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1st SAGA Biennial Conference and Exhibition
- Conference date: 29 Jun 1989 - 30 Jun 1989
- Location: Johannesburg, South Africa
- Published: 29 June 1989
21 - 40 of 49 results
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Data-Adaptive, Robust, Non-Linear Algorithms For Noise Removal On Stationary Or Non—Stationary Time Or Space Series Data
By M. HattinghBasically all geophysical data consist of readings made in a time and/or
space series manner. The general problem is to separate the noise
components from the signal components. To succeed, some knowledge of what
is noise and what is signal are necessary. Unfortunately most methods
break down when the data are not stationary and contain spurious peaks or
outliers. Sometimes no information of the noise can be obtained. In
this paper the results of some new algorithms will be shown that was
developed to tackle the problem in these circumstances. Four methods were
developed. The basic concepts of each method is outlined and examples on
synthetic and real data are given.
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Interpretational Processing Of Lateral. Seismic Profiles (Lsp)
Authors R.C. Hinds and W.J. BothaIn most presented cases, the development of LSP processing has followed the scenario of surface seismic processing, namely that one pseudo-migrated finished LSP section was the result given to the interpreter. The interpreter of the surface seismic data only occasionally had the desire or felt the need to re-examine the individual. results from the various processing steps that the input data had gone through. In surface seismic processing today, where so much averaging is taking place through stacking, signal enhancement and horizontal correlation methods, ïnterpreters are becoming very involved in the processing that has been done to the data and, consequently, are demanding to see the effect that various processes have on their data through intermediate data displays.
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Interpretational Processing Of Vertical Seismic Profiles (Vsp)
Authors R.C. Hinds and W.J. BothaIn most presented cases, the development of VSP processing has followed the scenario of surface seismic processing, namely that one finished section was the result given to the interpreter. The interpreter of the surface seismic data only occasionally had the desire or felt the need to re-examine the individual results from the various processing steps that the input data had gone through. In surface seismic processing today where so much averaging is taking place through stacking, signal enhancement and through horizontal correlation methods, interpreters are becoming very involved in the processing that has been done to the data and, consequently, are demanding to see the effect that various processes have on their data through intermediate data displays. In the interpretation of VSP datasets where the limited quantity data contains much information about the subsurface on or about the borehole, it has become imperative to design data presentation systems that allows one to fully examine the effect of the processing stages on the VSP data.
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Palaeomagnetic Studies In Western Dronning Maud Land, Antarctica
More LessSampling for palaeomagnetic purposes has been undertaken in the western part of Dronning Maud Land, Antarctica. The study area comprises three mountain ranges bounded by latitudes 72° S to 73° S and longitudes 4° W to 2° E (Fig 1). The fieldwork has been completed over three consecutive summer seasons starting in 1986/87. A total of 170 sites have been sampled covering most of the rock types in the two primary geological terrains.
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Application Of Seismic Sequence Concepts To Basin Evolution And Petroleum Exploration, Pletm0S Basin
By A. JollandsAs a result of shallow burial depths and slow subsidence rates, a total of 67 Type-1 and Type-2 unconformities were identified in the post-rift Cretaceous section of the Pletmos Basin, (figure 1). Purpose of this study was to develop a seismic sequence stratigraphic framework for the mid-Valanginian to mid-Campanian sequences as a basis for future petroleum exploration. The study further developed the recent stratigraphic techniques proposed by Exxon.
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Modelling The Deep Temperature Structure Of Witwatersrand Gold Mining Areas
Authors M.Q.W. Jones and P. BottomleyUnderground workings in Witwatersrand gold mines are likely to exceed depths of 4000 in. An important consideration in planning of deep mining is the refrigeration cost which depends on rock temperatures. Temperature measurements made during the past 50 years have resulted in a know-ledge of regional rock temperature variations (Jones and Bottomley, 1986; Jones, 1988), but the temperature structure of most goldfields is not well determined. Temperatures may be predicted using one-dimensional (vertical.) analysis where strata are horizontal, but structural complexities involving rocks of different thermal conductivity and radioactive heat production may result in non-vertical heat conduction. This paper discusses a numerical
technique that permits computation of the temperature field in such areas.
