On: “The straight‐slope method for basement depth determination revisited,” by J. R. Skilbrei (April 1993 GEOPHYSICS, 58, p. 593–595).

Geophysics ◽  
1994 ◽  
Vol 59 (5) ◽  
pp. 851-852
Author(s):  
Nelson C. Steenland
Keyword(s):  
Sedimentary Basins ◽  
Thin Plates ◽  
Aeromagnetic Data ◽  
Ancillary Data ◽  
Slope Method ◽  
Depth Determination ◽  
Basement Depth

After interpreting aeromagnetic data on a worldwide basis for more than 20 years without recourse to any ancillary data, subsequent basement drilling showed an accuracy of ±7.5 percent for the contoured maps, not individual depth values, of the bottom of new sedimentary basins. The fields were resolved into intrabasement, suprabasement, and intrasedimentary anomalies, and depths were computed to their sources of thick prisms and thin plates with two universally applied coefficients. More than once, intrasedimentary volcanics were handled routinely. The author’s statement in paragraph three of his Introduction is not correct.

Reply by the author to N. C. Steenland

Geophysics ◽  
1994 ◽  
Vol 59 (5) ◽  
pp. 852-852
Author(s):  
Jan R. Skilbrei
Keyword(s):  
Short Note ◽  
Volcanic Rocks ◽  
Sedimentary Basins ◽  
Slope Method ◽  
Depth Determination ◽  
Basement Depth ◽  
Limited Depth

Steenland writes that my statement in paragraph three of my Introduction is not correct. My statement is, “In most geological situations, and particular over sedimentary basins, the interpreter is unable to recognize bodies with limited depth extents.” It was implicit that I meant bodies within the basement with limited depth extents because the title of the short note is: “The straight‐slope method for basement depth determination revisited.” I believe that most interpreters agree with my statement. However, when it comes to recognizing intrasedimentary volcanics, I agree that it is often easy to distinguish these types of anomalies from those anomalies that are due to sources which exist within the basement when the volcanic rocks within the sediments are far removed above the basement.

scholarly journals Source Depth Determination from Aeromagnetic Data of Ilesha, Southwest Nigeria, Using the Peters’ Half Slope Method

2013 ◽  
Vol 3 (1) ◽  
Author(s):  
Vitalis Chidi Ozebo ◽  
Charles Olubunmi Ogunkoya ◽  
Victor Makinde ◽  
Gideon O. Layade
Keyword(s):  
Aeromagnetic Data ◽  
Source Depth ◽  
Slope Method ◽  
Depth Determination ◽  
Southwest Nigeria

Discussions of “An Evaluation of Basement Depth Determination from Airborne Magnetometer Data,” by Peter Jacobsen, Jr.

Geophysics ◽  
1961 ◽  
Vol 26 (3) ◽  
pp. 317-319 ◽  
Author(s):  
R. J. Bean ◽  
Walter R. Fillippone ◽  
Norman R. Paterson ◽  
Isidore Zietz
Keyword(s):  
Quantitative Analysis ◽  
Sedimentary Basins ◽  
Depth Determination ◽  
Magnetometer Data ◽  
Local Relief ◽  
Basement Depth ◽  
Basement Surface

In his discussion of the magnetic interpretations, Mr. Jacobsen rightly distinguishes between the determination of basement depth and configuration by analysis of anomalies originating from magnetization contrast within the basement and the delineation of local relief or faulting at the basement surface by analysis of smaller anomaly trends. It cannot be emphasized too strongly that the principal purpose of conducting aeromagnetic surveys is to outline the extent and depth of sedimentary basins, and the calculation of depth to basement by quantitative analysis of anomalies has progressed to the point where reliable results can be obtained by skilled interpreters.

