Marcel Elie

Are time and temperature the only constraints to the simulation of organic matter maturation

Abstract Confined pyrolysis, hydrous pyrolysis and high pressure hydrous pyrolysis were performed with various samples (Toarcian shale and kerogen, Woodford shale and kerogen, Manakam coal) and under different experimental conditions, in order to test the effects of pyrolysis variables on the simulation of maturation of organic matter. Results show that: (i) experimental time and temperature are not exchangeable parameters as suggested by first order kinetic law models; (ii) increasing confining pressure (300–1300 bars) in gold cell experiments performed on Woodford samples has a limited influence on the reduction rate of the oil potential, the TSOM (Total Soluble Organic Matter) yield and the structure of the polars; (iii) the presence of excess liquid water (0–100 weight %) in confined pyrolysis experiments does not significantly influence organic matter maturation. However, comparisons with classic hydrous pyrolysis (200 weight % water) could indicate major differences in timing and composition of the TSOM (bitumen + expelled fraction) as well as of the solid residue. It appears that excess water is not necessary to simulate organic matter maturation when the system is sufficiently confined. Hydrous pyrolysis conditions (low partial pressure of products) delay Woodford kerogen conversion. In addition, results concerning the Mahakam coal suggest that the structure of the organic matter plays an important role concerning the water effect; (iv) increasing water pressure in hydrous conditions (220–1300 bars) drastically lowers and delays Woodford kerogen maturation. Quantitative analysis of the water produced during confined pyrolysis and comparison of the extent of aromatization in hydrous and confined pyrolysis suggests that two competing hydrogen transfer mechanisms occur during organic matter pyrolysis. This study shows that additional parameters must be defined when comparing the results of the experimental simulation of organic matter maturation.

Low temperature air oxidation of n-alkanes in the presence of Na-smectite☆☆

Abstract This paper is the continuation of a study concerning the catalytic effects of clay on organic matter and especially n -alkanes during oxidation carried out at low temperature. The influences of clay minerals were investigated to understand their role better during natural oxidation of organic matter. n -Alkanes oxidation experiments in presence of Na-smectite were carried out at 100 °C during 512 h and reveal an important production of oxygen-bearing molecules to the detriment of initial n -alkanes. Thus, Na-smectite allows to initiate the auto-oxidation of n -alkanes due to its chemical (charged sheets) and/or physical (high specific area) properties. The evolution of oxygen-bearing molecules distribution enables to distinguish two competitive chemical pathways. On one hand, alcohols and ketones are produced with an aliphatic chain length similar to the starting n -alkanes. On the other hand, aliphatic chain cleavages occur and principally produce 1-alcohols, 2-ketones, carboxylic acids and 3-substitued γ-lactones. These oxygen-bearing compounds are more and more preponderant and evidence the fact that cleavage mechanisms become progressively dominant.

Pyrolysis of asphalt in the presence and absence of water

Abstract The bitumen used for the embedding of nuclear wastes has been pyrolysed in confined and hydrous systems, in order to evaluate while an elevation of the temperature in the deep geological repository could induce chemical transformations of the bitumen matrix, which could influence its confining properties. The pyrolysates have been extracted in chloroform and the extract has been separated in aliphatic and aromatic hydrocarbons, resins and asphaltenes. These different fractions have been analyzed by GC-MS and μ-IRTF. Few modifications of the bitumen structure are observed up to 300 °C. Above this temperature, the pyrolysis of the bitumen generates light hydrocarbons and an aromatic and condensed insoluble residue. The use of the time–temperature index allows to estimate the temperatures which have to be reached in the repository in order to observe the first transformations of the bitumen.

Oil-cracking processes evidence from synthetic petroleum inclusions

Abstract A correlated study of petroleum inclusions synthesised in open quartz surfaces with the parent and the residual oil has beenperformed up to 350 °C and 400 bar. Fourier transform infrared microspectrometry (FTIR), extracted fractions and GC-MS analysis have shown evidence of oil-cracking processes during the experiments. Results show that up to 250 °C-212 bar, synthetic petroleum inclusions, the parent oil and the residual oil have very similar FTIR spectra and CH 2 /CH 3 ratios. Although saturated and aromatic HC distributions of oils are similar, the asphaltene/resin ratio has been inverted. Such an inversion indicates that asphaltenes are cracked first during thermal maturation of oil. At 350 °C and 400 bar, FTIR spectra and CH 2 /CH 3 ratios are variable. Moreover, CO 2 and methane have been detected within the gas and the liquid phase of synthetic petroleum inclusions. Results show that the oil secondary cracking is effective at this temperature. The relative amount of aromatic nitrogen-, sulphur- or oxygen-containing heterocyclic compounds (NSO compounds) decreases. GC-MS analysis reveals that the cracking of the thermally most labile saturates and the dealkylation processes of aromatic hydrocarbons are more pronounced. Contemporaneous with these variations, the oil is enriched in saturates. Synthetic fluid inclusions act as a sampling of the oil at one p-T conditions and are thus the useful witnesses of the oil cracking during the experiments.

