AN EVALUATION OF BASEMENT DEPTH DETERMINATIONS FROM AIRBORNE MAGNETOMETER DATA

Geophysics ◽  
1961 ◽  
Vol 26 (3) ◽  
pp. 309-317 ◽  
Author(s):  
Peter Jacobsen
Keyword(s):  
Magnetic Data ◽  
Depth Information ◽  
Poor Agreement ◽  
Well Control ◽  
Depth Maps ◽  
Magnetometer Data ◽  
Local Relief ◽  
Basement Depth ◽  
Well Data ◽  
Basement Surface

Four years ago Creole Petroleum Corporation submitted identical airborne magnetometer data for a portion of the Eastern Venezuela basin to two different geophysical contractors for independent, detailed analysis. These contractors offer the customary generalized basement depth maps; but they specialize in delineating areas of relatively local relief on the basement surface. Both kinds of interpretation were requested by Creole. The main purpose of the study was to evaluate the reliability of interpretations of local basement relief from magnetic data. Accordingly, the region for study was deliberately chosen to include, in part, areas for which Creole had considerable knowledge of basement depths and local basement configuration from other sources. Local basement relief shown by the two magnetic interpretations is in poor agreement with basement depth information from seismograph and well data. Moreover, the two magnetic pictures bear little resemblance one to the other. With respect to regional basement depth contours, one of the magnetic interpretations compares statisfactorily with the picture based on seismograph and well control. A tentative conclusion is that local basement relief cannot be reliably interpreted from magnetometer data alone.

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.

DISCUSSION OF “AN EVALUATION OF BASEMENT DEPTH DETERMINATION FROM AIRBORNE MAGNETOMETER DATA” BY PETER JACOBSEN, JR.

Geophysics ◽  
1962 ◽  
Vol 27 (1) ◽  
pp. 162-162
Author(s):  
G. Ramaswamy
Keyword(s):  
World War Ii ◽  
Gravity Data ◽  
Data Gathering ◽  
Magnetic Data ◽  
World War ◽  
Depth Determination ◽  
Magnetometer Data ◽  
Exploration Tool ◽  
Basement Depth ◽  
Ground Magnetic

Mr. Jacobsen’s article and the accompanying discussions on the scope and outlook for the current interpretational practices in aeromagnetic surveys are very timely and deserve the attention of all geophysicists as well as exploration management. Since World War II the aeromagnetic surveys have replaced the ground magnetic surveys as a reconnaissance exploration tool chiefly because of the former’s rapidity and cheapness in data‐gathering. In this process, however, the aerial technique has lost one advantage going with the ground surveys. In land surveys the practice has been to make simultaneous magnetic and gravity observations and the interpretations of basement features are made from these paired observations. I believe that the absence of concurrent information on gravity has been a real handicap with aeromagnetic interpretation in reliably locating basement features in the early stages of exploration. Perhaps the present aerial gravitymeter instrumentation can be soon improved to desired sensitivity for exploration so that simultaneous gravity‐magnetic observations from the air will be possible. In large unexplored sedimentary areas the gravity data are as valuable, sometimes more, to the interpretation of magnetic data as a knowledge of the magnetic properties of any out‐cropping rocks.

scholarly journals Analysis of gravity and aeromagnetic data to determine structural trend and basement depth beneath the Ajdabiya Trough in northeastern Libya

2021 ◽  
Vol 3 (2) ◽  
Author(s):  
Abdelhakim S. Eshanibli ◽  
Abel Uyimwen Osagie ◽  
Nur Azwin Ismail ◽  
Hussin B. Ghanush
Keyword(s):  
Gravity Data ◽  
Depth Estimation ◽  
Magnetic Data ◽  
Aeromagnetic Data ◽  
Pass Filter ◽  
Magnetic Basement ◽  
Basement Depth ◽  
Well Data ◽  
High Pass ◽  
Modelling Process