On the half‐slope and straight‐slope methods of basement depth determination

Geophysics ◽  
1984 ◽  
Vol 49 (8) ◽  
pp. 1365-1368 ◽  
Author(s):  
D. Atchuta Rao ◽  
H. V. Ram Babu
Keyword(s):  
Horizontal Projection ◽  
The Past ◽  
Slope Method ◽  
Line Part ◽  
Straight Line ◽  
Depth Determination ◽  
Basement Depth ◽  
Prismatic Bodies ◽  
General Reliability ◽  
Exhaustive Study

Although a great variety of interpretation techniques for basement depth determination has been developed during the past two or three decades, the half‐slope and straight‐slope methods are still popular due to their simplicity and general reliability in manual interpretation and are widely used in oil exploration work (Nettleton, 1976). The half‐slope and straight‐slope rules are derived for a particular set of geologic/geophysical conditions and care should be taken in applying them in a more general way. For example, the half‐slope method of Peters (1949) was derived for magnetic anomalies over vertical dikes with vertical polarization. The straight‐slope method uses the horizontal projection of the straight‐line part of the steepest gradient at the inflection point on the anomaly curve as the depth estimator. This rule is purely empirical because mathematically there is no straightline part on the anomaly curve. Vacquier et al. (1951) made an exhaustive study of the straight‐slope method and presented several depth indices measured on different flanks of anomalies due to prismatic bodies.

The straight‐slope method for basement depth determination revisited

Geophysics ◽  
1993 ◽  
Vol 58 (4) ◽  
pp. 593-595 ◽  
Author(s):  
Jan Reidar Skilbrei
Keyword(s):  
Magnetic Anomaly ◽  
Inflection Point ◽  
Horizontal Projection ◽  
Slope Method ◽  
Source Estimation ◽  
Magnetic Source ◽  
Straight Line ◽  
Depth Determination ◽  
Basement Depth ◽  
General Reliability

The straight‐slope method is still popular for depth to magnetic source estimation due to its simplicity and general reliability in manual interpretation (e.g., Nettleton, 1976). Other commonly used manual slope methods are Peters rule (Peters, 1949) and Sokolov rule (Åm, 1972). The straight‐slope method uses the horizontal projection of the straightline part of the magnetic anomaly curve at the inflection point as the depth estimator (see Figure 1). Because no straight line exists mathematically, the rule is purely empirical, even though visually a certain part of a curve will appear to be straight.

scholarly journals Analytic Signal Depth from High Resolution Aeromagnetic Data over the Gongola Basin Upper Benue Trough Northeastern Nigeria

2021 ◽  
Vol 25 (4) ◽  
pp. 585-590
Author(s):  
H. Musa ◽  
N.E. Bassey ◽  
R. Bello
Keyword(s):  
High Resolution ◽  
Magnetic Structure ◽  
Horizontal Cylinder ◽  
Analytic Signal ◽  
Aeromagnetic Data ◽  
Polynomial Fitting ◽  
Benue Trough ◽  
Local Maxima ◽  
Depth Determination ◽  
Programming Software

The study of high-resolution aeromagnetic data was carried out over the Gongola basin, upper Benue trough, northeastern Nigeria, for analytic signal depth determination. Total intensity magnetic map obtained from the data using the Oasis Montaj TM programming software was used to get the residual map by polynomial fitting, from where the analytic signal was obtained with the use of anomaly width at half the amplitude (X1/2). This was used to carry out depth estimations over the study area. The results showed that it peaks over the magnetic structure with local maxima over its edges (boundaries or contact), and the amplitude is simply related to magnetization, likewise results also showed that the depth estimates were in the range of 1.2 to 5.9 km and were calculated for contact, dyke/sill and horizontal cylinder respectively. The lowest values are from DD profiles, while the highs are from AA profiles. This work is important in identifying dykes, contacts and intrusives over an area.

THE INTERPRETATION OF AEROMAGNETIC SURVEYS FOR HYDROCARBON EXPLORATION

1999 ◽  
Vol 39 (1) ◽  
pp. 494
Author(s):  
I. Kivior ◽  
D. Boyd
Keyword(s):  
Spectral Analysis ◽  
Sedimentary Basins ◽  
Hydrocarbon Exploration ◽  
Petroleum Exploration ◽  
Magnetic Data ◽  
Curve Matching ◽  
Aeromagnetic Data ◽  
Profile Data ◽  
Aeromagnetic Survey ◽  
New Approach

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.

