Print this pageRegional Sequence Stratigraphic Analysis of Regional 2D Lines in the Central Santos Basin, Offshore Brazil
The Santos basin, offshore Brazil, has recently generated great interest following large hydrocarbon discoveries in the pre-salt section. However, initial petroleum exploration focussed on the post-salt sequence. This consists of Albian carbonates deposited on top of a mobile evaporitic substratum, followed by a clastic sequence whose development reflects the interplay between local salt tectonics, regional subsidence, regional tectonics, and global sea level oscillations. Salt movement had a major impact on basin fill. It started as early as Albian times and accelerated during Santonian-Campanian times, when a large, apparently prograding clastic wedge formed. This “progradation” continued until late Eocene times, when a major phase of backstepping of depositional systems occurred. A common stratigraphic framework can be defined in the basin, but lateral changes in shelfedge trajectories for the same stratigraphic interval and formation of distinct depocentres indicate how sediment-starved areas or loci of preferential deposition formed in response to local controlling factors.
We present here results of a study on the Santonian-Recent sequence from the central part of the basin, based on six 2D regional PSTM lines, approx. 100km along depositional dip, 300km along depositional strike. The analysis used an original digital workflow for seismic-sequence stratigraphic interpretation. The workflow started with creation of a steering cube (where every sample position contains the dip and azimuth attributes of that particular seismic trace). Data conditioning was followed by automatic data-driven calculation of a chronostratigraphic framework over the entire section under consideration. A series of horizons were generated, auto-tracked simultaneously, placed in stratigraphic order and assigned a relative geological time. This chronostratigraphy includes stratal terminations that can be directly compared with the seismic data for quality control, and can be converted to a seismic Wheeler diagram to help with geological interpretation. The chronostratigraphy was detailed enough to extract subtle information on near seismic resolution scale.
Advantages of the workflow include: rapid automated generation of Wheeler diagrams, ideal for studying the development of depositional loci over time; the ability to use all seismic attributes in the Wheeler domain; and improved collaboration between remote teams thanks to the digital and repeatable nature of the results.
AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil