摘要:

ABSTRACTFor converted waves stacking requires a true common reflection point gather which, in this case, is also a common conversion point (CCP) gather. We consider converted waves of the PS‐ and SP‐type in a stack of horizontal layers.The coordinates of the conversion points for waves of PS‐ or SP‐type, respectively, in a single homogeneous layer are calculated as a function of the offset, the reflector depth and the velocity ratiovp/vs. Knowledge of the conversion points enables us to gather the seismic traces in a common conversion point (CCP) record. Numerical tests show that the CCP coordinates in a multilayered medium can be approximated by the equations given for a single layer. In practical applications, ana prioriestimate ofvp/vsis required to obtain the CCP for a given reflector depth.A series expansion for the traveltime of converted waves as a function of the offset is presented. Numerical examples have been calculated for several truncations. For small offsets, a hyperbolic approximation can be used. For this, the rms velocity of converted waves is defined. A Dix‐type formula, relating the product of the interval velocities of compressional and shear waves to the rms velocity of the converted waves, is

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1988.tb02186.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

ABSTRACTA novel process is used to coat glass spheres with a polymerizing thermo‐setting resin, only microns thick. Synthetic rocks of known grain size distribution and pore space characteristics are then made by heating the resin‐coated glass spheres under compression in a special mould. The dynamic Young's moduli of these rocks are found to be affected by the percentage of resin content (cement) and the synthetic diagenesis rather than the grain size and permeabil

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1988.tb02187.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

ABSTRACTBroad‐band ultrasonic impulses and the attenuation spectral ratio technique have been used to investigate the characteristics of synthetic rocks for different saturants, by obtaining the attenuation coefficients in the frequency range of 0.1‐1.0 MHz.The general trend of the data indicates that the experimental attenuation coefficient increases with an increase in the grain/pore size. Results show that large grains/pores can increase the attenuation coefficient in all mechanisms, and water‐saturated synthetic sandstone rocks result in a higher attenuation coefficient than similar oil‐saturate

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1988.tb02188.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

ABSTRACTAn increase in the grain/pore size can cause the received echo signal to be distorted due to the preferential attenuation of the high‐frequency components of the transmitted acoustic signal. Therefore, a rock acts as a low‐pass filter and the property of the filter has a linear relation to the grain/pore size. The results have shown that P‐ and S‐wave attenuations can be used to characterize selected internal characteristics of a rock. For example, an increase in the differential stress can cause an increase in the attenuation, due to the sensitivity of the S‐wave to mi

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1988.tb02189.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

ABSTRACTThe formula for the computation of the gravity field of a homogeneous polyhedral body is derived and transformed into the form which is most suitable when considering speed and simplicity of numerical calculation.

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1988.tb02190.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

ABSTRACTGold, as a trace element, is not directly detectable by geophysical borehole logging techniques. Geophysical logging methods have therefore been used to infer the presence of structural features and alteration processes associated with gold. Since these features and processes differ with the style of gold mineralization, a unique relation between geophysical anomalies and gold cannot be established. However, in a particular environment, such an association can be established. We examined geophysical log data (self potential, induced polarization, resistivity, gamma, temperature, and temperature gradient) and drill core from the Barber‐Larder property in NE Ontario. The geophysically detectable alteration processes associated with gold were identified as sericitization and pyritization, by means of factor analysis. A linear discriminant function was constructed which allowed the zones of economic mineralization (nominally 0.05 oz/ton or 1.5 ppm) to be identified with a 75% success rate based on geophysical log data alone. This rate was achieved without sophisticated non‐linear data transformati

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1988.tb02191.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

ABSTRACTIt is now believed that the negative transients observed in coincident‐loop transient electromagnetic (TEM) measurements are caused by polarizable bodies (bodies whose conductivity increases as a function of frequency). Ordinarily the TEM response of polarizable bodies is obtained by calculating the frequency‐domain response at many frequencies and transforming it to the time domain via Fourier, Laplace or Hankel transforms. This is normally a computationally laborious task. However, for some simple non‐polarizable bodies the time‐domain response is analytical and can be computed easily. When these simple bodies are weakly polarizable an approximate response can be obtained by convolving the easily‐calculated, non‐polarizable response with the impulse response of the polarization. The approximate response is found to be very similar to the exact response for the polarizabilities normally seen in geologica

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1988.tb02192.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1988.tb02193.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY