The effects of sodium sulfate on the emissions characteristics of an emulsified marine diesel oil-fired furnace

Degraded diesel oils are commonly used in marine power plants to conform to the demands of shipowners for fuel economy. The burning of these marine fuel oils, which frequently contain various extents of oxides of iron, silicon, calcium, vanadium and potassium, such as Na₂SO₄, Fe₂O₃, SiO₂, CaO, V₂O₅, etc., are susceptible to form much more complex compounds of either gaseous or solid phases. The release of these emissions to the environment may cause atmospheric pollution and a health hazard to human beings. Emulsification of a fuel oil with water to produce a micro-water-particles-dispersed-in-oil (W/O) emulsion has been considered as one of the promising techniques to improve combustion characteristics of low-grade marine oils and in turn effectively help to reduce the release of air pollutants. Marine fuel oil A, which approximates ASTM No. 2D oil was used as the test oil and the surfactant Span 80 was used to promote the affinity and integrating force between the components of the emulsion. An emulsifying/homogenizing machine was employed to stir the emulsion mixture of the marine oil, distilled water, surfactant Span 80 and sodium sulfate (Na₂SO₄) powder of 300 ppm. The mechanically blended emulsion mixture was injected, atomized and burned in an oil-fired furnace using an automatic burner. Burning gas composition, burning efficiency and gas temperature were measured and analyzed. Compared to neat marine diesel oil, W/O emulsions had higher combustion efficiencies, higher concentrations of O₂ and SO₂, while gas temperatures were lowered and CO and NO_x production was reduced. The addition of sodium sulfate decreased combustion efficiency and NO_x concentration and increased O₂, CO, and SO₂ concentrations.     

Effects of potassium sulfide content in marine diesel fuel oil on emission characteristics of marine furnaces under varying humidity of inlet air

Degraded fuel oils are generally used in marine power plants for economic purposes, so as to reduce operating expenses. These marine fuel oils commonly contain various oxides or sulfide compounds of metallic elements in the fuel ash, and affect the combustion and emission characteristics of marine power plants to different extents. Moreover, marine power plants are more often operated in a highly humid environment. As a result the emission and burning process may also be altered by the various humidity level of the inlet air. The effects of potassium sulfide in marine diesel on the combustion and emission characteristics of marine furnaces under varying levels of relative humidity of inlet air were experimentally investigated in this study. A cylindrical industrial furnace made of AISI 316 stainless steel, and an automatic oil-fired burner were used for the emission characteristics measurements and observation. A mechanically homogenizing machine was used to stir potassium sulfide (K₂SO₄) powder and marine diesel with a preset K₂SO₄ concentration. The relative humidity of the inlet air and temperature were adjusted to their assigned values by a large-size air conditioner before being pumped into the burner. The marine diesel oil mixture was atomized by the inlet air consequently ignited by an electrode and then burned within the horizontal furnace. There were eight rectangular slots cut in the upper portion of the furnace wall so that the probes of a gas analyzer and a thermocouple could be inserted into radial positions in the cylindrical furnace. The concentrations of gas emission and burning gas temperature and the combustion efficiency were analyzed. The experimental results show that the burning gas temperature, carbon dioxide emission and combustion efficiency decreased when the concentrations of excess air and oxygen emission increased with the addition of potassium sulfide in the marine diesel fuel. This is primarily attributed to the fact that the sulfide of an alkali compound such as K₂SO₄ may suppress the oxidation reaction process, leading to inferior combustion characteristics.     

