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In this study, average structural characteristics of amber were researched and used as an example to establish the three-dimensional (3D) average structure of resin. Two coal samples containing solid amber were collected from Fushun and Hunchun in Northeast China, from which pure amber samples were separated and resin was extracted. Solid-state nuclear magnetic resonance (13C NMR) spectroscopy was used to obtain structural information of amber, and matrix-assisted laser desorption ionization time-of-flight mass spectrometry was performed on the resins to determine their molecular mass. The results of these studies revealed that the average structure of amber was dominated by cycloalkane, with a small amount of aromatic carbon, and there were almost no aliphatic chains in the structure. The molecular masses of the compounds in the resin were mainly in the range 99-750 Da, and the average molecular mass was ∼370 Da. To characterize the resin chemical structure, two 3D molecular models based on density functional theory were established taking amber as the example, and the relevant molecular bond energies were calculated. Based on these models, the interactions among the components in oil were studied, and the binding energies of the different molecules were calculated. In summary, in this study, amber was used as a medium to establish an accurate molecular model of resin and proved that compared to hydrocarbon compounds, resin molecules were more likely to interact with bitumen.

The origin and geochemical significance of the rearranged hopanes in hydrocarbon source rocks or crude oil have attracted extensive attention. Despite numerous studies, there is not yet a proper conclusion. Therefore, this paper discusses the formation conditions of such compounds and points out their geochemical significance in more detail using a remarkably broad range of source rocks and crude oils from four basins in China. Varying content of rearranged hopanes was found in a total of 19 source rocks and oils from the Ordos, Sichuan, and Tarim basins and the North China Block. Gas chromatography–mass spectrometry (GC–MS) in combination with X-ray diffraction (XRD) and conventional geochemical parameters was used for Pearson correlation analysis to reveal the enrichment mechanisms of rearranged hopanes in the studied rock and oil samples. The GC–MS and XRD results showed that the studied source rocks with high rearranged hopane contents are closely associated with the high abundance of quartz rather than that of clay. Furthermore, the present study reveals that anoxic lacustrine conditions are the primary controlling factors of relatively high abundance of rearranged hopanes in the studied rocks and oils, whereas thermal maturity and terrigenous organic matter input are the secondary factors.

Twenty crude oil samples were obtained from the Gudong Oilfield and their organic geochemical characteristics were analyzed. The oil samples were classified into three families by hierarchical cluster analysis and principal component analysis based on 13 source-related and depositional environment-related biomarker parameters. Oils in family I have low ratios of C19/C23 tricyclic terpanes and C24 tetracyclic terpane/C26 tricyclic terpanes, and relatively high ratios of steranes/hopanes and C30 4-methylsteranes/ααα20R C29 sterane, thus indicating that microalgae were the dominant organic matter input for the source rocks of family I. The gammacerane/C30 hopane ratios are higher than that of family II and family III, whereas the C35/C34 homohopane ratios are lower, thus indicating a suboxic, brackish water environment for the source rocks. The inferred source rock is the first member of the Shahejie Formation in the Huanghekou Sag. Family II is characterized by high ratios of C19/C23 tricyclic terpanes and C24 tetracyclic terpane/C26 tricyclic terpanes but relatively low ratios of steranes/hopanes and C27/C29 αααR steranes. These findings suggest that the original organic matter of the source rocks had a greater contribution from terrigenous higher plants than from microalgal. The relatively low ratios of gammacerane/C30 hopane and C35/C34 homohopane suggest that the source rocks were deposited in an oxic environment with a low salinity, thus corresponding to the Dongying Formation in the Huanghekou Sag. Family III oils have high C27/C29 ααααR steranes ratios and low C30 4-methylsteranes/ααα20R C29 ratios, which indicate the contribution of microalgae (especially zooplankton algae) to the source rocks. The relatively high abundance of C35 homohopane and low gammacerane/C30 hopane ratios suggest a weakly reducing condition with low salinity, which is in accordance with the third member of the Shahejie Formation in the Gunan Sag. The C31S/(S + R) homohopane ratios imply that oil samples in this study are in the mature stage, although the ratios of C2920S/(20S + 20R) and C29ββ/(αα + ββ) steranes suggest that the maturity of family II is higher than that of family I and family III.

A total of 46 crude oil samples recovered from the surrounding Niuzhuang sag were investigated to gain insight into the petroleum systems in the Dongying depression. Chemometrics identified four genetically distinct oil families. Family 1 fails to match any of the source rocks that have been discovered thus far. The candidate source rock must contain algal organic matter that could produce more negative carbon isotopic composition, large quantities of wax, C29 steranes, and tricyclic terpenoids compared to the Eocene Shahejie (Es) Formation intervals Es3 and Es4 and deposited in a reducing, stratified saline water environment. Family 2 is featured by high ratios of sterane/hopane, gammacerane/hopane, and C35/C34 homohopane and low pristane/phytane ratios. The source rock is the upper Es4 interval. Family 3 is characterized by distinctive or even opposite features to family 2. The source rock is the lower Es3 interval. Family 4 is a mixed oil derived from the lower Es3 and upper Es4 source rocks at different thermal maturation. Three end-member oil samples, EM1, EM2, and EM3, were identified by alternating least-squares. As a minor contributor, EM1 has an average value of 10%. As the main contributors, EM2 and EM3 average 53% and 37%, respectively. Oil samples from EM1 and EM2 are derived from the upper Es4 source rock, but EM1 was generated at a lower thermal maturity than EM2. Oil from EM3 was derived from the lower Es3 source rock at peak hydrocarbon generation.

