摘要:

AbstractDuring the last couple of years there has been much research in the area of wavefield separation of borehole seismic data, and several articles have been published on various separation techniques. Methods involving the application of two‐dimensional Fourier transformation, the Radon transformation, multi‐level median filters or optimal filters, are all suggested as possible approaches to the wavefield separation problem.This paper compares some of these methods commonly used in the industry.The theories of the chosen methods are described to see how they are related. Using the different methods on synthetic and real data, we show how this theoretical relation is reflected in the relatively similar results obtained. We also show how the different filters treat coherent and random no

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1989.tb01826.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Abstract3D Kirchhoff migration and acoustic Born inversion of zero‐offset seismic data in a constant‐velocity medium can be uniformly factored as a cascade of two 2D diffraction integrals. The formal argument is based on a straightforward implementation of the original time‐domain approach of Gibson, Larner and Levin. The factorization differs from the factorization described by Jakubowicz and Levin in omitting all time‐dependent filters from the 2D operators in favour of ID filtrations performed as a preprocess and a post

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1989.tb01827.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThe study of wave propagation in media with elliptical velocity anisotropy shows that seismic energy is focused according to the horizontal component of the velocity field while the vertical component controls the time‐to‐depth relation. This implies that the vertical component cannot be determined from surface seismic velocity analysis but must be obtained using borehole or regional geological information. Both components of the velocity field are required to produce a correctly focused depth image. A paraxial wave equation is developed for elliptical anisotropic wave propagation which can be used for modelling or migration. This equation is then transformed by a change of variable to a second paraxial equation which only depends on one effective velocity field. A complete anisotropic depth migration using this transformed equation involves an imaging step followed by a depth stretching operation. This allows an approximate separation or splitting of the focusing and depth conversion steps of depth migration allowing a different velocity model to be used for each step. This split anisotropic depth migration produces a more accurate result than that obtained by a time migration using the horizontal velocity field followed by an image‐ray depth conversion using the vertical velocity field. The results are also more accurate than isotropic depth migration and yield accurate imaging in depth as long as the lateral variations in the anisotropy are

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1989.tb01828.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractEffective noise reduction of single‐sweep recorded data is achieved by application of a velocity filter process on a decomposed vibrator pattern. This technique promises high resolution results with a minimum effect on signal characteristic. A comparison of the stacked section of records vertically stacked in the field with the stacked section of velocity‐filtered receiver gathers shows a significant increase in resolution and signal‐to‐nois

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1989.tb01829.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractIn recent years, the use of wide source arrays in marine seismic surveys has been a topic of interest in the seismic industry. Although one motivation for wide arrays is to get more guns in a source array without increasing the in‐line array dimension, wide arrays can also provide the benefit of suppressing side‐scattered energy. Comparisons of common midpoint (CMP) stacks of data acquired offshore Washington and Alaska with wide and conventional‐width source arrays, however, show only small and sometimes inconsistent differences. These data were acquired in areas where side‐scattered energy is a problem. Comparisons of pre‐stack data, however, show substantial differences between the wide and conventional source array data.The disparity between the stacked and prestack data is explained by analysing the effective suppression of back‐scattered energy by CMP stacking. Energy reflected from scatterer positions broadside to a given CMP location has a lower stacking velocity than that of the primary reflection events. Thus, CMP stacking attenuates the side‐scattered energy. In both survey areas the action of CMP stacking was so powerful in suppressing the broadside energy that the additional action of the wide array was inconsequential in the final stacked sections. In other areas, where the scattering velocity is comparable to the primary stacking velocity, wide arrays could provide considerable advantage.Even though CMP stacked data from wide and conventional‐width arrays may appear similar, the reduced amount of side‐scattered energy in wide‐array prestack data may provide a benefit for data dependent processes such as predictive deconvolution and velocity analysis. However, wide arrays cannot be used indiscriminately because they can degrade cross‐dipping primary events. They should be considered primarily as a special tool for attacking severe source‐generated noise from back‐scattered waves in areas where the action of CMP

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1989.tb01830.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractMatrix equations are derived to transform the resistivity sounding data obtained in one type of a four‐electrode array to the corresponding resistivity sounding data that would be obtained using a different four‐electrode array. These expressions are based primarily on recent work in which we have established a linear relation between the apparent resistivity and the kernel function by using a powerful exponential approximation for the kernel function. It is shown that the resistivity sounding data of two different four‐electrode arrays have a linear relation through an essentially non‐singular matrix operator and, as such, one is derivable from the other for a one‐dimensional model and it can also be extended to two‐dimensions.Some numerical examples considering synthetic data are presented which demonstrates the efficiency of the method in such transformations. Two published field examples are also considered for transformation giving a reliable int

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1989.tb01831.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY