Connecting onshore-offshore Campos Basin structures: Interpretation of high-resolution airborne magnetic data

2014 ◽  
Vol 2 (4) ◽  
pp. SJ35-SJ45 ◽  
Author(s):  
Juarez Lourenço ◽  
Paulo T. L. Menezes ◽  
Valeria C. F. Barbosa
Keyword(s):  
Source Rocks ◽  
Magnetic Data ◽  
Data Sets ◽  
Hydrocarbon Migration ◽  
Data Set ◽  
Campos Basin ◽  
Turbidite Sedimentation ◽  
Edge Detection Method ◽  
Transfer Faults ◽  
Airborne Magnetic

We interpreted northwest-trending transfer faults whose extensions are not entirely mapped in the Precambrian basement of the onshore and offshore Campos Basin. To enhance the subtle northwest–southeast lineaments not clearly seen in the total-field data, we reprocessed and merged two airborne magnetic data sets aiming at producing a single merged magnetic data set. Next, we applied a directional filter to these integrated magnetic data. Finally, we applied a multiscale edge detection method to these filtered data. This combination allowed the detection of edges and ridges that are used to produce several northwest–southeast lineations. We interpreted these northwest-trending lineations as magnetic expressions of transfer faults that cut across the onshore adjacent basement of the Campos Basin to the shallow and deep Campos Basin waters. These interpreted northwest-trending faults suggested the continuity of the known northwest-striking transfer faults in the deep Campos Basin waters toward the shallow Campos Basin waters and the adjacent continent. Moreover, our interpreted northwest-trending faults revealed the control of several known oilfields in the Campos Basin. This result supported the hypothesis of the influence of the northwest–southeast-trending transfer faults on the petroleum system of Campos Basin, which were reactivated in the Tertiary providing a pathway for the turbidite sedimentation, reworking, and redistribution of several deepwater reservoirs. In addition, it was hypothesized that this faulting system controlled the hydrocarbon migration paths from the presalt source rocks through salt windows into basal suprasalt layers.

scholarly journals A fast methodology for large-scale focusing inversion of gravity and magnetic data using the structured model matrix and the 2-D fast Fourier transform

2020 ◽  
Vol 223 (2) ◽  
pp. 1378-1397
Author(s):  
Rosemary A Renaut ◽  
Jarom D Hogue ◽  
Saeed Vatankhah ◽  
Shuang Liu
Keyword(s):  
Fourier Transform ◽  
Fast Fourier Transform ◽  
Linear Systems ◽  
Large Scale ◽  
Surface Measurement ◽  
Magnetic Data ◽  
Uniform Grid ◽  
Data Sets ◽  
Inversion Algorithm ◽  
Data Set

SUMMARY We discuss the focusing inversion of potential field data for the recovery of sparse subsurface structures from surface measurement data on a uniform grid. For the uniform grid, the model sensitivity matrices have a block Toeplitz Toeplitz block structure for each block of columns related to a fixed depth layer of the subsurface. Then, all forward operations with the sensitivity matrix, or its transpose, are performed using the 2-D fast Fourier transform. Simulations are provided to show that the implementation of the focusing inversion algorithm using the fast Fourier transform is efficient, and that the algorithm can be realized on standard desktop computers with sufficient memory for storage of volumes up to size n ≈ 106. The linear systems of equations arising in the focusing inversion algorithm are solved using either Golub–Kahan bidiagonalization or randomized singular value decomposition algorithms. These two algorithms are contrasted for their efficiency when used to solve large-scale problems with respect to the sizes of the projected subspaces adopted for the solutions of the linear systems. The results confirm earlier studies that the randomized algorithms are to be preferred for the inversion of gravity data, and for data sets of size m it is sufficient to use projected spaces of size approximately m/8. For the inversion of magnetic data sets, we show that it is more efficient to use the Golub–Kahan bidiagonalization, and that it is again sufficient to use projected spaces of size approximately m/8. Simulations support the presented conclusions and are verified for the inversion of a magnetic data set obtained over the Wuskwatim Lake region in Manitoba, Canada.

Rapid multi-scale analysis of near-surface geophysical anomaly maps: Application to an archaeo-geophysical data set

Geophysics ◽  
2020 ◽  
pp. 1-41 ◽  
Author(s):  
Jens Tronicke ◽  
Niklas Allroggen ◽  
Felix Biermann ◽  
Florian Fanselow ◽  
Julien Guillemoteau ◽  
...  
Keyword(s):  
Random Noise ◽  
Geophysical Data ◽  
Magnetic Data ◽  
Engineering Practice ◽  
Data Sets ◽  
Stripe Pattern ◽  
Data Set ◽  
Near Surface ◽  
Multi Scale ◽  
Topographic Data