Type I and II kerogens, isolated from outcrop shales in the Songliao Basin, were performed a programed sealed-heating kinetic process. Both carbon isotope values of pyrolysis-residual kerogens and ...

Isotopic rollover refers to that δ13C value of a gas component decreases with maturity. Its occurrence is closely related to high productivity of shale gas. Isothermal confined pyrolysis experiments (gold capsules) were performed to simulate this phenomenon on whole rock Lucaogou and kerogens Saergan, Wuerhe and Fengcheng in the absence (anhydrous) and presence of added water (hydrous) at 50 MPa, 372 °C and heating duration 0–672 h, corresponding to 0.96–1.85 EASY%Ro. For kerogen Saergan isolated from source rock with hydrogen index (HI) 159 mg/g TOC and 1.10–1.30% Ro equivalent, none of δ13C1, δ13C2 and δ13C3 showed any rollover in both anhydrous and hydrous experiments. For Lucaogou whole rock with HI 856 mg/g TOC and 0.50–0.60%Ro, both δ13C2 and δ13C3 showed rollover in anhydrous experiments while all δ13C1, δ13C2 and δ13C3 showed rollover with greater magnitude in hydrous experiments starting at 1.49–1.64 EASY%Ro. For kerogens Wuerhe and Fengcheng isolated from source rocks with HI of 550 and 741 mg/g TOC, and 1.18 and 0.96%Ro respectively, both δ13C2 and δ13C3 demonstrated rollover in anhydrous experiments while only δ13C2 showed rollover with minor magnitude in hydrous experiments starting at 1.47–1.53 EASY%Ro. The different effects of water on isotopic rollover among samples Lucaogou, Wuerhe and Fengcheng can be ascribed to rate related isotopic fractionation. Higher generation rate leads to minor isotopic fractionation and rollover magnitude. It was suggested that isotopic rollover likely occurs in a source rock having higher amount of initial retained oil prior to bulk oil cracking and currently within the major stage of oil-cracking to gas (1.50–2.00%Ro).

Fifty-seven crude oil samples from the southern Dongying Depression were selected for detailed geochemical analysis. High C26/C25 tricyclic terpanes (0.81–1.26) and low C31 homohopane (R)/C30 hopane (0.15–0.26) ratios indicate that the oils are from lacustrine source rocks. The presence of C30 4α-methyl-24-ethylcholestanes and C30 tetracyclic polyprenoids imply the contribution of microalgal organic matter. Large variations of depositional environment-related biomarker parameters suggest differences in organofacies and water environment. Four genetically distinct oil families were differentiated by chemometrics of hierarchical cluster and principal component analyses using the parameter dataset of three isotope ratios and 15 molecular parameters, all related to source and depositional environment. Family I is mature and does not match any available source rocks. The inferred source rock contains microalgal material that could produce large quantities of wax, C29 steranes and tricyclic terpenoids in a reducing, salinity stratified water column. Family II is characterized by a strong phytane dominance, relatively high gammacerane and C35 homohopanes, and low diasterane and 4-methyl sterane contents. It has high values of sterane/hopane (S/H = 1.67–4.14), C35/C34 homohopane (C35H/C34H = 0.81–1.66) and gammacerane/C30 hopane (G/C30H = 0.57–1.13) and low pristane/phytane (Pr/Ph = 0.30–0.59), suggesting that the inferred source rock is the upper Es4 interval. Family III has characteristics distinct from families I and II: low S/H (0.15–0.27), C35H/C34H (0.39–0.49) and G/C30H (0.03–0.12) ratios and high Pr/Ph (0.48–1.90), C30-4M/C29 ααα20R (0.54–1.18) and C30 tetracyclic polyprenoid (0.54–0.66) ratios, suggesting that the source rock is the lower Es3 interval. The family IV oils are compositionally in-between the ranges of families II and III oils, and in line with them in plots of geochemical parameters. We suggest that family IV consists of mixed oils derived from the upper Es4 and lower Es3 intervals. Family II has a relatively low thermal maturity and the inferred source rock may be located in the Niuzhuang Sag and/or the southern gentle slope zone. Family III is mature and its inferred source rock may be situated in the Lijin and Boxing sags. The upper Es4 and lower Es3 source rocks in the three sags contribute the crude oils of family IV that occurs in the middle and eastern parts of the southern Dongying Depression.

Identification and quantification of mixed sources of petroleum reservoirs as well as the sources of oil spills generally requires the molecular composition information about the mixture. In this study, the relative concentrations of a series of polar acidic compounds, semiquantified by negative ion ESI FT-ICR MS, were calculated using alternating least-squares (ALS) to unmix a group of oil mixtures prepared in the laboratory using three endmember oils. It was shown that the ALS results were accurate based on the relative concentrations of polar acidic compounds, regardless of whether endmember oils and several samples were removed from the sample set. ALS was able to accurately calculate the composition of endmember oils, regardless of whether they were included in the sample set. This method is relatively simple, efficient, time-saving, and has potential for geological source identification of mixed oils or oil spills.

