R.P.W. Stancliffe1 and Y.Y. Chen2
1Imperial Oil Kearl Geoscience Team, Calgary, Alberta, Canada
2ExxonMobil Exploration Company, Biostratigraphy Group, Houston, Texas, USA
Kearl is a potential oil sands mine located in the Athabasca region of northeastern Alberta, Canada. The bitumen pay resides in the clastic McMurray Formation, inferred to be in the Aptian, Lower Cretaceous. The sedimentary package is regionally mapped as a fluvial to estuarine/marine environment of deposition, but a detailed facies and sequence stratigraphic model only recently has been developed from well logs, core and 2D seismic. Results show that there are some sandstone on sandstone contacts and a reduced suite of trace fossils in the McMurray Formation at Kearl. To increase the confidence in the interpretation, three cores were sampled for palynology and palynofacies analysis. Previous palynofacies work at IOL Cold Lake found that bitumen can hinder the recovery of organic material. To increase the chance of success, care was taken in selecting 37 samples of varying bitumen saturation, sediment grain size, and from within each interpreted sequence.
Analysis of the palynomorphs and organic matter recovered determined that the McMurray Formation in this area is Aptian in age: between 120.98 - 112.51 Ma. based on the SEPM Special Publication Number 60 time scale and cycle charts. Five third-order sequences are recognized along with evidence that higher order sequences may be present. Using a model developed initially for Cenozoic palynofacies, 15 depositional environments are identified ranging from braided river through coastal plain to estuarine and open marine. These are used to differentiate distinct palynofacies groupings, and the two pay intervals can now be mapped despite their sandstone on sandstone contact. Reworked Oxfordian dinoflagellate cysts are recorded, for the first time, in the lowest two sequences, but no evidence is found of palynomorphs of Barremian age, reported from competitor acreage. The overlying formation was confirmed to be the fully marine Wabiskaw Member of the Clearwater Formation deposited during the Lower Albian.
Palynofacies data are further integrated into climate and ocean models. Results suggest that during the Aptian the study area was on the edge of a shallow intercontinental seaway, which initially exited north into the Arctic Ocean. The area was microtidal and the sea temperature was temperate, even though the location was ~450 miles south of the Arctic Circle. As the sediments became more marine, the climate became wetter, though still seasonal. There was little chance of hurricanes, and the weak prevailing winds could have been from the Northeast as well as the Southwest. The climate and biota are therefore significantly different from the Mississippi River analog used by some for the McMurray Formation, environment of deposition. Also, the sparse and impoverished trace fossils found at Kearl are considered to be stressed by factors other than the marine conditions and climate, which are now known to be benign.
This palynofacies framework is being used for future development work at Kearl along with the new environment of deposition model. These concepts now will be used to test future sequence stratigraphic correlations over this and other parts of the Athabasca Basin.
AAPG Search and Discovery Article #90075©2008 AAPG Hedberg Conference, Banff, Alberta, Canada