Relationships among viscosity, composition, and temperature for two groups of heavy crudes from the Eastern Venezuelan Basin

A group of 44 crudes from the Eastern Venezuela Basin have been analyzed for their content of saturated and aromatic hydrocarbons, resins, and asphaltenes, and studied for their variation of viscosity with temperature. With respect to a general trend, heavy oils that flow with ease, and light oils that flow with difficulty have been found. A ‘limiting value’ of 2.3 of saturates/asphaltenes separates oils whose viscosity can be changed with ease or difficulty by chemical means.     

The influence of biodegradation on resins and asphaltenes in the Liaohe Basin

Asphaltenes are traditionally considered to be recalcitrant to microbial alteration. Resins and asphaltenes of seven biodegraded oils extracted from reservoir cores of two columns (Es3 and Es1) of the Lengdong oilfield in the Liaohe Basin, NE China, were studied to test this hypothesis. Elemental (C, H, N, O, S) and isotopic compositions (δ¹³C and δ¹⁵N) were measured, FT-IR was used to study the oxygenated functionalities of both resins and asphaltenes, and Py–GC–MS was used to elucidate how alkyl side chains of asphaltenes were altered during biodegradation. We conclude that the products of biodegradation, such as carboxylic acids, phenol and alcohols, may not only contribute to the resin fraction of crude oils, but also are linked with functionalities of resins and asphaltenes. The amount of asphaltenes increases because some resin molecules are enlarged and their polarity increased such that they can be precipitated by hexane as newly generated asphaltenes. Thus, the hydrocarbons that are progressively consumed during biodegradation can pull the δ¹³C of asphaltene fraction closer to the δ¹³C of the altered resins and hydrocarbons that were consumed.     

Pyrolysis of asphaltenes: a source of geochemical information

Pyrolysis of asphaltenes from crude oils yields significant amounts of crude oil-like material. Studies of asphaltenes and their pyrolysis products from biodegraded and non-biodegraded oils show that biodegradation does not affect the composition of asphaltene. The overall composition of the oil produced from them on pyrolysis is similar to, yet significantly different from, that of the parent oil. From these compositional differences, it is concluded that asphaltene and its pyrolysis products contain geochemical information which is characteristic, and therefore may shed light on the history of the oil prior to asphaltene formation.     

Geochemical significance of seep oil from the Subandino Norte,Northwest Bolivia

This report presents an interpretation of the geochemical significance of a surface seep oil sample from the Subandino Norte of Bolivia. The oil from this seep is unusual because it contains a limited range of low molecular weight normal paraffins. Normal paraffins containing more than 12 carbons are absent from the oil, while normal paraffins having fewer than 12 carbons are conspicuous components of the oil. The compositional peculiarities of the oil are attributed to transport of hydrocarbons in water, with water playing an active role in the final composition of the seep. The composition of the seep oil is qualitatively consistent with that anticipated if the hydrocarbons were moved in molecular solution in water.     

Conversion and degradation of crude oil by Bacillus SP3

The objective of this study is to demonstrate the basic characteristics of Bacillus SP3 and evaluate its effect on different crude oils. Strain SP3 is a motile, gram-positive, spore-producing rod that was isolated from a reservoir of the Shengli oil field in East China. The cells of strain SP3 grew at high temperatures up to 58℃ at the pH range of 5.5–8.5. Strain SP3 grew facultatively and could use different organic substrates, and produce some metabolites such as 4-hydroxy-4-methyl-2-pentanone, methyl-2-nitrogen benzene and 1, 2-benzenedicarboxylic acid bis ester. Laboratory studies have demonstrated that the strain converted and degraded different components and changed the physical and chemical properties of crude oils. Strain SP3 degraded crude oil and the growth of bacteria on crude oil resulted in loss of aromatic hydrocarbons, resins and asphaltenes. The bioconversion of crude oils would lead to an enrichment in lighter hydrocarbons and an overall redistribution of saturate hydrocarbons. The interactions of microorganisms with crude oils are variable, depending on the microbial species and the chemical compositions of crude oils.     