Sensitivity of three microalgae to crude oils and fuel oils

Four crude oils and five fuel oils have been tested for toxicity with three microalgae—a blue-green, a green and a diatom. The oils were absorbed on filter paper pads and the pads submerged in the growth medium. The crude oils were less inhibitory than equal amounts of fuel oils. Despite initial growth lags, the crude oils allowed growth at 30 μl/20 ml of culture medium (10⁵ cells/ml) while fuel oils were lethal at 10 μl/20 ml. The toxicity patterns of two of the whole fuel oils were different from that seen with their water soluble fractions (WSF); for example, the Baton Rouge fuel oil sample was very toxic to growth of the three test organisms whereas its WSF was relatively innocuous. Photosynthesis of a sensitive organism Chlorella autotrophica, strain 580 (10⁷ cells/ml), was only temporarily depressed by the crude oils (30 μl/20 ml). Four of the fuel oils inhibited photosynthesis, O₂ output decreasing to zero without recovery. When the fuel oils were heated in a stream of helium they were detoxified. Chemical analyses of two of the toxic fuel oils before and after heating were compared with analyses of the Montana sample, a largely non-toxic fuel oil, in an effort to determine what types of compounds might be involved. Classes of aromatic compounds which were not accountable for the toxicity observed here include naphthalene, methylnaphthalenes, dibenzothiophenes, phenanthrenes and compounds with volatilities greater than methylnaphthalenes. Paraffinic and asphaltic fractions of fuel oil were also non-toxic. The accumulated chemical data suggest that the toxicity of whole fuel oils is due to the less water soluble types of compounds in the higher boiling aromatic fraction.     

南海原油和燃料油对仔虾和仔鱼的急性毒性试验

测定了南海原油、0号柴油和20号柴油对斑节对虾Penaeusmonodon、日本对虾Penaeusjoponicus、刀额新对虾Metapenaeusensis3种仔虾和黄鳍鲷和Sparuslatus、黑鲷Sparusmacrocephalus、前鳞鲻MugilOphuyseni和七星鲈Lateolabraxjaponicus4种仔鱼的急性毒性。油类对仔虾和仔鱼的毒性大小顺序均为：0号柴油＞20号柴油＞南海原油。油类分散液的毒性大于其水溶性组分。在曝油的3种仔虾中,刀额新对虾对0号柴油和20号柴油的耐受力最弱,而日本对虾对南海原油最为敏感。曝油仔鱼对3种油类的耐受力顺序为：黄鳍绸＞黑鲷＞前鳞鲻,而七星鲈对0号柴油最为敏感。3种仔虾对油类的耐受力明显低于4种仔鱼。     

Cost-benefit evaluation of using biodiesel as an alternative fuel for fishing boats in Taiwan

Biodiesel, which is manufactured from vegetables oils, animal fats, or algae can be an excellent alternative fuel to petroleum diesel due to its superior fuel properties and lower pollutant emissions. In contrast, fishing-boat fuel generally has much poorer fuel properties and a high sulfur content that can reach several hundred times that of the premium diesel used in land-based vehicles. Pollutant emissions from fishing boats are known to be a significant source of air pollution in the global environment. This study examines the use of biodiesel to replace fishing-boat fuel A to reduce pollutant emissions from fishing boats. The incremental cost, reduction in emissions, and cost-benefit corresponding to various weight proportions of biodiesel to replace fishing-boat fuel A are evaluated. The results show that the annual consumption of fishing-boat fuel A by Taiwanese fishing boats amounts to 649,201 kiloliters (kl) and total emissions from burning the fuel is 958.93 tons per year. If all fishing-boat fuel A were replaced with biodiesel, then pollutant emissions would be decreased by 421.94 tons, or 44.0%. However, this would also result in a USD 144.45 million or 25.85% increase in fuel cost. This study also finds that a replacing 20 wt% of fishing-boat fuel A with biodiesel has the highest cost-benefit ratio, which implies a larger reduction in emissions with a lower fuel cost increase, and is the most suitable option for fishing boats in Taiwan.     

Sensitivity of two psychrophilic diatoms to crude oil and fuel oil

Two pure cultures of diatoms, a Nitzschia sp. and a Chaetoceros sp., were grown at 0°C or 10°C in the presence of two crude oils and two fuel oils. The petroleum samples were absorbed onto filter paper discs and added directly to the algal cultures. In all cases the organisms were much more sensitive to the crude oils or fuel oils when growing at 0°C than at 10°C. The rate of photosynthesis measured by an oxygen electrode for Nitzschia sp. grown and tested at 0°C was not affected during 3 hours' incubation with some four times the amount of a crude oil or fuel oil that blocked growth. The experiments lead to the cautious suggestion that psychrophilic algae will prove some fivefold more sensitive than mesophilic algae to petroleum pollution.     

