Evolution of Asphaltenes during Artificial Maturation:  A Record of the Chemical Processes

Abstract

Type II kerogens have been artificially matured by confined and hydrous pyrolysis. The asphaltenes recovered from the experiments were characterized by FT-IR, synchronous UV fluorescence, Py-GC-MS, and elemental analysis. The results show that important modifications related to the physicochemical maturation conditions affect the asphaltenes: (i) The asphaltenes yields are modified by temperature, pressure and by the presence of water. (ii) A progressive defunctionalization and increased aromatic content during maturation is recorded by the asphaltenes. This phenomenon is retarded by the presence of water in hydrous conditions. (iii) The asphaltenes expelled during hydrous pyrolysis have a different composition than the asphaltenes remaining in the bitumen. (iv) Data on the oxygen content of the asphaltenes strongly support the occurrence of interactions between asphaltenes and water, both in confined and hydrous pyrolysis. Therefore, it is suggested that hydrogen transfer reactions between water and the newly formed hydrocarbons are catalyzed by the asphaltenes and are based on a combination of reduction and oxidation reactions through a radical ion mechanism. (v) A comparison with the elemental composition of the residual kerogen leads to the conclusion that the excess of CO2 generated during hydrous pyrolysis is related to the oxidation of the asphaltenes. The study of the asphaltenes can bring important information concerning the chemical processes taking place during artificial maturation. It appears that the asphaltenes are not simple intermediates between the kerogen and the hydrocarbons during oil generation, but they actively participate to the chemical reactions involved in maturation.

Evolution of porosity and pore types in organic-rich, calcareous, Lower Toarcian Posidonia Shale

“…Behar et al (2008b) proposed a kinetic scheme where kerogen initially decomposes into a very viscous, NSO-rich liquid which is further decomposed into more soluble non-hydrocarbon compounds and finally, cracked into hydrocarbons. The occurrence of a heavy, intermediate bitumen phase was also proposed by Michels et al (1996) and Lewan (1997). In this study, RockEval data for unextracted and extracted samples confirm the presence of a substantial amount of a non-volatile bitumen phase within the low maturity Posidonia shale (cf.…”

Artificial maturation of a high volatile bituminous coal from Asturias (NW Spain) in a confined pyrolysis system

“…Peters et al [10], Rohrback et al [11], and Huang [12], among others, have simulated maturation processes through experimental maturation studies in the laboratory. Monthioux et al [13], Landais and Monthioux [14], Landais et al [15,16], Benkhedda et al [17], Gérard et al [18], Mansuy and Landais [19], Mansuy et al [20], Michels et al [21][22][23], Landais and Gérard [24], and Han et al [25] have also shown that this maturation technique is able to reproduce the thermal transformation of kerogen and the generation of oil and gas according to natural evolution trends.…”

Identification of nitrogen-polyaromatic compounds in asphaltene from co-processing of coal and petroleum residue using chromatography with mass spectrometry

“…Meanwhile, the fluorescence efficiency increases significantly with the increase of aromatic rings. In consideration of the ''red shift'' effect caused by alkylation and heteroatom, the numbers of aromatic rings of the compounds were summarized as follows: 270-300 nm for single-ringed aromatics, 300-340 nm for double-ringed aromatics, 340-400 nm for three aromatic rings, 400-425 nm for four aromatic rings, lager than 425 nm for five-and above five-ringed aromatics (Michels et al 1996).…”