Magnetic amplitude inversion for depth-to-basement and apparent magnetization-intensity estimates

Geophysics ◽  
2021 ◽  
Vol 86 (1) ◽  
pp. J1-J11
Author(s):  
Marlon C. Hidalgo-Gato ◽  
Valéria C. F. Barbosa ◽  
Vanderlei C. Oliveira
Keyword(s):  
Field Data ◽  
Regional Scale ◽  
Inversion Method ◽  
Magnetization Direction ◽  
Potential Field Data ◽  
Amplitude Inversion ◽  
Basement Rocks ◽  
Amplitude Data ◽  
Magnetization Intensity ◽  
Magnetic Amplitude

We have developed an inversion method to recover 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, our method is suitable for interpreting areas with remanent magnetization. Our method assumes constant magnetized basement rocks overlain by nonmagnetic sediments. To overcome the inherent ambiguity of potential field data, we assume knowledge of the average depth of the basement and use it as a constraint to regularize the inversion. A sensitivity analysis with synthetic data shows the weak dependency of the magnetic amplitude inversion on the magnetization direction. Different combinations of magnetization directions recover the interface separating sediments from basement rocks. Test on field data over the Foz do Amazonas Basin, Brazil, recovers the shape of the basement relief without any knowledge about the magnetization intensity and direction. The estimated basement relief reveals a smooth basement framework with basement highs in the central part of the area. In a regional-scale perspective, the deeper and constant estimated basement relief at the northernmost limit of the area may suggest changing in crustal domains from a hyperextended continental crust to homogeneous oceanic crust.

Quantifying the error level in computed magnetic amplitude data for 3D magnetization inversion

Geophysics ◽  
2018 ◽  
Vol 83 (5) ◽  
pp. J75-J84 ◽  
Author(s):  
Camriel Coleman ◽  
Yaoguo Li
Keyword(s):  
Field Data ◽  
Regularization Parameter ◽  
Three Dimensional ◽  
Inverse Model ◽  
Magnetic Data ◽  
Total Field ◽  
Noise Estimate ◽  
Amplitude Inversion ◽  
Amplitude Data ◽  
Magnetic Amplitude

Three-dimensional inversion plays an important role in the quantitative interpretation of magnetic data in exploration problems, and magnetic amplitude data can be an effective tool in cases in which remanently magnetized materials are present. Because amplitude data are typically calculated from total-field anomaly data, the error levels must be characterized for inversions. Lack of knowledge of the error in amplitude data hinders the ability to properly estimate the data misfit associated with an inverse model and, therefore, the selection of the appropriate regularization parameter for a final model. To overcome these challenges, we have investigated the propagation of errors from total-field anomaly to amplitude data. Using parametric bootstrapping, we find that the standard deviation of the noise in amplitude data is approximately equal to that of the noise in total-field anomaly data when the amplitude data are derived from the conversion of total-field data to three orthogonal components. We then illustrate how the equivalent source method can be used to estimate the error in total-field anomaly data when needed. The obtained noise estimate can be applied to amplitude inversion to recover an optimal inverse model by applying the discrepancy principle. We test this method on synthetic and field data and determine its effectiveness.

Application of magnetic amplitude inversion in exploration for volcanic units in a basin environment

Geophysics ◽  
2012 ◽  
Vol 77 (5) ◽  
pp. B219-B225 ◽  
Author(s):  
Yaoguo Li ◽  
Zhanxiang He ◽  
Yunxiang Liu
Keyword(s):  
Remanent Magnetization ◽  
Volcanic Rocks ◽  
Wiener Filter ◽  
Inversion Method ◽  
Magnetization Direction ◽  
Amplitude Inversion ◽  
Final Interpretation ◽  
Local Geology ◽  
Magnetic Amplitude

We have performed a case study on the use of magnetic amplitude inversion in imaging volcanic rocks that are buried in a sedimentary basin and have strong remanent magnetization. The application arises in exploration for natural gas hosted in volcanic rocks in basin environments. The weak anomaly associated with the volcanic units and the presence of remanent magnetization therein pose major challenges in the magnetic interpretation. We first use a Wiener filter based on an ensemble analysis to examine the depth characteristics of the anomalies, and then we use an inversion-based signal separation to extract the anomaly for final interpretation. We apply an amplitude inversion method to recover the distribution of effective susceptibility in the absence of the knowledge about the total magnetization direction. The result effectively identifies the volcanic rock units at large depths and the imaged distribution of these units is consistent with information from drillholes and local geology.

