- Home
- A-Z Publications
- Geophysical Prospecting
- Previous Issues
- Volume 28, Issue 4, 1980
Geophysical Prospecting - Volume 28, Issue 4, 1980
Volume 28, Issue 4, 1980
-
-
GEOPHYSICAL DATA BASES: SYSTEM CONSIDERATIONS*
Authors R.C. DILLAHUNTY, J.L. FASH, L.R. PARSLEY and D.W. TOWNSENDAbstractThe use of data file systems within the areas of geological well log and reservoir analysis is now accepted as a necessity in the storage and correlation of large volumes of diverse information.
Multi‐channel and three‐dimensional seismic recording techniques of various types result in a situation where the amount of processing parameters and derived seismic properties of a trace are rapidly approaching the amount of the recorded data themselves. The requirement to access these statistics efficiently has introduced the problems of data management to the seismic processing community.
Much software effort has been expended in the design of algorithms for cross reference and indexing of the statistics required in signal processing. These efforts, however, are generally in the direction of a localized solution to a specific requirement and tend to ignore the data base concepts well developed within the commercial data processing community.
This paper examines the applicability of commercial data base concepts to the problems of data handling in the area of geophysical exploration, sets forth some basic definitions and organizational characteristics, and describes a system for the integration of several earth disciplines within a single data base from which parameters and mapped information may be derived and indexed for the purpose of processing and interpretation.
-
-
-
ON THE RESPONSE OF MARINE SEISMIC STREAMER SYSTEMS*
Authors M.H. SAFAR and J.W.J. HOSKENAbstractThe response of transformer‐coupled and transformerless marine seismic streamers feeding seismic amplifiers with and without input transformer is analysed with the aid of equivalent circuits. Examples are calculated showing how improvements in the performance of two practical transformer‐coupled streamers, namely the increase in bandwidth and sensitivity and the decrease in the dependence on cable length, can be achieved when some of the streamers parameters are properly chosen.
Transformerless streamer systems driving either a voltage amplifier or a “charge” amplifier are shown to be inherently superior to those with coupling transformers, save possibly in respect of their sensitivity to cross‐feed.
-
-
-
ESTIMATION OF THE SIGNAL‐TO‐NOISE RATIO OF SEISMIC DATA WITH AN APPLICATION TO STACKING*
By E. RIETSCHAbstractThe amplitude of the signal and the energy of the noise on each of at least three traces can be estimated provided that the signal has the same form (but not necessarily the same amplitude) on these traces and that the noise on any trace is correlated with neither the signal nor the noise on any other trace. This estimation of signal amplitude and noise energy can be achieved by a rather simple algorithm. The accuracy of the estimate depends, of course, on the degree to which the assumption that signal and noise on the different traces are mutually uncorrelated is actually met. The accuracy tends to improve with increasing number of traces.
-
-
-
A PARAMETRIC APPROACH TO THE COMPRESSION OF SEISMIC SIGNALS BY FREQUENCY TRANSFORMATION*
Authors G. BERESFORD‐SMITH and I. M. MASONAbstractThe compression of seismic signals which have propagated through a dispersive medium can be achieved by a frequency‐domain transformation. This transformation is formally related to the dispersion characteristic of the medium and is independent of phase and group velocities. By defining a suitable cost‐function to measure the degree of dispersion of a time‐ signal, an iterative technique can be employed to find that transformation which gives minimum dispersion.
In this paper, we assume that the inverse of the dispersion characteristic can be adequately approximated by a finite polynomial in the region of maximum signal energy density. The coefficients of this polynomial are the parameters of dispersion of the medium. These parameters can be estimated both in the presence of noise and in the case of signals made up of multiple arrivals.
The techniques developed in this paper are applied to seismic signals which have been recorded underground by a set of geophones designed to detect and map discontinuities in coal‐seams. Results of dispersion estimation and signal compression are discussed for data collected in the Blackshale seam, Pye Hill Colliery, near Derby, in the United Kingdom.
