THE INTERPRETATION OF AEROMAGNETIC SURVEYS FOR HYDROCARBON EXPLORATION

Aeromagnetic surveys have been generally regarded in petroleum exploration as a reconnaissance tool for major structures. They were used commonly in the early stages of exploration to delineate the shape and depth of the sedimentary basin by detecting the strong magnetic contrast between the sediments and the underlying metamorphic basement. Recent developments in the application of computer technology to the study of the earth's magnetic field have significantly extended the scope of aeromagnetic surveys as a tool in the exploration for hydrocarbons. In this paper the two principal methods used in the analysis and interpretation of aeromagnetic data over sedimentary basins are: 1) energy spectral analysis applied to gridded data; and, 2) automatic curve matching applied to profile data. It is important to establish the magnetic character of sedimentary and basement rocks, and to determine the regional magnetic character of the area by applying energy spectral analysis. Application of automatic curve matching to profile data can provide results from the sedimentary section and deeper parts of a basin. High quality magnetic data from an experimental aeromagnetic survey flown over part of the Eromanga/Cooper Basin has recently been interpreted using this new approach. From this survey it is possible to detect major structures such as highs and troughs in the weakly magnetic basement, as well as pick out faults, and magnetic layers in the sedimentary section. The results are consistent with interpretation from seismic and demonstrate that aeromagnetic data can be used to assist seismic interpretation, for example to interpolate between widely spaced seismic lines and sometimes to locate structures which can not be detected from seismic surveys. This new approach to the interpretation of aeromagnetic data can provide a complementary tool for hydrocarbon exploration, which is ideal for logistically difficult terrain and environmentally sensitive areas.

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APPLICATION OF SEMI-AUTOMATED AND INTERACTIVE MAGNETIC INTERPRETATION TECHNIQUES IN PETROLEUM EXPLORATION

The APPEA Journal ◽

10.1071/aj76010 ◽

1977 ◽

Vol 17 (1) ◽

pp. 85

Author(s):

Robert J. Whiteley ◽

Barry F. Long ◽

David A. Pratt

Keyword(s):

Sedimentary Basin ◽

Sedimentary Basins ◽

Magnetic Anomalies ◽

Petroleum Exploration ◽

Magnetic Data ◽

Magnetic Method ◽

Magnetic Interpretation ◽

Geological Information ◽

Detailed Interpretation ◽

Insight Into

The magnetic method is used at many stages of a modern petroleum exploration program. Effective interpretation techniques are required to extract maximum geological information from magnetic data. Those techniques which provide the greatest flexibility and make full use of the talents of experienced interpreters are generally of a semi-automated and interactive nature.There are several practical methods for semi-automated quantitative magnetic interpretation in sedimentary basins. Initial interpretation can be achieved by automatic calculation of characteristic anomaly parameters continuously along original or processed magnetic data profiles. Detailed interpretation of more subtle magnetic features can then follow by theoretical anomaly comparison with field anomalies using interactive portfolio modelling or by direct computation.Examples of the use of these semi-automated techniques in the interpretation of basement and intra-sedimentary magnetic anomalies show that combined magnetic and seismic interpretations can provide considerable insight into the structural processes which have operated in a sedimentary basin.

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Interpretation of aeromagnetic data over Abeokuta and its environs, Southwest Nigeria, using spectral analysis (Fourier transform technique)

Materials and Geoenvironment ◽

10.1515/rmzmag-2016-0018 ◽

2016 ◽

Vol 63 (4) ◽

pp. 199-212 ◽

Cited By ~ 2

Author(s):

Oluwaseun T. Olurin ◽

Saheed A. Ganiyu ◽

Olaide S. Hammed ◽

Taiwo J. Aluko

Keyword(s):

Spectral Analysis ◽

Fourier Transform ◽

Ground Level ◽

Magnetic Data ◽

Depth Range ◽

Aeromagnetic Data ◽

Southwestern Nigeria ◽

Southwest Nigeria ◽

Below Ground ◽

Magnetic Basement

AbstractThis study presents the results of spectral analysis of magnetic data over Abeokuta area, Southwestern Nigeria, using fast Fourier transform (FFT) in Microsoft Excel. The study deals with the quantitative interpretation of airborne magnetic data (Sheet No. 260), which was conducted by the Nigerian Geological Survey Agency in 2009. In order to minimise aliasing error, the aeromagnetic data was gridded at spacing of 1 km. Spectral analysis technique was used to estimate the magnetic basement depth distributed at two levels. The result of the interpretation shows that the magnetic sources are mainly distributed at two levels. The shallow sources (minimum depth) range in depth from 0.103 to 0.278 km below ground level and are inferred to be due to intrusions within the region. The deeper sources (maximum depth) range in depth from 2.739 to 3.325 km below ground and are attributed to the underlying basement.

