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The detailed chemical composition of crude oil in subsurface reservoirs provides important information about reservoir connectivity and can potentially play a very important role for the understanding of recovery processes. Relying on studying produced oil samples alone to understand the rock-fluid and fluid-fluid interactions is insufficient as the heavier polar components may be retained by tight reservoirs and not produced. These heavy and polar compounds that constitute the resin and asphaltene fractions of crude oil are typically present in low concentrations and yet are determining for the physical-chemical properties of the oil because of their polarity. In order to obtain a fingerprint analysis of oils including polar compounds from different wells, the oil content of drill cores has been extracted and analyzed. Infrared spectroscopy has been used to perform chemical fingerprinting of the oil extracted from drill cores sampled in different geographical locations of the Danish North Sea. Statistical analysis has been employed to identify the chemical differences within the sample set and explore the link between chemical composition and geographic location of the sample. A principal component analysis, based on spectral peak fitting in the 1800-1400 cm-1 range, has allowed for statistical grouping of the samples and identified the primary chemical feature characteristic of these groups. Statistically significant differences in the quantities of polar oxygen- and nitrogen-containing compounds were found between the oil wells. The results of this analysis have been used as guidelines and reference to establish an express statistical approach based on the full-range infrared spectra for a further expansion of the sample set. The chemical information presented in this work is discussed in relation to oil fingerprinting and geochemical analysis.

Petroleum analysis presents many unique challenges as a result of the chemical complexity of petroleum composition. In the present work a novel chromatographic material has been developed and utilized to separate crude oils. A total number of 13 fractions have been collected using different solvent mixtures with increasing proportions of chloroform. UV and IR spectroscopy has been employed to show that the size of the aromatic ring system increases and the extent of molecular branching decreases with elution gradient. This observation suggests that intermolecular non-covalent π-π interactions between the material and the sample molecules are critical to the separation. This novel method for sequencing petroleum molecules based on the size of the aromatic ring systems has been applied to the 2D off-line analysis of crude oil samples. The 2D on-line separation (NPLC × NPLC) has been simulated by 2D off-line separation. A total number of 38 fractions have been obtained with two SPE columns based on the molecular branching and the aromatic ring system size. The chemical information obtained in this study of North Sea crude oil is complementary to standard SARA analysis. The material supports a potential solution to overcome the challenges of tandem NPLC and has demonstrated a new approach to the separation of crude oils into discrete compound classes.

A systematic study of the rotation constants, vibration–rotation constants and quartic centrifugal distortion constants has been performed for furan, pyrrole, thiophene, both oxazoles and thiazoles, 1,2,4- and 1,2,5-oxa- and -thiadiazoles, 1,2,5-selenadiazole, and several 6-membered heterocycles (azines). The main study used cc-pVTZ basis sets. There is a very close correlation between the observed constants above and those calculated, especially using the cc-pVTZ + B3LYP procedures; some trends in these appear on substitution of HC by N in the azoles. This strong correlation between experimental values and this theoretical procedure is also apparent with vibrational differences in rotation constants, all over large numbers of measured values. However, a small number of calculated values do not correlate well with experiment; this may be a result of some of the experimental values being subject to resonance perturbations not included in the calculations. In general, a TZ2P basis set with B3LYP methodology, and cc-pVTZ results with MP2 methodology, lead to correlations of similar quality, but the latter require markedly more computing power. The present study draws attention to a tetrad in the IR spectrum of 1,2,5-oxadiazole, where further analysis is necessary.

The high-resolution infrared absorption spectrum of an equilibrium mixture of HCN and HCl in a static gas long-path absorption cell is recorded in the 2500 2900 cm(-1) spectral region at 205 K. The spectrum shows rovibrational structure which has the typical appearance of a parallel band of a linear molecule and is assigned to the intramolecular H-Cl stretching vibration band upsilon(2) of the linear HCN-(HCl)-Cl-35 heterodimer. The rovibrational analysis of the band yield a band origin upsilon(0) of 2779.0968(12) cm(-1) together with a value for the upper-state rotational constant B' of 0.067722(2) cm(-1). The observed red shift of 107 cm(-1) for the upsilon(2) band of HCN- (HCl)-Cl-35 relative to the H-Cl stretching vibration band of monomer (HCl)-Cl-35 is in excellent agreement with results from the MP2/ 6-311++G** level of theory. The value of the upper-state rotational constant shows that the intermolecular hydrogen bond shortens by 0.022 Angstrom upon intramolecular vibrational excitation of the upsilon(2) mode. (C) 2004 Elsevier B.V. All rights reserved. (Less)

The high-resolution far-infrared spectrum of the intermolecular HC1 libration band v(4)(1) of the OC-H(35)C1 heterodimer is recorded in the gas phase by means of Fourier transform IR spectroscopy in a static multipass absorption cell at 137 K using a synchrotron radiation source. This is the first direct observation of an intermolecular vibration band of the OC-HC1 dimer in the gas phase. The rotational structure of the band has the typical appearance of a perpendicular band of a linear polyatomic molecule. The structure is analyzed to yield the band origin nu(0) = 201.20464(27) cm(-1) together with values for the upper state rotational constant, the upper state quartic and sextic centrifugal distortion constants, and the l-type doubling constant. The determined values for the rotational constant and the centrifugal distortion constants are used to obtain a Morse potential for the stretching of the intermolecular distance. The results are compared to the results from quantum-chemical calculations. (Less)

The high-resolution infrared absorption spectrum for (HCN)2 in the spectral region 3100–3300 cm−1 is recorded in a static multipass cell at 240 K under equilibrium conditions. The spectrum shows extensive rovibrational structures which are due to the bound C–H stretching vibration band ν2 of (HCN)2 and several hot bands associated to ν2. We manage to assign 63 new rovibrational transitions [P(97) to R(98)] associated with the ν2 band leading to an extended analysis of the ν2 band. This enables the assignment of 60 rovibrational transitions associated with the hot band ν2 + ν91 − ν91 in (HCN)2 together with the first rovibrational analysis of this hot band. The determined positive value of the anharmonicity constant X2,9 of 0.2569(13) cm−1 indicates that the intermolecular low-frequency bending vibration ν91 increases in frequency upon simultaneous excitation of the ν2 mode. This result confirms that the HCN dimer is stiffer and more tightly bound upon vibrational excitation of the bound C–H stretching mode.

A total of six high-resolution FT-IR spectra for trans-glyoxal-d2, trans-glyoxal-d1 and trans-glyoxal-13C2 were recorded with a resolution ranging from 0.003 to 0.004 cm−1. By means of a simultaneous ground state combination difference analysis for each of these isotopologues using the Watson Hamiltonian in A-reduction and Ir-representation the ground state rotational constants are obtained. An empirical equilibrium structure is determined for trans-glyoxal using these experimental ground state rotational constants and vibration–rotation interaction constants calculated at the CCSD(T)/cc-pVTZ level of theory. The least-squares fit yields the following structural parameters for trans-glyoxal: re(C–C) = 1.51453(38) A, re(C–H) = 1.10071(26) A, re(CO) = 1.20450(27) A, αe(CCH) = 115.251(24)°, and αe(HCO) = 123.472(19)° in excellent agreement with theoretical predictions at the CCSD(T)/cc-pVQZ level of theory.