O/W型TR-02稠油乳状液的配制及静态稳定性评价

针对河南油田L131井稠油,采用自制的TR-02乳化剂,根据稠油乳化降黏原理及O/W型乳状液的形成机制,研究了乳化剂的类型和含量、乳化方式、搅拌方式和搅拌速度、相体积分数等对O/W型稠油乳状液稳定性的影响,特别是初步探讨了在TR-02中加入纳米助剂TR-23,对O/W型稠油乳状液稳定性的影响,为纳米材料在稠油乳化降黏中的应用提供一个可参考的基础数据。     

Origin of crude oils from oilfields in the Zagros Fold Belt,southern Iraq: Relation to organic matter input and paleoenvironmental conditions

Crude oil samples from Cretaceous and Tertiary reservoir sections in the Zagros Fold Belt oil fields, southern Iraq were investigated using non-biomarker and biomarker parameters. The results of this study have been used to assess source of organic matter, and the genetic link between oils and their potential source rocks in the basin. The oils are characterized by high sulphur and trace metal (Ni, V) contents and relatively low API gravity values (17.4–22.7° API). This indicates that these oils are heavy and generated from a marine source rock containing Type II-S kerogen. This is supported by their biomarker distributions of normal alkanes, regular isoprenoids, terpanes and steranes and the bulk carbon isotope compositions of their saturated and aromatic hydrocarbons. The oils are characterized by low Pr/Ph ratios (<1), high values of the C₃₅ homohopane index and C₃₁-22R/C₃₀ hopane ratios, relatively high C₂₇ sterane concentrations, and the predominance of C₂₉-norhopane. These biomarkers suggest that the oils were generated predominantly from a marine carbonate source rock, deposited under reducing conditions and containing plankton/algal and microorganisms source input. The presence of gammacerane also suggests water column stratification during source rock deposition.The biomarker characteristics of the oils are consistent with those of the Middle Jurassic Sargelu carbonate as the effective source rock in the basin. Biomarker maturity data indicate that the oils were generated from early maturity source rocks.     

柴油的中重度风化鉴别指标研究

以柴油为研究对象,采用溢油风化模拟实验,从分子级水平揭示中长期风化作用对溢油组成的影响。利用相对偏差和重复性限法进行评价和筛选,研究表明,柴油在较短时间(10 d)内,phytane/n-C18和pristine/phytane特征比率可较好地作为油品鉴别的依据;在10~30 d的风化期间,pristine/phytane仍可作为油品鉴别的依据;较长期的风化过程后,上述三个正构烷烃特征比率对于油品鉴别已不再具备意义。所选多环芳烃诊断比值指标中,除MNR、MP/P外,其他参数(MPI-1,MPI-2,Rc,MPDF1,MPDF2,MNR)相对标准偏差在1.10%~5.40%,可较好地用于重度风化溢油源鉴定。     

Alteration and multi-stage accumulation of oil and gas in the Ordovician of the Tabei Uplift,Tarim Basin,NW China: Implications for genetic origin of the diverse hydrocarbons

The Ordovician is the most important exploration target in the Tabei Uplift of the Tarim Basin, which contains a range of petroleum types including solid bitumen, heavy oil, light oil, condensate, wet gas and dry gas. The density of the black oils ranges from 0.81 g/cm³ to 1.01 g/cm³ (20 °C) and gas oil ratio (GOR) ranges from 4 m³/m³ to 9300 m³/m³. Oil-source correlations established that most of the oils were derived from the Mid-Upper Ordovician marine shale and carbonate and that the difference in oil properties is mainly attributed to hydrocarbon alteration and multi-stage accumulation. In the Tabei Uplift, there were three main periods of hydrocarbon accumulation in the late Caledonian stage (ca. 450–430 Ma), late Hercynian stage (ca. 293–255 Ma) and the late Himalayan stage (ca. 12–2 Ma). The oil charging events mainly occurred in the late Caledonian and late Hercynian stage, while gas charging occurred in the late Hercynian stage. During the late Caledonian stage, petroleum charged the reservoirs lying east of the uplift. However, due to a crustal uplifting episode in the early Hercynian (ca. 386–372 Ma), most of the hydrocarbons were transformed by processes such as biodegradation, resulting in residual solid bitumen in the fractures of the reservoirs. During the late Hercynian Stage, a major episode of oil charging into Ordovician reservoirs took place. Subsequent crustal uplift and severe alteration by biodegradation in the west-central Basin resulted in heavy oil formation. Since the late Himalayan stage when rapid subsidence of the crust occurred, the oil residing in reservoirs was exposed to high temperature cracking conditions resulting in the production of gas and charged from the southeast further altering the pre-existing oils in the eastern reservoirs. A suite of representative samples of various crude oils including condensates, lights oils and heavy oils have been collected for detailed analysis to investigate the mechanism of formation. Based on the research it was concluded that the diversity of hydrocarbon physical and chemical properties in the Tabei Uplift was mainly attributable to the processes of biodegradation and gas washing. The understanding of the processes is very helpful to predict the spatial distribution of hydrocarbon in the Tabei Uplift and provides a reference case study for other areas.     