Kerogen was isolated from the source rock of Well L69, Zhanhua depression, Bohai Bay Basin and an artificial pyrolysis experiment was carried out in a closed gold tube system with a heating rate of 2 °C/h. Products were collected at eleven temperature points every ten degrees from 350 °C to 450 °C. The soluble organic matter and residual kerogens from the experiment were quantified by weighing. Furthermore, the residual kerogens were analysed by element analysis, X-ray photoelectron spectroscopy (XPS) and solid 13C nuclear magnetic resonance (13C NMR) spectroscopy to determine the chemical structural of kerogen during oil generation. Combining the data from the analyses, information on the elemental compositions as well as on how functional groups were connected in residues was obtained. Seven molecular models of initial and residual kerogens were established to trace the structure changes in kerogen with maturity. The results suggest that as the temperature increases, aliphatic chains and small clusters of aromatic groups break down from kerogens, generating soluble hydrocarbons at temperatures of less than 390 °C (Easy% Ro1.15). At higher thermal maturity, a few short aliphatic carbons remain in the structure of residues. The number of aromatic groups increases and their size grows with increasing maturity, with condensation occurring at aromatic groups at high temperature, while these residues have little potential for oil generation.

In recent years, the natural gas has displayed a growing significance in oil and gas exploration in the northwestern Junggar Basin (NWJB), although oil has been the main focus of exploration in the basin. Here, we systematically discuss the classification and origin of the natural gases from the NWJB based on the natural gas geochemistry and chemometric methods. The natural gases collected from the NWJB were chemometrically classified into three groups. Group A gases, defined as coal-derived gases, were likely generated from the mixing of the Jiamuhe Formation and Carboniferous strata. Group B gases, defined as the mixing of coal-derived and oil-associated gases, were restricted to the source rocks of group A and C gases. Group C gases, defined as oil-associated gases, were likely derived from both the Fengcheng and Wuerhe Formations, with a higher contribution from the latter strata. The result of this study suggests that the potential of oil generation in the Wuerhe Formation has been underestimated in the past. This is in accordance with geochemical and geological evidence. This study provides an effective chemometric method of natural gas classification and evaluation of hydrocarbon generation potential. This contributes to a better understanding of the origin of gases and distribution of oil and gas, assisting in exploration deployment in the basin.

The lacustrine black shales of the Chang 7 member are the main source rocks and the most important unconventional (shale oil) petroleum resources in the Ordos Basin, North China. A series of continuous core samples was analysed for main, trace, and rare earth elements. The development of thin or laminar tuffs and tuffaceous mudstones and the enrichment of Fe, Mn, and other elements demonstrate that the Chang 7 member was influenced by event deposition, such as volcanic and hydrothermal activity. The ancient lake had brackish water and a relatively high sedimentation rate during the deposition of the Chang 7 member. The palaeoclimate in the early stage was warmer and wetter than that in the middle-late stage of the Chang 7 period. The geochemical proxies for palaeoproductivity and palaeoredox indicate that the ancient lake had a relatively high primary productivity with an anoxic to euxinic sulphide bottom water in the Chang 73 stage, which decreased to dyoxic-oxic water during the Chang 71+2 periods. A parameter dataset comprising 11 elemental proxies related to the reconstruction or evaluation of the depositional environment and palaeoproductivity was analysed using principal component analysis (PCA). The first principal component (PC1) accounted for 59.88% of the total variance in the original dataset and mainly represented the characteristics of palaeoproductivity and redox conditions; thus, it can be interpreted as an indicator of these factors. Based on the excellent positive linear correlation between the total organic matter content of the Chang 7 samples and the PC1 scores, the enrichment of organic matter in the Chang 7 member was mainly controlled by palaeoproductivity and the preservation environment. PCA is an effective method for dimensionality reduction and visualisation of multi-element geochemical data, which allows for a more comprehensive and in-depth understanding of geological samples. This work provides a practical application of chemometrics in elemental geochemistry. This can serve as a model for other studies.

In this study, we rediscuss genetic types of natural gases from the Turpan-Hami Basin using classic diagrams and chemometric methods. In comparison with classic diagrams, chemometrics is an improve...

Chemometric methods have unique advantages regarding comprehensive consideration of multiple parameters and the classification of samples or variables. The above is especially suitable for the data mining of a large number of samples, data, as well as the regional oil-oil and oil-source rock correlations. This paper describes the frequently used chemometric methods for geochemical correlations in detail: hierarchical cluster analysis (HCA), principal component analysis (PCA), and the newly introduced method–multidimensional scaling (MDS). MDS and its suitable range, principles, and comparison of each method were also studied. Also, there is a need to discretely treat such issues (i.e., sample screening, correlation parameter, data preprocessing, and the measured distance between samples in high dimensional space) when the chemometric methods are adopted to conduct geochemical correlation in the studied area. These issues are closely related to the reliability of the correlation results. Keywords: Chemometrics, Biomarker, Oil-oil correlation, Oil-source rock correlation, A review

