Investigating Down-Slope Changes in Deep-Water Channel Stacking with a 3-D Digital Outcrop Model, Cretaceous Tres Pasos Formation, Southern Chile

Fletcher, Sean; Hubbard, Stephen M.; Macauley, Ryan V.; Pemberton, Erin; Romans, Brian; Stright, Lisa

Slope channel deposits comprise some of the most significant hydrocarbon reservoirs worldwide. The large-scale architecture of these deep-water conduits is often imaged in 3-D seismic data, yet the finer, reservoir-scale architecture that controls the efficiency of hydrocarbon recovery is typically difficult to characterize from subsurface datasets. We leverage an expansive outcrop of a slope channel system (Cretaceous Tres Pasos Formation, southern Chile) and document reservoir-scale architecture and consider implications for hydrocarbon recovery in analogous deposits. This 6.5 km long by 2 km wide outcrop consists of 300 m of stratigraphy, and we use a 3-D digital outcrop model to document and characterize slope channel stratigraphy: a hierarchy of channelform sedimentary bodies, including elements, complexes and complex sets. The outcrop model is constrained by high-resolution data collection methods including differential GPS (~10 cm resolution) surveying of stratigraphic surfaces, measured sections, and geo-referenced photomosaic interpretation. Measured sections provide the 1-D stratigraphic information used to identify and map channel boundaries and contacts, and populate lithologic data in 3-D models. Photomosaics and correlation panels provide 2-D perspectives and identification of key stratigraphic surfaces, which are in turn captured in 3-D through the use of dGPS surveying. Geo-referenced data is exported into 3-D modeling software (Petrel), where key stratigraphic surfaces are extrapolated.

Previous mapping of these outcrops suggested that the succession of slope deposits transitioned from laterally offset to more vertically stacked channels down-slope. We employed high-resolution 3-D mapping using differential GPS to better document the architecture and investigate channel-stacking patterns more quantitatively. The 3-D architectural model indicates that the spatial transition in channel stacking patterns - from more laterally offset to vertically stacked - occurs over only 2 km down the paleo-slope. This abrupt architectural transition is evident through 300 m of stratigraphy, which suggests a long-lived, and perhaps inherited, control on channel complex orientation such as foredeep basin geometry. Similar architectural transitions are common to conduits that transect topographically complex slope systems on numerous continental margins, including petroliferous regions of West Africa and the Nile Delta.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013