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1.
Biomarker distributions in a suite of asphaltenes and kerogens have been analysed by flash pyrolysis directly coupled to a GCMS system. Attention has been focussed on biomarkers of the sterane and triterpane types. The sample suite under investigation consists of sediments with different kerogen types and some crude oils. Biomarker distributions in the pyrolysates have been compared with the “free” biomarkers in the corresponding saturated hydrocarbon fractions.The analyses show significant differences between the distributions of the free biomarkers and those in the pyrolysates. The latter have lower amounts of steranes while diasteranes are absent or present at low concentrations only. In the triterpane traces a shift of maximum intensity from C30 (free compounds) to C27/C29 is observed. Furthermore, the pyrolysates contain a set of triterpenes (not present among the free compounds), and there is a selective loss of “non-regular” triterpanes that are present in the saturated hydrocarbon fractions. The observed differences between pyrolysates and free hydrocarbons can be explained partly by the processes occurring during pyrolysis such as bond rupture and subsequent stabilisation of primary pyrolysis products. To a certain extent these differences also show that maturation processes occurring in sediments have effects on free biomarker molecules different from those on molecules that are enclosed in a macromolecular matrix (kerogen or asphaltenes).Differences between biomarker distributions of asphaltene and kerogen pyrolysates are relatively small. A comparison with the pyrolysates from extracted whole sediments suggests that these differences are mainly caused by interactions between the organic material and the mineral matrix during pyrolysis.Oil asphaltenes behave differently from sediment asphaltenes as their pyrolysates are more similar to the corresponding saturated hydrocarbon fractions, i.e. the differences described above are observed to a much smaller extent. This different behaviour appears to be the result of coprecipitation of a part of the maltene fraction with the oil asphaltenes.  相似文献   

2.
Hydrous pyrolysis (HP) experiments were used to investigate the petroleum composition and quality of petroleum generated from a Brazilian lacustrine source rock containing Type I kerogen with increasing thermal maturity. The tested sample was of Aptian age from the Araripe Basin (NE-Brazil). The temperatures (280–360 °C) and times (12–132 h) employed in the experiments simulated petroleum generation and expulsion (i.e., oil window) prior to secondary gas generation from the cracking of oil. Results show that similar to other oil prone source rocks, kerogen initially decomposes in part to a polar rich bitumen, which decomposes in part to hydrocarbon rich oil. These two overall reactions overlap with one another and have been recognized in oil shale retorting and natural petroleum generation. During bitumen decomposition to oil, some of the bitumen is converted to pyrobitumen, which results in an increase in the apparent kerogen (i.e., insoluble carbon) content with increasing maturation.The petroleum composition and its quality (i.e., API gravity, gas/oil ratio, C15+ fractions, alkane distribution, and sulfur content) are affected by thermal maturation within the oil window. API gravity, C15+ fractions and gas/oil ratios generated by HP are similar to those of natural petroleum considered to be sourced from similar Brazilian lacustrine source rocks with Type I kerogen of Lower Cretaceous age. API gravity of the HP expelled oils shows a complex relationship with increasing thermal maturation that is most influenced by the expulsion of asphaltenes. C15+ fractions (i.e., saturates, aromatics, resins and asphaltenes) show that expelled oils and bitumen are compositionally separate organic phases with no overlap in composition. Gas/oil ratios (GOR) initially decrease from 508–131 m3/m3 during bitumen generation and remain essentially constant (81–84 m3/m3) to the end of oil generation. This constancy in GOR is different from the continuous increase through the oil window observed in anhydrous pyrolysis experiments. Alkane distributions of the HP expelled oils are similar to those of natural crude oils considered to be sourced from similar Brazilian lacustrine source rocks with Type I kerogen of Lower Cretaceous age. Isoprenoid and n-alkane ratios (i.e., pristane/n-C17 and phytane/n-C18) decrease with increasing thermal maturity as observed in natural crude oils. Pristane/phytane ratios remain constant with increasing thermal maturity through the oil window, with ratios being slightly higher in the expelled oils relative to those in the bitumen. Generated hydrocarbon gases are similar to natural gases associated with crude oils considered to be sourced from similar Brazilian lacustrine source rocks with Type I kerogen of Lower Cretaceous, with the exception of elevated ethane contents. The general overall agreement in composition of natural and hydrous pyrolysis petroleum of lacustrine source rocks observed in this study supports the utility of HP to better characterize petroleum systems and the effects of maturation and expulsion on petroleum composition and quality.  相似文献   