In near-surface geophysics, ground-based mapping surveys are routinely employed in a variety of applications including those from archaeology, civil engineering, hydrology, and soil science. The resulting geophysical anomaly maps of, for example, magnetic or electrical parameters are usually interpreted to laterally delineate subsurface structures such as those related to the remains of past human activities, subsurface utilities and other installations, hydrological properties, or different soil types. To ease the interpretation of such data sets, we propose a multi-scale processing, analysis, and visualization strategy. Our approach relies on a discrete redundant wavelet transform (RWT) implemented using cubic-spline filters and the à trous algorithm, which allows to efficiently compute a multi-scale decomposition of 2D data using a series of 1D convolutions. The basic idea of the approach is presented using a synthetic test image, while our archaeo-geophysical case study from North-East Germany demonstrates its potential to analyze and process rather typical geophysical anomaly maps including magnetic and topographic data. Our vertical-gradient magnetic data show amplitude variations over several orders of magnitude, complex anomaly patterns at various spatial scales, and typical noise patterns, while our topographic data show a distinct hill structure superimposed by a microtopographic stripe pattern and random noise. Our results demonstrate that the RWT approach is capable to successfully separate these components and that selected wavelet planes can be scaled and combined so that the reconstructed images allow for a detailed, multi-scale structural interpretation also using integrated visualizations of magnetic and topographic data. Because our analysis approach is straightforward to implement without laborious parameter testing and tuning, computationally efficient, and easily adaptable to other geophysical data sets, we believe that it can help to rapidly analyze and interpret different geophysical mapping data collected to address a variety of near-surface applications from engineering practice and research.

Limitations on digital filtering of the DNAG magnetic data set for the conterminous U.S.

Geophysics ◽  
1993 ◽  
Vol 58 (9) ◽  
pp. 1281-1296 ◽  
Author(s):  
V. J. S. Grauch
Keyword(s):  
Spatial Frequency ◽  
North American ◽  
Digital Filtering ◽  
Magnetic Data ◽  
Data Sets ◽  
Frequency Content ◽  
Long Distance ◽  
High Quality ◽  
Data Set ◽  
The U.S

The magnetic data set compiled for the Decade of North American Geology (DNAG) project presents an important digital data base that can be used to examine the North American crust. The data represent a patchwork from many individual airborne and marine magnetic surveys. However, the portion of data for the conterminous U.S. has problems that limit the resolution and use of the data. Now that the data are available in digital form, it is important to describe the data limitations more specifically than before. The primary problem is caused by datum shifts between individual survey boundaries. In the western U.S., the DNAG data are generally shifted less than 100 nT. In the eastern U.S., the DNAG data may be shifted by as much as 300 nT and contain regionally shifted areas with wavelengths on the order of 800 to 1400 km. The worst case is the artificial low centered over Kentucky and Tennessee produced by a series of datum shifts. A second significant problem is lack of anomaly resolution that arises primarily from using survey data that is too widely spaced compared to the flight heights above magnetic sources. Unfortunately, these are the only data available for much of the U.S. Another problem is produced by the lack of common observation surface between individual pieces of the U.S. DNAG data. The height disparities introduce variations in spatial frequency content that are unrelated to the magnetization of rocks. The spectral effects of datum shifts and the variation of spatial frequency content due to height disparities were estimated for the DNAG data for the conterminous U.S. As a general guideline for digital filtering, the most reliable features in the U.S. DNAG data have wavelengths roughly between 170 and 500 km, or anomaly half‐widths between 85 and 250 km. High‐quality, large‐region magnetic data sets have become increasingly important to meet exploration and scientific objectives. The acquisition of a new national magnetic data set with higher quality at a greater range of wavelengths is clearly in order. The best approach is to refly much of the U.S. with common specifications and reduction procedures. At the very least, magnetic data sets should be remerged digitally using available or newly flown long‐distance flight‐line data to adjust survey levels. In any case, national coordination is required to produce a consistent, high‐quality national magnetic map.

scholarly journals Petrophysically and geologically guided multi-physics inversion using a dynamic Gaussian mixture model

2020 ◽  
Vol 224 (1) ◽  
pp. 40-68 ◽  
Author(s):  
Thibaut Astic ◽  
Lindsey J Heagy ◽  
Douglas W Oldenburg
Keyword(s):  
Gaussian Mixture Model ◽  
Mixture Model ◽  
Gaussian Mixture ◽  
Quantitative Information ◽  
Geophysical Data ◽  
Magnetic Data ◽  
Data Sets ◽  
Data Set ◽  
Geophysical Surveys ◽  
Geological Information