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A Theory Of Seismic-Wave Propagation In Porous Rocks Çontaining Clays - Interrelation Between Seismic-Wave Attenuation And Permeability
More LessKlimentos and McCann (1988) have shown experimentally that clays increase the attenuation of seismic waves in porous rocks (see figure 1). They demonstrated that the attenuation of compressional. waves is directly proportional. to day content and inversely proportional to permeability (see Figure 2).
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Evaluation Of Prediction Ahead Of The Bit By Inversion Of Vsp Data
Authors S. Kuhlmann, H. Pferdekämper J. Fatti and M. GidlowOne of the applications of VSP surveys is to predict acoustic impedance
variations in a well ahead of the bit. The up going wave traces
obtained from the VSP processing are inverted to produce a pseudo-
acoustic impedance log for the sediments below T.D. This type of
inversion is expected to be more precise than the inversion of surface
seismic data for two reasons: a) An accurate estimation of the seismic
wavelet is obtained from the deconvolved down going waves. b) The
bandwidth of the VSP traces is wider than that of surface seismic data
and the signal/noise ratio is generally better in VSP data than in
surface seismic data.
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External Geomagnetic Field Variations And Magnetic Surveys
Authors G.J. Kühn and L. LoubserThe magnetic storm which started al 01h25 on the 131h of March 1989, was probably the largest event of its kind to be recorded in South Africa since magnetic held recordings began in 1932. Soon after its commencement, the Magnetic Observatory started receiving enquiries about the anticipated development of the storm from a few exploration groups who were doing aeromagnetic surveys al the time.
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Rock Mechanics And Seismological Research In A Deep South African Gold Mine
More LessA. summary of the mines rock mechanics related research is given, covering the period 1985 until present.
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Deep Grounded Source Tem Soundings In The Limpopo Belt Area
By C.L. Le RouxDuring 1988 deep Transient Electromagnetic (TEM) soundings were carried out
using a controlled grounded source, in the Limpopo Belt area of the Northern
Kaapvaal craton. This forms part of a National Geophysics Programme and CSIR
project to develop a grounded source TEM system suitable for South African
conditions. The purpose of this talk is to present results of the test survey
conducted jointly with scientists from the Exploration Geophysics group of
Dr. K.-M. Strack of the 1GM, University of Cologne, FRG. More technical
details and experimental research results will be covered in a talk for SAGA
later in 1989.
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The Electromagnetic Response Of Magnetically Permeabie Non-Conductors
By M.J. MaherElectromagnetic prospecting has been carried out for many years using
various field systems. In the past the targets of concern were assumed to
have high conductivities and to be located in resistive or mildly conductive-
host rocks. Generally it was further assumed that the magnetic
permeability was constant throughout the region and had the same value as
that of free space (411 x io-7 h/m). Electromagnetic systems using a magnetic field as a source will also produce induced magnetizations in
magnetically susceptible parts of the earth in the area of investigation.
These magnetizations will affect the primary field and produce observable
responses under certain conditions.
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Interpretation Of A Potential Field Profile Over The Cape Fold Belt
Authors M.J. Maher and B.E. PittsPrevious studies (Beattie, 1909, Hales and Cough, 1960, 1961 and De Beer,1983) have outlined major geophysical features associated with the Cape old Belt. These are the Beattie Magnetic Anomaly, the Southern Cape Conductive Belt and en isostatic gravity anomaly. In en attempt to Further elucidate the sources of the magnetic and gravity features over the Cape
Fold Belt interpretation of data along a north striking profile has been carried out. Magnetic and gravity data for this profile which is located along longitude 22 ° 32 E between 31 °S and 34 °S were extracted from aeromagnetic maps end a digital gravity data base.
