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The topic of thermal analytical methods in organic geochemistry covers many methods ranging from bulk characterization of organic matter in terms of total organic carbon content (TOC) and weight loss through thermal gravimetric analysis (TGA) to sophisticated fingerprinting of organic matter using microscale pyrolysis techniques combined with analytical techniques such as gas chromatography (GC), gas chro-matography-mass spectrometry (GCMS) and more recently gas chromatography-isotope ratio mass spectrometry (GCIRMS). In general, the methods can be divided into those which either involve degradation of organic matter or thermal desorption of extractable organic matter from various types of matrices. Organic geochemistry itself covers a broad spectrum of disciplines including environmental and forensic geochemistry (see for example Kaplan et al., 1997; Murphy and Morrison, 2001) as well as the more traditional topics of petroleum geochemistry (Hunt, 1996), fate of organic matter (Engel and Macko, 1992), or origin of life type studies (Calvin, 1964). The main idea behind this chapter will be to discuss and review the techniques associated with the thermal analytical methods, and examples of applications will be given wherever it might be deemed appropriate. For each technique a brief overview will be given along with a few key references and examples of applications. It is not proposed that this chapter be an exhaustive review of the all the pyrolysis work of the past few decades.

The Tertiary Green River petroleum system in the Uinta basin generated about 500 million bbl of recoverable, high pour-point, paraffinic crude oil from lacustrine source rocks. A prolific complex of marginal and open-lacustrine source rocks, dominated by carbonate oil shales containing up to 60 wt. % type I kerogen, occur within distinct stratigraphic units in the basin. Petroleum generation is interpreted to originate from source pods in the basal Green River Formation buried to depths greater than 3000 m along the steeply dipping northern margin of the basin. Producing fields in the Altamont-Bluebell trend have elevated pore-fluid pressures approaching 80% of lithostatic pressure and are completed in strata where open fractures provide permeability. Active hydrocarbon generation is one explanation for the origin of the overpressured reservoirs. In this study, experiments were undertaken to examine the mechanisms of hydrocarbon generation and accumulation in the Uinta basin. We combined analyses of representative source rocks from the entire Green River stratigraphic section with detailed laboratory simulation experiments using both open- and closed-system pyrolysis. This information provides new insights on lacustrine source rock lithofacies, gas-oil-source rock correlations, hydrocarbon generation kinetics, and basin modeling. The results show that the basal Green River Formation contains a unique type I source facies responsible for generation of paraffinic crude oils. The classic type I oil shales in the upper Green River Formation correlate well with low-maturity aromatic-asphaltic samples. We determined kinetic parameters for the source rocks and used them to develop basin models for hydrocarbon generation. The models show that hydrous pyrolysis kinetic parameters are more consistent with the natural data in terms of predicted timing and extent of oil generation as compared to models using Rock-Eval kinetics. (Begin page 1334)

Petroleum geochemistry has played an important role in many areas of exploration and production for fossil fuels. Many of the more recent developments can be seen to have developed in parallel with developments in analytical chemistry such as gas chromatography and gas chromatography−mass spectrometry. For the past two decades such analytical techniques have been used to search for trace amounts of compounds known as biomarkers present in oils and source rock extracts which can be used to provide valuable information on the origin and history of the oil. In the past two or three years much more effort has been placed on the development and utilization of such techniques as an aid to solving reservoir and production problems. In this paper it is proposed to provide an overview of major developments that have occurred in a number of areas of geochemistry in recent years. This will include developments in reservoir geochemistry such as the use of high-resolution gas chromatography for reservoir continuity st...

Paleozoic source rocks and crude oils from the Anadarko basin, Oklahoma, have been characterized by means of a variety of organic geochemical techniques. The potential source rocks investigated include the Viola Group, Sylvan Shale, Lower Mississippian limestone, Chester group, Springer Formation, and Morrow group. The Woodford Shale, which is an important source rock in the basin and has been discussed extensively in the literature, was used as a laboratory standard in this study. The crude oils examined in this study were obtained from reservoir formations of various ages from throughout the basin. The source rock screening analysis indicates that the lower and middle subfacies of the Viola, especially from the southeastern part of the basin, have substantial oil-generation potential. The Sylvan is not a source rock, although the black shales in the Springer and Morrow have substantial oil- and especially gas-generation potential. The results of this study support the proposal for multiple sources of oil and gas generation in the Anadarko basin. Selected source rock and oil samples were characterized in more detail, and the distributions and concentrations (both relative and absolute concentrations) of biomarkers in different source rocks and oils were determined. The biomarker characteristics were combined with other geochemical and geological data to interpret the sources, depositional environments, diagenesis and catagenesis processes, migration, and weathering. Oil­source rock correlations were made between source rocks and a number of crude oils based on quantitative and qualitative biomarker distributions. Petrographic descriptions and graptolite reflectance measurements were used to evaluate ©Copyright 1997. The American Association of Petroleum Geologists. All rights reserved.1Manuscript received November 1, 1995; revised manuscript received April 8, 1996; final acceptance September 13, 1996. 2ARCO International Oil and Gas Company, 2300 W. Plano Parkway, Plano, Texas 75057. 3School of Geology and Geophysics, University of Oklahoma, Norman, Oklahoma 73019.