-
-
-
AUTOREGRESSIVE PATTERN RECOGNITION APPLIED TO THE DELIMITATION OF OIL AND GAS RESERVOIRS*
By P. BOISAbstractIt is often difficult to precisely determine the boundaries of oil and gas reservoirs in the horizontal and vertical directions. Autoregressive pattern recognition is used to reveal lateral facies variations and to specify reservoir boundaries. The method is based on the calculation of autoregressive coefficients for short trace sectors between the top and bottom boundaries of the reservoir. These coefficients are determined by applying the maximum entropy principle. Once these coefficients are known, an estimate can be made of the power spectra of these trace sectors. Then these coefficients will act as characters for a pattern recognition algorithm.
A decision criterion is used to distinguish the trace sector corresponding to layers impregnated with oil or gas and those impregnated with water.
Two examples are given to show how autoregressive pattern recognition allows to accurately delimit gas or oil reservoirs.
-
-
-
SEISMIC AND GRAVITY TWO‐DIMENSIONAL INHOMOGENEOUS MODEL OF THE EARTH'S CRUST (ON THE EXAMPLE OF CENTRAL KAZAKHSTAN)*
Authors T.I. OBLOGINA and V.V. FEDYNSKYAbstractThe interpretation of deep seismic sounding (DSS) data has been made on the basis of a two‐dimensional inhomogeneous model. The refracted first arrivals as well as reflected and diffracted waves on the seismic records have been utilized. The seismic section was modeled in the iso‐veolcity lines v(x, y) = const, taking into account the zones of diffraction associated with deep faults.
Gravity observations have been used to construct a block model of the Earth's crust with vertical boundaries.
It is suggested to define the base of the crust as the zone with velocities between 7.8 and 8.2 km/s. The reflecting boundaries of different length occurring in this zone can be conformal or unconformal with the iso‐velocity lines near the base of the crust.
As an example of our approach to the interpretation of DSS data the folded‐blocky structure of the crust with horizontal inhomogeneities of velocity and density is shown in the Kzyl‐Orda‐Dzheskazgan profile in Central Kazakhstan.
-
-
-
THE INDUCTIVE RESPONSE OF A HORIZONTAL CONDUCTING CYLINDER BURIED IN A UNIFORM EARTH FOR A UNIFORM INDUCING FIELD*
Authors S.O. OGUNADE and H.W. DOSSOAbstractThe inductive response of a conducting horizontal cylinder embedded in a uniform earth is studied using numerical results obtained for an analytical solution for the problem of a conducting cylinder buried in a homogeneous earth for the case of a uniform inducing field. A check of the validity of the numerical results is made by a comparison with analogue model measurements for a number of cases. Numerical results for a range of cylinder radii (a = 1–10 km), depths of burial (d= 0–4 km), conductivity contrasts (σ2= 10−2‐10 Sm−1), and source frequencies (f= 10−1‐10−4 Hz) of interest in the interpretation of magnetotelluric field measurements are presented. The results indicate that for a uniform inducing field the conductivity and depth of burial of a horizontal cylindrical inhomogeneity are best determined through a measurement of the amplitudes Hy, Hz and Ex and the phases φy and Ψx.
-
-
-
DIGITAL LINEAR FILTER FOR COMPUTING TYPE CURVES FOR THE TWO‐ELECTRODE SYSTEM OF RESISTIVITY SOUNDING*
Authors U.C. DAS and S.K. VERMAAbstractIn this paper a technique for computing type curves for the two‐electrode resistivity soundings is presented. It is shown that the apparent resistivity due to the system can be represented by a convolution integral. Thus, it is possible to apply the principle of digital linear filtering and compute the desired type‐curves. The filter function required for the purpose is found to be identical with that used to compute the EM sounding curves for the two coplanar horizontal loop system.
It is further shown that from the two‐electrode apparent‐resistivity expression one can easily derive the apparent resistivities for other configurations. A comparison of depths of investigation for various systems reveals that the two‐electrode system has greater depth of investigation than other conventional systems. This is also supported by the field example presented in the end, which illustrates the relative performance of the two‐electrode system vis‐a‐vis the Wenner system.
