Search

Rock-Eval pyrolysis and the biomarker composition of organic matter were systematically studied in hydrate-bearing sediments from the Shenhu area, South China Sea. The n-alkane distribution patterns revealed that the organic matter in the sediments appeared to originate from mixed sources of marine autochthonous input, terrestrial higher plants, and ancient reworked organic matter. The low total organic carbon contents (average < 0.5%) and the low hydrogen index (HI, <80 mg HC/g TOC) suggested the poor hydrocarbon-generation potential of the deposited organic matter at a surrounding temperature of <20 °C in unconsolidated sediments. The abnormally high production index and the fossil-originated unresolved complex mixture (UCM) accompanied by sterane and hopane of high maturity indicated the contribution of deep hydrocarbon reservoirs. Preliminary oil-to-source correlation for the extracts implied that the allochthonous hydrocarbons in the W01B and W02B sediments might have originated from the terrestrial source rocks of mature Enping and Wenchang formations, while those of W03B seem to be derived from more reduced and immature marine source rocks such as the Zhuhai formation. The results of the organic extracts supported the previous identification of source rocks based on the isotopic composition of C2+ hydrate-bound gases. The biomarker of methanogens, squalane, was recognized in the sediments of this study, possibly suggesting the generation of secondary microbial gases which are coupled with the biodegradation of the deep allochthonous hydrocarbons. [ABSTRACT FROM AUTHOR]

The Jurassic coals of the Junggar and Turpan-Hami basins, Xinjiang, China, are characterized by abundant vitrinite. Microscopic analysis of Junggar coal samples indicates that they contain desmocollinite and hydrogen-rich vitrinite with a low reflectivity. The hydrocarbon-generating potential of various macerals follows the decreasing order of exinite>vitrinite>inertinite. However, desmocollinite is a principal maceral for hydrocarbon in this area because the content of vitrinite is higher than that of exinite. Data from simulating experiments and infrared spectra show that the hydrocarbon-generating process occurred primarily at the lower-mature stage in the Middle-Lower Jurassic coal measures. (Generally, crude oil from the Qigu oilfield has a close similarity in hopanoid distribution to the vitrinite and exinite from the Jurassic strata with C[sub 23]-C[sub 32] pentacyclic triterpanes and γ-lupane being present. The distribution of steranes is also similar. C[sub 29]-sitostane is dominant and C[sub 27] ergostane is subordinate. Only a trace amount of cholestane is present. All this suggests that the crude oil from the Qigu oilfield was derived from Jurassic coal measures. The Jurassic coals of the Junggar and Turpan-Hami basins, Xinjiang, China, are characterized by abundant vitrinite. Microscopic analysis of Junggar coal samples indicates that they contain desmocollinite and hydrogen-rich vitrinite with a low reflectivity. The hydrocarbon-generating potential of various macerals follows the decreasing order of exinite>vitrinite>inertinite. However, desmocollinite is a principal maceral for hydrocarbon in this area because the content of vitrinite is higher than that of exinite. Data from simulating experiments and infrared spectra show that the hydrocarbon-generating process occurred primarily at the lower-mature stage in the Middle-Lower Jurassic coal measures. (Generally, crude oil from the Qigu oilfield has a close similarity in... [ABSTRACT FROM AUTHOR]

Key message: The barley eceriferum-b.2 ( cer-b.2) mutant produces glossy leaf sheaths and is deficient in the cuticular wax component 14,16-hentriacontanedione. The mutated gene maps to a 1.3-cM interval on chromosome 3HL flanked by the genes MLOC_10972 and MLOC_69561. Abstract: The cuticular wax coating of leaves and stems in many grass species is responsible for the plants' glaucous appearance. A major component of the wax is a group of β-diketone compounds. The barley eceriferum-b.2 ( cer-b.2) mutant produces glossy leaf sheaths and is deficient for the compound 14,16-hentriacontanedione. A linkage analysis based on 708 gametes allowed the gene responsible for the mutant phenotype to be mapped to a 1.3-cM interval on chromosome 3HL flanked by the two genes MLOC_10972 and _69561. The product of the wild type allele may represent a step in the β-diketone synthesis pathway. [ABSTRACT FROM AUTHOR]

The total organic carbon (TOC) in the marine source rock of the Ordos Basin mostly ranges from 0.2% to 0.5%. The industrial standard commonly states that the TOC value has to be no less than 0.5% (0.4% for high mature or over-mature source rock) to form large petroleum reservoirs. However, gas source correlation indicates that the natural gas in the Jingbian gas field does receive contribution from marine source rocks. In order to determine the effect of carboxylate salts (or called as organic acid salts) on TOC in highly mature source rocks with low TOC value, we sampled the Ordovician marine source rock and the Permian transitional facies source rock in one drilled well in the southern Ordos Basin and performed infrared and GC-MS analysis. It is found that both kerogen-derived organic acids and carboxylate salt-conversed organic acids exist in both marine and transitional facies source rocks. The carboxylate salt-conversed organic acids mainly come from the complete acidification of carboxylate salts, which confirms the presence of carboxylate salts in the marine source rocks. Although the C 16:O peak is the main peak for the organic acids both before and after acidification, the carboxylate salt-conversed organic acids have much less relative abundance ahead of C 16:O compared with that of the kerogen-based and free organic acids. This observation suggests that the kerogen-based and free organic acids mainly decarboxylate to form lower carboxylic acids, whereas the carboxylate salt-conversed organic acids mainly break down into paraffins. By using calcium hexadecanoate as the reference to quantify the kerogen-derived and carboxylate salt-conversed organic acids, the high TOC (>2.0%) marine source rocks have low carboxylate salt content and the low TOC (0.2%–0.5%) marine source rocks contain high content of carboxylate salt. Therefore, for the marine source rocks with 0.2%–0.5% TOC, the carboxylate salts may be a potential gas source at high maturity stage. [ABSTRACT FROM AUTHOR]

Theoretical and practical knowledge regarding low-mature gasses is of significant importance to identifying potential natural gas resources. Light hydrocarbon parameters and C and H isotopes are useful tools to identify low-mature gas. Twenty gas samples were collected from the Turpan-Hami Basin for light hydrocarbon analyses. The results showed that the light hydrocarbon components of natural gases contain high methylcycloxane, high isoparaffin and low benzene. This implies that the gas-generating parent materials are of typical humus type and the paleoenvironment is a fresh water sedimentary environment. These features are consistent with the geological setting of the basin. Comparative studies of isoheptane, heptane, and the carbon isotopic compositions of methane in natural gases, and other maturity indices indicated that natural gases in the Turpan-Hami Basin are dominated by low-mature gas formed during the low evolution stage of Jurassic coal seams. The parent materials are of type III, and the maturation degree was in the low evolution stage. These are the fundamental characteristics of low-mature gas. Results of light hydrocarbon research provided further evidence to suggest that the Turpan-Hami Basin is a large-scale gas producer of low-mature gas in China. It is likely that this resource will play an important role in future exploration and development of low-mature gas in China. [ABSTRACT FROM AUTHOR]