Valeria C. F. Barbosa

Observatório Nacional · Coordination of Geophysics - COGE

We present a seafloor 4D gravity feasibility analysis for monitoring deep-water hydrocarbon reservoirs. To perform the study, we have simulated the gravity effect due to different density and pore pressure distributions derived from a realistic model of a turbiditic oil field in Campos Basin, offshore Brazil. These reservoirs are analogs of several...

We have presented alternative solutions for the displacement and stress fields outside and inside of a 3D right rectangular prism under constant pressure. These solutions are obtained by integrating the well-known nucleus-of-strain solution over the volume of the prism. They are based on the similarity between the gravitational potential yielded by...

Potential-field edge detection filters are powerful fault detection tools in mineral exploration. The application of these filters to electromagnetic (EM) data is not as accepted as those associated with potential field data. But they may be advantageous when dealing with mineralizations associated with non-magnetic rocks. This paper introduces the...

We present a fast equivalent layer method for processing large-scale magnetic data. We demonstrate that the sensitivity matrix associated with an equivalent layer of dipoles can be arranged to a Block-Toeplitz Toeplitz-Block (BTTB) structure for the case where observations and dipoles are aligned on a horizontal and regularly-spaced grid. The produ...

We developed a new ambiguity analysis method to investigate the remanence of a uniformly magnetized source. We wrote the unit vector of the total‐magnetization direction as the weighted sum of the unit vectors of the induced‐ and remanent‐magnetization directions. The unit vectors of the induced‐ and remanent‐magnetization directions are weighted,...

We present a method for inverting total-field anomaly data to estimate the geometry of a uniformly magnetized 3-D geological source in the subsurface. The method assumes the total-magnetization direction is known. We approximate the source by an ensemble of vertically juxtaposed right prisms, all of them with the same total-magnetization vector and...

We propose the use of the amplitude of the magnetic anomaly vector (amplitude data) for qualitative interpretation of large areas at low magnetic latitudes. The amplitude data are weakly dependent on the magnetization direction. Hence, the amplitude data require no prior knowledge of the source magnetization direction. The amplitude data produce ma...

We present an inversion method to recover both the depth and the total magnetization intensity of the basement under a sedimentary basin using the amplitude of the magnetic anomaly vector (amplitude data). Because the amplitude data are weakly dependent on the magnetization direction, the proposed method is suitable for interpreting areas with rema...

We develop an efficient and very fast equivalent-layer technique for gravity data processing by modifying an iterative method grounded on an excess mass constraint that does not require the solution of linear systems. Taking advantage of the symmetric Block-Toeplitz Toeplitz-Block (BTTB) structure of the sensitivity matrix, that arises when regular...

It is known from potential theory that a continuous and planar layer of dipoles can exactly reproduce the total-field anomaly produced by arbitrary 3D sources. We prove the existence of an equivalent layer having an all-positive magnetic-moment distribution for the case in which the magnetization direction of this layer is the same as that of the t...

We created a funnel-shaped magnetic body from magnetite powder dispersed in plaster and used a travelling 3-component fluxgate magnetometer to map the magnetic field at a low elevation above it. This provided a dataset with signal and noise characteristics similar to those of a field survey, but for a source much better known than any buried geolog...

We present a comparison between the computing of gravity gradient tensor components from the vertical component of the gravitational attraction using the fast Fourier transform and the equivalent-layer techniques. In this comparison, we consider that the observed data consist of: (1) the residual gravity field (produced by local sources) and (2) th...

This paper presents a preliminary feasibility study of ocean-bottom 4D gravimetry survey focused on oil production monitoring. We have conducted numerical simulations by computing the vertical component of the gravitational attraction exerted by a synthetic petroleum reservoir. Three parameters were tested regarded a detectability limit of 3 μGal:...

Euler deconvolution is a popular method for interpretation of potential field data. The method estimates the position and the base level for a given nature (i.e., structural index-SI) of a geologic source based on the magnetic dada. These estimates are computed inside a moving data window spanning the whole dataset. The selection of the best estima...

Reduction to the pole (RTP) is a popular filter that simulates how the magnetic data would be if both the geomagnetic field and the magnetization of the source were vertical. This process locates the horizontal position of the source through the maximum amplitude of the reduced-to-the-pole anomaly; therefore, it assists in the geologic interpretati...

The interpretation of total-field anomalies data presents complexities due to dipolar characteristics of the anomalies. Usually, the geophysicists apply some transformations to the measured total-field anomaly to assist the magnetic interpretation and inversion. However, it can lead to an unstable transformed data at low latitude regions. To transf...

We present a fast 3D regularized magnetic inversion algorithm for depth-to-basement estimation based on an efficient way to compute the total-field anomaly produced by an arbitrary interface separating nonmagnetic sediments from a magnetic basement. We approximate the basement layer by a grid of 3D vertical prisms juxtaposed in the horizontal direc...

