupt borders, so a judicious combination of both constraints may lead to solutions characterized by regions where the estimated density contrasts are virtually constant, separated by abrupt discontinuities. The method has been applied to synthetic data simulating the presence of intrusive bodies in sediments. The comparison of the results with those obtained with the global smoothness constraint applied to the same data, showed that that both methods locate the sources with good precision, but the entropic regularization delineates the contour of the bodies with greater resolution, even in the case of 100 m wide bodies separated by a distance as small as 50 m
Recent developments in hydrocarbon exploration offshore Portugal, in particular in the offshore A... more Recent developments in hydrocarbon exploration offshore Portugal, in particular in the offshore Algarve basin, have increased the interest in basement structure studies in this area. Basement morphology plays an important role in salt tectonics, basin development and thin-skinned mechanisms of rifting and tectonic inversion. Furthermore, geochemical data suggest the presence of a rich Paleozoic source rock that might be producing Meso-Cenozoic gas accumulations. Consequently, it is of paramount importance to comprehend the relief of the Paleozoic "basement" for predicting the Meso-Cenozoic depositional history and patterns as well as to understand the petroleum system of the area. However, the deformation suffered by the basin coupled with halokinetic processes and the scarcity of coverage and poor resolution of available seismic data makes it difficult to map the Paleozoic "basement" accurately. To address the aforementioned problem, an integrated geophysical interpretation was performed. The interpreted dataset comprised 58 lines of 2D seismic reflection data. The seismic interpretation was guided by 2D forward and 3D inversion gravity modelling and regional magnetic interpretation. Geochemical data collected from onshore outcrops, and offshore wells were later used as an input for 2D basin modelling studies to address source rock potential of the Paleozoic sediments. The Algarve Basin is delimited to the south by a series of basement highs with a NE-SW orientation (Guadalquivir Bank) and to the West by the Sao Vicente and Sagres Highs. The basin strikes around ENE-WSW direction and is bisected by NW-SE faults in three sub-basins (NE, Central and SW sub-basins). The Central basin, where the main depocenter strikes E-W, has a maximum depth of approximately 10 km and Meso-Cenozoic thicknesses of 9,000m. Some terraces associated with horsts and grabens were correlated with regional faults that extend onshore. Geochemical data from Paleozoic sediments shows that average TOC data TOC of 1.5% and type III kerogen. The 2D basin modelling concludes that despite de fact that the Paleozoic rocks could be presently overmature, they could have generated significant amounts of gas in earlier stages of basin development that afterwards migrated through salt windows to shallower Meso-Cenozoic reservoirs.
Suplementary material to article “3-D radial gravity gradient inversion”
We have provided supplementary material to our article titled “3-D radial gravity gradient invers... more We have provided supplementary material to our article titled “3-D radial gravity gradient inversion” and whose authors are Vanderlei C. Oliveira Jr, and Valeria C. F. Barbosa. In this material, we presented extra results obtained by inverting the gravity-gradient data from a survey over the Vinton salt dome (Louisiana, USA). In these extra results, we investigate the effect on the results caused by the assumption of uncertainties in the density contrast of the cap rock with the host rocks.
10th International Congress of the Brazilian Geophysical Society & EXPOGEF 2007, Rio de Janeiro, Brazil, 19-23 November 2007, 2007
13th International Congress of the Brazilian Geophysical Society & EXPOGEF, Rio de Janeiro, Brazil, 26–29 August 2013, 2013
Contents of this paper were reviewed by the Technical Committee of the 13 th International Congre... more Contents of this paper were reviewed by the Technical Committee of the 13 th International Congress of the Brazilian Geophysical Society and do not necessarily represent any position of the SBGf, its officers or members. Electronic reproduction or storage of any part of this paper for commercial purposes without the written consent of the Brazilian Geophysical Society is prohibited.
Pinga-Lab/Magnetic-Radial-Inversion
No description provided.
pinga-lab/magnetic-radial-inversion: Magnetic radial inversion
No description provided.
Correct structural index defined by base level estimates in Euler deconvolution
15th International Congress of the Brazilian Geophysical Society & EXPOGEF, Rio de Janeiro, Brazil, 31 July-3 August 2017
The main goal of Euler deconvolution is to define the source nature and its depth position. Besid... more The main goal of Euler deconvolution is to define the source nature and its depth position. Besides that, it estimates base level of the data and horizontal positions of the sources. To define the correct structural index most authors take advantage of the clustering in depth estimates. Some authors assume constant, linear or nonlinear base levels in their formulation, thus they estimate or eliminate this parameter from their analysis. With a tentative structural index, we take advantage of base level clustering when the correct structural index is used. We modeled three bodies with different structural indices and show that minimum variation of depth is sufficient to indicate the correct structural index when no interfering anomalies are present. In the presence of interfering anomalies, the minimum variation of base level estimates indicates the correct structural index. We simulated constant and nonlinear base levels in our tests. Application to a real data set shows that nonlinear base level is present possibly due to interfering anomalies. These results are valid independent of geomagnetic field incidence.