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Supplemental material: Guides to understanding the aeromagnetic expression of faults in sedimentary basins: Lessons learned from the central Rio Grande rift, New Mexico

10.1130/geos.s.12237731.v1 ◽

2007 ◽

Author(s):

V.J.S. Grauch ◽

Mark R. Hudson

Keyword(s):

Rio Grande ◽

Sedimentary Basins ◽

Lessons Learned ◽

Rio Grande Rift ◽

Aeromagnetic Data ◽

File Size ◽

Aeromagnetic Survey ◽

Map Projection ◽

Map Scale ◽

Shaded Relief

Geosphere, December 2007, v. 3, p. 596-623, doi: 10.1130/GES00128.1. Plate 1 - Color shaded-relief image of reduced-to-pole (RTP) aeromagnetic data for the central Rio Grande rift, compiled from Sweeney et al. (2002) and Bankey et al. (2006). The colors primarily reflect the broad variations in the data, whereas the illumination (from the west) emphasizes detailed variations, especially linear features associated with faults. Selected geographic, geologic, and interpretative features are labeled. Map projection is NAD27, UTM zone 13, in units of meters. Inset shows locations and names of aeromagnetic survey areas. Map scale 1:250,000. File size is 9.2 MB.

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INTEGRATING SEISMIC, GRAVITY AND AEROMAGNETIC DATA IN THE STRUCTURAL INTERPRETATION OF THE MERLINLEIGH SUB-BASIN, WESTERN AUSTRALIA

The APPEA Journal ◽

10.1071/aj96012 ◽

1997 ◽

Vol 37 (1) ◽

pp. 205

Author(s):

A. J. Mory ◽

R. P. lasky

Keyword(s):

Potential Field ◽

Gravity Data ◽

Low Cost ◽

Late Carboniferous ◽

Petroleum Exploration ◽

Magnetic Data ◽

Limited Information ◽

Aeromagnetic Data ◽

Near Surface ◽

Potential Field Data

The southern Merlinleigh Sub-basin is a frontier area for petroleum exploration within the onshore Southern Carnarvon Basin, with limited seismic coverage and only two deep exploration wells. High resolution aeromag- netic and semi-detailed gravity data acquired in 1995 provide relatively low cost structural inf ormation"comple- mentary to the regional seismic coverage.Two-dimensional seismic data can be mapped with confidence if the lines are closely spaced. By identifying lineaments on potential-field images, orientations for structures within the sedimentary succession, and at basement or intra-basement levels, can assist in the interpretation of faults and structures in areas of limited seismic coverage, and to extrapolate them outside areas of seismic control. Consequently, by integrating seismic and potential-field data, a more rigorous interpretation of the structural geometry can be achieved and thereby assists in reconstructing the evolution of a sedimentary basin.The aeromagnetic data provided only limited information about the structure of the Merlinleigh Sub-basin because magnetic anomalies appear to be dominated either by near-surface or deep intra-basement sources. In contrast, the gravity data provide a more reliable definition of the structure at basement level and, to a lesser extent, within the sedimentary sequence.Seismic, gravity and magnetic data show that the region is a large north-trending Late Carboniferous to Permian depocentre and can be sub-divided into two main troughs east of the Wandagee and Kennedy Range Faults. These are en-echelon fault systems with syn- depositional growth during the main period of rifting in the Late Carboniferous to Early Permian.

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Correlation between aeromagnetic data rejection and geomagnetic indices

Geophysics ◽

10.1190/1.2057982 ◽

2005 ◽

Vol 70 (5) ◽

pp. J33-J38 ◽

Cited By ~ 3

Author(s):

Marc A. Vallée ◽

Larry Newitt ◽

Régis Dumont ◽

Pierre Keating

Keyword(s):

Goodness Of Fit ◽

Rate Of Change ◽

Magnetic Data ◽

Aeromagnetic Data ◽

Aeromagnetic Survey ◽

Geomagnetic Indices ◽

Global Indices ◽

Ap Index ◽

Global And Local ◽

Survey Planning

Predicting the rejection of aeromagnetic data would be a useful tool for aeromagnetic survey planning. To relate aeromagnetic survey requirements to geomagnetic activity monitoring and prediction, we analyzed the relationship between the rejection of aeromagnetic data as it is measured during surveys and the variations in existing geomagnetic indices. The magnetic data were collected at Canadian magnetic observatories during 2001 and covered the polar cap, auroral, and subauroral zones. The geomagnetic indices were global and local indices. The global indices included the Kp, ap, and Dst indices. The local indices were the three-component hourly ranges, the three-component maximum rate of change, and the Pc3 pulsation index. The goodness of fit was used to compare the results between the different indices at different locations. In general, there was some correlation between global geomagnetic indices and the rate of rejection of aeromagnetic data. Good correlation with a global index was obtained with the daily mean of the Ap index for a station located in the subauroral zone. The best correlation was obtained with local indices and particularly with the Pc3 index amplitude. From these results we conclude that forecasting Pc3 index amplitude would be a useful tool for planning aeromagnetic surveys.