Geochemistry and charge history of oils from the Yuqi area of Tarim Basin,NW China

The geochemistry, origin and charge history of oils from the Yuqi area of Tarim Basin have been investigated, through GC, GC-MS and fluid inclusion microthermometry analysis. The Yuqi oils accumulated mainly in three intervals: (1) in the Lower-Middle Ordovician Yingshan Formation (O_1-2y) carbonate reservoirs; (2) in the overlying Upper Triassic Halahatang Formation (T₃h); and (3) in the Lower Cretaceous Yageliemu Formation (K₁y) sandstones. Oils from different reservoirs have distinct physical properties, varying from extra-heavy (O_1-2y), heavy (T₃h), to light oils (T₃h and K₁y). However, their geochemical compositions show a high degree of similarity, which indicates that they derive from the same source rock. Abundant tricyclic terpanes, gammacerane, dibenzothiophene and C₂₁C₂₂steranes, together with a low level of diasteranes, indicate an anoxic marine source rock for oils in the Yuqi area. Oil-oil correlation shows that Yuqi oils derive from the same source bed as Tahe oils. The co-occurrence of intact n-alkanes and 25-norhopanes in all the samples supports the proposition that there is a mixture of an early filled severely biodegraded oil and a late filled fresh oil.In this study, charge history is examined on the basis of integration of fluid inclusion homogenization temperature data with 1D burial-thermal history models. Two episodes of oil charging are identified in the O_1-2y reservoir (well YQX1-1) at around 436-420 Ma (Middle-Late Silurian) and 10-3 Ma (Miocene to Pliocene), respectively. For the samples from the T₃h and K₁y intervals, only one episode of oil charge is indicated by the homogenization temperatures of coexisting aqueous inclusions with an inferred timing around 10-3 Ma. The T₃h heavy oil reservoir is assumed to be a secondary hydrocarbon pool, which accumulated by re-migration and re-distribution of hydrocarbons from O_1-2y hydrocarbon pools. The few early biodegraded oils in the K₁y light oils were probably picked up along the migration pathway during the late fresh oil charging.     

The origin and charging directions of Neogene biodegraded oils: A geochemical study of large oil fields in the middle of the Shijiutuo Uplift,Bohai Sea,China

