Brazil Pre-Salt: Role of Seismic Technology in Full Cycle Hydrocarbon Maturation Process

Abstract

The very prolific Brazilian pre-salt play has captured the world’s attention by translating a very impressive deep-water exploration campaign into some of the largest oil discoveries in the region and the world. The advent of such great success and the need to improve production rates in an extremely complex geologic environment required innovative developments in acquisition technology and processing under very difficult economic conditions.

Successful solutions must address critical geophysical challenges related to limited offset/azimuth, complex multiples caused by salt, complex anisotropic velocity modelling inherent to the overlying highly layered evaporitic successions, complex overburden with steep dips, mini-basin configuration, presence of volcanism, small keel fault identification, consistency of the dynamic range of amplitudes and improvement of illumination of drilling targets associated with deeper reservoirs. Understanding the highly heterogeneous carbonate reservoirs across pre-salt trend is of paramount importance.

The challenges highlighted above require a systematic approach starting with an intelligent acquisition design utilizing all available velocity models to understand the role of azimuth and required subsurface illumination. This should be followed by a broadband processing approach to enhance the S/N ratio by deploying robust noise attenuation techniques with specific emphasis on ultra-low frequencies. Full 3D deghosting should be applied to create a stable, stationary and more interpretable ghost-free wavelet. Application of a true azimuth and flexible 3D SRME algorithm that can handle any type of acquisition geometry as well as utilize all available data for multiple prediction is a critical step in the sequence.

The earth model building flow can include early arrivals FWI, post-FWI tomography, salt bodies interpretations with dirty salt updates, through-salt and subsalt tomography. To achieve both higher quality & higher magnitude deep velocity updates, we can also employ reflection full waveform inversion which capitalizes on the strong impedance signatures. Non-seismic data, such as gravity measurements can complement the seismic imaging for salt interpretation.

Accurate velocity models along with broadband processed data enable the generation of high resolution Kirchhoff and Reverse Time Migration (RTM) images, as well as least square migrations, which demonstrate significant image uplift when compared to legacy images.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018