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Aeromagnetic regional survey of onshore Australia

Geophysics ◽

10.1190/1.1442460 ◽

1988 ◽

Vol 53 (2) ◽

pp. 254-265

Author(s):

D. H. Tucker ◽

I. G. Hone ◽

D. Downie ◽

A. Luyendyk ◽

K. Horsfall ◽

...

Keyword(s):

Data Base ◽

Mineral Resources ◽

Sedimentary Basins ◽

Petroleum Exploration ◽

Quality Data ◽

Magnetic Data ◽

Regional Survey ◽

Wide Range ◽

Line Spacing ◽

Airborne Magnetic

The Australian Bureau of Mineral Resources (BMR) is responsible for the National Airborne Magnetic Database. This data base consists of results from approximately 3 500 000 line‐km of regional survey flying carried out over 35 years, recording total magnetic intensity. The magnetic data base is one of the most important geophysical data bases for Australia and is used extensively by the minerals and petroleum exploration industries. First‐pass coverage of onshore Australia is aimed for completion in 1992. This coverage contains data from surveys with a wide range of specifications, resulting in a wide range of data quality; some of the areas covered by poorer quality data may be reflown later. For the most part, the intention has been to acquire data at a continuous ground clearance of 150 m and with a line spacing of 1500 m. However, over some sedimentary basins, the line spacing is in excess of 3200 m. New color and grey‐scale (image processed type) digital magnetic maps (pixel maps) are in preparation; these will supersede the 1976 digital magnetic map of Australia, which was gridded on a 1.2 minute mesh (2000 m) mostly by digitizing contours on maps. The new map, produced from flight‐line data, will have a grid size of 0.25 minutes. Initially, a series of maps will be produced with each one covering a block of 4 degrees latitude by 6 degrees longitude, coinciding with standard 1 : 1 000 000 map sheets. An example included for the Adelaide 1 : 1 000 000 map sheet in Southern Australia shows a dramatic increase in the number of anomalies over those that were evident in earlier contour presentations.

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RESISTIVITY SOUNDINGS IN A PETROLEUM PROSPECT IN THE COONAMBLE BASIN, N.S.W., AUSTRALIA

Geophysics ◽

10.1190/1.1440034 ◽

1969 ◽

Vol 34 (4) ◽

pp. 601-614 ◽

Cited By ~ 3

Author(s):

R. J. Henderson ◽

D. W. Emerson

Keyword(s):

Seismic Reflection ◽

New South ◽

Sedimentary Basins ◽

Petroleum Exploration ◽

Well Log ◽

Aeromagnetic Data ◽

Resistivity Data ◽

South Wales ◽

Actual Field ◽

Dipole Configuration

Preliminary investigations at well sites in the Coonamble Basin, New South Wales, have demonstrated that deep resistivity soundings can provide valuable information in petroleum exploration with relative ease. The correct thickness of the unmetamorphosed basin sediments was accurately defined from resistivity data whereas interpretation of seismic reflection and aeromagnetic data had previously yielded large over‐estimates. Field procedures can be conducted in a manner suitable to routine prospecting. The dipole configuration has certain advantages in this respect, not the least of which is its ability to resolve low dips in sedimentary basins. Synthetic sounding curves calculated on a digital computer from digitized well log resistivity data are useful to predict the results to be expected from an actual field sounding and greatly facilitate the interpretation of the results.

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The north-east Baffin Bay region, offshore Greenland – a new frontier petroleum exploration region

Geological Survey of Denmark and Greenland Bulletin ◽

10.34194/geusb.v15.5046 ◽

2008 ◽

Vol 15 ◽

pp. 65-68 ◽

Cited By ~ 2

Author(s):

Ulrik Gregersen

Keyword(s):