Two large oil fields (QHD32-6 and QHD33-1), located in the middle part of the Shijiutuo Uplift, have generally suffered mild biodegradation. Based on multivariate statistical analysis of the biomarker parameters, this study discussed the origin and charging directions for these two oil fields.In contrast to Ed₃-derived oil, all available oil samples from these two large oil fields displayed low C₁₉/C₂₃, C₂₄/C₂₆ and high G/H and 4-MSI, which are attributed to the mixtures of oils derived from the Shahejie (Es₁ and Es₃) source rocks. Oils in QHD32-6, which contain relatively more Es₃-derived oil, are called Group I oils, and most oils in QHD33-1, which share relatively more Es₁-derived oil, are called Group II oils. Our mixed oil experiments reveal the predominant Es₃- and Es₁-derived oil contribution for Group I and Group II oil groups, respectively; however, the selection of end member oils warrants further research.Based on comparisons of biomarker parameters, the QHD32-6 oil field was mainly charged in the north by oil generated from Shahejie formation source rocks in the Bozhong depression. However, oils from the north of QHD32-6 field display a remarkable difference to the oils in the south of this field, which may indicate that a charging pathway exists from the QHD33-1 field. Considering the variations in biomarker compositions in the west to -east and northwest to -southeast sections across the QHD33-1 and QHD32-6 oil fields, it can be deduced that Es₃-sourced oil migrated westward to the QHD32-6 traps, and then charging by Es₁ oil from the Bozhong Sag resulted in the QHD33-1 oil field being characterized by the mixture of Es₃- and Es₁-sourced oil. Moreover, migration of Es₁-derived oil from the Qinnan Sag was not identified, implying that the QHD33-1 oil field is mainly charged from the northeast of the Bozhong Sag.     

The petroleum geochemistry of the Termit Basin,Eastern Niger

Sixty crude oils from the Termit Basin (Eastern Niger) were analysed using biomarker distributions and bulk stable carbon isotopic compositions. Comprehensive oil-to-oil correlation indicates that there are two distinct families in the Termit Basin. The majority of the oils are geochemically similar and characterized by low Pr/Ph (pristane to phytane ratios) and high gammacerane/C₃₀ hopane ratios, small amounts of C₂₄ tetracyclic terpanes but abundant C₂₃ tricyclic terpane, and lower δ¹³C values for saturated and aromatic hydrocarbon fractions. All of these geochemical characteristics indicate possible marine sources with saline and reducing depositional environments. In contrast, oils from well DD-1 have different geochemical features. They are characterized by relatively higher Pr/Ph and lower gammacerane/C₃₀ hopane ratios, higher amounts of C₂₄ tetracyclic terpane but a low content of C₂₃ tricyclic terpane, and relatively higher δ¹³C values for saturated and aromatic hydrocarbon fractions. These geochemical signatures indicate possible lacustrine sources deposited under freshwater, suboxic-oxic conditions. This oil family also has a unique biomarker signature in that there are large amounts of C₃₀ 4α-methylsteranes indicating a freshwater lacustrine depositional environment.The maturity of the Termit oils is assessed using a number of maturity indicators based on biomarkers, alkyl naphthalenes, alkyl phenanthrenes and alkyl dibenzothiophenes. All parameters indicate that all of the oils are generated by source rocks within the main phase of the oil generation stage with equivalent vitrinite reflectance of 0.58%–0.87%.     

Source diagnostic and weathering indicators of oil spills utilizing bicyclic sesquiterpanes

Bicyclic Sesquiterpanes (BSs) are ubiquitous components of crude oils and ancient sediments. BSs in crude oils and diesel oil were identified and characterized, the effects of moderate weathering on BS distributions were discussed, and a methodology using diagnostic indices of BSs was developed for oil correlation and differentiation. The results showed that crude oils and oil products had different abundances and distributions of BSs and, consequently, resulted in different diagnostic ratios. The selected diagnostic ratio indices of BSs, such as BS4/BS5 (ratio of 4,4,8,9,9-pentamethyl-decahydronaphthalene to 8β (H)-drimane), BS6/BS5 (ratio of 4,4,9,9,10-pentamethyl-decahydronaphthalene to 8β (H)-drimane), BS8/BS9 (ratio of the second peak to the third peak of C 16 sequiterpane), and BS8/BS10 (ratio of C 16 sequiterpane to 8β (H)-homodrimane), still maintained better stabilities (%RSD < 5%) after weathering for 30 d. The longer weathering process (150 d) had some effect on such ratios (5% < %RSD < 10%). The facts of the uniqueness, abundance in petroleum, and chemical stability of BSs enable them to be suitable as an effective diagnostic means for identifying spilled oil with moderate weathering, particularly for lighter refined product samples that are difficult to identify by current techniques.     

