High pressure water pyrolysis of coal to evaluate the role of pressure on hydrocarbon generation and source rock maturation at high maturities under geological conditions

This study investigates the effect of water pressure on hydrocarbon generation and source rock maturation at high maturities for a perhydrous Tertiary Arctic coal, Svalbard. Using a 25 ml Hastalloy vessel, the coal was pyrolysed under low water pressure (230–300 bar) and high water pressure (500, 700 and 900 bar) conditions between 380 °C and 420 °C for 24 h. At 380 °C and 420 °C, gas yields were not affected by pressure up to 700 bar, but were reduced slightly at 900 bar. At 380 °C, the expelled oil yield was highest at 230 bar, but reduced significantly at 900 bar. At 420 °C cracking of expelled oil to gas was retarded at 700 and 900 bar. As well as direct cracking of the coal, the main source of gas generation at high pressure at both 380 °C and 420 °C is from bitumen trapped in the coal, indicating that this is a key mechanism in high pressure geological basins. Vitrinite reflectance (VR) was reduced by 0.16 %Ro at 380 °C and by 0.27 %Ro at 420 °C at 900 bar compared to the low pressure runs, indicating that source rock maturation will be more retarded at higher maturities in high pressure geological basins

Stabilité thermique de la fraction aromatique de l'huile brute Safaniya (Moyen Orient) : étude expérimentale, schéma cinétique par classes moléculaires et implications géochimiques

The thermal evolution of reservoired oils is controlled by the kinetics of cracking reactions. The present work is concerned with the study of the thermal stability of the light aromatic components (C6-C14) of crude oils under geological conditions. The aim is to predict this stability through a model derived from laboratory pyrolyses. The light cut <250 °C of Safaniya crude oil, corresponding to the C15- components, was obtained by fractionated distillation; pure aromatic fraction was then separated by liquid chromatography. Detailed molecular characterisation of the aromatic fraction was acquired using HPLC, GC and GC/MS. Then, quantified individual aromatic compounds were lumped into six molecular classes: BTXN, methylaromatics, alkylaromatics, naphthenoaromatics, indenes and sulphur-containing aromatics. Pyrolyses of the aromatic fraction were performed in gold tubes at 100 bars and different temperature/time conditions in a wide range (1 to 93%) of global conversion. Pyrolysis effluents were analysed and lumped into classes. The pyrolysis data were used to elaborate a semi-empirical kinetic scheme of 13 stoichiometric reactions for the primary and secondary cracking of the unstable classes. The scheme kinetic parameters were first estimated, and then numerically optimised, with the constraints of mass balance and hydrogen conservation. A set of pyrolysis experiments was performed at 375 °C under high pressures: 400, 800 and 1200 bars. Increasing slowing down in conversion rate with increasing pressure was thus observed compared to experiments at 100 bars. A slight selective effect of pressure on the different aromatic classes of the charge and on the product distribution was evidenced. The extrapolation of the kinetic model to the conditions of Elgin Field (North Sea) showed that pressure effect should shift the thermal cracking of light aromatics to higher temperatures by almost 8 °C.L'évolution thermique des huiles dans les réservoirs est contrôlée par la cinétique du craquage. Cette étude traite de la stabilité thermique des composés aromatiques légers (C6-C14) des huiles brutes dans les conditions géologiques. L'objectif est de prédire cette stabilité par un modèle dérivé des expériences au laboratoire. La coupe légère de l'huile brute Safaniya <250 °C, correspondant aux composés en C15- , est séparée par distillation fractionnée. Une fraction aromatique pure est ensuite isolée par chromatographie liquide. La caractérisation moléculaire complète de cette fraction est réalisée par HPLC, GC et GC/MS. Les composés aromatiques ainsi identifiés et quantifiés sont regroupés selon leurs structures et leurs stabilités thermiques estimées dans six classes moléculaires: les BTXN, les méthylaromatiques, les alkylaromatiques, les naphténoaromatiques, les indènes et les composés aromatiques soufrés. Les pyrolyses sont effectuées en milieu fermé dans des tubes en or sous une pression de 100 bars et pour différentes conditions (température/temps) couvrant une très large gamme de conversion (1 à 93 %). Les effluents de pyrolyse sont fractionnés, analysés et regroupés en classes. L'évolution de l'ensemble des classes a été interprétée par l'élaboration d'un schéma cinétique semi-empirique composé de 13 réactions stoechiométriques qui rendent compte du craquage de la charge et du craquage secondaire des produits instables. Les paramètres cinétiques estimés de ce schéma ont été ensuite calibrés par optimisation numérique sous la contrainte des bilans de masse et de la conservation d'hydrogène. Afin d'évaluer l'effet de la pression sur le craquage thermique, nous avons réalisé une série de pyrolyses à 375 °C sous de hautes pressions de 400, 800 et 1200 bars. La comparaison des résultats de ces expériences à ceux obtenus à 100 bars a montré que l'augmentation de la pression retarde le craquage. Nous avons également mis en évidence une certaine sélectivité dans l'action de la pression sur les différentes classes que contient la charge et sur la distribution des produits de pyrolyse. L'extrapolation du modèle construit dans cette étude aux conditions du Bassin d'Elgin (Mer du Nord) a montré que l'augmentation de la pression aurait augmenté la stabilité thermique de la fraction aromatique légère en décalant son craquage de 8 °C

