摘要:

ABSTRACTSynergism of 3‐D seismic data, wavelet processing, colour display and interactive interpretation has been exploited in the study of a Gulf of Mexico gas reservoir. Seismic amplitude has been used as a measure of the proportion of a sand/shale reservoir capable of producing gas. This has led to the mapping of net producible thickness of gas sand. The tuning phenomena resulting from geometric effects alone were studied in detail, and tuning curves of various levels of sophistication were used as the basis for amplitude editing. Statistical tuning curves were derived by interactive cross‐plotting and deterministic curves by wavelet extraction. Multiple wavelet side lobes cause multiple maxima in the tuning curve. Depositional effects and intrareservoir communication have also been studied by interactive cross‐plo

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1986.tb00485.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

ABSTRACTThis paper reviews computer techniques used in the automatic zoning and correlation of well‐logs. Prior to correlating, well‐logs are to be segmented–or ‘zoned’–so as to delineate sections that have similar properties. Techniques discussed include statistical methods such as variance tests and Student's t‐test, linguistic analysis, the use of Walsh functions and spectral analysis.Well‐log correlation, which may be between traces from different wells or between traces from the same hole (as in dip logs), is used in basin studies and the determination of structural dip. A variety of methods are reviewed including conventional time and frequency correlation, sequence slotting, pattern recognition and frequency analysis. Future directions for investigati

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1986.tb00486.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

ABSTRACTThe low‐frequency response of the P400 watergun is an improvement over that of the S80 version. It has been further enhanced by deployment in a vertically staggered array. The notch in the amplitude spectrum at about 35 Hz due to the interference between the precursor and main implosion pulse has been virtually eliminated, and depth notches due to the free surface interface at the upper end of the spectrum have been greatly reduced. The spectral band is thus very broad and well‐shaped and corresponds to an even shorter signature.After convolution with the streamer ghost, the amplitude of the implosion pulse from the composite far‐field signature is more than 30 times the composite precursor amplitude. Thus the signal approaches the minimum‐phase condition.Shot‐generated noise scattered back by diffractors located at or near seabed is the single greatest impediment to increased penetration, especially in high resolution surveys. Such noise decays much less rapidly than signal, particularly so with broad band data. Furthermore, back‐scattered interference coming from a cone of bearings between 15–45° with respect to the line is particularly damaging since in these directions the stack enhances the interference and confuses the primary velocity analysis. The watergun source patterns are therefore element‐weighted to maximize directivity within these critical directions in the frequency band 50–155 Hz.When spatial aliasing is reduced by increased streamer spatial sampling and by discrete anti‐alias filters during the record cycle,f‐kfiltering can be applied to the field records as an effective supplement to the source and receiver patterns without the aliased ‘wrapped around’ noise alignments destroying the upper end of the spectrum of genuine reflectors. Furthermore, increased spatial sampling is a pre‐requisite in thef‐k‐migration process if the valuable higher frequencies of broad band data are to be migrated in steep‐dip situations without aliasing.Thus, spatial resolution is a necessary complement to temporal resolution if maximum advantage of the broad‐band P4

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1986.tb00487.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

ABSTRACTThis paper collects certain results concerning wave propagation in two‐and‐one‐half dimensions, i.e., three‐dimensional (3‐D) wave propagation in a medium that has variations in two dimensions only. The results of interest are for sources and receivers in the plane determined by the two directions of parameter variation. The objective of this work is to reduce the analysis of the in‐plane propagation to 2‐D analysis while retaining–at least asymptotically–the proper 3‐D geometrical spreading. We do this for the free space Green's function and for the Kirchhoff approximate upward scattered field from a single reflector. In both cases the derivation is carried out under the assumption of a background velocityc(x, z) with the special cas

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1986.tb00488.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

ABSTRACTThe standard Kirchhoff algorithm can be generalized for migration of pre‐stack finite‐offset data from variable‐velocity media. The concentric ellipses over which the data are spread in constant velocity media become significantly distorted (even multi‐valued) in the variable velocity case. The specific shapes can be explicitly defined by kinematic extrapolation of the source and recorded wave fields with the ray equation.The use of Kirchhoff migration with a surface source and a subsurface recorder requires that two sets of Kirchhoff loci be superimposed. For each trace, the first set of loci is computed with the source and the actual recorder position as foci; the second set is computed with the source and the virtual recorder position as foci. This dual procedure explicitly incorporates the primary diffracted energy and the free‐surface reflections, respectively.Implementation involves the construction of a virtual medium, lying above the free surface, with a velocity distribution that is the mirror image of the actual distribution below the free surface. Ray‐equation extrapolation is performed through the real/virtual boundary. The resulting image is produced in a split form, with all the contributions of the primary reflected and diffracted energy lying in the lower ‘real’ half and all the contributions of the energy that was reflected at the free surface lying in the upper ‘virtual’ half. The final image is produced by folding the split image about the free surface and adding the two halves. A practical advantage is that the origin of various contributions (and artifacts) can be more readily identified (for interpretation or removal) in the split images.The ray‐equation pre‐stack migration algorithm is very general. It is applicable to all source‐recorder geometries and variable velocity media and reduces exactly to the standard Kirchhoff algorithm when applied to zero or finite‐offset surface survey data. The algorithm is illustrated by application to VSP data. For the VSP geometry, the algorithm does not require any specific trace spacing (in depth) and can be used for data from deviate

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1986.tb00489.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

AbstractThe potential field and its derivatives at points above an irregular surface can be approximately obtained from the sampled potential field data acquired on that surface.A method of minimizing the truncation effect, which appears when gravity and magnetic maps are processed with the aid of surface integrals, is derived.The results are compared with those of the most relevant similar methods by using a theoretical, but realistic, model.

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1986.tb00490.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

ABSTRACTThe complex resistivity of synthetic samples has been measured over the frequency range 0.01 Hz to 1.0 MHz. The synthetic samples were made of a quartz matrix and sulphide particles. Grain sizes, volume fractions, and sulphide particles of different nature were used. The samples were saturated to different degrees, with different types of electrolyte. The results obtained were used to check the validity of the theoretical electrochemical model developed by Wong (1979). This model fits the experimental data reasonably well in the frequency range where the dispersion and the phase maxima occur. Against the model expectations, the experiment did not duplicate the Debye‐form of spectra because most of the common metals are oxidized to the ionic form and an electrochemical charge transfer reaction occurs at the interface. The model prediction regarding the effect of the distribution of the grain radii on the complex resistivity could not be duplicated experimentall

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1986.tb00491.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

摘要:

ABSTRACTTheoretically exact type curves are presented to show the effect on response shape of changing dip, strike, transmitter‐receiver separation, depth of burial and target conductance. Relatively small dip variations produce a marked asymmetry in response shape. For steeply dipping conductors, strike can be determined from the cross‐over width of the anomaly. The curves illustrate the dynamic character of the transient process, and suggest how the spatial disposition and quality of large sheet conductors might be inferred from the extent of peak‐amplitude displacement with time, and rate of eddy‐current diffusion. A generalized interpretation scheme is proposed based on dimensionless response characteristics which will facilitate the rapid determination of conductor dip, conductance and depth of burial for any time

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1986.tb00492.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1986.tb00493.x

出版商:Blackwell Publishing Ltd    

年代:1986

数据来源: WILEY