Imaging challenges and processing solutions in the Brazilian Equatorial Margin: A case study in the Barreirinhas Basin

Abstract

The Barreirinhas Basin is located in northeast Brazil and is part of the Brazilian Equatorial Margin, a new exploration frontier with complex geology. This basin is characterized by a rugose water bottom, a fast carbonate platform, shallow gas pockets, and a complex channel network. All of these elements represent a significant challenge for velocity model building and imaging of the depositional system. From preprocessing to final imaging, high-end technologies were required to meet the processing objectives. The 3D designature and 3D deghosting were crucial to remove bubble energy and ghosts related to canyon diffractions. The velocity model building exploited offset-dependent dip information in the nonlinear slope tomography — i.e., dip-constrained tomography (DCT) — to deal with small-scale lateral velocity variations. The full-waveform inversion, up to 20 Hz, was able to efficiently capture small velocity anomalies and resolve high-spatial-resolution variations that DCT could not totally solve. Even with a detailed velocity model, some dim zones and amplitude variations were still observable in the depth-migrated image. Gas pockets, responsible for the absorption and phase distortion of the seismic signal (commonly denoted by the quality factor of attenuation, Q), were detected and delineated using volumetric Q tomography. The resultant interval Q model was consistent with the geology, and its use was beneficial in a Q-compensating Kirchhoff prestack depth migration.