The Huhehu Sag is one of the most important oil and gas depressions in the Hailar Basin. However, the origin of Huhehu oil is still controversial. Previous studies on source rocks have mainly focused on the Nantun Formation (K1n); a few studies have investigated the Damoguaihe Formation (K1d). Based on the Rock–Eval pyrolysis parameters, 172 drill cutting samples from the Huhehu Sag were analyzed to evaluate their geochemical characteristics. Based on the Rock–Eval data, the mudstones from the first member of the Damoguaihe Formation (K1d1) and the second member of the Nantun Formation (K1n2) have moderate to high hydrocarbon generation potential, while mudstones from the first member of the Nantun Formation (K1n1) have poor to good hydrocarbon generation potential. Additionally, both the K1n1 and K1n2 coal members have poor to fair hydrocarbon generation potential, but the K1n2 coal member has a better generative potential. Fifteen Huhehu oils were collected for molecular geochemical analyses to classify the oils into genetic families and to identify the source rock for each oil using chemometric methods. The Huhehu oils were classified into three groups with different maturity levels using hierarchical cluster analysis and principal component analysis. Group A oils (high maturity) are characterized by relatively moderate ratios of Pr/Ph, Pr/n-C17, and Ph/n-C18, as well as an abundance of C29 steranes, mainly derived from the K1n2 and K1n1 mudstone members. In comparison, group B oils (moderate maturity) have relatively low Pr/Ph ratios, moderate Pr/n-C17 and Ph/n-C18 ratios, and low concentrations of C29 steranes. Group C oils (low maturity) show relatively high ratios of Pr/Ph, Pr/n-C17, and Ph/n-C18, as well as high concentrations of C29 steranes. Furthermore, group B oils derived from the K1d1 mudstone member and group C oils derived from the K1n2 coal member were also identified by principal component analysis score plots. Correlation studies suggest a major contribution from the K1n mudstone Formation and the K1d1 mudstone member to the oils of the Huhehu Sag. So, the Nantun Formation and relatively shallow strata of the Damoguaihe Formation (e.g., the K1d1 member) represent important targets for future oil-reservoir exploration in the Huhehu Sag.

In this study, a series of 3D molecular models of solid bitumen from the Sichuan Basin were established using solid-state 13C nuclear magnetic resonance (NMR) spectroscopy and density functional theory (DFT). To investigate the stages of hydrocarbon generation of natural solid bitumen, pyrolysis was performed. Ten residues with different maturity were prepared by pyrolysis for the establishment of molecular models. During the pyrolysis, the aliphatic chains cracked from solid bitumen and the aliphatic clusters underwent the reaction of condensation. To evaluate the structural changes, CnB and Pm were proposed to estimate the average length of aliphatic chains and the development of micro-pores in residues. And the relationship between structural parameters and hydrocarbon generation of solid bitumen were established for the first time in this research. In the process of methane generation was divided into three stages by the maturity points of 1.07 and 2.65%, and within the maturity range from 1.07 to 1.52%, the solid phase matter of solid bitumen transformed from asphaltene to residue. Combining the structural parameters and hydrocarbon generation characteristics, DFT method RB3LYP was used to develop and optimize eleven molecular structure 3D models of residues. Triangular configuration models were used to evaluate residue models and the data indicated that the solid bitumen molecular models showed a “flake–cube–flake” trend during the pyrolysis. Raman spectroscopy for each model was predicted and the maturity has been calculated based on the spectra, and the results of them were consistent with the pyrolysis. This research demonstrates the utility of molecular simulations in macromolecular geological organic matter.

To characterize molecular structure evolution of Type I kerogen, we performed gold tube pyrolysis experiments on a Cretaceous Qingshankou lacustrine mudstone in the Songliao Basin during artificial maturation. The hydrocarbons generated at 320–600 °C at two heating rates, 2 and 20 °C/h were quantified, and the maximum yields of C14+, C6-14 and C2-5 gaseous products corresponded to vitrinite reflectance (Ro) nodes of 1.18%, 1.76% and 2.5%, respectively. Chemical compositions of solid residues (pyrolysis products remaining after extraction by dichloromethane and methanol) with Easy%Ro values ranging from 0.49 to 2.5% were studied by elemental analysis and nuclear magnetic resonance. With increasing temperature, the solid residues presented sharp decreases in aliphatic fractions and significant increases in aromatic fractions, while a condensation reaction occurring in the residue was related to secondary coking and cracking reactions occurring after the peak oil window. Four structural models of the residues were investigated, demonstrating that three positive nonlinear stages occurred between fused aromatic carbon (XE BP) structures and hydrocarbon generation. At Easy%Ro

The chemometric methods alternating least squares and multidimensional scaling were employed in this study to quantify the relative contribution of the sources and identify the affinities of sixty–five crude oil samples collected in the Zhanhua Depression. The circos diagram was used to reflect the relative contributions of different source rocks. Based on these techniques, two end–members (EMs) were identified which represent the geochemical characteristics of two regional source–rocks (Es3L and Es4U). The EM1 composition assigned to Es3L is characterized by relatively low C35/C34 homohopane ratio and relatively low abundance of gammacerane. This EM is consistent with a source facies that was deposited in freshwater lacustrine environment that contained a non–stratified water column and suboxic to dysoxic bottom waters. Distributions of the regular steranes and tricyclic terpanes, the relatively low steranes/hopanes ratio suggest the organic matter input into this source facies were combined microalgal material and terrestrial organic matter. Oils from the Bonan Sag and Gubei Sag were derived mainly from this source facies. In contrast, EM2 has been assigned to the Es4U source rock and is characterized by relatively high abundance of gammacerane, C35/C34 homohopane ratio greater than one, suggesting deposited in a saline to hypersaline lacustrine environment that contained a stratified water column with strongly reducing bottom waters. Distributions of the regular steranes and tricyclic terpanes as well as relatively high steranes/hopanes ratio suggest the organic matter deposited in this setting was mainly derived from microalgal/bacterial sources. Oils from the Luojia Nose and Chanjiazhang High were derived mainly from this source facies. Mixed contributions of these two source facies (end–members) account for the compositions of crudes produced in the Yihazhuang Arch and Gudao High. In the case of the Yihezhuang Arch the crudes appear to have near equal contributions from the two source faces, whereas crudes from the Gudao High appear to have slightly higher contributions from the Es3L source facies than from the Es4U source facies.

