摘要:

AbstractThe geological sequence rock‐coal‐rock represents a seismic low‐velocity channel. Channel waves generated in a coal seam and their reflections from discontinuities can be used for proving the minability of the seam. To investigate the process of reflection, two‐dimensional models of the sequence rock‐coal‐rock have been investigated by means of the ultrasonic transducer technique. Two‐dimensional models have the advantage that the wave field can be observed at an arbitrarily chosen point of the model plate. Thus, by means of these models the direct and the reflected Rayleigh channel wave can be observed along their path of propagation.From the geophysical point of view the various types of discontinuities of a coal seam can be divided into two basic types: one is restricted to the seam, the other includes in addition a fractured zone in the adjoining rock.The investigation of the symmetrical Rayleigh channel wave reflected by a discontinuity yields the following results:For dip angles γ between approximately 90° and approximately 60° the reflectivity is virtually independent of the type of discontinuity. This does not hold for the limiting case of γ= 90° (vertical dip) for which the reflectivity increases with increasing influence of the fractured zone. For dip angles γ between approximately 60° and approximately 40° the reflectivity is still independent of the fractured zone but the shape of the reflected wave deteriorates with increasing influence of the fractured zone.For dip angles γ below approximately 40° the reflected wave deteriorates such that the application of the in‐seam seismic reflection method will be difficult or even impossible.The conversion of the direct wave of the symmetrical fundamental mode into a reflected wave of the antisymmetrical fundament

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1978.tb01574.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

AbstractThe problem of detecting discontinuities which interrupt coal seams is of great importance to the coal mining industry. One possible method of detecting such discontinuities is that of in‐seam seismology where both source and detectors are placed under‐ ground on the coal face. In this paper the propagation of SH waves from a line source in the seam is investigated. There exists a particular set of waves–channel waves–, confined to the coal seam. These waves are dispersive and have an associated Airy phase whose geometrical attenuation is least. However, if absorption of energy within the coal is included then the Airy phase is the dominant wavegroup only for distances less than a certain maximum. If a detection criterion proposed by Dresen and Freystätter applies, then there is a lower limit to the frequency that should be used for exploration. This requirement may be in conflict with attenuation consid

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1978.tb01575.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

AbstractSeismic exploration for coal as well as basic scientific research indicate the existence of unsolved problems. These problems arise partly because the requirements are different from those in exploration for gas and oil and are partly due to the geological situation. The medium to be investigated is composed of cyclically changing layers with extremely high velocity and density contrast. Furthermore, the structure of the carboniferous rock is highly fractured and folded. This leads to difficulties in interpreting the seismic response of carboniferous rock. To overcome these difficulties synthetic seismograms are a useful tool.Calculating synthetic seismograms the carboniferous rock has been modelled as a sequence of seams and rock. The following results have been obtained(i)A single seam gives rise to a distinct reflection signal even for a thickness of 1/50 of the wavelenght.(ii)Individual reflections are not visible from a sequence of layers containing a great number of seams and interfaces. Due to constructive interference only a few high amplitudes appear. These high amplitudes are labelled “interference reflections”.(iii)With increasing travel time the interference reflections are mainly composed of short lag multiples such that the primary reflections have no significant influence.(iv)The sequence of seams acts on the reflected seismic signal as a high pass filter and on the transmitted signal as a low pass filter. The cut‐off frequencies are determined by the average seam thickness, and the steepness of the slopes increases with increasing number of seams.(v)The interference reflections can be used for determining the geological structure at least for the upper part of the seq

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1978.tb01576.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

AbstractA method to compute the parameters of a multilayered medium with dipping interfaces is described. The input data are time‐distance curves of diving waves. The output data are the thickness of the layers, dips, and parameters characterizing the increase of velocity with depth. Three examples are presente

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1978.tb01577.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

AbstractReflections and refractions from curved interfaces were studied on two dimensional scale models. Time of arrival, amplitude and character of reflected, converted, and refracted waves were mainly used for this study. Some reflected refractions, refracted reflections and diffractions were also considered. It was possible to separate PS and SP waves and to study their amplitude and character separately. From the amplitude study of refracted arrivals it was concluded that the refracted ray path penetrates into the high velocity layer rather than propagating along the interface. Although most of the results are interesting from the theoretical point of view, a few applications to exploration problems are suggested.

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1978.tb01578.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

AbstractThe usefulness of IP‐technique for different geophysical purposes is discussed on the basis of field examples. IP and resistivity results are not always correlated, and the IP‐information may be unique in prospecting for very low grade sulphide mineralizations. The IP‐technique seems to be useful sometimes in prospecting for disseminated Ni‐Cu‐ mineralizations. A massive sulphide mineralization could be localized using IP.The disturbances from different kinds of geological objects other than prospecting targets generally are smaller in IP‐work than in resistivity work. It was possible to discriminate between apparent resistivity anomalies caused by shear zones and by sulphide mineralizations by means of IP‐measurements. The influence of magnetite on IP‐ measurements is briefly discussed. The relation between ground magnetic measurements ΔZ and the IP‐parameter is in many areas weak and does not seriously influence the interpretation of the IP‐measurements. A high correlation between ΔZ and IP‐measurements has been found on a titaniferous iron ore. This ore body gives strong IP‐anomalies indicating that it is a good IP‐target. Finally, the application of small moving arrays in very detailed IP‐measurements is found useful for detailed mapping of a mineralized zone under a thin overburden and for determination of

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1978.tb01579.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

AbstractAnalytical solutions exist for the potential of a Point Source in media with depth dependent conductivity of the form σ(z) =σ0(1 +αz)n.Of particular importance is the case of the linear gradient (n= 1). More general distributions of conductivity with depth can be approximated by equivalent sequences of homogeneous layers. Comparison between such approximations and the analytical solution for media with linear gradient of conductivity indicates that already a coarse step function yields a reasonably good approximati

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1978.tb01580.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

AbstractThis final part of our study of the resistivity sounding method in the presence of transitional layers deals with the direct application of the theoretical developments, previously reported, to both theoretical and field examples. The former are used to explain in more detail all steps of the direct procedure of interpreting resistivity measurements, when transitional layers with different dispositions are present in the assumed earth section. An alternate sequence of uniform and transitional layers is at first considered, then the case of a random sequence of these layers, and finally a sequence of only transitional layers. Then we give some logical considerations about the best fields of application of the new interpretation theory, with particular reference to hydrogeological, geological‐ structural, and mining exploration problems. Representative field examples are finally presented and discussed in detail for each of the exploration fields above listed. The comparison of the geophysical models obtained with the old interpretative scheme and the new system shows the greater resolving power of the new theory, provided that preliminary geological considerations, and where existing–borehole evidence justify the use of the new appro

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1978.tb01581.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

AbstractThe results of specific processing of seismic sections on an actual oil field have proved that it is possible to find a link between a seismic parameter (amplitude of a reflecting horizon) and petrophysical characteristics of a reservoir whose changes modify well productivity.A good correlation appears between the values of good oil productivity and the weakness of the amplitudes of one horizon close to the oil producing layers.

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1978.tb01582.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

AbstractIt is not possible to determine accurate geological velocities from seismic velocity analysis for thin layers or complex structural features, especially under an unconformity. Instead, we can approach the problem of interval velocity with seismic amplitudes analysis and compute the reflection coefficient along the unconformity surface.An error estimation has been made on a model to test the possibility of such a method and to choose the best parameters to be used. The method has been applied on an actual case: the computed interval velocities show good correlation with the values obtained by a sonic log.

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1978.tb01583.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY