Fil: Gelpi, Gabriel Ricardo. Universidad Nacional de La Plata. Facultad de Ciencias Astronomicas y Geofisicas; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - La Plata; Argentina

Automatic well tying and wavelet phase estimation with no waveform stretching or squeezing

This paper presents Levinson (1947)-type algorithms for (i) polynomial fitting (ii) obtaining a Q decomposition of Vandermonde matrices and a Cholesky factorization of Hankel matrices (iii) obtaining the inverse of Hankel matrices The algorithm for the least-squares solution of Hankel systems of equations requires 3n/sup 2/+9n+3 multiply and divide operation (MDO) The algorithm for obtaining an orthogonal representation of an (m/spl times/n) Vandermonde matrix X and computing the Cholesky factors F of Hankel matrices requires 5mn+n/sup 2/+2n-3m MDO, and the algorithm for generating the inverse of Hankel matrices requires 3(n/sup 2/+n-2)/2 MDO Our algorithms have been tested by means of fitting of polynomials of various orders and Fortran versions of all subroutines are provided in the Appendix >

Levinson-type algorithms for polynomial fitting and for Cholesky and Q factors of Hankel and Vandermonde matrices

A multioffset VSP (vertical seismic profiling) geometry is used in this thesis to acquire data for AVO (amplitude-versus-offset) analysis of a reservoir zone. The VSP geometry consists of ten surface source positions and eleven downhole receiver positions. The downhole receivers are placed immediately above the reservoir zone. A zero-offset and an offset VSP were also acquired and analysed. A three-component processing flow is developed, and tested here using synthetic data, to extract the true seismic amplitudes from VSP data. AVO analysis of the multioffset VSP data suggests a lower P-wave velocity in the reservoir zone based on forward modeling. Well-log interpretation indicates that the reservoir zone is a gasbearing dolomite with porosities as high as 18 %. Generalized-linear-inversion methods are developed to invert the zero-offset VSP corridor stack for the acoustic impedance, and to invert the multioffset VSP P-P and PSV reflectivity traces jointly for the elastic parameters Vp, Vs, andp. The zero offset inversion resulted in an inverted impedance curve that matched the higher frequency trends but failed to match the low frequency trends of the initial-guess impedance curve. The joint P-P/P-SV inversion is found to update the elastic parameters in a realistic manner; however there is some residual error. The resulting P-wave velocity in the reservoir is higher than the initial guess which is the opposite of the forward modeling results.

Amplitude-versus-offset analysis using vertical seismic profiling and well-log data

This study uses VSP and well log data to analyze the AVO response of a subsurface gas-saturated carbonate zone. Analysis of the well log data show that the gas-saturated zone is dolomitized with a porosity as high as 18 %. The VSP data consist of three surveys; a zero-offset VSP; an offset VSP, and a multioffset VSP. The P-SV converted-wave reflections from the offset VSP and multioffset VSP were found to correlate well with the pure P-wave reflections from each VSP. Forward modeling was used to analyze the AVO response of the gas-saturated zone. It was found that there is extreme tuning in the reservoir zone, causing the combined AVO response of the layers within 1/2 of the seismic wavelength to be very complicated. It was also found that a better match of the forward model data with the field multioffset VSP data could be made by lowering the P-wave velocity in the reservoir zone.

AVO analysis of VSP and well log data

A method for identifying AVO response with VSP data

LOW pass filtering of sonic logs is often desired to remove high frequency measurement errors, to allow a valid comparison with a particular inversion scheme, and simply to make interpretation easier. However, because abrupt changes in velocity require high frequencies for their represenation, conventional low pass filtering tends to smear the important features of the signal. This has lead to non linear techniques such as median filtering, which however, can also degrade edges producing ‘edge artifacts’, especially for longer filter lengths. Recently the signal conditions necessary for the production of edge artifacts have been established (Leaney and Clrych 1987) and an extension to median filtering, compound median filtering, has been shown to preserve signal edges. In addition, compound median filtering has lead to a signal decomposition which allows greater flexibiltiy in the filtering operation. In this paper compound median filtering and decomposition are discussed and two applications of the decomposition, significant event reconstruction and time varying compound median filtering, are demonstrated as applied to sonic well log data.

W. Scott Leaney

Papers

Compound Median Filtering Applied to Sonic Logs

Extended Yule‐Walker equations, nonwhite deconvolution and roots of polynomials