In this study, swelling experiments for three natural solid bitumen samples in two types of organic solvents were conducted to explore the location of the swelling between the solid organic matter and solvent in the chemical structure. The relationships between the x-ray diffraction results and chemical structure changes were also investigated during swelling. The results indicated that solid organic matter with a high proportion of aliphatic carbon could dissolve more organic solvents during the swelling reaction. Additionally, aromatic hydrocarbon compounds were more prone to dissolution in solid organic matter than saturated hydrocarbons. In the chemical solid organic matter structure, almost all of the solvent swelling occurred in the aliphatic carbon region, and the micro-crystals formed by the stacking of aromatic carbon clusters were not greatly influenced by the swelling reflection. The ratio of the γ and 002-peak heights in the x-ray diffraction spectra was affected by increases in the proportion of aliphatic carbon during the swelling process, and we proposed an equation for this change. In this study, we determined the swelling site, investigated the swelling process via x-ray diffraction, and proposed several related structural parameter calculation methods to aid future research on the structure of macromolecular organic geological matter.

Artificial maturation of Maoming oil shale kerogen (Type I) was performed at a heating rate of 5 °C/h in a closed Au tube system. Yields of pyrolysis products (C 1–5 , C 6–14 , C 14+ and insoluble residue) were quantified. The insoluble kerogen residue was analyzed using Rock-Eval, elemental analysis and quantitative 13 C direct polarization/magic angle spinning (DP MAS) nuclear magnetic resonance (NMR) spectroscopy. Peak oil generation was achieved at Easy %R o 0.95. A “three-stage” relationship existed between aromaticity and Easy %R o because of the relatively pronounced cleavage of aliphatic carbons and the formation of new aromatic structures in the kerogen residue. Five models of kerogen representing five stages in the oil window were drawn to provide a visualized kerogen structure modification with evolution. A novel jump in the structure of the kerogen residue was observed at ca. Easy %R o 0.80–0.90, corresponding to the peak oil window. Our results suggest that aromatic carbon, replacing aliphatic carbon and becoming the dominant carbon in the residue, was the cause of the dramatic changes in the Easy %R o interval of 0.80–0.90. Both aliphatic and aromatic structures contributed to hydrocarbon generation before peak oil generation. CH 2 groups contributed most to the hydrocarbon generation potential. Me groups contributed little to hydrocarbon generation within the oil window.

Forty-eight crude oil samples collected from different reservoirs in the Tahe oilfield of the Tarim Basin were investigated. Based on geochemical characteristics, it is concluded that the oil samples originated from multiple marine source rocks deposited in various sedimentary environments and subsequently altered by different levels of thermal maturation. These mixtures were de-convoluted to three endmember oils (EM1, EM2 and EM3) by alternating least squares regression using 38 concentration parameters. EM1 is the minimum contributor with an average of 13%, while EM2 and EM3 are the main contributors to the mixtures with averages of 52% and 35%, respectively. EM1 oil originated from Cambrian–Lower Ordovician source rocks in the early to peak oil window and subsequently experienced two phases of mixing and biodegradation. EM2 and EM3 oils originated from Middle–Upper Ordovician source rocks, but EM2 was generated at lower thermal maturity than EM3. The EM2 oil underwent two phases of mixing and one stage biodegradation, while the EM3 oil mixed with previous existing mixtures in the reservoirs. The final mixtures that might be affected by secondary processes, such as evaporative fractionation, are currently produced from the Tahe oilfield. The general orientation of oil filling was from south to north and east to west based on variations in the relative contributions of EMs, and the total concentrations of dibenzothiophenes and dibenzofurans in the oils. Considering the histories of sedimentary tectonic evolution, hydrocarbon generation and expulsion, and the de-convolution results, a model of three stages of oil charge and two phases of mixing and biodegradation was established for the Tahe oilfield oils.

This study was performed in order to evaluate shale oil in the first member of the Qingshankou formation (K2qn1) in the Songliao basin in northeastern China. The evaluation was carried out using immature type I kerogen kinetics in a closed system, two wells drilled into oil prone source rocks, in order to apply Rock-Eval, mineral composition and residual hydrocarbon analysis, and the hydrocarbon sorption method. The “oil windows” for K2qn1 in mudstone and shale wells range from 0.6% to 1.05%, with maximum hydrocarbon generation at around 420 mg of hydrocarbon per gram of total organic carbon. In addition, the brittle mineral contents of K2qn1 conform to the requirements for industrial oilfield development and exploitation. Our results demonstrate that there is clear potential for shale oil exploration in the K2qn1; a highly potential zone is defined as low risk at burial depths of greater than 2065 m for well H14, while well X83 exhibits relatively discrete depth based on oil saturation and production ind...

One hundred and twenty-five rock and oil samples collected from the Fangzheng Fault Depression were analyzed by GC–MS. Principal component analysis (PCA) and multidimensional scaling (MDS) based on nine biomarker ratios were used for oil–source rock correlation in this region. The oils are characterized by a predominance of low to middle molecular weight normal alkanes (n-C12–n-C20 or n-C12–n-C25), moderate to high Pr/Ph ratios (1.44–5.3), relatively low C27/C29 regular steranes, C35/C34 hopanes and gammacerane/C31R ratios, all of which suggest relatively oxic conditions under fresh water depositional conditions with significant terrigenous organic matter input. PCA and MDS results show that the investigated oils were derived mainly from the Xinancun-Wuyun Formation and also illustrate the maturation and depositional conditions of the rocks and oils through an MDS plot. We show that MDS is a reliable, multi-parameter oil–source rock correlation method.