Biomarkers are compounds, generally hydrocarbons, present in crude oils and source rocks whose carbon skeletons can be readily related to a precursor molecule occurring in the original source material. The use of biomarkers in source rock extracts and crude oils for the purpose of determining source materials, thermal maturity, extent of biodegradation and migration and for making oil/oil and oil/source rock correlation studies has been well documented. One of the major problems with this approach is the possibility of contamination either naturally, through crude oil migration, or artificially during sample collection or work-up procedures. A solution to this potential problem can be found in the use of biomarkers produced by kerogen pyrolysis. The actual isolation of the kerogen eliminates any potential contaminants and pyrolysis of the kerogen produces indigenous biomarkers. In this paper it is intended to review progress that has been made in the study of biomarkers produced by kerogen pyrolysis. The various techniques that have been used in this approach will be discussed and examples given to show, in particular, the distributions of triterpanes and steranes produced by kerogen pyrolysis. In addition, results obtained from a combination of hydrous pyrolysis to artificially mature kerogens, and anhydrous pyrolysis to characterize the artificially matured kerogens, will be discussed. Certain biomarkers such as the C 28 -bisnorhopane and gammacerane are not produced during anhydrous pyrolysis and possible reasons for these observations will be discussed. Finally, the production of sulphur-containing compounds during pyrolysis reactions will be briefly discussed with reference to their role as possible indicators of maturity and depositional environments.

The classic organic chemical studies by the German chemist Alfred Treibs on the structures of tetrapyrrole-type compounds in crude oils led him to propose a biological origin for crude oils (Treibs 1934, 1 936). Treibs based his proposal on structural determinations, made by classical chemical methods, of porphyrins (I) in the oils and their structural relationship with chlorophyll (II) molecules (known to be widely distributed in plants) and compounds with similar structures in animals and bacteria. These obser­ vations can be thought of as the beginning of the biomarker concept and precursor/product relationships. Although the idea was initially proposed in the 1 930s, it was not widely exploited until major analytical advances occurred in the 1 960s and 1 970s. In this time period major breakthroughs were made in the coupling of gas chromatographs and mass spectrometer systems and the development of capillary gas chromatography columns.

The average stable carbon isotope ratio of 21 oils from the Taranaki Basin of New Zealand suggests that the source rocks date from the Cretaceous period, when sedimentation in this basin began. Stable carbon isotope ratios also confirm the grouping of these oils into the genetic families which were previously suggested by the correlation of source-related biomarkers. Stahl isotope type-curves for the oils also reflect the correctness of these relationships. A plot of the saturate versus aromatic δ13C values for the New Zealand oils is particularly valuable for oil correlation in this basin and clearly demonstrates that the Ahuroa and Stratford oils, while separated from the McKee field by some 30 km, probably originate from the same oil-source formation as do the oils of the McKee field. The plot also indicates, that the Kaimiro, Mangahewa, Pukearuhe and Waihapa oils are discrete in situ accumulations of petroleum which do not have the characteristics of oils from adjacent fields. These conclusions are further supported by the values of the Sofer canonical variable for all of the oils. Additionally, the Sofer plot provides clear evidence of the predominantly terrigenous origin of the oils in the Taranaki basin. Consideration of the data for these oils, leads to a hypothesis that three independent sources of organic material, microbes, gymnosperms and angiosperms, gave rise to the oils in this region.

The hexane-soluble fractions of hydroliquefied products from three Yallourn brown coal lithotypes have been separated into five fractions by combined silica-alumina packed column chromatography. Analyses of various fractions by g.c.-m.s. permitted the identification of ≈50 components in the saturate fraction and 40 components in the diaromatic fraction, together with 30 components in the monoaromatics. The components identified were quite similar among hexane-soluble portions of all three lithotypes. A marked predominance of even carbon number alkane (C23-C29) was observed in the hydrocarbon fractions from pale lithotype over ZnCl 2 KCl , and medium light lithotype over both pure ZnCl2 and ZnCl 2 KCl . However, medium dark lithotype over both melt catalysts produced a saturate fraction with an odd carbon number(C22-C28) preference. Based on spectral methods, Soxhlet extracts obtained from untreated lithotypes (hexane and benzene solubles) were characterized as complex mixtures of higher molecular weight(300–1000) aliphatic hydrocarbons, which were supposed to be a precursor of the saturates produced from the corresponding lithotype in the catalytic hydroliquefaction.

