Isotopic Compositions Of Individual Hydrocarbons Research Articles

Accumulation process and pattern of oolitic shoal gas pools in the platform: A case from Member 3 of Lower Triassic Feixianguan Formation in the Heba area, northeastern Sichuan Basin

Abstract Combined with the regional sedimentary burial history and trap tectonic evolution history, the gas source, pool-forming periods and accumulation process of the oolitic shoal limestone gas pool in the Lower Triassic Feixianguan Formation Member 3 were researched in the Heba area of northeast Sichuan Basin. The gas source was mainly derived from the underlying Upper Permian Wujiaping Formation (or Longtan Formation) according to the analysis results of carbon isotopic compositions of individual hydrocarbons. The analysis of homogenization temperature for fluid inclusions shows, the gas pool has experienced multi-stage gas charging and migration, which occurred in the Late Jurassic to Early Cretaceous, matched with the generating peak of the Upper Permian source rocks, and represented the main period for hydrocarbon accumulation. The structure formation process of the Heba area had structural prototype in Indo-Chinese Epoch, and was relatively stable stage in the Jurassic to Early Cretaceous, and was formed like present structure in the Late Cretaceous, and was complicated in the Cenozoic Himalayan period. It is predicted that the sedimentary micro-paleogeomorphology highs, faults or fracture relative development area and the ancient-modern structure development zone are favorable for oolitic shoal limestone gas pools in Northeast Sichuan.

Use of biomarker distributions and compound specific isotopes of carbon and hydrogen to delineate hydrocarbon characteristics in the East Sirte Basin (Libya)

Biomarker ratios, together with stable carbon (δ 13C) and hydrogen (δD) isotopic compositions of individual hydrocarbons have been determined in a suite of crude oils ( n = 24) from the East Sirte Basin to delineate their sources and respective thermal maturity. The crude oil samples are divided into two main families (A and B) based on differences in source inputs and thermal maturity. Using source specific parameters including pristane/phytane (Pr/Ph), hopane/sterane, dibenzothiophene/phenanthrene (DBT/P), Pr/ n-C 17 and Ph/ n-C l8 ratios and the distributions of tricyclic and tetracyclic terpanes, family B oils are ascribed a marine source rock deposited under sub-oxic conditions, while family A oils have a more terrigenous source affinity. This genetic classification is supported by the stable carbon isotopic compositions (δ 13C) of the n-alkanes. Using biomarker maturity parameters such as the abundance of Pr and Ph relative to n-alkanes and the distribution of sterane and hopane isomers, family A oils are shown to be more thermally mature than family B oils. The contrasting maturity of the two families is supported by differences between the stable hydrogen isotopic compositions (δD) of Pr and Ph and the n-alkanes, as well as the δ 13C values of n-alkanes in their respective oils.

The effect of source and maturity on the stable isotopic compositions of individual hydrocarbons in sediments and crude oils from the Vulcan Sub-basin, Timor Sea, Northern Australia

Recent work has demonstrated the effect of maturation on the stable hydrogen isotopic compositions (δD) of individual sedimentary hydrocarbons ( n-alkanes, pristane and phytane) in a series of marine source rocks from the Perth Basin (Western Australia). There was an enrichment in deuterium (D) in the hydrocarbons with increasing maturity, attributed to isotopic exchange associated with thermal maturation. An initial, large (≈115‰) biologically derived difference between the δD values of n-alkanes and isoprenoids gradually decreased as pristane and phytane became enriched in D, while the n-alkanes generally remained at constant isotopic composition. This work has now been extended to include a series of Late Jurassic sediments from the lower Vulcan Formation of the Vulcan Sub-basin (Timor Sea, Northern Australia), where the δD values of n-alkanes and isoprenoids show similar trends to those observed for the Perth Basin. The enrichment in D in isoprenoids correlates strongly with traditional maturity parameters and is shown to be related to the epimerisation of pristane and phytane. Pristane and phytane extracted from a post-mature Paqualin-1 sediment are significantly enriched in D relative to the n-alkanes, indicating that D enrichment persists at very high maturity, more so for regular isoprenoids than n-alkanes. This supports the notion that hydrogen (H/D) exchange causes the observed shift in δD values, and not free radical hydrogen transfer. A mechanism is proposed which can account for both H/D exchange and epimerisation of pristane and phytane in the sedimentary environment. Pristane is enriched in D relative to phytane throughout the Vulcan Sub-basin sequences, attributed to a lower relative algal input to the isoprenoids, and indicating that they exchange hydrogen at similar rates during maturation. Crude oils and condensates from the sub-basin were also analysed to evaluate their source and thermal maturity and the results complement previous molecular and stable carbon isotopic analysis. The δD values of n-alkanes and regular isoprenoids largely support the previous classification of Vulcan Sub–basin crude oils and condensates into two groups: Group A, having a marine source affinity and Group B, a terrigenous source affinity. Some oils and condensates are suggested to be a mixture of sources A and B, or A and other as yet unknown sources. Tenacious-1 crude oil (formerly a Group A oil) contains n-alkanes with more positive δD values than other Group A oils and is suggested to have been mixed with another source of more mature hydrocarbons. The Group A crude oils and condensates show an upward inflection in the n-alkane δD profile from n-C 11 to n-C 15, which is suggested to represent an addition of D-enriched lower molecular weight n-alkanes from a more mature wet gas/condensate to an initial oil charge. The small differences between the δD values of the n-alkanes and regular isoprenoids in the crude oils and condensates indicate that significant H/D exchange has taken place, implying that the samples were generated from mature source rocks.

Geochemical study of stable carbon isotopic compositions of individual hydrocarbons

Geochemical study of stable carbon isotopic compositions of individual hydrocarbons

Geochemical study of stable carbon isotopic composition of individual hydrocarbons in recent sediments

Geochemical study of stable carbon isotopic composition of individual hydrocarbons in recent sediments

95/00006 Carbon Isotopic composition of individual hydrocarbons and associated gases evolved from micro-scale sealed vessel (MSSV) pyrolysis of high molecular weight organic material

95/00006 Carbon Isotopic composition of individual hydrocarbons and associated gases evolved from micro-scale sealed vessel (MSSV) pyrolysis of high molecular weight organic material

Carbon isotopic composition of individual hydrocarbons and associated gases evolved from micro-scale sealed vessel (MSSV) pyrolysis of high molecular weight organic material

The molecular carbon isotopic composition of pyrolytically generated gaseous and non-gaseous compounds was monitored by compound specific isotopic ratio mass spectrometry. The instrument used for this study was a modified commercial GC-C-IRMS system onto which a micro-scale sealed vessel (MSSV) injection assembly has been mounted. The use of two different GC columns (Poraplot Q for gases and SE 54 for liquids) permitted analysis of the δ 13C of the pyrolysates for their C 1−C 30 + n-alkane content. In addition, CO 2 could be analysed together with the methane to hexane content in a single GC-C-IRMS run. Data obtained from the analysis of asphaltenes were contrasted with those obtained from the molecular isotopic analyses of their parent oils. Additional materials including sediments, coals, and humic matter were amenable to the MSSV pyrolysis procedure and provided isotopic information that could be exploited in terms of kerogen type but failed to show any maturity relationships. A relationship between the isotopic composition of pyrolytically generated carbon dioxide and the depositional paleoenvironments of candidate source rocks was found.