3.
从西北地区侏罗纪煤中分离出来的不同显微组分热解油生物标志物总体上比较相似,但在一些特殊生物标志物的分布上存在明显差异。藻类体、孢子体、角质体热解油Pr/Ph比值一般在1.5～2.0之间,镜质体和基质镜质体热解油Pr/Ph比值在3～4之间,但均只有相应原煤抽提物Pr/Ph比值的一半。在常规生物标志物甾烷和萜烷组成中,藻类体和孢子体含有相对丰富的C27甾烷,角质体其次,镜质体和基质镜质体C27甾烷含量很低或者基本不含C27甾烷;藻类体和角质体含有较高的伽马蜡烷,而与藻类体来自相同原煤的孢子体伽马蜡烷含量很低;镜质体和基质镜质体基本上不含伽马蜡烷;分离显微组分的原煤伽马蜡烷含量均很低。由此可见,伽马蜡烷的含量不仅与有机质沉积水体的盐度有关,与母源的成分也有关系。显微组分热解油与煤系原油生物标志物组成特征对比表明,煤系原油是藻类体、孢子体、角质体等富氢组分和相对贫氢的镜质组生成产物的混合物。不同油气藏中的原油,每一类显微组分的贡献可能不尽相同,有些原油可能主要来源于藻类体和孢子体等富氢显微组分,而有些原油除了富氢显微组分有贡献外,镜质组对其也有一定的贡献,但富氢显微组分应该是煤系含油气盆地中主要的生油显微组分。  相似文献   

4.
The extent of sterane isomerisation reactions and the moretane/hopane ratios of 234 crude oils, taken world wide, from a wide variety of source rocks of differing geological ages, have been measured.This data indicates that in 78 crude oils derived from Tertiary source rocks, sterane isomerisation reactions as determined by the 20S/(20S + 20R) ration of the C29 5α(H), 14α(H), 17α(H) normal-steranes and the C29 iso/(iso + normal) ratio [iso = 5α (H), 14β(H), 17β(H)] are mainly incomplete and sometimes considerably so. In addition, the same crude oils have 17β(H), 21α(H)-moretane/17α(H), 21β(H)-hopane ratios which are significantly greater (predominantly in the range 0.10–0.30) than those of crude oils derived from older, mature source rocks (mainly less than 0.1).This data, for crude oils, lends support to the hypothesis, proposed by Mackenzie and McKenzie (1983) for source rock extracts, that the time/temperature constraints of sterane isomerisation reactions are such that the time available for isomerisation in Tertiary sediments is generally insufficient, despite generation of crude oil at relatively high temperatures.An alternative hypothesis is that the incomplete sterane isomerisation of Tertiary crude oils may be due to generation of these crude oils from their deltaic, land plant-containing source rocks under low heating conditions.A third hypothesis proposes that the Tertiary crude oils may have picked up the incompletely isomerised steranes from immature sediments during migration. Although possible in particular instances, such a mechanism does not appear to be generally applicable since, in that case, the phenomenon would then appear to be restricted to the Tertiary.The higher moretane/hopane ratios of the Tertiary crude oils could suggest that constraints, similar to those applying in sterane isomerisation, also operate in the conversion of moretane to 17α(H)-hopane.  相似文献   

