Abstract
Detailed examination of the mineralogy of the Cretaceous McMurray Formation within a facies framework is used to assess the use of natural gamma-ray spectroscopy (NGS) and a pulsed neutron generator (PNG) tool in delineating variation in clay mineral and bitumen contents. Characterization of the mixed-layer (interstratified) clay phases in the McMurray Formation provides an improved understanding of clay interaction in bitumen processing and tailings settling behavior, important for mine planning and tailings remediation schemes. Mineral diversity in the McMurray Formation was determined on facies attributed samples using whole rock X-ray diffraction (XRD), cation exchange capacity (CEC) measurements, elemental analysis (XRF), clay size fraction (<2 µm) XRD analysis, reflected light microscopy, and cryogenic-scanning electron microscopy (cryo-SEM). Kaolinite was ubiquitous in the entire McMurray Formation with lower and middle McMurray Formation sediments also containing mixed-layered illite–smectite (I-S) with a low expandability≈ 20–30%. Upper McMurray Formation sediments by contrast had higher expandability (≈ 60–70%). In floodplain sediments of the lower McMurray Formation an additional clay mineral was quantified as a kaolinite-expandable mixed-layer (clay) mineral. The associated CEC values of this mineral are 10 times the baseline for the McMurray Formation. NGS spectra from cores showed that yields of potassium (K), uranium (U), and thorium (Th) had distinct facies associations, correlated with a clay mineral signature. The resultant indicator is capable of highlighting zones within an oil sands ore body that are empirically known, by industry, to process poorly through extraction plants. A bitumen indicator from the carbon yield derived from a PNG logging tool assesses bitumen content. NGS and PNG allow a full assessment of clay mineral (fines) and bitumen profiles, with the future prospect that these techniques could be used to assess ore and tailings behavior in near-real time.
Highlights
Heavy-oil and oil-sands represent an approximate 1.7 trillion-barrel reserve [17,19,1,25] of extractable hydrocarbons from the Athabasca oil sand deposit in western Canada
Note the 06,33 band which appears to be a doublet in the tidal channel sample with a component that can attributed to kaolinite (1.488 Å) but is broadened and shifted to larger d-spacing (1.495 Å) in the back-swamp sample i.e. a position that is intermediate between kaolinite and montmorillonite
The oriented clay size fraction traces show the relatively unresponsive clays in the tidal channel sample compared to the clays in the back swamp sample where kaolinite/expandable and vermiculitic clays are evident from the various responses and changes between airdried, ethylene glycol solvated and heated X-ray diffraction (XRD) traces
Summary
Heavy-oil and oil-sands represent an approximate 1.7 trillion-barrel reserve [17,19,1,25] of extractable hydrocarbons from the Athabasca oil sand deposit in western Canada. Open pit bitumen mining and tailings remediation operations occur at many localities north of Fort McMurray, Alberta, Canada. Prior focus has been placed on the broad geochemical aspects of the oil-sands [17] and have, via biomarker [1] and geochemical means [41], tied the biodegraded bitumen to source rocks in the eastern Canadian Rocky Mountains, with the McMurray Formation charged by oils from the Devonian/Carboniferous Exshaw Shales. The geological framework of the McMurray Formation across most of the areal extent of the bitumen mining operations in Alberta has been synthesized by Hein et al [24] where much work has relied on field, core, and well-log analysis
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