Molecular Simulation of Resin and the Calculation of Molecular Bond Energy.

In this study, average structural characteristics of amber were researched and used as an example to establish the three-dimensional (3D) average structure of resin. Two coal samples containing solid amber were collected from Fushun and Hunchun in Northeast China, from which pure amber samples were separated and resin was extracted. Solid-state nuclear magnetic resonance (13C NMR) spectroscopy was used to obtain structural information of amber, and matrix-assisted laser desorption ionization time-of-flight mass spectrometry was performed on the resins to determine their molecular mass. The results of these studies revealed that the average structure of amber was dominated by cycloalkane, with a small amount of aromatic carbon, and there were almost no aliphatic chains in the structure. The molecular masses of the compounds in the resin were mainly in the range 99-750 Da, and the average molecular mass was ∼370 Da. To characterize the resin chemical structure, two 3D molecular models based on density functional theory were established taking amber as the example, and the relevant molecular bond energies were calculated. Based on these models, the interactions among the components in oil were studied, and the binding energies of the different molecules were calculated. In summary, in this study, amber was used as a medium to establish an accurate molecular model of resin and proved that compared to hydrocarbon compounds, resin molecules were more likely to interact with bitumen.

Simultaneous determination of compound-specific isotopic compositions of acyclic isoprenoids and n-alkanes in light crude oil.

Stable carbon and hydrogen isotope ratios of individual n-alkanes and acyclic isoprenoids are important tools in petroleum geochemistry. However, the analysis requires baseline separation and peak profiles using gas chromatography-isotope ratio mass spectrometry to obtain accurate compound-specific isotope data. Time-consuming isolation or purification is typically conducted to separate the compounds to avoid co-elution with other compounds or matrices in crude oils. We developed a simple gas chromatography separation method to simultaneously measure the compound-specific carbon or hydrogen isotope compositions of n-alkanes and acyclic isoprenoids. It was achieved by direct injection of the whole crude condensate and light oil or the saturated fractions of different types of crude oils using a 60 m DB-17ms column. This method simplifies the pre-treatment of compound-specific isotope analysis, saves manpower and time, and reduces the use of organic solvents to be more environmentally friendly.

Characterisation of copal resin and amber by negative-ion electrospray ionisation Fourier transform ion cyclotron resonance mass spectrometry.

Copal resin and amber from Columbia were analysed by negative-ion electrospray ionisation (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), with particular focus on polar compounds with relatively high molecular weights. A total of 4038 and 2755 compounds were identified between m/z 150 and 1,000 in the spectra of the copal resin and amber DCM extracts, respectively. The CHO classes were the most abundant species in the detected polar compounds. The petrochemical process of converting copal resin to amber is accompanied by evaporation and dispersion of volatile molecules and polymerisation of relatively smaller molecules. Thus, the most abundant compounds in copal resin comprised more than one C5 basic unit compared to amber, and the relative abundances of compounds with a high number of carbon and oxygen atoms in amber were higher than those in copal resin. There were strong positive correlations between the double-bond equivalence (DBEav ) values and the number of oxygen atoms in both samples. The slopes and y-intercepts of the linear relationship indicated that the C5 pentadienoic acid is the basic structure of heteroatom compound molecules in copal resin and amber. FT-ICR MS analysis focuses on the characterisation of heteroatom compounds with relatively high molecular weight and is helpful to provide supplementary information on the origin and evolution of complex organic mixtures such as copal resin and amber at the molecular level in a fast and convenient way.

Geochemically Distinct Oil Families in the Gudong Oilfield, Zhanhua Depression, Bohai Bay Basin, China.

Twenty crude oil samples were obtained from the Gudong Oilfield and their organic geochemical characteristics were analyzed. The oil samples were classified into three families by hierarchical cluster analysis and principal component analysis based on 13 source-related and depositional environment-related biomarker parameters. Oils in family I have low ratios of C19/C23 tricyclic terpanes and C24 tetracyclic terpane/C26 tricyclic terpanes, and relatively high ratios of steranes/hopanes and C30 4-methylsteranes/ααα20R C29 sterane, thus indicating that microalgae were the dominant organic matter input for the source rocks of family I. The gammacerane/C30 hopane ratios are higher than that of family II and family III, whereas the C35/C34 homohopane ratios are lower, thus indicating a suboxic, brackish water environment for the source rocks. The inferred source rock is the first member of the Shahejie Formation in the Huanghekou Sag. Family II is characterized by high ratios of C19/C23 tricyclic terpanes and C24 tetracyclic terpane/C26 tricyclic terpanes but relatively low ratios of steranes/hopanes and C27/C29 αααR steranes. These findings suggest that the original organic matter of the source rocks had a greater contribution from terrigenous higher plants than from microalgal. The relatively low ratios of gammacerane/C30 hopane and C35/C34 homohopane suggest that the source rocks were deposited in an oxic environment with a low salinity, thus corresponding to the Dongying Formation in the Huanghekou Sag. Family III oils have high C27/C29 ααααR steranes ratios and low C30 4-methylsteranes/ααα20R C29 ratios, which indicate the contribution of microalgae (especially zooplankton algae) to the source rocks. The relatively high abundance of C35 homohopane and low gammacerane/C30 hopane ratios suggest a weakly reducing condition with low salinity, which is in accordance with the third member of the Shahejie Formation in the Gunan Sag. The C31S/(S + R) homohopane ratios imply that oil samples in this study are in the mature stage, although the ratios of C2920S/(20S + 20R) and C29ßß/(αα + ßß) steranes suggest that the maturity of family II is higher than that of family I and family III.

Separation of crocetane and phytane and measurement of their compound-specific carbon isotopic compositions.

Crocetane and phytane are two isoprenoids isomers with similar molecular structures and often present together in methane-seep sediments and some Palaeozoic crude oils. Their commonly co-elution on gas chromatography is challenging for quality and quantity analysis, making it impossible to determine their compound-specific isotopic composition, and thus, insight their geological and geochemical significance. A new gas chromatography method is reported here using a DB-17MS column (50%-phenyl-methyl polysiloxane as the stationary phase) that successfully achieved baseline separation of crocetane and phytane and can be used to accurately identify and quantify them on gas chromatography and gas chromatography-mass spectrometry. Routine steroids and terpenoids biomarkers can also be analysed simultaneously. Additionally, their compound-specific carbon isotopic compositions were also measured without matrix influence using this method. This is the first time that a simple chromatographic method for direct determination of compound-specific carbon isotopic composition of crocetane has been reported publicly.

Chemometric Unmixing of Petroleum Mixtures by Negative Ion ESI FT-ICR MS Analysis.

Identification and quantification of mixed sources of petroleum reservoirs as well as the sources of oil spills generally requires the molecular composition information about the mixture. In this study, the relative concentrations of a series of polar acidic compounds, semiquantified by negative ion ESI FT-ICR MS, were calculated using alternating least-squares (ALS) to unmix a group of oil mixtures prepared in the laboratory using three endmember oils. It was shown that the ALS results were accurate based on the relative concentrations of polar acidic compounds, regardless of whether endmember oils and several samples were removed from the sample set. ALS was able to accurately calculate the composition of endmember oils, regardless of whether they were included in the sample set. This method is relatively simple, efficient, time-saving, and has potential for geological source identification of mixed oils or oil spills.