Potential Field Interpretation Research Articles

Distance-regularized level set inversion of magnetic data

Inversion is one of the key and difficult issues in potential field data processing and interpretation, and high-precision inversion has long been a popular research topic. We develop the distance-regularized level set inversion of the magnetic data (DRLSI-M) method. A double-well function is introduced into the objective function of the level set inversion, and we take advantage of its mathematical properties to minimize the gradient of the level set function so that it reaches a minimum value at points 0 and 1. As a result, the distance-regularized term not only replaces the costly reinitialization process so that the level set function maintains a signed distance property but also stabilizes the evolution of the level set function. When solving for the minimum value of the objective function, we transform the optimization problem into an initial-boundary value problem and solve it with the finite-difference method. The distance-regularized level set inversion method and the reinitialization level set inversion method are tested using three models: a single-level-set double-inclined plate model, a double-level-set double-inclined plate model, and a multiple-level-set three-cuboid model. Through model tests, the soundness of our method is verified and compared with the reinitialization level set inversion method. Our method avoids the limitations such as low efficiency and instability caused by the reinitialization of the level set inversion method. Furthermore, we apply our method for the inversion of aeromagnetic data from the Jinchuan copper-nickel mine. The results are consistent with the known geologic information, thus validating the practicality and effectiveness of DRLSI-M. The distance-regularized level set inversion method provides a theoretical basis for deep mine exploration.

Mapping structural lineaments using the edge filters of the potential field: a case study of the Rizhao–Lianyungang area, East China

Background: Edge enhancement plays an important role in potential field data processing and interpretation, which facilitate regional tectonic studies, mineral and energy exploration. This is because edges on potential field often indicate linear geological structures such as fractures, edges of geological bodies and so on. With the development of meticulous edge enhancement on potential field, the phenomenon of false edges caused by the associated anomalies when detect ing edges from magnetic field cannot be ignored.Methods: Aiming at this problem, we proposes a modified magnetic edge detection method (SP Mag) based on the second order spectral moment. This method has been tested on both synthetic and field data. The synthetic test show that SP Mag cannot only balanced edges no matter from strong or weak anomalies, but also eliminates those false edges caused by the associated anomalies in magnetic field, which provide more effective information for subsequent interpretation.Results: We apply this new method to the RTP aero magnetic field and gravity field of Rizhao Lianyungang area. The lineaments recognized by the SP Mag method correspond well with geologic structures through comparing with geological maps.Discussion: The results illustrate the usefulness of the method for potential field interpretation. Furthermore, more geological and geophysical data should be still combined for comprehensive interpretation in the actual interpretation, though the SP Mag method can recognize lineaments effectively.

3D joint interpretation of potential field, geology, and well data to evaluate a salt dome in the Qarah‐Aghaje area, Zanjan, NW Iran

AbstractAs geophysical parameters are not always functionally related, treating multiple geophysical data sets to have a realistic geological model is not straightforward. An effective strategy to derive a geological interpretation is a combination of several geophysical methods with geological and well observations, each with its advantages and limitations. Gravity and magnetic methods are encouraging tools to investigate salt domes due to enough density and susceptibility contrasts between salt minerals and the background sedimentary rocks. In this paper, the dome‐shaped salt unit in the Qarah‐Aghaje area in Zanjan, located in the northwestern part of Iran, is investigated through the integration of 3D inversion models obtained from gravity and magnetic data and geological and well information. The 3D inversion of both data sets is made using a weighted damped minimum length solution for which model weighting is constructed from multiplying depth weighting and compactness constraints. At first, a synthetic case with a high degree of similarity to the real case is considered to evaluate the efficiency of the adopted inverse algorithm. Then, the inversion algorithm is implemented on the collected gravity and magnetic methods, and interpretation is made utilizing 3D obtained inverse models and geologic and well data. The result shows a dome‐shaped potash‐bearing salt unit that starts from a depth of 12 m and continues to the depth of 200 m. The drilled well in the centre of the main source of the salt (Well 3) demonstrates a depth range of 11–115 m.

Lithosphere Density Model of the Middle Urals Segment

For the Middle and North Urals segments and adjacent territories of the East European Platform and West Siberian Plate (within the graticular trapezoid with geographic coordinates 53–65° N, 48–72° E), ten deep seismic sounding (DSS) profiles were reprocessed using two-dimensional (2D) seismic tomography method, and gradient sections of crustal velocities were constructed in the form of grid functions. In the same format, density sections were constructed. The coefficients of density–velocity empirical correlation were calculated using the solution algorithm of 2D inverse problem of gravimetry. The method and calculation technology of a three-dimensional (3D) density distribution with tying to 2D data from reference seismic sections are embedded in the procedure of quantitative interpretation of potential fields with construction of 3D geophysical models. A stable solution of the 3D inverse problem of gravimetry is sought on the correctness set of the family of horizontal layers with 2D density distribution.

