FIELD TRIP IN FORT MCMURRAY, ALBERTA
be higher than that of the mud-dominated IHS. The lowest porosity should present within the thick shale or mudstone interval. Thus,
Permeability: From the Kozeny-Carmen equation,
We know that the shape factor (which accounts for sort- ing and the tortuosity) could presumably be similar, but the surface area which considers the grain size and clay content underscores the influence of grain size. From the above equa- tion, it can be seen that a small difference in grain size would result in a considerable difference in permeability, potentially representing orders of magnitude.
So based on the porosity, grain size and clay content it follows that:
ers which act as flow barriers, the ratio of muddy to sandy layers sometimes exceeding 1, and its non-continuous pres- ence vertically. The reason is that the discontinuity of the sandstone only exists vertically but not laterally, suggesting that it could function as a lateral migration path for fluids owing to its relatively coarse grain sizes, good sorting, good roundness, and its estimated clay content of less than 1%. Another feature that I interpret is that the muddy layer act- ing as a vertical barrier could make the lateral migration or flow more efficient compared with the vertical flow, because the fluid would be subjected to a relatively high and stable driving pressure rather than decreasing driving pressure. Its continuity within the outcrop scale also is relatively good.
Flow unit with shale/mudstone: Strictly speaking it could belong to the flow unit, but it has obvious and significant negative properties related to potential fluid migration and performance. So considering potential for economic produc- tion, this flow unit should be avoided due to its small grain size and more than 95% clay content from the estimation.
Differences between the IHS Amphitheater outcrop and the Hangingstone outcrop
Stratigraphy, facies and flow unit continuity interpretation
At the Amphitheatre outcrop, the thickness of IHS was
observed to thin considerably from outcrop location � to �, moving south (Table 1). Precisely, the mud-dominated IHS
became nearly non-existent, not reaching the location of �. Only the thinner sand-dominated IHS presented there. This phenomenon might be due to different tidal influences and different tectonic activities acting on the two facies. The under- lying FA1 remained nearly the same in thickness between the two logs, as a result of similar depositional environments along that facies.
At the Daphne Island outcrop, the filled channel facies
thickened from location � to �, toward the west. And the thickness of the IHS facies became thinner that same southern
direction. It is probably because location � is near the chan- nel center which represents a deeper incision or truncation of the underlying IHS and that mid-channel feature could accumulate larger volumes of deposited sediment.
Flow units comparison
The following order is ranked from the most favorable to the lowest potential contribution to reservoir performance.
Flow unit within channel fill deposits: Its performance should be the best, which is demonstrated by the fact that the bitumen can directly leak off the surface once it is exposed due to its larger local grain size and thickness, and its estimated clay content of less than 1%. It is easy to predict its longitu- dinal continuity along the channel flow direction.
Flow unit with FA1: Its apparent properties include rela- tively large grain sizes, good sorting, good roundness, large thickness, less than 1% clay content from the estimation and relatively good continuity. These characteristics suggest rela- tively good flow and reservoir performance.
Flow unit with IHS: This sandstone could still represent an acceptable flow unit despite repeating mudstone interlay-
There are overlying shale intervals at the very top of both these outcrops. Even though these outcrops may represent the result of the similar stratigraphic stacking patterns and geological events, their thicknesses are different. There are typical IHS facies present underlying the shale intervals. The main difference between these two sets of IHS facies is that the Amphitheater outcrop is mud-dominated and the Hangingstone outcrop is sand-dominated.
Conclusions
1) The depositional environments that formed the McMurray Formation are mainly fluvial and tidal settings.
2) The facies vary considerably as a result of a set of different depositional settings; however, a regular sequence pattern could be correlated laterally.
3) Different facies correspond to different flow units. The favorable flow units for petroleum production are mainly the unit with channel fill deposits, the unit with cross bedded sandstones (FA1), and the unit with muddy and sandy interlayers (IHS).
4) Even though there are distinct heterogeneities within the McMurray Formation, the reservoir performance is still excellent due to the abundance of clean sandstones con- taining extremely high bitumen saturation and displaying large-scale lateral continuity.
References
Carrigy, M. A., 1959. Geology of the McMurray Formation. Geological Division, Memoir 1, Research Council of Alberta.
Ranger, M. and Gingras, M., 2010. Field Guide & Overview Geology of the Athabasca Oil Sands.
After receiving his first Master degree in petroleum geology at University of Alberta, Zexuan Wang currently conducts research in the field of deep marine seismic stratigraphy of the Gulf of Mexico as a current Masters student at University of New Orleans. His career goal is to work for an oil & gas company as a researcher. To achieve this, he always keeps an eye on PHD positions within some reservoir characterization- oriented research groups.
www.aipg.org
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