Maturity Of Bitumen Research Articles

The genesis of bitumen and its effect on hydrocarbon accumulation

ABSTRACT In recent years, large amounts of bitumen have been discovered in the Permian Lower Wuerhe Formation (P2w) reservoir exploration of the Mahu Sag on the northwestern margin of the Junggar Basin. However, bitumen genesis and its influence on oil accumulation remain unclear, affecting the subsequent exploration and development in this area. Therefore, this study analyzed the genesis and source of bitumen and its influence on hydrocarbon accumulation through chromatography, microscopic observation, inclusion temperature tests, and reservoir physical property experiments. Studies have shown that the crude oil produced in the early period of the Fengcheng Formation (P1f) was destroyed due to tectonic movement. Crude oil undergoes biodegradation, where the lighter components are dispersed and lost. The remaining heavy components undergo high temperature conditions during long-term burial to form bitumen. Microscopic observation showed that the overlying reservoir has a higher bitumen content and the underlying reservoir has a lower bitumen content. After the bitumen was dissolved, the porosity and permeability of the overlying reservoir increased by 6.77% and 34.67 mD from the original 3.53% and 3.41 mD, respectively. The porosity and permeability of the underlying reservoir increased by 3.21% and 27.68 mD from the original 5.86% and 1.51 mD, respectively. This shows that the initial physical properties of the overlying reservoir were better than those of the underlying reservoir. Therefore, early crude oil is more likely to enter the overlying reservoir, resulting in a higher bitumen content. The difference in the homogenization temperature of inclusions and the maturity of bitumen indicates that the oil and gas accumulation in this area has undergone two stages. Early filling with oil occurred in the late Permian, but the reservoir was destroyed because of tectonic movements. The residual components formed bitumen during the long burial, which occupied most of the reservoir space and made it difficult for late crude oil to enter the pores.

Molecular structure and origin of solid bitumen from northern Sichuan Basin

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.

Geochemical features of bitumen shows in the Lower-Middle Devonian deposits of the Northern-Western part of Kotelny Island (Novosibirsk Island Archipelago) v

The work presents the results of organic matter (OM) study of rocks, the composition, chemical structure of chloroform bitumen (CB), their fractions and the nature of the hydrocarbon biomarkers distribution in samples taken from outcrops. The obtained results confirmed the existing idea of ​​the domanicoid nature of OM and the high oil and gas potential of the studied deposits. According to our data, the aquagenic type of OM is indicated by a high content of Corg, a high yield of CB, a high content of oils in the composition of synbitumoids, and the predominance of relatively low molecular weight n-alkanes with a maximum at nС15-18. A sufficient maturity of bitumen can be judged by CPI coefficients close to unity and low absorption coefficients of oxygen-containing groups and bonds in the CB, thus deposits entered the main oil generation zone and generated liquid hydrocarbons that could migrate and form clusters. According to the data of Chromato Mass Spectrometry, it is shown that a feature of the composition of CB from the Lower Devonian sediments is the presence of high concentrations of dibenzothiophenes, in contrast to the Middle Devonian, which may be associated with the formation of the initial OM in an environment with higher hydrogen sulfide contamination of sediments. It has been suggested that naphthides generated by aquagenic OM of the Lower Devonian deposits can be enriched with dibenzothiophenes. The studied bitumen shows are mainly syngenetic in nature and have been influenced by hypergenic oxidation (judging by the nature of the IR spectra of resinous components) and contact metamorphism. According to the characteristics of the distribution of saturated hydrocarbons, it was shown that, in the Middle Devonian, bitumen occurrences along with chemical oxidation were affected to a different degree of bacterial oxidation processes, in contrast to the Lower Devonian bitumen shows. The results can be used to assess the generation potential of oil source strata and to forecast the prospects of oil and gas potential in the shelf of the eastern sector of the Russian part of the Arctic.

Paleo-reservoir bitumen of the Middle Protozoic Jixian System in the southwest margin of the Ordos Basin, China

Abstract Solid bitumen was found in the outcrops of laminated algal dolomite of the Middle Protozoic Jixian System in the southwest margin of the Ordos Basin. Bitumen was distributed through the Jixian System and migrated upward into the overlying purple sandstone of the Lower Cretaceous Luohandong Formation. Bitumen was distributed on rock bed surfaces and in rock pores and fractures as lamina and small veins. Distribution characteristics of chloroform bitumen A normal alkanes and the analysis of terpene and steroid biomarkers show that the bitumen is sourced from lower aquatic and algal organisms. The laminated algal dolomite of the Jixian System is the most probable source rocks of the bitumen. The measured bitumen reflectance is 2.7%–3.6%, which is very inconsistent with the degree of thermal maturation of the coal beds of the Jurassic Yan'an Formation in the study area (where the vitrinite reflectance ( R o ) is 0.6%–0.8%), suggesting that the bitumen maturity was controlled by local abnormal thermal events. The paleo-reservoir was destroyed by the Tongcheng alkaline magmatic intrusion and the oil and gas inside the paleo-reservoir was transformed to bitumen because of thermal cracking under high temperature. The study area has the source rock and accumulation conditions for the formation of oil and gas. The potential of hydrocarbon generation and exploration should be recognised and deserves further study.

