Full waveform inversion of a Brazilian pre-salt OBN dataset using a concentric circle source geometry

Abstract

We have designed a workflow to apply full-waveform inversion (FWI) to a new type of acquisition recorded on ocean-bottom nodes (OBNs) in the Brazilian presalt area. The data set consists of three large-radius concentric circles of seismic source points recorded on OBN placed within the area of the circles. This geometry provides full azimuth distribution and benefits from long offsets in which the effect of diving waves is strong. These diving waves carry information about the presalt targets of interest. In the FWI workflow, we retrieve the P-wave velocity using the density as a propagation parameter. We test three objective functions: ℓ2-norm, ℓ1-norm, and nonparametric residuals objective function (NPR-FWI), which have different abilities to handle low signal-to-noise ratio data. In our inversion tests, the ℓ1-norm and NPR-FWI retrieve more information about the presalt reservoir than the ℓ1-norm. We find through several inversion experiments that we can recover structures related to the presalt reservoir, demonstrating the potential for this new type of OBN circular source geometry. We also discuss implications for low-cost data acquisition that take advantage of the sparse nature of sources and receivers needed in this survey geometry, including its extension to time-lapse target-oriented reservoir monitoring.