Stages Of Catagenesis Research Articles

Incipient bitumen generation in Miocene siliceous sedimentary rocks from the Japan Sea

Samples of Quaternary through Miocene diatomaceous sediment and siliceous sedimentary rock from the Japan Sea (ODP Leg 128, Site 799) were examined to determine the origin of bitumen encountered during drilling, whether previously published studies using Rock-Eval pyrolysis have accurately assessed organic matter type and maturity, and if evidence exists to postulate the presence of a Kuroko-type massive sulfide deposit at depth or along depositional strike. Whole-rock total organic carbon:total nitrogen ratios have values ranging from 31 to 4. Elemental atomic H:C and O:C kerogen ratios decrease from ca 1.3 and 0.3, respectively, in Quaternary and Pliocene samples to 1.2 and 0.1, respectively, in samples obtained from the bottom of the hole. The bitumen ratio of these rocks increases from 50 mg bitumen/g OC at 700 mbsf to 150 mg bitumen/g at 1000 mbsf. The kerogen in these samples comprises a mixture of marine and terrigenous organic material that reaches the earliest stages of catagenesis in the bottom part of this hole. The bitumen is dominated by asphaltenes, resins and polar components. Because these compounds have very high boiling points, Rock-Eval pyrolysis does not assess the thermal maturity, or organic matter type accurately in the early stages of catagenesis. The bitumens have a very low thermal maturity and the observed degree of thermal alteration is consistent with the modern geothermal gradient in the Kita-Yamato trough.

Catagenesis of light acyclic isoprenoids in petroleum

The article presents three sets of experimental data related to the subject of the alteration of light acyclic isoprenoid alkanes in petroleum: (a) distributions of C 9C 20 isoprenoids in crude oils and oil shales, (b) thermocracking reaction studies of oil shales, and (c) thermocracking of three individual isoprenoids, pristane, phytane and squalane, in a pure state and in the presence of acidic minerals. A combination of the data is used as a basis of a hypothesis that most C 9C 16 acyclic isoprenoids were formed in the latest stage of petroleum catagenesis in a sequence of thermo-radical and acidic clay-catalyzed cracking reactions of heavier isoprenoid precursors, mostly pristane and phytane.

A NEW SCHEME FOR THE FORMATION AND CLASSIFICATION OF BITUMENS

This paper discusses models of bitumen formation. Most liquid bitumens are formed during the middle stages of catagenesis (between approx. Ro equivalents of 0.4 and 1.15, respectively).“Progressive”naphthide formation is a process whereby organic matter and its derivatives gradually pass through a number of stages of alteration — three stages are generally recognized. By contrast, “regressive”naphthide formation is a “superimposed” process, involving microbial alteration and biochemical oxidation.In addition to the above two general processes, three other, less important schemes of naphthide formation are recognised:“Pyrodestructive bitumogenesis”results in the formation of “naphthoids”; these are bitumens generated close to an intruded heat source, which causes thermal destruction of organic matter.“Dynamic‐hydrothermal bitumogenesis”results in the generation of a complex group of bitumens, known as “naphthido‐naphthoids”, which are formed under conditions of dynamic metamorphism and hydrothermal activity accompanied by metasomatism. Thirdly, the process of “phase‐migrational” bitumogenesis results in the formation of two groups of bitumens: “asphaltenites” and “beta‐asphaltenites”.This paper summarizes the Author's views on bitumen formation, based on new geological and geochemical data.

Acyclic components in dewaxed heavy distillates

The analysis of thermocracking products of dewaxed heavy petroleum distillates indicates that naphthenic components in the distillates contain numerous n-alkyl and long isoprenoid-type substituents attached to naphthenic cores. These substituents are not characteristic for most multi-ringed biological markers present in ancient sediments. These data suggest that the biological precursors of crude oils underwent extensive skeletal modifications during the petroleum catagenesis stage. The modifications could include the grafting of various long n-alkyl and isoprenoid chains to indigenous naphthenic chemical fossils.

Precambrian vein pyrobitumen: evidence for petroleum generation and migration 2 Ga ago

Abstract Isotopic, optical reflectance, and chemical analyses of large pure samples of Lower Proterozoic vein pyrobitumens (anthraxolite and thucholite of older reports) collected from five widely separated localities in the Great Lakes region of the United States and Canada suggest that in the Lower Proterozoic oil was generated from kerogen and migrated in much the same way as during the Phanerozoic. Furthermore, maturation and organic metamorphism followed the same successive stages that mark the generation and destruction of Phanerozoic petroleum. Kerogens derived from algae and bacteria were deposited with subaqueous muds that ultimately became black shales or slates. Some of the kerogen, however, yielded petroleum, which migrated into fractures and subsequently became pyrobitumen. The δ13C values average −32.6%. (PDB). This value compares favorably with those from Phanerozoic petroleum and asphaltites and is consistent with the proposition that the carbon isotopes were fractionated by biological activity. Reflectance values of the pyrobitumens range from 0.9% for Elliot Lake, Ontario, to 9.5% for Iron River, Michigan, and H/C ratios range from 0.6 for Elliot Lake to 0.1 for Sudbury, Ontario. When compared with the stages of petroleum maturation, these values indicate maturation which ranges from the catagenesis stage through the metagenesis stage of petroleum generation and metamorphism.