The study of natural products in plants, animals, bacteria, fungi, and other living systems has long been of interest to chemists, biochemists, and analytical chemists. Generally, however, these scientists are concerned only with the isolation and identification of compounds present in living systems. A relatively small but rapidly growing scientific discipline has emerged over the past two decades involving scientists primarily interested in the fate of organic material and associated natural products after their demise and deposition in the sedimentary record and conversion into fossil fuels or chemical fossils. Organic compounds present in the original source material whose carbon skeleton is preserved throughout the geological record are referred to as biomarkers. In this Report the authors will introduce some of the basic concepts of petroleum geochemistry and the key role that analytical chemistry has played in the development of this discipline. They will also discuss areas in which geochemical research is most likely to develop in the next few years, and they will examine the major analytical challenges the organic geochemist will meet in conducting geochemical research during the next decade.

The bi-, tri- and tetracyclic terpenoids in crude oils from the Taranaki basin of New Zealand have been studied. The distribution of C14, C15 and C16 bicyclanes was essentially invariant amongst the various fields. A suggestion is made that the proportion of rearranged to total drimanes may be related to maturity and the ratio of homodrimane to drimane may be related to depositional environment. Mass spectra are reported for a number of unidentified sesquiterpanes, including possibly norbisabolane and bisabolane. The distribution of bi-, tri- and tetracyclic diterpanes was very similar to that of crude oils from the Gippsland basin of south-east Australia. The occurrence of rimuane was confirmed, 8α(H)-labdane was identified and 4α(H)-18-norisopimarane was tentatively identified. Isopimarane dominated the diterpane distribution of oils from the Maui field in the south-west of the basin and its abundance gradually diminished in a north-westerly direction until it became a minor component of oil from the New Plymouth field. This trend coincided with an increase in the complexity of the triterpane distribution and with the oleanane content of the oils. These northwards trends also followed the evolution of coal deposits in the region. The diterpanes in these oils had the same structure as those which occur in extant trees of the Araucariaceae and Podocarpaceae which flourish in New Zealand today and did so even more extensively in the past. Coal measures, formed from forests of such trees, are probably the source of the diterpanes, a situation analogous to that in the Gippsland basin of south-eastern Australia. Tricyclanes of the cheilanthane series were not detected in any of the Taranaki oils, lending support to the view that these tricyclanes occur most abundantly in oils derived from marine sources. C24-Tetracyclanes (secotriterpanes) occurred abundantly in all the oils as they do in terrigenous oils from other parts of the world.

The biomass from which hydrocarbons were formed and the organisms responsible for its production are usually deduced by the use of biochemical markers. In the present study, using a simulated sedimentary system, cyanobacterial organic matter was buried in sediments and exposed to sequential environmental changes ranging from microaerobic conditions at ambient temperature to strongly reducing conditions at a biologically extreme temperature and pressure. Significant changes occurred in the composition of hydrocarbons and fatty acids isolated from the biomass that masked the characteristic patterns exhibited by the original cyanobacterial material. The changes depended on the particular environmental conditions to which the organic matter was exposed. The results stress the need for caution in interpreting biochemical markers in terms of their source material in sediments.

In the past decade, environmental forensics has emerged as a discipline directed toward determining parties liable for causing spills of contaminants into the environment. Such investigations, while geared toward determining the guilty parties in order to recover costs of the cleanup and remediation, require various questions to be addressed. These include determination of the nature of the product; Where did it come from?; Extent of weathering, if any; How long has it been there?; and Is it degrading naturally? Traditionally, these studies have been addressed through utilization of techniques such as gas chromatography (GC) and gas chromatography–mass spectrometry (GCMS). However, in recent years, stable isotopes, primarily determined through the use of combined gas chromatography–isotope ratio mass spectrometry (GCIRMS), have emerged as an equally important tool in environmental forensics. For relatively low molecular, volatile compounds such as MTBE, BTEX, or chlorinated solvents, the isotopes, primarily carbon and hydrogen, have been used extensively for evaluating the onset of natural attenuation. For larger molecules such as PCBs or PAHs, in which the effects of biodegradation on the isotope composition of these molecules is minimal, the isotopic fingerprints of the individual compounds can be used for correlation purposes. In this paper, a brief introduction to isotope geochemistry will be given, followed by a review of applications of stable isotopes to a variety of environmental problems. While the review may not necessarily be exhaustive, it will provide a comprehensive overview of areas where isotopes have been used and potential applications for the future. Most of the review is concerned with carbon and hydrogen isotopes, although a brief overview of the emerging area of chlorine isotopes will also be discussed.

Pale, medium-light and medium-dark lithotypes of Yallourn coal were hydrogenated with and without ZnCl 2 -containing catalysts (400 °C, 9.8 MPa H 2 and 3 h). The degree of hydroliquefaction was examined petrographically. Without catalyst, the amounts of water produced can be correlated with the amounts of humodetrinite; whereas with catalyst, either humotelinite or humocollinite may contribute to coal liquefaction in addition to humodetrinite; with pale lithotypes in the presence of catalyst, three submaceral groups may be converted.