Cretaceous heavy oils

Tn this work the sulfur compounds in the gas oil of three Cretaceous - heavy oils from the edge of the Alberta sedimentary basin were investigated. These crude oils were obtained from the Athabasca, Cold Lake, and Lloydminster deposits and are believed (I) to belong to the same oil system which implies like modes of origin. The geographic location of these deposits is shown in Figure 1. This investigation was conducted to develop the analytical capability used to follow the maturation of the sulfur compounds in these oils (2). 

Sulfur compounds in the gas oil fractions from two bitumens (Athabasca oil sand and Cold Lake deposit)> a heavy oil (Lloydminster) from Cretaceous reservoirs along the western Canada sedimentary basin, and a Cretaceous oil from a deep reservoir that may be mature (Medicine River) are investigated. The gas oil distillates were separated to concentrates of different hydrocarbon types on a liquid adsorption chromatographic column. The aromatic hydrocarbon types with their associated sulfur compounds were resolved by gas chromatographic simulated distillation and then by gas solid chromatography. Some sulfur compounds were further characterized by mass spectrometry. The predominant sulfur compounds in these fractions are alkyl-substituted benzo- and dibenzothiophenes with short side chains which have few dominant isomers. 

The tar sands situated in Alberta consist of oil-bearing sandstones. Surface exposures occur in parts of the Athabasca deposit, but much of the deposit lies 100 m or more beneath the surface. Oil present in these Lower Cretaceous sandstone deposits is very viscous, thick, and partially oxidized so that it cannot be recovered by pumping alone. Hence, the term tar or bitumen describes this heavy oil fraction, which averages about 12% ranging up to as much as 18% of the deposit by weight. Deposits with less than 2-3% bitumen are excluded from the reserve data given in Table 17.4. 

Figure 14. Variation in the carbon number distribution of the bicyclic terpenoid sulfides as a function of depth as shown by the m/z =183 fragmentograms from the SIR-GC/MS experiment. All traces are normalized to the most abundant peak. The oils vary from a heavy Cretaceous oil (Lloydminster) to a light Devonian oil (Leduc). Increasing thermal maturity results in the gradual loss of the isoprenoid side chain until in the Leduc the C13 compound dominates the distribution. Note the intensity distribution of the peaks. Minima occur at C12, C17, and C23. (Reproduced from Ref. 10 with permission. Copyright 1986, Pergamon Journals Ltd.)...

Tar sand deposits in Venezuela occur in the Officina/Tremblador tar belt that are believed to contain bitumen-impregnated sands of a similar extent to those of Alberta, Canada. The Guanaco Asphalt Lake occurs in deposits that rest on a formation of mid-Pliocene age and is closely associated with the Guanaco crude oil field that produces heavy crude oil from shale and fractured argillite of the Upper Cretaceous group. The tar sands of the Orinoco deposit are located along the southern flanks of the eastern Venezuelan basin. 

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