Source Rock Potential of an Eocene Carbonate Slope: The Armancies Formation of the South-Pyrenean Basin, Northeast Spain: ABSTRACT

The Armancies Formation is an Eocene carbonate slope succession in the Catalonian South Pyrenean basin. It ranges from 500 to 700 m in thickness. The first 200 m are made of a thin-bedded facies of wackestones alternating with dark pelagic fauna of miliolid, ostracods, bryozoans, and planktonic foraminifers and show significant bioturbation. They also show a low organic content (< 0.5% TOC). The lime-mudstone beds show a massive structure or planar millimeter laminations. They may contain sparse pelagic fossils of planktonic foraminifers, ostracods, and dinoflagellates; they do not show any bioturbation, and have high TOC values, which can reach individual scores of about 14%. They qualify, therefore, as a typical oil shale. Rock-Eval Pyrolysis analysis affords a mean S{sub 2} value of 25 mg HC/g. Mean S{sub 1} value is around 1.0 mg HC/g. As is typical of an initial oil window, T{sub max} maturity parameter ranges from 432 to 440{degree}C (mean = 434{degree}C). This degree of evolution is in accordance with the very low value of carbonyl and carboxyl groups, as determined by IR spectrometry and NMR on Fischer assay extract. The proton NMR shows an aromatic/aliphatic hydrocarbon ratio of 1:4, as expected in earlier stages of catagenesis. N-alkanemore » gas chromatography profiles show n-C{sub 15} to n-C{sub 19} prevalence and that neither even nor odd carbon numbers prevail. This distribution perfectly matches that of typical sediments of marine origin and also agrees with obtained hydrogen index values (mean HI = 500 mg HC/g TOC). Sedimentological and geochemical results indicate an autochthonous marine organic matter and the potential of these slope shales is good oil-prone source beds.« less

Catagenesis and composition of petroleum: Origin of n-alkanes and isoalkanes in petroleum crudes

Distribution of n-alkanes and isoalkanes in ca. 50 petroleum crudes have been examined by the gas chromatography. Molar distributions of n-alkanes with respect to their c atom numbers in the majority of crudes follow the exponential law, which signifies a random, chemical nature of n-alkane-generating processes occurring in the catagenesis stage of petroleum maturation. Similar distributions of n-alkanes were found in the products of mild thermolysis of heavy n-alkanes. Isoalkanes represent a major, 10–25%, petroleum component. The principal types of isoalkanes in crudes are monomethyl-branched, with the branches randomly positioned in the chains, and dimethyl-branched with one of the methyl groups predominantly in the second position in the chains. Thermolysis studies of individual n-alkanes, alkanoic acids, and esters in the presence of various minerals provided an explanation of the n-alkane and isoalkane distributions. Selected heavy n-alkanes are initially formed in decarboxylation reactions of heavy n-alkanoic acids and esters. Extensive thermocracking produces mixtures of lighter n-alkane and α-olefins. The olefins, in the presence of acidic clays, are converted in cationic reactions into mixtures of predominantly mono- and dimethyl-branched isoalkanes.

Thermal behavior of immature asphalts and related kerogens

Immature asphalts suggested to originate from early stages of catagenesis and related kerogens were submitted to various pyrolysis analyses. We have examined the idea that, under certain conditions, parts of kerogen cleave off to yield asphalt. Bulk parameters were recorded as well as gas chromatograms of the trapped pyroproducts. Thermal changes were followed through analyses of gases, condensates, and extracts formed. The residual kerogens/asphalts were examined for structural changes. Both closed and open systems experiments were conducted. Some aspects of high concentrations of organic sulfur bonded (8.0–12.9% S) and low concentrations (normal 1.5–2.1% S) and their influence on thermal behavior were studied using samples from the Dead Sea Rift Valley and Green River Shale Gilsonite. The results obtained indicate very similar thermal behavior for kerogen-immature asphalts pairs, marked differences between various modes of thermal treatment and surprisingly marginal differences between hydrous/ nonhydrous, closed system experiments.

Characteristics of oil formation in various sediments and their associations

Geochemical data are used to comparatively analyze the dynamics of oil formation processes in various types of sedimenary rocks containing varying concentrations of organic matter, primarily of the aline type. In clays and argillites with dispersed organic matter, the principal phase of oil formation is clear-cut and proceeds in a regular fashion. A two-stage intensification of the rate of migration of bitumoids is noted and the reasons for it are discussed. In carbonates, the generation of bitumoids proceeds at a constant or slightly varying rate and migration is often extended over many stages of catagenesis. The largest maximum generally occurs at greater depths than in the case of argillaceous rock and the process is less regular.The possibilities for realization of the oil matrix potential of organic matter in tuffogenic rock are also discussed. The characteristics of the process are closely associated with the specific lithologic and physicochemical properties of the sedimentary type, and also depend on the nature of the alteration of rocks in various types of associations. (JMT)