Palaeoenvironmental assessment of Westphalian fluvio-lacustrine deposits of Lorraine (France) using a combination of organic geochemistry and sedimentology

Abstract The quality and the quantity of organic carbon preserved in modern and ancient terrestrial sediments is the result of a complex interactions of sedimentological factors, such as in-situ productivity, allochtonous supply of organic matter, oxidation processes, biodegradation and sediment accumulation rates. The study aims at utilizing multidisciplinary information in order to characterize the palaeoenvironment in Westphalian fluvio-lacustrine deposits of the Lorraine Coal Basin (NE France). In this basin, the lack of outcrops is the major difficulty. To compensate for this problem, sedimentology, and molecular geochemistry are combined in order to significantly improve the palaeoenvironmental assessment of the area. Geochemical analyses and sedimentology have been carried out on several core samples of the Saulcy drill hole to evaluate local palaeoenvironmental variability. The lithofacies associations in the Upper Carboniferous of the Lorraine basin suggest an alluvial plain environment without marine incursions. Sedimentological interpretations of the core, as well as comparison with sedimentological models, suggests the recognition of different depositional environments from braided and/or meandering rivers to swamp and lakes. The organic geochemistry is focussed on the recognition of aliphatic hydrocarbons and especially on molecular biomarkers, which provide valuable information about the original organic matter and the transformations that took place during sedimentation and diagenesis. In the Lorraine basin, the botanical variability is high and clearly related to the position of the vegetation communities in the fluvial system. The biomarkers (e.g., diterpanes, steranes) show variations, which can be related to the diversity of this ecosystem. In this study, a reinterpretation of the environmental zonation in the sterane ternary diagram adapted to a fluvio-lacustrine sedimentology is proposed. The correlation between sedimentological and geochemical interpretation permits characterization of various depositional environments. A palaeoenvironment model, relating sediment deposition conditions and organic matter characteristics is proposed.

Analysis of confined pyrolysis effluents by thermodesorption-multidimensional gas chromatography

Various types of pyrolysis systems have been developed in order to simulate the natural maturation of petroleum source rocks. However, some difficulties arise in quantifying the amounts of volatile hydrocarbons, CO2 and H2O generated during pyrolysis in closed vessels. Hence, a new system, called thermodesorption-multidimensional gas chromatography (TD-MDGC), has been developed in order to improve the efficiency of pressurized pyrolysis in gold tubes for kerogen characterization. In this study, two immature kerogens of type II (Taorcian of Paris basin) and type III (Mahakam delta) are heated under confined pyrolysis conditions, and their effuents analyzed using this new technique.

Influence of paleoenvironment and radiolytic alteration on the geochemistry of organic matter from Autunian shales of the Lodeve uranium deposit, France

Thirty-three samples of shales from the Lodeve Permian uranium deposit were examined by different analytical techniques. Samples were analyzed by Rock-Eval pyrolysis and by gas chromatography-mass spectrometry after extraction and fractionation. The determination of uranium content was carried out by atomic emission spectrometry. The composition of the organic extracts allows two groups of shales to be distinguished: the first one is marked by a high proportion of aliphatic hydrocarbons and the second by the predominance of aromatic compounds. These two groups exhibit distinctive biomarker characteristics. One group is characterized by (1) pristane/phytane ratios higher than 1, (2) distributions of terpanes dominated by the tricyclic terpanes and (3) the predominance of C 29 and C 28 steranes. The second group is marked by (1) pristane/phytane ratios lower than 1, (2) the predominance of the pentacyclic terpanes over the tricyclic terpanes and (3) the predominance of C 27 and C 29 steranes. It is suggested that the differences observed are mainly related to different depositional environments, although the uranium content may also influence some parameters such as the hydrogen index and the extraction yield.

Natural Analogues of Cement: Overview of the Unique Systems in Jordan

In many radioactive waste repository designs, cement-based materials are expected to dominate the repository and models of cement evolution predict that leaching of the cementitious material in the repository by groundwater will produce an initial stage of hyperalkaline (pH∼13.3) leachates, dominated by alkali hydroxides, followed by a longer period of portlandite and C-S-H (CaO-SiO2 -H2 O) buffered (pH∼12.5) leachates. It has also been predicted that, as the hyperalkaline porewater leaches out of the near-field, significant interaction with the repository host rock and bentonite buffer and backfill may occur. This could possibly lead to deterioration of those features for which the host rock formation and bentonite were originally chosen (e.g. low groundwater flux, high radionuclide retardation capacity etc). The precise implications of cement leachate/repository host rock interaction has been studied in the laboratory and in underground research laboratories (URLs) and this work has been supported by study of natural cements in Jordan. These natural cements have been produced by the combustion of organic-rich clay biomicrites and are very close analogues of industrial cement. Following interaction with groundwaters, natural hyperalkaline leachates are produced and these move out of the cement into the surrounding host rock, subsequently interacting with and altering it.Copyright