Subbasalt Marchenko imaging with offshore Brazil field data

Abstract

Subbasalt imaging for hydrocarbon exploration faces challenges with the presence of multiple scattering, attenuation, and mode conversion as seismic waves encounter highly heterogeneous and rugose basalt layers. A combination of modern seismic acquisition that can record densely sampled data and advanced imaging techniques make imaging through basalt feasible. Yet, the internal multiples, if not properly handled during seismic processing, can be mapped to reservoir layers by conventional imaging methods, misguiding geologic interpretation. Traditional internal multiple elimination methods suffer from the requirement of picking horizons of multiple generators and/or a top-down adaptive subtraction process. Marchenko imaging provides an alternative solution to directly remove the artifacts due to internal multiples, without the need of horizon picking or subtraction. In this paper, we evaluate a successful application of direct Marchenko imaging for subbasalt demultiple and imaging with an offshore Brazil field data set. The internal multiples in this example are generated from the seabed and basalt layers, causing severe artifacts in conventional seismic images. We have determined that these artifacts are largely suppressed with Marchenko imaging, and we have developed a general workflow for data preprocessing and regularization of marine streamer data sets. We find that horizontally propagating waves also can be reconstructed by the Marchenko method at far offsets.