What to expect from Euler deconvolution estimates for isolated sources
15th International Congress of the Brazilian Geophysical Society & EXPOGEF, Rio de Janeiro, Brazil, 31 July-3 August 2017
Euler deconvolution is a technique based anomaly measurements, its derivatives and structural ind... more Euler deconvolution is a technique based anomaly measurements, its derivatives and structural index. The objective is to estimate the base level of the data, horizontal and vertical positions of the source, usually assuming a tentative structural index. Derivatives are calculated using different techniques and different methodologies exist to indicate the correct structural index. Most of the approaches define the correct depth estimates based on structural index estimated. We modeled anomalies magnetized by vertical and inclined directions, generated by an isolated magnetic monopole and calculated its analytical derivatives in order to show what expect from Euler deconvolution estimates for single sources. We then analyzed estimates over the sourceinfluence area and at the borders. These examples clearly show an outstanding pattern for depth and base level estimates when the correct structural index is used. The estimates at these cases, and only at these cases, are constant over the anomaly position. For these cases, this pattern can clearly identify the correct structural index, related to the nature of the source.
Base-level estimates to define the correct structural index in Euler deconvolution
SEG Technical Program Expanded Abstracts 2017
The main goal of Euler deconvolution is to define the nature of the source (i.e., the structural ... more The main goal of Euler deconvolution is to define the nature of the source (i.e., the structural index – SI) and its depth position. To define the correct structural index most authors take advantage of the clustering in depth estimates. With tentative structural indices, we take advantage of base level clustering when the correct SI is used. We modeled three bodies with different structural indices simulating interfering magnetic anomalies; even when we assume a null base level in the data the base level estimated by Euler deconvolution generate a nonlinear pattern. The minimum standard deviation of base level estimates over an area delineated by depth estimates can define the correct SI. Application to a real data set shows a nonlinear pattern of the estimated base level, possibly due to interfering anomalies. Our result may infer that the real body of the study is a plug intrusion.
Geophysical Journal International, 2016
The Python code that produces the results presented here is available under a BSD 3-clause open-s... more The Python code that produces the results presented here is available under a BSD 3-clause open-source license at github.com/pinga-lab/paper-moho-inversion-tesseroids Moho model and data: The Moho depth model for South America and the data used to generate it are available under a Creative Commons Attribution 4.0
Synthetic total-field magnetic anomaly data and code to perform Euler deconvolution on it
Presentation: Deep-pass — An aeromagnetic data filter to enhance deep features in marginal basins
How two gravity-gradient inversion methods can be used to reveal different geologic features of ore deposit — A case study from the Quadrilátero Ferrífero (Brazil)
Journal of Applied Geophysics, 2016
Abstract Airborne gravity gradiometry data have been recently used in mining surveys to map the 3... more Abstract Airborne gravity gradiometry data have been recently used in mining surveys to map the 3D geometry of ore deposits. This task can be achieved by different gravity-gradient inversion methods, many of which use a voxel-based discretization of the Earth's subsurface. To produce a unique and stable solution, an inversion method introduces particular constraints. One constraining inversion introduces a depth-weighting function in the first-order Tikhonov regularization imposing a smoothing on the density-contrast distributions that are not restricted to near-surface regions. Another gravity-gradient inversion, the method of planting anomalous densities, imposes compactness and sharp boundaries on the density-contrast distributions. We used these two inversion methods to invert the airborne gravity-gradient data over the iron-ore deposit at the southern flank of the Gandarela syncline in Quadrilatero Ferrifero (Brazil). Because these methods differ from each other in the particular constraint used, the estimated 3D density-contrast distributions reveal different geologic features of ore deposit. The depth-weighting smoothing inversion reveals variable dip directions along the strike of the retrieved iron-ore body. The planting anomalous density inversion estimates a compact iron-ore mass with a single density contrast, which reveals a variable volume of the iron ore along its strike increasing towards the hinge zone of the Gandarela syncline which is the zone of maximum compression. The combination of the geologic features inferred from each estimate leads to a synergistic effect, revealing that the iron-ore deposit is strongly controlled by the Gandarela syncline.
3D gravity Gradient Inversion by Planting Density Anomalies
73rd EAGE Conference and Exhibition incorporating SPE EUROPEC 2011, 2011
ABSTRACT We present a new gravity gradient tensor inversion for estimating a 3D density-contrast ... more ABSTRACT We present a new gravity gradient tensor inversion for estimating a 3D density-contrast distribution defined on a user-specified grid of prisms. Our method consists of an iterative algorithm that does not require the solution of large equation system. Instead, the solution grows systematically around user-specified prismatic elements called “seeds”. Each seed can have a different density contrast, allowing the interpretation of multiples bodies with different density contrasts. The compactness of the solution is imposed by means of a regularizing function that favors compact bodies closest to the priorly specified seeds. The solution grows by accreting neighboring prisms of the current solution. The prisms for the accretion are chosen by systematically searching the set of current neighboring prisms. Therefore, this approach allows that the columns of the Jacobian matrix be calculated on demand. This is a known technique from computer science called “lazy evaluation”, which greatly reduces the demand of computer memory and processing time. Test on synthetic data from multiple buried sources at different depths and on real data collected over iron deposits located in the Quadrilátero Ferr'ifero, southeastern region of Brazil, confirmed the ability of our method in detecting sharp and compact bodies.
