Anatomy and Evolution of a Slope Channel-Complex Set (Neoproterozoic Isaac Formation, Windermere Supergroup, Southern Canadian Cordillera): Implications for Reservoir Characterization

Abstract

A detailed architectural analysis was conducted in Isaac Unit 5 of the Isaac Formation in the Castle Creek area (east-central B.C., Canada). Isaac Unit 5 developed within a turbidite-dominated slope system on the Neoproterozoic passive margin of western North America where sediment gravity flows and mass movements were common.Isaac Unit 5 crops out over a 3.5-km-long section oriented oblique to mean paleoflow direction and represents a long-lived pathway for transport and deposition that accumulated , 100 m of mostly sand in a deep-marine slope setting. It consists of three stacked, high net-to-gross channel-complex fills (8-30 m thick) that correspond to shorter-term flow conduits, which, in turn, are capped by mudstone-rich units. Fine-grained conglomerate and sandstone beds deposited from high-concentration sediment flows constitute most of channel-complex fills. In addition, muddy debrite and slump deposits occur, but although laterally extensive, are volumetrically minor. Laterally persistent, thin-bedded strata (4-20 m thick) composed mostly of Bouma Tc-e turbidites occur at the top of each channel complex and indicate episodes of local complex abandonment (interchannel complex deposition).Different kinds of channel-fill elements were identified within Isaac Unit 5, each characterized by a unique combination of facies assemblage, internal geometry, and bounding surfaces. Most commonly, channel fills consist of amalgamated, thickbedded, normally graded sandstone (Bouma Ta and Tab divisions) associated with backfilling processes. Poorly stratified mudstone-clast breccia, associated with Ta beds and dune cross-stratified sandstones occur in channel fills that exhibit aggradational and laterally migrating stacking patterns. Inner-bend levee deposits are associated with this type of channel fill. Channel fills with inclined sandstone-and mudstone-rich strata, on the other hand, relate to non-aggradational, high-sinuosity channel conditions that developed during gradual abandonment of the pathways for coarse-sediment transport. In contrast, sudden deactivation of these pathways, most probably related to abrupt updip channel avulsion, led to accumulation of structureless sandstone passively filling the deactivated thalweg.In terms of hydrocarbon reservoir analogues, each of the five different channel-fill elements have unique reservoir attributes (connectivity and continuity), amalgamated and poorly stratified elements having the best (excellent to good) reservoir attributes. Due to high amalgamation at channel-fill scale, channel complexes would represent individual fluid-flow units where only laterally discontinuous permeability barriers (, 500 m long) are present. On the other hand, extensive thin-bedded elements and muddy debrites constitute kilometer-scale barrier-type facies that would effectively compartmentalize channel complexes within the channel-complex set. Strata of Isaac Unit 5 document the detailed stratigraphic complexity, evolution, and reservoir characterization that can be expected in turbidite-...

Genesis and character of thin-bedded turbidites associated with submarine channels

“…Outcrop studies of internal levees (Kane and Hodgson, 2011) and depositional terraces (Hein and Walker, 1982;Schwarz and Arnott, 2007), and cores from internal levee and depositional terrace environments in modern depositional systems (Babonneau et al, 2010;Paull et al, 2013), show that the sedimentary facies in these systems are superficially similar and both are composed of thin-bedded turbidites ( Table 1). The major difference is that depositional terraces (and sandstone beds within them) do not diminish in thickness away from the adjacent channel.…”

“…as well as the Isaac Formation of the Windermere Supergroup in Canada(Schwarz and Arnott, 2007) where they have been termed inner bend levees although they show no evidence of a tapering geometry; depositional terraces on the inner bend of a sinuous channel are likely deposited on point bars created by the continuous migration of a channel (analogous to deposition on fluvial point bars)(Schwarz and Arnott, 2007). A subsurface example where depositional terrace facies may have been penetrated occurs in the Magnolia field in the Gulf of Mexico Kane et al (2012).…”

Evolution of deep-water stratigraphic architecture, Magallanes Basin, Chile

“…Pickering et al (1995) applied an architectural element approach to the 2-D and 3-D expression of deep-water architectural bodies. The convention of characterizing 2-D cross sections of channel-form and sheet-like sedimentary bodies within a hierarchy originated from petroleum-related research in the 1990s and appeared in the literature soon thereafter (Beaubouef et al, 2000;Campion et al, 2000;Gardner and Borer, 2000;Grecula et al, 2003;Schwarz and Arnott, 2007;Prelat et al, 2009;McHargue et al, 2011). Architectural elements in this approach typically cluster with similar elements collectively making up a complex (e.g., channel elements and channel complexes).…”

Sedimentology, architecture, and sequence stratigraphy of coarse-grained, submarine canyon fills from the Pleistocene (Gelasian-Calabrian) of the Peri-Adriatic basin, central Italy

“…Sediments similar to those occurring within LF-B have been reported in numerous publications (e.g. Mutti, 1977;Bruhn and Walker, 1997;Hickson and Lowe, 2002;Beaubouef, 2004;Butterworth and Macdonald, 2007;Kane et al, 2007;Navarro et al, 2007;Schwarz and Arnott, 2007) and considered to form from levee-overbank deposition of moderateto low-concentration turbidity currents that spilled out of the confinement of an adjacent channel. Palaeocurrent indicators, indicating flows directed away from the channel complexes, further support a levee interpretation of this lithofacies.…”

“…At a finer scale, however, deep-water canyon and channel fills reveal a high level of architectural complexity that is very difficult to assess with conventional exploration datasets and creates large uncertainties in predicting the ultimate reservoir quality. In this context, representative outcrop analogues have proved to be crucial to improve the general understanding of compartmentalisation commonly encountered within subsurface reservoir systems (e.g., Cronin and Kidd, 1998;Eschard et al, 2003;Beaubouef, 2004;Sullivan et al, 2004;Fugelli and Olsen, 2005;Hubbard et al, 2005;Satur et al, 2005;Schwarz and Arnott, 2007;Thurmond et al, 2007;Labourdette et al, 2008;Fildani et al, 2009;Figueiredo et al, 2010;Kane et al, 2010;Labourdette and Bez, 2010;Pyles et al, 2010). Unfortunately, finding such suitable exposures is commonly difficult because many outcrops are discontinuous, faulted, or poorly exposed.…”