Application of waveform tomography at Campos Basin field, Brazil

Abstract

Campos Basin field has been continuously characterized inside the Reservoir Characterization Project (RCP). Past research includes poststack and prestack joint inversions of PP and PS data which increased the reservoir resolution and could predict a porosity map. To further improve characterization of the Campos Basin field, waveform tomography (WT), or full waveform inversion (FWI), is performed for a 2D line from the 2010 ocean bottom cable (OBC) data under a 2D acoustic isotropic medium assumption. The goal is to bring high resolution and accuracy to the P wave velocity model for better quality reservoir imaging. In order to achieve the best results the application of WT to the 2D dataset required defining the suitable parameters to these data, where the main options in the inversion are the type of objective function, the time domain damping, and the frequency discretization. The waveform inversion has improved the final velocity model, as verified by migrated images showing more continuous and focused horizons at the reservoir depth. The improved seismic image and velocity model are possible inputs, respectively, to a new geological interpretation and to acoustic/elastic attributes inversion. However, only the background velocity was updated and the inversion failed in enhancing the resolution of the final velocity model. Waveform inversion was also performed on synthetic dataset with larger offsets generated for a reliable velocity model of the Campos Basin field. The combination of a larger offset with a waveform inversion strategy that includes amplitude and phase residuals in the objective function proved to be efficient in increasing the resolution of the final velocity model. Synthetic modeling suggests that if a new seismic acquisition program is conducted over the field, it would be highly beneficial for velocity analysis and reservoir characterization to acquire longer offsets.