Crocetane and phytane are two isoprenoids isomers with similar molecular structures and often present together in methane-seep sediments and some Palaeozoic crude oils. Their commonly co-elution on gas chromatography is challenging for quality and quantity analysis, making it impossible to determine their compound-specific isotopic composition, and thus, insight their geological and geochemical significance. A new gas chromatography method is reported here using a DB-17MS column (50%-phenyl-methyl polysiloxane as the stationary phase) that successfully achieved baseline separation of crocetane and phytane and can be used to accurately identify and quantify them on gas chromatography and gas chromatography-mass spectrometry. Routine steroids and terpenoids biomarkers can also be analysed simultaneously. Additionally, their compound-specific carbon isotopic compositions were also measured without matrix influence using this method. This is the first time that a simple chromatographic method for direct determination of compound-specific carbon isotopic composition of crocetane has been reported publicly.

In this study, closed-system Fischer-Tropsch synthesis was conducted at 380°C and 30 MPa for 72 h with magnetite as a catalyst. The isotopic composition of the closed-system Fischer-Tropsch synthesis gas and the composition of known abiogenic gas were systematically studied, and the deep Songliao Basin gas was also investigated. The results show that closed-system Fischer-Tropsch synthesis of gaseous hydrocarbon isotopes exhibits a partial reverse order, which includes the reverse order of methane and ethane such as δ13C-C1>δ13C-C2<δ13C-C3 and δ2H-C1>δ2H-C2<δ2H-C3. Furthermore, experimental data on the control of NaBH4 content indicates that the carbon isotopes demonstrate a reverse order on condition that the H2/CO2 (mole ratio) is equal to or greater than 4.0; meanwhile, the hydrogen isotopes show a normal order. The deep Songliao Basin hydrocarbon gas component is similar to thermogenic gas and has a trend of a transition to oceanic hydrothermal system abiogenic gas. In addition, the deep Songliao Basin gas isotopic pattern is different from both Lost City and Kidd Creek where the deep Basin gas carbon isotopic pattern has a reverse order, and the hydrogen isotopic pattern has a normal order. Therefore, the deep Basin gas might be a mixture of the oil-type gas and the coal-formed gas, which could be the cause of the isotopic reverse.

Four natural solid bitumen samples were collected from the Guangyuan area (northwest Sichuan Basin, southwest China) to characterize their structure. Samples were ground to power (120 mesh), purified by ZnBr2 solution to remove mineral and soluble impurities, and analyzed using Rock-Eval pyrolysis, elemental analysis, Raman spectroscopy, solid bitumen reflectance, and solid-state 13C nuclear magnetic resonance to determine the maturity degree of samples and obtain structural information. Results showed that Guangyuan solid bitumen samples are in low maturity, and three solid bitumen maturity detection methods are compared in this research. With respect to the solid bitumen molecular structure, less than 10 carbon atoms were determined in aliphatic chains and the solid bitumen aromatic clusters ranged from two to four rings, which indicates that the solid bitumen comprises complex geological organic matter, such as kerogen. Four molecular models were established in this research to reflect the basic molecular configuration of natural solid bitumen. Samples were classified into two types based on the structural information and models, and the results imply that the solid bitumen samples may have been derived via different evolutionary processes. This phenomenon indicates that structural studies could play an important role in the research of oxidation and carbon isotope changes in solid bitumen. In summary, this investigation provides an understanding of the evolutionary stages of Guangyuan bitumen, establishes associated molecular structure models, and researches the role of structural information in bitumen source studies. As the focus of this study, the four molecular models were used to restore the structural characteristics of natural solid bitumen as possible. And this study tried to find out the relationship between the solid bitumen structure information and it geology evolution. As the carbon isotope may not accurately determine the source of solid bitumen because of oxidation, molecular information could be used to research the solid bitumen source and associated evolution.

The Junggar Basin is a major oil producing province in China. Most of the oil originated from Permian lacustrine oil-prone source rocks in the basin. Kinetic parameters for oil and gas generation were obtained from confined pyrolysis experiments using gold capsules at heating rates of 20 °C/h and 2 °C/h on kerogen samples from two Permian lacustrine oil-prone source rocks (J23S3 and SS1S3) having hydrogen indices of 663 and 698 mg HC/g TOC, respectively. The kinetic properties for oil and gas generation vary substantially between these two source rocks. Assuming a burial heating rate of 5 °C/My, the temperature for 50% transformation ratio to oil is 132 °C for J23S3 and 168 °C for SS1S3. The maximum oil yields are about 604 and 770 mg/g TOC, while the maximum yields of total gaseous hydrocarbons are about 306 and 348 mg/g TOC for J23S3 and SS1S3, respectively. Gaseous hydrocarbons from the confined pyrolysis experiments include primary cracking components from kerogen and secondary cracking components from the generated oil. The secondary cracking gaseous hydrocarbons comprise up to 84.9% and 95.1% of the total, respectively, for the two source rocks in the highest temperature experiments. A practical method estimates the amount of gaseous hydrocarbons generated from these source rocks under geological conditions based on: (1) kinetic parameters for gas generation obtained from kerogen confined pyrolysis experiments in the present study, (2) the maximum yield of gaseous hydrocarbons from oil confined pyrolysis experiments from previous studies, and (3) the maximum amount of expelled oil. The maximum amounts of expelled oil range from 509–588 and 724–750 mg/g TOC with oil expulsion efficiencies in the ranges 84.3–97.4% and 94.0–97.4% for J23S3 and SS1S3, respectively, assuming that the amounts of retained oil range from 30–160 and 50–110 mg/g TOC for the two source rocks after oil expulsion based on the amounts of extracted bitumen. Consequently, the maximum yields of total gaseous hydrocarbons could be in the ranges 53.1–87.0 and 25.5–36.8 mg/g TOC, respectively, for J23S3 and SS1S3 in nature. Using the kinetic parameters for these two source rocks determined from pyrolysis experiments, oil and gas generation and expulsion were modeled for source rocks within the Lower Permian Fengcheng (P 1f ) and Middle Permian Lower Wuerhe formations (P 2w ) in the central area of the Mahu Depression, the source kitchen for most oilfields in the basin.

