A key aspect that affects the prospectivity of Mannville heavy oil petroleum systems (Fig. 17) is the heterogeneity within KU55933 (Fustic et al., 2012). In subsurface production, oil is recovered with paired subsurface horizontal wells using the steam assisted gravity drainage (SAGD) technology. Steam injected in the upper well liquefies the oil and allows it to drain into the lower well and then pumped to the surface. Extensive muddy inclined heterolithic layers (IHS), associated with point bars (Fig. 17C) are barriers that impede steam injection and inhibit flow of the oil, and prediction of these barriers is thus critical (Thomas et al., 1987). In areas where oil sands are mined, the IHS mudstone layers slow the mining operation, as they do not contain oil and must be excavated and disposed of before processing of sands can resume. Understanding that Mannville point bars are formed by a continental-scale river is reflected in the large-scale of channel belts. As a consequence, individual inclined layers are laterally more extensive than the typical well spacing, thus allowing them to be correlated and mapped explicitly, versus modeled stochastically (e.g., Fustic et al., 2013). Muddy inclined drapes may form as counter-point bars in upstream reaches (Smith et al., 2009) and by tidal processes in more downstream reaches (Thomas et al., 1987). In the more-distal reaches of the ancient river systems, within the backwater limit, tides were more important as reflected in the abundance of bioturbation and other marine indicators. Given the continental scale of the river systems, gradients were certainly low, and probably on the order of 10− 4 (Musial et al., 2012). Backwater lengths would correspondingly have been on the order of 400 km, allowing tidal effects to propagate far upstream. Regional paleogeographic maps of Smith (1994) show that the heavy oil deposits in the McMurray were deposited within a few hundred kilometers of the shoreline and were thus likely within the backwater length of the system. Blum (2015) in contrast, used 3D seismic images to document the migration patterns of Mannville channels and suggested that the high sinuosity and the high degree of lateral migration of meanders require the channels to have been landward of the backwater reach and thus beyond the limit of tidal influence, although this is incompatible with the observation of marine microfossils in associated mudstone drapes.
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