AbstractIn this study, we analyse both ground gravity and aeromagnetic data in order to delineate structural trends, fault systems and deduce sedimentary thicknesses within the Ajdabiya Trough in Libya’s northeast. A high-pass filter and a reduced-to-the-pole (RTP) transformation are applied to the gravity and aeromagnetic data respectively. Different filters are used to enhance the structural signatures and fault trends within the study area. The Werner deconvolution and source parameter imaging (SPI) techniques are applied to the RTP magnetic data for source depth estimation. Four well-data within the area are used as constraints in the two-dimensional forward modelling process. The results show that the Ajdabiya Trough is characterised by gravity anomaly highs and magnetic anomaly lows. The analysis of gravity data shows predominant Northeast–Southwest structural trends, whereas the analysis of magnetic data shows predominant North–South magnetic lineaments within the Ajdabiya Trough. The Euler deconvolution depth estimates of faults depths range between 1500 and 9500 m. The SPI estimates of the magnetic basement range between 2500 and 11,500 m beneath the study area (deepest beneath the Ajdabiya Trough). Constrained by the well-data, six major layers characterize the four profiles that are taken within the area. One of the profiles shows a high-density intrusion (about 4 km from the surface) within the sedimentary sequence. The intrusion may be the result of the rifting Sirt Basin which caused a weakening of the crust to allow for mantle intrusion.

scholarly journals Magnetometer data from the GRACE satellite duo

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Nils Olsen
Keyword(s):  
Mean Squared Error ◽  
Incident Angle ◽  
Magnetic Data ◽  
Grace Data ◽  
Magnetometer Data ◽  
Geophysical Investigations ◽  
Grace Satellites ◽  
Grace Satellite ◽  
The Difference ◽  
Grace Mission

AbstractThis paper describes and discusses the preprocessing and calibration of the magnetic data taken by the navigational magnetometers onboard the two GRACE satellites, with focus on the almost 10 years period from January 2008 to the end of the GRACE mission in October 2017 for which 1-Hz magnetic data are available. A calibration of the magnetic data is performed by comparing the raw magnetometer sensor readings with model magnetic vector values as provided by the CHAOS-7 geomagnetic field model for the time and position of the GRACE data. The presented approach also accounts for magnetic disturbances produced by the satellite’s magnetorquer and for temperature effects, which are parametrized by the Sun incident angle. The root-mean-squared error of the difference between the calibrated data and CHAOS-7 model values is about 10 nT, which makes the GRACE magnetometer data relevant for geophysical investigations.

Application of raypath modelling to verify the mapping of Gippsland gas fields

1989 ◽  
Vol 20 (2) ◽  
pp. 325
Author(s):  
M. Megallaa
Keyword(s):  
Oil And Gas ◽  
Synthetic Data ◽  
Production Capacity ◽  
Normal Incidence ◽  
Wave Theory ◽  
Seismic Profiles ◽  
Well Control ◽  
Depth Maps ◽  
Petroleum Resources ◽  
Gas Fields

One of the Victorian Government's policies in the oil and gas area is to enhance the benefits to the State in the energy sector by assessing the nature and extent of the petroleum resources. To evaluate the production capacity of developed and undeveloped gas fields, a comprehensive study was commissioned by the DITR in 1988. The first step in a study of this type is to check the accuracy of the depth maps, to see if they adequately describe the reservoir geometry. Raypath modelling, using the Advanced Interpretation Mapping System (AIMS ? Version III), was carried out by Geophysical Services International (GSI), Sydney, on a number of selected profiles over the Snapper, Marlin-Turrum, Barracouta, Kipper and Emperor fields for the DITR. Input data for the models were extracted from the operator's maps. The software simulates the normal incidence raypaths (or wave theory solution) for all shotpoints, and from this information it generates gather records and/or synthetic seismic profiles. By comparing the model data with those from data acquisition, processing and interpretation, it was possible to check the validity of the interpretation of the reservoir's geometry. This modelling work showed that the synthetic data were comparable with the acquisition and processing data, confirming that the depth maps (tied to well control) produced by the operator using its proprietary software are adequate and most likely to represent subsurface configuration of the reservoirs.