Geochemical characteristics of 61 crude oil samples collected from Palaeozoic reservoirs in the Tarim Basin (60 from the Tabei Uplift and one from the Tazhong Uplift) were analyzed. The samples proved to be mixed oils of different maturity from diverse source rocks. Concentrations of 40 biomarkers and carbon isotopic compositions for the whole oils were analyzed by alternating least squares (ALS) regression to de-convolute the mixtures. Three endmember (EM) oils were identified. EM1 is the minimum contributor to the mixed oils, accounting for less than 10% of most oils. EM1 originated from Cambrian–Lower Ordovician source rocks in the early to peak oil window stage and experienced two phases of mixing and biodegradation. EM2 is the secondary contributor with proportions ranging from 10% to 40% in most oil samples. EM2 originated from Middle–Upper Ordovician source rocks at the early oil generation stage and underwent two phases of mixing and one stage biodegradation in the reservoirs. EM3 is the major contributor to most samples with proportions ranging from 13% to 95%. EM3 was generated from Middle–Upper Ordovician source rocks at the late oil generation stage and mixed with earlier emplaced mixtures in the reservoirs. The final mixtures that were not biodegraded are currently exploited from Palaeozoic reservoirs in the Tabei Uplift. Biomarkers in the crude oils reveal mixed characteristics, including evidence for two phases of oil charge and severe biodegradation.

In this study, chemometrics was used to unmix a set of oil samples that had been mixed in the laboratory using three end-member oils. It was shown that the concentrations of individual compounds in the mixed oil varied linearly with the fractional contribution of each end-member oil. However, biomarker ratios in the mixed oils varied non-linearly with the amount of each end-member oil. This study demonstrates that concentrations and ratios of biomarkers yield different results when de-convoluting mixed oils. Concentrations of biomarkers are therefore more suitable than the biomarker ratios for unmixing mixed oils. Alternating least squares of biomarker concentrations (ALS-C) provides an excellent way to calculate the number, proportions, and compound compositions of the end-members in mixed oil samples. The ALS-C results are accurate, regardless of whether end-member oils are included in the sample set. The biomarker ratios of end-member oils cannot be directly obtained by ALS, but can instead be calculated using related compound concentrations computed by ALS-C. This method should be applied and verified widely using actual geochemical data.

Inorganic minerals were separated from mudstone and shale to investigate their oil adsorption potential. A conceptual model was developed to reconstruct the oil adsorption capacity of underground mudrock/shale by combining adsorption and organic matter swelling data. The predictions for the free hydrocarbon oversaturation sorption zones in the Well NY1 profile were taken as a case study. The results suggest that the best depth for the shale oil prospect of the Es4s member strata lies between 3400 and 3600 m in the Dongying Depression. Hydrocarbon starvation zones occur mainly at a depth of

13C solid-state NMR and XPS techniques were used to investigate structural changes in kerogen during oil generation process across a range of maturity. Kerogen was isolated from an shale rock collected from Well W161 in the Dongying Depression, Bohai, China. An artificial pyrolysis experiment was carried out in a closed gold tube system using a heating rate of 2 ℃/h during which 11 temperature-point samples were collected between 350 ℃ and 450 ℃ (Easy%Ro = 0.80 to 1.98). The initial kerogen was analysed using Rock-Eval and the samples were analysed using X-ray photoelectron spectroscopy (XPS) and solid-state 13C nuclear magnetic resonance (13C NMR) to study their functional groups and chemical structures. Six averaged molecular structure models of the initial kerogen and its residues (can not be dissolved by organic reagent) were established to study the changes occurring during oil and gas generation. The results showed that with an increase in temperature, the proportion of aliphatic carbon declined while aromatic carbon increased. After reaching peak oil maturity, a condensation reaction occurred in the residue; some aromatic carbons cracked from the kerogen and combined with the residue structure. Average aromatic cluster increment was calculated to quantify the increase in the size of aromatic clusters within the structures. It was established to evaluate the changes occurring in the molecular structure of type Ⅰ kerogen during heating. Based on these results, ConU (maximum condensation degree) and ConL (lowest condensation degree) are proposed to estimate the degree of condensation of samples with different maturities.

