Elastic full-waveform inversion of 4C ocean-bottom seismic data: Model parameterization analysis

Abstract

Full waveform inversion (FWI), as an efficient seismic imaging tool, is widely used in the investigation of the structure of the Earth. For the oil & gas industry, in addition to the subsurface image, a quantitative estimation of elastic properties from seismic data is crucial for the geophysical characterization and monitoring of the subsurface lithology and reservoirs. In marine surveys, with the emergence of the four- component (4C) ocean-bottom acquisition systems (deploying 1C hydrophone plus 3C geophone on the seabed), more elastic wave propagation effects can be recorded in the seismic data for an elastic property estimation of the subsurface, i.e. extracting medium shear modulus from the S-wave velocity model. Multi-parameter elastic FWI offers the possibility to reconstruct the P-wave (Vp) and S-wave velocity (Vs) models jointly. However, compared with the mono-parameter acoustic FWI, the multi-parameter elastic FWI can be more vulnerable due to the parameter coupling, wave modes conversion and interference. For the purpose of building a robust multi-parameter elastic inversion of the 4C seismic data, we consider a workflow design from the aspect of model parameterization analysis. Three different elastic model parameterizations, m1 = (Vp,Vs), m2 = (Vp,Vp/Vs) and m3 = (Vp,s) (s is the Poisson’s ratio), are analyzed in terms of data sensitivity and model gradient feature. Together with synthetic case studies on a series of overburden models with increasing elastic effects and a realistic geological model, we conclude that a workflow of first inverting hydrophone data with (Vp, Vp/Vs) parameterization and then 3C geophone data with (Vp, Vs) parameterization contributes to a robust and reliable Vp and Vs model reconstruction.