Estimating the relief of the Moho from gravity data is a computationally intensive non-linear inverse problem. What is more, the modeling must take the Earths curvature into account when the study area is of regional scale or greater. We present a regularized non-linear gravity inversion method that has a low computational footprint and employs a s...

In most applications, the Euler deconvolution aims to define the nature (type) of the geologic source (i.e., the structural index [SI]) and its depth position. However, Euler deconvolution also estimates the horizontal positions of the sources and the base level of the magnetic anomaly. To determine the correct SI, most authors take advantage of th...

Discrete wavelet transform (DWT) is a valuable tool in signal and imaging processing, in particular for denoising. Its performance in denoising potential-field data has been proven to be superior to that of traditional techniques. We analyze the most common thresholding techniques: soft and hard with cycle spinning, for denoising magnetic data. To...

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 indic...

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...

We have developed codes to calculate the local amplitude, the local phase, and the local orientation of the nonscale and the Poisson’s scale-space monogenic signals of potential-field data in version 1.0 of the open-source program Monogenic. The monogenic vector of a generic function is calculated in the wavenumber domain and then transformed back...

We have developed a new iterative scheme for processing gravity data using a fast equivalent-layer technique. This scheme estimates a 2D mass distribution on a fictitious layer located below the observation surface and with finite horizontal dimensions composed by a set of point masses, one directly beneath each gravity station. Our method starts...

DOWNLOAD PDF AND CODE AT http://www.leouieda.com/papers/paper-moho-inversion-tesseroids-2016.html --------------------------- Estimating the relief of the Moho from gravity data is a computationally intensive nonlinear inverse problem. What is more, the modelling must take the Earths curvature into account when the study area is of regional scale...

DOWNLOAD PDF + SOURCE CODE: http://www.leouieda.com/papers/paper-tesseroids-2016.html We present the open-source software Tesseroids, a set of command-line programs to perform the forward modeling of gravitational fields in spherical coordinates. The software is implemented in the C programming language and uses tesseroids (spherical prisms) for t...

PDF available at: http://www.pinga-lab.org/papers/paper-quadrilatero2-2016.html 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 p...

We have presented a new edge-detection filter to enhance potential-field data by using the local phase in the Poisson scale-space monogenic signal. The local phase in the monogenic signal is a phase-based filter that uses the firstorder Riesz transform and the data. The Poisson scalespace representation of the data is equivalent to perform an upwar...

We have developed a new phase-based filter to enhance the edges of geologic sources from potential-field data using the local phase in the Poisson scale-space monogenic signal. The Poisson scale-space representation of a potential-field data is equivalent to performing an upward continuation of the data. We created a band-pass filter by taking the...

We have presented an edge-detection method to enhance potential-field data in the monogenic scale space based on the local phase. First, we compute the x- and y-components of the first-order Riesz transform of the band-pass filtered data. Next, these components are transformed back into the space domain by the inverse Fourier transform. Finally, th...

We have developed a fast total-field anomaly inversion to estimate the magnetization direction of multiple sources with approximately spherical shapes and known centres. Our method is an overdetermined inverse problem that can be applied to interpret multiple sources with different but homogeneous magnetization directions. It requires neither the p...

We interpreted northwest-trending transfer faults whose extensions are not entirely mapped in the Precam-brian basement of the onshore and offshore Campos Basin. To enhance the subtle northwest–southeast linea-ments not clearly seen in the total-field data, we reprocessed and merged two airborne magnetic data sets aiming at producing a single merge...

We have developed a fast total-field anomaly inversion to estimate the magnetization direction of multiple sources with approximately spherical shape and known centres. Our method can be applied to interpret multiple sources with different magnetization directions. It neither requires the prior computation of any transformation like reduction to th...

DOWNLOAD PDF: http://www.pinga-lab.org/papers/paper-quadrilatero-2014.html The Quadrilátero Ferrífero in southeastern Brazil hosts one of the largest concentrations of lateritic iron ore deposits in the world. Our study area is over the southern flank of the Gandarela syncline which is one of the regional synclines of the Quadrilátero Ferrífero. T...

We developed a method that drastically reduces the number of the source location estimates in Euler deconvolution to only one per anomaly. We use the analytical estimators of the Euler solutions. Our approach consists in detecting automatically the regions of the anomaly producing consistent estimates of the source horizontal coordinates. These reg...

We present a 3-D gravity-gradient inversion approach that retrieves the geometry of an isolated geological body with known density contrast and depth of the top. The geological body is approximated by an ensemble of vertically juxtaposed right prisms with pre-established thickness and horizontal cross-sections described by polygons. The horizontal...

Presented at EAGE 2014

OPEN-ACCESS ARTICLE. DOWNLOAD PDF: http://dx.doi.org/10.1190/tle33040448.1 DOWNLOAD SOURCE: http://www.leouieda.com/papers/paper-tle-euler-tutorial-2014.html In this tutorial, we will talk about a widely used method of interpretation for potential-field data called Euler de-convolution. Our goal is to demonstrate its usefulness and, most importa...

