ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1994.tb00191.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractAn attempt to resolve non‐uniqueness in the interpretation of transient electromagnetic (TEM) sounding data using measured data alone is made. It is shown in the various examples studied that sufficiently early time measurements can be the determining factor in reducing the ambiguity caused by model equivalence. The early delay times thus play a dual role in transient soundings: they are responsible for resolving shallow structures and they may eliminate the ambiguity in the interpretation of geoelectric parameters of deeper targets. This is illustrated by the results of a follow‐up TEM survey at the Dead Sea coast of Israel where the use of supplementary early time measurements allowed non‐uniqueness in the determination of the depth to fresh/saline groundwater interface to be res

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1994.tb00192.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractFlow of fluids in many hydrocarbon reservoirs and aquifers is enhanced by the presence of cracks and fractures. These cracks could be detected by their effects on propagation of compressional and shear waves through the reservoir: several theories, including Hudson's, claim to predict the seismic effects of cracks. Although Hudson's theory has already been used to calculate crack densities from seismic surveys, the predictions of the theory have not yet been tested experimentally on rocks containing a known crack distribution. This paper describes an experimental verification of the theory. The rock used, Carrara marble, was chosen for its uniformity and low porosity, so that the effect of cracks would not be obscured by other influences. Cracks were induced by loading of laboratory specimens. Velocities of compressional and shear waves were measured by ultrasound at 0.85 MHz in dry and water‐saturated specimens at high and low effective pressures. The cracks were then counted in polished sections of the specimens. In ‘dry’ specimens with both dry and saturated cracks, Hudson's theory overpredicted observed crack densities by a constant amount that is attributed to the observed value being systematically underestimated. The theory made poor predictions for fully saturated specimens. Shear‐wave splitting, caused by anisotropy due to both crystal and crack alignment, was observed. Cracks were seen to follow grain boundaries rather than the direction of maximum compression due to loading. The results demonstrate that Hudson's theory may be used in some cases to determine crack and fracture densities from compressional‐ and shear‐wave ve

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1994.tb00193.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe paper by Slob and Ziolkowski (1993) is apparently a comment on my paper (Szaraniec 1984) on odd‐depth structure. In fact the basic understanding of a seismogram is in question. The fundamental equation for an odd‐depth model and its subsequent deconvolution is correct with no additional geological constraints. This is the essence of my reply which is contained in the following points.1The discussion by Slob and Ziolkowski suffers from incoherence. On page 142 the Goupillaud (1961) paper is quoted:“… we must use a sampling rate at least double that… minimum interval…”. In the following analysis of such a postulated model Slob and Ziolkowski say that “… two constants are used in the model: Δtas sampling rate and 2Δtas two‐way traveltime”. By reversing the Goupillaud postulation all the subsequent criticism becomes unreliable for the real Goupillaud postulation as well as the odd‐depth model.2Slob and Ziolkowski take into consideration what they call the total impulse response. This is over and above the demands of the fundamental property of an odd‐depth model.Following a similar approach I take truncated data in the form of a source function,S(z), convolved with a synthetic seismogram (earth impulse response), R̃(z), the free surface being included. The problem of data modelling is a crucial one and will be discussed in more detail below. By my reasoning, however, the functionmay be considered as a mathematical construction introduced purely to work out the fundamental property. In this connection there is no question of this construction having a physical meaning.It is implicit that in terms of system theory,K(z)stands for what is known as input impedance.3Our understandings of data are divergent but Slob and Ziolkowski state erroneously that:“Szaraniec (1984) gives (21) as the total impulse response…”. This point was not made.This inappropriate statement is repeated and echoed throughout the paper making the discussion by Slob and Ziolkowski, as well as the corrections proposed in their Appendix A, ineffective.Thus, my equation (2) is quoted in the formwhich is in terms of the reflection responseGscand holds true at least in mathematical terms. No wonder that “this identity is not valid for the total impulse response” (sic), which is denoted asG(z).None the less a substitution ofGforGscis made in Appendix A, equation (A3). The equation numbers in my paper and in Appendix A are irrelevant, but (A3) is substituted for (32) (both numbers of equations from the authors’ paper). Afterwards, the mathematical incorrectness of the resulting equation is proved (which was already evident) and the final result (A16) is quite obviously different from my equation (2). However, the substitution in question is not my invention.4With regard to the problem of data modelling, I consider a bi‐directional ID seismic source located just below the earth's surface. The downgoing unit impulse response is accompanied by a reflected upgoing unit impulse and the earth response is now doubled. The total impulse response for this model is thus given bywhere (—r0) =— 1 stands for the surface reflection coefficient in an upward direction. Thusthat is to say, the total response to a unit excitation is identical with the input impedance as it must be in system theory.The one‐directional 1D seismic source model is in question. There must be a reaction to every action. When only the downgoing unit impulse of energy is considered, what about the compensation?5In more realistic modelling, an early part of a total seismogram is unknown (absent) and the seismogram is seen in segments or through the windows. That is why in the usual approach, especially in dynamic deconvolution problems, synthetic data in the presence of the free surface are considered as an equivalent of the global reflection coefficient. It is implicit that model arises from a truncated total seismogram represented as a source function convolved with a truncated global reflection coefficient.Validation or invalidation of the truncation procedure for a numerically specified model may be attempted in the frame of the odd‐depth assumption. My equations (22) and (23) have been designed for investigating the absence or presence of truncated energy.The odd‐depth formalism allows the possibility of reconstructing an earlier part of a seismogram (Szaraniec 1984), that is to say, a numerical recovery of unknown moments which are u

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1994.tb00194.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1994.tb00195.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1994.tb00196.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1994.tb00197.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1994.tb00198.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1994.tb00199.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY