Core- and Log-Based Recognition Criteria for Deep-Water Channel Bodies: Using Outcrops to Inform Stratigraphic Architecture Predictions Beyond the Wellbore

Abstract

Deep-water slope channel elements and their stratigraphic arrangement within larger composite channelform bodies (>60-120 m thick, ~1-5 km wide) are key controls on reservoir productivity. Seismic data is critical for delineating the large-scale reservoir framework of composite units. However, their internal architecture is below typical seismic resolution, and can be difficult to predict from well data. Recognition of component slope channel elements (typically up to 10-20 m thick and 300 m wide) in core and wireline datasets is critical to predictions of inter-well reservoir heterogeneity. We leverage a vast outcrop dataset from the Cretaceous Tres Pasos Formation of southern Chile to provide recognition criteria that enables informed, sub-seismic-scale correlations of slope channel strata.

Outcropping slope channel system deposits of the Tres Pasos Formation contain stratigraphic successions similar in architecture and scale to those of productive reservoirs on the margins of Africa, Brazil, the Gulf of Mexico, Southeast Asia, and the North Sea. Composite channelform bodies range from 60-120 m thick in outcrop, and can be mapped along paleoslopes for >30 km in some cases. Their constituent channel elements are characterized in >6,650 m of 1D measured sections. Identifying element bases and tops is not always intuitive in 1D data (i.e., well logs), however, the lateral extent of the outcrop allows these contacts to be confidently discerned. Statistical analysis of 220 sections through individual channel elements shows that upward-fining grain size trends are not diagnostic; rather, they are subtle and only preserved in the axial portions of elements. Moreover, the basal erosion surface of channel elements is overlain by concordant, thin-bedded strata in 55-60% of channel sections; this has been widely linked to sediment bypass or deposition from small, dilute flows that passed through the channel. As such, a large proportion of channel element sections are observed to coarsen upwards. We use these observations to establish an objective and informed approach to reservoir characterization. The data guide core- and log-based predictions of inter-well stratigraphic architecture within slope channel system reservoirs, enabling construction of predictive geomodels that more closely mimic realistic stratigraphic architecture.

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