Geochemical study of a series of biodegraded oils: Microtexture and structure of their coked asphaltenes

The asphaltenes extracted from eight oils and a bituminous sand were coked and studied by transmission electron microscopy and X-ray diffraction to observe the microtextural and structural changes caused by increasing biodegradation. The pyrolysis effluents of asphaltenes were analyzed by chromatography. Biodegradation causes an increase of aromatic hydrocarbons and sulfur during heat-treatment of isolated asphaltenes. During thermal treatment, the more biodegraded the sample, the earlier and the greater the release of aromatics. The microtexture of the asphaltene coke is very sensitive to this early release of aromatics and is used to classify samples as to their degree of biodegradation. In the series, two groups were distinguished.     

Geochemical significance of chemical composition and ESR properties of asphaltenes in crude oils from Alberta,Canada

More than 100 crude oils and 12 oil sands from Alberta, Canada, from stratigraphie units ranging in age from Upper Cretaceous to Middle Devonian, were processed to separate the asphaltenes which were then analysed for C, H, N, O and S and the ESR spectra run to determine g-value, spin number and line width. A factor analysis of these data, together with selected crude oil and reservoir properties, was interpreted in terms of a number of non-thermal processes which can affect the content and composition of asphaltenes during and after thermal maturation. Experiments on the effect of temperature on the signal intensity of free radicals indicate that more than half, and possibly all, the free radicals observed in asphaltenes must arise from charge transfer or closely related equilibria. An important solvent effect is demonstrated in further experiments, in which the more polar the solvent, the more the solvent dispersive forces overcome the associative forces of the asphaltene layers thus leading to lower molecular weights and a change in the charge transfer forces responsible for the ESR signal. The average molecular weight of asphaltenes from heavy, asphaltic, biodegraded crude oils and oil sands is considerably greater than the average molecular weight of asphaltenes from the more paraffinic, mature, non-biodegraded crude oils, and it seems likely that the differences in molecular weight of these asphaltenes are due to the solvent effect of the crude oils, and thus the laboratory observations have been confirmed in the Alberta basin.     

Chemical structural units of macromolecular coal components

Chemical degradations of coal resins, coal asphaltenes and coal residues have been performed with selective, non-oxidative reagents. The coal comprise samples a rank interval 0.30–1.21 %R_m. Degraded low-molecular-weight compounds were analyzed by GC-MS. The distributions of pentacyclic terpanes, isoprenoids, n-alkanes, acids and alcohols obtained as degradation products illustrate a considerable variability between the macromolecular coal fractions. A structural study on the molecular level of the degraded compounds from coal resins and coal asphaltenes show their potential to generate hydrocarbons during coalification process.     

Estimation of bioavailability of polycyclic aromatic hydrocarbons in river sediments

This study aimed to evaluate the total concentration of polycyclic aromatic hydrocarbons in sediments of Iguassu River in Southern Brazil. Alongside the concentration, the amount of such compounds bioavailable was also evaluated. This is accomplished by comparing its total amount present in sediments and the amount extracted by n-butanol. The results showed that the total concentration of polycyclic aromatic hydrocarbons presented in sediment ranged from 4.49 to 58.75???g/g. The total amount of polycyclic aromatic hydrocarbons extracted by n-butanol ranged from 1.22 to 17.07???g/g. The use of n-butanol represents the mimetic conditions that hydrocarbons, derived from oil, could be taken up by organisms. Most of the hydrocarbons extracted by n-butanol were those with lower octanol?Cwater partition constant, usually those with three and four rings. Compounds with more than four rings were extracted in lower or insignificant amounts. Even the hydrocarbons with lower molecular weight available may be degraded or eliminated by organisms, when accumulated. Estimating bioavailability of hydrocarbons represents what specific hydrocarbons could be available to be taken up by organisms.     