Characteristics and source of inorganic and organic compounds in the sediments from two hydrothermal fields of the Central Indian and Mid-Atlantic Ridges

A combined inorganic and organic geochemical study was carried out on sediments collected from the Kairei hydrothermal field on the Central Indian Ridge (CIR) and the Logatchev hydrothermal field on the Mid Atlantic Ridge (MAR). Analysis of the major and trace elements as well as the minerals shows that the Kairei hydrothermal sediments are formed by the mixing of silica-rich hydrothermal fluids with Mg-rich seawaters, but the Logatchev sediments are associated with pelagic carbonate oozes containing some precipitates derived from hydrothermal plume fall-out. The rare earth element (REE) patterns of Kairei sediments show a character of light REE (LREE) enrichment and positive Eu anomaly, whereas two of the three Logatchev sediment samples lack positive Eu anomaly and have negative Ce anomaly. Patterns of aliphatic hydrocarbon fractions in the sediments from both hydrothermal fields exhibit high relative concentrations of volatile resolved components, smooth n-alkane distributions and high concentrations of the isoprenoids pristane and phytane. The composition of organic matter and C isotope composition of individual n-alkanes indicate that they come from marine photosynthetic autotrophs and hydrothermal organisms, as well as terrestrial inputs in the Kairei and the Logatchev hydrothermal fields. Several parameters of organic geochemistry, used for assessing the maturity of bitumen, are well correlated with one another. In general, these parameters indicate that the Kairei sediments are more mature than the Logatchev sediments. The relationship between the inorganic parameters (REE/Fe and Eu/Eu ∗) and the organic parameter (bitumen maturity) might reflect changes of the hydrothermal influence on the sediments. The results of this study provide an insight into the variation of inorganic and organic geochemistry in deep-sea hydrothermal systems.

New Maturity Indicators Based on the Spectral Fluorescence of Alginite and Bitumen, Monterey Formation, California

Conventional assessment of maturation level in the Monterey has been problematic, since sporinite and vitrinite are rare or absent. Organic matter is largely alginite and amorphous material, and reliable vitrinite reflectance (R{sub o}%) and Thermal Alteration Index (TAI) are difficult to obtain. Large amounts of bitumen often imbedded in the highly fractured Monterey shales cause a suppression of T{sub max} and low values of S{sub 1}S{sub 1} + S{sub 2}. It is often difficult to determine whether bitumen is indigenous or migrated from other more mature strata. Spectral fluorescence measurements of alginite and bitumen have proved useful in assessing the maturity of the Monterey. A maturity scale based on red/green quotient (Q{sub v}) measured as the fluorescence of alginite B when excited by violet-light has been developed and applied to the Monterey. Alginite B is common in the Monterey, and accurate fluorescent measurements can be readily obtained given the highly fluorescent character of alginite B. A total scanning fluorescence technique was used to develop a maturity scale based on bitumen aromatic content and composition. The maturity parameter (R{sub 1}) developed in this study uses the intensity of fluorescence emitted at 360 nm ratioed to that at 320 nm when themore » solvent-dissolved bitumen is excited at the 270 nm. These parameters allow for the evaluation of the thermal maturity of algal organic matter and bitumen from the Monterey with R{sub o}% {lt} 1. Indigenous bitumen is also indicated by a comparison of maturity based on Q{sub v} (the solid phase) and bitumen maturity (the liquid phase) based on R{sub 1}.« less

Source and Thermal Maturity of Bitumen in Precambrian Nonesuch Formation Inferred from Isotopic Compositions of Individual Normal Alkanes

As part of a continuing study of organic geochemistry of the 1.05 Ga Nonesuch Formation in the North American Mid-Continents rift, isotopic compositions of individual normal alkanes were measured using compound-specific isotopic analysis. This is a relatively new technique that can be used in conjunction with traditional biomarker analysis in interpretation of thermal maturity, oil-source rock correlation, and paleoecologic reconstruction. Carbon-isotopic compositions of individual normal alkanes from C{sub 15} to C{sub 25} in five bitumens and one oil from Nonesuch strata vary from {minus}28.8 to {minus}34.5{per thousand} (versus PDB). Within a given sample, isotopic compositions of n-alkanes span a range of 2 to 4 {per thousand}%. Homologues from C{sub 15} to C{sub 19} are isotopically light (depleted) by approximately 0.5{per thousand} relative to higher homologues from C{sub 20} to C{sub 25}. Two sources of normal alkanes are interpreted from the distribution of isotopic compositions. Based on chain length, the series from C{sub 15} to C{sub 19} may have been derived from algal components. Isotopically heavy, higher homologues are suspected to have been derived from bacterial sources. The pattern of isotopic compositions of bitumens is similar to that of the oil, demonstrating an oil-source rock relationship. Superimposed upon this primary, bimodalmore » distribution of normal alkanes is the influence of thermal maturity on isotopic composition. Normal alkanes in samples of higher thermal maturity are enriched isotopically by 0.25 to 2{per thousand} relative to those of lower thermal maturity. Isotopic enrichment with increasing thermal maturity is interpreted to be the result of either addition of isotopically heavy components derived from kerogen and/or preferential loss through cracking of isotopically light components in bitumen.« less

Relationship Between Bitumen Maturity and Organic Facies in Devonian Shales from the Appalachian Basin: ABSTRACT

Relationship Between Bitumen Maturity and Organic Facies in Devonian Shales from the Appalachian Basin: ABSTRACT