Abstract
We used high-quality three-dimensional (3-D) seismic data to quantify the timing and magnitude of differential compaction over a Late Miocene submarine channel complex in SE Brazil (Espirito Santo Basin). A thickness-relief method was applied to quantify the thickness variations in strata deposited over the channel complex. We found that differential compaction started after the channel complex was buried by ∼200 m of strata, as revealed by thinning horizons observed over a compaction-related anticline. The size of the anticline is greatest in the south of the study area, reaching heights of 41 ms (∼50 m). Fluid expelled through faults on the margins of the channel complex formed large depressions. These depressions increased in size after deep-water currents removed the fluid-rich sediment filling them. Differential compaction also occurred over deposits downslope of knickpoints, reaching maximum heights of 29 ms (∼35 m). Seismic reflections onlap the knickpoint face and are believed to comprise slumped strata and debrites. Two-way traveltime isochron and amplitude maps indicate that there are limited connectivity and lateral continuity of the coarse-grained units. Differential compaction over these deposits created anticlines with four-way dip closure. As a consequence, isolated reservoirs were closed vertically by the compaction anticlines and laterally by strata onlapping the knickpoint face. These unique reservoirs could have been charged by migration of hydrocarbons along sands at the base of the channel complex. A fill-to-spill model is hypothesized using the above mechanism: Once an isolated anticlinal trap reached spill point, hydrocarbons migrated upslope into the next trap. Traps like these could form above submarine channels in similar basins around the world (e.g., Gulf of Mexico, west coast of Africa) after early burial.
Highlights
Compaction of sediments during the early stages of burial is closely related to lithology and water content (Athy, 1930; Trask, 1931)
This study focused on a single channel complex cutting through early Miocene–age pelagites, with differential compaction occurring above the channel sands (Fig. 1B)
This study used thickness-relief plots and seismic volume attributes to help understand how and when differential compaction occurred over a submarine channel complex in the Espírito Santo Basin, Brazil
Summary
Compaction of sediments during the early stages of burial is closely related to lithology and water content (Athy, 1930; Trask, 1931). Previous studies have focused on the seismic expression of differential compaction structures, their potential for forming hydrocarbon traps, and the causes for overpressure and fluid expulsion (Chopra and Marfurt, 2012; Corcoran, 2006; Cosgrove and Hillier, 1999; Gay et al, 2006a; Xu et al, 2015). Most of these studies have provided qualitative data on large, discrete structures. This process occurred throughout the Cenozoic, peaking during the Eocene–early Oligocene, and
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