Geophysical studies around abu gharadig basin, North Western desert, Egypt

The current study aims to determine the basement configuration and basement-related structural elements of the Abu Gharadig basin.: We delineated subsurface features that affect the configuration of reservoirs in the study area using an integrated interpretation of potential field and seismic reflection data. The study area lies in the North-Western Desert of Egypt to the east of the Qattara Depression, between latitudes 29° 00’ and 30° 00’ N and longitudes 28° 00’ and 30° 00’ E. Gravity data interpretation delineates shallow features, with NNE-SSW as the major trend and NW-SE as the minor trend. Given that the Euler structural index is approximately zero, these trends probably represent major faults with steep dips and large throws, which juxtapose considerable thicknesses of rocks with contrasting magnetization. On the other hand, the most common tectonic trends prevailing in the deeper levels are the NEN-SWS and NW-SE as the major trends and ENE-WSW as a minor trend. At the same time, the dominant tectonic trend from the Euler solution is NNW-SSE as a major trend and NNE -SSW and WNW-ESE as minor trends. The interpretation of magnetic data indicates the study area dissect by different trends where the trends of shallow features are NNW-SSE as a major trend and E-W as a minor trend. On the other hand, the most common tectonic trends prevailing in the deeper levels are the NNE-SSW and WNW-ESE as major trends and E-W, ENE-WSW, NEN-SWS, and NWN-SES as minor trends. At the same time, the dominant tectonic trend from the Euler solution is N-S as a major trend and NW-SE and NE-SW as minor trends. In the study area, the depth to the top of the basement rocks ranges from 1731.7 m to more than 4736.6 m. Main faults only affect the Lower and Upper Cretaceous sequences, according to seismic interpretation, and appear to be in two trends, the NW-SE and NWN-SES. These structural trends affect the configuration of oil reservoirs in the study area. The study area contains valuable reservoirs according to boreholes drilled in the stud area.

Geoscience Poster G16: Potential field interpretation and modelling in the deep-water Otway Basin

Poster G16 The NW–SE trending Otway Basin is a well-established hydrocarbon province with onshore and shallow-water offshore discoveries. However, the deep-water offshore is underexplored due to the sparsity of data in the past. New 2D seismic, gravity and magnetic data, acquired during the 2020 Otway Basin Seismic Program, were combined with legacy seismic data to improve the understanding of this part of the basin. The new data have been processed and integrated with existing open-file data to derive Moho and lithosphere–asthenosphere boundary surfaces. Additional wavelength filtering of the newly acquired magnetic and gravity data, using constraints from seismic data, provides valuable information on the geometry and the spatial extent of igneous rocks in the deep-water basin. While extrusive igneous rocks and related intrusive rocks in the Otway Basin can be inferred from seismic reflection data, the new magnetic and gravity data provide additional constraints that help to map their distribution across the basin. To access the poster click the link on the right. To read the full paper click here

Potential field interpretation and modelling in the deep-water Otway Basin

The NW–SE trending Otway Basin is a well-established hydrocarbon province with onshore and shallow-water offshore discoveries. However, the deep-water offshore is underexplored due to the sparsity of data in the past. New 2D seismic, gravity and magnetic data, acquired during the 2020 Otway Basin Seismic Program, were combined with legacy seismic data to improve the understanding of this part of the basin. The new data have been processed and integrated with existing open-file data to derive Moho and lithosphere–asthenosphere boundary surfaces. Additional wavelength filtering of the newly acquired magnetic and gravity data, using constraints from seismic data, provides valuable information on the geometry and the spatial extent of igneous rocks in the deep-water basin. While extrusive igneous rocks and related intrusive rocks in the Otway Basin can be inferred from seismic reflection data, the new magnetic and gravity data provide additional constraints that help to map their distribution across the basin.

Statistical methods for potential fields interpretation: studies of structural and tectonic architecture of oil and gas promising territories

Statistical methods for potential fields interpretation: studies of structural and tectonic architecture of oil and gas promising territories

An improved approach for detecting ridge locations to interpret the potential field data for more accurate structural mapping: A case study from Vredefort dome area (South Africa)

Approximating boundaries of causative sources is an important task in potential field interpretation. Many techniques have been proposed for approximating the edges including derivative and phase-based methods. The derivative-based methods cannot equalize the signal amplitudes, and although the phase-based methods do not have this problem, they maybe produce false edges, or the obtained edges are diffused. To overcome these problems, the ridges of some edge detection functions can be determined using the algorithms such as the Blakely and Simpson's algorithm or the curvature analysis algorithm. However, these algorithms cannot fully identify all the peaks of the data or produce some spurious ridges in output maps. In this study, we introduce an improved method to locate the peaks of the data. The efficiency of the algorithm is demonstrated on two synthetic gravity data, as well as real gravity data of the Vredefort dome area (South Africa). Compared with two traditional methods, the proposed algorithm produces more precise and detailed results.