Changes in gas composition during simulated maturation of sulfur rich type II-S source rock and related petroleum asphaltenes

Asphaltenes extracted from crude oils are proposed to possess structural features of the related source rock kerogen. For the present study micro-scale sealed vessel pyrolysis (MSSV) and combustion isotope ratio mass spectrometry (GC–C–IRMS) were used to compare gas generation from a whole rock (type II-S kerogen) from southern Italy with that from related sulfur rich asphaltenes isolated from a low maturity heavy crude oil. The purpose of was to determine whether experimental pyrolysis of oil asphaltenes can be used to predict the timing and the chemical and isotopic composition of hydrocarbon gases generated from genetically related kerogen in the source rock during burial maturation. The results show that parameters such as (gas to oil ratio) GOR and oil and gas formation timing are very similar for these two sample types, whereas gas composition, product aromaticity and sulfur content are remarkably different. Slight differences in GOR are mainly due to differences in gas formation characteristics at very high levels of thermal alteration. Secondary gas formation from the whole rock covers a much broader temperature range under geological conditions than that from the asphaltene products. However, it is remarkable that both the onset and the maximum temperature are nearly identical under geological conditions. The observed differences in gas generation characteristics are supported by discrepancies in the carbon isotopic characteristics of the gas range compounds and indicate different precursors and/or mechanisms for gas generated from whole rock and asphaltenes.     

A comparison of results from two different flash pyrolysis methods on a solid bitumen sample

A Cambrian solid bitumen from northwestern Sichuan Basin, southern China was analyzed using two different flash pyrolysis methods coupled with gas chromatography–mass spectrometry analysis, including Pyroprobe® and analytical laser micropyrolysis. Results show that pyrolysis products from a Pyroprobe® (model 5000) analysis are dominated by mono-, di- and tricyclic aromatic hydrocarbons, whilst those from laser micropyrolysis are dominated by aliphatic hydrocarbons (n-alk-1-ene/n-alkane doublets), which is consistent with the results from an FT-IR spectrum of the solid bitumen. According to the molecular compositions of the pyrolysates from two types of pyrolysis, results from a 532 nm continuous wave laser may be more suitable for pyrolysis research of bitumen/asphaltene. Thus, differences in pyrolysis techniques must be considered when used to characterize oil asphaltenes or source rock kerogens.     

柯坪隆起阿克苏油苗的地球化学特征及其成因研究

柯坪隆起区是塔里木盆地海相烃源岩露头发育较好的地区之一,但相关的油气研究报道不多。本文详细研究了塔里木盆地柯坪隆起区油苗的有机地球化学特征并进行了相关的成因分析。阿克苏油苗经历了严重的生物降解作用,饱和烃生物标志物所能提供的成因信息十分有限。原油沥青质组分及储层吸附/包裹烃受后生作用影响较小,综合分析油苗沥青质热解产物与吸附/包裹烃的生物标志物及其碳同位素组成可以获得更多有效的成因信息。研究结果表明,阿克苏油苗与其储层吸附/包裹烃具有不同来源。油苗、沥青质以及沥青质热解产物的碳同位素特征与已经报道的多数海相原油及其沥青质较为接近,与典型的寒武系烃源来源的原油差异显著。而储层吸附/包裹烃与已报道的典型寒武系烃源岩来源油的生物标志物及碳同位素特征比较类似,可能形成于较高的热演化阶段。     

Distribution of hydrocarbons in water and bottom sediments of the Northern and Middle Caspian Sea

A study of two classes of hydrocarbons (HCs)—aliphatic and polycyclic aromatic—in suspended matter of the surface waters and bottom sediments of the Northern and Middle Caspian Sea (R/V Nikifor Shurekov, October 2015) is described. It has been determined that oil pollution transported by river runoff and fluid streams flowing from sedimentary formations in the northeastern part are the main sources of hydrocarbons in the river–sea boundaries of the Volga, Terek, and Sulak rivers.     

High-molecular heteroatomic components of crude oils of the Timan–Pechora petroliferous basin

Based on the experimentally measured parameters of elemental composition, average molecular masses, and PRM spectrometry data, we calculated the average structural parameters of resin and asphaltene molecules in Paleozoic crude oil of some oilfields in the Timan–Pechora petroliferous basin. The values of the structural parameters of cyclic and aliphatic fragments in the molecules of resin–asphaltene components of the crudes studied here are within the ranges established earlier for high-molecular compounds of crudes from other petroliferous basins. The average structural-group characteristics of resins in crudes from carbonate reservoirs vary over narrow ranges of values independently of the age and depth of occurrence of the reservoir. The resinous fractions of crudes from terrigenous horizons show symbatic enrichment with paraffin fragments and depletion with naphthene fragments of molecules with depth. This points to the presence of a paragenesis of petroleum hydrocarbons and heteroatomic compounds in the Earth’s interior.     