scholarly journals Structural interpretation of High-resolution aeromagnetic data over the Dahomey basin, Nigeria: implications for hydrocarbon prospectivity

2021 ◽  
Vol 11 (4) ◽  
pp. 1545-1558
Author(s):  
E. M Okoro ◽  
K. M Onuoha ◽  
C. G Okeugo ◽  
C. I. P. Dim
Keyword(s):  
High Resolution ◽  
Oil And Gas ◽  
Low Cost ◽  
Sedimentary Basins ◽  
Data Interpretation ◽  
Aeromagnetic Data ◽  
Horizontal Derivative ◽  
Dahomey Basin ◽  
First Vertical Derivative ◽  
Total Horizontal Derivative

AbstractThe renewed quest to boost Nigeria’s dwindling reserves through aggressive search for oil and gas deposits in Cretaceous sedimentary basins has re-ignited the need to re-evaluate the hydrocarbon potentials of the Dahomey Basin. Aeromagnetic data are a low-cost geophysical tool deployed in mapping regional basement structures and determination of basement depths and sedimentary thickness in frontier basin exploration. In this study, high-resolution aeromagnetic (HRAM) data covering the Dahomey Basin Nigeria have been interpreted to map the basement structural configuration and to identify mini-basins favorable for hydrocarbon prospectivity. The total magnetic intensity grid was reduced to the equator (RTE) and edge detection filters including first vertical derivative (FVD), total horizontal derivative (THDR), tilt derivative (TDR) and total horizontal derivative of upward continuation (THDR_UC)) were applied to the RTE grid to locate the edges and contacts of geological structures in the basin. Depth to magnetic sources were estimated using the source parameter imaging (SPI) method. Data interpretation results revealed shallow and deep-seated linear features trending in the NNE-SSW, NE-SW, NW-SE and WNW-ESE directions. The SPI map showed a rugged basement topography which depicted a horst-graben architecture on 2D forward models along some selected profiles. Two mini-basins ranging in basement depths between 4.5 – 6.3km were mapped offshore of the study area. It appears the offshore Dahomey Basin holds greater promises for hydrocarbon occurrence due to the presence of thicker succession of sedimentary deposits in the identified mini-basins.

scholarly journals ANALYSIS OF HIGH RESOLUTION AEROMAGNETIC DATA OF SOME PARTS OF BENUE TROUGH, NIGERIA

2020 ◽  
Vol 4 (2) ◽  
pp. 76-85
Author(s):  
Nuraddeen Usman ◽  
Ibrahim Jibril
Keyword(s):  
Spectral Analysis ◽  
Magnetic Anomalies ◽  
Aeromagnetic Data ◽  
Benue Trough ◽  
First Order ◽  
Qualitative Interpretation ◽  
Maximum Value ◽  
Magnetic Source ◽  
Analysis Technique ◽  
Basement Depth

This work is aimed to determine the depth to basement of some magnetic sources in the study area. Four aeromagnetic sheets were acquired from the Nigerian Geological Survey Agency which includes (Bajoga, 131, Gulani, 132, Gombe, 152 and Wuyo, 153). The study area covers an estimated area of about 12100km2 between latitude 90N-110N and longitude 110E-130E. The total magnetic field of the study area have been evaluated. In order to determine the basement depth, spectral analysis technique was applied. Detailed analysis of the aeromagnetic data for the study area was performed. The procedure involved in the analysis include reduction to equator to remove the effect of inclination, contouring of the total magnetic intensity, separation of the regional and residual anomalies using polynomial fitting of first order, qualitative interpretation and quantitative interpretation. The residual field of the study area composes of low magnetic anomalies reaching a minimum value of -158.6nT as observed in the northern and southern parts and high magnetic anomalies reaching a maximum value of 178.1nT as observed in the western part of the study area. The result from the spectral analysis for each block shows that the depths to the magnetic source are 5.20Km for block 1, 5.74Km for block 2, 7.59Km for block 3 and 3.56Km for block 4. The average depth to magnetic source in the study area was found to be 5.52Km. Based on the computed average sedimentary thickness obtained in this study area, hydrocarbon accumulation in the study area is feasible.

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