Elastic mineral facies: Selecting site-specific elastic moduli of clay

Geophysics ◽  
2017 ◽  
Vol 82 (4) ◽  
pp. MR111-MR119
Author(s):  
Uri Wollner ◽  
Jack P. Dvorkin
Keyword(s):  
Elastic Moduli ◽  
Rock Physics ◽  
Data Sets ◽  
Depth Range ◽  
Chemical Formula ◽  
Rock Matrix ◽  
Well Control ◽  
Physics Model ◽  
Well Data ◽  
Rock Physics Model

The elastic moduli of the mineral constituents of the rock matrix are among the principal inputs in all rock-physics velocity-porosity-mineralogy models. Published experimental data indicate that the elastic moduli for essentially any mineral vary. The ranges of these variations are especially wide for clay. The question addressed here is how to select, based on well data, concrete values for clay’s elastic constants where those for other minerals are fixed. The approach is to find a rock-physics model for zero-clay intervals and then adjust the clay’s constants to describe the intervals dominated by clay using the same model. We examine three data sets from clastic environments, each represented by three wells, where the selected constants for clay were different between the fields but stable within each field. These constants can then be used for seismic forward modeling and interpretation in a specific field away from well control and within a depth range represented in the wells. In essence, we introduce the concept of elastic mineral facies where we identify clay as a mineral with certain elastic moduli rather than by its chemical formula.

Mapping horizons and fracture patterns in coal measures using magnetics for coalbed methane exploration in Queensland

2015 ◽  
Vol 55 (2) ◽  
pp. 443
Author(s):  
Irena Kivior ◽  
Stephen Markham ◽  
David Warner ◽  
Leslie Mellon
Keyword(s):  
Coalbed Methane ◽  
Magnetic Data ◽  
Mapping Technique ◽  
Stress Regime ◽  
Rock Fabric ◽  
Fracture Patterns ◽  
Eastern Australia ◽  
Hill Area ◽  
Well Data ◽  
Coal Measures

High resolution magnetic data has successfully been used to map the top and base of coal measures, related faults and fracture patterns across the Red Hill area in the northern Bowen Basin, eastern Australia. A horizon mapping technique, based on energy spectral analysis (ESA), was used to detect magnetic susceptibility contrasts that were laterally merged to form two magnetic interfaces, corresponding to the top of the Fair Hill Formation and base of the Goonyella Middle Seam in the Permian Moranbah coal measures. The depth estimates were made at stations on a regular mesh of 400 m x 400 m and at nine wells. The final detailed mapping of both horizons was constructed from spectral depth estimates on a regular mesh of 100 m x 100 m. Major faults, associated structures and fractures were mapped in 3D from the magnetic data by using automatic curve matching (ACM). This technique was applied to detect single magnetic anomalies produced by inter-sedimentary sources. These results were used to interpret magnetic lineaments in, above and below the coal measures to produce a rock fabric model. The results obtained from the interpretation of the magnetic data are consistent with structures mapped from existing seismic and well data. The mapped rock fabric was also confirmed by well results to be a fair representation of the open fracture set, which has an orientation that is consistent with the existing stress regime.

scholarly journals A framework for estimating relative depth in video

2021 ◽  
Author(s):  
Richard Rzeszutek
Keyword(s):  
Depth Estimation ◽  
Theoretical Background ◽  
Depth Information ◽  
Relative Depth ◽  
Depth Estimate ◽  
New Approach ◽  
Depth Maps ◽  
Computational Overhead ◽  
Two Stages