5.
Being the heaviest fraction of crude oils, asphaltenes are liable to aggregate, and other molecules in the oils can be steadily adsorbed onto, and even occluded inside the macromolecular structures of the asphaltenes. These occluded compounds inside the asphaltenes can survive over geological time in oil reservoirs owing to effective protection by the macromolecular structures of the asphaltenes. The asphaltenes of a crude oil (ZG31) from the central Tarim Basin, NW China, were hierarchically degraded by increasing the amount of H2O2/CH3COOH to release the occluded compounds. Besides the common components, series of even numbered n-alk-1-enes and 3-ethylalkanes were detected among the occluded compounds. Comparison of the biomarker distributions and the compound-specific C isotopic results between the compounds from the maltenes and those from the occluded fraction, the ZG31 reservoir was suggested to have been charged multiple times, with different charges being derived from different strata of source rocks.  相似文献   

6.
This paper deals with natural temperature records in the heavy (asphaltenes) and the light fractions (C7—light hydrocarbons) of petroleum. Two sets of marine oils formed from different source rocks and petroleum systems were studied using asphaltene kinetics and light hydrocarbon analysis. Both fractions have been reported to contain information about the temperature the respective oils have been exposed to in the subsurface. These indicated temperatures generally correspond to the conditions in the source rock when expulsion occurred. Bulk kinetic analysis of reservoir oil asphaltenes as well as light hydrocarbon (LH) analysis (of dimethylpentanes) were used here in order to evaluate the expulsion temperatures. Surprisingly, when considering information coming from both fractions, an inverse trend between LHs expulsion temperatures (Ctemp) and asphaltenes (Tasph.) can be observed—high Tasph (asphaltene temperatures) occur with low LH Ctemp (light hydrocarbon expulsion temperatures) and low Tasph can be observed when Ctemp is high. These differences are of fundamental importance for the use of such geochemical data in calibrating numerical basin models. The reason for this inverse behaviour is possibly due to the different expulsion behaviour of light hydrocarbons and the heavy fraction of oils, especially when the source rocks contain only moderate amounts of organic matter. In addition it has to be considered that the temperature predictions obtained using asphaltene kinetic analysis are related to the onset temperature of petroleum expulsion, while light hydrocarbons provide, at best, average expulsion temperatures.  相似文献   

7.
1-Alkyl-2,3,6-trimethylbenzenes and a high relative amount of 1,2,3,4-tetramethylbenzene (TTMB) have been previously detected in the marine oils and asphaltenes in the oils from the Tarim Basin. In the present study, the stable carbon isotopic compositions of TTMB and n-alkanes in the pyrolysates of asphaltenes in the marine oils from the northern Tarim Basin and Silurian tar sands from the Tarim Basin were determined. TTMB has stable carbon isotopic compositions in the range from −23‰ to −24‰ and are about 12‰ more enriched in 13C than concomitant n-alkanes (−35‰ to −37‰) in the pyrolysates. The results indicate a contribution from green sulfur bacteria (Chlorobiaceae) to TTMB. Thus, the depositional environments of the source rocks for the marine oils and the bitumen in tar sands from the Tarim Basin are characterized by periods of euxinic conditions within the photic zone.  相似文献   

8.
Biodegraded oils are widely distributed in the Liaohe basin, China. In order to develop effective oil-source correlation tools specifically for the biodegraded oils, carbon isotopic compositions of individual n-alkanes from crude oils and their asphaltene pyrolysates have been determined using the gas chromatography–isotope ratio mass spectrometry technique. No significant fractionation in the stable carbon isotopic ratios of n-alkanes in the pyrolysates of oil asphaltenes was found for anhydrous pyrolysis carried out at temperatures below 340°C. This suggests that the stable carbon isotopic distribution of n-alkanes (particularly in the C16–C29 range) in the asphaltene pyrolysates can be used as a correlation tool for severely biodegraded oils from the Liaohe Basin. Comparison of the n-alkane isotopic compositions of the oils with those of asphaltene pyrolysates shows that this is a viable method for the differentiation of organic facies variation and post-generation alterations.  相似文献   