SUMMARY In a previous paper, we introduced a framework for carrying out petrophysically and geologically guided geophysical inversions. In that framework, petrophysical and geological information is modelled with a Gaussian mixture model (GMM). In the inversion, the GMM serves as a prior for the geophysical model. The formulation and applications were confined to problems in which a single physical property model was sought, and a single geophysical data set was available. In this paper, we extend that framework to jointly invert multiple geophysical data sets that depend on multiple physical properties. The petrophysical and geological information is used to couple geophysical surveys that, otherwise, rely on independent physics. This requires advancements in two areas. First, an extension from a univariate to a multivariate analysis of the petrophysical data, and their inclusion within the inverse problem, is necessary. Secondly, we address the practical issues of simultaneously inverting data from multiple surveys and finding a solution that acceptably reproduces each one, along with the petrophysical and geological information. To illustrate the efficacy of our approach and the advantages of carrying out multi-physics inversions coupled with petrophysical and geological information, we invert synthetic gravity and magnetic data associated with a kimberlite deposit. The kimberlite pipe contains two distinct facies embedded in a host rock. Inverting the data sets individually, even with petrophysical information, leads to a binary geological model: background or undetermined kimberlite. A multi-physics inversion, with petrophysical information, differentiates between the two main kimberlite facies of the pipe. Through this example, we also highlight the capabilities of our framework to work with interpretive geological assumptions when minimal quantitative information is available. In those cases, the dynamic updates of the GMM allow us to perform multi-physics inversions by learning a petrophysical model.

Interpolation artifacts as a result of spatial aliasing: A case study of the airborne magnetic data set of southeastern Minas Gerais, Brazil

Geophysics ◽  
2020 ◽  
Vol 85 (6) ◽  
pp. B193-B205
Author(s):  
Tobias Maia Rabelo Fonte-Boa ◽  
Aline Tavares Melo ◽  
Tiago Amâncio Novo
Keyword(s):  
High Frequency ◽  
Interpolation Method ◽  
Acute Angle ◽  
Magnetic Data ◽  
Aeromagnetic Survey ◽  
Data Set ◽  
Linear Pattern ◽  
Spatial Aliasing ◽  
Geologic Interpretation ◽  
Airborne Magnetic

Linear features at an acute angle with the flight direction are imaged as a series of aligned circular anomalies in the images of Area 15 aeromagnetic survey, which covered part of the Brazilian southeastern region. These features are interpolation artifacts, a recurring problem found in airborne magnetic images that cause problems for qualitative and quantitative geophysical-geologic interpretation. This imaging problem is attributed to spatial aliasing. By running simulations of magnetic data on a synthetic model, we have physically demonstrated that the interpolation artifacts from Area 15 are due to inappropriate survey design. Besides the most common expression of artifacts, we described a geologically noncoherent linear pattern as a new type of artifact. Supported by spectral analyses, we found that the Area 15 aliased spectrum is similar to geologic high-frequency magnetic features, which constitutes a motive for unearthing the correct geophysical signal. Thus, we made use of four techniques for removing the artifacts. The trend enforcement method partially improved the images, whereas the inverse interpolation method was ineffective, apparently because Area 15 data are severely aliased. The constrained coherence diffusion and multitrend gridding methods were able to significantly reduce the presence of artifacts. Despite the high-frequency attenuation, these tools adequately enhanced the magnetic trends and minimized the artifacts. Therefore, the improved images are better suited for reliable geologic interpretation.

Geophysical helicopter-based magnetic methods for locating wells

Geophysics ◽  
2018 ◽  
Vol 83 (5) ◽  
pp. B269-B279 ◽  
Author(s):  
Vladislav Kaminski ◽  
Richard W. Hammack ◽  
William Harbert ◽  
Garret A. Veloski ◽  
James Sams ◽  
...  
Keyword(s):  
Magnetic Susceptibility ◽  
Accurate Determination ◽  
Likelihood Estimation ◽  
Vertical Gradient ◽  
Magnetic Data ◽  
Small Subset ◽  
Data Sets ◽  
Successful Recovery ◽  
Tilt Derivative ◽  
Airborne Magnetic

We studied the problem of determining accurately the location of abandoned and sometimes undocumented wells and the challenging and increasingly important task related to subsurface reservoir integrity and regional economic development. We reviewed a variety of semiquantitative methods based on geophysical workflows, and we tested these with airborne magnetic data collected at two field sites. Our main conclusion is that airborne magnetic surveys represent a high-value tool to aid in the accurate determination of abandoned well locations and characteristics. At one site, two surveys were collected at slightly different altitudes to compare workflow robustness and allow the observed vertical magnetic gradient to be included in well detection workflows. We also investigated using focal zone anomaly statistics (using the magnetic field intensity and its first and second horizontal derivatives), analytic signal, tilt derivative, and calculated vertical gradient. In addition, we used a 3D inversion of a small subset of data to investigate the successful recovery of well-related magnetic susceptibility distribution and estimate subsurface well topology. The recovered magnetic susceptibility volume showed distinctive vertically elongated objects that correspond to known wells. Maximum likelihood estimation and confidence calculations were then applied to these data sets and indicated that high-confidence well locations could be determined and characterized using such airborne total magnetic data.