The combination of the regularized operators for horizontal/vertical differentiation and downward continuation in potential fields interpretation

The differentiation operators (with respect to the Cartesian variables x, y and z) are part of several transformations of the potential fields. The resolution of these operators can be improved if the input filed is continued downward at first. We show the performance of the integrated operator, which combines differentiation and downward continuation in the single operation. The presented combined operator is a regularized by means of the Tikhonov regularization, which provides a strong answer to the instability and ambiguity of gravity and magnetic inverse problems. The solution obtained by combining differentiation and downward continuation into a single operator is more efficient as we will demonstrate by showing tests on synthetic and real data sets.

Revisiting Austfonna, Svalbard, with potential field methods – a new characterization of the bed topography and its physical properties

Abstract. With hundreds of metres of ice, the bedrock underlying Austfonna, the largest icecap on Svalbard, is hard to characterize in terms of topography and physical properties. Ground-penetrating radar (GPR) measurements supply ice thickness estimation, but the data quality is temperature dependent, leading to uncertainties. To remedy this, we include airborne gravity measurements. With a significant density contrast between ice and bedrock, subglacial bed topography is effectively derived from gravity modelling. While the ice thickness model relies primarily on the gravity data, integrating airborne magnetic data provides an extra insight into the basement distribution. This contributes to refining the range of density expected under the ice and improving the subice model. For this study, a prominent magmatic north–south-oriented intrusion and the presence of carbonates are assessed. The results reveal the complexity of the subsurface lithology, characterized by different basement affinities. With the geophysical parameters of the bedrock determined, a new bed topography is extracted and adjusted for the potential field interpretation, i.e. magnetic- and gravity-data analysis and modelling. When the results are compared to bed elevation maps previously produced by radio-echo sounding (RES) and GPR data, the discrepancies are pronounced where the RES and GPR data are scarce. Hence, areas with limited coverage are addressed with the potential field interpretation, increasing the accuracy of the overall bed topography. In addition, the methodology improves understanding of the geology; assigns physical properties to the basements; and reveals the presence of softer bed, carbonates and magmatic intrusions under Austfonna, which influence the basal-sliding rates and surges.

Redefining the relationship between the oil company and its vendor

During 2016, BHP committed to produce a petroleum systems model for the complete Exmouth Sub-basin area; such a model would require knowledge of the sub-basin’s evolution through time and a uniquely qualified team to deliver within the agreed time frame. Existing seismic coverage rarely illuminated the deepest portion of the basin; however, through a collaboration with WesternGeco Multiclient, a basin-wide broad-band 3D seismic survey was acquired to underpin the new study to ensure its success. To facilitate this acquisition and the development of the petroleum systems model, BHP and WesternGeco Multiclient created a virtual world-wide team to combine their expertise of seismic acquisition and processing, seismic and potential field interpretation, geochemistry and basin modelling. Although the work was coordinated in Perth (WA, Australia), team members were located in Australia, Europe and the US, where particular specific expertise was located. Both companies made a commitment before the commencement of the project to have open exchange of data, interpretations and knowledge transfer, with one project coordinator. Although individual contributors were located in Australia, Europe and the US, monthly video or telephone coordination meetings combined with weekly meetings between individual specialists, as needed, allowed for the project to be completed to the highest technical quality within the scheduled time frame. The collaborative interpretation from this new seismic data and the resulting petroleum system model has created significant value for both companies, with insights benefiting the industry as a whole as a result of this redefined relationship between company and vendor.

Combined potential field and airborne electromagnetic interpretation to unravel the geological history of the Curaca Valley Region, Bahia, Brazil

Integrated geological-geophysical interpretation offers a robust way to answer geoscientific questions by providing better and faster decisions on where to explore in a regional context, and ultima...