9.
Biomarkers produced by microscale pyrolysis of extracted source rocks, kerogens and asphaltenes have been analysed directly by gas chromatography-mass spectrometry in the MID mode. A series of experiments have been undertaken. These include an investigation into the production of the hopanes at different pyrolysis temperatures and a comparison of results obtained from Curie point pyrolysis and the Chemical Data Systems pyroprobe. Steranes and triterpanes produced by pyrolysis of a series of vitrinites were investigated and correlated with maturity variations. Finally, the biomarkers produced from asphaltenes were compared with those produced from the extract and extracted rock in order to further investigate the theory that asphaltenes are a liquid kerogen. The results of these experiments showed that the biomarkers released by pyrolysis of source rocks have a potential use for source and maturity determinations. The method is advantageous in that it can be said with some certainty that the biomarkers are indigenous to the rock and not present in the rock as a possible result of migration.  相似文献   

10.
Hydrous pyrolysis of asphaltenes has been tested as a method to reconstruct the chemical composition of biodegraded oils and oil seeps. The asphaltenes of three oils (a nondegraded oil, a biodegraded oil, and a biodegraded oil seep) from the Monterey Formation were studied. Results show that the aliphatic fraction generated by hydrous pyrolysis is very similar in chemical composition to the non-degraded oil. This makes the method very useful in correlation studies of biodegraded and nondegraded oils. It also allows to roughly estimate the maturity of the source of the biodegraded oil or oil seep.  相似文献   

11.
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.  相似文献   

12.
The 9 and 34 GHz EPR spectra of eight asphaltenes from different locations have been studied at 294 K in an attempt to correlate the observed g-values with the heteroatom content. It is found that the EPR linewidths are larger and the g-values are smaller at 34 GHz than at 9 GHz. Quantitative statistical analysis of the g-values observed in those asphaltenes derived from tar sand bitumens and crude oils shows that they are uncorrelated with the heteroatom content, unlike those from coal. It is concluded that g-values may not be a good analytical tool for elucidating the structure of those asphaltenes not derived from coal.  相似文献   

13.
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.  相似文献   

14.
The present paper deals with the biomarker characteristics of crude oils and source rocks from different environments(fresh,fresh-brackish and salt waters)of nonmarine depositional basins of different ages in China.Their characters are summarized as follows:1)Souce rocks and crude oils derived from fresh-water lacustrine facies have an odd/even predominance of n-alkanes and high pristine/phytane ratios.Oils from the fresh-water lacustrine facies differ from typical marine oils in the relative contents of total steranes and terpanes,the concentrations of hopanes and organic sul-phur compounds and the values of methylphenanthrene indices and C,H,S stable isotopes.2)The source rocks and crude oils derived from saline lacustrine facies possess an even/odd predominance of n-alkanes and high phytane/pristine ratios.There are also some differences between saline lacustrine oils and freshwater lacustrine oils in the concentrations of steranes,tricyclic terpanes and organic sulphur compounds,as well as in the values of methylphenanthrene indices and C,H,S stable isotopes.3)Oils derived from fresh-brackish water lake facies differ from oils from fresh-water lacustrine or samline lacustrine environments in respect of some biomarkers.According to the various distributions of these biomarkers,a number of geochemical parameters can be applied synthetically to differentiating and identifying the nature of original depositional environments of crude oils and source rocks and that of organisms-primary source materials present in those environments.  相似文献   