Presentation: Source geometry estimation using the mass excess criterion to constrain 3-D radial inversion of gravity data
Deconvolu��o de Euler: passado, presente e futuro - um tutorial
Presentation: Polynomial Equivalent Layer
Presentation: 3D depth-to-basement and density contrast estimates using gravity and borehole data
Reconstitui��o gravim�trica compacta
9th International Congress of the Brazilian Geophysical Society & EXPOGEF, Salvador, Bahia, Brazil, 11-14 September 2005, 2005
We present a new gravity inversion method, which produces an apparent density contrast mapping on... more We present a new gravity inversion method, which produces an apparent density contrast mapping on the horizontal plane, based on the combination of the minimization of the first-order entropy with the maximization of the zeroth-order entropy. The interpretation model consists of a horizontal grid of 3D vertical prisms, and the parameters to be estimated are the prisms density contrasts. The maximization of the zeroth-order entropy is equivalent to the global smoothness constraint whereas the minimization of the first-order entropy favors solutions presenting abrupt borders, so a judicious combination of both constraints may lead to solutions characterized by regions where the estimated density contrasts are virtually constant, separated by abrupt discontinuities. The method has been applied to synthetic data simulating the presence of intrusive bodies in sediments. The comparison of the results with those obtained with the global smoothness constraint applied to the same data, showed that that both methods locate the sources with good precision, but the entropic regularization delineates the contour of the bodies with greater resolution, even in the case of 100 m wide bodies separated by a distance as small as 50 m
Recent developments in hydrocarbon exploration offshore Portugal, in particular in the offshore A... more Recent developments in hydrocarbon exploration offshore Portugal, in particular in the offshore Algarve basin, have increased the interest in basement structure studies in this area. Basement morphology plays an important role in salt tectonics, basin development and thin-skinned mechanisms of rifting and tectonic inversion. Furthermore, geochemical data suggest the presence of a rich Paleozoic source rock that might be producing Meso-Cenozoic gas accumulations. Consequently, it is of paramount importance to comprehend the relief of the Paleozoic "basement" for predicting the Meso-Cenozoic depositional history and patterns as well as to understand the petroleum system of the area. However, the deformation suffered by the basin coupled with halokinetic processes and the scarcity of coverage and poor resolution of available seismic data makes it difficult to map the Paleozoic "basement" accurately. To address the aforementioned problem, an integrated geophysical interpretation was performed. The interpreted dataset comprised 58 lines of 2D seismic reflection data. The seismic interpretation was guided by 2D forward and 3D inversion gravity modelling and regional magnetic interpretation. Geochemical data collected from onshore outcrops, and offshore wells were later used as an input for 2D basin modelling studies to address source rock potential of the Paleozoic sediments. The Algarve Basin is delimited to the south by a series of basement highs with a NE-SW orientation (Guadalquivir Bank) and to the West by the Sao Vicente and Sagres Highs. The basin strikes around ENE-WSW direction and is bisected by NW-SE faults in three sub-basins (NE, Central and SW sub-basins). The Central basin, where the main depocenter strikes E-W, has a maximum depth of approximately 10 km and Meso-Cenozoic thicknesses of 9,000m. Some terraces associated with horsts and grabens were correlated with regional faults that extend onshore. Geochemical data from Paleozoic sediments shows that average TOC data TOC of 1.5% and type III kerogen. The 2D basin modelling concludes that despite de fact that the Paleozoic rocks could be presently overmature, they could have generated significant amounts of gas in earlier stages of basin development that afterwards migrated through salt windows to shallower Meso-Cenozoic reservoirs.
Suplementary material to article “3-D radial gravity gradient inversion”
We have provided supplementary material to our article titled “3-D radial gravity gradient invers... more We have provided supplementary material to our article titled “3-D radial gravity gradient inversion” and whose authors are Vanderlei C. Oliveira Jr, and Valeria C. F. Barbosa. In this material, we presented extra results obtained by inverting the gravity-gradient data from a survey over the Vinton salt dome (Louisiana, USA). In these extra results, we investigate the effect on the results caused by the assumption of uncertainties in the density contrast of the cap rock with the host rocks.
10th International Congress of the Brazilian Geophysical Society & EXPOGEF 2007, Rio de Janeiro, Brazil, 19-23 November 2007, 2007
13th International Congress of the Brazilian Geophysical Society & EXPOGEF, Rio de Janeiro, Brazil, 26–29 August 2013, 2013
Contents of this paper were reviewed by the Technical Committee of the 13 th International Congre... more Contents of this paper were reviewed by the Technical Committee of the 13 th International Congress of the Brazilian Geophysical Society and do not necessarily represent any position of the SBGf, its officers or members. Electronic reproduction or storage of any part of this paper for commercial purposes without the written consent of the Brazilian Geophysical Society is prohibited.