Many small and medium-sized Paleogene pull-apart basins in southern China contain an abundance of biogenic gas shows. Such shallow gas with biogenic characteristics has been thoroughly investigated only in Baise Basin. Hence, the research results from Baise Basin could serve as a model for the origin and characteristics of shallow gases in similar basins and areas in Southern China. There are ten gas fields with a total of proven reserves of 20 billion cubic meters discovered in Baise Basin. Three gas fields are located on the western and southern flank of the basin, and they are gas caps to heavy oil pools from depths between 600 m and 850 m. These accumulations contain dry biogenic gases, with C1/C1-5 exceeding 0.99, light δ13C1 (–76 to −54‰), and heavy δD1 (−218‰). Trace heavy gaseous hydrocarbons are strongly biodegraded (iC4/nC4>3). The other seven gas fields are located in the northern fault zone and the central Nakun uplift of the basin at depths between 300 m and 700 m. Gases are mainly unassociated and condensed gases. The condensed gases are depleted in 13C (δ13C1: −67 to −53.7‰, δ13C2: −52.3 to −36.1‰, δ13C3: −43.3 to −33.4‰), but wet with C1/C2+3 mostly less than 20, suggesting a mainly thermal origin at low maturity. The unassociated gases are dominated by methane, with C1/C2+3 ratio above 100, variable N2 (0 to 5.4%), and traces of CO2. The δ13C value of methane in the unassociated gases is between −76 to −60‰, and δD1 values from −248 to −213.7‰. These gases also contain isotopically light ethane with δ13C2 values of −64.5 to −42‰, which we infer to have originated from deeper horizons as a result of migration or diffusion from low-maturity thermal gases with light stable carbon isotopic compositions (C1/C2+3

Carboniferous source rocks have been gaining increasing attention after the discovery of the Kelameili gasfield in the Eastern Junggar Basin in 2005. Two sets of source rocks within the Lower Carboniferous Dishuiquan Formation (C 1d ) and Upper Carboniferous Batamayineishan Formation (C 2b ), respectively, have been identified in this area. In this paper, clear differences between these two source rocks are demonstrated in molecular and carbon isotopic compositions. The C 1d source rocks, in comparison with the C 2b source rocks, have remarkably lower Pr/ n- C 17 ratio, higher Ts/(Ts + Tm) and C 30 diahopane/(C 30 diahopane + C 30 hopane) ratios, lower concentration of C 24 tetracyclic terpane relative to C 23 and C 26 tricyclic terpanes and higher gammacerane/C 31 hopane ratio. δ 13 C values of individual n -alkanes decrease with carbon number for C 1d source rocks while the opposite is true for C 2b source rocks. Among the 10 oils collected from the studied area, four were generated exclusively from C 1d source rocks while the others were mainly derived from C 1d source rocks but contaminated by a small or trace amount of oil components which were derived from the C 2b , Middle Permian Pingdiquan Formation (P 2p ) and Lower Jurassic source rocks. The free, adsorbed and inclusion oils from three oil-containing volcanic reservoir rocks within the C 2b formation generally correlate with C 1d source rocks based on molecular and carbon isotopic data. However, the three types of oil from the same reservoir rock vary significantly in molecular and carbon isotopic compositions, reflecting facies and maturity changes of charging oil during the reservoir filling.

Biogenic gases were reported to exhibit a ‘‘normal’’ carbon isotope order, whereas abiogenic gaseous hydrocarbons in igneous rocks and meteorites exhibit a reversed order. In this study, closed-system Fischer–Tropsch synthesis was conducted at 350°C and 380°C under 30 MPa and 390°C under 30, 100, and 200 MPa, respectively, with magnetite as a catalyst. The results do not show an expected reversed order, even though the features of partially reversed order in carbon isotope values can still be commonly observed. Studies have shown that the essential constraint factor on the carbon isotopic pattern of abiogenic gases is the molar ratio of H2/CO2.

Although CO2 is a common non-hydrocarbon gas in sedimentary basins and is significant in studying geofluid evolution, its origin is still a matter of debate. Light δ13CCO2 values have been suggested as a good indicator for discriminating CO2 of organic origin from that of inorganic origin (such as from the mantle or from carbonate mineral dissolution). However, here we present evidence suggesting that large quantities of isotopically heavy CO2 can be liberated from deeply buried source rocks. An immature coal has been pyrolyzed in confined dry gold reactors at temperatures from 250 °C to 600 °C with different heating rates and under a pressure of 30 MPa. The results suggest that isotope fractionation and origin from various oxygenated functional groups with different δ13C compositions make the late generated CO2 (over 40% of potential) enriched in 13C. The 44% of CO2 late-produced from the coal has an average δ13C value of − 6.7‰ (VPDB); the latest 20% has an average δ13C value of + 1.5‰; and the latest 10% is most enriched in 13C, with a δ13C value of + 5.0‰. This paper presents two cases highlighting organic, isotopically heavy CO2 in natural gases occurring at variable concentrations in different sedimentary contexts.

An investigation of groundwater contamination around the Likeng landfill, Guangzhou, was carried out. Major ions and elements of 34 groundwater samples were measured, and the Piper trilinear diagram and expanded Durov diagram were used to analyze the chemical types and hydro-geochemical processes of the groundwater. End Member Mixing Analysis was used to find the types and sources of pollutants. The results show that the hydro-geochemical process was mainly mixing and ion exchange; the shallow groundwater around the Likeng landfill was contaminated mainly by both anthropogenic/agricultural sources and leachate pollution. There are different types of major ions, hydro-chemical processes and distributions for the two pollution sources.