Comparative Analysis of the Geologic Setting, Sequence Stratigraphy and Reservoir Architecture of the Canadian Athabasca Tar Sands and the Venezuelan Orinoco Heavy Oil Belt

Suter, John R., ConocoPhillips, Houston, TX

The Athabasca Tar Sands of Canada and the Faja Petrolifera del Orinoco, or Orinoco Heavy Oil Belt, of Venezuela contain enormous quantities of bitumen and heavy oil. The over­all Athabasca resource is estimated at about 1.7 trillion barrels of bitumen, with some 935 billion barrels in the lower Cretaceous McMurray Formation. Around 1.4 trillion barrels of heavy and ultra-heavy oil occur in the Early Miocene Oficina Formation of the Orinoco Heavy Oil Belt. ConocoPhillips operates or participates in SAGD production (Surmont) and mining (Syncrude) from the McMurray Formation and multilateral cold horizontal well production from the Oficina Formation (Petrozuata, Hamaca). Despite some obvious differences, the McMurray and Oficina show many similarities in their geologic setting, sequence stratigra­phy, and reservoir architecture. Both of these huge accumulations lie on the peripheral bulges of foreland basins, with their principal sediment sources in granitic shield terrains. Neither has been buried to substantially greater depths than present day; consequently their unconsolidated, dominantly quartzose reservoir sands have extremely good permeabilities and porosities. The hydrocarbons of the respective deposits were generated from prolific shallow marine source rocks, and emplaced as conventional oils into broad, low-amplitude traps with significant or dominant stratigraphic components. Subsequent biodegradation and/or water washing produced the present-day bitumen and heavy oils. Sedimentologic, ichnologic, and biostratigraphic analyses of cores and outcrops, coupled with interpreta­tions of extensive well log and 3D seismic datasets, reveal that both formations comprise non-marine to marginal marine deposits, with principal reservoir facies mainly channelized fluvial, tidal-fluvial, and estuarine deposits within incised valley complexes. Understanding and predicting reservoir heterogeneity and compartmentalization within this overall frame­work is crucial to the ongoing and future success of projects within both the Venezuelan Heavy Oil Belt and the Athabasca Tar Sands.