This dissertation proposes a novel framework for recovering relative depth maps from a video. The framework is composed of two parts: a depth estimator and a sparse label interpolator. These parts are completely separate from one another and can operate independently. Prior methods have tended to heavily couple the interpolation stage with the depth estimation, which can assist with automation at the expense of flexibility. The loss of this flexibility can in fact be worse than any advantage gained by coupling the two stages together. This dissertation shows how by treating the two stages separately, it is very easy to change the quality of the results with little effort. It also leaves room for other adjustments. The depth estimator is based upon well-established computer vision principles and only has the restriction that the camera must be moving in order to obtain depth estimates. By starting from first principles, this dissertation has developed a new approach for quickly estimating relative depth. That is, it is able to answer the question, “is this feature closer than another," with relatively little computational overhead. The estimator is designed using a pipeline-style approach so that it produces sparse depth estimates in an online fashion; i.e. a depth estimate is automatically available for each new frame presented to the estimator. Finally, the interpolator applies an existing method based upon edge-aware filtering to generate the final depth maps. When temporal filters are used, the interpolation stage is able to very easily handle frames without any depth information, such as when the camera was stationary. However, unlike the prior work, this dissertation establishes the theoretical background for this type of interpolation and addresses some of the associated numerical problems. Strategies for dealing with these issues have also been provided

Seismic refraction study of the Raft River geothermal area, Idaho

Geophysics ◽  
1979 ◽  
Vol 44 (2) ◽  
pp. 216-225 ◽  
Author(s):  
Hans D. Ackermann
Keyword(s):  
Seismic Refraction ◽  
Water System ◽  
Hot Water ◽  
Geothermal System ◽  
Convective System ◽  
Lateral Velocity ◽  
Basement Complex ◽  
Deep Circulation ◽  
Well Data ◽  
Basement Surface

The Raft River geothermal system in southeastern Idaho is a convective hot water system, presently being developed to demonstrate the production of electricity from low‐temperature (≊150°C) water. Interpretation of seismic refraction recordings in the area yielded compressional velocities from near the surface to the crystalline basement at a maximum depth of approximately 1600 m. The results show a complex sequence of sediments and volcanic flows overlying basement. Velocities in the sedimentary section vary laterally. Correlation with well data suggests that zones of higher velocities may correspond to zones where sediments are hydrothermally altered. Flowing hot wells occur near the boundary between inferred shallow altered and unaltered rocks. The basement surface does not appear to be displaced by large faults, although there is ample surface evidence of faulting. The deep circulation of hot water necessary for a convective system may be through many small faults and fractures. Fracturing is suggested on the basis of lateral velocity variations within the basement complex.

Variogram analysis of helicopter magnetic data to identify paleochannels of the Omaruru River, Namibia

Geophysics ◽  
1999 ◽  
Vol 64 (3) ◽  
pp. 785-794 ◽  
Author(s):  
Stefan Maus ◽  
K. P. Sengpiel ◽  
B. Röttger ◽  
B. Siemon ◽  
E. A. W. Tordiffe
Keyword(s):  
Geomagnetic Field ◽  
Sedimentary Basins ◽  
Source Model ◽  
High Accuracy ◽  
Groundwater Exploration ◽  
Magnetic Data ◽  
Magnetic Signal ◽  
Variogram Analysis ◽  
Power Spectral ◽  
Basement Depth

The geomagnetic field over sedimentary basins is very sensitive to variations in basement depth. Therefore, magnetic surveys are widely used to map basement topography in petroleum and groundwater exploration. We propose variogram analysis as a more accurate alternative to power spectral methods. Data variograms are computed from aeromagnetic flight‐line data. To estimate depth, the data variograms are compared with model variograms for a range of source depths. We use the exact space domain counterparts of a fractal power spectral model as model variograms. To demonstrate the utility of this method for groundwater exploration, we map the basement topography of the Omaruru Alluvial Plains in Namibia. A comparison with electromagnetic (EM) resistivities and drilling information confirms the high accuracy—but also the limitations—of variogram analysis depth. Variogram analysis makes maximum use of short‐wavelength contributions to the magnetic signal, which is the key to the resolution of shallow basement topography. Moreover, by using a realistic source model and avoiding extensive data preconditioning and the transform to wavenumber domain, variogram analysis is likely to provide improved magnetic depth estimates even for deep basins.

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