Uncovering the Canning Basin: a new comprehensive SEEBASE® model

2018 ◽  
Vol 58 (2) ◽  
pp. 793
Author(s):  
Karen Connors ◽  
Cedric Jorand ◽  
Peter Haines ◽  
Yijie Zhan ◽  
Lynn Pryer
Keyword(s):  
Western Australia ◽  
Potential Field ◽  
Field Data ◽  
Regional Scale ◽  
Structural Evolution ◽  
Potential Field Data ◽  
Canning Basin ◽  
The North ◽  
Wide Range ◽  
Order Of Magnitude

A new regional scale SEEBASE® model has been produced for the intracratonic Canning Basin, located in the north of Western Australia. The 2017 Canning Basin SEEBASE model is more than an order of magnitude higher resolution than the 2005 OZ SEEBASE version — the average resolution is ~1 : 1 M scale with higher resolution in areas of shallow basement with 2D seismic coverage — such as the Broome Platform and Barbwire Terrace. Post-2005 acquisition of potential field, seismic and well data in the Canning Basin by the Geological Survey of Western Australia (GSWA), Geoscience Australia and industry provided an excellent opportunity to upgrade the SEEBASE depth-to-basement model in 2017. The SEEBASE methodology focuses on a regional understanding of basement, using potential field data to interpret basement terranes, depth-to-basement (SEEBASE), regional structural geology and basement composition. The project involved extensive potential field processing and enhancement and compilation of a wide range of datasets. Integrated interpretation of the potential field data with seismic and well analysis has proven quite powerful and illustrates the strong basement control on the extent and location of basin elements. The project has reassessed the structural evolution of the basin, identified and mapped major structures and produced fault-event maps for key tectonic events. In addition, interpretative maps of basement terranes, depth-to-Moho, basement thickness, basement composition and total sediment thickness have been used to calculate a basin-wide map of basement-derived heat flow. The 2017 Canning Basin SEEBASE is the first public update of the widely used 2005 OZ SEEBASE. All the data and interpretations are available from the GSWA as a report and integrated ArcGIS project, which together provide an excellent summary of the key features within the Canning Basin that will aid hydrocarbon and mineral explorers in the region.

Application of 3D magnetic amplitude inversion to iron oxide-copper-gold deposits at low magnetic latitudes: A case study from Carajás Mineral Province, Brazil

Geophysics ◽  
2015 ◽  
Vol 80 (2) ◽  
pp. B13-B22 ◽  
Author(s):  
Marcelo Leão-Santos ◽  
Yaoguo Li ◽  
Roberto Moraes
Keyword(s):  
Iron Oxide ◽  
Gold Deposits ◽  
Magnetic Data ◽  
Magnetic Latitude ◽  
Amplitude Inversion ◽  
Carajás Mineral Province ◽  
Amplitude Data ◽  
Copper Gold ◽  
Magnetic Amplitude

Strong hydrothermal alteration modifies rock physical properties in iron oxide-copper-gold deposits (IOCGs) and may result in characteristic signatures detectable in geophysical surveys. Magnetic data are commonly used in characterizing orebodies, and 3D inversions are often used to assist in interpretations. In areas with strong remanence and self-demagnetization, the total magnetization can have directions different from the inducing field direction. This deviation precludes the use of traditional inversion methods. Magnetic amplitude inversion offers one solution to this challenge because the amplitude data are weakly dependent on the magnetization direction. In addition, the low magnetic latitude also imposes difficulty in amplitude data calculation due to the instability in the component conversion in the wavenumber domain. To formulate a practical approach, we present a case study on applying the magnetic amplitude inversion to the Furnas southeast IOCG deposit at the low magnetic latitude in Carajás Mineral Province, Brazil, and demonstrate that the approach can reliably recover an interpretable distribution of effective magnetic susceptibility and identify massive magnetite from hydrothermal alterations associated with the high-grade ore.

Generalized radial inversion of 2D potential‐field data

Geophysics ◽  
2004 ◽  
Vol 69 (6) ◽  
pp. 1405-1413 ◽  
Author(s):  
João B. C. Silva ◽  
Valéria C. F. Barbosa
Keyword(s):  
Potential Field ◽  
Field Data ◽  
Physical Property ◽  
Quantitative Information ◽  
Fixed Number ◽  
Polar Coordinates ◽  
Inversion Method ◽  
Potential Field Data ◽  
Convexity Constraint ◽  
Interpretation Model

We introduce a new 2D method for inverting potential‐field data with model constraints designed by the interpreter. Our method uses an interpretation model consisting of a source with polygonal cross‐section whose vertices are described by polar coordinates with an origininside the source. With this coordinate system, constraints in an inversion are easier to develop and apply. Our inversion method assumes a known physical property contrast for the source and estimates the radii associated with the polygon vertices for a fixed number of equally spaced angles from 0° to 360°. A wide variety of constraints may be used to stabilize the solutions by introducing information about the source shape. The method recovers stable solutions whose shapes range from almost circular or pear‐shaped to elongated in one or more directions. The convexity constraint applied to the source shape, despite requiring no quantitative information, is more versatile than the other constraints. The convexity constraint efficiently recovers source geometries that are either isometric or elongated in one direction.

