An AVO method toward direct detection of lithologies combining P-P and P-S reflection data

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Title: An AVO method toward direct detection of lithologies combining P-P and P-S reflection data
Author: Carcuz Jerez, Juan Ramon de Jesus
Abstract: I here present a combined AVO analysis of P -P and P -S reflection data whose objective is to improve the identification of lithology by estimating the specific values of Poisson's ratio , [sigma] , for each rock formation in a given geological model , rather than a contrast between formations . Limited knowledge on the elastic parameters of a given rock formation and difficulty regarding the availability and processing of P -S data constitute hindrances of lithology identification . Considering that ocean bottom seismology (OBS ) has aided in solving the problem of P -S data availability , limited information on elastic parameters is still a challenge , and the focus of this thesis . The present analysis is based on Zoeppritz' solution for the P -P and P -S reflection coefficients , RPP and RPS , with a slight modification . We used the normalized P -S reflection coefficient ; i .e . , R'PS = RPS / sin [theta] for [theta] > 0 , instead of RPS , where [theta] is the incident angle . By normalizing RPS , we avoid dealing with the absence of converted S -waves at small incident angles and enhance the similar linear behavior of the P -P and normalized P -S reflection coefficients at small angles of incidence . We have used the linearity of RPP and R'PS at angles smaller than 35 degrees to simultaneously estimate the average VP /VS ratio , the contrasts of P - and S -wave velocities , and the contrast of density . Using this information , we solve for Poisson's ratio of each formation , which may enable lithology discrimination . The feasibility of this analysis was demonstrated using nonlinear synthetic data (i .e . , finite -difference data ) . The results in estimating Poisson's ratio yielded less than 5 percent error . We generalize this new combined P -P and P -S AVO analysis for dipping interfaces . Similarly to the nondipping interface case , our derivations show that the amplitude variation with offset (AVO ) of P -P and P -S for a dipping interface can be cast into intercepts and gradients . However , these intercepts and gradients depend on the angle of the dipping interface . Therefore , we further generalize our analysis by including a migration step that allows us to find the dipping angle . Because seismic data is not available in terms of RPP and R'PS , this process includes recovery of reflection coefficients after migrating the data and correcting for geometrical spreading , as done by Ikelle et al . (1986 and 1988 ) . The combination of all of these steps , namely geometrical -spreading correction , migration , and AVO analysis , is another novelty of this thesis , which leads to finding the specific values of Poisson's ratio of each rock formation directly from the seismic data .
URI: http : / /hdl .handle .net /1969 .1 /38
Date: 2004-09-30

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An AVO method toward direct detection of lithologies combining P-P and P-S reflection data. Available electronically from http : / /hdl .handle .net /1969 .1 /38 .

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