Zewen Liao

Characterization of nC(7)-soluble fractions of the products from mild oxidation of asphaltenes

Abstract A significant quantity of hydrocarbons (including alkanes) is occluded in the skeleton of the asphaltene molecule. The hydrocarbons are probably remnants of the “original oil” which had been retained within the asphaltene matrix and protected from the secondary alteration processes that occurred subsequently in the oil reservoirs. In this work we report that oxidation of asphaltenes by stirring with 30%H 2 O 2 –HAc or NaIO 4 –NaH 2 PO 4 can release n C 7 -soluble oxidized products, including the occluded hydrocarbons. Characterization of the n C 7 -soluble fractions of oxidized products can be applied to highlight some geochemical problems, such as in studies of oil–oil correlation, oil–source correlation and secondary alterations of oil reservoirs. It will be especially useful to recover the original geochemical information of some oil reservoirs heavily degraded by post-depositional processes.

Kinetic studies of asphaltene pyrolyses and their geochemical applications

Abstract Pyrolysis kinetics are determined for a series of asphaltene samples associated with different types of kerogens. The activation energy distributions obtained for asphaltenes related to type I kerogens cover a wide range, with significant hydrocarbon generation with activation energies above 350 kJ/mol. The ranges of activation energy distributions are relatively narrow for asphaltenes associated with type II and III kerogens, with little hydrocarbons generated with activation energies above 350 kJ/mol. If the type of associated kerogen can be reasonably constrained, the pyrolysis kinetics of the asphaltenes is potentially a very useful tool for assessing the maturity levels of reservoired oils. The results of pyrolysis kinetics indicate that there is still significant potential for asphaltenes to regenerate hydrocarbons.

Geochemical characterization of free versus asphaltene-sorbed hydrocarbons in crude oils: implications for migration-related compositional fractionations

Based on the existing petroleum migration models that focus on the role of organic sorption, a laboratory study has been performed to simulate the migration effects on the various fractions of oil. In this study, one free oil fraction (defined as Bitumen 1, existing outside of or loosely attached to asphaltene), and three to four absorbed oil fractions (defined as Bitumens 2, 3, 4 and 5, more strongly attached to asphaltene macromolecules) that were obtained from three oil samples collected from the Bohai Bay Basin, East China, were analyzed in detail. Based on the laboratory partition of oil components between the solvent phase (oil) and the asphaltene phase, petroleum migrationrelated effect on saturate fraction was re-evaluated. Our observation indicates that the compositional variation from Bitumen 1 to Bitumen 4 or 5 includes the following: (1) The resin content increases while the saturate content and saturates/aromatics ratio decrease; (2) The relative abundance of short chain n-alkanes decreases while that of the long chain n-alkanes increases; (3) Pr/nC17, Ph/nC18 and Pr/Ph ratios stay virtually unchanged while the relative abundances of terpanes to n-alkanes and steranes to n-alkanes decrease; (4) The ratios of C21/(C21 þ C29) steranes and C23/(C23 þ C30) terpanes in the free oil fraction are similar to or even lower than those in the whole absorbed fraction, suggesting relatively stronger affinities of these smaller terpane and sterane molecules to asphaltenes in contrast to the relatively larger ones and (5) The isomerization parameters of C27 and C29 steranes are slightly higher in the free fraction than in the whole absorbed oil fraction. Large variations were observed in the distributions of steranes among the four bitumen fractions of the X52 oil, and were considered to be related to the heterogeneity of the source rocks, in addition to the partition of these compounds between the asphaltene phase and the solvent phase. q 2002 Elsevier Science Ltd. All rights reserved.

The Geochemical Characterization of Adsorbed/Occluded Hydrocarbons Inside Solid Bitumen in the Kuangshanliang Area of the Northwestern Sichuan Basin and Its Significance

The geochemical characterizations of adsorbed and occluded components of solid bitumen in the Kuangshanliang area of northwestern Sichuan Basin were studied by comparing the results of conventional extraction and mild oxidative degradation. The results indicate that the solid bitumen originated from Sinian–Cambrian ancient oil reservoirs. The main source of the parent material is lower-order aquatic deposited in a high-sulfur anoxic marine environment. Exposed solid bitumen suffered from severe biodegradation, altering the tricyclic terpane/pentacyclic terpane and (pregnane + homo-pregnane)/regular sterane ratios as compared to the earlier parent material.

Asphaltenes in oil reservior recovery

Asphaltene is one of the important compositions in oil reservoirs, while it is also a major factor that causes difficulties in oil recovery and oil post-processings. Up to date, study on asphaltenes in oil recovery is still a bottleneck problem. In this paper, the advances of studies on asphaltenes are reviewed, and some directions for further studying are suggested. What is reviewed in the paper includes the precipitation studies of asphaltenes, the degradation studies of asphaltenes and the applications of asphaltene’s studying in oil recovery; furthermore, it is regarded as a promising direction to study the possible applications of asphaltene’s selectively decomposing by chemical reagents in oil recovery.

