Baffles and Barriers in a Passive-Margin Slope Channel-Complex Set (Neoproterozoic Isaac Formation, Canadian Cordillera): Implications for Scale of Internal Heterogeneities in Slope Turbidite Reservoirs

Ernesto Schwarz and R. William C. Arnott
University of Ottawa, Ottawa, ON

Channel 5 (Isaac Formation, Castle Creek, B.C., Canada) represents a long-lived transport and depositional pathway (channel-complex set) that accumulated ~100 m of mostly sand in a deep-marine slope setting. Channel 5 consists of sandstone-rich channel fills (grouped into channel complexes) interbedded with mudstone-rich, thin-bedded turbidites and debris-flow/slump deposits. These fine-grained deposits, which would form important permeability baffles and barriers (barrier-type facies), occur at different scales in Channel 5.

1) Laterally discontinuous (< 150 m long) mudstone-clast breccia layers with sandstone matrix and thinly bedded turbidite units (< 1 m thick) occur within channel fills (intrachannel). Breccias most probably form local baffle-type facies (retard fluid flow), whereas thin-bedded intervals represent local barriers.

2) Interchannel barrier-type facies consist of uncommon debrites (< 1.5 m, < 1 km long) and stacked thin-bedded turbidites (< 5 m thick). Typically these strata are eroded locally by later channel reactivation, and accordingly would not prevent completely pressure communication between adjacent channel fills within a channel complex.

3) Thick (5-11 m) debris-flow deposits and thin-bedded overbank units form uninterrupted units between channel complexes that extend across the study area (1.5-3 km). These units would form regional permeability barriers and as a consequence effectively compartmentalize individual channel complexes.

The good correlation between stratigraphic and depositional context and hierarchy of barrier-type facies in Channel 5 may help better predict the distribution and scale of internal heterogeneities and related connectivity in subsurface slope reservoirs (e.g. offshore West Africa and Brazil).