Linearized elastic parameter sections¹

Abstract

Contrasts in elastic parameters can be estimated directly from seismic data using offset-dependent information in the PP reflection coefficient. A linear approximation to the PP reflection coefficient including three coefficients is fitted to the data, and relative contrasts in various elastic parameters are obtained from linear combinations of the estimated coefficients. Linearized elastic parameter sections for the contrasts in P-wave impedance, P-wave velocity, density, plane-wave modulus, and the change in bulk modulus and shear modulus normalized with the plane-wave modulus are estimated. If the average P-to S-wave velocity ratio is known, linearized parameter sections including the contrast in the average P-to S-wave velocity ratio and a fluid factor section can be computed. Applied to synthetic data, visual comparison of the estimated and true elastic parameter sections agree qualitatively, and the results are confirmed by an analysis of the standard deviation of the estimated parameters. The parameter sections obtained by inversion of a shallow seismic anomaly in the Barents Sea are promising, but the reliability is uncertain because neither well data nor regional trends are available. lntroduction Amplitude-versus-offset (AVO) analysis is based on offset-or angle-dependent reflection coefficients, and is successfully used as a qualitative tool for lithology and fluid prediction in many regions.AVO inversion, which is still in an early stage, is quantitative and estimates the elastic parameters in the subsurface. AVO inversion assumes that all offsetdependent amplitude effects, other than the reflection coefficient, are corrected for. In this case, at least theoretically, contrasts in elastic parameters can be estimated from seismic data.AVO inversion methods based on a linear approximation to the PP reflection coefficient result in weighted stacking schemes (Smith and Gidlow 1987;Ursin and Dahl 1990;Gidlow, Smith and Vail 1992).In general, AVO inversion is non-unique I

Prediction of Elastic Properties Within CO2 Plume at Sleipner Field Using AVS Inversion Modified for Thin‐Layer Reflections Guided by Uncertainty Estimation

“…True amplitudes in the time‐offset domain are spherical wave reflections, which deviate significantly from those predicted by the plane wave Zoeppritz equations, particularly, at near‐critical angle. By applying a τ ‐𝑝 transform (preferably cylindrical) to the seismic data, amplitudes of the transient waves are reconstructed, and hence, the plane wave reflection coefficients can be used for amplitude analysis accurately for both precritical and critical angles (Brysk & McCowan, 1986; Chapman, 1981; Ursin et al, 1996) and in anisotropic media (Sen & Mukherjee, 2003; Sil & Sen, 2009). Another advantage of working in the τ ‐𝑝 domain is that no geometric spreading and polarization corrections are required.…”