Aliphatic biomarkers distribution in crude oil-impacted soils: An environmental pollution indicator

Abstract The occurrence and distributions of aliphatic biomarkers in oil contaminated soils from Owaza, Niger Delta, Nigeria, were investigated by gas chromatography-mass spectrometry (GC-MS). The concentrations of the n-alkanes Σ(nC14 to nC29) in the soils ranged from 18,680.4 to 35,615.8 μg/g (average 24,664.0 μg/g). The abundance of n-alkanes in the soils extracts show that the effect of environmental degradation on the impacted soils has been minimal. N-alkanes diagnostic indices, source and maturity parameters computed for the terpanes and steranes in the soils extracts indicate Niger Delta oil as the source of contamination. This study reveals the significance of aliphatic biomarkers in serving as organic pollution source indicator.

Occurrence and Distribution of Carbazoles and Benzocarbazoles in Tertiary Niger Delta Source Rocks

The distributions of carbazoles and benzocarbazoles in source rocks from the Northern depobelt of the Tertiary Niger Delta, Nigeria, have been investigated by gas chromatography-mass spectrometry (GC-MS). Biomarker compositions of the source rocks indicate that the source rocks were formed from organic matter of mixed origin (terrestrial and marine) and are either immature or at early maturity stage. The carbazoles distributions in the source rocks are dominated by C0-C2-carbazoles and strong variation was observed in their distributions with increasing maturity. Among the C1-carbazoles, 1-methylcarbazole shows a decrease trend at the immature stage and an increase trend at higher maturity levels. 2- and 3-methylcarbazoles display an increasing trend with increasing maturity while 4-methylcarbazole exhibits a decreasing pattern with increasing maturity. Within the C2-carbazoles isomers, 1,8- and 2,7-dimethylcarbazoles, show an increasing trend with increasing maturity while the partially exposed isomers 1,3- and 1,6-dimethylcarbazoles decrease with increasing maturity. The ratio of benzo[a]carbazole/benzo[a]carbazole +benzo[c]carbazole varies significantly from 0.36 to 0.55 in the entire maturity range, indicating a strong maturity dependence. These results show that maturity will have great effect on the use of carbazoles and benzocarbazoles distributions as oil migration parameter in the Niger Delta.

Kinetic studies on the pyrolysis of asphaltenes from different types of kerogens

The pyrolysis kinetics of a series of asphaltenes, from different types of kerogens, are studied in this work. The results indicate that the distributions of activation energy are over a wide range for the asphaltenes from type I kerogens. There is still a large potential of hydrocarbon generation in case the activation energy is above 350 kJ ·mol−1. While the distributions of activation energy are comparatively over a narrow range for the asphaltenes from type II and in kerogens, there is a little or almost no potential of hydrocarbon generation with the activation energy above 350 kJ · mol−1 respectively. For the asphaltenes from some specific type of kerogens, the pyrolysis kinetics can be applied to marking their maturity. Furthermore, based on detailed discussions of the kinetics parameter frequency factor, the asphaltenes from type I kerogens are considered to be of great potential to regenerate oils, while the asphaltenes’ potential for oil-to-gas conversion tends to go down in order of primitive kerogen types of III, II and I.

The Mild Oxidative Degradation of the Heavy Constituents in Viscous Crude Oils/Oil Sands and Its Prospect in Oil Recovery

Abstract Viscous crude oils and oil sands are important energy resources, but it is difficult to exploit them due to the dominated heavy constituents such as asphaltenes. In this work, the mild oxidative degradation of the heavy constituents (oxidized by NaIO4/NaH2PO4 and 30% H2O2/CH3COOH) has been carried out. In the viscous oils, more than 45% asphaltenes has been degraded, and the asphaltenes are mainly chemically changed into the resin fractions, which is favorable to the stability of viscous crude oils. After the degradation, the total amount of extractable organic compounds from oil sands has been markedly increased than that of the blank experiment. The experimental results indicate that the mild oxidative degradation of asphaltenes can improve the physicochemical properties of the viscous oils and oil sands, which is particularly in favor of the exploitation of these energy resources.

The geochemical characteristics of Tazhong crude oils from the Tarim Basin, northwestern China:

Recent exploration work in the Tazhong district has gradually transferred to the exploitation of high and over mature oils in deep and ultra-deep layers. This has proved problematic, however, as the distribution of crude oils in the Tazhong is complex. This means that the geochemical characterization of high and over mature oils, especially for light crude oils, have become increasingly important. The stability of concerted ring structure of aromatics makes them having stronger thermal stability and resistance to biodegradation. This means that there are abundant aromatic compounds in high and over mature oils. This study presents a series of geochemical analyses of the maturity parameters of 89 crude oils from the Tazhong area, including stable carbon and hydrogen isotope analyses of compounds from 43 light crude oils. These analyses are then compared with other data from the Tazhong Number I fault zone, as well as the Tazhong Number 10 and Tazhong Uplift structural zones. Results show that the geochemical parameters of oils from Tazhong Number I fault zone generally encompass a wider range than those from the Tazhong Number 10 structural zone, which indicates that the Tazhong Number I slope belt is more active than its counterpart structural belt and generates oils with more complex geochemical characteristics. The positive correlation between the toluene/methyl cyclohexane ratio and the dibenzothiophene/phenanthrene ratio, as well as with the naphthalene/phenanthrene ratio indicates that aromatization parameters can be used to evaluate the maturity of light crude oils, and there may be inherited relationships between toluene and methyl cyclohexane in crude oils.