Joint modeling of potential-field data and geodynamic interpretation for northeast Algeria

The crustal structure beneath the northeastern continental part of Algeria is still largely unknown. Here we use potential field data processing, modeling and interpretation in order to investigate the deep sedimentary layers of this area and the transition with the basement. Indeed the gravimetric and magnetic field maps unveil the main geological domains of North Algeria: the AlCaPeKa domain, the Tellian Nappes, the Atlas and the South-Atlasic Fault (SAF). Our modeling approach combines the prediction of gravimetric and magnetic field signals along 4 N–S profiles that cross those domains and using constraints from seismic lines. The resulting cross-sections reveal the roots of the main E-W tectonic detachments of this area: the northern Suture Zone, the Tell Front, and the SAF. It seems that they are all initiated in the lower crust, nearby the continental/oceanic crustal transition for the Suture Zone, and several tenths of kilometers south from this transition for the Tell Front and the SAF detachments. Using these detachments, the lower parts of the crust are sometimes uplifted to only 5 km deep in the crust, while the upper crust is sometimes thickened to reach 15 km of thickness. Large magnetization and density contrasts are observed right beneath the Suture Zone.

Complex geophysical model of the Earth’s crust and upper mantle along the profile of RP-VI (Carpathians)

A complex geophysical model is presented along the regional profile of RP-VI, which is located near the outlet to the terrestrial surface of the eastern boundary of the Skiba zone at its contact with, mainly, the Borislav-Pokuta zone of the Precarpathian trough. For the interpretation of magnetic data, the results of an aeromagnetic survey of a scale of 1 : 200 000 at a flight altitude of 2000 m were used, for the gravitational field — state gravimetric maps of the territory of the USSR in the Bouguer reduction of scale 1 : 200 000. For geoelectrical data, the magnetotelluric sounding curves obtained over the last 30 years have been used. Interpretation of gravimetric and magnetometric data was performed using the computer technology of data analysis KOSKAD3D, which is intended for analysis of three-dimensional digital geoinformation by the methods of a probabilistic-statistical approach. Interpretation of geoelectrical data is performed using the two-dimensional modeling program (inverse problem) — using the REBOCC algorithm. For the analysis of seismic data, the results of both the last century and the last decade are involved. The results of interpretation of different geophysical methods are presented in the form of vertical sections of physical parameters and their complex models of the earth’s crust and upper mantle to a depth of 90 km. The results of the geological and geophysical data presented in this paper differ from those obtained earlier by a new approach to the complex interpretation of potential fields and their comparison with previously unknown geoelectrical models. On the basis of the interpretation of potential fields, a peculiar element of the structure of the Earth’s crust was revealed, ap-parently connected with a sharp change in the composition of the rocks along the profile. The roof of this object undulates from the outlet to the surface at the northwest end of the profile to 25 km in its southeastern part. The sole of the layer from the end of the profile to the point 150 remains constant at a depth of about 25 km, drastically changing from 150 to the depths of the M boundary. It is shown that a sharp change in this object is accompanied by the presence of a low-resistance object that extends from 25 to 80 km with a maximum width of about 40 km. It is suggested that the position of this heterogeneity is related to the Tyachiv-Nadvornyansko-Monastyrtsky fault. The possible connection of a part of the selected element with oil and gas content is considered.

Determination of maximum tilt angle from analytic signal amplitude of magnetic data by the curvature-based method