-
-
-
A FIELD OCCURRENCE OF SIGN REVERSALS WITH THE TRANSIENT ELECTROMAGNETIC METHOD*
By B. R. SPIESAbstractSign reversals have been observed with the one‐loop version of the TEM method in an area near Cloncurry, Queensland. This is the only area in which such a response has been recorded in seven years of field surveys by the Australian Bureau of Mineral Resources.
The geology of the area consists mainly of pyrrhotitic graphitic shale, which has resistivities as low as 0.1 Ωm and frequency effects up to 30%. The sign reversals could be due to magnetic phenomena, reflections from layers, or complex conductivity effects.
-
-
-
INVERSION OF SURFACE AND BOREHOLE ELECTROMAGNETIC DATA FOR TWO‐DIMENSIONAL ELECTRICAL CONDUCTIVITY MODELS*
Authors M.L. ORISTAGLIO and M.H. WORTHINGTONAbstractA method for inverting electromagnetic fields induced by a line source in an earth of two‐dimensional conductivity structure is developed. Certain unique features of the finite element method are used to construct an efficient algorithm for the accurate calculation of the Jacobian matrix of partial derivatives, and the resulting linearized equations are solved using the damped least squares method.
Case studies of theoretical data generated from a simple model of interest in geophysical prospecting show that, in general, it is impossible to obtain, from surface data alone, accurate estimates of the conductivity of structures buried deeper than 0.2 skin depths under a conducting overburden. The addition of borehole data to the surface data is found to increase the resolving power of the electromagnetic method dramatically. In particular, the borehole data appear to stabilize the inverse when only a poor initial estimate of the likely structure is given.
-
Volumes & issues
-
Volume 72 (2023 - 2024)
-
Volume 71 (2022 - 2023)
-
Volume 70 (2021 - 2022)
-
Volume 69 (2021)
-
Volume 68 (2020)
-
Volume 67 (2019)
-
Volume 66 (2018)
-
Volume 65 (2017)
-
Volume 64 (2015 - 2016)
-
Volume 63 (2015)
-
Volume 62 (2014)
-
Volume 61 (2013)
-
Volume 60 (2012)
-
Volume 59 (2011)
-
Volume 58 (2010)
-
Volume 57 (2009)
-
Volume 56 (2008)
-
Volume 55 (2007)
-
Volume 54 (2006)
-
Volume 53 (2005)
-
Volume 52 (2004)
-
Volume 51 (2003)
-
Volume 50 (2002)
-
Volume 49 (2001)
-
Volume 48 (2000)
-
Volume 47 (1999)
-
Volume 46 (1998)
-
Volume 45 (1997)
-
Volume 44 (1996)
-
Volume 43 (1995)
-
Volume 42 (1994)
-
Volume 41 (1993)
-
Volume 40 (1992)
-
Volume 39 (1991)
-
Volume 38 (1990)
-
Volume 37 (1989)
-
Volume 36 (1988)
-
Volume 35 (1987)
-
Volume 34 (1986)
-
Volume 33 (1985)
-
Volume 32 (1984)
-
Volume 31 (1983)
-
Volume 30 (1982)
-
Volume 29 (1981)
-
Volume 28 (1980)
-
Volume 27 (1979)
-
Volume 26 (1978)
-
Volume 25 (1977)
-
Volume 24 (1976)
-
Volume 23 (1975)
-
Volume 22 (1974)
-
Volume 21 (1973)
-
Volume 20 (1972)
-
Volume 19 (1971)
-
Volume 18 (1970)
-
Volume 17 (1969)
-
Volume 16 (1968)
-
Volume 15 (1967)
-
Volume 14 (1966)
-
Volume 13 (1965)
-
Volume 12 (1964)
-
Volume 11 (1963)
-
Volume 10 (1962)
-
Volume 9 (1961)
-
Volume 8 (1960)
-
Volume 7 (1959)
-
Volume 6 (1958)
-
Volume 5 (1957)
-
Volume 4 (1956)
-
Volume 3 (1955)
-
Volume 2 (1954)
-
Volume 1 (1953)