The Method of Curvature Attribute applied in the Depth Inversion of the Geological Bodies Edge by Potential Field Data

2020 ◽  
Author(s):  
Jinlan Liu ◽  
Wanyin Wang ◽  
Shengqing Xiong
Keyword(s):  
Objective Function ◽  
Potential Field ◽  
Field Data ◽  
Small Scale ◽  
Inversion Method ◽  
Potential Field Data ◽  
Upward Continuation ◽  
Extraction Algorithm ◽  
Key Technologies ◽  
Key Techniques

<p>It is vital to quickly and effectively determine the extent and depth of geological body by using potential field data in gravity and magnetic survey. In this study, three key techniques studying the extent and depth of geological sources based on curvature attribute are studied: the optimal solutions to the objective function, the edge of geological bodies and picking out solutions. Firstly, the optimal solution to the objective function is studied, that is, the key extraction algorithm about the curvature attribute. The Huber norm is introduced into the extraction algorithm of curvature attribute, which more accurately detect the depth of edge of the geological bodies. Secondly, the normalized vertical derivative of the total horizontal derivative (NVDR-THDR) technique is introduced into curvature attribute, which shows more continuous results about the edge position of the geological bodies and more sensitive to the small-scale tectonic structure. Finally, we study the way to pick out the inversion solution, that is, to solve the multi-solution equations in the inversion. The upward continuation of a certain height with strict physical significance was introduced into the inversion method, which was used to suppress the noise, and the final and actual inversion depth was equal to the inversion depth minus the height of upward continuation. And the average value of threshold limitation technology of the potential fields data was also introduced into this method. Using the two technologies, solutions of non-field source edge positions were eliminated, and make the inversion solutions closer to the actual situation. Through the above three key techniques, the accuracy, continuity and recognition to the small-scale structure of the inversion result are optimized. The theoretical models are used to verify the effectiveness of the above key technologies, the results show that the three key technologies have achieved good results, and the combined models are used to verify the effectiveness of the optimized inversion method. The measured aeromagnetic data were used to inversing the edge depth of the intrusive rock in a mining area, and the inversion results are in good agreement with the rock depth revealed by borehole.</p>

scholarly journals OpenMP Implementation of a Novel Potential-Field-Data Source-Growth-Based Inversion Approach for 3D Salt Imaging in Deepwater Gulf of Mexico

2020 ◽  
Vol 10 (14) ◽  
pp. 4798
Author(s):  
Naín Vera ◽  
Carlos Couder-Castañeda ◽  
Jorge Hernández ◽  
Alfredo Trujillo-Alcántara ◽  
Mauricio Orozco-del-Castillo ◽  
...  
Keyword(s):  
Gulf Of Mexico ◽  
Potential Field ◽  
Field Data ◽  
Three Dimensional ◽  
Synthetic Data ◽  
Complex Salt ◽  
Research Field ◽  
Inversion Method ◽  
Potential Field Data ◽  
Simultaneous Inversion

Potential-field-data imaging of complex geological features in deepwater salt-tectonic regions in the Gulf of Mexico remains an open active research field. There is still a lack of resolution in seismic imaging methods below and in the surroundings of allochthonous salt bodies. In this work, we present a novel three-dimensional potential-field-data simultaneous inversion method for imaging of salt features. This new approach incorporates a growth algorithm for source estimation, which progressively recovers geological structures by exploring a constrained parameter space; restrictions are posed from a priori geological knowledge of the study area. The algorithm is tested with synthetic data corresponding to a real complex salt-tectonic geological setting commonly found in exploration areas of deepwater Gulf of Mexico. Due to the huge amount of data involved in three-dimensional inversion of potential field data, the use of parallel computing techniques becomes mandatory. In this sense, to alleviate computational burden, an easy to implement parallelization strategy for the inversion scheme through OpenMP directives is presented. The methodology was applied to invert and integrate gravity, magnetic and full tensor gradient data of the study area.

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