Integration of aeromagnetic data acquired at different times with varying elevations and line spacings

Geophysics ◽  
1979 ◽  
Vol 44 (4) ◽  
pp. 742-752 ◽  
Author(s):  
B. K. Bhattacharyya ◽  
R. E. Sweeney ◽  
R. H. Godson
Keyword(s):  
Ground Surface ◽  
Magnetic Data ◽  
Reference Level ◽  
Data Sets ◽  
Observation Data ◽  
Aeromagnetic Data ◽  
Data Set ◽  
Using Data ◽  
Quadratic Surfaces ◽  
The Magnetic Field

The methods required for integrating magnetic data sets from surveys flown with contrasting specifications at different times are described. The first requirement in the process of integration is to bring the data sets obtained at different elevations to the same reference level. Various methods are available to continue magnetic fields from one horizontal plane to another. The procedure for continuation of the magnetic field from a draped surface to a constant barometric level requires an equivalent source representation of the field at all points of observation. Data sets continued to the same elevation over adjacent areas are found to exhibit mismatch along the area boundaries. The mismatch between data values along profiles running across a boundary can be explained by changes in level, gradient, and curvature of the fields in the two data sets in the neighborhood of the boundary. The method discussed for making the two fields compatible depends, basically, upon the adjustment of quadratic surfaces representing the fields on both sides of a boundary. Examples are also provided to demonstrate the usefulness of these methods in the preparation of an integrated data set at a reference level using data sets flown at different elevations above the ground surface in the state of Nevada.

An assessment of long-wavelength magnetic anomalies over Canada

1996 ◽  
Vol 33 (1) ◽  
pp. 12-23 ◽  
Author(s):  
Mark Pilkington ◽  
Walter R. Roest
Keyword(s):  
Magnetic Field ◽  
Magnetic Anomalies ◽  
Time Span ◽  
Magnetic Data ◽  
Data Sets ◽  
Independent Data ◽  
Data Set ◽  
Long Wavelength ◽  
The Magnetic Field

The reliability of the long-wavelength portion (> 300 km) of the magnetic field over Canada, as represented by the national aeromagnetic anomaly database compiled by the Geological Survey of Canada (GSC), is assessed by comparison with two independent data sets: a high-altitude country-wide survey carried out by the former Earth Physics Branch (EPB) and data from the MAGSAT and POGO satellite missions. The different altitudes at which each data set was measured (300 m, ~4 km, and ~400 km), and their different resolution and time span of observations allow a determination of the integrity of selected wavelength bands in each data set. The (upward-continued) EPB and MAGSAT–POGO fields compare well for wavelengths of 300–2500 km. The GSC data show significant differences to the former, indicating that the levelling and merging of several hundred individual surveys has degraded the longer wavelength components of the magnetic field. Replacing the GSC wavelength components >300 km with those from the EPB field produces a magnetic data set containing more dependable information within the largest possible waveband.

Efficient 3D inversion of magnetic data via octree-mesh discretization, space-filling curves, and wavelets

Geophysics ◽  
2013 ◽  
Vol 78 (5) ◽  
pp. J61-J73 ◽  
Author(s):  
Kristofer Davis ◽  
Yaoguo Li
Keyword(s):  
Wavelet Transform ◽  
Magnetic Data ◽  
Data Sets ◽  
Magnetic Survey ◽  
Space Filling ◽  
Sensitivity Matrix ◽  
Desktop Computer ◽  
Data Set ◽  
One Dimensional ◽  
The One

Airborne magnetic survey data sets can contain from hundreds of thousands to millions of observations and typically cover large areas. The large number of measurements combined with a model mesh to accommodate the survey extent can render an inversion of these data intractable. Faced with this challenge, we have developed a three-step procedure to locally optimize the degree of model discretization and to compress the corresponding sensitivity matrix for the inversion of magnetic data. The mesh optimization is achieved through the use of adaptive octree discretization. The compression is achieved by first reordering the model cells using the Hilbert space filling curve and then applying the one-dimensional wavelet transform to the corresponding sensitivities. The fractal property of the Hilbert curve groups the spatially adjacent cells into algebraically adjacent positions in the reordered model mesh and thereby maximizes the number of zero or near-zero coefficients in the one-dimensional wavelet transform. Winnowing these insignificant coefficients finally leads to a highly sparse representation of the sensitivity matrix, which dramatically reduces the required memory and CPU time in the inversion. As a result, the proposed algorithm is capable of inverting huge data sets ([Formula: see text] measurements) with commensurate model sizes in a short time on a single desktop computer. As a test, we inverted an entire magnetic data set with 170,000 observations from a large uranium exploration program and achieved a reduction in computational cost exceeding 10,000 times.

Sign in / Sign up

Export Citation Format

Share Document