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 have provided supplementary material to our article titled “Estimating the nature and the horizontal and vertical positions of 3D magnetic sources using Euler deconvolution” and whose authors are Felipe F. Melo, Valeria C. F. Barbosa, Leonardo Uieda, Vanderlei C. Oliveira Jr, and João B. C. Silva. In this material, we presented an extra sy...

We have developed a new method that drastically reduces the number of the source location estimates in Euler deconvolution to only one per anomaly. Our method employs the analytical estimators of the base level and of the horizontal and vertical source positions in Euler deconvolution as a function of the x- and y-coordinates of the observations. B...

We have presented a joint inversion of all gravity-gradient tensor components to estimate the shape of an isolated 3-D geological body located in subsurface. The method assumes the knowledge about the depth to the top and density contrast of the source. The geological body is approximated by an interpretation model formed by an ensemble of vertical...

This paper is in Portuguese. We present a numerical characterization of the ambiguity involved in the relationship gravimetric source signal, showing that different mass distributions in the same volume can produce almost the same signal gravimetric. Additionally, we characterize numerically whereas the degree of ambiguity can not depend on source...

This paper is in Portuguese. We present a new 3D gravity-gradient inversion approach that retrieves the geometry of an isolated geologic source with known density contrast and depth of the top. We approximate the source by an ensemble of vertically juxtaposed right prisms whose horizontal cross-sections are described by polygons. The horizontal coo...

This paper is in Portuguese. We present numerical analysis of the decrease in the vertical component of the gravity anomaly produced by deepening simulated in a elementary mass of a synthetic sedimentary basin and characterize the depth from which this mass does not produce, on the surfasse, sensitive signal to the instrumentation. We also evaluate...

The Almada Basin, located in the southern Bahia State segment of NE Brazil, shares a similar sedimentation history and stress regime with the other eastern Brazilian basins. But when considering the composition of the transitional crust, a remarkably different behaviour is observed between the Almada Basin and the other eastern Brazilian basins. Th...

DOWNLOAD PDF + SOURCE CODE: http://www.pinga-lab.org/papers/paper-polynomial-eqlayer-2013.html We have developed a new cost-effective method for processing large-potential-field data sets via the equivalent-layer technique. In this approach, the equivalent layer is divided into a regular grid of equivalent-source windows. Inside each window, the p...

>>> PDF and talk recording: http://www.leouieda.com/talks/scipy2013.html <<< Geophysics is the science of using physical observations of the Earth to infer its inner structure. Generally, this is done with a variety of numerical modeling techniques and inverse problems. The development of new algorithms usually involves copy and pasting of code,...

Dados graviméticos, magnetométricos e sísmicos na por- ção o�shore rasa da Bacia de Campos e embasamento adjacente são integrados de forma a se obter o arcabou ço estrutural do graben de São João da Barra. A linha sísmica aqui modelada mostra que o referido graben possui uma estrutura complexa com uma sucessão de altos e baixos internos.

The Algarve is located a few hundred kilometres north of the crossing of the E–W Eurasia–Africa plate boundary and is characterised by a moderate seismicity, with some important historical and instrumental earthquakes causing loss of lives and significant material damages. The area is affected not only by plate boundary generated earthquakes but al...

DOWNLOAD PDF + SLIDES: http://www.leouieda.com/talks/seg-carlos2012.html We have interpreted the airborne gravity gradiometry data from Carajás Mineral Province (CMP), Brazil, by using two different 3D inversion methods. Both inversion methods parameterized the Earth‟s subsurface into prismatic cells and estimate the 3D density-contrast distributi...

An aeromagnetic data filter was tested as a tool in enhancing the magnetic responses of deep sources associated with marginal basins. Our approach consists in amplifying the responses of magnetic sources which extend through the continental slope and continental rise. This amplification compensates for the magnetic response attenuation over the con...

DOWNLOAD PDF: http://www.leouieda.com/talks/seg2012.html We present an improvement to the method of 3D gravity gradient inversion by planting anomalous densities. This method estimates a density-contrast distribution defined on a grid of right-rectangular prisms. Instead of solving large equation systems, the method uses a systematic search algori...

DOWNLOAD PDF + SOURCE CODE: http://www.leouieda.com/papers/paper-planting-anomalous-densities-2012.html We have developed a new gravity gradient inversion method for estimating a 3D density-contrast distribution defined on a grid of rectangular prisms. Our method consists of an iterative algorithm that does not require the solution of an equation...

We provide supplementary material to Uieda and Barbosa (2012). The material included are: (1) plots of the predicted and synthetic gyy and gyz components from the section "Application to synthetic data", (2) plots of the results of the sensitivity analysis to uncertainties in the density-contrast value of the seeds, (3) the contour maps of the synt...