Comparison of bulk kinetic parameters for asphaltenes from long-time stored and related fresher-produced crude oils

Two investigated long-time stored oils, which were produced in the 1960s, show strong compositional changes compared to fresher oil samples from the same well and production zones. Asphaltenes isolated from stored and fresher-produced oil pairs show highly similar results from open-system pyrolysis. However, asphaltenes from long-time stored oils show higher reactivity compared to those from fresher oils. The study shows that differences exist in kinetic models based on asphaltenes from fresh-produced oil and those based on oil that has undergone long-term storage, and that these differences may impact geological predictions using such models. Factors controlling the chemical differences between stored and fresher asphaltenes are unclear and hard to determine, because of a broad range of factors controlling compositional differences between these oil pairs. The difference in chemical kinetics might be related to chemical storage effects, but different well-site sampling techniques between decades, or even incomplete homogenization of the long-time stored oils in barrels before sampling may also have an impact.     

REE distribution in the resin-asphaltene fractions as a geochemical criterion for identification of sources of trace elements in oil

This paper reports REE data on resin-asphaltene components of oil from six oil-gas-bearing provinces and on bitumoids from inferred oil-source rocks (domanikites and bazhenites). It was shown that, regardless of geological-tectonic structure of the regions, oil composition, depth of reservoirs, and host lithologies, oil exhibits significant REE fractionation, and, unlike bitumoids, positive Eu anomaly. The (Eu/Sm)_n ratio increases from asphaltenes to resins and further to oils. Based on REE distribution in oil, source rocks, and bitumoids, it was concluded that deep-seated fluids were one of the possible sources that defined the trace element composition of oil.     

塔北隆起深层海相油藏中原油及族组分碳同位素组成的纵向分布特征及其地质意义

利用MAT252同位素质谱仪分析了塔里木盆地塔北隆起深层海相油藏中原油及族组分的碳同位素组成。研究表明该区深层海相油藏中原油的全油碳同位素组成主要受生源控制,受热力作用影响较小;而在继承生源的碳同位素组成的基础上,热力作用将对原油族组分的碳同位素组成及其逆转和分馏产生重要影响。总的趋势是随着油藏埋藏深度的增大和热力作用的加强,饱和烃组分的碳同位素组成逐渐变重,而沥青质组分的碳同位素组成不断变轻,族组分碳同位素逆转程度和分馏程度有所加强,并出现饱和烃﹥芳烃﹥非烃﹥沥青质的整体逆转现象。塔北隆起深层海相原油族组分的碳同位素组成的纵向变化特征,可以反映出热力作用对原油稳定性的影响。     

Evaluation of the diagnostic ratios for the identification of spilled oils after biodegradation

Biodegradation, one of the most important weathering processes, alters the composition of spilled oil, making it difficult to identify the source of the release and to monitor its fate in the environment. A laboratory experiment was conducted to simulate oil spill weathering process of microbial degradation to investigate compositional changes in a range of source- and weathering-dependent molecular parameters in oil residues, and the conventional diagnostic ratios for oil spill identification were also evaluated. The conventional diagnostic ratios of n-alkane displayed obvious changes after biodegradation, especially for Pr/n-C₁₇ and Ph/n-C₁₈ with relative standard deviation more than 118.84 %, which suggests they are invalid for oil source identification of the middle-serious spill. Many polycyclic aromatic hydrocarbons (PAHs) are more resistant to biodegradation process than their saturated hydrocarbon counterparts, thus making PAHs to be one of the most valuable fingerprinting classes of hydrocarbons for oil identification. Biomarker ratios of hopanes and steranes were also useful for source identification even after moderate biodegradation, and the diagnostic ratios from them could be used in tracking origin and sources of hydrocarbon pollution. Finally, the carbon isotopic type curve may provide another diagnostic means for correlation and differentiation of spilled oils, and be particularly valuable for lighter refined products or severely biodegraded oils, the source of which may be difficult to identify by routine biomarker techniques.