摘要:

ABSTRACTElastic, acoustic and electromagnetic waves in media consisting of vertically inhomogeneous layers are considered in a common formulation. The spectral function of a vertically inhomogeneous medium is the downward energy flux due to an impulsive source at the top of the first layer. A propagation‐invariant form is used to derive several identities for the reflection and transmission matrices. When the top layer is bounded by a free surface, one of the expressions reduces to a formula derived by Kunetz for the one‐dimensional wave equation.A source radiating upwards and downwards gives a discontinuity in the propagation‐invariant form which is equal to the source energy. A new formula is derived for when the source is located just beneath the top interface of the l

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1988.tb02147.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

ABSTRACTMoving source profiling is a modification of walk‐away vertical seismic profiling in which the source is moved along a line across a well while the signal is recorded in the well at a certain depth. The method was designed to better predict the target horizon below the drill bit and away from the well location. The method has several advantages in areas of complicated overburden.In overthrust regions, the receiver is placed below much of the complicated structure to minimize distortion of the reflected signal. The final seismic image is a depth presentation of the subsurface structure and stratigraphy based on wavefront calculations. This depth estimation is obtained without extensive processing of the recorded data. The final result is available within a few days and can help interpreters to decide if and where to sidetrack the well. The method is demonstrated using an example from the overthrust zone of the Lower Saxonian Basin and the Pompeckj's well in Northern German

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1988.tb02148.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

ABSTRACTThe wavefield in, and at the surface of, a homogeneous, isotropic, perfectly elastic half‐space, excited by a traction distribution at the surface of the medium is investigated. The emitted wavefield is a spatial convolution of the surface tractions and the spatial impulse response. The properties of the wavefield in the far‐field of the medium are derived and it is shown that the far‐field particle velocity is essentially equal to a weighted sum of the time derivative of the integrated surface tractions, that is, of the components of the ‘ground force’. The theory is valid for an arbitrary geometry and orientation of the surface tractions, and is independent of the boundary conditions at the surface of the medium.The surface tractions are related to a source that consists of a mass distribution with an arbitrary force distribution imposed upon it. A boundary condition is introduced that accounts for the mass load and the forces applied to it but neglects vibrations within the mass. The boundary condition follows from the equation of motion of the surface mass load.The theory is applied to the Vibroseis configuration, using a P‐wave vibrator model with a uniformly distributed force imposed on top of the baseplate, and assuming that horizontal surface traction components are absent. The distribution of displacement and stress directly underneath the baseplate of a single vibrator and an array of vibrators is investigated. Three different boundary conditions are used: (1) assuming uniform pressure, (2) assuming uniform displacement, (3) using the equation of motion of the baseplate as a boundary condition. The calculations of the distribution of stress and displacement over the plate for different elastic media and several frequencies of operation show that only the results obtained with the mixed boundary condition agree with measurements made in the field.The accuracy of three different phase‐feedback signals is compared using synthetic data. Baseplate velocity phase‐feedback leads to huge deviations in the determination of the far‐field wavelet; reaction mass acceleration phase‐feedback looks stable but neglects the differentiating earth filter; and phase‐feedback to a weighted sum of baseplate and reaction mass accelerations becomes unstable with increasing frequency. The instability can be overcome using measurements over the whole baseplate.The model can be extended to

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1988.tb02149.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

ABSTRACTThe concept of multifrequency induction logging simulations in the frequency range of 10 kHz to 1 MHz, applied to two‐dimensional, axial symmetric model geometries, is presented. The scalar Helmholtz equation has been solved by a finite‐element procedure. The model domain has been discretisized under the condition that the discontinuities in conductivity are represented by the nodes of the adjacent triangular elements. The modification of the signal distribution by the skin effect is illustrated for several models. Several sets of induction logs have been calculated with particular consideration of the frequency‐dependent conductivities and permittivities.The improvement of a multifrequency inversion technique, based on standard least‐squares methods, is shown for a two‐layer model including borehole and invasion zones. Using this improved inversion technique we can state, as an additional inversion parameter, the frequency dependence of each inverted rock con

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1988.tb02150.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

ABSTRACTThis paper describes a method of generating pseudovelocity logs using measurements of electrical resistivity. A theoretical relation between electrical resistivity and transit time, which is applicable to a wide range of lithologies, has been developed. The application of this relation using a method which defines lithoresistivity zones as lithological intervals related to the same formation and showing small resistivity variations, has been tested in the Recôncavo sedimentary basin in Bahia, Brazil. A comparison of derived pseudovelocity logs with actual sonic logs for five wells whows the validity of the present approach

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1988.tb02151.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.tb02152.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.tb02153.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY