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Abstract: This study investigates the origin and evolution of adamantanes and diamantanes in petroleum, based on the results of pyrolysis experiments on different group components of crude oil and quantitative analyses of diamondoids in the pyrolysates. Results show that the formation and evolution of lower diamondoids in petroleum occurs in three main stages: (1) early generation during the formation of oil (< ca. 0.8–1.0% EasyRo), (2) generation during the cracking of oil (>1.0% EasyRo), and (3) destruction during the late period of oil cracking. The lower diamondoids that formed during the early generation stage include free diamondoids present in the original oil and diamondoids released or transformed from group fractions of oil at relatively low levels of maturity (< ca. 0.8–1.0% EasyRo). During the process of oil cracking, all four group fractions (saturated, aromatic, resin, and asphaltene fractions) can produce adamantanes and diamantanes. Overall, adamantanes are generated primarily within the maturity range 1.0–2.3% EasyRo, and diamantanes within the maturity range 1.6–2.7% EasyRo. Group composition of the oil is probably a major factor controlling the yield and distribution of diamondoids in the main generation stage. The yield ratios of diamondoids can be used as maturity indices to assess the thermal maturity of oil, while the isomerization ratios of diamondoids are potential source facies indices for the generation stage of diamondoids. The destruction of diamondoids is observed at thermal maturity ranges >2.3% EasyRo in adamantanes and >2.7% EasyRo in diamantanes. The thermal stability of diamondoid compounds becomes a critical factor influencing the isomerization index of diamondoids during the destruction stage. The isomerization ratios of some diamondoids (e.g., MAI, DMAI-1, DMAI-2, TMAI-1, TMAI-2, and EAI) are well correlated with maturity within certain maturity ranges, indicating that isomerization indices provide good estimates of the thermal maturity of highly cracked oils. Bivariate diagrams of concentration versus isomerization indices of diamondoids are introduced to assess the maturity of oils; these diagrams provide more refined maturity assessments over a wider range of maturities than are available from single diamondoid parameters only. [Copyright &y& Elsevier]

Abstract: In this study, a simple solvent dilution followed by highly selective and sensitive gas chromatography–triple quadrupole mass spectrometry (GC–MS–MS) detection was employed to quantify diamondoids in crude oils. Runtime parameters, i.e., parent and daughter ions, collision energy (CE) and scan time, were optimized to obtain maximum selectivity and sensitivity for target analytes. Under optimum conditions, the reproducibility and accuracy of the method were tested and found to be satisfactory. Comparison of GC–MS–MS and GC–MS methods for the determination of diamondoids indicates that GC–MS–MS yields higher sensitivity (method quantitation limits of 0.08–0.37μg/goil) and better selectivity than GC–MS (method quantitation limits of 0.78–8.44μg/goil) due to the elimination of matrix ion interferences using the selected reaction monitoring (SRM) mode. In addition, quantitative data confirm that group separation has a considerable effect on the quantification of diamondoids and the effect appears to depend on multiple factors. Two crude oils (TZ261 and TD2) from the Tarim Basin, China were used to evaluate the GC–MS–MS method. The results prove that the GC–MS–MS method is a promising tool for quantitative analysis of diamondoids in crude oils, especially for oil samples with low diamondoid concentrations. [Copyright &y& Elsevier]

Abstract: In this study, headspace single-drop microextraction (HS-SDME) coupled with gas chromatography–isotope ratio mass spectrometry (GC–IRMS), was employed to determine compound specific carbon isotopic values (δ13C) of gasoline range hydrocarbons. The reproducibility of the method was found to be satisfactory. By comparison with the δ13C values of the twelve target compounds determined using direct injection of their n-C16 solution, no obvious isotopic fractionation was observed during the HS-SDME procedures. Some parameters that could affect the carbon isotopic fractionation, such as ionic strength of working solutions and inlet split ratio, were examined. The results also suggest that these factors had no significant effect on the carbon isotopic determination of gasoline range hydrocarbons. The application of HS-SDME to a crude oil sample proved that this method could be a promising tool for the determination of carbon isotopic values of gasoline range hydrocarbons in oils or aqueous samples. [Copyright &y& Elsevier]

Abstract: In this study, headspace single-drop microextraction (HS-SDME) coupled with gas chromatography-flame ionization detection (GC-FID) was tested to determine C6–C12 light hydrocarbons (LHs) in petroleum and aqueous samples. Several significant experimental parameters, such as drop solvent type, drop volume, sample solution ionic strength, agitation speed and extraction time were optimized. Under optimum extraction conditions, specifically, a 1.5μl microdrop of n-hexadecane, 30min extraction of a 5ml aqueous sample placed in a 10ml vial, and stirring at 1000rpm at room temperature, the reproducibility and accuracy of this method were found to be satisfactory. Two examples using this method indicated that HS-SDME is a simple, efficient and promising technique for the determination of volatile C6–C12 LHs in complex matrices. [Copyright &y& Elsevier]

Abstract: In this study, hollow fiber based liquid-phase microextraction (HF-LPME), coupled with GC, GC–MS and GC–IRMS detections, was employed to determine petroleum hydrocarbons in spilled oils. According to the results, the HF-LPME method collected more low-molecular weight components, such as C7–C11 n-alkanes, naphthalene, and phenanthrene, than those collected in conventional liquid–liquid extraction (LLE). The results also showed that this method had no remarkable effect on the distributions of high-molecular weight compounds such as >C18 n-alkanes, C1–C3 phenanthrene, and hopanes. Also, the carbon isotopic compositions of individual n-alkanes in the two preparation processes were identical. Accordingly, HF-LPME, as a simple, fast, and inexpensive sample preparation technique, could become a promising method for the identification of oil spill sources. [Copyright &y& Elsevier]

Since the Shu103 well was successfully drilled in 1995, the Buried Hill reservoir is receiving a new exploration emphasis in the Liaohe Basin, China. The Buried Hill oils can be divided into 3 main types in the Shuguang-Huangxiling area based on their chemical and isotopic compositions. The first type is collected mostly from the Shuguang area. The similarity to the Es4 oils and the Es4 source rock extracts indicates that they were mainly expelled from the fourth member of the Shahejie formation (Es4) in the Chenjia Sag and/or Panshan Sag, deposited in a stratified paleolake system. The second is charactized by a relative high Pr/Ph ratio, low gammacerane content and depletion of 12C in individual n-alkanes. These characteristics represent a typical origin from dominantly freshwater paralic lacustrine sediments. Various biomarker indices of the other Buried Hill oils fall between the former two types. The authors infer that these oils may be derived from the adjacent Qingshui Sag and/or Panshan Sag, and were likely generated from transitional sedimentary facies between well-circulated freshwater paralic lacustrine and relatively closed saline lacustrine. [Copyright &y& Elsevier]

Highlights • Different diamondoid indices are available for certain thermal maturity stages. • Oil maturities can be broadly constrained by diamondoid concentrations. • Some diamondoid concentration ratios can differentiate the sources of oils. • Diamondoid concentration ratios can be used to assess the maturity of normal oils. • Diamondoid isomerization ratios are effective for maturity evaluation of condensates. Abstract Here we discuss three types of diamondoid parameters for oils from the Junggar Basin. These are: absolute concentrations, concentration ratios, and isomerization ratios. According to the absolute diamondoid concentrations, the oils collected from different areas of the basin were broadly divided into three maturity stages: (1) low-mature (<100 ppm adamantanes; <5 ppm diamantanes); (2) mature (100–1000 ppm adamantanes; 5–50 ppm diamantanes); and (3) highly mature (>1000 ppm adamantanes; >50 ppm diamantanes). The oils in the northwestern region of the Junggar Basin are in the low-mature to mature stages. Based on a combination of diamondoid concentration ratios and biomarker indices, these oils can be divided into three groups, i.e., Group I oils in the Wuxia Zone derived from the lower Permian Fengcheng Formation (P 1f), Group II oils in the Kebai Zone sourced from middle Permian Lower Wuerhe Formation (P 2w), and Group III oils in the Mahu Depression generated from more mature source rocks of Jiamuhe Formation (P 1j) or the P 1f. Diamondoid concentrations and isomerization ratios were used to precisely evaluate the thermal maturity of mature oils and highly mature condensates, respectively. Our results indicate that the oils in the central part of the basin have decreasing thermal maturity from south to north, whereas the oils in the Kelameili area display increasing thermal maturity from east to west. In this study we found that different diamondoid indices are useful only in certain thermal maturity ranges. Therefore, at least for the Junggar Basin, it is crucial to know which thermal region one is in before using diamondoid ratios for maturity assessment. [ABSTRACT FROM AUTHOR]

Branched glycerol dialkyl glycerol tetraethers (brGDGTs), likely produced by bacteria in soil and peat, are widely distributed, easily detected, newly adopted biomarker compounds. In this study, brGDGTs were used to explore the relationship between the absolute abundance of brGDGTs and the distribution of oil and gas fields in the Duoshiqiao area of the Jiyang depression. The results showed that the concentrations at the Xiakou fault and in the oil and gas fields were obviously higher than those in the contrast areas. The clear relationship among the concentration of brGDGTs, the distribution of oil and gas fields, and the acidolysis hydrocarbon (ethane) indicates that the concentration effectively responds to hydrocarbon seeps from the oil and gas field below. brGDGTs may become some of the most important indicators in surface geochemical prospecting for oil and gas. [ABSTRACT FROM AUTHOR]

Oil cracking gas plays an important role in the resources of natural gas in the basins with high and over mature marine source rocks in China. The prediction of the oil cracking gas resources becomes necessary and urgent in the gas exploration in these basins. A marine crude oil sample was pyrolyzed using sealed gold tubes system. The pyrolysates including gas, liquid and solid were quantitatively analyzed. Based on the pyrolysis data and kinetic calculation, the yield correlativity among gas, liquid and solid products was regressed with high correlative coefficients to establish a prediction model suitable for the resource estimation of oil cracking gas. The verification formula for this model was also established on the principle of mass conservation. The affecting factors and the application preconditions of this prediction model were discussed. This model would enlighten and provide some new ideas for the resource assessment of natural gas in the high and over mature marine carbonate source rock areas in China. It is expected to be valuable in gas exploration. [ABSTRACT FROM AUTHOR]

Reservoir alteration of crude oils is ubiquitous in petroleum reservoirs. Alteration can change the composition and physicochemical properties of crude oils, and complicate oil–source correlations and origin studies of crude oils. Thus, the identification and assessment of reservoir alteration could provide a better understanding of the formation and evolution of crude oils. In this study, the effects of reservoir alteration (e.g., biodegradation, gas washing, water washing, and mixing) on oils in the Junggar Basin, northwest China, were identified and assessed by combining diamondoid indices with other commonly studied crude oil properties. The results indicate that: (1) diamondoid indices can be used to evaluate the intensity of reservoir alteration on oils (e.g., slight biodegradation and water washing has no effect on diamondoids; moderate biodegradation and water washing can result in a marked increase in diamondoid concentrations; severe biodegradation and water washing significantly changes diamondoid concentration and isomerization ratios); (2) diamondoid indices can assist in determining the type of reservoir alteration of oils (e.g., condensate formed by gas washing has a lower diamondoid concentration than that generated by thermal cracking; differing from biodegradation and water washing, gas washing can affect diamondoid ratios; mixing can be identified by a combination of diamondoid concentrations and other parameters, such as API gravity and biomarker indices in oils). Therefore, diamondoids provide specific information as to the reservoir alteration of oils, which is useful in further understanding of the origin and evolution of crude oils in the Junggar Basin. • Slight to moderate biodegradation affects diamondoid concentrations not ratios. • Variations in diamondoid ratios might reflect severe biodegradation of oils. • Only severe water washing affects diamondoid isomerization and concentration ratios. • Diamondoid concentration can be used to differentiate origins of condensates. • Discrepancies between diamondoid concentration and other indices reflect oil mixing. [ABSTRACT FROM AUTHOR]

Two classification methods, the distribution of biomarkers and the alternating least squares (ALS) chemometric analysis were used to investigate the genetic characteristics of oils collected from the Baiyun deep-water area of the Pearl River Mouth Basin in the South China Sea. Results of the two methods were generally consistent that most of the oils were originated from the shallow lacustrine source rocks, but oils from the West Sub-Sag (WSS) and the South Sub-Sag (SSS) have a distinct geochemical characteristic with low abundances of bicadinanes and oleanane, and relatively lighter δ13C value (<−28.0‰). The ALS chemometric analysis can quantitatively determine the sources of the oils. It shows that mixing has commonly occurred between the oils, and three end-member oils were identified (i.e., EM1, EM2, and EM3), which were derived from the semideep–deep Wenchang Formation source rocks that are characterized by a predominance of C 27 steranes and low concentrations of bicadinanes and oleanane, the shallow lacustrine Enping Formation source rocks in the Main Sub-Sag (MSS) that are rich in bicadinanes but depleted in oleanane, and the shallow lacustrine Wenchang and/or Enping formations source rocks in the East Sub-Sag (ESS) that have a relatively high abundance of bicadinanes, a moderate content of oleanane, and a predominance of C 29 steranes, respectively. The oils from the Panyu Low Uplift (PLU) are dominated by >83% of EM2 oil. Oils from the SSS and WSS are dominated by EM1 oil (68.0%–93.1%). Oils from the ESS and eastern part of the MSS (E-MSS) are mixed oils consisting mainly of EM2 and EM3 oil, with an increasing proportion of EM3 moving from the E-MSS to central ESS. The maturity of the oils was assessed based on diamondoid indices, and oils from the PLU have the highest maturities (1.43%–1.59% Rc), whereas oils from the SSS have the lowest maturities (1.23%–1.25% Rc), corresponding to the different maturities of their source rocks. The semideep–deep lacustrine oils discovered in the WSS and SSS highlight the hydrocarbon generation potential of these types of source rocks in the Wenchang Formation, where further oil exploration should be focused. • Oils from different structural belts have different origins on a regional scale. • Alternating least squares analysis shows three end-member oils in the Baiyun Sag. • The end-member oils are correlated to the source rocks in the Baiyun Sag. • Maturity studies based on diamondoid indices support the genetic analysis. • Semideep–deep lacustrine oils in the WSS and SSS are a new exploration target. [ABSTRACT FROM AUTHOR]

[Display omitted] • Pyrolysis experiments on four organic matter types simulate diamondoid evolution. • Principal component analysis explains the main factors affecting diamondoid indices. • PCA-Fisher discriminant analysis model objectively identifies oil source types. • PCA-regression analysis model quantitatively predicts oil thermal maturity. Assessing the origins and thermal maturity of oils is an important issue in applied petroleum geochemistry. In this study, we extracted information regarding the sources and thermal maturity of oils from diamondoid data using multivariate statistical analysis based on four series of thermal simulation experiments conducted on Type I, II, and III kerogens and a crude oil. Using principal component analysis (PCA) and discriminant analysis (DA), we established the relationship between diamondoid indices and kerogen type, which was then used to identify the source of oils in some oil fields in China. PCA and regression analysis (RA) were used to determine the quantitative relationship between diamondoid indices and thermal maturity, which was then used to estimate the thermal maturity of the studied oils. Our results indicate that this approach is effective for determining the source and maturity of oils, particularly for condensates. [ABSTRACT FROM AUTHOR]