Article pubs.acs.org/EF
A Rheological and Chemical Investigation of Canadian Heavy Oils From the McMurray Formation Kejing Li,† Casey R. McAlpin,‡ Babajade A. Akeredolu,† Ala Bazyleva,† Kent J. Voorhees,‡ Robert J. Evans,∇ Michael Batzle,§ Matthew W. Liberatore,† and Andrew M. Herring*,† †
Department of Chemical and Biological Engineering, ‡Department of Chemistry and Geochemistry, and §Department of Geophysics, Colorado School of Mines, Golden, Colorado 80401, United States ∇ Microchem Technologies, Inc., Boulder, Colorado 80301, United States S Supporting Information *
ABSTRACT: The prediction of viscosity in the extraction of heavy and viscous oil resources is essential for the economically viable production of these resources. A rheological and chemical investigation of oils from the McMurray formation produced at different depths was undertaken. Chemical analysis using high-resolution time-of-flight mass spectrometry (TOF MS), Fourier transform infrared spectroscopy (FTIR), and nuclear magnetic resonance spectroscopy (NMR) suggested specific compounds representative of the compound classes observed in these heavy oils: [1] water, [2] sec-hexadecyl naphthalene, [3] 2,2′,5,5′tetramethyl-1,1′-biphenyl, [4] 1-methylanthracene, and [5] cyclopentylcyclopentane. All three analytical techniques detected the monoaromatic, diaromatic, and triaromatic ring hydrocarbons as being the most abundant species in this heavy oil. Specific molecules with intense FTIR modes near 1600 cm−1 and 1380 cm−1 were not identified, and these may account for unknown species in asphaltene fractions. Correlations between heavy-oil chemistry and its viscosity were built using a partial linear square fit (PLS) regression from vibrational modes in the FTIR spectra, predicting an inverse correlation between water and viscosity. oils.8 The influence of resins and asphaltenes and the inconsistencies of the SARA method possess significant disadvantages. Thus, more-detailed chemical information and a robust method to correlate the chemical and physical properties of heavy crude oil are needed. Among contemporary analytical technologies, advances in high-resolution mass spectrometry (MS) allow accurate elemental and chemical formula information to be obtained and derived from finite isotope combinations and exact mass determination.9 Although the mass range of asphaltenes has been debated in the recent MS literature,10−12 the identifiable molecular structures are not so controversial.4,13 Molecular structure identification generally requires intricate MS techniques, such as high-resolution and/or tandem MS, such as electrospray ionization/Fourier transform ion cyclotron resonance mass spectroscopy (ESI/FTICR MS).4,13,14 Soft ionization methods such as ESI, atmospheric pressure ionization, and laser desorption ionization (LDI), have been used to maintain the molecular ion information.4,10,13,14 While hard ionization such as electron ionization (EI) can be used to provide conformational information and confirm the hypothesized structures through predictable fragmentation. A thermal evaporator can be used to volatilize and crack heavy components of viscous hydrocarbon mixtures. All species, whether stable or unstable obtained from thermal desorption can be detected using a molecular beam mass spectrometer (MBMS) in which the molecular beam quenches the thermal energy of the species while also preserving reactive and
1. INTRODUCTION The efficient extraction of viscous and heavy oils would preferentially require a viscosity map of the resource, rather than more conventional geophysical information obtained from more-conventional seismic surveys. For this reason, it would be highly desirable to correlate the chemical and rheological properties of these nonconventional resources with in-field measurements. Compositional analysis of heavy oils remains a significant analytical challenge, because of the variation in sample origin and the chemical complexity of the oil. However, more-detailed knowledge of heavy-oil chemistry can enhance recovery from reservoirs, upgrading qualities, and improve environmental stewardship.1 Although separated fractions are desirable to give simple and accurate component information, the existence of different compound classes in heavy oil and the uncertainty in the results from common separation methods makes detailed petroleomic analysis difficult and inconsistent, especially when the separated subfractions still contain thousands of species, e.g., in the distillation cuts, or saturates, aromatics, resins, asphaltene (SARA) extractive analysis.2−6 Therefore, there is increasing interest to apply new methods of analysis to heavy oils, before or after separation, to achieve a greater understanding of heavy-oil chemistry, especially as it relates to its rheological properties. Correlations between SARA fractions and viscosity are somewhat successful in relating chemistry and rheology of light crude oils. However, SARA correlates with viscosity in only some cases for heavy oils. Previous rheological studies by Argillier et al. show a direct proportionality between asphaltene content and the complex viscosity.7 Further work by Hinkle et al. corroborates this claim, but further observes that resin content also contributes significantly to the viscosity of heavy © 2012 American Chemical Society
Received: April 11, 2012 Revised: June 8, 2012 Published: June 11, 2012 4445
dx.doi.org/10.1021/ef300608w | Energy Fuels 2012, 26, 4445−4453
Energy & Fuels
Article
condensable compounds.15 In this work, we report the use of LDI/TOF-MS and thermal desorption/EI/quadrupoleMBMS.8,16 This work assigns specific molecular constituents of the heavy oil from the MS using both techniques. Without tandem MS, spectroscopic methods are necessary to confirm the chemical nature of the predominant constituents, since more than one formula can be derived from IUPAC masses of the most-abundant isotopes. For example, a measured mass of 288.1105 amu can be from at least five formulas with a deviation of
