Abstract: Seismic Criteria to Recognize Potential Deep-Sea Sandstones in Brazilian Passive Margin Basins

Cesar Cainelli, Mario Carminatti

Searching for deep-sea sand-rich deposits requires careful approaches for successful hydrocarbon exploration. That is crucial when only seismic data support the selection of potential deep-water prospects. What to look for? What to choose? How to create the necessary "feeling"?

Experience, analogy and imagination help to recognize criteria applied in deep-water prospects of Brazilian basins. Such seismic criteria can include: (1) anomalies of amplitude in sand-rich tabular turbidites; (2) single/amalgamated mounds with internal chaotic/hummocky facies or bidirectional downlaps in turbidites/bottom-current reworked turbidites covering unconformities; (3) high-amplitude backstepping tabular sandy bodies; (4) high-amplitude/low-continuity facies inside migrating channels between paleogeomorphic highs or salt diapirs; and (5) single reflectors pinching out bathymetric highs.

Seismic criteria do not guarantee the presence of deep-sea sandstones, which will be controlled by the nature of the available sediments on the shelf and by its efficiency to transfer sands to slope/basin sites. The shelf usually provides well-defined pathways rather than a widespread downslope deliver of sands. Portions of the shelf margin may become unstable by movements of underlying shale or salt developing scars, canyons and channels, which reach and reroute platform-stored or river-borne sands to deeper waters. The originally deposited sandy turbidites can be partially or entirely resedimented as contourites.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994