15.
Hydrous pyrolysis (closed vessel autoclaving in the presence of excess water) of organic-rich rocks is said to generate oils which closely resemble natural crude oils in their broad characteristics and composition. However there are only a few accounts of the proportions and compositions of hydrocarbons in hydrous pyrolysates and none of these discuss the aromatic hydrocarbon composition in detail. The present paper presents some data on the latter.Hydrous pyrolysis (3 days) of a dolomitic siltstone (Permian, Marl Slate) at 280, 300,320, 340 and 360°C produced significant amounts of oils in which the aromatic hydrocarbons were one and a half to two times as abundant as the saturated hydrocarbons.The overall composition of the aromatic hydrocarbons was similar to most crude oils; the major components isolated by our methods from natural oils and from pyrolysates were C1–4 alkylnaphthalenes. At the lowest pyrolysis temperature (280°C) the distributions of the more minor components of the pyrolysates (e.g. alkylphenanthrenes, aromatic steroids) were also generally similar to those found in natural crudes. However, a number of components (e.g. methylanthracenes, Diels' hydrocarbon) which are not usually reported in crudes, were also detected and the relative proportions of these increased at the higher temperatures. Hydrous pyrolysis (340°C) of an organic-rich oil shale (Jurassic, Kimmeridge) and an asphaltic-material containing no minerals produced pyrolysates in which many of these unusual compounds were also present. In addition the pyrolysate of the oil-shale contained higher proportions of organic sulphur compounds. It appears that the formation of the unusual compounds is not simply a function of the type of organic matter or mineralogy but rather of the high temperatures or fast heating rates employed.  相似文献   

16.
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.  相似文献   

17.
塔里木盆地哈拉哈塘凹陷东侧轮古地区有丰富的海相稠油产出,其中包括大型的塔河油田群,在凹陷的西北缘也有海相稠油发现。凹陷东侧海相稠油的地球化学成因已经有较多的研究报道,而西北缘针对海相稠油的研究工作仍然十分薄弱,其地球化学成因仍需深入探讨。本工作以哈拉哈塘凹陷东西两侧的稠油LG7井和DH1－6－9井为例,对比研究其地球化学特征,重点对比分析稠油沥青质中吸附／包裹烃类化合物的地球化学应用。研究结果表明凹陷东西两侧的稠油藏至少经历了两期油气的充注,其中第一期充注来自同一套烃源岩,后期遭受了,严重的生物降解改造;第二期充注来自另一套烃源岩,其正构烷烃仍然具有完整的分布模式。凹陷两侧稠油经历了相似的后期成藏过程,在西北缘相应的构造单元中可望发现更多海相来源的油气资源。  相似文献   

18.
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。  相似文献   

19.
The present study aims to establish the factors controlling the stable carbon isotopic compositions (δ13C) of individual aromatic hydrocarbons analysed by compound specific isotope analysis (CSIA) in crude oils from western Australian petroleum basins of varying age and facies type. This paper reports δ13C values of individual aromatic hydrocarbons, like alkylbenzenes, alkylnaphthalenes, alkylphenanthrenes and methylated biphenyls. The main aims are to confirm the origin (source) and age of these oils based on CSIA of selected aromatic compounds and to understand why the Sofer plot is ineffective in establishing the source of western Australian petroleum systems. The bulk δ13C of saturated and aromatic hydrocarbon fractions of crude oils have been previously used to differentiate sources, however, many Australian crude oils are not classified correctly using this method. The oils were classified as marine by the δ13C values of individual aromatic compounds and as terrigenous based on the bulk δ13C data (Sofer plot).The oils where the δ13C values of 1,6-DMN and 1,2,5-TMN isomers are most negative are indicative of a marine source, whereas oils with a less negative values for the 1,6-DMN and 1,2,5-TMN isomers are derived from marine source rocks that contain a significant terrigenous component. Similarly, oils with the least negative δ13C values for the 1-MP and 1,9-DMP isomers reflect varying inputs of terrigenous organic matter to the their marine source rocks. Plots of P/DBT and Pr/Ph concentration ratios versus δ13C values of DMP, 1,6-DMN, 1,2,5-TMN, 1-MP and 1,9-MP are constructed to establish the relative amount of terrigenous organic matter contributing to the source rock of a series of marine oils. The ratios of P/DBT and Pr/Ph plotted against the δ13C values of the aromatic isomers (such as 1,6-DMN, 1,2,5-TMN, 1-MP and 1,9-MP) provide a novel and convenient way to discriminate crude oils derived from different source rocks that contain varying amounts of marine and terrigenous organic matter.  相似文献   

20.
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.  相似文献   

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