渤海古近系东营组三角洲相油田地质特征研究

渤海古近系东营组三角洲相油田是渤海油田的主力含油层系.从构造、储层与沉积、流体和油藏等方面对渤海海域东营组三角洲相油田地质特征进行了研究,按河流三角洲和辫状河三角洲相砂岩油藏两种沉积相类型分别对储层分布特征进行了描述.在此基础上探讨了此类油田的流体分布特点和油藏模式,并认为渤海东营组三角洲相油田以中到大型为主,储层岩性大都属于高孔高渗的疏松砂岩,储层具有分布较稳定、油层厚和物性好等特点,原油以普通稠油为主,其次是中、低黏油.     

Oil-oil and oil-source rock correlations in the Alpine Foreland Basin of Austria: Insights from biomarker and stable carbon isotope studies

The Alpine Foreland Basin is a minor oil and moderate gas province in central Europe. In the Austrian part of the Alpine Foreland Basin, oil and minor thermal gas are thought to be predominantly sourced from Lower Oligocene horizons (Schöneck and Eggerding formations). The source rocks are immature where the oil fields are located and enter the oil window at ca. 4 km depth beneath the Alpine nappes indicating long-distance lateral migration. Most important reservoirs are Upper Cretaceous and Eocene basal sandstones.Stable carbon isotope and biomarker ratios of oils from different reservoirs indicate compositional trends in W-E direction which reflect differences in source, depositional environment (facies), and maturity of potential source rocks. Thermal maturity parameters from oils of different fields are only in the western part consistent with northward displacement of immature oils by subsequently generated oils. In the eastern part of the basin different migration pathways must be assumed. The trend in S/(S + R) isomerisation of ααα-C₂₉ steranes versus the αββ (20R)/ααα (20R) C₂₉ steranes ratio from oil samples can be explained by differences in thermal maturation without involving long-distance migration. The results argue for hydrocarbon migration through highly permeable carrier beds or open faults rather than relatively short migration distances from the source. The lateral distance of oil fields to the position of mature source rocks beneath the Alpine nappes in the south suggests minimum migration distances between less than 20 km and more than 50 km.Biomarker compositions of the oils suggest Oligocene shaly to marly successions (i.e. Schoeneck, Dynow, and Eggerding formations) as potential source rocks, taking into account their immature character. Best matches are obtained between the oils and units a/b (marly shale) and c (black shale) of the “normal” Schöneck Formation, as well as with the so-called “Oberhofen Facies”. Results from open system pyrolysis-gas chromatography of potential source rocks indicate slightly higher sulphur content of the resulting pyrolysate from unit b. The enhanced dibenzothiophene/phenanthrene ratios of oils from the western part of the basin would be consistent with a higher contribution of unit b to hydrocarbon expulsion in this area. Differences in the relative contribution of sedimentary units to oil generation are inherited from thickness variations of respective units in the overthrusted sediments. The observed trend towards lighter δ¹³C values of hydrocarbon fractions from oil fields in a W-E direction are consistent with lower δ¹³C values of organic matter in unit c.     

短期风化对混合溢油组成的影响

对两种原油进行混合配比实验,将混合后油样置于人工气候箱进行风化模拟实验,采用气相色谱质谱联用仪(GC-MS)检测风化样品中的生物标志化合物,短期风化作用对混合溢油的油指纹、生物标志化合物诊断指标等的影响。结果表明,混合溢油的正构烷烃总质量变化与单一原油油品的变化规律相近,即前期风化较快,质量减损较多,而后期风化趋缓,不同混合比例的溢油表现差异不明显。常用于短期风化的诊断比值对各混合油样的风化具有指示意义,但难以定性鉴别油品是否发生混合。重复性限法检验只能判定短期风化过程前后的油样为同一油源,而难以反映油样是否为混合油源的特征,各诊断比值的RSD%值较大可能是混合溢油的一个表现。     