Separation and Characterisation of the C

The purpose of this work is to isolate and characterise the light fraction of Safaniya, a conventional nonbiodegraded type II crude oil. This fraction is devoted to perform a kinetic study on the thermal stability of the light aromatic fraction of crude oil. The light cut <250°C, corresponding to the C15- components, was obtained by fractionated distillation. This cut contains saturated and aromatic hydrocarbons. Kinetic studies on the thermal stability of aromatics require to separate the aromatic fraction without any trace of saturated compounds and derive detailed information on its composition. We have therefore developed a method permitting to achieve a clear-cut separation of these two families. Liquid phase chromatography on activated silica gel column was thus optimised for separating a complete and pure aromatic fraction, in large enough amounts for characterisation and all subsequent kinetic studies. Thereafter, Preparative High Performance Liquid Chromatography (PHPLC) of an aliquot was used to separate the aromatic compounds according to aromatic ring number into monoaromatics, indenes, diaromatics and biphenyls. Detailed molecular characterisation of the aromatic sub-fractions thus obtained was achieved by Gas Chromatography coupled to Mass Spectrometry (GC/MS). Then, individual aromatic compounds were quantified by GC-FID. These compounds are benzene, C1-C7 benzenes, naphthalene, C1-C7 naphthalenes, indane, C1-C4 indanes, indene, C1-C7 indenes, C1-C3 tetralins and and sulphur-containing aromatics (methyl- and ethylbenzothiophenes). The detailed knowledge thus derived on the composition of different class and its relative abundance in the total C15- aromatics will allow following its temporal evolution during subsequent pyrolysis experiments

A laboratory pyrolysis study to investigate the effect of water pressure on hydrocarbon generation and maturation of coals in geological basins

This study investigates the effect of water pressure on hydrocarbon generation and maturation of coals. Using a 25 ml Hastalloy pressure vessel, two high-volatile coals (Longannet, UK 0.75% Ro, and perhydrous Svalbard (Spitsbergen), Norway 0.68% Ro) were pyrolysed under non-hydrous, hydrous at 175 bar pressure, and high water pressure hydrous (500 bar and 900 bar) conditions at 350 °C for 24 h. The bitumen yield obtained during pyrolysis, together with the Rock–Eval S2, hydrogen index (HI) and vitrinite reflectance (VR) results from the pyrolysed coal residues indicated that water under relatively low pressure (175 bar) hydrous conditions promoted hydrocarbon generation and coal maturation in relation to non-hydrous conditions, consistent with previous work. However, under high water pressure (500 and 900 bar) conditions, a combination of the hydrocarbon gas (C1–C4) and bitumen yields, Rock–Eval S2, HI, VR and solid state 13C NMR results demonstrated that the changes in reaction pathways occurring with increasing pressure resulted in both hydrocarbon generation and maturation being retarded. The observed effect of pressure implies that for Type III source rocks, hydrocarbon generation will be retarded in high pressure geological basins, with gas yields being proportionally reduced more than bitumen yields. Source rock maturation (or coalification) is also retarded, with the decreases in vitrinite reflectance and carbon aromaticity being relatively small but significant in terms of explaining retardation in geological basins