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Determination Of Hydraulic Aquifer Characteristics From Resistivity Sounding Parameters
Authors R. Meyer and V. d A. CoetseeGeophysical techniques, and geoelectrical techniques in
particular, have been employed in geohydrological studies for
many years. Apart from determining layer thicknesses and
resistivities, and linear features with which ground water is
often associated, geoelectrical parameters can also be applied to
approximate geohydrological parameters such as hydraulic
conductivity, porosity, transmissivity, specific capacity, etc.
The geohydrological parameters are traditionally derived from
pumping tests and are expensive and time consuming.
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Moho Depth And Crüst-Mantle Velocity Contrast Determinations For South Africa From Teleseismic P-Wave Spectral Ratios
By K.R. MüllerTeleseismic events, recorded on long period or broadband seismometers at three component stations, m y be used to model crustal and upper mantle ]layering beneath the stations. The
method used in this study is referred to as the spectral ratio or crustal transfer ratio technique (Phinney, 1964), this involves the analysis of the ratios of the Fourier spectra of the vertical and radial components of the P-wave.
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Coda Q And Site Effect Of Mine Tremors
Authors E. Peberdy and R.W.E. GreenRecordings of mining induced tremors at increasing distances from the gold
mining region south of Carletonville were used to determine the seismic
quality factor Q.
This Q, used as a measure of attenuatlon, was determined independently for
a number of seismic stations along two azimuths, traversing vastly
different geologies. The small tremors that were used (ML<3,0) were all
observed at distances of less than 80 km and the Q was determined using a
version of the coda delay technique proposed by Aki (1969).
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Computer Plotting Software Applications Within Anglo American
By M.D.P. ReedRadian Corporation in Texas market contour plotting software (CPS)
which is mainly directed at the oil industry. Anglo American has
owned a mainframe version of this software for sate time, and after
sate market investigation Ma purchased several copies of CPSPC, the
personal computer product.
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Evidence For Velocity Anisotropy In Sediments Of The Central Bredasdorp Basin
Authors G.C. Smith and R.W. DworschakOil exploration boreholes drilled in the central part of the offshore
Bredasdorp basin (fig. 1) revealed systematic errors in the prediction
of depths to target horizons.
Initially, in the absence of borehole data, depth conversions from
seismic reflection time measurements were made using stacking
velocities. Because of the very small dips present in the central
Bredasdorp basin down to horizons of interest, stacking velocity was
assumed to be equal to root-mean-square (ns) velocity without any
correction for dip.
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Integrated Geophysical Interpretation On A Complex Structure
More LessIn 1986 Verwoerd et al published the discovery of a carbonatite on the farm
Stukpan east of Bothaville in the Orange Free State (figure 1). The
intrusive was initially outlined by an interpretation of gravity data.
Subsequent drilling of 2 boreholes (ZL1, RP2) intersected this intrusive and
also intersected shallow Central Rand Group rooks, thus implying a horst in
the Witwatersrand Super-group. Seismic data in the vicinity of the intrusive
are poor and difficult to interpret (figure 2). The deterioration of the
data is thought to be caused by the intrusive. Since the intrusive contains
magnetite, the aeromagnetic data provides a means by which its position and
shape along the seismic section can be determined.
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Automatic 3D Modelling Of Gravity And Aeromagnetic Data In The Witwatersrand Basin - A Poster Presentation
More LessThe usefulness of the magnetic and gravity methods in the total exploration
effort and the tact that these methods are relatively cheap, warrant
extensive research into the development of new interpretation techniques.
Since most of the gold bearing reefs in the Witwatersrand basin are covered
by younger, transgressive geological units, magnetic and gravity data are
particularly useful for determining depths to these reefs and for resolving
large structural features. The presented here bas been developed to
automatically invert digital magnetic and gravity maps. The resulting depth
maps can be used to indirectly estimate depths to target horizons.
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