Espalhamento geométrico em modelos plano-estratificados

Abstract

Themeasurementofphysicalparametersofreservoirsisofgreatimportancetothedetectionofhydrocarbons. Toobtaintheseparameters, an amplitude analysis is performed with the determination of the reflection coefficients. For this, it is necessary the application of special processing techniquesabletocorrectthesphericaldivergenceeffectsonseismictimesections. Aproblemcanbeestablishedthroughthefollowingquestion: What is the relatively more important effect responsible for the amplitude attenuation: geometrical spreading or the loss by transmissivity? A justification for this question resides in that the theoretical dynamic correction applied to real data aims exclusively to the geometrical spreading. On the other side, a physicalanalysisoftheproblembydifferentdirectionsplacestheanswerinconditionsofdoubt,whatisinterestingandcontradictorywiththepractice. A more physically based answer to this question can give better grounds to other works in progress. The present work aims at the calculus of the spherical divergence according to the Newman-Gutemberg theory, and to correct synthetic seismograms calculated by the reflectivity method. The test model considered is crustal in order to have critical refraction events besides reflection events, and to better position with respect to the time window for application of the spherical divergence correction, which results in obtaining the denoted The simulated medium is formed by plane-horizontal, homogeneous and isotropic layers. The reflectivity method is a form of solution of the elastic wave equation for this reference model, what makes possible an understanding of the structured problem. To arrive at the obtained results, synthetic seismogram were calculated by using the fortran program P-SV-SH written and supplied by Sandmeier (1998), and reflection geometrical spreading curves as function of time were calculatedasdescribedbyNewman(1973). Asaconclusion, wehavedemonstratedthatfromthemodelinformation(velocities, thicknesses, densities and depths) it is not simple to obtain an equation for geometrical spreading correction aiming at the true amplitudes. The major aim would then be to obtain a panel of the spherical divergence function to correct for true amplitudes.