Imaging buried geological boundaries is one of a major objective during the interpretation of magnetic field data in Geophysics. Therefore, edge detection and edge enhancement techniques assist a crucial role on this aim. Most of the existing edge detector methods require to obtain special points such as in general the maxima of the resulting image. One of the useful tools in estimating edges from magnetic data is the tilt angle of the analytical signal amplitude due to its value slightly dependence on the direction of magnetization. In this study, the maxima of the tilt angle of analytical signal amplitudes of the magnetic data was determined by a curvature-based method. The technique is based on fitting a quadratic surface over a 3×3 windows of the grid for locating any appropriate critical point that is near the centre of the window. The algorithm is built in Matlab environment. The feasibility of the algorithm is demonstrated in two cases of synthetic data as well as on real magnetic data from Tu Chinh-Vung May area. The source code is available from the authors on request.ReferencesAkpınar Z., Gürsoy H., Tatar O., Büyüksaraç A., Koçbulut F., Piper, JDA., 2016. Geophysical analysis of fault geometry and volcanic activity in the Erzincan Basin, Central Turkey, Complex evolution of a mature pull-apart basin. Journal of Asian Earth Sciences, 116, 97-114. Beiki M., 2010. Analytic signals of gravity gradient tensor and their application to estimate source location, Geophysics, 75(6), 159-174.Blakely R. J., and Simpson R.W., 1986. Approximating edges of source bodies from magnetic or gravity anomalies, Geophysics, 51, 1494-1498.Chen An-Guo, Zhou Tao-Fa, Liu Dong-Jia, Zhang Shu, 2017. Application of an enhanced theta-based filter for potential field edge detection: a case study of the LUZONG ORE DISTRICT, Chinese Journal of Geophysics, 60(2), 203-218.Cooper G.RJ., 2014. Reducing the dependence of the analytic signal amplitude of aeromagnetic data on the source vector direction, Geophysics, 79, 55-60.Cordell L., 1979. Gravimetric Expression of Graben Faulting in Santa Fe Country and theEspanola Basin, New Mexico. In Ingersoll, R.V., Ed., Guidebook to Santa Fe Country, New Mexico Geological Society, Socorro, 59-64.Cordell L and Grauch V.J.S., 1985. Mapping Basement Magnetization Zones from Aeromagnetic Data in the San Juan Basin, New Mexico, The Utility of Regional Gravity and Magnetic Anomaly Maps, Society of Exploration Geophysicists, Tulsa, 181-197.Hsu S.K., Coppense D., Shyu C.T., 1996. High- resolution detection of geologic boundaries from potential field anomalies: An enhanced analytic signal technique, Geophysics, 61, 1947-1957.Le D.C., Application of seismic exploration methods to identify geological structural characteristics supporting for hydrocarbon potential assessment in TuChinh - Vung May basin, Ph.D. Thesis, Hanoi University of Mining and Geology.Li X., 2006. Understanding 3D analytic signal amplitude: Geophysics, 71(2), 13-16.Miller H.G. and Singh V., 1994. Potential Field Tilt a New Concept for Location of Potential Field Sources, Journal of Applied Geophysics, 32, 213-217.Nabighian M.N., 1972. The analytic signal of two-dimensional magnetic bodies with polygonal cross-section: Its properties and use of automated anomaly interpretation, Geophysics, 37, 507-517.Nguyen N.T., Bui V.N., Nguyen T.T.H., 2014. Determining the depth to the magnetic basement and fault systems in Tu Chinh - Vung May area by magnetic data interpretation, Journal of Marine Science and Technology, 14(4a), 16-25.Nguyen X.H, San T.N, Bae W., Hoang M.C, 2014. Formation mechanism and petroleum system of tertiary sedimentary basins, offshore Vietnam, Energy Sources, Part A, 36, 1634-1649.Phillips J.D., Hansen R.O. and Blakely R.J., 2007. The use of curvature in potential-field interpretation, Exploration Geophysics, 38(2), 111-119.Rao D.B., and Babu N.R., 1991. A rapid method for three-dimensional modeling of magnetic anomalies, Geophysics, 56(11), 1729-1737.Roest W.R., Verhoef J., and Pilkington M., 1992. Magnetic interpretation using the 3-D analytic signal, Geophysics, 57, 116-125.Tran N., 2017. Sediment geology of Vietnam, VNU Press.Tran T.D., Tran N., Nguyen T.H., Dinh X.T., Pham B.N., Nguyen T.T., Tran T.T.T.N., Nguyen T.H.T., 2018. The Miocenedepositional geological evolution of Phu Khanh, Nam Con Son and Tu Chinh - Vung May basins in Vietnam continental shelf, VNU Journal of Science: Earth and Environmental Sciences, 34(1), 112-135.Vo T.S., Le H.M., Luu V.H., 2005. Three-dimensional analytic signal method and its application in interpretation of aeromagnetic anomaly maps in the Tuan Giao region, Proceedings of the 4th geophysical scientific and technical conference of Vietnam, Publisher of Science and Engineering 2005.Wijns C, Perez C and Kowalczyk P, 2005, Theta map: Edge detection in magnetic data, Geophysics, 70, 39-43.

GamField 2.0 - Significant advances to synthetic potential fields data generator

GamField is an integrated system tool, released in 2011 and available for free, able to construct and visualize subsurface sources in 3-D space and to compute their gravimetric and magnetic effects. Since its first release, we have received feedback and features implementation requests from scientists worldwide. According to such requests, significant advances have been introduced into the software to broaden its field of application in potential field analysis and interpretation as described in this paper.

Software system for automated data interpretation of potential fields (GMT-Auto)

Software system for automated data interpretation of potential fields (GMT-Auto)

Interpretation of Potential Fields and Detection of Deep Faults of Kut-Dewania- Fajir Area, Central Iraq

Interpretation of Potential Fields and Detection of Deep Faults of Kut-Dewania- Fajir Area, Central Iraq

Новая геолого-геофизическая интерпретация потенциальных полей в районе Средне-Уральского трансекта. Статья 2. Восток Урала и Западная Сибирь

Новая геолого-геофизическая интерпретация потенциальных полей в районе Средне-Уральского трансекта. Статья 2. Восток Урала и Западная Сибирь