FIELD TRIP IN FORT MCMURRAY, ALBERTA
the clay content in the clean sandstone as almost 5%, in the mudstones as almost 95%, and in the interlayers as almost 50%. The overall trend is inversely proportional to the trend of bitumen saturation.
Facies description
Based on three kinds of particular lithology and sedimen- tary structure features, the reservoir facies generally include FA1, Inclined Heterolithic Stratification (IHS), and filled channels.
FA1: This lithology is sandstone. The grain size in this facies ranges from very fine to medium, but typically is dominated by finer grain sizes combined with good sorting, good roundness, and little clay content. The sedimentary structures within this part are mainly planar cross bedding, trough cross bedding, ripple lamination and mud rip-up clasts.
IHS: The lithology represents repeating sets of sandstone and mudstone layers. The grain size of muddy layers is usually clay. In contrast, the grain size of the sandy layers is usually fine to coarse size combined with good sorting, good roundness, and little clay content. The sedimentary structures within this part represent primarily lateral accretions with very low dip and bioturbation leading to the mud-filled burrows pierc- ing into the underlying sandy layer. Sometimes differential weathering could be seen as an apparent result of differences in the weathering resistivity characteristics.
Filled channel: This lithology is sandstone. The grain sizes in this facies typically are dominated by coarse or very coarse sizes combined with moderate sorting, moderate roundness, and little clay content. The sedimentary structures within this part were difficult to observe due to the very coarse grain sizes and the transverse cross section we were facing. Only one cross bedding feature was observed.
Based on this single lithology and sedimentary structure features, the non-reservoir facies usually include the thick shale or mudstone interval.
Shale/mudstone interval: The grain size in this facies is very small and is full of clay with little porosity, permeability and oil saturation.
Facies vertical continuity
The individual facies are roughly continuous in each log. Despite the occasional unexpected laminations that were pres- ent, the laminations do not affect the overall vertical distribu- tion of facies. At the Amphitheatre outcrop, the FA1 facies is continuous within the lower part. The IHS facies is continuous within the upper part above the FA1 and alternates from sand- dominated to mud-dominated. The shale facies is continuous at the very top above the IHS. At the Daphne Island outcrop, the FA1 was hardly seen. The sand-dominated IHS was continuous until encountering the sequence boundary which represents the underlying IHS facies that was truncated by the channel fill deposits. Meanwhile, the filled channel facies is only continuous for several meters, and is covered by the paleosol at the head.
Facies lateral continuity and correlation
Because of the considerable thicknesses observed in all the facies and the proximity of the logged sections within the same outcrop, the facies should be continuous laterally, but needed to be confirmed by the correlation. To perform the correlation, the first thing is to determine the datum level that matches the elevations of the logs. For the Amphitheater outcrop, the shale capstone marks the horizontal maximum flooding sur-
face that was used for this purpose. For the Daphne Island, the paleosol on the top was used for correlation.
Outcrop descriptions (details in Table 1)
During the logging, the elevations initially recorded were actually measured along the dip instead of along the vertical profile. Thus, I converted these measurements into vertical elevations by estimating the dip of each outcrop. Some linea- tions containing very coarse or even pebble quartz grains and some clay layers were observed to exist sporadically. But due to the ignorable influence on overall reservoir production, these variations were not considered in the facies distribution.
The Amphitheatre outcrop represents the well-exposed
middle McMurray formation. The outcrop identified as � was logged at the north, and � was logged to the south. The distance between these two logs is roughly 300 meters.
The well-exposed Daphne Island outcrop represents the
lower McMurray formation. The outcrop � was logged at the east, and � was logged at to the west. The distance between these two logs was roughly 150 meters.
The Hangingstone outcrop was not well logged due to inclement weather limitations.
Discussion Depositional setting interpretation
Based on the observed petrophysical properties of differ- ent outcrops, the various depositional environments could be interpreted by analysis of the lithologies, grain size and sedimentary structures.
The middle McMurray Formation: The IHS which presents here represents the subaerial point bar within the estuarine system containing brackish water. The FA1 which always underlies the IHS here indicates a subaqueous dune and bar setting, and the reverse ripple lamination and reversed cross bedding represent a strong tidal influence (Rangers and Gingras, 2010).
The lower McMurray Formation: There are several meters of distinct horizontal paleosols covering the top of lower McMurray formation, which should be interpreted as alluvial plains. The large scale, very coarse grained migrating channel fill deposits could be regarded as incised valleys belonging to the fluvial system, and are stratigraphically consistent with the underlying sediments that were truncated due to sea level regression (lowstand). That angular unconformity indicates a sequence surface. Below the angular unconformity, the IHS facies represents a similar estuarine system as that observed within the middle McMurray Formation (Rangers and Gingras, 2010).
Flow units defined
There are mainly four types of flow units defined that indicate variable flow performances respectively. These units include filled channel facies, FA1 facies, IHS facies, and the unit with shale/mudstone intervals.
Porosity and permeability interpretation
Porosity: This is reflected by the combination of grain sizes and clay content because of the proportional relationship between porosity and grain size. The overall porosity should be highest within the filled channel facies. The overall poros- ity of FA1 also should be considerable. The overall porosity of the sand-dominated IHS facies should be less, but still
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