盘锦红海滩重金属与石油污染调查

本文选取了辽宁省盘锦市红海滩6个采样点的沉积物,通过测定其中重金属和石油各组分的含量,调查盘锦红海滩的重金属和石油的污染情况。结果表明,各采样点中除退化区的Cu和茂盛区的Pb含量高于《海洋沉积物质量标准》(GB18668-2002)Ⅰ类标准外,其他各区域重金属含量均低于(GB 18668-2002)Ⅰ类标准。茂盛区的植物必需金属Fe、Mg、K含量在36.9～46.1 g/kg之间,高于退化区和光滩区的30.7～38.0 g/kg;退化区和茂盛区的土壤样品含油浓度较高,在1.6～5.2 mg/kg之间,光滩区的土壤样品含油浓度较低,为2.5mg/kg,均远低于(GB18668-2002)Ⅰ类标准500mg/kg;退化区的土壤中多环芳烃各组分含量在0.4～51.8ng/g之间,相比于其他地区的0.2～25.0ng/g较高,而光滩区土壤中多环芳烃各组分含量在0.2～3.8 ng/g之间,相比于其他地区的0.3～51.8 ng/g较低;不同区域土壤正构烃的组成(C10～C35)基本相同,但是分布特征存在较大差别。     

Characteristics and origin of carbon isotopes of n-alkanes in crude oils from the western Pearl River Mouth Basin,South China sea

The quantitative characterization of carbon isotopes of n-alkanes is commonly carried out in organic geochemical studies. Possible controls on carbon isotopes include source organic matter, maturity, fractionation during oil expulsion and migration, and the mixing of different oils. In this study of the origin of crude oils in the western Pearl River Mouth Basin, the influences of all of these factors have been considered in reaching a conclusion. Carbon isotopes of n-alkanes in the crude oils, and the extracts of the two effective source rocks (the Wenchang and Enping formations) in the basin, exhibit clear differences. The Wenchang source rocks have heavy δ¹³C values that remain almost constant or become slightly heavier with increasing carbon number. The Enping source rocks have light δ¹³C values that become lighter with increasing carbon number. Two groups of oils in this area were identified based on the carbon isotopes of the n-alkanes; groupIoils are similar to extracts of the Wenchang source rocks. However, the groupIIoils are different from both the Wenchang and Enping source rocks and the carbon isotopic profiles of their n-alkanes exhibit a “V” feature with increasing carbon number. The results of artificial thermal maturation experiments indicate that, from the early stage to the peak stage of oil generation (with EasyRo between 0.64% and 1.02%), the δ¹³C values of n-alkanes in the pyrolysis oils become heavier by about 3‰ with increasing thermal maturity, but the shape of the carbon isotopic profiles are not significantly changed. Calculated δ¹³C values of n-alkanes in “mixed” artificial pyrolysis oils indicate that the mixture of oils generated from the same source rocks with different maturities could not change the carbon isotopic profile of the n-alkanes, however, a mixing of the Wenchang and Enping oils could give the “V” feature in the profiles, similar to the groupIIoils in this area. The groupIIoils appear to be mixed Wenchang and Enping oils, the latter being the dominant component in the mixture. We conclude that the source organic matter and the degree of mixing are the main factors controlling the carbon isotopic characteristics of n-alkanes in crude oils in the western Pearl River Mouth Basin.     

Geochemical investigation of oils from Cretaceous to Eocene sedimentary sequences of the Abadan Plain,Southwest Iran

Oil samples from Lower Cretaceous to Eocene reservoirs in southwest Iran were analyzed using gas chromatography–mass spectrometry and gas chromatography–isotope ratio mass spectrometry for genetic classification of oil families and determining their maturity. The Studied oil samples are non-biodegraded and their gravity range from 18.3 to 37° API. The slight even/odd n-alkane predominance, coupled with low Pr/Ph values, suggests their likely source rocks with a predominance of algal organic matter, type IIS kerogen deposited under strongly reducing marine environments. The biomarker distribution of investigated oils is characterized by high concentration of both C₂₉ and C₃₀ hopanes and ratios of C₂₉/C₃₀H are generally greater than unity. There is a marked predominance of C₂₉ regular sterane over C₂₇ and C₂₈ homologs in our studied oils. High sterane/hopane values and cross plot of the δ¹³C sat versus δ¹³C aro show contribution of marine organic matter. Medium value of gammacerane index and other salinity indices show water density stratification and high salinity conditions of the environment of deposition. It can be concluded that the studied reservoirs, due to their variable maturity have different API gravity and contain two oil families (types A and B) with latter being deeper and comprising more mature oils.