Gravity Data ◽

Sedimentary Basins ◽

Hydrocarbon Exploration ◽

Reservoir Rock ◽

Petroleum Exploration ◽

The Arctic ◽

Structural Element ◽

Baffin Bay ◽

North East ◽

The North

In recent years the Arctic has come into focus for hydrocarbon exploration, and areas offshore both West and East Greenland have been evaluated as promising frontier hydrocarbon provinces. Seven hydrocarbon exploration and ex ploitation licenses were awarded in 2007–2008 offshore the Disko–Nuussuaq region (Fig. 1), and two more have been awarded in the open-door region offshore south-western Greenland. In 2007, an extensive amount of new seismic and aeromagnetic data was acquired by the TGS-NOPEC Geop hysical Company in the north-eastern Baffin Bay region. Geophysical mapping has been initiated by the Geological Survey of Denmark and Greenland (GEUS) in the Melville Bugt region offshore North-West Greenland (Fig. 1) with the purpose of evaluating the hydrocarbon prospectivity. Initial interpretation of seismic and gravity data suggests the presence of deep sedimentary basins separated by structural highs. Geological information on source rock, reservoir rock and seal intervals from surrounding regions suggest that the Melville Bugt region is likely to have a significant petroleum potential. The study is based on public domain magnetic and gravity data, and all proprietary and public 2-D seismic data (Fig. 1) acquired before 2003. Seismic horizons from the ‘seismic basement’ to ‘base Quaternary’ are being interpreted regionally. Based on the seismic interpretation, a structural element map, depth-structure maps and isopach maps will be produced in order to assess the prospectivity of the Melville Bugt region.

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Mapping geology beneath volcanics using magnetic data

The APPEA Journal ◽

10.1071/aj17205 ◽

2018 ◽

Vol 58 (2) ◽

pp. 821

Author(s):

Irena Kivior ◽

Stephen Markham ◽

Leslie Mellon ◽

David Boyd

Keyword(s):

South Australia ◽

Sedimentary Basins ◽

Seismic Signal ◽

Petroleum Exploration ◽

Seismic Survey ◽

Source Distribution ◽

Magnetic Data ◽

Large Area ◽

Magnetic Susceptibilities ◽

Passive Seismic

Volcanic layers within sedimentary basins cause significant problems for petroleum exploration because the attenuation of the seismic signal masks the underlying geology. A test study was conducted for the South Australia Government to map the thickness of volcanics and sub-volcanic geology over a large area in the Gawler Range Volcanics province. The area is covered by good quality magnetic data. The thickness of volcanics and basement configuration was unknown as there has only been a limited amount of drilling. The Automatic Curve Matching (ACM) method was applied to located magnetic data and detected magnetic sources within different rock units, providing their depth, location, geometry and magnetic susceptibility. The magnetic susceptibilities detected by ACM allowed the differentiation of the volcanics and the underlying basement. The base of volcanics and the depth to the top of basement was mapped along 75 km NS profiles, that were spaced 1 km apart over a distance of 220 km. The volcanic and basement magnetic susceptibilities and the magnetic source distribution pattern were used as key determinants to interpret the depth to the two interfaces. The results for each interface were gridded, and images of the base of volcanics and depth to basement were generated. The mapped volcanics thickness was validated by comparison with the results from drilling, with the volcanics thickness matching very well. After project completion, a passive seismic survey was conducted in part of the test area, indicating a base of volcanics of ~4 km, which further confirmed the results.

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Deep crustal structures interpreted from potential field data along deep seismic sounding transects in Australia

The APPEA Journal ◽

10.1071/aj14085 ◽

2015 ◽

Vol 55 (2) ◽

pp. 450

Author(s):

Irena Kivior ◽

David Boyd ◽

David Tucker ◽

Stephen Markham ◽

Francis Vaughan ◽

...

Keyword(s):

Spectral Analysis ◽

Potential Field ◽

Field Data ◽

Gravity Data ◽

Sedimentary Basins ◽

Deep Seismic Sounding ◽

Magnetic Data ◽

Potential Field Data ◽

Seismic Sounding ◽

Crustal Structures

Energy spectral analysis techniques have been applied to magnetic and gravity data acquired across the Olympic Dam cratonic area in Australia and sedimentary basins along the Equatorial Margin of Brazil. Analysis has been conducted along two Deep Seismic Sounding lines (DSS) acquired by Geoscience Australia. There is a good correlation between interfaces found in this analysis and structures interpreted from the seismic data. Interpretation of gravity data using energy spectral analysis along the DSS survey lines show a number of deep crustal structures are evident, including the Moho which was detected using gravity data, while similar analysis of the magnetic data show indications of the Curie isotherm. In addition, the analysis was extended away from the seismic lines to detect many deep crustal horizons and structures at considerable distances from the DSS lines. The results obtained from energy spectral analysis across this area in Australia encouraged the application of this technique on the Equatorial Margin of Brazil, where the potential field data is of much lower resolution. This suggests that a much wider application of this approach could be highly valuable to investigate the deep structure under other sedimentary basins and to assist heat flow studies.

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